Msc biology

8/7/2019 Msc biology

1/34

Inside the nucleus of each human cell there are 46 chromosomes organized into two sets of 23chromosomes.1Packaged inside these chromosomes is our DNA, the genetic material we receive

from our parents. The DNA within our cells is continually being exposed to DNA-damaging

agents. These agents include ultraviolet light, natural and man made mutagenic chemicals andreactive oxygen species generated by ionizing radiation.2 When cells are exposed to ionizing

radiation, radiochemical damage can occur either by direct action or indirect action. Direct action

occurs when alpha particles, beta particles or x-rays create ions which physically break one orboth of the sugar phosphate backbones or break the base pairs of the DNA. The base pairs

adenine, thymine guanine and cytosine are held together by weak hydrogen bonds. Adenine

always pairs with thymine (except in RNA where thymine is substituted by uracil) and guaninealways pairs with cytosine. The bonding of these base pairs can also be affected by the direct

action of ionizing radiation.

Direct Action

Please note: This diagram gives the impression that alpha particle breaks the backbone of theDNA, the beta particle breaks hydrogen bonds, and X-rays damage bases when in fact all three

types of radiation can cause all three types of direct damage. However, heavy charged particles

such as alpha particles have a greater probability of causing direct damage compared to lowcharged particles such as X-rays which causes most of its damage by indirect effects.

The DNA base pairs form sequences called nucleotides which in turn form genes. Genes tell the

cell to make proteins which determine cell type and regulate cell function. When such breaksoccur, DNA usually repairs itself through a process called excision. The excision process hasthree steps:

1. Endonucleases cut out the damaged DNA

2. Resynthesis of the original DNA by DNA polymerase

3. Ligation whereby the sugar phosphate backbone is repaired.3
http://www.cna.ca/curriculum/cna_bio_effects_rad/direct_indirect-eng.asp?bc=Direct%20and%20Indirect%20Action%20of%20Ionizing%20Radiation%20on%20DNA&pid=Direct%20and%20Indirect%20Action%20of%20Ionizing%20Radiation%20on%20DNA#noteshttp://www.cna.ca/curriculum/cna_bio_effects_rad/direct_indirect-eng.asp?bc=Direct%20and%20Indirect%20Action%20of%20Ionizing%20Radiation%20on%20DNA&pid=Direct%20and%20Indirect%20Action%20of%20Ionizing%20Radiation%20on%20DNA#noteshttp://www.cna.ca/curriculum/cna_bio_effects_rad/direct_indirect-eng.asp?bc=Direct%20and%20Indirect%20Action%20of%20Ionizing%20Radiation%20on%20DNA&pid=Direct%20and%20Indirect%20Action%20of%20Ionizing%20Radiation%20on%20DNA#noteshttp://www.cna.ca/curriculum/cna_bio_effects_rad/direct_indirect-eng.asp?bc=Direct%20and%20Indirect%20Action%20of%20Ionizing%20Radiation%20on%20DNA&pid=Direct%20and%20Indirect%20Action%20of%20Ionizing%20Radiation%20on%20DNA#noteshttp://www.cna.ca/curriculum/cna_bio_effects_rad/direct_indirect-eng.asp?bc=Direct%20and%20Indirect%20Action%20of%20Ionizing%20Radiation%20on%20DNA&pid=Direct%20and%20Indirect%20Action%20of%20Ionizing%20Radiation%20on%20DNA#noteshttp://www.cna.ca/curriculum/cna_bio_effects_rad/direct_indirect-eng.asp?bc=Direct%20and%20Indirect%20Action%20of%20Ionizing%20Radiation%20on%20DNA&pid=Direct%20and%20Indirect%20Action%20of%20Ionizing%20Radiation%20on%20DNA#noteshttp://www.cna.ca/curriculum/cna_bio_effects_rad/direct_indirect-eng.asp?bc=Direct%20and%20Indirect%20Action%20of%20Ionizing%20Radiation%20on%20DNA&pid=Direct%20and%20Indirect%20Action%20of%20Ionizing%20Radiation%20on%20DNA#noteshttp://www.cna.ca/curriculum/cna_bio_effects_rad/direct_indirect-eng.asp?bc=Direct%20and%20Indirect%20Action%20of%20Ionizing%20Radiation%20on%20DNA&pid=Direct%20and%20Indirect%20Action%20of%20Ionizing%20Radiation%20on%20DNA#noteshttp://www.cna.ca/curriculum/cna_bio_effects_rad/direct_indirect-eng.asp?bc=Direct%20and%20Indirect%20Action%20of%20Ionizing%20Radiation%20on%20DNA&pid=Direct%20and%20Indirect%20Action%20of%20Ionizing%20Radiation%20on%20DNA#notes


2/34

These repair processes are highly efficient since we have evolved as a species in a sea of

radiation. DNA repair takes place continuously, involving every cell in our bodies several times

per year. Occasionally, however, damage to the base pair can occur when the DNA is incorrectlyrepaired and the wrong nucleotide is inserted which can lead to cell death or a mutation.

Remember your DNA is the code which determines the type and function of the cell. There are

two basic types of mutations:

Substitutions this is the replacement of one base by another. For example, if a DNAmolecule usually contains guanine at a certain position, but adenine takes the place of the

guanine, then a base substitution has occurred. There are two types of base substitutions:

o transitions these involve the replacement of one purine with the other purine,

(adenine and thymine), or the replacement of one pyrimidine with the other

pyrimidine (cytosine and guanine)

o transversions these involve the replacement of a purine with a pyrimidine or

vice versa

Mutations these change the reading frame of a gene (the triplet code). There are twotypes of frameshift mutations:

o insertions as the name implies, these involve the insertion of one or more

extra nucleotides into a DNA chain

o deletions these result from the loss of one or more nucleotides from a DNA

chain

To illustrate the effects of these mutations, consider the following phrase, read as a triplet code

(groups of three letters):

Introduction

The purpose of this section is to provide information on the basics of ionizing radiation for

everyone.

Energy emitted from a source is generally referred to as radiation. Examples include heat or lightfrom the sun, microwaves from an oven, X rays from an x-ray tube, and gamma rays from

radioactive elements.


3/34

Ionizing radiation is radiation with enough energy so that during an interaction with an atom, it

can remove tightly bound electrons from the orbit of an atom, causing the atom to become

charged or ionized.

Ionizing radiation has enough energy to electrically charge or ionize matter. The cells in living

organisms are also made of matter, so they too can be ionized. Cosmic rays, x-rays, gamma rays,

alpha particles and beta particles are forms of ionizing radiation. Ionizing radiation may come

from a natural source such as the Sun or it may come from a man made source such as an x-raymachine. The possibility of overexposure to ionizing radiation among members of the general

public is minimal. However, there are environments such as hospitals, research laboratories and

areas of high level natural background radiation where some potential health risks do exist. Theeffect of ionizing radiation on the human body or any other living organism depends on three

things:

1. The amount and the rate of ionizing radiation which was absorbed.

2. The type of ionizing radiation which was absorbed.3. The type and number of cells affected.

The amount of radiation an organism receives is a very important factor in determining its

biological effect. The greater the amount of ionizing radiation and the greater the number oftimes an organism is exposed, the greater the health risk if the doses are high. The averageCanadian receives about 2.7 mSv (millisieverts) of ionizing radiation per year from both natural

and manmade sources but a single CT scan can give you 10 times that amount (27 mSv) all at

once. A lethal dose is about 5 Sv (sieverts). This means that at 2.7 mSv per year, you would haveto live over 1800 years or until the year 3807 AD to receive the equivalent dose from your

environment, but in order to be lethal that total dose would need to be given all at once.

The type of radiation absorbed is a factor in determining the biological effect of ionizing

radiation on an organism. Each type of ionizing radiation has its own characteristics. Alphaparticles are fairly large in size and carry a double positive charge, so they tend to travel only a

short distance and do not penetrate very far into tissue if at all. However alpha particles willdeposit their energy over a smaller volume (possibly only a few cells if they enter a body) andcause more damage to those few cells. Beta particles are much smaller and carry a single

negative charge. They will penetrate farther into the body, which means they tend to damage

more cells, but with lesser damage to each. Gamma rays and x-rays are pure energy and have nomass. They are deeply penetrating and can easily pass completely through your body, but may

still interact with many atoms as they pass through. Both x-rays and gamma rays spread their

energy over a larger volume, which causes less damage per collision. Of course, at very high


4/34

levels of exposure they can still cause a great deal of damage to tissues. Because of their

penetrating ability, they can easily reach internal organs and bones which is why large doses can

be used to damage cancer tissue.

The type and number of cells affected is also an important factor. Some cells and organs in the

body are more sensitive to ionizing radiation than others. Cells that divide rapidly like thosefound in bone marrow, stomach, intestines, male and female reproductive organs, and developing

fetuses are more sensitive to ionizing radiation than cells that make up skin, kidney or livertissue. Children and young adolescents also are more sensitive to ionizing radiation because their

bodies are still growing. The biological effects of ionizing radiation are well known. The nuclear

industry is closely monitored and inspected to ensure that safety procedures and regulations areprecisely followed to protect workers in the industry, as well as the public and the environment.

Sources: World Health Organization

www.who.int/ionizing_radiation/about/what_is_ir/en/index.html

How ionizing radiation enters the body depends on the source of the ionizing radiation. X-rays

and gamma rays can pass directly through the body when it is exposed to an irradiating sourcesuch as an x-ray machine. Alpha and beta particles do not penetrate very far into the body but

radioactive materials that emit alpha, beta or gamma radiation can be taken into the body alone

or with other materials which have become contaminated in the following ways:

1. In the air or mixed with the dust in the air.2. Dissolved in water.

3. Mixed with soil on the ground through fertilizers and absorbed by

plants that we may eat.

4. By consumption of plants and animals that have become contaminated.

The main entry pathways for materials contaminated with radioactive isotopes

include the nose and mouth, around the eyes and any breaks or cuts in the skin.

Materials contaminated with radioactive isotopes may also become trapped under the fingernails,in hair follicles and in folds and creases in the skin. If the contaminated materials remain outside

the body the health risks are fairly low. However, if the contaminated

material enters the body either by ingesting or inhaling, the risks

become greater depending on the quantity and type of radioactiveisotope absorbed.

Once inside the body, the radioactive isotope will ionize the cells

around it sometimes causing irreparable damage.
http://www.who.int/ionizing_radiation/about/what_is_ir/en/index.htmlhttp://www.who.int/ionizing_radiation/about/what_is_ir/en/index.html


5/34

Radioactive isotopes migrate in the body in the same way as inert isotopes of the same element.

For example, iodine-131 migrates to the thyroid gland which normally uses iodine and requires a

steady supply to remain healthy. This is especially true in children and young adults whosethyroid glands are more active than they are in adults. Strontium-90 mimics calcium and travels

to bone tissue. In large enough doses, these isotopes will cause cancer and other diseases.

The migration of radioactive isotopes within the body is of extreme benefit to patients requiring

treatment in the field of nuclear medicine and diagnostic imaging. In these instances, short livedradioactive isotopes and isotopes that can easily be flushed from the body are deliberately

inhaled or ingested for medical treatments and tests.

RADIATION HAZARD

Agent Information: Radiological agents are used in health care, industry, energy productionand as warfare agents, measured by the number of atoms disintegrating per unit time. Adisintegrating atom can emit a beta particle, an alpha particle, a gamma ray, or somecombination.Signs and Symptoms: Exposure to radiation can cause two kinds of health effects.Deterministic effects are observable health effects that occur soon after receipt of large doses.These may include hair loss, skin burns, nausea or death. Stochastic effects are long-termeffects, such as cancer. The radiation dose determines the severity of a deterministic effect andthe probability of a stochastic effect in conjunction with the type of emission usually man-made.Route of Exposure: Alpha particles, beta particles, gamma rays and x-rays affect tissue indifferent ways. Alpha particles disrupt more molecules in a shorter distance than gamma rays.As radiation moves through the body, it dislodges electrons from atoms, disrupting moleculesand depositing energy. The energy the radiation deposits in tissue is called the dose or theabsorbed dose. A person can receive an external dose by standing near a gamma or high-energy beta-emitting source. A person can receive an internal dose by ingesting or inhalingradioactive material.The external exposure stops when the person leaves the area of the source. The internalexposure continues until the radioactive material is flushed from the body by natural processesor decays. When a person inhales or ingests a radionuclide, that radionuclide is distributed todifferent organs and stays there for days, months or years until it decays or is excreted. Theradionuclide will deliver a radiation dose over a period of time. The dose that a person receivesfrom the time the nuclide enters the body until it is gone is the committed dose.

Transmission: Only victims who are contaminated with radioactive particles, either externallyor internally, can expose other people to radiation. 24/7 Emergency Contact Number: 1-888-295-5156 Revised:


6/34

Protection against radiation hazards : Regulatory bodies, safetynorms, does limits and protection devices3/2007 Page 2 of 2

There are various Regulatory Bodies at the international and National level, which lay

down norms for radiation protection. These are the International Commission forRadiation Protection (ICRP) the National Commission for Radiation Protection (NCRP)in America, and the Atomic Energy Regulatory Board (AERB) in India. These bodiesrecommend norms for permissible doses of radiation from X ray tubes and the shieldingrequired for the walls of an X ray room. Data is also available from the work ofInvestigators regarding the room shielding required in a CT suite. The recommendedlead equivalent in shielding apparel to be worm by radiation workers is 0.5 mm. Theregulatory bodies also lay down safe dose limits for radiation workers and for thegeneral public. The duties of the Radiation Safety Officer (RSO) are also specified bythe regulatory bodies, as are the radiation surveillance and radiation safetyprogrammers.

Introduction

In our earlier article we have elaborated the biological hazards of radiation and theradiation doses which lead to these effects. In this article we introduce to the reader thevarious regulatory bodies especially the Indian Regulatory Body (AERB) and also therole of Radiation Safety Officer (RSO). We also appraise the reader of the objectives ofradiation protection, the principles, methods and practices of radiation protection andthe safe dose limits.

The Regulatory Bodies

The Regulatory bodies lay down norms for protection against radiation and alsorecommend the dose limits for radiation workers and the general public. The ICRP orthe International Commission for radiation protection is the international regulatorybody. Each country has its national counterpart of the ICRP. In America the counterpartis the NCRP or The National Commission for Radiological Protection and in India it isthe AERB or the Atomic Energy

Regulatory Board.

The International Commission of Radiation Protection (ICRP) was formed in 1928 on

the recommendation of the first International Congress of Radiology in 1925. Thecommission consists of 12 members and a chairman and a secretary who are chosenfrom across the world based on their expertise. The first International Congress alsoinitiated the birth of the ICRU or the International Commission on Radiation Units andmeasurements [1].

The Indian regulatory board is the AERB, Atomic Energy Regulatory Board. The AtomicEnergy Regulatory Board was constituted on November 15, 1983 by the President of
http://www.ijri.org/article.asp?issn=0971-3026;year=2002;volume=12;issue=2;spage=157;epage=167;aulast=Grover#ref1http://www.ijri.org/article.asp?issn=0971-3026;year=2002;volume=12;issue=2;spage=157;epage=167;aulast=Grover#ref1


7/34

India by exercising the powers conferred by Section 27 of the Atomic Energy Act, 1962(33 of 1962) to carry out certain regulatory and safety functions under the Act. Theregulatory authority of AERB is derived from the rules and notifications promulgatedunder the Atomic Energy Act, 1962 and the Environmental (Protection) Act, 1986. Themission of the Board is to ensure that the use of ionizing radiation and nuclear energy in

India does not cause undue risk to health and environment. Currently, the Boardconsists of a full-time Chairman, an ex-officio Member, three part-time Members and aSecretary [2].

Objectives of Radiation protection

The ICRP in 1991 stated that "the overall objective of radiation protection is to providean appropriate standard of protection for man without unduly limiting the beneficialpractices giving rise to radiation exposure". The NCRP (1993), issued a similarstatement in its Report (No. 116) that "the goal of radiation protection is to prevent theoccurrence of serious radiation induced conditions (acute and chronic deterministic

effects) in exposed persons and to reduce stochastic effects in exposed persons to adegree that is acceptable in relation to the benefits to the individual and to society fromthe activities that generate such exposure" [1]. Furthermore, the ICRP suggested that"current standards of protection are meant to prevent occurrence of deterministic effectsby keeping doses below relevant thresholds and ensure that all reasonable steps aretaken to reduce induction of stochastic effects"[1].

Radiation safety act in India

Radiation safety in handling of radiation generating equipment is governed by section17 of the Atomic Energy Act, 1962, and the Radiation Protection Rules (RPR), G.S.R. -

1601, 1971 issued under the Act. The "Radiation Surveillance Procedures of MedicalApplications of Radiation, G.S.R. - 388, 1989", issued under rule 15 specify generalrequirements for ensuring radiation protection in installation and handling of X-rayequipment. Guidance and practical aspects on implementing the requirements of thisCode are provided in revised documents issued by AERB in the year 2001 [2].

Role of AERB (India)

AERB of India recommends and lays down guidelines regarding the specifications ofmedical X-ray equipment, for the room layout of X-ray installation, regarding the workpractices in X-ray department, the protective devices and also the responsibilities of theradiation personnel, employer and Radiation Safety Officer (RSO). AERB is theauthority in India which exercises a regulatory control on the approval of new models ofX-ray equipment and the layout of any new proposed X-ray installation. It also is theregulatory authority for registration and commissioning of new X-ray equipment,inspection and decommissioning of X-ray installation, certification of a RSO and ofservice engineers and also for imposing penalties on any person contravening theserules [2].
http://www.ijri.org/article.asp?issn=0971-3026;year=2002;volume=12;issue=2;spage=157;epage=167;aulast=Grover#ref2http://www.ijri.org/article.asp?issn=0971-3026;year=2002;volume=12;issue=2;spage=157;epage=167;aulast=Grover#ref1http://www.ijri.org/article.asp?issn=0971-3026;year=2002;volume=12;issue=2;spage=157;epage=167;aulast=Grover#ref1http://www.ijri.org/article.asp?issn=0971-3026;year=2002;volume=12;issue=2;spage=157;epage=167;aulast=Grover#ref2http://www.ijri.org/article.asp?issn=0971-3026;year=2002;volume=12;issue=2;spage=157;epage=167;aulast=Grover#ref2http://www.ijri.org/article.asp?issn=0971-3026;year=2002;volume=12;issue=2;spage=157;epage=167;aulast=Grover#ref2http://www.ijri.org/article.asp?issn=0971-3026;year=2002;volume=12;issue=2;spage=157;epage=167;aulast=Grover#ref1http://www.ijri.org/article.asp?issn=0971-3026;year=2002;volume=12;issue=2;spage=157;epage=167;aulast=Grover#ref1http://www.ijri.org/article.asp?issn=0971-3026;year=2002;volume=12;issue=2;spage=157;epage=167;aulast=Grover#ref2http://www.ijri.org/article.asp?issn=0971-3026;year=2002;volume=12;issue=2;spage=157;epage=167;aulast=Grover#ref2


8/34

Principles of radiation protection

The current radiation protection standards are based on three general principles :-

a) Justification of a practice i.e. no practice involving exposures to radiation should be

adopted unless it provides sufficient benefit to offset the detrimental effects of radiation.

b) Protection should be optimized in relation to the magnitude of doses, number ofpeople exposed and also to optimize it for all social and economic strata of patients.

c) Dose limitation, on the other hand, deals with the idea of establishing annual doselimits for occupational exposures, public exposures, and exposures to the embryo andfetus [1].

Hazards of Ionising and Non-Ionising Radiations

A Guide to the Hazards of Ionising and Non-Ionising Radiations

CONTENTS

General Radiation Hazards

RadioisotopesX-Rays

Pregnancy

Mobile Phones

MicrowavesUV Lamps includingCosmetic Tanning

UV and SunlightLasersincluding Laser Pointers

GENERAL

The Health Protection Agency, (formerly the National Radiological Protection Board), have an

excellent series of interactive modules (Understanding Radiation)

Modules for Radon, Transport of Radioactive Materials, Nuclear Emergencies, Radio-Waves

and Doses from Discharges currently exist, along with an electronic version of the HPASunsense poster. Future modules include Electric and Magnetic Fields, Ultraviolet Radiation andMaps and Magnitudes.

RADIOISOTOPES
http://www.ijri.org/article.asp?issn=0971-3026;year=2002;volume=12;issue=2;spage=157;epage=167;aulast=Grover#ref1http://www.liv.ac.uk/radiation/information.htm#generalhttp://www.liv.ac.uk/radiation/information.htm#sourceshttp://www.liv.ac.uk/radiation/information.htm#xrayhttp://www.liv.ac.uk/radiation/information.htm#pregnanthttp://www.liv.ac.uk/radiation/information.htm#mobilehttp://www.liv.ac.uk/radiation/information.htm#microwavehttp://www.liv.ac.uk/radiation/information.htm#uvlamphttp://www.liv.ac.uk/radiation/information.htm#tanninghttp://www.liv.ac.uk/radiation/information.htm#tanninghttp://www.liv.ac.uk/radiation/information.htm#sunlighthttp://www.liv.ac.uk/radiation/information.htm#laserhttp://www.liv.ac.uk/radiation/information.htm#laserhttp://www.liv.ac.uk/radiation/information.htm#Laser_Pointershttp://www.hpa.org.uk/radiation/understand/at_a_glance/index.htmhttp://www.liv.ac.uk/radiation/information.htm#TABLEhttp://www.ijri.org/article.asp?issn=0971-3026;year=2002;volume=12;issue=2;spage=157;epage=167;aulast=Grover#ref1http://www.liv.ac.uk/radiation/information.htm#generalhttp://www.liv.ac.uk/radiation/information.htm#sourceshttp://www.liv.ac.uk/radiation/information.htm#xrayhttp://www.liv.ac.uk/radiation/information.htm#pregnanthttp://www.liv.ac.uk/radiation/information.htm#mobilehttp://www.liv.ac.uk/radiation/information.htm#microwavehttp://www.liv.ac.uk/radiation/information.htm#uvlamphttp://www.liv.ac.uk/radiation/information.htm#tanninghttp://www.liv.ac.uk/radiation/information.htm#sunlighthttp://www.liv.ac.uk/radiation/information.htm#laserhttp://www.liv.ac.uk/radiation/information.htm#Laser_Pointershttp://www.hpa.org.uk/radiation/understand/at_a_glance/index.htm


9/34

There are two categories of radioactive material, closed and other.

Closed sources are sources in which the radioactive material is contained within a permanentlysealed housing or is permanently bonded to a surface or foil

Other sources are all sources that are not closed sources. These are normally sources that aresupplied as a liquid or powder and which are therefore dispersible once the containment vial has

been opened

The hazard from radiation emitted by radioisotopes varies according to decay emission (Alpha,

Beta, Gamma or Neutron) and the emission energy. For the most common radioisotopes used in

the University the hazards are listed inIsotope Hazards.

Local Rules are required for each registered radiation laboratory. Local Rules within the

University of Liverpool are divided into three sections. Document LR1 is General Local Rules

applicable throughout all laboratories within the university. Document LR2 is General

Contingency Plan applicable throughout the univeristy. Document LR3 is Local Rules specific toa particular department or section thereof. LR1 and LR2 can be found on the Documentation

page of this site together with a Template for LR3

All persons using radioisotopes must be registered with the Radiation Protection Office

(Registration of radioisotope user)

X-RAYS

The electromagnetic radiation from X-rays is only emitted when the X-ray unit is energised andthe shutter opened. There is no radiation hazard when the X-ray unit is off

Emission from the X-ray unit is usually limited by collimator to a specific beam size. Persons

outside the beam path may receive scattered x-radiation from the target in the beam path.

In the case of diagnostic X-ray units the scattered x-radiation to the critical organs may be

significantly reduced by wearing lead equivalent aprons.

In the case of crystallography units the beam should be totally enclosed within an interlocked

housing. There is then no hazard to workers outside the housing

All persons using X-ray units must be registered with the Radiation Protection Office

(Registration of X-ray user)

X-RAY SAFETY

If you are worried about the safety implications of having an x-ray you can download a safety

leaflet here
http://www.liv.ac.uk/radiation/pdf/SP1.pdfhttp://www.liv.ac.uk/radiation/pdf/SP1.pdfhttp://www.liv.ac.uk/radiation/pdf/SP1.pdfhttp://www.liv.ac.uk/radiation/doc/RP6.dochttp://www.liv.ac.uk/radiation/doc/RP6.dochttp://www.liv.ac.uk/radiation/pdf/X_ray_Safety.pdfhttp://www.liv.ac.uk/radiation/information.htm#TABLEhttp://www.liv.ac.uk/radiation/information.htm#TABLEhttp://www.liv.ac.uk/radiation/pdf/SP1.pdfhttp://www.liv.ac.uk/radiation/doc/RP6.dochttp://www.liv.ac.uk/radiation/doc/RP6.dochttp://www.liv.ac.uk/radiation/pdf/X_ray_Safety.pdf


10/34

PREGNANCY

To enable the University to accept its responsibility for the welfare of the new baby the mother-

to-be must notify the University as soon as the pregnancy is confirmed. This should be done, in

writing, to the Head of Department.

For the majority of mothers-to-be there will probably be no requirement to alter their

job/research practices as the radiation doses received during the pregnancy will be well belowthe permitted limit (1mSv) for the foetus. However it may be desirable to limit the handling of

stock materials of the higher energy Beta and Gamma emitting sources. Advice may be obtained

from the Radiation Protection Office

The HSE have published an excellent and informative document entitled Guidelines for

expectant or breast-feeding mothers. These guidelines give advice on how expectant and breast-

feeding mothers may work safely with ionising radiation. The document can be downloaded in

PDF formatThe HSE also has a website entitledHealth and Safety for new and expectant mothers which has

much information for the new and expectant mother about general safety at work duringpregnancy

MOBILE PHONES

Information on the Health effects of mobile phones and mobile phone masts can be found on the

Department of Health website

Available for download are :-

Guide to the nature and use of radio-waves issued by the Health Protection Agency, (formerly

the National Radiological Protection Board)

Information leafletissued by Department of Health

An update on "Mobile Phones and Health" issued by the Health Protection Agency, (formerly

the National Radiological Protection Board)

The University's Code of Practice forBase Station Installations on University premises

NRPB Summary on Exposure to Radio Waves near Base Stations

MICROWAVES

High frequency electromagnetic fields are known as microwave radiation. The main effect of
http://www.hse.gov.uk/pubns/indg334.pdfhttp://www.hse.gov.uk/pubns/indg334.pdfhttp://www.hse.gov.uk/pubns/indg334.pdfhttp://www.hse.gov.uk/mothers/index.htmhttp://www.hse.gov.uk/mothers/index.htmhttp://www.dh.gov.uk/PolicyAndGuidance/HealthAndSocialCareTopics/MobilePhones/fs/enhttp://www.hpa.org.uk/radiation/understand/at_a_glance/index.htmhttp://www.liv.ac.uk/radiation/pdf/mobilephone.pdfhttp://www.liv.ac.uk/radiation/pdf/mobilephone.pdfhttp://www.liv.ac.uk/radiation/mobile.htmhttp://www.liv.ac.uk/radiation/pdf/basestation.pdfhttp://www.liv.ac.uk/radiation/pdf/mobile%20base.pdfhttp://www.liv.ac.uk/radiation/information.htm#TABLEhttp://www.hse.gov.uk/pubns/indg334.pdfhttp://www.hse.gov.uk/pubns/indg334.pdfhttp://www.hse.gov.uk/mothers/index.htmhttp://www.dh.gov.uk/PolicyAndGuidance/HealthAndSocialCareTopics/MobilePhones/fs/enhttp://www.hpa.org.uk/radiation/understand/at_a_glance/index.htmhttp://www.liv.ac.uk/radiation/pdf/mobilephone.pdfhttp://www.liv.ac.uk/radiation/mobile.htmhttp://www.liv.ac.uk/radiation/pdf/basestation.pdfhttp://www.liv.ac.uk/radiation/pdf/mobile%20base.pdf


11/34

exposure to such radiation is heat deposition in tissue. The most obvious result of this heating

effect has been shown to be the temporary disruption of learned behaviour in animals. The

average level of specific absorption rate required to produce temporary disruption has beenshown to be 2 - 8 Watts per kilogram. The Health Protection Agency, (formerly the National

Radiological Protection Board), has therefore recommended a maximum exposure level of 0.4

Watts per kilogram. Although some work with microwave transmission is conducted in theDepartment of Electrical Engineering and Electronics and in the Department of Physics, the main

use of microwave radiation within the University is in microwave ovens.

All microwave ovens, whether used for heating in experiments such as agar solutions or for

domestic cooking, must be registered with the Radiation Protection Office. The information

required is Manufacturer, Model, Serial Number, Department, Room/Lab Number. This

information may be sent as an e-mail

UV RADIATION

Ultra Violet radiation lies within the wavelength range 100 - 400nm. The direct effects are

limited to the skin and eyes because of its non-penetrating nature. There are acute effects such as

erythema (sunburn) of the skin and conjunctivitis of the eye and chronic effects such as

premature skin ageing, skin cancer and cataracts of the eye. The UV wavelengths are dividedinto three sections :-

UVA - 400-315nmUVB - 315-280nm

UVC - 280-100nm

The most common sources of UV radiation within the University are UV Reactors (for

accelerating or inducing chemical reactions), germicidal lamps (for sterilising benches or flow

cabinets), and transilluminators. All these use lamps having shorter wavelengths than the UVA

lamps used in most sunbeds and the effect of exposure on skin or eyes may be noted after veryshort inadvertent exposure. In no circumstances should any part of the body be exposed to the

UVB and UVC radiation from reactors, germicidal lamps or transilluminators.

Units containing germicidal lamps should be interlocked to prevent access whilst the lamp is on.

Transilluminators must be used with gauntletted gloves and must be used with either the fittedperspex UV shield or separate full face shield

Local Rules for work with UV radiation are available from Radiation Protection Office and maybe downloaded in WORD orPDF format

COSMETIC TANNING

The Health Protection Agency, (formerly the National Radiological Protection Board), have

issued Information on Sunbeds and Cosmetic Tanning which provides warning on the use of
http://www.liv.ac.uk/radiation/doc/LR_uv.dochttp://www.liv.ac.uk/radiation/pdf/LR_uv.pdfhttp://www.liv.ac.uk/radiation/sunbeds.htmhttp://www.liv.ac.uk/radiation/information.htm#TABLEhttp://www.liv.ac.uk/radiation/doc/LR_uv.dochttp://www.liv.ac.uk/radiation/pdf/LR_uv.pdfhttp://www.liv.ac.uk/radiation/sunbeds.htm


12/34

sunbeds and other cosmetic tanning.

The International Commission on Non-Ionising Radiation Protection have issued a paper on theHealth Issues of Ultra Violet Tanning Appliances used for Cosmetic Purposes

UV AND SUNLIGHT

HSE have issued two information sheets re UV in sunlight. The first is 'Sun Protection forOutdoor Workers' and the second is 'Keep Your Top On'

Cancer Research UK have two information sheets with regard to dangers of overexposure to

sunlight. The first is 'Strategies for the Workplace' and the second is entitled 'Skin Cancer'

LASERS

The most vulnerable organs from laser light are the eyes. Light from a laser is concentrated into anarrow beam. This beam can be further concentrated by the lens of the eye onto the retina and

cause temporary or permanent blindness. The blink reflex of the eye will normally protect the

eye from a Class 1 laser but care must be used in the design of an experiment to ensure that lightfrom Class 2 (and higher Class) lasers cannot impinge upon any person's eye

Guidance Notes for Users of Lasers in Education and Research issued by the Association of

Unervsity Radiation Protection Officers may be downloaded here

It is policy among most universities in the UK that laser pointers used in lecture theatres are

limited to Class 1 or Class 2

Laser Safety Code of Practice, Generic Laser Local Rules and Generic Laser Risk Assessment

are available on the Documentation page

Lasers (other than laser pointers) must be registered with the Radiation Protection Office and the

laser form in Documentation should be used (Registrationof Laser)

LASER POINTERSThe Health Protection Agency, (formerly the National Radiological Protection Board), have

issued an Information Sheet on Laser Pointers.

Please also read Note on Laser Pointers issued by University Radiation Protection Advisor.
http://www.liv.ac.uk/radiation/tanning.htmhttp://www.liv.ac.uk/radiation/pdf/HSE_sunemployers.pdfhttp://www.liv.ac.uk/radiation/pdf/HSE_sunemployers.pdfhttp://www.liv.ac.uk/radiation/pdf/HSE_sunemployers.pdfhttp://www.liv.ac.uk/radiation/pdf/HSE_sunemployers.pdfhttp://www.liv.ac.uk/radiation/pdf/HSE_top_on.pdfhttp://www.liv.ac.uk/radiation/pdf/sunsmart_workplace.pdfhttp://www.liv.ac.uk/radiation/pdf/sunsmart_workplace.pdfhttp://www.liv.ac.uk/radiation/pdf/sunsmart_skincancer.pdfhttp://www.liv.ac.uk/radiation/pdf/sunsmart_skincancer.pdfhttp://www.liv.ac.uk/radiation/pdf/GN7_%20Lasers.pdfhttp://www.liv.ac.uk/radiation/doc/RP_reglaser.dochttp://www.liv.ac.uk/radiation/doc/RP_reglaser.dochttp://www.liv.ac.uk/radiation/pdf/laserpointers.pdfhttp://www.liv.ac.uk/radiation/pdf/laserpointers.pdfhttp://www.liv.ac.uk/radiation/pdf/L_Pointers.pdfhttp://www.liv.ac.uk/radiation/information.htm#TABLEhttp://www.liv.ac.uk/radiation/information.htm#TABLEhttp://www.liv.ac.uk/radiation/information.htm#TABLEhttp://www.liv.ac.uk/radiation/tanning.htmhttp://www.liv.ac.uk/radiation/pdf/HSE_sunemployers.pdfhttp://www.liv.ac.uk/radiation/pdf/HSE_sunemployers.pdfhttp://www.liv.ac.uk/radiation/pdf/HSE_top_on.pdfhttp://www.liv.ac.uk/radiation/pdf/sunsmart_workplace.pdfhttp://www.liv.ac.uk/radiation/pdf/sunsmart_skincancer.pdfhttp://www.liv.ac.uk/radiation/pdf/GN7_%20Lasers.pdfhttp://www.liv.ac.uk/radiation/doc/RP_reglaser.dochttp://www.liv.ac.uk/radiation/pdf/laserpointers.pdfhttp://www.liv.ac.uk/radiation/pdf/L_Pointers.pdf


13/34

Radiation protection

From Wikipedia

Jump to: navigation, search

A lead castle built to shield a radioactive sample in a lab

Radiation protection, sometimes known as radiological protection, is the science of protecting

people and the environment from the harmful effects ofionizing radiation, which includes bothparticle radiation and high energy electromagnetic radiation.

Ionizing radiation is widely used in industry and medicine, but presents a significant health

hazard. It causes microscopic damage to living tissue, resulting in skin burns andradiation

sickness at high exposures and statistically elevated risks ofcancer, tumorsandgenetic damageat low exposures.

Principles of radiation protection

Radiation protection can be divided into occupational radiation protection, which is theprotection of workers; medical radiation protection, which is the protection of patients; and

public radiation protection, which is protection of individual members of the public, and of the

population as a whole. The types of exposure, as well as government regulations and legal

exposure limits are different for each of these groups, so they must be considered separately.
http://wiki.ask.com/Radiation_protection#column-onehttp://wiki.ask.com/Radiation_protection#searchInputhttp://wiki.ask.com/Lead_castle?qsrc=3044http://wiki.ask.com/Ionizing_radiation?qsrc=3044http://wiki.ask.com/Ionizing_radiation?qsrc=3044http://wiki.ask.com/Particle_radiation?qsrc=3044http://wiki.ask.com/Electromagnetic_radiation?qsrc=3044http://wiki.ask.com/Electromagnetic_radiation?qsrc=3044http://wiki.ask.com/Radiation_sickness?qsrc=3044http://wiki.ask.com/Radiation_sickness?qsrc=3044http://wiki.ask.com/Radiation_sickness?qsrc=3044http://wiki.ask.com/Cancer?qsrc=3044http://wiki.ask.com/Cancer?qsrc=3044http://wiki.ask.com/Tumor?qsrc=3044http://wiki.ask.com/Tumor?qsrc=3044http://wiki.ask.com/Genetic_damage?qsrc=3044http://wiki.ask.com/Genetic_damage?qsrc=3044http://en.wikipedia.org/wiki/File:Lead_shielding.jpghttp://en.wikipedia.org/wiki/File:Lead_shielding.jpghttp://wiki.ask.com/Radiation_protection#column-onehttp://wiki.ask.com/Radiation_protection#searchInputhttp://wiki.ask.com/Lead_castle?qsrc=3044http://wiki.ask.com/Ionizing_radiation?qsrc=3044http://wiki.ask.com/Particle_radiation?qsrc=3044http://wiki.ask.com/Electromagnetic_radiation?qsrc=3044http://wiki.ask.com/Radiation_sickness?qsrc=3044http://wiki.ask.com/Radiation_sickness?qsrc=3044http://wiki.ask.com/Cancer?qsrc=3044http://wiki.ask.com/Tumor?qsrc=3044http://wiki.ask.com/Genetic_damage?qsrc=3044


14/34

There are three factors that control the amount, or dose, of radiation received from a source.

Radiation exposure can be managed by a combination of these factors:

1. Time: Reducing the time of an exposure reduces the effective doseproportionally. An example of reducing radiation doses by reducing the timeof exposures might be improving operator training to reduce the time theytake to handle a source.

2. Distance: Increasing distance reduces dose due to the inverse square law.Distance can be as simple as handling a source with forceps rather thanfingers.

3. Shielding: The term 'biological shield' refers to a mass of absorbing materialplaced around a reactor, or other radioactive source, to reduce the radiationto a level safe for humans.[1] The effectiveness of a material as a biologicalshield is related to its cross-section for scattering and absorption, and to afirst approximation is proportional to the total mass of material per unit areainterposed along the line of sight between the radiation source and theregion to be protected. Hence, shielding strength or "thickness" isconventionally measured in units ofg/cm2. The radiation that manages to getthrough falls exponentially with the thickness of the shield. In x-ray facilities,the plaster on the rooms with the x-ray generator contains barium sulfateand the operators stay behind a leaded glass screen and wear lead aprons.Almost any material can act as a shield from gamma or x-rays if used insufficient amounts.

Practical radiation protection tends to be a job of juggling the three factors to identify the most

cost effectivesolution.

In most countries a national regulatory authority works towards ensuring a secure radiation

environment in society by setting requirements that are also based on the international

recommendations for ionizing radiation (ICRP - International Commission on RadiologicalProtection): - Justification: No unnecessary use of radiation is permitted, which means that the

advantages must outweigh the disadvantages. - Limitation: Each individual must be protected

against risks that are far too large through individual radiation dose limits. - Optimization:Radiation doses should all be kept as low as reasonably achievable. This means that it is not

enough to remain under the radiation dose limits. As permit holder, you are responsible for

ensuring that radiation doses are as low as reasonably achievable, which means that the actualradiation doses are often much lower than the permitted limit.

Types of radiation

Different types ofionizing radiationbehave in different ways, so different shielding techniques

are used.

Particle radiation consists of a stream of charged or neutral particles, bothcharged ions and subatomic elementary particles. This includes solar wind,cosmic radiation, and neutron flux in nuclear reactors.

o Alpha particles (heliumnuclei) are the least penetrating. Even veryenergetic alpha particles can be stopped by a single sheet of paper.
http://wiki.ask.com/Effective_dose?qsrc=3044http://wiki.ask.com/Inverse_square_law?qsrc=3044http://wiki.ask.com/Forceps?qsrc=3044http://wiki.ask.com/Radiation_protection#cite_note-0http://wiki.ask.com/Cross_section_(physics)?qsrc=3044http://wiki.ask.com/X-ray?qsrc=3044http://wiki.ask.com/Plaster?qsrc=3044http://wiki.ask.com/Barium_sulfate?qsrc=3044http://wiki.ask.com/Lead_glass?qsrc=3044http://wiki.ask.com/Lead_shielding?qsrc=3044http://wiki.ask.com/Gamma_ray?qsrc=3044http://wiki.ask.com/Cost-effectiveness?qsrc=3044http://wiki.ask.com/Cost-effectiveness?qsrc=3044http://wiki.ask.com/Ionizing_radiation?qsrc=3044http://wiki.ask.com/Ionizing_radiation?qsrc=3044http://wiki.ask.com/Particle_radiation?qsrc=3044http://wiki.ask.com/Particle_radiation?qsrc=3044http://wiki.ask.com/Solar_wind?qsrc=3044http://wiki.ask.com/Cosmic_radiation?qsrc=3044http://wiki.ask.com/Neutron_flux?qsrc=3044http://wiki.ask.com/Nuclear_reactor?qsrc=3044http://wiki.ask.com/Alpha_particle?qsrc=3044http://wiki.ask.com/Alpha_particle?qsrc=3044http://wiki.ask.com/Helium?qsrc=3044http://wiki.ask.com/Atomic_nucleus?qsrc=3044http://wiki.ask.com/Alpha_particle?qsrc=3044http://wiki.ask.com/Effective_dose?qsrc=3044http://wiki.ask.com/Inverse_square_law?qsrc=3044http://wiki.ask.com/Forceps?qsrc=3044http://wiki.ask.com/Radiation_protection#cite_note-0http://wiki.ask.com/Cross_section_(physics)?qsrc=3044http://wiki.ask.com/X-ray?qsrc=3044http://wiki.ask.com/Plaster?qsrc=3044http://wiki.ask.com/Barium_sulfate?qsrc=3044http://wiki.ask.com/Lead_glass?qsrc=3044http://wiki.ask.com/Lead_shielding?qsrc=3044http://wiki.ask.com/Gamma_ray?qsrc=3044http://wiki.ask.com/Cost-effectiveness?qsrc=3044http://wiki.ask.com/Ionizing_radiation?qsrc=3044http://wiki.ask.com/Particle_radiation?qsrc=3044http://wiki.ask.com/Solar_wind?qsrc=3044http://wiki.ask.com/Cosmic_radiation?qsrc=3044http://wiki.ask.com/Neutron_flux?qsrc=3044http://wiki.ask.com/Nuclear_reactor?qsrc=3044http://wiki.ask.com/Alpha_particle?qsrc=3044http://wiki.ask.com/Helium?qsrc=3044http://wiki.ask.com/Atomic_nucleus?qsrc=3044http://wiki.ask.com/Alpha_particle?qsrc=3044


15/34

o Beta particles (electrons) are more penetrating, but still can beabsorbed by a few millimeters ofaluminum. However, in cases wherehigh energy beta particles are emitted shielding must be accomplishedwith low density materials, e.g.plastic, wood, water or acrylic glass(Plexiglas, Lucite) [1]. In the case of beta+ radiation (positrons), thegamma radiation from the electron-positron annihilation reaction poses

additional concern.o Neutron radiation is not as readily absorbed as charged particle

radiation, which makes this type highly penetrating. Neutrons areabsorbed by nuclei of atoms in a nuclear reaction. This most-oftencreates a secondary radiation hazard, as the absorbing nucleitransmute to the next-heavier isotope, many of which are unstable.

o Cosmic radiation is not a common concern, as the Earth's atmosphereabsorbs it and the magnetosphere acts as a shield, but it poses aproblem for satellites and astronauts and frequent fliers are also at aslight risk. Cosmic radiation is extremely high energy, and is verypenetrating.

Electromagnetic radiation consists of emissions ofelectromagnetic waves,the properties of which depend on the wavelength.

o X-ray and gamma radiation are best absorbed by atoms with heavynuclei; the heavier the nucleus, the better the absorption. In somespecial applications, depleted uranium is used, but lead is much morecommon; several centimeters are often required. Barium sulfate isused in some applications too. However, when cost is important,almost any material can be used, but it must be far thicker. Mostnuclear reactors use thick concrete shields to create a bioshield with athin water cooled layer of lead on the inside to protect the porousconcrete from the coolant inside.

o Ultraviolet (UV) radiation is ionizing but it is not penetrating, so it canbe shielded by thin opaque layers such as sunscreen, clothing, andprotective eyewear. Protection from UV is simpler than for the otherforms of radiation above, so it is often considered separately.

In some cases, improper shielding can actually make the situation worse, when the radiation

interacts with the shielding material and createssecondary radiation that absorbs in the

organisms more readily.

Shielding design

Shielding reduces the intensity of radiation exponentially depending on the thickness.

This means when added thicknesses are used, the shielding multiplies. For example, a practical

shield in a fallout shelteris ten halving-thicknesses of packed dirt, which is 90 cm (3 ft) of dirt.

This reduces gamma rays by a factor of 1/1,024, which is 1/2 multiplied by itself ten times.Halving thicknesses of some materials, that reduce gamma ray intensity by 50% (1/2) include[2]

(see also Kearney, ref):

Material Halving Halving Density, Halving Mass,
http://wiki.ask.com/Beta_particle?qsrc=3044http://wiki.ask.com/Beta_particle?qsrc=3044http://wiki.ask.com/Electrons?qsrc=3044http://wiki.ask.com/Aluminum?qsrc=3044http://wiki.ask.com/Plastic?qsrc=3044http://wiki.ask.com/Wood?qsrc=3044http://wiki.ask.com/Water?qsrc=3044http://wiki.ask.com/Acrylic_glass?qsrc=3044http://www.oseh.umich.edu/TrainP32.pdfhttp://wiki.ask.com/Positron?qsrc=3044http://wiki.ask.com/Electron-positron_annihilation?qsrc=3044http://wiki.ask.com/Neutron_radiation?qsrc=3044http://wiki.ask.com/Neutron_radiation?qsrc=3044http://wiki.ask.com/Neutron?qsrc=3044http://wiki.ask.com/Atomic_nucleus?qsrc=3044http://wiki.ask.com/Nuclear_reaction?qsrc=3044http://wiki.ask.com/Cosmic_ray?qsrc=3044http://wiki.ask.com/Cosmic_ray?qsrc=3044http://wiki.ask.com/Earth's_atmosphere?qsrc=3044http://wiki.ask.com/Magnetosphere?qsrc=3044http://wiki.ask.com/Satellite?qsrc=3044http://wiki.ask.com/Astronaut?qsrc=3044http://wiki.ask.com/Electromagnetic_radiation?qsrc=3044http://wiki.ask.com/Electromagnetic_radiation?qsrc=3044http://wiki.ask.com/Electromagnetic_wave?qsrc=3044http://wiki.ask.com/Wavelength?qsrc=3044http://wiki.ask.com/X-ray?qsrc=3044http://wiki.ask.com/X-ray?qsrc=3044http://wiki.ask.com/Gamma_radiation?qsrc=3044http://wiki.ask.com/Atom?qsrc=3044http://wiki.ask.com/Atomic_nucleus?qsrc=3044http://wiki.ask.com/Depleted_uranium?qsrc=3044http://wiki.ask.com/Lead?qsrc=3044http://wiki.ask.com/Barium_sulfate?qsrc=3044http://wiki.ask.com/Ultraviolet?qsrc=3044http://wiki.ask.com/Ultraviolet?qsrc=3044http://wiki.ask.com/Sunscreen?qsrc=3044http://wiki.ask.com/Bremsstrahlung?qsrc=3044#Secondary_radiationhttp://wiki.ask.com/Bremsstrahlung?qsrc=3044#Secondary_radiationhttp://wiki.ask.com/Fallout_shelter?qsrc=3044http://wiki.ask.com/Radiation_protection#cite_note-1http://wiki.ask.com/Radiation_protectionhttp://wiki.ask.com/Beta_particle?qsrc=3044http://wiki.ask.com/Electrons?qsrc=3044http://wiki.ask.com/Aluminum?qsrc=3044http://wiki.ask.com/Plastic?qsrc=3044http://wiki.ask.com/Wood?qsrc=3044http://wiki.ask.com/Water?qsrc=3044http://wiki.ask.com/Acrylic_glass?qsrc=3044http://www.oseh.umich.edu/TrainP32.pdfhttp://wiki.ask.com/Positron?qsrc=3044http://wiki.ask.com/Electron-positron_annihilation?qsrc=3044http://wiki.ask.com/Neutron_radiation?qsrc=3044http://wiki.ask.com/Neutron?qsrc=3044http://wiki.ask.com/Atomic_nucleus?qsrc=3044http://wiki.ask.com/Nuclear_reaction?qsrc=3044http://wiki.ask.com/Cosmic_ray?qsrc=3044http://wiki.ask.com/Earth's_atmosphere?qsrc=3044http://wiki.ask.com/Magnetosphere?qsrc=3044http://wiki.ask.com/Satellite?qsrc=3044http://wiki.ask.com/Astronaut?qsrc=3044http://wiki.ask.com/Electromagnetic_radiation?qsrc=3044http://wiki.ask.com/Electromagnetic_wave?qsrc=3044http://wiki.ask.com/Wavelength?qsrc=3044http://wiki.ask.com/X-ray?qsrc=3044http://wiki.ask.com/Gamma_radiation?qsrc=3044http://wiki.ask.com/Atom?qsrc=3044http://wiki.ask.com/Atomic_nucleus?qsrc=3044http://wiki.ask.com/Depleted_uranium?qsrc=3044http://wiki.ask.com/Lead?qsrc=3044http://wiki.ask.com/Barium_sulfate?qsrc=3044http://wiki.ask.com/Ultraviolet?qsrc=3044http://wiki.ask.com/Sunscreen?qsrc=3044http://wiki.ask.com/Bremsstrahlung?qsrc=3044#Secondary_radiationhttp://wiki.ask.com/Fallout_shelter?qsrc=3044http://wiki.ask.com/Radiation_protection#cite_note-1


16/34

Thickness, inchesThickness, cm g/cm g/cm

lead 0.4 1.0 11.3 12

concrete 2.4 6.1 3.33 20

steel 0.99 2.5 7.86 20

packed soil 3.6 9.1 1.99 18

water 7.2 18 1.00 18

lumber or other

wood11 29 0.56 16

depleted

uranium0.08 0.2 19.1 3.9

air 6000 15000 0.0012 18

Column Halving Mass in the chart above indicates mass of material, required to cut radiation by

50%, in grams per square centimetre of protected area.

The effectiveness of a shielding material in general increases with its density.

ALARP

Main article: ALARP

ALARP, is an acronym for an important principle in exposure to radiation and otheroccupational health risks and stands for "As Low As Reasonably Practicable".[3]The aim is to

minimize the risk ofradioactive exposure or other hazard while keeping in mind that some

exposure may be acceptable in order to further the task at hand. The equivalent term ALARA,"As Low As Reasonably Achievable", is more commonly used in the United States and Canada.

This compromise is well illustrated in radiology. The application ofradiationcan aid the patient

by providing doctors and other health care professionals with a medical diagnosis, but the

exposure should be reasonably low enough to keep the statistical probability ofcancers or

sarcomas (stochastic effects) below an acceptable level, and to eliminate deterministic effects(e.g. skin reddening or cataracts). An acceptable level of incidence of stochastic effects is

considered to be equal for a worker to the risk in another work generally considered to be safe.

This policy is based on the principle that any amount of radiation exposure, no matter how small,can increase the chance of negative biological effects such as cancer, though perhaps by a

negligible amount. It is also based on the principle that the probability of the occurrence of

negative effects of radiation exposure increases with cumulative lifetime dose. These ideas are
http://wiki.ask.com/Lead?qsrc=3044http://wiki.ask.com/Concrete?qsrc=3044http://wiki.ask.com/Soil?qsrc=3044http://wiki.ask.com/Depleted_uranium?qsrc=3044http://wiki.ask.com/Depleted_uranium?qsrc=3044http://wiki.ask.com/Earth's_atmosphere?qsrc=3044http://wiki.ask.com/ALARP?qsrc=3044http://wiki.ask.com/Radiation_protection#cite_note-2http://wiki.ask.com/Radiation_protection#cite_note-2http://wiki.ask.com/Radioactive_exposure?qsrc=3044http://wiki.ask.com/Radiology?qsrc=3044http://wiki.ask.com/Ionizing_radiation?qsrc=3044http://wiki.ask.com/Ionizing_radiation?qsrc=3044http://wiki.ask.com/Ionizing_radiation?qsrc=3044http://wiki.ask.com/Cancer?qsrc=3044http://wiki.ask.com/Cancer?qsrc=3044http://wiki.ask.com/Sarcoma?qsrc=3044http://wiki.ask.com/Radiation_protectionhttp://wiki.ask.com/Radiation_protectionhttp://wiki.ask.com/Radiation_protectionhttp://wiki.ask.com/Radiation_protectionhttp://wiki.ask.com/Lead?qsrc=3044http://wiki.ask.com/Concrete?qsrc=3044http://wiki.ask.com/Soil?qsrc=3044http://wiki.ask.com/Depleted_uranium?qsrc=3044http://wiki.ask.com/Depleted_uranium?qsrc=3044http://wiki.ask.com/Earth's_atmosphere?qsrc=3044http://wiki.ask.com/ALARP?qsrc=3044http://wiki.ask.com/Radiation_protection#cite_note-2http://wiki.ask.com/Radioactive_exposure?qsrc=3044http://wiki.ask.com/Radiology?qsrc=3044http://wiki.ask.com/Ionizing_radiation?qsrc=3044http://wiki.ask.com/Cancer?qsrc=3044http://wiki.ask.com/Sarcoma?qsrc=3044


17/34

combined to form the linear no-threshold model. At the same time, radiology and other practices

that involve use of radiations bring benefits to population, so reducing radiation exposure can

reduce the efficacy of a medical practice. The economic cost, for example of adding a barrieragainst radiation, must also be considered when applying the ALARP principle.

There are four major ways to reduce radiation exposure to workers or to population:

Shielding. Use proper barriers to block or reduce ionizing radiation. Time. Spend less time in radiation fields. Distance. Increase distance between radioactive sources and workers or

population. Amount. Reduce the quantity of radioactive material for a practice.

What Are Radioactive Isotopes?ByWendy Morgan, eHow Contributor

Radioactive isotopes, also called radioisotopes, are atoms with a different number of neutrons

than a usual atom, with an unstable nucleus that decays, emitting alpha, beta and gamma raysuntil the isotope reaches stability. Once it's stable, the isotope becomes another element entirely.

Radioactive decay is spontaneous so it's often hard to know when it will take place or what sortof rays it will emit during decay.

How Many?

1. There are around 3800 radioactive isotopes. At present there are up to 200radioactive isotopes used on a regular basis, and while some are found innature, most others have to be manufactured to suit specific needs, such asfor hospitals, research labs and manufacturers.

How Are They Manufactured?

2. Radioactive isotopes can be manufactured in several ways, the most commonby neutron activation in a nuclear reactor which involves capturing a neutronby the nucleus of an atom which results in an excess of neutrons (neutronrich). Some radioactive isotopes are produced in a cyclotron in which protons
http://wiki.ask.com/Linear_no-threshold_model?qsrc=3044http://www.ehow.com/members/ds_01d83f49-9bd7-4932-8234-e4aa576731fb.htmlhttp://wiki.ask.com/Linear_no-threshold_model?qsrc=3044http://www.ehow.com/members/ds_01d83f49-9bd7-4932-8234-e4aa576731fb.html


18/34

are introduced to a nucleus resulting in a deficiency of neutrons (proton rich).(source:http://www.eoearth.org/article/Radioisotopes_in_industry)

Significance

3. Radioactive isotopes have very useful properties. Alpha, beta and gammaradiation can permeate solid objects like an x-ray, but are progressivelyabsorbed by them. The amount of this penetration depends on severalfactors including the energy of the radiation, mass of the particle, and densityof the solid. These properties can lead to many uses for radioisotopes in thescientific, medical, archaeological and industrial fields.The uses of radioactiveisotopes in these fields depend on what element they become after theyreach stability.

Uses in the Medical Field

4. Chromium-51, for example, which forms from emitted alpha rays duringradioactive isotope decay, is used in the classifying of blood cells andmeasuring protein loss in the human body. Cobalt-60, another elementformed from radioactive isotopes emitting beta and gamma rays, is oftenused in cancer treatment. Oxygen-18 and Technetium-99 are used asbiological tracers, helping doctors locate tumors and other problems invarious parts of the human body. They are also used in x-rays and boneimaging.They are used in killing off damaged cells and treating abnormal cellgrowth as rapidly dividing cells are particularly sensitive to radiation.

Uses in Archaeology and Industry

5. They can also be used in the field of archaeology. Radioactive isotopeelements such as Carbon-14, Lead-210, and Potassium-40 are used in datingof rocks and historical earth. Chlorine-36 and Tritium are used in measuringthe age of ground water up to millions of years. In industry they are used asfuel for nuclear reactors, in the manufacturing of domestic smoke alarms,tracing factory waste that may cause pollution, and predicting the behavior ofheavy metals in water. Sodium-24 and Magnesium-27, for example, are usedto locate leaks in water pipes, while iridium-192 is used in wire in radiographydevices.

Other Uses

6. Other uses of these isotopes are in the study of chemical and biologicalprocesses in plant life for agriculture, treating and preserving food in order tomake it safer for consumption and to have a longer shelf-life when in storesfor purchase, and for chemical pest control


19/34

What Are Radioactive Isotopes?ByWendy Morgan, eHow Contributor

Radioactive isotopes, also called radioisotopes, are atoms with a different number of neutrons

than a usual atom, with an unstable nucleus that decays, emitting alpha, beta and gamma rays

until the isotope reaches stability. Once it's stable, the isotope becomes another element entirely.Radioactive decay is spontaneous so it's often hard to know when it will take place or what sort

of rays it will emit during decay.

How Many?

1. There are around 3800 radioactive isotopes. At present there are up to 200radioactive isotopes used on a regular basis, and while some are found innature, most others have to be manufactured to suit specific needs, such asfor hospitals, research labs and manufacturers.

How Are They Manufactured?

2. Radioactive isotopes can be manufactured in several ways, the most commonby neutron activation in a nuclear reactor which involves capturing a neutronby the nucleus of an atom which results in an excess of neutrons (neutronrich). Some radioactive isotopes are produced in a cyclotron in which protonsare introduced to a nucleus resulting in a deficiency of neutrons (proton rich).(source:http://www.eoearth.org/article/Radioisotopes_in_industry)

Significance

3. Radioactive isotopes have very useful properties. Alpha, beta and gammaradiation can permeate solid objects like an x-ray, but are progressivelyabsorbed by them. The amount of this penetration depends on severalfactors including the energy of the radiation, mass of the particle, and densityof the solid. These properties can lead to many uses for radioisotopes in thescientific, medical, archaeological and industrial fields.The uses of radioactiveisotopes in these fields depend on what element they become after theyreach stability.

Uses in the Medical Field

4. Chromium-51, for example, which forms from emitted alpha rays duringradioactive isotope decay, is used in the classifying of blood cells andmeasuring protein loss in the human body. Cobalt-60, another elementformed from radioactive isotopes emitting beta and gamma rays, is oftenused in cancer treatment. Oxygen-18 and Technetium-99 are used asbiological tracers, helping doctors locate tumors and other problems invarious parts of the human body. They are also used in x-rays and bone
http://www.ehow.com/members/ds_01d83f49-9bd7-4932-8234-e4aa576731fb.htmlhttp://www.ehow.com/members/ds_01d83f49-9bd7-4932-8234-e4aa576731fb.html


20/34

imaging.They are used in killing off damaged cells and treating abnormal cellgrowth as rapidly dividing cells are particularly sensitive to radiation.

Uses in Archaeology and Industry

5. They can also be used in the field of archaeology. Radioactive isotopeelements such as Carbon-14, Lead-210, and Potassium-40 are used in datingof rocks and historical earth. Chlorine-36 and Tritium are used in measuringthe age of ground water up to millions of years. In industry they are used asfuel for nuclear reactors, in the manufacturing of domestic smoke alarms,tracing factory waste that may cause pollution, and predicting the behavior ofheavy metals in water. Sodium-24 and Magnesium-27, for example, are usedto locate leaks in water pipes, while iridium-192 is used in wire in radiographydevices.

Other Uses

6. Other uses of these isotopes are in the study of chemical and biologicalprocesses in plant life for agriculture, treating and preserving food in order tomake it safer for consumption and to have a longer shelf-life when in storesfor purchase, and for chemical pest control

Agricultural Applications - radioactive tracers

Radioisotopes can be used to help understand chemical and biological processes in plants. This is

true for two reasons: 1)radioisotopes are chemically identical with other isotopes of the sameelement and will be substituted in chemical reactions and 2)radioactive forms of the element can

be easily detected with a Geiger counter or other such device.

Medical Uses

Bone imaging is an extremely important use of radioactive properties. Supposed a runner isexperiencing severe pain in both shins. The doctor decides to check to see if either tibia has a

stress fracture. The runner is given an injection containing 99Tcm. This radioisotope is a gamma

ray producer with a half-life of 6 hours.


21/34

After a several hour wait, the patient undergoes bone imaging. At this point, any area of the body

that is undergoing unusually high bone growth will show up as a stronger image on the screen.

Therefore if the runner has a stress fracture, it will show up on the bone imaging scan.

This technique is also good for arthritic patients, bone abnormalities and various other

diagnostics.

Still need to describe mechanism!!

Radioactive Preparation

in medicine, a preparation that is used in the radioisotope diagnosis of disease and the

radiotherapy of tumors. Radioactive preparations are either radioactive isotopes or compounds of

radioactive isotopes and various inorganic or organic substances.

Of the several hundred natural and artificial radioactive isotopes, only those are useddiagnostically that upon introduction into the organism either participate in the metabolic process

or the organic or systematic activity under study. These radioactive preparations have a short

effective half-life, which results in an insignificant radiation load on the organism being studied;the preparations are characterized by the type and energy of radiation (beta or gamma rays),

which are recorded using radiometric methods.

The most widely used radioactive preparations include various compounds of99mTc (in the

diagnosis of brain tumors and in the study of central and peripheral hemodynamics), 131I and itscompounds (in studies of iodine exchange and kidney and liver function), 111In and 113In (in liver

studies), such colloid solutions and macroaggregates as 99mTc, 198Au, 131I, and 111In (in the study of

the lungs, liver, and brain), and such gaseous radioactive preparations as 133Xe, 85Kr, and 15O (inthe study of lung function and central and peripheral hemodynamics).

The major criterion used in selecting a radioactive preparation for the radiotherapy of a

malignant tumor is the ability to apply a therapeutic dose of ionizing radiation to the focus of the

affection, while at the same time maximally sparing surrounding tissues. This is achieved by

using radioactive preparations in various aggregate statestrue and colloid solutions,suspensions, granules, rods, needles, beads, wire, and bandagesand by using isotopes with

optimal radiophysical characteristics (type and energy of radiation).

In clinical practice, solutions of Na131I are used in the treatment of iodine-absorbing metastasesof malignant tumors of the thyroid gland; colloids and suspensions of90Y, 198Au, and 32P are used

in the interstitial and intracavitary radiotherapy of tumors; and granules, rods, beads, and needles


22/34

that contain 90Y, 60Co, and 192Ir are used in the treatment of tumors of the female reproductive

organs, cancer of the oral mucosa and the lungs, and brain tumors.

Measurement of radioactivity.

Radioactive decay is arandom process and therefore fluctuations are

expected in the radioactivity measurement. That is why measurement of

radioactivity must be treated by statistical methods.

In every measurement a deviation from the true value or error is likely to

occur. There are two types oferrors - systematic and random. The accuracy of a

measurement indicates how closely it agrees with the true value. The precision of aseries of measurements describes the reproducibility and indicates the deviation

from the average or mean value. The closer the measurement is to the averagevalue, the higher the precision, whereas the closer the measurement is to the true

value, the more accurate is the measurement. It is important to keep in mind, that a

series of measurements may be quite precise but their value may be far from the

true value. Precision can be improved by eliminating the random errors, better

accuracy is obtained by removing both the random and systematic errors.

The average or mean value is obtained by adding the values of all

measurements divided by the number of measurements. The standard deviation

indicates the deviation from the mean value and is a measure of precision. Thestandard deviation in radioactive measurements indicates the statistical fluctuations

in radioactive disintegration. If the number of measurements is large, the

distribution can be approximated by a Gaussian distribution even if the radioactive

decay follows the Poisson distribution law. For practical reasons, only single

measurement is obtained on radioactive sample instead of multiple repeat counts to

determine the mean value. The precision of a count of a radioactive sample can be

increased by accumulating a large number of counts in a single measurement

because of decreasing the standard deviation.

Interaction of radiation with matter.

All radiations may interact with the atoms of the matter during their passage

through it producing ionization and excitation of the atoms. These radiations are


23/34

called ionizing radiation. The mechanism of interaction differ for particulate and

electromagnetic type of radiation.

The interaction of beta particles as a charged particles and gamma radiation

as an electromagnetic radiation is the most important from the point of view of

using them in nuclear medicine.

Beta particles interact primarily with the electrons of the absorber atoms andrarely with the nucleus.

Ionization occurs when beta particle transfers sufficient amount of its energy

to the orbital electron and ejects it from the atom. As a result ion pair is formed.

This process may rupture chemical bonds in the molecules. Ionization is used

namely in the radiation therapy and also serves as a mean of the detection of

charged particles in ion chambers.

When energetic beta particles, namely electrons, pass close to the nucleus of

the atom, they lose energy as a result of deceleration. This loss of energy appears

as an x ray and is called bremsstrahlung. Bremsstrahlung production increases withthe kinetic energy of the beta particles and the atomic number of the absorber. That

is why high energy beta particles are stored in plastic rather than shielding by lead.

Beta plus particles, positrons, combine with the orbital electrons andproduce two 511 keV photons of gamma radiation, so called annihilation

radiation, that are emitted in exactly opposite directions. This is the basis ofpositron emission tomography.

Gamma rays interact with orbital electrons and if their energy is very high

they may also interact with the nucleus of the absorber atoms. They travel a long

path in the absorber before losing all energy and so they are called penetrating

radiations.

There are three mechanisms by which gamma rays interact with absorberatoms from which two are important for nuclear medicine.

Photoelectric effect means transfer of all energy of gamma photon to anorbital electron, called photoelectron, and ejecting it from the atom. The

photoelectron then loses its energy by ionization and excitation.


24/34

Compton scattering means transfer of only a part of energy of gamma

photon to an electron and ejecting it. The gamma photon with less energy is

deflected from its original direction. The scattered photon may then undergo

further photoelectric or Compton interaction and the Compton electron may cause

ionization or excitation.

Depending on the photon energy and the density and thickness of the

absorber, some photons may pass through the absorber without any interaction.

Attenuation of gamma radiations by means of their interaction with absorberis an important factor in radiation protection. The term half-valuelayeris defined

as the thickness of the absorber that reduces the intensity of a photon beam by one

half. It depends on the energy of the radiation and the atomic number of the

absorber.

Radiation detection.

Interaction of ionizing radiations with the matter is also used for their

detection and measurement. There are several principles of radiation detection in

nuclear medicine. Some of them are used in radiation protection, others in

measurement and imaging.

The oldest principle is darkening of photographic emulsion. This principle isused in the personnel dosimetry. The film badge is most popular and cost-effective

for personnel monitoring and gives reasonably accurate readings of exposures from

beta, gamma and x radiations. The film badge consists of a radiation sensitive filmheld in a plastic holder. Filters of copper and lead are attached to the holder to

differentiate exposure from different types and energies of radiation.

Another principle is thermoluminiscence. Several inorganic crystals (e.g.LiF) can accumulate radiation energy and hold it. If the crystal is heated from 300

to 400 degrees of Celsius, it emits light in amount proportional to the absorbed

energy. Thermoluminiscent dosimeters, so called TLD, are mostly used as a fingerdosimeters, so inorganic crystals are held in a plastic holders and plastic rings. It

gives an accurate exposure reading and can be reused.


25/34

Another principle is converting the energy of radiation to electriccurrent.

There are two basic principles based on ionization and excitation.

First is ionization of gas molecules, the second is excitation and ionization ofsolid, liquid or plastic material, called scintilator, which emits photons of light

after absorbing radiation. Light is then converted to the electric current by means

of photomultiplier tube.

Gas-filled detectors collect the ion pairs as a current with the application of avoltage between two electrodes. The measured current is proportional to the aplied

voltage and the amount of radiation.

At a lower voltages from 50 to 300 V, only the primary ion pairs formed by

the initial radiation are collected. Ionization chambers operate in this region. Thedetector is a cylindrical chamber with a central wire filled with air or different

gases. These detectors are primarily used for measuring high intensity radiation.

Dose calibrators and pocket dosimeters are the common ionization chambers usedin nuclear medicine.

The dose calibrator is one of the most essential instrument in nuclear

medicine for measuring the activity of radionuclides and radiopharmaceuticals. Itmust be regularly checked for constancy, accuracy, linearity and geometry.

At higher voltages from 1000 to 1200 V, the current becomes identical

regardless of how many ion pairs are produced by the incident radiation. Geiger-

Mller counters operate in this region. Geiger-Mller counters are used to monitor

the radiation level in different work areas and they are called area monitors or

survey meters. They are more sensitive than ionization chambers but they cannotdiscriminate between energies. They are almost 100% efficient for counting alpha

and beta particles but have only 1 to 2% efficiency for counting gamma and x rays.

Scintillation detectors consist of scintilator emitting flashes of light afterabsorbing gamma orx radiation. The light photons produced are then converted to

an electrical pulse by means of a photomultiplier tube. The pulse is amplified by a

linear amplifier, sorted by a pulse-height analyzer and then registred as a count.


26/34

Different solid or liquid scintillators are used for different types of radiation. In

nuclear medicine, sodium iodide solid crystals with a trace of thallium NaI(Tl) are

used for gamma and x ray detection.

The basic solid scintillation counter consists of na NaI(Tl) crystal or

detector, a photomultiplier (PM) tube , a preamplifier, a linear amplifier, a pulse-

height analyzer (PHA) and a recording device.

NaI(Tl) crystals are hermetically sealed in aluminium containers. They are

fragile and must be handled with care. Room temperature should not be changed

suddenly because of possibility of cracks in the crystal. In well counters and

thyriod probes smaller and thicker crystals are used, whereas larger and thinner

crystals are employed in imaging devices like gamma cameras.

PM tube consists of a light-sensitive photocathode facing the crystal, seriesofdynodes in the middle and an anode at the other end - all enclosed in a vacuum

glass tube. A high voltage about 1000 V is applied between the photocathode and

the anode of the PM tube. The electron pulse reaching the anode is delivered to the

preamplifier. The amplitude of the pulse is proportional to the number of light

photons received by the photocathode and in turn to the energy of gamma ray

photon absorbed in the crystal. The applied voltage must be very stable.

A linear amplifier amplifies further the signal from the preamplifier and

delivers it to the pulse height analyzer for analysis of its amplitude.

A pulse height analyzeris a device that selects for counting only those pulsesfalling within preselect voltage intervals and rejects all others. Desired pulses are

ultimately delivered to the recording devices such as scalers, computers, films and

so on.

In the output of scintillation counter a distribution of pulse heights will be

obtained depicting a spectrum of gamma ray energies. In an ideal situation each

gamma ray would be seen as a line on the gamma ray spectrum. In reality, the

photopeakis broder, which is due to various statistical fluctuations in the process

of forming the pulses.

When gamma rays interact with the scintillation crystal by means of

Compton scattering, the Compton electrons of variable energies result in a pulse

height smaller than that of photopeak. Thus the gamma ray spectrum will show a

continuum of pulses corresponding to Compton electron energies between zero and

photopeak, so called Compton continuous spectrum. The relative hights of the


27/34

photopeak and the Compton scattering depend on the photon energy as well as the

size of the crystal.

There are several basic characteristics of counters important from the pointof view of using them in nuclear medicine procedures.

Backgroundof the detector means registered count rate without presence ofany measured specimen. It is caused namely by cosmic radiation, natural

radioactivity, radioactivity of building material and of the material the detecting

system consists of. It can be minimized by shielding detector in lead cover, by

using special material for its construction or by means of pulse-height analyzer to

exclude inappropriate radiation energy from detection.

The energy resolution simply means the width or the sharpness of thephotopeak or the ability to discriminate the gamma ray photons of similar

energies.

The detection efficiency is given by the observed count rate divided by the

disintegration rate of a radioactive sample. It depends on the type and energy ofthe detected radiation, size and thickness of the detector crystal and geometric

efficiency of the measuring.

The dead time is the time period during which the counter is insensitive for

the radiation detection. This time enclosed time needed to process a radiation event

starting from interaction in the crystal all the way up to forming and recording

pulse. Dead time for Geiger-Mller detectors is from 100 to 500 microseconds, for

NaI(Tl) crystal from 0,5 to 5 microseconds. Dead time loss of counts is a seriousproblem at high count rates. Either count rates must be lowered or corrections must

be made to the observed count rates.


28/34

Scintillation detectors can be used as a part of both nonimagingand imaging

devices. From the nonimaging devices, scintillation well counters and thyroid

probes are used.

The gamma well counterconsists of a scintillation detector with a hole in the

center, for a sample to be placed inside for increasing the geometric efficiency and

hence the counting efficiency of the counter, and other associated electronics. Well

counters are used namely for in vitro measurements of different samples. They are

usually available with automatic sample changers and are mostly programmable

with computers. Their major advantage is high detection efficiency which is from

50% to 70% for 140 keV gamma photons.

The thyroid probe is a scintillation counter used for measuring radioacitivity

above the thyroid gland to assess the uptake of 131I after its oral administration. In

contrast to well counter the thyroid probe must be equipped with collimator, whichlimits the field of view. This is a cylindrical barrel made of lead and it covers all

the detector including PM tube. It prevents the gamma radiations from other organs

to reach the detector.

Radionuclide imaging devices.

Radionuclide imaging is based on the ability to detect electromagnetic

radiation emitted from an injected radioactive tracer that has been taken up by the

organ to be studied. The electromagnetic radiation used is in the form of gamma

rays orx rays. The radiation absorbed by the detector is used to generate a digital

image by the computer, which is then interpreted by the physician. This imaging

device is called scintillation camera or gamma camera. It also employs sodium


29/34

iodide scintillation detector and the associated electronics like nonimaging systems

do.

The most frequently used scintillation camera is ofAnger type (Hal O. Angerinvented it in the 1960), it means it has a large scintillation crystal which makes

possible to detect radiation from the entire field of view simultaneously and

therefore it is capable of recording dynamic as well as static images of the area of

interest in the patient. Many sophisticated improvements have been made of the

cameras over the years, but the basic principles of the operation are essentially the

same.

Like nonimaging probe also scintillation camera consists of a collimator, a

scintillation crystal, PM tubes, a preamplifier, an amplifier, a pulse-height analyser

and recording or display devices. In addition it must have an X,Y positioningcircuit to localize the point of interaction of gamma ray with the crystal. Theoperation of a camera is performed by a computer built in it and is very convenient

for the staff. The detector head (collimator, scintillation crystal, PM tubes and

amplifiers) is mounted on a stand called gantry, which moves the head to theappropriate position for patient imaging.

Detectors have usually large (about 50 cm in diameter) circular or

rectangular NaI(Tl) crystal with about 1 cm thickness. In front of the crystal, acollimator is attached to limit the field of view so that gamma radiations from

outside the field of view cannot reach the crystal.

Collimatoris usually a plate of lead with many holes. Most frequently used

are parallel-hole colimators with holes parallel to each others and perpendicular tothe detector face. They are of different types according to energy of radionuclides

used for imaging and according to their spatial resolution. Thus we can distinguish

high resolution, high sensitivity and all purpose (with compromise parameters)

types orlow, medium and high energy types. The spatial resolution of the parallel-hole collimators decreases with the increasing distance of the object from the front

of the collimator but the sensitivity is the same. That is why every data collection


30/34

must be performed with the minimal space between collimator forhead and the

patient body surface.

The collimator of conical shape with one up to three holes on the top iscalled pinhole and is used for imaging of small and near to the surface lying

organs, such as a thyroid gland, tight join or infant kidneys. It has very good

resolution but very poor sensitivity. Nowadays also collimators with special

converging holes called fan-beam are made for small organs imaging, such as abrain. Also collimators with divergingholes can be used, namely in cameras with

small crystal to make possible imaging of large organs. Collimators designed for

higher energy are thicker with thicker septa between holes to prevent penetration

of photons through them.

Gamma cameras have many photomultiplier tubes (up to 90) mounted to the

back of the crystal with optical grease. They are used to be of hexagonal shape and

the output from each is used to define the X and Y coordinate of the point of

interaction of the gamma ray in the crystal by the use of an X,Y positioning circuit.

The X and Y pulses are than projected on a cathode ray tube or oscilloscope tocreate image or can be stored in the computer in a square matrix for further

processing. The larger the number of PM tubes, the better the spatial resolution on

the image.

The use ofdigital computers in nuclear medicine has considerably increased

and today all nuclear medicine studies are being analyzed by the computers. Data

from a gamma camera must be digitized by the analog-to-digital converter. Thecomputer memory approximates the area of the detector as a square matrix from

32x32 up to 1024x1024 size. Each element of this matrix is called pixel andcorresponds to a specific X and Y location in the detector. The number in each

pixel corresponds to the number of pulses detected in this specific location of thecrystal. In this manner of storing data in computer memory, called frame mode (themost common mode in nuclear medicine), we must preset the matrix size, the

number of images (frames) in the study, and the time of collection of data per

frame or total counts to be collected per frame.


31/34

Computers are very important part of imaging devices, current cameras

cannot operate without it, namely ECT is impossible without computers. The basic

function of computers during image construction is to correct and maintain

cameras performance parameters, such as high voltage in the PM tubes and

photopeak setting in pulse-height analyzer.

Another improvement of image quality is achieved by images smoothing and

filtering, mathematical operation with images, background subtraction, creation of

parametric and tomographic images, regions of interest (ROI) creation, dynamic

curves creation and their mathematical processing with computing quantitative

data of physiological processes, by using of interpolation to reduce digital raster

effect on matrix image, smoothing images by means of temporal and spatial filters

or by color coding according to number of counts in each pixel.

Very important camera parameter, field of view uniformity, can beeffectively improved by means of computers. Detector uniformity means a uniform

response throughout the field of view. Even properly tuned and adjusted gamma

cameras produce nonuniform images with count density variation of up to 10%.

There are several possibilities of using computer for nonuniformity correction.

These are: correction of number of counts in each pixel of image matrix to an

average value, setting of the own photopeak for each pixel in image matrix,different gain of high voltage for each photomultiplier tube and spatial distortion

correction.

To ensure a high quality of images, quality control tests must be performed

routinely on these devices. The most common tests are the positioning of the

photopeak, field of view uniformity and background check, which must be

performed daily. The spatial resolution of the camera should be checked wee

Msc biology

Documents

Transcript of Msc biology