RadiationRadiation

Samar El-Sayed

RadiationRadiation

Radiation is an energy in the form of Radiation is an energy in the form of electro-magnetic waves or particulate electro-magnetic waves or particulate matter, traveling in the air.matter, traveling in the air.

The structure of the atomThe structure of the atomELECTRON negative,

mass nearly nothing

PROTON positive

mass (“1”)NEUTRON neutral

mass (“1”)

The structure of the atomThe structure of the atom

Particle Relative Mass Relative Charge

Proton 1 +1

Neutron 1 0

Electron 0 -1

MASS NUMBER = number of protons + number of neutrons

SYMBOL

ATOMIC NUMBER = number of protons

IsotopesIsotopesAn isotope is an atom with a different number of neutrons

Each isotope has 8 protons – if it didn’t then it just wouldn’t be oxygen any more.

Notice that the mass number is different.

RadioactivityRadioactivitySpontaneous emission of particles and/or electromagnetic radiation from an unstable nucleus.

Radiation

The nucleus is more stable after emitting some radiation – this is called “radioactice decay”.

Half lifeHalf life The time required for radioactive matter to decrease by one half (lose 50% of its activity). The decay of radioisotopes can be used to measure the material’s age. …

At start there are 16 radioisotope

s

After 1 half life, half have decayed

(that’s 8)

After 2 half lives, another half

have decayed

(that’s 12)

= radioisotope = new atom formed

Physical half lifePhysical half life Time required for the radioactive substance to lose 50% Time required for the radioactive substance to lose 50%

of its activity by radioactive decayof its activity by radioactive decay

Biological half lifeBiological half life Time required by the body to eliminate 50% of internally Time required by the body to eliminate 50% of internally

deposited quantity of radioactive substancedeposited quantity of radioactive substance

Effective half lifeEffective half life Time required for radionuclide in body to decrease by Time required for radionuclide in body to decrease by

50% as a result of biological elimination & radioactive 50% as a result of biological elimination & radioactive decaydecay

Linear energy transfer Linear energy transfer (LET)(LET)

linear collision stopping powerlinear collision stopping power The ionization density (e.g., ion pairs/cm of tissue) The ionization density (e.g., ion pairs/cm of tissue) along the path of the radiation. along the path of the radiation.

The energy a charged particle imparts to matter per The energy a charged particle imparts to matter per unit length as it traverses the matter unit length as it traverses the matter

Depends on:Depends on:

Charge Charge

Velocity Velocity

High LET : alphaHigh LET : alpha

Low LET: beta particles, x-ray, gamma rayLow LET: beta particles, x-ray, gamma ray

Ionizing RadiationIonizing Radiation Radiation that has sufficient energy to dislodge Radiation that has sufficient energy to dislodge

orbital electronsorbital electrons

Non-Ionizing RadiationNon-Ionizing Radiation Radiation that does not have the ability to Radiation that does not have the ability to

dislodge dislodge electrons, but can still cause biological electrons, but can still cause biological damage by damage by causing chemical changes or by heating causing chemical changes or by heating (vibrating) (vibrating) molecules. molecules.

Examples are ultraviolet light, microwavesExamples are ultraviolet light, microwaves..

Types of RadiationTypes of Radiation

Ionizing radiationIonizing radiationIonizing radiationIonizing radiation

IonizationIonizationRadiation is dangerous because it “ionises” atoms – in other words, it turns them into ions by “knocking off” electrons.

particulateparticulate

Ionizing radiation

Short wave electromagnetic

unchargedCharged

-ve

beta neutronsgamma rays

x-ray

alpha

+ve

Types of ionizing radiation Types of ionizing radiation

X and gamma radiation are penetrating radiation X and gamma radiation are penetrating radiation and an EXTERNAL HAZARD.and an EXTERNAL HAZARD.

stopped by lead

naturally present in soil and cosmic radiation

found in medical uses

can’t penetrate skininternal hazard

stopped by paper

found in soil, radon and other radioactive materials

Alpha RadiationAlpha Radiation

It is only a hazard when inside body (internal It is only a hazard when inside body (internal hazard)hazard)

Beta Radiation is a Skin, Eye and Beta Radiation is a Skin, Eye and Internal HazardInternal Hazard

skin, eye and internal hazard

stopped by plastic

found in natural food, air and water

The Penetrating Power of Radiation

Alpha

Beta

Gamma/X-ray

Dangers of radioactivityDangers of radioactivity

OUTSIDE the body and are more dangerous as radiation is blocked by the skin.

INSIDE the body an source causes the most damage because it is the most ionising.

Alpha

Beta

Gamma

Measurement units

Air

Exposure in air

Radioactivity

Absorbed dose in matter

Absorbed dose in tissue

(Dose equivalent)

RadioactivityRadioactivity

Number of disintegration nuclei / unit time (sec).Number of disintegration nuclei / unit time (sec).

Disintegration : spontaneous transformation in Disintegration : spontaneous transformation in number or internal arrangement of protons, number or internal arrangement of protons, neutrons in the nucleus.neutrons in the nucleus.

Units:Units:

Becquerel (Bq) = 1 disintegration/second (dps)Becquerel (Bq) = 1 disintegration/second (dps)

Curie (Ci) 1 Ci = 3.7 X 10Curie (Ci) 1 Ci = 3.7 X 1010 10 BqBq

ExposureExposure

A measure of what is emittedA measure of what is emitted

Charge (number of ions) produced in air Charge (number of ions) produced in air from ionization by gamma and x-raysfrom ionization by gamma and x-rays

Units: Units: – coulomb/ Kg aircoulomb/ Kg air– Roentgen (R)Roentgen (R)

Absorbed DoseAbsorbed Dose

The amount of energy absorbed by a The amount of energy absorbed by a given mass (e.g. water or tissue ) given mass (e.g. water or tissue )

Units:Units:

Gray (Gy)Gray (Gy)

Rad (Roentgen Absorbed Dose)Rad (Roentgen Absorbed Dose)

1 Gy = 100 rad1 Gy = 100 rad

Dose EquivalentDose Equivalent

Risk adjusted absorbed dose. Risk adjusted absorbed dose.

The absorbed dose is weighted by the radiation The absorbed dose is weighted by the radiation type and tissue susceptibility to biological damagetype and tissue susceptibility to biological damage

Takes into account the biological effect of the Takes into account the biological effect of the various types of radiationvarious types of radiation

= = absorbed dose X Radiation Weighting Factorabsorbed dose X Radiation Weighting Factor

Units Units

Sievert (Sv) 1 Sv = 100 remSievert (Sv) 1 Sv = 100 rem

rem rem

The Radiation Weighting Factor The Radiation Weighting Factor (RWF)(RWF)

Reflects differences in the amount of Reflects differences in the amount of each type of radiation necessary to each type of radiation necessary to produce the same biologic effect produce the same biologic effect

Type of radiationType of radiation RWFRWF

X-ray , gamma, or betaX-ray , gamma, or beta 11

Neutrons and High-energy protonsNeutrons and High-energy protons 1010

Alpha particlesAlpha particles 2020

What is an individual's dose equivalent from 10 What is an individual's dose equivalent from 10 mrad of gamma rays, 5 mrads of Beta particles mrad of gamma rays, 5 mrads of Beta particles and 10 mrads of neutrons? (m = milli = 1/1000) and 10 mrads of neutrons? (m = milli = 1/1000)

Dose Equivalent = mrads X RWF = mremsDose Equivalent = mrads X RWF = mrems

Gamma dose equivalent = 10 x 1 = 10Gamma dose equivalent = 10 x 1 = 10

Beta dose equivalent = 5 x 1 = 5 Beta dose equivalent = 5 x 1 = 5

Neutron dose equiv. = 10 x 10 = Neutron dose equiv. = 10 x 10 = 100100

Total 115 mrems Total 115 mrems

An exposure to 1 mrad of gamma, 10 An exposure to 1 mrad of gamma, 10 mrad of Beta particles, and 5 mrad of mrad of Beta particles, and 5 mrad of fast neutron radiations would give an fast neutron radiations would give an individual a dose equivalent of: individual a dose equivalent of:

16 mrem 16 mrem

16 µ Ci 16 µ Ci

61 mrem 61 mrem

61 mrads61 mrads

What dose of X-ray would produce the What dose of X-ray would produce the same biologic effect as 50 mrad of same biologic effect as 50 mrad of gamma or beta radiation? gamma or beta radiation?

The RWF for X-ray is also one;The RWF for X-ray is also one;

therefore, a dose of 50 mrads of X-ray therefore, a dose of 50 mrads of X-ray radiation would produce the same biologic radiation would produce the same biologic effect as 50 mrads of gamma or beta effect as 50 mrads of gamma or beta radiation. radiation.

If the radioactive material in the case study had If the radioactive material in the case study had been an alpha-emitter instead of a beta and been an alpha-emitter instead of a beta and gamma emitter, would the biologic effects be gamma emitter, would the biologic effects be greater? Explain.greater? Explain.

if the radioactive material was emitting alpha if the radioactive material was emitting alpha particles the biologic effectiveness would be particles the biologic effectiveness would be greater. greater.

The RWF for alpha particles is 20, which indicates The RWF for alpha particles is 20, which indicates a given dose of alpha radiation is twenty times a given dose of alpha radiation is twenty times more biologically effective than the same dose of more biologically effective than the same dose of beta or gamma radiation. beta or gamma radiation.

If a physicianIf a physician calculates that a young boy at the calculates that a young boy at the scene of an accident received a maximum beta scene of an accident received a maximum beta or gamma radiation radiation dose of 50 millirads or gamma radiation radiation dose of 50 millirads (mrad). Express this dose in millirems (mrem) (mrad). Express this dose in millirems (mrem) and Sieverts (Sv).and Sieverts (Sv).

The RWF for beta or gamma radiation is one; The RWF for beta or gamma radiation is one; therefore, a dose of 50 mrads of beta or gamma therefore, a dose of 50 mrads of beta or gamma radiation is equivalent to 50 mrem or 0.05 rem. radiation is equivalent to 50 mrem or 0.05 rem. One Sievert = 100 rem; therefore, 0.05 rem = One Sievert = 100 rem; therefore, 0.05 rem = 0.0005 (5×10−4) Sv 0.0005 (5×10−4) Sv

Sources of radiationSources of radiation

Natural SourcesNatural Sources Artificial sourcesArtificial sources

Exposure to ionizing radiationExposure to ionizing radiation

Internal contaminationInternal contamination (i.e., radionuclide (i.e., radionuclide deposited within the deposited within the body)body)

External contaminationExternal contamination (i.e., radionuclide (i.e., radionuclide deposited on the body deposited on the body surface)surface)

External exposureExternal exposure (Irradiation by an external (Irradiation by an external source. source.

ExternalExposure

InternalContamination

ExternalContamina

tion