Principles of Radiation - International Atomic Energy … –some areas of titanium dioxide pigment...

IAEAInternational Atomic Energy Agency

Principles of Radiation

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Radiation and radioactivity

• The German scientist Wilhelm Roentgendiscovered radiation in 1895

• He observed a mysterious form of invisibleradiation that had the power to fogphotographic film.

• This radiation became known as X-radiation.

• In the following year Henri Becquerelobserved that radiation with similarproperties was being emitted from certainnaturally occurring mineral ores (NORM).

Module 1: Overview of mining technologies and uranium mining

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The structure of matter and elements

Similar atoms group together to form elements, the number ofprotons in the nucleus of the atoms determining the particularelement e.g. an atom with one proton only is an atom of the elementhydrogen.


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Isotopes

• By definition, all atoms of a specific element must have the samenumber of protons in the nucleus (the atomic number).

• However they may have differing numbers of neutrons in thenucleus (mass number). These differing atoms are referred to asisotopes of a particular element.

• Isotopes are therefore atoms with the same number of protonsbut different numbers of neutrons.

• Stable atoms are required to have the correct ratio of protons andneutrons within the nucleus.

• Atoms that do not satisfy these criteria are unstable, and achievestability by the emission of ionising radiation.


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Unstable isotopes

• These unstable atoms are, therefore, “radioactive” andare referred to as radioisotopes or radionuclides. Theprocess of emitting radiation is called radioactivedecay.

• For example natural isotopes 238U, 234U and 235U, 232Thand 228Th, 228Ra and 226Ra


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Radiation and radioactivity

Radioactivity can be defined as theprocess by which unstable atoms ‘try’ tobecome more stable by emitting ionisingradiation.

There are three principal types ofradiation emitted during radioactivedecay:

• alpha particle radiation

• beta particle radiation

• gamma radiation

Note: Uranium ore emits all three typesof radiation


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Types of radiation

Ionizing Radiation


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• Radiation: Energy in the form of particles or electromagnetic waves

• Ionising radiation: Radiation with sufficient energy to remove an electron from an atom or molecule.

Definitions


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Alpha particles

• An alpha particle consists of two protons and twoneutrons tightly bound together and is ejected with ahigh velocity from the nucleus of the atom.

• The symbol for alpha particle radiation is α.

• There are many natural alpha emitters e.g. 238U, 232Th,222Rn and 226Ra.


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Alpha particles

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Alpha-radiation is only a hazard when inside your body (internal hazard)

Cannot penetrate skin Internal hazard

Stopped by paper

Found in soil, air (radon) and other radioactive materials


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Beta particles

• A beta particle decay involves the emission of anenergetic electron from the nucleus of the atom.

• The electron is referred to as the beta particle, with thesymbol β.

• The range of a beta particle is up to several metres inair and it can also penetrate a short distance into livingtissue.

• Beta particle radiation rarely presents a significantpotential external exposure hazard in mining facilities.


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Beta particles

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Beta-radiation is a skin, eye and internal hazard

Skin, eye and internal hazard

Stopped by aluminium, plastic

Found in natural food, air and water


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Gamma radiation

• Gamma radiation is a pulse of high energy,electromagnetic radiation emitted from the nucleus ofthe atom.

• Gamma radiation has the symbol and oftenaccompanies alpha or beta radiation.

• Gamma rays may travel considerable distances in airdepending on their energy and may require asignificant thickness of dense material to stop them(i.e. concrete or lead).


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Gamma radiation

Gamma-radiation is a hazard when outside your body (external, and to a lesser degree, internal hazard)

Stopped by lead

Used in medicine (X-rays)

Naturally present in soil and cosmic radiation


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Neutrons

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Neutrons are very penetrating, but only observed in nuclear industry –none in mining


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Penetrating power of radiation


Alpha particles travel only a few centimetres in air and are incapable of penetratingthe skin.Beta particles have a range of more than one meter in air and up to one centimetrein tissue.Gamma rays can be very penetrating, they can pass through the walls of plant andequipment.

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Naturally occurring radioisotopes

Naturally occurring radionuclides include the uraniumseries and the thorium series.

• A long-lived isotope is at the head of each series while astable isotope of lead ends each one.

• The uranium series originates with 238U which has ahalf-life of 4.5 thousand million years and decaysthrough a series of radioisotopes involving the emissionof alpha, beta and gamma radiation to stable 206Pb.


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238U Decay chain


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232Th Decay chain


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Decay and half-life

• The half-life is the time it takes for half of the originalradioactive material to decay.

• The half-life is a constant for a specific radioisotope.

• Natural radionuclides comprise a wide range of halflives from a few seconds to billions of years.


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Radiation quantities and units

The quantities and units used in radiation protection andsafety are based on the SI system for scientific units andare developed by the International Commission onRadiological Units (ICRU).

The main quantities of interest include:

• Activity e.g. the Becquerel (Bq)

• Dose e.g. the Sievert (Sv)


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Physical : Absorbed dose is measured in Grays (Gy)and one Gray is the radiation that is absorbed inmatter producing 1 Joule/ kg

Note: 1 Joule = the energy necessary to raise 9.8 kg toa height of 1 meter.

Biological : Dose equivalent is measured in Sieverts(Sv) which has the same definition and units asabsorbed dose (J/kg), but depends on the biologicaltissue in which it is absorbed and on the type ofparticle (alpha, beta, gamma, neutron).

Units of radiation : Gray and Sievert


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• Different radiation has different biological effects, mainlydependent on the density of ionization

• This is reflected in the “Radiation Weighting Factor”, a factorrelative to gamma radiation which shows how much the effect ismultiplied if not gamma

• It is also important to note that different body parts would beaffected differently, and this is presented by special tissueweighting factors

Not all radiation has the same biological effect


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Harmful effects of radiation

• The damaging effects of ionizing radiation becameapparent only a few years after the discovery ofradiation (X-ray researchers burns and cancers).

• Extensive research carried out in many countriesaround the world has enabled increasingly detailedestimates of the effects of low doses of radiation to bemade.


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Natural radiation is the greatest source of human exposure

We are all exposed to radiation (average annual dose = 2.0 – 2.4 mSv):

– Cosmic rays from space

– Gamma rays from soil and building materials

– Radon gas emitted from soil and rock (buildings, tunnels, cellars, etc)

– Higher exposure at higher altitudes

– Traces of radioactive materials in food and drink

There are some areas in the world (Brazil, India, China), where the ‘background’ radiation exposure can be much higher, between 10 and 200 mSv per year


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Some comparisons…

If we take a typical gamma radiation level per hour as 1, the following comparative values can be derived:

1 – typical natural background (may be higher or lower, by a small margin)3 – typical for an exploration site with U mineralisation of 0.05 – 0.06%4 – some cement5 – typical for an exploration site with U mineralisation of 0.10%5 – certain phosphate fertilisers6 – some ceramic tiles7 – typical for an exploration site with U mineralisation of 0.14 – 0.15%7 – coal burning slag

10 – on board of a local flight 14 – a phosphate mine16 – titanium minerals20 – typical for an exploration site with U mineralisation of 0.40%22 – zirconium minerals25 – geothermal energy generation waste30 – water treatment sludge40 – heavy mineral sands concentrate60 – on board of an international flight80 – tin concentrate

120 – uranium mine/processing plant250 – rare earth processing plant400 – coal mine (underground water discharge points on the surface)500 – some areas of titanium dioxide pigment plant

1000 – contaminated equipment from oil and gas industry2500 – rare earth mineral (monazite)


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The comparison below demonstrates the levels of radiation exposure indifferent industries, in milliSieverts per year

Doses comparison

Mineral sands mining: 0.1-0.7 mSv/yearPhosphate ore handling: 0.01-0.8 mSv/yearOperation of nuclear-powered ships, average: 0.8 mSv/yearIlmenite handling: 0.01-0.9 mSv/yearZircon handling: 0.5-0.9 mSv/yearUranium exploration: 0.1-1.5 mSv/yearRare earth ore mining, expected maximum: 1.0-6.0 mSv/yearMedical uses of radiation (X-ray, dentistry, nuclear medicine, etc), average: 0.5-1.5 mSv/yearScientific research (radiochemistry, linear accelerators, etc), average: 2.5 mSv/yearMineral sands processing, average: 2.7 mSv/year (can be up to 10-15 mSv/year)Industrial uses of radiation (food irradiation, density measurements, X-rays of steel), average: 2.7 mSv/yearNuclear reactor operation, average: 2.5 mSv/yearUranium milling, average: 3.3 mSv/yearAir crew on international flights, average: 4.0 mSv/yearUranium mining, average: 5.0 mSv/yearMonazite processing: 1.5 – 10.0 mSv/yearRemoval of scale, titanium dioxide pigment production: 0.01-20.0 mSv/yearRemoval of scale, oil and gas exploration/production: 0.01-33.0 mSv/year


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How dangerous is radiation?

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This amount of radiation (1000 mSv)

could cause serious harm

This is the radiationexposure limit

in one year (20 mSv)

And this is the typical radiation dose that a worker could receive at a uranium mine (5 mSv)


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General Public: 1 mSv / year

Radiation workers: 20 mSv / year(derived from 100 mSv in five years, provided that the dose does

not exceed 50 mSv in any single year)

Annual exposure limits


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Two ways we can be exposed to radiation

Exposure from a radiation source outside the body

(external radiation)

Exposure due to inhaling or ingesting radioactive material

(internal radiation)


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Summary

• Ionizing radiation was discovered just over 100 years ago.

• Radioactive materials are unstable isotopes of elements.

• They emit alpha, beta and gamma radiation.

• Naturally occurring radioactive materials occur in theenvironment.

• Human exposure to radiation involves both internal and externalexposure pathways from both natural and industrial sources.

• The harmful effects of radiation were noted at an early stage.

• Radiation doses require to be limited to reduce the risk ofharmful effects.


Principles of Radiation - International Atomic Energy … –some areas of titanium dioxide pigment...

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