Radiation Protection Today - Spring 2022 - Page 35

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BACK TO BASICS

Do you know anyone who ' d like to learn a bit more about radiation ? These pull-out sheets will help .
Shielding materials for radioactive sources
Sources can require little to extensive shielding to allow people to work safely around them . The amount and type of shielding depends on the amount and type of radiation emitted by various radionuclides , and how close people need to be to the source .
The diagram below shows the effectiveness of different materials to reduce transmission of the main types of radiation .
As you can see , alpha radiation is easily shielded with paper or clothing but is very dangerous if its particles are inhaled . Shielding is therefore not required for sources that only emit alpha radiation . Beta transmission can be attenuated to safe levels of radiation with thin layers of
Alpha
Beta
Gamma or X-ray
Neutron
Neutron
Paper or clothing
Few millimetres of aluminium or thin lead
aluminium or lead . An example is the use of Phosphorus-32 in research laboratories . P-32 emits high energy beta radiation , but 10mm of clear acrylic plastic is very effective at shielding it and also allows operators to see what they are working on .
Gamma or X-ray radiation is more penetrating and requires very dense material to shield it . The half value layer is the thickness of material required to reduce the intensity of incident radiation by half .
The table overleaf shows the half value layer of different materials for shielding gamma radiation emitted from different radionuclides commonly used in sealed sources .
Bremsstrahlung radiation
Dense materials , e , g . Several centimetres of lead or metres of concrete
Secondary gamma radiation may require additional shielding
Material of low atomic number , e , g . hydrogen-rich material such as water , polyethylene or paraffin wax
Secondary gamma radiation
Gamma , X-rays and neutrons only attenuated , not completely absorbed
Radiation Protection Today Summer 2022 35