When operators are likely to have direct exposure to high energy betas , the dose received by the eye must be considered . This is measured using the same types of detector as extremity measurements , but in a band which is worn on the head . From experience it is key to ensure the wearer remembers to have the white attenuator between the source of radiation and the head , because this gives a dose equivalent to a depth of 3 mm , to replicate that received by the lens of the eye .
Neil demonstrates the use of the headband dosemeter .
Where staff may be exposed to neutron radiation ( e . g . those working with fissile isotopes and those that have been mixed with beryllium such as Ra-226 / Be and Am-241 / Be ) they will need to be supplied with a suitable neutron badge . Interestingly these do not measure the neutrons directly , but use a plastic called polyallyl diglycol carbonate ( PADC , also known as CR-39 ) which is processed using an electro-chemical etching process to reveal the damage tracks left by the protons that result from neutron interactions . These tracks , which become visible under a microscope as etched pits , are then counted by image analysis , with the number of pits proportional to the neutron dose . When I first started in dosimetry these pits had to be counted by eye , but thankfully today there is technology on the market that counts them automatically .
Radon dosemeters using the same type of plastic ( PADC ) provide measurements of committed effective dose from exposure to radon and its decay products . These are less commonly used than neutron badges , but are a key consideration when handling radium , as we do at The Grove Centre .
The aforementioned types of dosemeter are all options for external radiation sources . Other dosimetry techniques are available to measure internal doses , i . e . exposure due to radionuclides deposited within the body by injection , ingestion or inhalation .
Portable Air Sampling ( PAS ) pumps are issued to staff at The Grove Centre when working with alpha-emitting nuclides . These consist of a pump connected by plastic tubing to a metal intake which holds a small filter paper . The pump runs at 2 litres per minute ( half the average breathing rate ), and the intake is worn on the chest close to the mouth and nose , so the PAS samples the air breathed by the operator . By removing the filter paper and putting it in a proportional counter , the inhalation dose received by the operator is calculated .
Where internal exposure is due to radionuclides which emit radiation which can penetrate out of the body , whole body counters can be used . These consist of shielded chambers containing external detectors , and have the advantage that they measure radiation emanating from the body directly , rather than relying on indirect bioassay methods . However , a key disadvantage is they can only be used to detect gamma emitters , due to self-shielding of the human body .
For the direct determination of internal exposure due to alpha or beta nuclides , bioassay sampling ( in-vivo monitoring ) is necessary . This measures the concentration of radioactivity in urine and faecal samples to calculate the amount of activity in the body . To estimate the dose received it is necessary to determine when the person received the intake , in order to correct for decay .
A key function of the RRA is to determine which dosimetry techniques are appropriate for a planned task . This requires close cooperation between the operator and the Radiation Protection Adviser ( RPA ).
8 Radiation Protection Today www . srp-rpt . uk