AN EXTREMITY WRIST DOSEMETER BASED ON THE LANDAUER INLIGHTTM WHOLE BODY DOSEMETER Christopher A Perks*a and Stephane Faugoina a LANDAUER EUROPE, 33 Avenue du General Leclerc, F-92266, Fontenay-aux-Roses CEDEX, France. To perform extremity personal dosimetry around the wrist, LANDAUER EUROPE previously supplied customers in France with standard InLight dosemeters enclosed within a soft plastic pouch and a band to secure the dosemeter. Clients requested a smaller and more comfortable design. This poster gives an overview of the new design and reports on type testing of the proposed wrist badge on an ICRU pillar (wrist) phantom, in terms of the energy and angular response. Modifications were made to our dose calculation algorithm and the results of the type testing compared with the international standards. LANDAUER EUROPE EXTREMITY WRIST BADGE DESIGN The LANDAUER EUROPE extremity dosemeter is based on the standard InLight dosemeter which is used for whole body monitoring. The processing and read out of this dosemeter is the same as for the standard dosemeter. The dosemeter consists of : s A CASE THAT CONTAINS METAL AND plastic filters, s APLASTICSLIDETHATCONTAINSDETECTOR elements. > Case and slide of the InLight The detector element is a layer of dosemeter Al2O3:C sandwiched between two layers of polyester for a total thickness of 0.3mm. For the extremity wrist dosemeter the case and slide are enclosed in a heat sealed polythene pouch, together with a paper label. The pouch is designed to allow a wrist strap to be attached. This design is substantially smaller than the previous wrist badge and gives the client greater comfort while allowing the badges themselves to be read out using the same readers and procedures as our standard whole body dosemeters. A neutron dosemeter can > Extremity wrist dosemeter also be included in this badge. THE ANALYSIS OF THE EXTREMITY WRIST BADGE The InLight dosemeters are readout in readers based on the widely used conventional Panasonic readers. Those have been modified for OSL readout, principally by employing light emitting diodes as a light source. Dosemeters can be read automatically at a speed approaching 10 seconds per dosemeter, with very little need for operator intervention. An algorithm is used to determine the quantities of interest, including Hp(10) and Hp(0.07), from the individual responses of the four OSL detectors. In addition, the algorithm indicates > Automatic reader for 500 dosemeters the radiation quality (photon energy or beta particle) of the exposure. TYPE TESTING Irradiation Irradiations were performed at the Health Protection Agency’s Laboratory in the UK. Eighty badges were irradatied in accordance with international > The irradiation configuration standard procedures for photons and beta particles on an ISO standard pillar wrist phantom. A secondary standard ion chamber was used to determine the doses. Dosemeters were irradiated with a nominal 3 mSv dose. Analysis Dosemeters were read out and analysed using the standard algorithm during normal operations for whole body dosemeters at our facilities. Results for Hp(0.07) were compared to the exposed doses reported by the Health Protection Agency in their certificate for the irradiations performed. Further analysis was performed using a modification of the standard algorithm. RESULTS Energy response (Hp(0.07)) for photon energy Energy response for beta radiation Beta source 90 Sr/90Y 85 Kr Measured/reported dose (Standard algorithm) 0.67 ± 0.14 0.25 ± 0.04 Measured/reported dose (Modified algorithm) 0.97 ± 0.22 0.99 ± 0.16 Angular response for 65 keV photons MODIFICATIONS TO ALGORITHM In view of the under-response for beta particles, particularly for the lower energy 85Kr particles, changes to the algorithm were considered to improve it. A simple change to the algorithm was tested in which the results for the assessment of low energy beta particles was multiplied by a factor of four and those for the higher energy photons multiplied by a factor of 1.5. The doses assessed in this way are those given in the column for the modified algorithm. These changes have now been incorporated into the operational version of the algorithm which has been tested by comparison with these results. DISCUSSION Most of the international standard requirements in terms of type testing are common to the wrist badge and whole body. The principal differences regard the energy and angular response. International standards requirements (ISO 12794) LANDAUER EUROPE extremity dosemeter responses Energy response for photons (15 keV to 3 MeV) The response (Hp(0.07)) shall not vary Response is within ISO standard. by more than ± 50%. Energy response for beta radiation (0.5 MeV to 3 MeV (Emax)) The response (Hp(0.07)) shall not vary Under-response has been corrected by more than ± 50%. by modifications to the algorithm. Angular response (65 keV photons) The mean value of the response The response is within the Hp(0.07) at angles of incidence of 0°, requirements of the standard with 20°, 40° and 60° from normal shall the exception of the response at -60° not vary for normal incidence by more for horizontal rotation. than ± 15%. CONCLUDING REMARKS A development of the InLight dosemeter has been adopted as LANDAUER EUROPE’s extremity wrist dosemeter. Type testing revealed that doses Hp(0.07) assessed using this dosemeter were significantly low. Nevertheless, simple changes to the dose calculation algorithm have been adopted which correct this under-response.The dosemeter, with results assessed using the modified algorithm, meets the requirements of the international standard with the exceptions of angular response at -60° vertical. The tendency in this condition is for over-estimation of the dose and the dosemeter has been adopted for use for our clients requiring this service. * Presenting author, E-mail: cperks@landauer-fr.com