A study of the angular response of personnel dosimeters and their conceptual design

The American National Standard includes angular response measurements as part of personnel dosimeter performance testing. Currently, dosimeters are designed and calibrated to provide isotropic responses, i.e. constant readings irrespective of changes in incident radiation angles of exposure. However, the human body does not uniformly respond to radiation incident from different exposure angles as documented in the International Commission on Radiation Units and Measurement (ICRU) Reports 39, 43 and 47. The PC version of Monte Carlo Neutron-Photon transport code (MCNP 4A) was used to model various thermoluminescent dosimeters to evaluate the dependence of dosimeter response on off-normal angles of incident radiation. Energies and radiation angles recommended by HPS N13.11 were used in the Monte Carlo simulations. The results were compared with an empirical equation for optimum dosimeter angular response function for off-normal radiation angles proposed in previous research. The results also discussed the overestimate caused by the use of isotropic dosimeters in assessing the effective dose equivalent (HE), the limiting quantity defined in International Commission on Radiological Protection (ICRP) Publication 26. A conceptual dosimeter with optimum angular response was designed on MCNP. In conclusion, the design criteria for next generation dosimeters was summarized