The New Operational Quantity Ambient Dose in Environmental Radiation Monitoring

In ICRU Report 95, the International Commission on Radiation Units and Measurements (ICRU) has proposed jointly with the International Commission on Radiological Protection (ICRP) new operational quantities for external radiation. The quantity for environmental monitoring is ambient dose H*. This paper analyses how present ambient dosimeters and monitors for photons would respond to the new operational quantity. The results show that passive environmental dosimeters designed for determining ambient dose equivalent and capable of registering photons to energies as low as 10 keV show a strong overestimate of ambient dose in the energy interval from 15 keV to approximately 50 keV. Active dosimeters exhibit a low-energy cut-off and are not affected by the overestimation. In spectrometer-type ambient monitors, the operational quantity can be calculated by multiplying the unfolded count-rate spectrum with the conversion coefficient for H*.