Measurement of Ambient Dose Equivalent Using a NaI(Tl) Scintillation Detector

Abstract

Ambient dose equivalent rates for terrestrial radiation fields were measured by a 3" diam. x 3" NaI(Tl) scintillation spectrometer. The factor for converting the measured pulse height spectrum of the NaI(Tl) scintillation detector to ambient dose equivalent was calculated using the response matrix of the detector. The relationship between air kerma rates and ambient dose equivalent rates for the measured terrestrial radiation fields at different locations was found to be H*(10) = 1.21 Ka + 1.26 where H*(10) is ambient dose equivalent rate in nSv.h-1 and Ka is air kerma rate in nGy.h-1. This linear relationship comes mainly from the facts that the ratio H*(10)/Ka for monoenergetic photons in the energy range from 300 keV to 3 MeV falls within 1.2 ± 10% and the effective energy of the terrestrial fields is usually within the above range. Ambient dose equivalent rate for the measured terrestrial field can be estimated using this formula within an error of ±7% from the measured air kerma rate in the range 80 ~ 280 nGy.h-1.