Development of a Detector for Measuring Effective Dose (Equivalent) for External Photon Exposures in Natural Environment

Abstract

We have developed a new shaped NaI(Tl) scintillation detector for the direct measurement of “effective dose, (E)” or “effective dose equivalent, (H^E )” for external photon exposures. These quantities related to human risk are generally difficult to be evaluated directly from measurements, because these depend not only on the energy distribution but also on the angular distribution of the gamma ray field. The present work, however, solved the problem concerning the angular dependence, by considering a detector shape that satisfies the angular response similar to human body's. The optimum dimensions of NaI(Tl) crystal for H_E and for E were determined respectively by a Monte Carlo simulation. The detector subject to H_E was manufactured and tested. The angular characteristics of the developed detector indicate a fairly good coincidence with those of the theoretical values, H_E . Together with the dose conversion method, so called “G(E) Function method”, it was made possible to directly measure effective dose (equivalent).

KEYWORDS:

• effective dose
• effective dose equivalent
• external photon exposure
• environmental radiation
• NaI(Tl) scintillation detector
• specific shaped detector
• angular sensitivity
• angular distribution
• angular correlation
• G(E) function