Abstract
A method for converting a ${\gamma}$-ray spectrum measured by a NaI(TI) scintillation detector to a dose, namely, conversion of a spectrum to an exposure, a spectrum to an air kerma, and a spectrum to a dose equivalent, is presented. A Monte Carlo simulation code was developed to calculate the response functions of the NaI(TI) scintillation detector for arbitrary ${\gamma}$-ray energies. The effect of the detector cap, the nonlinear light output of the NaI(TI) crystal in the low-energy region, and all possible processes involved in photon and electron transport, such as the photoelectric effect, compton scattering, pair production, and bremsstrahlung, were taken into account in the course of the simulation procedure. Response matrices of three different sizes($30\;{\times}\;30,\;40\;{\times}\;40,\;and\;50{\times}\;50$) were constructed by combining the response functions of a $3"{\phi}\;{\times}3"$ NaI(TI) spectrometer for ${\gamma}$-ray energies up to 3 MeV. Conversion factors for the measured spectrum to dose were evaluated by weighting the diagonal components of the inverse matrices so that the deviation deduced from the theoretical values might be the least. In order to confirm the applicability of the calculated conversion factors, the factors were used in the conversion of a measured spectrum to a dose, and the result was compared with those obtained by the G(E) operator and the energy-band methods.