CALCULATION OF EFFICIENCY AND CROSS SECTION OF CYLINDRICAL SCINTILLATORS IN AXISYMMETRICAL GAMMA-RAY FIELDS

A method is described for the accurate numerical calculation of efficiency and cross section (i.e. the ratio of the rate detected quanta to the nondirectional flux) of cylindrical scintillators in axisymmetrical γ-ray fields. Sample results are presented for 3″ × 3″ and 5″ × 5″ NaI scintillators for the following angular distributions of the radiation: 1) isotropic radiation (100 keV - 100 MeV); 2) extended parallel beams at angles of 0°, 22.5°, 45°, 67.5° and 90° to the axis of the ocintillator, results plotted vs μR; 3) a field of multiply scattered γ-rays in an extended scattering medium with initial energy E0 = 1 MeV approximated by a) Gaussian angular distribution, broadening with decreasing energy, b) angular distributions given by Berger36) and c) by Stehfest37). The direction of symmetry of these radiation fields is taken parallel to the axis of the scintillator. The approaches to efficiency and cross section used hitherto for multiply scattered γ-radiation are briefly discussed. The exact results presented here differ remarkably from these simple approximations. © 1969.