Measurements for determining detection efficiencies of three NaI scintillators having dimensions of 1in. ∅×1in. to 2in. ∅×2in. were made for various gamma-ray sources distributed uniformly in water tanks. Gamma-ray energies are ranged between 0.13 MeV and 1.84 MeV, and water tanks are cylindrical ones having the diameter equal to the depth. Results were expressed by approximation formulae as a function of radii of volume-equivalent spherical water tanks, and the responses in infinite water volume were extrapolated. Counting efficiencies for a unit gamma emitter per unit volume can be calculated by this equation with reproducing errors of ±5%. The energy response was fairly flat over a wide energy range with a small tank of about 20 cm in radius, independent of the size of scintillator. Furthermore, photon number buildup factors were derived from the formula and compared with those calculated from energy buildup factors given by Goldstein, et al. The values obtained experimentally were about one half of Goldstein's. This fact implies that it would cause big errors in the determination o f counting efficiencies of gamma detectors to use the buildup factors for photon numbers calculated from those for energy or dose.
A simple and rapid method is proposed for the determination of95Zr-95Nb in sea water. The method is based on the coprecipitation of95Zr-95Nb on lanthanum hydroxide followed by the extraction with 5% tri-n-butyl phosphate in toluene from 10N hydrochloric acid solution. A high decontamination from other fission products was attained and the yield of95Zr-95Nb was larger than 99%.
The determination of gold in refined soybean oils by neutron activation analysis is described. The method which purifies radioactivated gold consists of ashing the sample in a muffle furnace, dissolving the ash in mineral acid, and preparing soild samples by reduction. The activity of gold is measured by beta-gamma coincidence and gamma counting. The detection limit is 10-8 grams for gold when the sample of 2-3 grams is irradiated by a thermal neutron flux of about 1011n/cm2⋅sec for maximum 30 hrs.