A computer method is developed for generating response functions of a NaI detector to monoenergetic γ-rays. The method is based on an interpolation between measured response curves by a detector. The computer programs are constructed for Heath's response spectral library. The principle of the basic mathematics used for interpolation, which was reported previously by the author, et al., is that response curves can be decomposed into a linear combination of intrinsic-component patterns, and thereby the interpolation of curves is reduced to a simple interpolation of weighting coefficients needed to combine the component patterns. This technique has some advantages of data compression, reduction in computation time, and stability of the solution, in comparison with the usual functional fitting method. The processing method of segmentation of a spectrum is devised to generate useful and precise response curves. A spectral curve, obtained for each γ-ray source, is divided into some regions defined by the physical processes, such as the photopeak area, the Compton continuum area, the backscatter peak area, and so on. Each segment curve then is processed separately for interpolation. Lastly the estimated curves to the respective areas are connected on one channel scale. The generation programs are explained briefly. It is shown that the generated curve represents the overall shape of a response spectrum including not only its photopeak but also the corresponding Compton area, with a sufficient accuracy.
Loss of radon-222 in water sample stored in a polyethylene bottle was analyzed. The radon content was measured by a liquid scintillation spectrometer. The radon content (corrected for radioactive decay) was plotted against the storage period in the polyethylene bottle, and the decrease with the lapse of time was observed. The loss of radon was caused by adsorption on polyethylene surface. The radon content decreased according to the first order kinetics. Apparent rate constant of the adsorption was proportional to the surface area of the polyethylene and to the reciprocal of the sample water volume. The proportionality constant was obtained as a function of temperature, K=10200 exp (-4382/T) em·h-1. Apparent activation energy was 36 kJ·K-1·mol-1. The result supports physical adsorption. On the basis of the result, correction for radon content of a sample water stored in a polyethylene bottle was made possible.
Daily Fluctuation of Background Count Rate of a Liquid Scintillation Counter. Hiroshi SATAKE: Department of Earth Sciences, Faculty of Science, Toyama University, 3190, Gofuku, Toyama-shi 930, Japan 3H channel count rate of 3 background samples were measured for 8 days. Sample A and C were different scintillators in 100 ml teflon vials and sample B in a 20 ml glass vial. Count rate of sample A fluctuated from 3 to 7 cpm, and that of C from 6 to 12 cpm, respectively. However, count rate of sample B was about 6 cpm and rather constant. Trend of fluctuation in count rate of sample A and C were observed to be similar. On weekdays, count rate increased at night and decreased in day time. At weekend, count rate increased from Saturday evening and was constant from Sunday noon till Monday morning. Tritium Research Center where LSC is placed is ventilated from 9 a.m. to 6 p.m. on weekdays, and the ventilation is suspended on Sunday. The observed fluctuation of background was apparently related to the operation and suspension of ventilation. When ventilation was operated continuously, count rates of sample A (4 cpm) and sample C (6 cpm) became constant and corresponded to their minimum value. The fluctuation of background may be caused by radon, concentration of which varies in association with the operation and suspension of ventilation.
The concentration levels of As, Au, Hg, and Sb in the fleshy tissues of the giant African land snails (Archachatina Marginata) and periwinkles (Littorina littorea) have been measured by neutron activation analysis (NAA) . Post-irradiation separation of76As, 198Au, 197Hg, and122Sb as bromides after wet-ashing the samples in a concentrated H2SO4-HBr medium was employed. The concentration ranges of 0.015-2.48, 0.037-0.091, 0.018-0.072, and <0.01- 0.25μg/g wet weight were determined for As, Au, Hg, and Sb, respectively. The periwinkles showed higher concentrations of As, Au, and Hg than the snails. The concentrations of 16 elements, Al, Br, Ca, Cl, Co, Eu, Fe, K, La, Mn, S, Sc, Si, Sm, Sr, and Zn also have been determined in the calcareous shells of these molluscs.