A suitable calculation method to get the averaged values of the radioactivities scattered in wide regions is discussed. A preliminary analytical calculation in which no background exists is carried out before a computer simulation is done. In this case, an exact maximum-likelihood solution can be obtained, if only the distribution of the parent mean of the activities is assumed to have a gamma-distribution. In this calculation, the simplest arithmetic mean suggests to give good estimates to the parent mean. In the case that the backgrounds are to be considered, no exact maximum-likelihood solution can be obtained, and the computer simulation method can only be applied to compare the methods. The parent mean of the activities is assumed to be beta-distributed by the reason of the easiness of the treatment of the functional forms. The computer simulations are carried out to get two averaging methods, the simplest arithmetic mean and conventional weighted mean used for Gaussian-distributed data, the accumulation times being decided by the random numbers. Three to ten measured data in the region are averaged according to the methods, and the same procedures are repeated 10 000 times with the different random number series. In the results, the simplest arithmetic means always give good results for estimating the parent mean. The conventional weighted means always give not good estimates and give the smaller values than the parent mean. An exact method to get a sample standard distribution for Poisson-distributed data cannot be applied in the present case, because the parent mean distributes and has no constant value. In the case that the parent mean does not distribute, a comparison of the methods to get standard deviations is carried out for the exact method and the conventional one for Gaussian-data. The former gives always close values to the theoretical parent standard deviations and the latter gives strong discrepancies from the parent values, if the data numbers are small. The ratios of the both values do not depend on the parent means, in spite of their strong dependences on the data numbers. This suggests that the ratios can be used as the correction factors to get good estimates of the errors which are to be reported. The standard deviation obtained by the conventional method in the computer simulation are multiplied by the correction factors, and the good results can be obtained.
Monthly atmospheric concentrations of7Bewere observed at Sakai, and monthly depositions of7Bewere also observed at two places in Osaka for more than ten years, and the results of observation were compared with variation of sun spot number. The monthly average atmospheric concentrations of7Bewere found to range 1.8-9.6 mBq/m3, and the monthly depositions of7Bewere found to range 6.8-360 Bq/m2.A strong maximum of annual average atmospheric7Beconcentration was observed in 1987, in the period from 1979 through 1992. The maximum annual concentration seen in 1987 were found to be higher by factor of 1.6 than the minimum annual concentration seen in 1991. As the result of calculation, it appears that on the average about 36% of the total atmospheric concentration of7Beis ascribed to galactic cosmic-ray. Using the results of observation on monthly depositions of7Be, the amount of annual7Bedeposition ascribed to galactic cosmic-ray were estimated. The7Bedeposition in 1987 was estimated to be about 500 Bq/m2/y, in the south Osaka.
We constructed a γ-ray irradiation system with a commercial irradiation instrument, Sangyo Kagaku Co. Ltd., Model SK-951. The system is composed of an irradiator mounted with60Co (3.7 GBq) and137Cs (11.1 GBq and 111 GBq), and a mobile exposure deck having a lead shield sandwiched with iron (1200 mm (W) × 1200 mm (H) × 50 mm (D) ) at back side. This shield provides low exposure rate at wall, floor and ceiling in the present room. To limit irradiation field size within dimension of the shield, three kinds of square collimator (6.03°, 9.27° and 20.02°) were equipped around the irradiator beam, exit. The selection of collimators is automatically controlled. The abilities of shield and collimator were evaluated by calculation and measurement of exposure rate at points on the wall. By these improvements, exposure rate was lowered to the dose-equivalent limit in law.
Correlation of LU3 (LU15) which represents the cumulative uptake of99mTc-GSA from 3 (15) to 4 (16) min after injection and hepatic blood flow or receptor quantity was studied. The subjects consisted of 14 patients, including 13 patients with liver cirrhosis or chronic hepatitis and 1 patient with normal liver. LU3 and L U15 showed a good correlation with the ratio of99mTc-GSA binding to receptor and the total injected99mTc-GSA, estimated by whole body scan. LU3 and LU15 also well correlated with the maximal removal rate by nonlinear compartment model, on the other hand, they showed a poor correlation with the hepatic blood flow. It was concluded that LU3 and LU15 chiefly reflect the amount of receptors in the liver.
Kinetics of99mTc-GSA was compared by two different compartment modes, one is linear 1 compartment model and the other is nonlinear 5 compartment model. The subjects consisted of 15 patients, including 14 patients with liver cirrhosis or chronic hepatitis and 1 patient with normal liver. Both model parameters showed a good correlation with the ratio of99mTc-GSA binding to receptor and the total injected99mTc-GSA, estimated by whole body scan. Hepatic clearance (Ku) and the ratio of he-patic clearance and total excretion rate (Ku/Ke) by linear model were well correlated with the maximal removal rate by nonlinear model. On the other hand, Kuand Ku/Keshowed a poor correlation with the hepatic blood flow. It was concluded that the parameters by linear model chiefly reflect the amount of receptors in the liver.