The Monte Carlo code PEAK was developed to calculate the peak efficiency of Ge (Li) and high purity Ge (HPGe) detectors to voluminal sources of cylindrical and Marinelli-type shapes. The accuracy of the PEAK code has already been verified for Ge (Li) detectors and in this study its accuracy to HP Ge detectors was investigated. First, the sensitive region of the HP Ge detector was determined from the combination of the collimated beam and the standard point source experiments. By using this shape of the sensitive region, the peak efficiencies to radioactive agar, activated alumina and manganese dioxide samples encapsulated in a cylindrical vessel were calculated and showed very good agreement within about several % with the ex-perimental results.
Cylindrical concrete and stainless steel blocks were irradiated one week by the cyclotron of Institute for Nuclear Study of University of Tokyo. Their gamma-ray activities were measured by a high-purity Ge (HPGe) detector and simultaneously the residual exposure rates were measured by the GM survey-meter. Radionuclides and their gamma-ray activities were obtained by dividing the peak counts of the measured pulse height spectra by the peak efficiencies. For this purpose, the HP Ge detector having known sensitive region in good accuracy was used, and its peak efficiency to these cylindrical sources was calculated by the PEAK Monte Carlo code including the self-absorption correction. The residual exposure rates were obtained from the simple analytical calculation by using these gamma-ray activities uniformly distributed in the concrete and stainless steel blocks. The calculated exposure rates showed very good agreement with those measured by the GM survey-meter. From this comparison, the relationship between gamma-ray activities and residual exposure rates were evaluated in good accuracy for these volume samples.
An Escherichia coli strain, CR34, harboring both pSC101 and ColEl-amp plasmids was exposed to media containing rifampicin (100μg/ml) and/or chloramphenicol (180 μg/ml) and the cells were labeled for 20 min with3H-thymine at 3, 25 and 50 min after exposure to drug (s) . The plasmid DNA synthesis was assayed by DNA-DNA hybridization with14C-labeled pSC 134 DNA as internal marker. In the presence of rifampicin, the replication of pSC 101 was from 57 to 104% that in its absence, and that of ColEl-amp was from 17 to 26%. The DNA replication of pSC 101 after addition of chloramphenicol was reduced to 35 to 75%, and that of ColEl-amp was reduced to 39% and then restored to 92%. This restoration was not observed in the presence of rifampicin.
The technique of freezing whole body autoradiography using positron emitting nuclides has been developed in the present study. Because of rapid decay of positron emitters, a frozen section to contact with a X-ray film must be prepared within a few hours. All the procedures to obtain autoradiograms of rats using18F-2-deoxy-2-fluoro-D-glucose (18F-FDG) or11C-glucose-fructose mixture (11C-glucose) were described in detail. In the present technique, exposure must be performed at-20°C to keep a section frozen. Density of X-ray films after exposure at 20°C or-20°C was examined using various radioactive sections. The reduction of the density exposured at-20°C was observed. But the density exposured at-20°C was proportional to the radioactivity. Freezing whole body autoradiography of rats bearing subcutaneous AH109A tumors was performed using18F-FDG (half life of 109.7 min) and11C-glucose (half life of 20 min) . Density of tumors and other organs on the autoradiogram was comparable with tissue distribution studies of18F-FDG and11C-glucose. Freezing whole body autoradiography can be feasible for the analysis of tissue distribution on positron emitting radiopharmaceuticals.
A substoichiometric radiochemical method for the determination of mercury has been developed using 1- (2 pyridylazo) -2-naphthol (PAN) as a chelating agent. The chelate was extracted at pH 9.5 (Na2CO3NaHCO3buffer) into chloroform. 15-65 μg of mercury was determined with an accuracy ±0.9%. Effects of many diverse metal ions have been studied and procedures were developed for the suppression of interference due to these ions.
Though the mechanism of201Tl accumulation in thyroid tumours is not known yet, there are some hypotheses. In order to study the mechanism, potassium contents and Na, K-ATPase, of various organs of rats and human thyroid glands were analized. The conclusion through these experiments is as follows, (1) as the potassium contents and Na, K-ATPase activity of thyroid glands are not obviously higher than those of other organs, the201Tl accumulation in thyroid is thought to be not owing to the similarity to the potassium ion, (2) pointing out high activity of Na, K-ATPase in heart and kidney, the accumulation mechanism of201Tl in these organs has high relation to this activity, (3) though there is a tendency to have higher potassium contents among thyroid tumours, the difference in potassium contents between their histopathology is small; so that the tumour specificity is not explained from the potassium contents, and (4) as for Na, K-ATPase activity of thyroid tumours, papillary adenocarcinoma and follicular adenoma, which take more in201Tl, have tendency to show higher activity; adenomatous goitre, which take less in201Tl, has tendency to show lower activity. We suggested that the factor relating to the accumulation mechanism of201Tl may be multiple, and Na, K-ATPase plays an important role in201Tl specific uptake in thyroid tumours.