It has been shown that the fluctuation of background spectrum of γ rays measured by pure germanium detector is caused by the variation of atmospheric radioactivity (222Rn, 220Rn and their daughters) . In order to diminish the fluctuation, nitrogen gas from the cryogen tank of the detector is flown into the lead vessel for shielding natural radiations. With the aid of the gas flow, peak counts of γ rays from daughters of222Rn and220Rn in the background spectrum can be so decreased that their fluctuations become within statistical uncertainties. The fluctuation of the total count (0-2800 keV) also becomes within the statistical uncertainty although the decrease of the count by the gas flow is at most 4%.
The natural abundance of15N (expressed as δ15N per mil relative to air N2) in the tissues and the change of15N abundance during the digestion processess in cattle, pig, and goat were investigated. The15N abundances of cattle tissues differed by about 3.5‰ with high values in heart, urinary bladder and diaphragm. The ages of cattle did not affect on the15N abundances of liver and kidney in cattle. The15N abundances of urine were lower, and those of feces were a little higher than the values of diets in cattle and pigs. The δ15N values of milk and blood were higher than the value of diets. Two peaks of15N abundances at forestomach and caecum were observed during the digestion processes of diet in goats. The mechanisms of the variation of15N abundances in animal bodies were briefly discussed.
Serum neuron-specific enolase (NSE) levels were studied in 105 patients with malignant neoplasms (lung cancer 38, others 67) , 13 patients with various benign diseases and 7 healthy adults. The mean serum NSE level in adult control subjects was 7.4±0.8 ng/ml, and cut of level was decided 10 ng/ml. Serum NSE levels were elevated in 14/38 (37%) of patients with lung cancer and in 14/ 67 (21%) of patients with the other malignant neoplasms. In patients with benign diseases, serum NSE level was elevated only in one patient with pituitary adenoma. In 7 patients with small cell lung cancer, the positive rate was higher (86%) than in those with non-small cell lung cancer (26 %), and serum NSE levels were higher than 25 ng/ml except one case. There was no correlation between serum NSE and CEA (carcinoembryonic antigen) levels in patients with small cell lung cancer, also in patients with lung cancer. The measurement of serum NSE level seemed to be useful for diagnosis in patients with small cell lung cancer.