The Gamma-ray Spectrometry of Fission Products, (III)

The gamma radiation from products of slow neutron fission of 235U was analyzed with a well type Nal crystal γ ray spectrometer. 0.6500 mg of natural uranium (in the chemical form of U3O8) were irradiated for 2 hr by a flux of 1011neutrons·cm-2·sec-1 in the JRR-1 reactor. The γ ray scintillation spectra between 1 and 200 days after irradiation have been recorded and compared with the calculated ones in the previous report (II). In general, the agreement of both spectra was good, but there retained some discrepancies in the following respects:(1) Relative heights of each peak compared with that of peak VIII proved that the experimental spectra in the lower energy range was less than calculated figure; on the other hand, the result was reverse in the higher energy range.(2) Experimental relative height of peak V to peak VIII was about half of the calculated one, consequently it disappeared from the spectra at an earlier time after fission than predicted from the calculation.(3) The relative abundance of 239Np, a daughter of an activation product of 238U, was three to four times of predicted one.Further, the decay rates of each peak and total counts of gamma radiation from gross fission products were measured and there were also found good agreements between the experimental results and the calculated predictions.