THE RATIO OF THE DIRECT TO THE CUMULATIVE YIELD OF 135Xe IN THE THERMAL NEUTRON FISSION OF 233U, 235U, 239Pu, AND 241pu

Abstract

The ratio of the direct to cumulative yields of 135Xe produced in thermal neutron fission has been determined by measuring the growth and decay of this nuclide in irradiated 233U, 235U, 239Pu, and 241Pu. After a short irradiation in a low neutron flux, the amount of 135Xe increases and reaches a maximum at about 11 hours after the end of the irradiation. The direct yield of 135Xe modifies the time this maximum is reached. The ratio of the direct to cumulative yields was determined by measuring the time shift of the growth and decay curve. The amount of 135Xe was measured as a function of time after the end of irradiation by counting the 249-keV γ ray accompanying the β decay of 135Xe with a lithium-drifted germanium-diode spectrometer. The ratio of the direct to the cumulative yield was found to be 0.195 ± 0.016, 0.044 ± 0.017, 0.162 ± 0.025, and 0.070 ± 0.040 for 233U, 235U, 239Pu, and 241Pu fission respectively.