Measurement of the Thermal Neutron Cross Section of the⁹⁰Sr(<i>n, γ</i>)⁹¹Sr Reaction

Abstract

To obtain fundamental data for the research of the transmutation of nuclear waste, the thermal neutron cross section of the reaction 90Sr(n, γ)91Sr has been measured by means of a radiochemical method. Strontium chloride targets containing about 2 MBq of 90Sr were irradiated for 10 min with reactor neutrons. Activation detectors of Co/Al and Au/Al alloy wires were irradiated simultaneously to monitor the neutron flux and Westcott's epithermal index r (T/T 0)1/2. The irradiated Sr samples were purified chemically and their r-ray spectra were measured with a high purity Ge detector. Since the targets included 85Sr, a γ-ray emitter and a tracer for 90Sr, and a ratio of the amount of 85Sr to that of 90Sr was measured in advance, an effective cross section of the 90Sr(n, γ)91Sr reaction for a reactor neutron spectrum was determined from the ratio of radioactivities of 91Sr and 85Sr, and neutron flux data. The resonance integral was also measured by a modified Cd-ratio measurement. Considering an upper limit of the resonance integral to be 0.16 b, the thermal neutron cross section (2,200 m/s neutron cross section) of 90Sr(n, γ)91Sr reaction was found to be 0.0153 ±S:0.0013 0.0042b. The value obtained is only 1/50 of the value reported by Zeisel (1966), and is in good agreement with the figure reported by McVey et al. (1983).