Reliability of Prompt γ-Ray Intensities for the Measurement of Neutron Capture Cross Sections

We examined the reliability of prompt γ-ray intensities by measuring ratios of thermal neutron capture cross sections on 23Na, 27Al, 51V, 55Mn, 64Ni, 65Cu, 141Pr, 186W, and 197Au at the Kyoto University Research Reactor Institute. The cross sections were obtained by two methods: the first is detecting prompt γ-rays (which we call the prompt-γ method), and the other is detecting γ-rays following β-decay (the activation method). Intensities of prompt γ-rays and decay γ-rays have been reported to have an uncertainty of about 5% and 1%, respectively. It is found that values of 65Cu and 186W have large discrepancies in the results of the two methods, by about 30%. The disagreement would be caused by inaccuracy of the absolute intensities of prompt γ-rays. The inaccuracy is estimated to be due to the incompleteness of level schemes and the detector efficiency of prompt γ-rays. We need to examine absolute intensities of prompt γ-rays when we use the prompt-γ method