Yield of delayed neutrons in the thermal-neutron-induced reaction 245 Cm( n, f )
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CLEI Experiment
Yield of Delayed Neutrons in the Thermal-Neutron-Induced Reaction
245
Cm(n, f )
V. R. Andrianov1) , V. N. Vyachin2), N. A. Gundorin1) , A. A. Druzhinin2) , K. V. Zhdanova1) , A. N. Lihachev1), L. B. Pikelner1) , N. V. Rebrova1), I. M. Salamatin1), and V. I. Furman1) Received March 11, 2008
Abstract—The yield of delayed neutrons, νd , from thermal-neutron-induced fission of 245 Cm is measured. Experiments aimed at studying the properties of delayed neutrons from the fission of some reactor isotopes and initiated in 1997 were continued at the upgraded Isomer-M facility by a method according to which a periodic irradiation of a sample with a pulsed neutron beam from the IBR-2 reactor was accompanied by recording emitted neutrons in the intervals between the pulses. The accuracy of the resulting total delayedneutron yield νd = (0.64 ± 0.02)% is two times higher than that in previous measurements. This work was performed at the Frank Laboratory of Neutron Physics at the Joint Institute for Nuclear Research (JINR, Dubna). PACS numbers: 28.20.-v, 25.85.Ec DOI: 10.1134/S1063778808100037
1. INTRODUCTION Delayed-neutron emission in actinide fission induced by neutrons is of fundamental importance for accomplishing a controlled nuclear chain fission reaction. Yields and time characteristics of delayed neutrons from the neutron-induced fission of major and minor reactor isotopes are important nuclear constants used in calculations of nuclear-reactor kinetics. Knowing these constants for many transuranium elements, one can better understand the fission process, reveal its regularities, construct models, and predict properties of delayed neutrons for as-yet-unexplored nuclei. However, the accuracy of experimental data on delayed neutrons for the major and most of the minor actinides is insufficient for calculating nuclear-reactor kinetics, especially in the case of a large burnup, with a reliability required for nuclear safety. Therefore, more accurate measurements of the properties of delayed neutrons or their repeated measurement by independent methods is a topical problem. In addition, such measurements would make it possible to test and improve computational procedures and phenomenological systematics important for extrapolating the characteristics of delayed neutrons to as-yet-unmeasured isotopes and for estimating the reliability of available experimental
data, which are often markedly different from the calculated results. In this study, we continued exploring delayed neutrons emitted in nuclear fission induced by thermal neutrons at the upgraded Isomer-M facility [1] using the method proposed in [2] and based on a periodic exposure of a sample to a pulsed neutron beam from the IBR-2 reactor with a subsequent detection of emitted neutrons in the intervals between the pulses. The main objective of the study was to measure the absolute delayed-neutron yield in the thermal-neutroninduced fission of the 245 Cm nucleus. The properties of delayed neutrons from 245 Cm fission induced by thermal neutrons of the reactor s
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