Measurement of Fission Fragment Mass Distribution in Resonance Region

1986 Fiscal Year Final Research Report Summary

• Project/Area Number: 60580181
• Research Category: Grant-in-Aid for General Scientific Research (C)
• Allocation Type: Single-year Grants
• Research Field: Nuclear engineering
• Research Institution: Kyoto University
• Principal Investigator: NAKAGOME Yoshihiro Research Reactor Institute, Kyoto University ; Research Associate, 原子炉実験, 助手 (50027455)
• Co-Investigator(Kenkyū-buntansha): TAMAI Tadaharu Research Reactor Institute, Kyoto University ; Associate Professor, 原子炉実験所, 助教授 (10027427) ; FUJITA Yoshiaki. Research Reactor Institute, Kyoto University ; Professor, 原子炉実験所, 教授 (60027422) ; KIMURA Itsuro Research Reactor Institute, Kyoto University ; Professor, 原子炉実験所, 教授 (40027404)
• Project Period (FY): 1985 – 1986
• Keywords: Nuclear Fission / Spin-dependence of Fragment Mass Distribution / Plutonium-239 / Very Thin Sample / 薄膜試料 / 二重エネルギー測定法

Research Abstract

The purpose of this project is to measure the spin-dependence of fission fragment mass distribution for resonance neutron-induced fission of <^(239)Pu> and analyse that theoretically.
The mass distribution has been obtained by measuring each fragment energy simultaneouly. This is called a double-energy measurement method. In this measurement, a very thin plutonium sample was required because the framgent energy loss in the sample should be small as possible. We designed a double-glove box to treat plutonium. The plutonium sample was prepared by picking up a thin film which was made by dropping a plutonium-collodion solution onto the surface of th water. This method was established by trial and errors. The sample thickness was measured about 1 <micro> gPu/ <cm^2> by a <^(239)Pu> -decay- <alpha> counting and measuring fission events, and was calculated by using some quantities obtained in the sample preparation.
The fragment mass distribution for resonance neutron-induced fission of <^(239 )Pu> was measured by using an electron linear accelerator. The resonance neutron energies used in this experiment were 0.3 eV(J <pi> =1+) and 15.5 eV(J <pi> =0+) which were determined by a time-of-flight method. Insufficient fragment mass distributions were obtained because of very low intensity of the resonance neutrons at the plutonium sample. Then we measured the fragment mass distribution for thermal neutron-induced fission for <^(239)Pu> , and obtained good result. Thermal neutron is not resonant, but the strong influence of J <pi> =1+ to the mass distribution is expected. The thermal neutron data gives very useful informations for 1+ spin-dependent mass distribution.
Althogh we could not experimentally compare the fragment mass distributions for different resonance neutron energies, we estimated a yield ratio of 1+ resonance mass distribution to 0+ one with a spin-dependent statistical theory which was proposed by us.
We advance this experiment including improvement in an intense resonance neutron source, and compare the experimental with theoretical results.