21-29 July 2022
US/Pacific timezone

Measurement of neutron-induced fission cross sections of U-235 and U-238 relative to n-p scattering at CSNS Back-n facility

25 Jul 2022, 12:45
Folsom ()



Yonghao Chen


Neutron-induced fission cross sections of U-235 and U-238 are ones of the most important nuclear data since they are fundamental to nuclear energy. Fission cross sections of U-235 and U-238 have been evaluated as standard data up to 200 MeV and they are always used as references for other cross section measurements. However, the experimental data in high neutron energy region are scarce. Especially above 30 MeV of neutron energy, there are only a few measurements with obvious discrepancies. Thus conducting a measurement in high energy region is quite necessary meaningful.

The back-streaming neutron facility (Back-n) at China Spallation Neutron Source (CSNS) is a newly built neutron beamline started commissioning since 2018. Back-n provides neutrons from 0.5 eV to 200 MeV with an achievable flux of 1.6×10^7 n/cm2/s at 55 meters away from the spallation target. It is therefore a good platform for nuclear data measurement. We performed an experiment at Back-n for measuring the fission cross sections of U-235 and U-238 relative to n-p elastic scattering. The U-235 and U-238 samples are sealed in an ionization chamber for measuring their fission reactions. A polythene (PE) foil and several recoiling proton telescopes (RPT), consisting of silicon detectors and cesium iodide scintillators, are setup in a vacuum chamber located at the downstream of the fission chamber. The proton events are selected by the ΔE-E identification. The proton events produced via 12C(n, p) reactions are obtained by measuring a graphite sample with equivalent thickness, which is used to correct the proton reaction rate measured with the PE sample.

We will firstly introduce the CSNS Back-n facility. Then we will go to details of the data analysis of fission chamber and RPT. Finally the preliminary results of fission cross section of U-235 and U-235 from 10 to 100 MeV will be shown.

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