Measurements of the Prompt Fission Neutron Spectrum at LANSCE: The Chi-Nu Experiment

The goal of the Chi-Nu experiment at the Los Alamos Neutron Science Center is to measure the prompt fission neutron spectra from major actinides using a double time-of-flight method with a pulsed, white incoming neutron source. Fission events are detected with a parallel-plate avalanche counter and outgoing neutrons are detected with either a 6Li-glass or liquid scintillator detector array for low- or high-energy neutrons, respectively. A detector response matrix for the interaction of neutrons with the experimental environment for neutrons measured with the Chi-Nu 6Li-glass detector array has been calculated to obtain a full understanding of the measured Chi-Nu data and also to allow for nearly instantaneous production of simulated Chi-Nu data spectra. Prompt fission neutron spectra corresponding to 19 incoming neutron energy ranges from 0.7-20 MeV have been extracted using the ratio-of-ratios method with Chi-Nu 6Li-glass data on the neutron-induced fission of 235U.

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Prompt Fission Neutron Spectra for Neutron-Induced Fission of 239Pu and 235U

EPJ Web of Conferences ◽

10.1051/epjconf/202023901003 ◽

2020 ◽

Vol 239 ◽

pp. 01003

Author(s):

Matthew Devlin ◽

Jaime A. Gomez ◽

Keegan J. Kelly ◽

John M. O'Donnell ◽

Robert C. Haight ◽

...

Keyword(s):

Fission Neutron ◽

Science Center ◽

Detector Arrays ◽

Neutron Spectra ◽

Lithium Glass ◽

Wide Range ◽

Induced Fission ◽

Large Effort ◽

Prompt Fission ◽

Prompt Fission Neutron

We report the current results of a large effort to accurately measure the Prompt Fission Neutron Spectra (PFNS) for neutron-induced fission of 235U and 239Pu for incident neutrons with energies from 1 to 20 MeV. The Chi-Nu experiment at the Los Alamos Neutron Science Center used an unmoderated, white spectrum of neutrons to induce fission in actinide samples that were placed inside a parallel plate avalanche counter to provide a fast fission signal. A double time-of-flight technique was used to determine the incoming and outgoing neutron energies. Two neutron detector arrays, one with 54 liquid scintillators and another with 22 lithium glass detectors, were used to detect the outgoing neutrons and measure the PFNS distributions over a wide range in outgoing neutron energy, from below 100 keV to 10 MeV. Extensive Monte Carlo modeling was used to understand the experiment response and extract the PFNS. Systematic errors and uncertainties in the method have been examined and quantified. A summary of these results for incoming energies from 1 to 5 MeV is presented here.

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First Results on 238U(n,f) Prompt Fission Neutron Spectra from 1 to 200 MeV incident neutron energy

EPJ Web of Conferences ◽

10.1051/epjconf/201819303002 ◽

2018 ◽

Vol 193 ◽

pp. 03002 ◽

Cited By ~ 1

Author(s):

Paola Marini ◽

Benoit Laurent ◽

Gilbert Belier ◽

Thomas Bonnet ◽

Audrey Chatillon ◽

...

Keyword(s):

Neutron Energy ◽

Energy Region ◽

Fission Neutron ◽

High Energy ◽

Incident Neutron ◽

Good Precision ◽

Incident Neutron Energy ◽

Neutron Spectra ◽

Prompt Fission ◽

Prompt Fission Neutron

A new 238U(n,f) prompt fission neutron spectra (PFNS) measurement has been recently performed at the WNR facility of the Los Alamos National Laboratory. The measurement allows one to explore the dependence of the prompt fission neutron energy spectra on the incident neutron energy. The experimental setup couples the Chi-Nu scintillator array to a newly developed fission chamber, characterized by an improved alphafission discrimination and time resolution, a reduced amount of matter in the neutron beam and a higher actinide mass. The dedicated setup and the high statistics collected allow us to obtain a good precision on the measured fission neutron energy, as well as to explore the low energy region, down to 650keV, and the high energy region, above 5 MeV, of the emitted neutron spectrum. These are indeed the regions where discrepancies in the evaluated PFNS data are found. We present here the first preliminary results of the experiment.

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