Measurement of very high threshold reactions using ²⁵²Cf source

Area of Science:

• Nuclear physics
• Neutron cross-section measurements
• Nuclear data validation

Background:

• The Californium-252 (Cf-252) spontaneous fission neutron spectrum is the only standard, but its high-energy tail has high uncertainty.
• Validated cross sections with low uncertainty are crucial for reducing uncertainties in nuclear data.
• Several threshold reactions are important for nuclear data validation and integral experiments.

Purpose of the Study:

• To measure spectral averaged cross sections (SACS) for threshold reactions, including dosimetric ones, for the first time.
• To validate nuclear data libraries by comparing experimental SACS with calculated values.
• To improve the accuracy of the Cf-252 neutron spectrum standard by reducing uncertainties.

Main Methods:

• Experimental measurement of SACS for ⁵⁸Ni(n,X)⁵⁷Co, ¹⁶⁹Tm(n,3n)¹⁶⁷Tm, ¹⁹⁷Au(n,3n)¹⁹⁵Au, ²⁰⁹Bi(n,3n)²⁰⁷Bi, and ²⁰⁹Bi(n,4n)²⁰⁶Bi reactions.
• Determination of reaction rates using gamma spectrometry with a high-purity germanium detector.
• Comparison of experimentally derived SACS with values from nuclear data libraries (e.g., IRDFF-II, TENDL-2017, ENDF/B-VIII).

Main Results:

• First-time measurements of SACS for ¹⁶⁹Tm(n,3n)¹⁶⁷Tm, ²⁰⁹Bi(n,3n)²⁰⁷Bi, and ²⁰⁹Bi(n,4n)²⁰⁶Bi reactions.
• Good agreement (1.45% difference) for ¹⁶⁹Tm(n,3n)¹⁶⁷Tm with the IRDFF-II library.
• Reasonable agreement for ¹⁹⁷Au(n,3n)¹⁹⁵Au using the TENDL-2017 library.
• Agreement within uncertainty achieved for ²⁰⁹Bi(n,4n)²⁰⁶Bi with IRDFF-II, but not for ²⁰⁹Bi(n,3n)²⁰⁷Bi.
• Best agreement for ⁵⁸Ni(n,X)⁵⁷Co with the ENDF/B-VIII library.

Conclusions:

• The study provides crucial new experimental data for several threshold reactions, contributing to nuclear data validation.
• Discrepancies highlight the need for further refinement of nuclear data libraries, particularly for bismuth reactions.
• Improved cross-section data will aid in reducing uncertainties associated with the Cf-252 neutron spectrum standard.