Neutron capture measurement of the 165Ho at the CSNS Backn facility in the resonance energy region

TL;DR

This work measures the neutron capture cross section of $^{165}$Ho in the resonance-energy region using the Back-n white neutron beam and the 4π BaF$_2$ GTAF detector. A Bayesian SAMMY analysis in the Reich-Moore framework yields resonance parameters for 18 $s$-wave resonances below $100$ eV, revealing $D_0 = 4.53(3)$ eV and a neutron strength function $10^{-4}S_0 = 2.01(1)$, with an average radiative width $\langle \Gamma_\gamma \rangle = 88.10 \pm 1.98$ meV. The resonance kernels are largely consistent with ENDF/B-VIII.0, supporting the reliability of the extracted parameters, though some discrepancies near certain resonances highlight areas for reevaluation of the evaluated data. The measured data, including detailed uncertainty and background analyses, strengthen $^{165}$Ho as a potential standard in specific experimental setups and provide valuable inputs for nuclear data evaluations and statistical-model tests. Future improvements (e.g., incorporating $^{10}$B absorbers) could reduce background further and enable precise measurements beyond $100$ eV.

Abstract

The neutron capture yield of 165Ho have been measured at the Back-streaming White neutron beam line (Back-n) of the China Spallation Neutron Source (CSNS) using a 4π BaF2 Gamma Total Absorption Facility (GTAF). The resonance shapes in the 1eV to 1.0keV region were analyzed with the Bayesian R-matrix code SAMMY. For 18 s-wave resonances below 100eV, the resonance energy ER, neutron width Γn, and radiative width Γγ were extracted. The statistical analyses of the resonance parameters show that the nearest-neighbour level-spacing distribution follows a Wigner-Dyson form with mean spacing D0 = 4.53(3)eV,indicating chaotic compound-nucleus behaviour; Using the extracted parameters, the s-wave neutron strength function for 165Ho was derived to be 10-4S0 = 2.01(1), in excellent agreement with the values reported in both the Atlas of Neutron Resonances and ENDF/B-VIII.0 data.

Figures (13)

• Figure 1: (Color online) In the resonance energy region of $^{165}$Ho neutron capture cross section of ENDF/B-0VIII.0 compared with the data from Asghar et al.1968Asghar and Konks et al.1968Konk.
• Figure 2: (Color online) The setup of the GTAF in the measurement.
• Figure 3: (Color online) Total deposited energy $E_{sum}$ for $^{165}$Ho, empty target and beam off.
• Figure 4: (Color online) (a)The $E_{sum}$ corresponding to various $m_{cr}$ ranges with normalization performed relative to the maximum value in the $1eV \textless E_n \textless 10eV$, the area within the two arrows divided by the total area was recognized as the capture-to-background ratio. (b) The $E_{sum}$ distribution of the $^{165}$Ho(n,$\gamma$) measurement in various $m_{cr}$ ranges.
• Figure 5: (Color online) Comparisons between the $^{165}$Ho spectrum, empty sample and beam off spectrum.