New experimental measurement of ${}^{\mathrm{nat}}\mathrm{Er}(n,\gamma )$ cross sections between 1 and 100 eV

${}^{162}\mathrm{Er}$ and ${}^{164}\mathrm{Er}$ are two of the 35 $p$ nuclei, and their ($n,\gamma$) cross sections are important input parameters in nuclear astrophysics network calculations. The neutron capture cross section in the resonance region of isotopes and even the natural erbium (${}^{\mathrm{nat}}\mathrm{Er}$) sample has not been measured experimentally according to the EXFOR database. The ($n,\gamma$) cross section of ${}^{\mathrm{nat}}\mathrm{Er}$, using ${\mathrm{C}}_6{\mathrm{D}}_6$ liquid scintillator and pulse height weighting techniques to measure prompt $\gamma$ rays, has been measured in the energy range of 1–100 eV using a back streaming white neutron facility at China Spallation Neutron Source. The deduced neutron capture cross sections matches the evaluation databases ENDF/B-VIII.0, ENDF/B-VII.1, JENDL-4.0, and ROSFOND-2010, and resonance parameters extracted from the $R$-matrix code in the 1–100 eV region.

Figure 1

The main nucleosynthesis path for ${}^{\mathrm{nat}}\mathrm{Er}$ in massive stars. Black boxes represent stable isotopes; yellow, blue, and red boxes represent unstable isotopes. Yellow color indicates that the nucleus decays via EC; red indicates decay via $\beta$ decay; while blue indicates that the nucleus decays via both EC and $\beta$ decay.

Figure 2

The neutron cross section ${\sigma }_c$ of natural erbium calculated by their isotopes capture cross section ${\sigma }_c$ and was normalized by their abundance weights.

Figure 3

Relative positions and setup of the detectors. (a) Detector distance is 14.87 cm and 17.18 cm in plane setup. (b) The detector PMT plane to target is 7.3 cm. (c),(d) Rotate the $x$ axis by 12 degrees and the $y$ axis by 20 degrees to get the final detector layout

Figure 4

(a) The ${\mathrm{C}}_6{\mathrm{D}}_6$ original efficiency. (b) Weighted efficiency. (c) The ratio of weighted efficiency to $\gamma$ ray energy. For below 1.5 MeV, the weighted efficiency is not proportional to the energy to eliminate the influence of the weight function failure by setting a threshold when processing the PH spectrum.

Figure 5

The capture cross section, capture yield, target thickness correction factor ($f_c$) in the top and counting yield of the natural erbium target, empty, and carbon target (normalized to the neutron flux rate) in the bottom.

Figure 6

Neutron spectrum in Back-n ES#2

Figure 7

The contribution of the in-beam $\gamma$ background to the error of the Er target experimental results.

Figure 8

(a) The experimental data were compared with existing experimental data and evaluation data in the range of 0.1–100 keV to evaluate their validity. (b) In the 50–80 keV energy region, the results of the three experiments are closer to those of JEFF-3.3, but significantly lower than those of the other evaluation databases considered.

Figure 9

(a) Resonance fits of the experimental data (solid symbols with error bars). Blue curve represents the evaluated data listed in the ENDF/B-VIII.0 database, and black curve shows the present fits. Dotted lines represent the contribution of isotopes. (b) The experimental data show that there is a resonance structure near 44.506 eV and 47.086 eV; the former may be contributed by ${}^{162}\mathrm{Er}$, but we cannot find an obvious source for the latter. (c),(d) ${}^{162}\mathrm{Er}$ has a resonance structure at 51.4 eV and 67.8 eV, but there is no clear resonance peak in the experimental data. (e) There is a resonance structure near 87.875 eV, which is contributed by ${}^{170}\mathrm{Er}$, but we cannot identify a clear source.