Measurement and resonance analysis of the ${}^{33}\mathrm{S}(n,\alpha ){}^{30}\mathrm{Si}$ cross section at the CERN n_TOF facility in the energy region from 10 to 300 keV

The ${}^{33}\mathrm{S}(n,\alpha ){}^{30}\mathrm{Si}$ cross section has been measured at the neutron time-of-flight ($\mathrm{n}\_\mathrm{TOF}$) facility at CERN in the neutron energy range from 10 to 300 keV relative to the ${}^{10}\mathrm{B}(n,\alpha ){}^7\mathrm{Li}$ cross-section standard. Both reactions were measured simultaneously with a set of micromegas detectors. The flight path of 185 m has allowed us to obtain the cross section with high-energy resolution. An accurate description of the resonances has been performed by means of the multilevel multichannel $R$-matrix code sammy. The results show a significantly higher area of the biggest resonance (13.45 keV) than the unique high-resolution ($n,\alpha$) measurement. The new parametrization of the 13.45-keV resonance is similar to that of the unique transmission measurement. This resonance is a matter of research in neutron-capture therapy. The ${}^{33}\mathrm{S}(n,\alpha ){}^{30}\mathrm{Si}$ cross section has been studied in previous works because of its role in the production of ${}^{36}\mathrm{S}$ in stars, which is currently overproduced in stellar models compared to observations.

Figure 1

Scatter plot of the signal amplitude in arbitrary units (channels) versus TOF for a ${}^{33}\mathrm{S}$ sample.

Figure 2

Scatter plot of the signal amplitude in arbitrary units (channels) versus TOF for a blank sample (substrate of a ${}^{33}\mathrm{S}$ sample).

Figure 3

Pulse height distribution of the amplitude of the signals detected in a MGAS detector. The points correspond to the experimental data with statistical uncertainties, and the red line corresponds to the fit of the distribution. The dashed blue line indicates a cut which corresponds to the cancellation of the background signals. The dashed green line indicates the selected amplitude threshold for the detector in the DAQ during the experiment.

Figure 4

Simulated efficiency for the detection of $\alpha$ particles emitted in the forward direction with the MGAS detector configuration in the present experiment.

Figure 5

Left $Y$ axis: Experimental data of the ${}^{33}\mathrm{S}(n,\alpha ){}^{30}\mathrm{Si}$ reaction measured at $\mathrm{n}\_\mathrm{TOF}$ (black points) and the fit performed in Sec. 5 (red line) in the energy range from 10 to 300 keV. Both are affected by the multiple scattering, Doppler broadening, self-shielding, and resolution function of the facility at EAR1. Right $Y$ axis: ${}^{33}\mathrm{S}(n,\alpha ){}^{30}\mathrm{Si}$ cross section at 300 K reconstructed from the resonance parameters obtained in the analysis performed in Sec. 5, only affected by Doppler broadening.

Figure 6

$R$-matrix analysis from 12.8 to 14.2 keV. The $\mathrm{n}\_\mathrm{TOF}$ data (red points) are compared with the description of ORNL [5] (dashed green line), Geel [6] (blue line), and the present work (black line).

Figure 7

$R$-matrix analysis from 50 to 100 keV. The $\mathrm{n}\_\mathrm{TOF}$ data (red points) are compared with the description of ORNL [5] (dashed green line), Geel [6] (blue line), and the present work (black line). Geel and ORNL are coincident from 60 to 100 keV.

Figure 8

$R$-matrix analysis from 124 to 132 keV. The $\mathrm{n}\_\mathrm{TOF}$ data (red points) are compared with the description of ORNL [5] (dashed green line), Geel [6] (blue line), and the present work (black line).

Figure 9

$R$-matrix analysis from 200 to 240 keV. The $\mathrm{n}\_\mathrm{TOF}$ data (red points) are compared with the description of ORNL [5] (dashed green line), Geel [6] (blue line), and the present work (black line).