Accelerator mass spectrometry measurement of the reaction ${}^{35}\mathrm{Cl}(n,\gamma ){}^{36}\mathrm{Cl}$ at keV energies

The nuclide ${}^{35}\mathrm{Cl}$ can act as a minor “neutron poison” in the stellar slow neutron capture process. Neutron activation combined with accelerator mass spectrometry (AMS) was applied to measure the $(n,\gamma )$ cross section of ${}^{35}\mathrm{Cl}$ for neutron spectra simulating Maxwell-Boltzmann distributions of $kT\approx 30$ and 40 keV. The neutron activations were performed at the Karlsruhe Van de Graaff accelerator and at the superconducting linear accelerator of the Soreq Applied Research Accelerator Facility utilizing the ${}^7\mathrm{Li}(p,n){}^7\mathrm{Be}$ reaction. AMS measurements of the irradiated samples were performed at the 3 MV Vienna Environmental Research Accelerator, the 6 MV tandem accelerator at the Dresden AMS facility, and the 14 UD tandem accelerator of the Australian National University in Canberra. Our method is independent of previous measurements. For an energy of $kT=30\mathrm{keV}$, we report a Maxwellian averaged cross section of 8.33(32) mb. Using this new value in stellar isotopic abundance calculations, minor changes for the abundances of ${}^{35}\mathrm{Cl}$, ${}^{36}\mathrm{Cl}$, and ${}^{36}\mathrm{S}$ are derived.

Figure 1

Schematic of the activation setup at KIT.

Figure 2

Neutron irradiation spectra at KIT (a) and SARAF (b). The solid line shows the simulated neutron spectrum using the Monte Carlo codes pino [35] (a) and SimLit [36] (b), respectively. The dashed-dotted lines show Maxwell-Boltzmann fits of the data cut at 80 and 100 keV, respectively, as the high-energy part of the distribution cannot be described by a MB fit.

Figure 3

Identification spectra for a blank (a) and the irradiated sample SPI9 (b) as obtained at DREAMS. As an example the energy-loss signal from the third anode ($\mathrm{\Delta }{E}_3$) is plotted versus the energy-loss signal from the fourth anode ($\mathrm{\Delta }{E}_4$). Additional energy-loss signals from the other two anodes were combined to improve the identification.

Figure 4

${}^{36}\mathrm{Cl}/{}^{35}\mathrm{Cl}$ ratios for the three neutron irradiated samples measured at the three AMS facilities with their uncertainties. The solid lines are the weighted averages of all individual AMS samples from the same material. The dashed lines show the associated uncertainties. Due to the inconsistencies during the neutron irradiation of KIT2 (see Sec. 4a), the KIT2 data was not considered for the calculation of the MACS.

Figure 5

MACS from this work for energies in the range $kT=(2–100)$ keV compared to the values of Macklin [7] and Guber et al. [8], and the results obtained directly with the resonance parameters from ENDF/B-VII.1 [17].

Figure 6

MACS at $kT=30\mathrm{keV}$ from this work compared to previous values.