Speaker
Description
The ${}^{140}$Ce(n,$\gamma$)${}^{141}$Ce is recognized as an important reaction in the flow of neutron-capture nucleosynthesis due to the neutron-magic character of ${}^{140}$Ce and a corresponding small neutron capture cross section. We present here [1] measurements of the neutron-capture Maxwellian-averaged cross section (MACS) of stable cerium isotopes performed by activation in the quasi-Maxwellian ${}^{7}$Li(p,n) neutron field ($kT \sim 34\,\mathrm{keV}$) produced by the Liquid-Lithium Target (LiLiT) at Soreq Applied Research Accelerator Facility (SARAF). The MACS values ($kT= 30\,\mathrm{keV}$) are generally consistent with previous measurements and for ${}^{140}$Ce smaller by approximately 15-20%. In contrast a recent study of the ${}^{140}$Ce(n,$\gamma$)${}^{141}$Ce cross section measured via time of flight [2] leads to MACS values larger by ~20-40% than quoted in the experimental database KADoNIS [3] in the $kT \sim 5-10\,\mathrm{keV}$ (see also [4]). We note here that the the activation and time-of-flight experiments were focused on different $kT$ regions ($\sim 30\,\mathrm{keV}$ and $\sim 10\,\mathrm{keV}$, respectively), possibly affecting the MACS determinations for $kT$ values out of their respective regions. In order to contribute to the understanding of neutron-capture nucleosynthesis in this region of nuclides, an independent experiment is being planned, based on activation in the quasi-Maxwellian neutron field ($kT \sim 5\,\mathrm{keV}$) of the ${}^{18}$O(p,n) reaction close to threshold. This experiment will enable direct comparison between a quasi-Maxwellian activation and the time-of-flight measurement without the need of extrapolation and hence has the potential to resolve the discrepancy. The ${}^{18}$O(p,n) reaction was originally proposed by Heil et al. [5] for astrophysical MACS determinations and its study was recently revisited [6] for our experiments. With a proton beam of $2581\,\mathrm{keV}$ incident on a ${}^{18}$OTa$_2$O$_5$ target at the PTB-PIAF facility, the outgoing neutron energy distribution was measured by means of time of flight with a thin ${}^{6}$Li detector at angles of $0^\circ - 60^\circ$. The angle-integrated neutron spectrum closely resembles a thermal flux distribution at $kT= 5\,\mathrm{keV}$. The results, under final analysis stages, will be presented.
M.F. and M.P. acknowledge support by the European Union (ChETEC-INFRA, project no. 101008324).
[1] R.N. Sahoo et al., Phys. Rev. C 109, 025808 (2024).
[2] S. Amaducci et al., Phys, Rev. Lett. 132, 122701 (2024).
[3] I. Dillmann et al., AIP Conf. Proc. 819, 123 (2006).
[4] K. Wright, APS Physics Magazine, March 25, 2024.
[5] M. Heil et al., Phys. Rev. C 71, 025803 (2005).
[6] M. Friedman, "Measurement of Thick-Target ${}^{18}$O(p,n)${}^{18}$F Neutron Energy Spectrum, Yield and Angular Distribution at $E_p=2582\,\mathrm{keV}$", ChETEC-INFRA 2nd General Assembly, 20 June 2022, Padova, Italy.
