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Stellar s-process neutron capture cross sections on A-Se and A-Ce

R. N. Sahoo, M. Tessler, S. Halfon, Y. Kashiv, D. Kijel, A. Kreisel, M. Paul, A. Shor, L. Weissman

TL;DR

This work develops MACS measurements for Se and Ce isotopes relevant to the weak and main s-process using a high-intensity quasi-Maxwellian neutron field produced at the SARAF-LiLiT facility. Activation of natSe and natCe targets followed by gamma spectroscopy enables extraction of MACS at 30 keV, with corrections to separate (n,γ) from (γ,n) channels and normalization to Au monitors. Preliminary results show MACS values generally agree with recommended data, validating the approach for short-lived decay products and expanding the isotopes available for s-process networks. The study demonstrates a practical path to improve stellar nucleosynthesis inputs and disentangle s-, r-, and p-process contributions in Se and Ce.

Abstract

We report on experiments at the Soreq Applied Research Accelerator Facility - Liquid-Lithium Target (SARAF-LiLiT) laboratory dedicated to the study of s-process neutron capture reactions. The kW-power proton beam at 1.92 MeV (1-2 mA) from SARAF Phase I yields high-intensity 30 keV quasi-Maxwellian neutrons (3-5x10^10 n/s). The high neutron intensity enables Maxwellian averaged cross sections (MACS) measurements of samples with short-lived decay products. Neutron capture reactions on nat-Se and nat-Ce were investigated by activation in the LiLiT neutron beam and γ-spectrometry measurements of their decay products.

Stellar s-process neutron capture cross sections on A-Se and A-Ce

TL;DR

This work develops MACS measurements for Se and Ce isotopes relevant to the weak and main s-process using a high-intensity quasi-Maxwellian neutron field produced at the SARAF-LiLiT facility. Activation of natSe and natCe targets followed by gamma spectroscopy enables extraction of MACS at 30 keV, with corrections to separate (n,γ) from (γ,n) channels and normalization to Au monitors. Preliminary results show MACS values generally agree with recommended data, validating the approach for short-lived decay products and expanding the isotopes available for s-process networks. The study demonstrates a practical path to improve stellar nucleosynthesis inputs and disentangle s-, r-, and p-process contributions in Se and Ce.

Abstract

We report on experiments at the Soreq Applied Research Accelerator Facility - Liquid-Lithium Target (SARAF-LiLiT) laboratory dedicated to the study of s-process neutron capture reactions. The kW-power proton beam at 1.92 MeV (1-2 mA) from SARAF Phase I yields high-intensity 30 keV quasi-Maxwellian neutrons (3-5x10^10 n/s). The high neutron intensity enables Maxwellian averaged cross sections (MACS) measurements of samples with short-lived decay products. Neutron capture reactions on nat-Se and nat-Ce were investigated by activation in the LiLiT neutron beam and γ-spectrometry measurements of their decay products.
Paper Structure (4 sections, 4 figures, 1 table)

This paper contains 4 sections, 4 figures, 1 table.

Table of Contents

  1. Introduction
  2. The Soreq Applied Research Accelerator Facility (SARAF) and the Liquid-Lithium Target (LiLiT): activation experiments
  3. $^{A}$Se and $^{A}$Ce measurements
  4. Acknowledgments

Figures (4)

  • Figure 1: Layout of SARAF Phase I; see text for acronyms
  • Figure 2: (right) Schematic drawing of the Liquid-Lithium Target (LiLiT). (left) Diagram of the Liquid-Lithium Target (LiLiT) and activation target assembly. The (1-2 mA, $\approx$ 9 mm full width) proton beam (dashed red arrow) impinges directly on the windowless liquid-lithium film. The light blue shows the liquid-lithium circulating flow (see HAL14 for details). The activation samples are mounted at the center of a ring target holder made of Al and positioned in the outgoing neutron cone (green dashed lines) at a distance of $\approx$ 6 mm from the liquid-lithium film surface. The targets are in a vacuum chamber separated from the LiLiT chamber by a 0.5 mm stainless steel concave vacuum wall.
  • Figure 3: Gamma spectra accumulated with a shielded High-Purity Ge detector for targets of natSe (top) and natCe (bottom) activated in the neutron spectrum from LiLiT. The identified lines of the respective ($n, \gamma$) reaction products are indicated. The top left spectrum is for the short-lived 81,83Se isotopes, and the top right spectrum is for the longer-lived 75Se isotope.
  • Figure 4: Gamma spectra accumulated with a shielded High-Purity Ge detector for targets of natCe (left) and natSe (right), activated below the neutron production threshold, resulting in only gamma rays and no neutrons. The 139,141Ce and 81mSe counts are then subtracted to obtain only the ($n, \gamma$) cross sections.