Determining neutron capture cross sections via the surrogate reaction technique

Abstract

Indirect methods play an important role in the determination of nuclear reaction cross sections that are hard to measure directly. In this paper we investigate the feasibility of using the so-called surrogate method to extract neutron-capture cross sections for low energy compound-nuclear reactions in spherical and near-spherical nuclei. We present the surrogate method and develop a statistical nuclear-reaction simulation to explore different approaches to utilize surrogate reaction data. We assess the success of each approach by comparing the extracted cross sections with a predetermined benchmark. In particular, we employ regional systematics of nuclear properties in the 34 ≤ Z ≤ 46 region to calculate (n, γ) cross sections for a series of Zr isotopes, and to simulate a surrogate experiment and the extraction of the desired cross section. We identify one particular approach that may provide very useful estimates of the cross section, and we discuss some of the limitations of the method. General recommendations for future (surrogate) experiments are also given.PACS numbers: 24.10. 24.60.Dr, 25.40.Lw, 98.80.Ft

Spin differences in the Zr90 compound nucleus induced by (p,p′) , Ota1, Burke2, Casperson3 et al. 2015Phys. Rev. C233280View full textAdd to dashboardCite

“…As predicted in [17], P i (E x ) for 90 Zr is expected to show a significant J dependence around S n due to the low level density in the neighboring nucleus, 89 Zr. As shown in Fig.…”

“…The presence of closed proton (Z=40) and neutron (N =50) (sub)shells in the Zr mass region (A ∼90) is manifest in the low level densities in the nuclei studied. This, in turn, leads to a competition between γ decay and neutron emission that is quite sensitive to the J π distributions of the decaying compound nuclei and can be expected to be visible in the measured discrete γ-ray emission probabilities [7,14,17]. The effect is smaller in well-deformed nuclei with high level densities, such as rare-earth and actinide nuclei that have been studied in [15,23].…”

“…While this has a smaller effect on the extraction of fission cross sections [9], the γ-ray emission of the compound nucleus can be quite sensitive to the initial J π distribution [14,15,[17][18][19][20][21]. Therefore, in order to extract (n, γ) cross sections from surrogate data it becomes necessary to take into account the J π distribution of the decaying compound nucleus.…”

87Y(n,γ) and89,90Zr(n,γ) cross sections from a surrogate reaction approach

“…However, some recent research showed promise for inferring (n,J) cross sections by accounting for spin-parity distribution of the compound nucleus [18]. One goal of the present work is to test the validity of the approach for Y-Zr nuclei which are more spherical and therefore more sensitive to differences in the spin-parity distributions because of their lower level densities compared to minor actinides and rare-earth nuclei [7,17]. The 87 Y(n,J) and 89 Zr(n,J) cross sections are very important e.g., for stockpile stewardship.…”

“…While the applicability of the surrogate reaction approach has been demonstrated for (n,f) cross sections [8][9][10][11][12], it has been difficult to determine (n,J) cross sections due primarily to the discrepancy in the spin-parity distributions of the compound nucleus created by the (n,J) and the surrogate reaction [13][14][15][16][17]. However, some recent research showed promise for inferring (n,J) cross sections by accounting for spin-parity distribution of the compound nucleus [18].…”