Compound-nuclear reaction cross sections from surrogate measurements

Abstract

Nuclear reaction cross sections are important for a variety of applications in the areas of astrophysics, nuclear energy, and national security. When these cross sections cannot be measured directly or predicted reliably, it becomes necessary to develop indirect methods for determining the relevant reaction rates. The surrogate nuclear reactions approach is such an indirect method. First used in the 1970s for estimating ðn; fÞ cross sections, the method has recently been recognized as a potentially powerful tool for a wide range of applications that involve compound-nuclear reactions. The method is expected to become an important focus of inverse-kinematics experiments at rareisotope facilities. The present paper reviews the current status of the surrogate approach. Experimental techniques employed and theoretical descriptions of the reaction mechanisms involved are presented and representative cross section measurements are discussed.

r Process (n, \(\gamma \)) Rate Constraints from the \(\gamma \) Emission of Neutron Unbound States in \(\beta \)-Decay

“…However it should be noticed that in general resonances with different spin and parity J π are populated in the two processes. This limitation is also present [5] for other (n,γ) surrogate reactions, in particular at the relevant neutron energies (up to few hundred keV). One needs models for both processes in order to convert the information obtained.…”

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

“…In other words, once the compound nucleus is created by a reaction, the decay does not depend on the formation process. This assumption does not take into account width-fluctuation corrections which are typically small and are not included at the moment [7]. Therefore, the (n,J) cross sections (V (n,γ) ) can be written as…”

“…[7]. Here, we briefly explain the principle of the surrogate reaction approach with a focus on (n,J) measurements.…”

“…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.…”

“…Although the surrogate reaction approach was developed for measurements of neutron-induced fission ((n,f)) cross sections of actinides in 1970's [5,6], it has attracted a renewed attention in the past decade due to interest in minor actinides from nuclear reactor physics and stockpile stewardship [7]. 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].…”