Determining (n,f) cross sections for actinide nuclei indirectly: Examination of the surrogate ratio method

Abstract

The validity of the Surrogate Ratio method for determining (n,f) cross sections for actinide nuclei is examined. This method relates the ratio of two compound-nucleus reaction cross sections to a ratio of coincidence events from two measurements in which the same compound nuclei are formed via a direct reaction. With certain assumptions, the method allows one of the cross sections to be inferred if the other is known. We develop a nuclear reaction-model simulation to investigate whether the assumptions underlying the Ratio approach are valid and employ these simulations to assess whether the cross sections obtained indirectly by applying a Ratio analysis agree with the expected results. In particular, we simulate Surrogate experiments that allow us to determine fission cross sections for selected actinide nuclei. The nuclei studied, 233 U and 235 U, are very similar to those considered in recent Surrogate experiments. We find that in favorable cases the Ratio method provides useful estimates of the desired cross sections, and we discuss some of the limitations of the approach.

Compound-nuclear reactions with unstable nuclei: Constraining theory through innovative experimental approaches

“…This is different from surrogate applications to (n,f) reactions. In the fission case the G CN χ= f ission (E ex , J, π) are much less sensitive to spin and parity and approximations can be employed which allow for analysis methods that do not require the knowledge of the CN spin-parity distributions [17][18][19][20].…”

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

“…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.…”

“…While the applicability of the surrogate reaction approach has been successfully demonstrated for (n, f ) cross sections (e.g. * ota2@llnl.gov [8][9][10][11][12][13]), it has been difficult to determine (n, γ) cross sections (e.g., [14][15][16]). …”

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

“…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].…”