Pre-equilibrium mechanisms in theNb93(p⃗,α)inclusive reaction at incident energies from 65 to 160 MeV

Abstract

The reaction mechanism of pre-equilibrium proton-induced α-particle emission from 93 Nb at an incident energy of 100 MeV was investigated with polarized projectiles. A formalism based on the statistical multistep direct emission model of Feshbach, Kerman and Koonin was found to give a reasonably good reproduction of cross section and analyzing power angular distributions at various emission energies. Existing experimental distributions for the same reaction at an incident energy of 65 MeV were also analyzed with the same model. The incident-energy variation from 65 MeV up to 160 MeV was found to be consistent with the predictions of the basic model. However, whereas knockout of an α cluster is the dominant reaction mechanism in the final stage at the lowest-and highest incident energies, at 100 MeV a pickup process competes with comparable intensity in yield.

Recent insight into the mechanism of proton-induced composite particle emission in inclusive reactions

“…In our most recent work [5] we confirmed that knockout dominates in the mechanism of 93 Nb(p,α) reaction at incident energies of 65 and 160 MeV. However, at an intermediate incident energy of 100 MeV pickup is the most important process.…”

“…This behaviour was observed for the first time in Ref. [5], and it needs to be interpreted in terms of the respective dynamics of knockout and pickup.…”

“…It should be mentioned that at 100 MeV incident energy there is evidence of some contribution from knockout, but it is definitely not dominant [5].…”

“…Experimental incident energy dependence of the cross sections extracted from Ref. [5] shown as a function of effective momentum transfer for knockout and pickup, respectively. At incident energies of 65 and 160 MeV (lowest and highest momentum points), where knockout is dominant, a 10% pickup contribution was adopted as a reasonable limit.…”

“…In comprehensive studies [3][4][5] of the (p,α) reaction to the continuum of excitation on various targets at incident energies in the range of interest from 65 to 200 MeV, with one notable exception, we identify the knockout process as terminating a statistical multistep mechanism. In these studies, analyzing power angular distributions at various emission energies are very sensitive to identify both the intranuclear statistical N-N multisteps, and also the terminating process leading to emitted α-particles.…”