Speaker
Description
Theoretical analysis of astrophysical S-factors of nuclear reactions
$^{7}$Be(n,$\alpha )^{4}$He and $^{7}$Be(n,p)$^{7}$Li
V.I. Zhaba, V.S. Vasilevsky, Yu.A. Lashko
Bogolyubov Institute for Theoretical Physics, National Academy of Sciences
of Ukraine
In this report, we study a range of reactions induced by the interactions $^{7}$Li+p, $^{7}$Be+n and $^{6}$Li+d. Special attention is paid to the low-energy region in the input channels of reactions that take into account the dynamics of synthesis and decay of $^{6}$Li, $^{7}$Li and $^{7}$Be nuclei. This study is performed within a microscopic three-cluster model, which allows us to involve all binary channels of the $^{8}$Be decay. Besides, this model takes into account polarizability of interacting nuclei (clusters) [1, 2]. In Ref. [3], this model was successfully applied to study the structure of the $^{8}$Be nucleus and the nature of high-energy resonance states of $^{8}$Be.
Within the framework of our model, the astrophysical S-factors of the reactions $^{7}$Be(n,$\alpha )^{4}$He, $^{7}$Be(n,p$_{0})^{7}$Li and $^{7}$Be(n,p$_{1})^{7}$Li in the energy range E$_{cm}$=0-2 MeV were calculated. The dependence of the astrophysical S-factors on the form and intensity of the nucleon-nucleon interaction was investigated in detail. For the astrophysical S-factor of $^{7}$Be(n,$\alpha)^{4}$He reaction, the partial 2$^{+}$ wave dominates over the entire energy range, and is then enhanced by the 0$^{+}$ wave. The calculated S-factors for $^{7}$Be(n,$\alpha )^{4}$He reaction are further decomposed into contributions from reactions with $^{7}$Be in its ground and first excited states. For $^{7}$Be(3/2$^{-}$)(n,$\alpha)^{4}$He reaction, the 2$^{+}$ wave has a maximum that is due to resonance. In our microscopic model, this 2$^{+}$ resonance state appears at energy E$\approx $1.27 MeV above $^{7}$Be+n decay threshold, which is in good agreement with the experimental data obtained in [4].
For $^{7}$Be(n,p$_{0})^{7}$Li reaction, the 3$^{+}$ partial wave dominates in the region of the maximum at Ecm=0.5 MeV, while the 2$^{-}$ partial wave determines the behavior at low and high energies. For $^{7}$Be(n,p$_{1})^{7}$Li reaction, the 1$^{-}$ partial wave dominates in the entire energy range and together with the $^{+}$, 2$^{-}$, 2$^{+}$ states provide the main contribution to the astrophysical S-factor. It was demonstrated that the cluster polarization has a large impact on value and energy dependence of the S-factor for the $^{7}$Be(n,p)$^{7}$Li reaction.
The calculated astrophysical S-factors for the reactions $^{7}$Be(n,$\alpha)^{4}$He and $^{7}$Be(n,p)$^{7}$Li are in good agreement with experimental data from leading laboratories. Our partial astrophysical S-factors for the $^{7}$Be+n reactions are compared with calculations in the R-matrix theory and with data in the ENDF database.
[1] Y.A. Lashko, G.F. Filippov, V.S. Vasilevsky. Nucl. Phys. A 958, 78 (2017).
[2] V.S. Vasilevsky, F. Arickx, J. Broeckhove, T.P. Kovalenko. Nucl. Phys. A
824, 37 (2009).
[3] V.I. Zhaba, Yu.A. Lashko, V.S. Vasilevsky. Phys. Rev. C 112 014328 (2025).
[4] D.R. Tilley, J.H. Kelley, J.L. Godwin et al. Nucl. Phys. A 745 155 (2004).
