Speaker
Description
The interaction of neutrons with 7Be that was measured at the SARAF in Israel with a quasi-Maxwellian neutron beam at 49.5 keV reveals a strong B(E1: 2- ---> 2+) ~ 0.04 W.u., decay of the 2- state at 18.91 MeV in 8Be to the alpha-cluster 2+ state at 3.03 MeV [1]. This strong E1 decay leads to large cross section of the 7Be(n,g_1)*8Be(3.03) reaction at the “BBN window". It implies s-waves dominance of the cross section at the “BBN window”, in contrast to previous extrapolations into the “BBN window” from lower energies (the n_TOF measurement [2]) and extrapolation from higher energies (the Kyoto measurement [3]). In addition, the phenomenological structure of all states below 19.5 MeV in 8Be (including the 2- state at 18.91 MeV) provides good evidence for particle-hole (p-h) states in the newly proposed Cluster Shell Model (CSM) of Della Roca and Iachello [4]. The states near the neutron and proton thresholds in 8Be show the characteristic of the p-h states predicted by the CSM. The measured B(E1) of the 2- state at 18.91 MeV is in accordance with other measured decays of the p-h CSM states to the well-known cluster ground-states and 2+ state at 3.03 MeV in 8Be. The new CSM model of Della Roca and Iachello [4] will be introduced with emphasize on the similarity between p-h states in 8Be and single particle states in 9Be.
The material presented in this paper is based upon work supported by the U.S.-Israel Bi National Science Foundation, Award No. 2012098, and the U.S. Department of Energy, Office of
Science, Nuclear Physics, Award No. DE-FG02-94ER40870.
[1] M. Gai, arXiv:1812.09914v1, (2018).
[2] M. Barbagallo et al., Phys. Rev. Lett. 117, 152701 (2016).
[3] T. Kawabata et al., Phys. Rev. Lett., 118, 052701 (2017).
[4] V.DellaRocca and F.Iachello, Nucl. Phys. A 973, 1 (2018).
