Unexpected high-energy γ emission from decaying exotic nuclei

Abstract

International audienceThe N=52 Ga83 β decay was studied at ALTO. The radioactive 83 Ga beam was produced through the ISOL photofission technique and collected on a movable tape for the measurement of γ -ray emission following β decay. While β -delayed neutron emission has been measured to be 56–85% of the decay path, in this experiment an unexpected high-energy 5–9 MeV γ -ray yield of 16(4)% was observed, coming from states several MeVs above the neutron separation threshold. This result is compared with cutting-edge QRPA calculations, which show that when neutrons deeply bound in the core of the nucleus decay into protons via a Gamow–Teller transition, they give rise to a dipolar oscillation of nuclear matter in the nucleus. This leads to large electromagnetic transition probabilities which can compete with neutron emission, thus affecting the β -decay path. This process is enhanced by an excess of neutrons on the nuclear surface and may thus be a common feature for very neutron-rich isotopes, challenging the present understanding of decay properties of exotic nuclei

Pseudospin Symmetry and Microscopic Origin of Shape Coexistence in the Ni78 Region: A Hint from Lifetime Measurements

“…Ni. This may well happen due to the formation of a neutron skin, actually predicted by relativistic Hartree-Fock-Bogoliubov (HFB) calculations [44], whose spectroscopic manifestations have just been experimentally noticed [47].…”

“…It is a manifestation of the tensor ρ-exchange potential, but as PSS is a dynamical symmetry in nature, originating from the cancellation of several terms contributing to the SP energy [49], it contains richer spin-isospin properties than can be exhaustively captured in the usual tensor schematic picture. In particular, since this short-range potential is essentially manifested through exchange terms it naturally links shell evolution and formation of giant halos or neutron skins [44] involving large s and p orbits-whose spectroscopic expression has incidentally long passed unnoticed in the 78 Ni region [47]. Thus, while quantitative relativistic calculations and more precise experimental results for this mass sector are certainly called for, it can already be conjectured that PSS concepts and the related role of the ρ potential are to become more and more useful for understanding observed shell evolutions in very neutron-rich, medium-to-heavy mass nuclei.…”

β decay of In133 : γ emission from neutron-unbound states in SnKorgul1, Fraile2, Benito3 et al. 2019Phys. Rev. CSelf Cite158312View full textAdd to dashboardCite

“…Nonetheless this assumption is known to be not correct [3]. Recently, a strong competition between neutron and γ decay of levels above S n was observed both in the 78 Ni and in the 132 Sn regions [4,5]. The fact that the γ deexcitation of neutron-unbound states can be observed and studied opens the possibility to hunt for those s. p. as well as single-hole (s. h.) states that are neutron unbound and were so far unobserved.…”

The BRIKEN Project: Extensive Measurements of $\beta $-delayed Neutron Emitters for the Astrophysical r Process

“…The process of βn emission itself is not fully understood. For example, the competition between γ and neutron emission from neutron unbound states populated in β-decay has just started to be studied in a more systematic way [24][25][26][27][28]. The competition between β-delayed one-neutron and multiple-neutron emission channels has not been properly addressed [29], the main reason being the scarcity of known βxn emitters.…”