Gamma Decay of Unbound Neutron-Hole States in Sn133

Abstract

Excited states in the nucleus133 Sn, with one neutron outside the doubly-magic 132 Sn core, were populated following one-neutron knockout from a 134 Sn beam on a carbon target at relativistic energies at the Radioactive Isotope Beam Factory at RIKEN. Besides the γ rays emitted in the decay of the known neutron single-particle states in 133 Sn additional γ strength in the energy range 3.5-5.5 MeV was observed for the first time. Since the neutron-separation energy of 133 Sn is low, Sn=2.402(4) MeV, this observation provides direct evidence for the radiative decay of neutronunbound states in this nucleus. The ability of electromagnetic decay to compete successfully with neutron emission at energies as high as 3 MeV above threshold is attributed to a mismatch between the wave functions of the initial and final states in the latter case. These findings suggest that in the region south-east of 132 Sn nuclear structure effects may play a significant role in the neutron vs. γ competition in the decay of unbound states. As a consequence, the common neglect of such effects in the evaluation of the neutron-emission probabilities in calculations of global β-decay properties for astrophysical simulations may have to be reconsidered.

Investigation of Low-lying States in $^{133}$Sn Populated in the $\beta $ Decay of $^{133}$In Using Isomer-selective Laser Ionization

“…The impurities of the beam of 133 In ions in these two states were found to be negligible. Our data are consistent with the previous results on the low-lying level structure of 133 Sn [2][3][4][5][6][7], and provide further support for the adopted spin assignments of low-lying states in 133 Sn.…”

“…The first investigation of 133 Sn was performed with β-decay spectroscopy of 134 In, for which the large probability of β-delayed neutron emission (P n = 65% [1]) opens great possibilities to study the states of interest by measuring γ rays in coincidence with delayed neutrons [2,3]. These measurements were later followed by reaction studies based on one-neutron transfer reactions [4][5][6][7]. The aforementioned investigations provided mutually consistent information about SP energies for νp 3/2 (E = 854 keV), νp 1/2 (E = 1363 keV), νh 9/2 (E = 1591 keV) and νf 5/2 (E = 2005 keV) neutron orbitals relative to the νf 7/2 ground state of 133 Sn.…”

“…Nevertheless, the question of the position of the neutron unbound νi 13/2 state remains open for investigation. In addition, recent studies indicate the need to study highly-excited states in 133 Sn, for which γ-ray emission was found to be a decay mode, competing with β-delayed neutron emission [7].…”

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.…”

Prominence of Pairing in Inclusive (p,2p) and (p,pnPaul1, Obertelli2, Bertulani3 et al. 2019Phys. Rev. Lett.Self Cite7030View full textAdd to dashboardCite

“…We note that no obvious shell effects are visible, though the N=50 shell closure is traversed in this data set at A=80 ( 80 Zn), suggesting that in the considered nuclei the S n is sufficiently high so that shell effects are significantly integrated out in the inclusive cross sections. This may not always be the case, as observed recently in [43] where the neutron removal cross section from 134 Sn was found to be half of that from 133 Sn, attributed to a 5 MeV difference in S n of the daughter nuclei.…”