In-beam γ-ray spectroscopy of Te 136 at relativistic energies

The reduced transition probability B(E2;01+→21+) to the first excited 2+ state of the neutron-rich nucleus Te136, with two protons and two neutrons outside the doubly magic Sn132 core, was measured via Coulomb excitation at relativistic energies at the RIKEN Radioactive Isotope Beam Factory. A value of B(E2)=0.191(26) e2b2 was extracted from the measured inelastic scattering cross section on an Au target taking into account the contributions from both Coulomb and nuclear excitations. In addition, an upper limit for the transition strength to a 2+ state of mixed-symmetry character in the excitation energy range of 1.5-2.2 MeV was determined and compared to the predictions of various theoretical calculations. Because of the high statistics gathered in the present experiment the error of the deduced B(E2) value is dominated by the systematic uncertainties involved in the analysis of Coulomb excitation experiments at beam energies around 150 MeV/u. Therefore, the latter are for the first time assessed in detail in the present work

Shell structure of the neutron-rich isotopes Co 69,71,73

The structures of the neutron-rich Co69,71,73 isotopes were investigated via (p,2p) knockout reactions at the Radioactive Isotope Beam Factory, RIKEN. Isotopes of interest were studied using the DALI2 γ-ray detector array combined with the MINOS target and tracker system. Level schemes were reconstructed using the γ-γ coincidence technique, with tentative spin-parity assignments based on the measured inclusive and exclusive cross sections. Comparison with shell-model calculations using the Lenzi-Nowacki-Poves-Sieja LNPS and PFSDG-U interactions suggests coexistence of spherical and deformed shapes at low excitation energies in the Co69,71,73 isotopes. The distorted-wave impulse approximation (DWIA) framework was used to calculate the single-particle cross sections. These values were compared with the experimental findings

Shell evolution of N = 40 isotones towards 60Ca: First spectroscopy of 62Ti

Excited states in the N=40 isotone 62Ti were populated via the 63V(p,2p)62Ti reaction at ∼200 MeV/nucleon at the Radioactive Isotope Beam Factory and studied using γ-ray spectroscopy. The energies of the 21+→0gs+ and 41+→21+ transitions, observed here for the first time, indicate a deformed 62Ti ground state. These energies are increased compared to the neighboring 64Cr and 66Fe isotones, suggesting a small decrease of quadrupole collectivity. The present measurement is well reproduced by large-scale shell-model calculations based on effective interactions, while ab initio and beyond mean-field calculations do not yet reproduce our findings. The shell-model calculations for 62Ti show a dominant configuration with four neutrons excited across the N=40 gap. Likewise, they indicate that the N=40 island of inversion extends down to Z=20, disfavoring a possible doubly magic character of the elusive 60Ca

Spectroscopy of 98Cd^{98}\mathrm{Cd} by two-nucleon removal from 100In^{100}\mathrm{In}

International audienceLow-lying states of Cd98 have been populated by the two-nucleon removal reaction (In100,Cd98+γ) and studied using in-beam γ-ray spectroscopy at the Radioactive Isotope Beam Factory at RIKEN. Two new γ transitions were identified and assigned as decays from a previously unknown state. This state is suggested to be based on a π1g9/2−12p1/2−1 configuration with Jπ=5−. The present observation extends the systematics of the excitation energies of the first 5− state in N=50 isotones toward Sn100. The determined energy of the 5− state in Cd98 continues a smooth trend along the N=50 isotones. The systematics are compared with shell-model calculations in different model spaces. Good agreement is achieved when considering a model space consisting of the π(1f5/2, 2p3/2, 2p1/2, 1g9/2) orbitals. The calculations with a smaller model space omitting the orbitals below the Z=38 subshell could not reproduce the experimental energy difference between the ground and first 5− states in N=50 isotones, because proton excitations across Z=38 subshell yield a large amount of correlation energy that lowers the ground states

Shell structure of the neutron-rich isotopes Co 69,71,73

Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UA

Gamma decay of unbound neutron-hole states in 133Sn

Excited states in the nucleus 133Sn, with one neutron outside the doubly-magic 132Sn core, were populated following one-neutron knockout from a 134Sn beam on a carbon target at relativistic energies at the Radioactive Isotope Beam Factory at RIKEN. Besides the rays emitted in the decay of the known neutron single-particle states in 133Sn additional strength in the energy range 3.5-5.5 MeV was observed for the fi rst time. Since the neutron-separation energy of 133Sn is low, Sn=2.402(4) MeV, this observation provides direct evidence for the radiative decay of neutron- unbound 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 fi ndings suggest that in the region south-east of 132Sn nuclear structure effects may play a signifi cant role in the neutron vs. 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 b -decay properties for astrophysical simulations may have to be reconsidered

Inclusive cross sections for one- and multi-nucleon removal from Sn, Sb, and Te projectiles beyond the N = 82 shell closure

6 pags., 4 figs., 1 tab.-- Open Access funded by Creative Commons Atribution Licence 4.0Inclusive one- and multi-nucleon removal cross sections have been measured for several Sn, Sb and Te isotopes just beyond the N=82 neutron shell closure. The beams were produced in the projectile fission of a U beam at the Radioactive Isotope Beam Factory at RIKEN. The experimental cross sections are compared to predictions from the most recent version of the Liege intranuclear cascade model. Although the overall agreement is good, severe discrepancies are observed for the cases of one- and two-neutron removal from Sn and Sb projectiles and one-proton knockout from all measured N=84 isotones. These discrepancies, as well as the relevance of quasi-elastic reaction channels to the one-neutron removal cross sections, are discussed. In addition, the measured inclusive one-proton knockout cross section for the semi-magic Sn projectile is compared to eikonal direct reaction theory calculations to assess if the suppression factors to these calculated cross sections, deduced from data on reactions of lighter projectile nuclei, are also applicable to heavy nuclei.We thank the staff of the RIKEN Nishina Center accelerator complex for providing high-intensity beams to the experiment. This work was supported by the Spanish Ministerio de Economía y Competitividad under contracts FPA2014-57196-C5-4-P and FPA2017-84756-C4-2-P. J.A.T. acknowledges the support of the Science and Technology Facilities Council (UK) grant ST/L005314/1 and R.O. that of JSPS KAKENHI Grant No. 26887048. G.M.T. grate-fully acknowledges funding of this research from the Research Council of Norway, Project Grant No. 222287

In-beam γ -ray spectroscopy of Te 136 at relativistic energies

14 pags., 11 figs-. 3 tabs.The reduced transition probability B(E2;01+→21+) to the first excited 2+ state of the neutron-rich nucleus Te136, with two protons and two neutrons outside the doubly magic Sn132 core, was measured via Coulomb excitation at relativistic energies at the RIKEN Radioactive Isotope Beam Factory. A value of B(E2)=0.191(26) e2b2 was extracted from the measured inelastic scattering cross section on an Au target taking into account the contributions from both Coulomb and nuclear excitations. In addition, an upper limit for the transition strength to a 2+ state of mixed-symmetry character in the excitation energy range of 1.5-2.2 MeV was determined and compared to the predictions of various theoretical calculations. Because of the high statistics gathered in the present experiment the error of the deduced B(E2) value is dominated by the systematic uncertainties involved in the analysis of Coulomb excitation experiments at beam energies around 150 MeV/u. Therefore, the latter are for the first time assessed in detail in the present work.We thank Dirk Weisshaar for valuable discussions and the staff of the RIKEN Nishina Center accelerator complex for providing high-intensity beams to the experiment. This work was supported by the Spanish Ministerio de Economía y Competitividad under Contracts No. FPA2014-57196-C5-4-P, No. FPA2017-84756-C4-2-P, and No. FIS2014-53448-C2-1-P