Discovery and Cross-Section Measurement of Neutron-Rich Isotopes in the Element Range from Neodymium to Platinum at the FRS

With a new detector setup and the high-resolution performance of the fragment separator FRS at GSI we discovered 57 new isotopes in the atomic number range of 60$\leq Z \leq 78$: \nuc{159-161}{Nb}, \nuc{160-163}{Pm}, \nuc{163-166}Sm, \nuc{167-168}{Eu}, \nuc{167-171}{Gd}, \nuc{169-171}{Tb}, \nuc{171-174}{Dy}, \nuc{173-176}{Ho}, \nuc{176-178}{Er}, \nuc{178-181}{Tm}, \nuc{183-185}{Yb}, \nuc{187-188}{Lu}, \nuc{191}{Hf}, \nuc{193-194}{Ta}, \nuc{196-197}{W}, \nuc{199-200}{Re}, \nuc{201-203}{Os}, \nuc{204-205}{Ir} and \nuc{206-209}{Pt}. The new isotopes have been unambiguously identified in reactions with a $^{238}$U beam impinging on a Be target at 1 GeV/u. The isotopic production cross-section for the new isotopes have been measured and compared with predictions of different model calculations. In general, the ABRABLA and COFRA models agree better than a factor of two with the new data, whereas the semiempirical EPAX model deviates much more. Projectile fragmentation is the dominant reaction creating the new isotopes, whereas fission contributes significantly only up to about the element holmium.Comment: 9 pages, 4 figure

Single-particle isomeric states in 121Pd and 117Ru

Neutron-rich nuclei were populated in a relativistic fission of 238U. Gamma-rays with energies of 135 keV and 184 keV were associated with two isomeric states in 121Pd and 117Ru. Half-lives of 0.63(5) microseconds and 2.0(3) micrisecondss were deduced and the isomeric states were interpreted in terms of deformed single-particle states

High-spin states in 212Po above the α-decaying (18+) isomer

The nucleus Po has been produced through the fragmentation of a U primary beam at 1 GeV/nucleon at GSI, separated with the FRagment Separator, FRS, and studied via isomer γ-decay spectroscopy with the RISING setup. Two delayed previously unknown γ rays have been observed. One has been attributed to the E3 decay of a 21 isomeric state feeding the α-emitting 45-s (18) high-spin isomer. The other γ-ray line has been assigned to the decay of a higher-lying 23 metastable state. These are the first observations of high-spin states above the Po (18) isomer, by virtue of the selectivity obtained via ion-by-ion identification of U fragmentation products. Comparison with shell-model calculations points to shortfalls in the nuclear interactions involving high-j proton and neutron orbitals, to which the region around Z∼100 is sensitive.This work was partially supported by the Ministry of Science, and Generalitat Valenciana, Spain, under the Grants SEV-2014-0398, FPA2017-84756-C4, PID2019-104714GB-C21, PROMETEO/2019/005 and by the EU FEDER funds. The support of the UK STFC, of the Swedish Research Council under Contract No. 2008-4240 and No. 2016-3969 and of the DFG (EXC 153) is also acknowledged. The experimental activity has been partially supported by the EU under the FP6-Integrated Infras-tructure Initiative EURONS, Contract No. RII3-CT-2004-506065 and FP7-Integrated Infrastructure Initiative ENSAR, Grant No. 262010

Broken seniority symmetry in the semimagic proton mid-shell nucleus ⁹⁵Rh

Lifetime measurements of low-lying excited states in the semimagic ( N = 50 ) nucleus 95Rh have been performed by means of the fast-timing technique. The experiment was carried out using γ -ray detector arrays consisting of LaBr3(Ce) scintillators and germanium detectors integrated into the DESPEC experimental setup commissioned for the Facility for Antiproton and Ion Research (FAIR) Phase-0, Darmstadt, Germany. The excited states in 95Rh were populated primarily via the β decays of 95Pd nuclei, produced in the projectile fragmentation of a 850 MeV/nucleon 124Xe beam impinging on a 4 g / cm2 9Be target. The deduced electromagnetic E2 transition strengths for the γ -ray cascade within the multiplet structure depopulating from the isomeric Iπ = 21 / 2+ state are found to exhibit strong deviations from predictions of standard shell model calculations which feature approximately conserved seniority symmetry. In particular, the observation of a strongly suppressed E2 strength for the 13 / 2+ → 9 / 2+ ground state transition cannot be explained by calculations employing standard interactions. This remarkable result may require revision of the nucleon-nucleon interactions employed in state-of-the-art theoretical model calculations, and might also point to the need for including three-body forces in the Hamiltonian

Magnetic moment of the 11/2 − isomeric state in 99 Mo and neutron spin g factor quenching in A∼100 nuclei

International audienceThe gyromagnetic factor of the low-lying Ex=684.10(19)keV isomeric state of the nucleus 99Mo was measured using the time-dependent perturbed angular distribution technique. This level is assigned a spin and parity of Jπ=11/2−, with a half-life of T1/2=742(13)ns. The state of interest was populated and spin-aligned via a single-neutron transfer on a highly enriched 98Mo target. A magnetic moment μexpt.=−0.627(20)μN was obtained. This result is far from the Schmidt value expected for a pure single-particle νh11/2 state. A comparison of experimental spectroscopic properties of this nucleus is made with results of multishell Interacting boson-fermion Model (IBFM-1) calculations. In this approach, the Jπ=11/2− isomeric state in 99Mo has a pure νh11/2 configuration. Its magnetic moment, as well as that of other two excited states could be reasonably well reproduced by reducing the free neutron spin g factor with a quenching factor of 0.45. This low value is not appropriate only for this case, similar values for the quenching factor being also required in order to describe magnetic moments in other nuclei from the same mass regio

First observation of the decay of a 15- seniority v=4 isomer in Sn128

Isomeric states in the semimagic 128-130Sn isotopes were populated in the fragmentation of a Xe136 beam on a Be9 target at an energy of 750 A•MeV. The decay of an isomeric state in Sn128 at an excitation energy of 4098 keV has been observed. Its half live has been determined to be T 1/2=220(30) ns from the time distributions of the delayed γ rays emitted in its decay. γγ coincidence relations were analyzed in order to establish the decay pattern of the newly established state toward the known (7-) and (10+) isomers at excitation energies of 2092 and 2492 keV, respectively. Based on a comparison with results of state-of-the-art shell-model calculations the new isomeric state is proposed to have the νh11/2-3d3/2-1 configuration with the four neutron holes in Sn132 maximally aligned to a total spin of Iπ=15-. © 2011 American Physical Society.We acknowledge financial support from the Spanish Ministerio de Ciencia e Innovacion under Contracts No. ´ FPA2007-66069 and No. FPA2009-13377-C02-02, the Spanish Consolider-Ingenio 2010 Programme CPAN (CSD2007- 00042), the German Federal Ministry of Education and Research (06KY205I), the Swedish Science Council, STFC/EPSRC (UK), the Polish Ministry of Science and Higher Education (N N202 309135), and the EU Access to Large Scale Facilities Programme (EURONS, EU Contract No. 506065).Peer Reviewe