No Arabic abstract
Medium-spin excited states of the neutron-rich nucleus $^{87}$Br were observed and studied for the first time. They were populated in fission of $^{235}$U induced by the cold-neutron beam of the PF1B facility of the Institut Laue-Langevin, Grenoble. The measurement of $gamma$ radiation following fission has been performed using the EXILL array of Ge detectors. The observed level scheme was compared with results of large valence space shell model calculations. The medium-spin level scheme consists of three band-like structures, which can be understood as bands built on the ${pi}f_{5/2}$, ${pi}(p_{3/2}+f_{5/2})$ and ${pi}g_{9/2}$ configurations. The behavior of the observed ${pi}g_{9/2}$ band at high spins shows a considerable deviation from the shell model predictions. This deviation in this band is probably the result of an increased collectivity, which can be understood assuming that the ${pi}g_{9/2}$ high-$it j$ proton polarizes the core.
The structure of the nucleus 25F was investigated through in-beam {gamma}-ray spectroscopy of the fragmentation of 26Ne and 27,28Na ion beams. Based on the particle-{gamma} and particle-{gamma}{gamma} coincidence data, a level scheme was constructed and compared with shell model and coupled-cluster calculations. Some of the observed states were interpreted as quasi single-particle states built on top of the closed-shell nucleus 24O, while the others were described as states arising from coupling of a single proton to the 2+ core excitation of 24O.
High-resolution gamma-ray spectroscopy of 18N is performed with the Advanced GAmma Tracking Array AGATA, following deep-inelastic processes induced by an 18O beam on a 181Ta target. Six states are newly identified, which together with the three known excitations exhaust all negative-parity excited states expected in 18N below the neutron threshold. Spin and parities are proposed for all located states on the basis of decay branchings and comparison with large-scale shell-model calculations performed in the p-sd space, with the YSOX interaction. Of particular interest is the location of the 0^-_1 and 1^-_2 excitations, which provide strong constrains for cross-shell p-sd matrix elements based on realistic interactions, and help to simultaneously reproduce the ground and first-excited states in 16N and 18N, for the first time. Understanding the 18N structure may also have significant impact on neutron-capture cross-section calculations in r-process modeling including light neutron-rich nuclei.
The Penning trap mass spectrometer JYFLTRAP, coupled to the Ion-Guide Isotope Separator On-Line (IGISOL) facility at Jyvaskyla, was employed to measure the atomic masses of neutron rich 85 to 92Br and 94 to 97Rb isotopes with a typical accuracy less than 10 keV. Discrepancies with the older data are discussed. Comparison to different mass models is presented. Details of nuclear structure, shell and subshell closures are investigated by studying the two-neutron separation energy and the shell gap energy.
Vector analyzing power for the proton-6He elastic scattering at 71 MeV/nucleon has been measured for the first time, with a newly developed polarized proton solid target working at low magnetic field of 0.09 T. The results are found to be incompatible with a t-matrix folding model prediction. Comparisons of the data with g-matrix folding analyses clearly show that the vector analyzing power is sensitive to the nuclear structure model used in the reaction analysis. The alpha-core distribution in 6He is suggested to be a possible key to understand the nuclear structure sensitivity.
The neutron rich nucleus $^{193}$Os was produced in the $^{192}$Os($^{7}$Li,$^{6}$Li)$^{193}$Os reaction. An isomeric state based on the $9/2^-$[505] nilsson orbital was identified in the present work. Half-life of the isomeric state was extracted and discussed in terms of the $K$ quantum number. Level scheme built on the isomeric state was proposed based on the experimental data.