In-beam gamma-ray spectroscopy of two-step fragmentation reactions at relativistic energies - The case of 36Ca

A two-step fragmentation experiment has been performed at GSI with the RISING setup. It combines the fragment separator FRS, which allows for the production of radioactive heavy ions at relativistic energies, with a high resolution g-spectrometer. This combination offers unique possibilities for nuclear structure investigations like the test of shell model predictions far from stability. Within the present work the question if the N = 14(16)shell stabilisation in Z = 8 oxygen isotopes and the N = 20 shell quenching in 32Mg are symmetric with respect to the isospin projection quantum number Tz has been addressed. New gamma-ray decays were found in the neutron deficient 36Ca and 36K by impinging a radioactive ion beam of 37Ca on a secondary 9Be target. The fragmentation products were selected with the calorimeter telescope CATE and the emitted g-rays were measured with Ge Cluster, MINIBALL, and BaF2 HECTOR detectors. For 36Ca the 2+ -> 0+ transition energy was determined to be 3015(16) keV, which is the heaviest T = 2 nucleus from which gamma-spectroscopic information has been obtained so far. A comparison between the experimental 2+ energies of 36Ca and its mirror nucleus 36S yielded a mirror energy difference of MED = -276(16) keV. In order to understand the large MED value, the experimental single-particle energies from the A=17, T =1/2 mirror nuclei were taken and applied onto modified isospin symmetric USD interactions in shell model calculations. These calculations were in agreement with the experimental result and showed that the experimental single-particle energies may account empirically for the one body part of Thomas-Ehrman and/or Coulomb effects. A method to extract the lifetime of excited states in fragmentation reactions was investigated. Therefore, the dependence between the lifetime of an excited state and the average de-excitation velocity and trajectory of the nuclei in relativistic fragmentation experiments has been studied. Known lifetime values in 34Cl could be confirmed and new values were found for 36K

Rotational level structure of sodium isotopes inside the "island of inversion"

The neutron-rich nuclei 33,34,35Na were studied via in-beam γ-ray spectroscopy following nucleon removal reactions from a 36Mg secondary beam at ~220 MeV/u. Excited states of 34,35Na are reported for the first time. A third transition was observed for 33Na in addition to the known 7/2+ 1 → 5/2+ 1 → 3/2+ g.s. cascade and is suggested to be the 9/2+ 1 → 7/2+ 1 transition. Similarly, a 7/2+ 1 → 5/2+ 1 → 3/2+ g.s. cascade is proposed for the decay pattern observed for 35Na. The transition energy ratios are close to expectation values for K = 3/2 rotational bands in the strong coupling limit. Comparisons to large-scale shell model calculations in the sd-p f model space support the spin-parity assignments. © The Author(s) 2014.published_or_final_versio

Structure of 136Sn and the Z = 50 magicity

The first 2+ excited state in the neutron-rich tin isotope 136Sn has been identified at 682(13) keV by measuring γ -rays in coincidence with the one proton removal channel from 137Sb. This value is higher than those known for heavier even-even N = 86 isotones, indicating the Z = 50 shell closure. It compares well to the first 2+ excited state of the lighter tin isotope 134Sn, which may suggest that the seniority scheme also holds for 136Sn. Our result confirms the trend of lower 2+ excitation energies of even-even tin isotopes beyond N = 82 compared to the known values in between the two doubly magic nuclei 100Sn and 132Sn. © The Author(s) 2014.published_or_final_versio

Investigating nuclear shell structure in the vicinity of 78Ni: Low-lying excited states in the neutron-rich isotopes 80,82Zn

L

Isotope production in proton-, deuteron-, and carbon-induced reactions on Nb 93 at 113 MeV/nucleon

Isotope-production cross sections for p-, d-, and C-induced spallation reactions on Nb93 at 113 MeV/nucleon were measured using the inverse-kinematics method employing secondary targets of CH2, CD2, and C. The measured cross sections for Mo90, Nb90, Y86,88 produced by p-induced reactions were found to be consistent with those measured by the conventional activation method. We performed benchmark tests of the reaction models INCL-4.6, JQMD, and JQMD-2.0 implemented in the Particle and Heavy Ion Transport code System (PHITS) and of the nuclear data libraries JENDL-4.0/HE, TENDL-2017, and ENDF/B-VIII.0. The model calculations also showed generally good agreement with the measured isotope-production cross sections for p-, d-, and C-induced reactions. It also turns out that, among the three nuclear data libraries, JENDL-4.0/HE provides the best agreement with the measured data for the p-induced reactions. We compared the present Nb93 data with the Zr93 data, that were measured previously by the same inverse kinematics method (Kawase et al., Prog. Theor. Exp. Phys. 2017, 093D03 (2017)2050-391110.1093/ptep/ptx110), with particular attention to the effect of neutron-shell closure on isotope production in p- and d-induced spallation reactions. The isotopic distributions of the measured production cross sections in the Zr93 data showed noticeable jumps at neutron number N=50 in the isotopic chains of ΔZ=0 and -1, whereas no such jump appeared in isotopic chain of ΔZ=0 in the Nb93 data. From INCL-4.6 + GEM calculations, we found that the jump formed in the evaporation process is smeared out by the intranuclear cascade component in Nb91 produced by the Nb93(p,p2n) and (d,d2n) reactions on Nb93. Moreover, for Nb93, the distribution of the element-production cross sections as a function of the change in proton number ΔZ is shifted to smaller ΔZ than for Zr93, because the excited Nb prefragments generated by the cascade process are more likely to emit protons than the excited Zr prefragments, due to the smaller proton-separation energies of the Nb isotopes

Coulomb breakup reactions of 93,94 Zr in inverse kinematics

Coulomb breakup reactions of 93,94 Zr have been studied in inverse kinematics at incident beam energies of about 200 MeV/nucleon in order to evaluate neutron capture reaction methods. The 93 Zr(n,γ) 94 Zr reaction is particularly important as a candidate nuclear transmutation reaction for the long-lived fission product 93 Zr in nuclear power plants. One- and two-neutron removal cross sections on Pb and C targets were measured to deduce the inclusive Coulomb breakup cross sections, 375 ± 29 (stat.) ± 30 (syst.) and 403 ± 26 (stat.) ± 31 (syst.) mb for 93 Zr and 94 Zr, respectively. The results are compared with estimates using the standard Lorentzian model and microscopic calculations. The results reveal a possible contribution of the pygmy dipole resonance or giant quadrupole resonance in the Coulomb breakup reactions of 94 Zr