No abstract available

No abstract available

[en] This work explores how nuclear collectivity arises in singly-closed shell nuclei where particle–particle correlations may be the dominant degree of freedom. The trends of B(E2;2₁⁺→0₁⁺) values in the Ni and Sn superfluids with N⪆Z are predicted from proton and neutron pairing gaps extracted from atomic masses. Nuclear collectivity is enhanced for the combination of large and close-lying proton and neutron pairing gaps. The agreement with the Ni isotopes is excellent, and recent experimental results support the enhanced trend predicted for the neutron-deficient Sn isotopes. This work shows that many-body microscopic properties such as nuclear collectivity could be inferred directly from macroscopic average properties such as atomic masses. (paper)

[en] It is the purpose of this paper to illustrate some of the low-energy nuclear physics that we want to pursue at the new HIE-ISOLDE radioactive-ion-beam facility at CERN. The University of the Western Cape leads an experimental proposal and co-authors two Letters of Intent, in collaboration with European institutions, at HIE-ISOLDE. Timely topics such as the ''Exploration of K-isomerism using unique high-K isomeric beams – CERN-INTC-I-101'' and ''Shape changes and proton-neutron pairing around the N = Z line – CERN-INTC-I-102'' are addressed in these Letters of Intent. Our experimental proposal aims at performing a multi-step Coulomb-excitation of radioactive ⁷⁰Se ion beams using the ²⁰⁸Pb(⁷⁰Se,⁷⁰Se*)²⁰⁸Pb* reaction at a bombarding energy of 5.5 MeV/u. The physics goal is a precise measurement of the (2⁺₁ || Ê2 || 2⁺₁) diagonal matrix element, related to the spectroscopic quadrupole moment, in ⁷⁰Se. Full simulations presented in this work show distinct angular distributions for plausible values of the spectroscopic quadrupole moment; with a predicted uncertainty of approximately ±0.1 eb. Additional diagonal and transitional matrix elements will also be obtained. These results will shed light onto the origin of rarely-found oblate shapes and shape coexistence in this region of rapidly-changing shell structure

[en] Reaching new depths in nuclear structure investigations requires new experimental equipment and new techniques of data analysis. The modern γ -ray spectrometers, like AGATA and GRETINA are now built of new-generation segmented germanium detectors. These most advanced detectors are able to reconstruct the trajectory of a γ -ray inside the detector. These are powerful detectors, but they need careful characterization, since their output signals are more complex. For instance for each γ -ray interaction that occurs in a segment of such a detector additional output signals (called proportional crosstalk), falsely appearing as an independent (often negative) energy depositions, are registered on the non-interacting segments. A failure to implement crosstalk correction results in incorrectly measured energies on the segments for two- and higher-fold events. It affects all experiments which rely on the recorded segment energies. Furthermore incorrectly recorded energies on the segments cause a failure to reconstruct the γ -ray trajectories using Compton scattering analysis. The proportional crosstalk for the iThemba LABS segmented clover was measured and a crosstalk correction was successfully implemented. The measured crosstalk-corrected energies show good agreement with the true γ -ray energies independent on the number of hit segments and an improved energy resolution for the segment sum energy was obtained. (paper)

[en] The low-lying, low-spin levels of ¹⁴¹Pr were investigated using (n,n^'γ) techniques. Level energies, branching ratios, and tentative spin assignments for more than 100 states, linked by nearly 300 transitions, were obtained from two angular distributions (E_n=2.0 and 3.0 MeV) and an excitation function measurement (E_n=1.5-3.2 MeV). The application of the Doppler-shift attenuation method led to the determination of lifetimes. The obtained spectroscopic data provide insight into the wave functions of the states observed. A detailed analysis of the [2₁⁺ x d_5/2] and [2₁⁺ x g_7/2] multiplets provides the first quantitative evidence for Pauli blocking in a spherical odd-mass nucleus. The unpaired particle is used to probe the microscopic structure of the first 2⁺ state of the adjacent core nuclei ¹⁴⁰Ce and ¹⁴²Nd

[en] Gamma-ray angular distribution measurements following the ^natNi(n,n^'γ) reaction were carried out at 1.6 and 1.8 MeV neutron energies. Through the Doppler-shift attenuation method, the lifetime of the 2₁⁺ state in ⁵⁸Ni is determined as τ=1.00_-0.10^+0.15 ps, which yields a B(E2;2₁⁺→0₁⁺) value of 9.4_-1.2^+1.0 W.u. From previous measurements and this work, average values of τ=0.94(3) ps and B(E2;2₁⁺→0₁⁺)=10.0(4) W.u. are recommended as standards for normalization. In addition, a longer lifetime of τ=1.30_-0.20^+0.30 ps has been determined for the 2₁⁺ state in ⁶⁰Ni, which yields an E2 strength of 10.7_-2.5^+1.7 W.u. Our results support an enhancement of proton-core excitations and related quadrupole and pairing strengths in the light Ni isotopes, in agreement with mean-field and shell-model calculations

[en] The low-spin structure of 127I has been studied using the (n,n'γ) reaction at neutron energies ranging from 1.2 to 2.3 MeV and the (n,n'γγ) reaction at 3 MeV. New excited levels and γ-rays have been identified by using excitation functions and coincidence data. Lifetimes were also determined from an angular distribution experiment. Future work involves determining multipolarities and spin assignments in order to obtain B(M1) and B(E2) values

[en] The low-spin structure of ⁹⁴Zr has been studied with the (n,n^'γ) reaction, and branching ratios, lifetimes, multipolarities and spin assignments were determined. The 2₂⁺ state at 1671.4 keV has been identified as the lowest mixed-symmetry state in ⁹⁴Zr. The 752.5-keV transition from this state to the 2₁⁺ level has a large B(M1) value of 0.33(5) μ_N², and the B(E2) of the transition to the ground state has an unusually large value of 8(1) W.u. The M1 transition strength is in agreement with IBM-2 predictions in the U(5) vibrational limit, whereas the large B(E2;2_1,MS⁺→0₁⁺) value significantly exceeds the E2 strength predicted by the IBM-2. For the first time, the 2_1,MS⁺→0₁⁺E2 transition is observed to have a larger E2 transition strength than the 2₁⁺→0₁⁺ decay

[en] The lifetime of the 2₁⁺ state at 1256.7 keV in ¹¹²Sn has been determined using the (n,n^'γ) reaction. Angular distribution measurements were carried out at a neutron energy of 1.7 MeV, above the 2₁⁺ energy threshold and below that of the second excited level. Through the Doppler-shift attenuation method, the lifetime of the 2₁⁺ state is determined as 750_-90⁺¹²⁵ fs, which gives a B(E2;2₁⁺→0₁⁺) value of 10.9_-1.6^+1.5 W.u. This E2 strength in ¹¹²Sn also allows a redetermination of the B(E2;2₁⁺→0₁⁺) in ¹⁰⁸Sn as 10.8(3.0) W.u. These values result in a symmetric trend around the neutron midshell in the systematics of E2 strengths in the even-mass tin isotopes and do not support N=64 or N=66 subshell gaps. The symmetric trend is in agreement with recent shell model predictions, where proton-core excitations were allowed in the calculations