0000000000880292
AUTHOR
J. Elseviers
Microscopic structure of coexisting $0^+$ states in $^{68}$Ni probed via two-neutron transfer
© 2019 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. The structure of low-spin states originating from shape-coexisting configurations in Ni284068 was directly probed via the two-neutron transfer reaction Ni66(t,p)Ni68 in inverse kinematics using a radioactive ion beam on a radioactive target. The direct feeding to the first excited 0+ state was measured for center-of-mass angles 4-16 and amounts to an integral of 4.2(16)% rela…
Single-neutron orbits near Ni-78: Spectroscopy of the N=49 isotope Zn-79
5 pags., 6 figs.
Collective 2$^{+1}$ excitations in$^{206}$Po and$^{208,210}$Rn
In the present study, $B(E2; 2^{+}_{1}\rightarrow 0^{+}_{1})$ values have been measured in the 208,210Rn and 206Po nuclei through Coulomb excitation of re-accelerated radioactive beams in inverse kinematics at CERN-ISOLDE. These nuclei have been proposed to lie in, or at the boundary of the region where the seniority scheme should persist. However, contributions from collective excitations are likely to be present when moving away from the N=126 closed shell. Such an effect is confirmed by the observed increased collectivity of the $2^{+}_{1}\rightarrow 0^{+}_{1}$ transitions. Experimental results have been interpreted with the aid of theoretical studies carried out within the BCS-based QRP…
β-delayed fission andαdecay ofAt196
A nuclear-decay spectroscopy study of the neutron-deficient isotope $^{196}\mathrm{At}$ is reported where an isotopically pure beam was produced using the selective Resonance Ionization Laser Ion Source and On-Line Isotope Mass Separator (CERN). The fine-structure $\ensuremath{\alpha}$ decay of $^{196}\mathrm{At}$ allowed the low-energy excited states in the daughter nucleus $^{192}\mathrm{Bi}$ to be investigated. A $\ensuremath{\beta}$-delayed fission study of $^{196}\mathrm{At}$ was also performed. A mixture of symmetric and asymmetric fission-fragment mass distributions of the daughter isotope $^{196}\mathrm{Po}$ (populated by $\ensuremath{\beta}$ decay of $^{196}\mathrm{At}$) was deduce…
Coulomb excitation of re-accelerated 208Rn and 206Po beams
In the present study, B( E2; 2(+)-> 0(+) ) values have been measured in the Rn-208 and Po-206 nuclei through Coulomb excitation of re-accelerated radioactive beams in inverse kinematics at CERN-ISOLDE. The resulting B(E2; 2(+)-> 0(+)) in 208Rn is similar to 0.08 e(2)b(2). These nuclei lie in, or at the boundary of the region where seniority scheme should persist. However, contributions from collective excitations may be present when moving away from the N = 126 shell closure. To date, surprisingly little is known of the transition probabilities between the low-spin states in this region.
Testing refined shell-model interactions in thesdshell: Coulomb excitation ofNa26
Background: Shell-model calculations crucially depend on the residual interaction used to approximate the nucleon-nucleon interaction. Recent improvements to the empirical universal $sd$ interaction (USD) describing nuclei within the $sd$ shell yielded two new interactions---USDA and USDB---causing changes in the theoretical description of these nuclei.Purpose: Transition matrix elements between excited states provide an excellent probe to examine the underlying shell structure. These observables provide a stringent test for the newly derived interactions. The nucleus $^{26}\mathrm{Na}$ with 7 valence neutrons and 3 valence protons outside the doubly-magic ${}^{16}\mathrm{O}$ core is used a…
Single-neutron orbits near 78 Ni: Spectroscopy of theN=49isotope 79 Zn
Single-neutron states in the Z=30, N=49isotope 79Zn have been populated using the 78Zn(d,p)79Zn transfer reaction at REX-ISOLDE, CERN. The experimental setup allowed the combined detection of protons ejected in the reaction, and of γrays emitted by 79Zn. The analysis reveals that the lowest excited states populated in the reaction lie at approximately 1MeV of excitation, and involve neutron orbits above the N=50shell gap. From the analysis of γ-ray data and of proton angular distributions, characteristic of the amount of angular momentum transferred, a5/2+configuration was assigned to a state at 983keV. Comparison with large-scale-shell-model calculations supports a robust neutron N=50shell…
Testing refined shell-model interactions in the sd shell: Coulomb excitation of 26Na
Background: Shell-model calculations crucially depend on the residual interaction used to approximate the nucleon-nucleon interaction. Recent improvements to the empirical universal sd interaction (USD) describing nuclei within the sd shell yielded two new interactions—USDA and USDB—causing changes in the theoretical description of these nuclei. Purpose: Transitionmatrix elements between excited states provide an excellent probe to examine the underlying shell structure. These observables provide a stringent test for the newly derived interactions. The nucleus 26Na with 7 valence neutrons and 3 valence protons outside the doubly-magic 16O core is used as a test case. Method: A radioactive b…
The Miniball spectrometer
The Miniball germanium detector array has been operational at the REX (Radioactive ion beam EXperiment) post accelerator at the Isotope Separator On-Line facility ISOLDE at CERN since 2001. During the last decade, a series of successful Coulomb excitation and transfer reaction studies have been performed with this array, utilizing the unique and high-quality radioactive ion beams which are available at ISOLDE. In this article, an overview is given of the technical details of the full Miniball setup, including a description of the γ-ray and particle detectors, beam monitoring devices and methods to deal with beam contamination. The specific timing properties of the REX-ISOLDE facility are hi…
Spectroscopy of $^{46}$Ar by the (t,p) two-neutron transfer reaction
States in the $N=28$ nucleus $^{46}$Ar have been studied by a two-neutron transfer reaction at REX-ISOLDE (CERN). A beam of radioactive $^{44}$ at an energy of 2.16~AMeV and a tritium loaded titanium target were used to populate $^{46}$ by the t($^{44}$,p) two-neutron transfer reaction. Protons emitted from the target were identified in the T-REX silicon detector array. The excitation energies of states in $^{46}$ have been reconstructed from the measured angles and energies of recoil protons. Angular distributions for three final states were measured and based on the shape of the differential cross section an excited state at 3695~keV has been identified as $J^\pi = 0^+$. The angular diffe…
Charge radii and electromagnetic moments of At195–211
Hyperfine-structure parameters and isotope shifts of At195-211 have been measured for the first time at CERN-ISOLDE, using the in-source resonance-ionization spectroscopy method. The hyperfine structures of isotopes were recorded using a triad of experimental techniques for monitoring the photo-ion current. The Multi-Reflection Time-of-Flight Mass Spectrometer, in connection with a high-resolution electron multiplier, was used as an ion-counting setup for isotopes that either were affected by strong isobaric contamination or possessed a long half-life; the ISOLDE Faraday cups were used for cases with high-intensity beams; and the Windmill decay station was used for short-lived, predominantl…
Cluster-transfer reactions with radioactive beams: A spectroscopic tool for neutron-rich nuclei
An exploratory experiment performed at REX-ISOLDE to investigate cluster-transfer reactions with radioactive beams in inverse kinematics is presented. The aim of the experiment was to test the potential of cluster-transfer reactions at the Coulomb barrier as a mechanism to explore the structure of exotic neutron-rich nuclei. The reactions Li7(Rb98,αxn) and Li7(Rb98,txn) were studied through particle-γ coincidence measurements, and the results are presented in terms of the observed excitation energies and spins. Moreover, the reaction mechanism is qualitatively discussed as a transfer of a clusterlike particle within a distorted-wave Born approximation framework. The results indicate that cl…