M. Sawicka

g-factor measurements of μs isomeric states in neutron-rich nuclei around 68Ni produced in projectile-fragmentation reactions

We report the first g factor measurement on microsecond isomers of neutronrich nuclei produced in projectile-fragmentation reactions at intermediate energies. The nuclides in the vicinity of 68 Ni were produced and spin oriented following the fragmentation of a 76 Ge, 61.4 MeV u −1 beam at GANIL. The LISE spectrometer was used to select the nuclei of interest. The time-dependent perturbed angular distribution (TDPAD) method was applied in combination with th eh eavy-ion–gamma correlation technique to measure the g factors of 69m Cu (J π = 13/2 + , T1/2 = 350 ns) and 67m Ni (J π = 9/2 + , T1/2 = 13.3 µs). Specific details of the experimental technique and the comparison of the results (|g( 69m Cu) |= 0.225(25) and |g( 67m Ni) |= 0.125(6)) with theoretical calculations are discussed. These results provide another indication of the importance of proton excitations across the Z = 28 shell gap.

Coupling of valence particles/holes to 68,70Ni studied via measurements of the B(E2) strength in 67,69,70Ni and 71Cu

Coupling of valence particles/holes to 68,70Ni studied via measurements of the B(E2) strength in 67,69,70Ni and 71Cu.

Magnetic moment of the fragmentation-aligned 61Fe (9/2(+)) isomer.

We report on the g factor measurement of an isomer in the neutron-rich (61)(26)Fe (E(*)=861 keV and T(1/2)=239(5) ns). The isomer was produced and spin aligned via a projectile-fragmentation reaction at intermediate energy, the time dependent perturbed angular distribution method being used for the measurement of the g factor. For the first time, due to significant improvements of the experimental technique, an appreciable residual alignment of the nuclear spin ensemble has been observed, allowing a precise determination of its g factor, including the sign: g=-0.229(2). In this way we open the possibility to study moments of very neutron-rich short-lived isomers, not accessible via other production and spin-orientation methods.

Beta decay of 56Cu

Abstract The proton-rich isotope 56 Cu was produced at the GSI On-Line Mass Separator by means of the 28 Si( 32 S, p3n) fusion–evaporation reaction. Its β -decay properties were studied by detecting β -delayed γ rays and protons. A half-life of 93±3 ms was determined for 56 Cu. Compared to the previous work, six new γ rays and three new levels were assigned to the daughter nucleus 56 Ni. The measured Gamow–Teller strength values for five 56 Ni levels are compared to shell-model predictions.

NUCLEAR STRUCTURE STUDIES OF EXOTIC NUCLEI VIA THE STRENGTH OF E2 TRANSITIONS; ADVANCED TIME-DELAYED γγ SPECTROSCOPY AT THE EXTREME

Nuclear structure studies of exotic nuclei via the strength of E2 transitions; advanced time-delayed γγ spectroscopy at the extreme

Beta decay of 56 Cu

AbstractThe proton-rich isotope 56 Cu was produced at the GSI On-Line Mass Separator by means ofthe 28 Si( 32 S, p3n) fusion–evaporation reaction. Its β -decay properties were studied by detecting β -delayed γ rays and protons. A half-life of 93± 3 ms was determined for 56 Cu. Compared to theprevious work, six new γ rays and three new levels were assigned to the daughter nucleus 56 Ni. Themeasured Gamow–Teller strength values for five 56 Ni levels are compared toshell-model predictions.  2001 Elsevier Science B.V. All rights reserved. PACS: 21.10.-k; 23.40.-s; 21.60.Cs; 27.40.+zKeywords: R ADIOACTIVITY 56 Cu ( β + ) [from 28 Si( 32 S, p3n)]; Measured E γ , I ; Deduced β -intensity and β -strength distribution; 56 Ni deduced levels J,π ; On-line mass separation; Plastic scintillation detectors; Gedetectors. N UCLEAR STRUCTURE 56 Ni; Calculated levels; Gamow–Teller strength; S HELL MODEL * Corresponding author.E-mail address:e.roeckl@gsi.de (E. Roeckl). 1 Present address: Instituut voor Kern- und Stralingsfysica, University of Leuven, B-3001 Leuven, Belgium.

Measurement of the g factors of isomers near the proposed N ≈ 40 subshell closure

We report results from a pioneering experiment to measure the g factors of isomeric states of neutron-rich nuclei around 68Ni, far from the valley of β stability.For the first time, the time-dependent perturbed angular distribution method was applied in combination with the heavy-ion-γ correlation technique to study g factors of spin-aligned isomers produced in a projectile fragmentation reaction and mass-separated. Some technical aspects are discussed and illustrated with preliminary results.

New spectroscopy of heavy neutron rich nuclei: Isomeric studies following relativistic fragmentation

Gamma spectroscopy methods have been used to search for microsecond isomers among fragmentation products of 1 GeV/nucleon 208Pb beam. Decays of several known K-isomers in the rare earth region of A∼180 were observed, including the K=35/2 isomer in 179W. Several new isomeric decays in the very neutron rich systems, such as 190W, have been identified. In addition, in the course of this work, a number of neutron rich rare earth isotopes have also been synthesised and identified for the first time.

Low-lying isomeric levels in {sup 75}Cu

Isomeric low-lying states were identified and investigated in the 75Cu nucleus. Two states at 61.8(5)- and 128.3(7)-keV excitation energies with half-lives of 370(40)- and 170(15)-ns were assigned as 75m1Cu and 75m2Cu, respectively. The measured half-lives combined with the recent spin assignment of the ground state allow one to deduce tentatively spin and parity of the two isomers and the dominant multipolarities of the isomeric transitions with respect to the systematics of the Cu isotopes. Shell-model calculations using an up-to-date effective interaction reproduce the evolution of the 1/2 , 3/2 , and 5/2 states for the neutron-rich odd-mass Cu isotopes when filling the g9/2. The results indicate a significant change in the nuclear structure in this region, where a single-particle 5/2 state coexists with more and more collective 3/2 and 1/2 levels at low excitation energies.

Isomeric island in the vicinity of 66Fe

An island of isomers have recently been observed on both sides of the N=40 shell below the Ni isotopes. Isomeric states in the 65Fe and 67Fe allow the knowledge of the single particle structure around the νg9/2 shell. Moreover, the excitation energy of the first 2+ and 4+ states in the 68Fe have been established by β‐γ correlation. The evolution of the structure of the Fe isotopes going far away from the valley of stability is, for the first time, given for N>40.