A. Emsallem

COLLECTIVE STRUCTURE OF THE NEUTRON-RICH NUCLEI, RU-110 AND RU-112

Abstract The collective structure of 110 Ru and 112 Ru has been studied at the IGISOL facility through the beta decay of 110 Tc and 112 Tc. Neutron-rich technetium isotopes were produced by the 238 U(p, f) reaction at 20 MeV bombarding energy. The new isotope 112 Tc was found to decay with a half-life of 280(30) ms. The observed energies of the 2 + and 4 + ground state band levels in 108,110,112 Ru are almost the same. However, a steady energy decrease of the proposed gamma band head is observed with increasing neutron number, suggesting importance of triaxiality in these nuclei. In fact, only in 192 Os the second 2 + state has been observed at lower excitation than in 112 Ru. The static deformation of 108,110,110 Ru isotopes has been investigated in microscopic lattice Hartree-Fock calculations. The obtained potential energy surfaces predict that these isotopes are deformed (β ∼ 0.3), with a quasidegeneracy associated with γ-deformation, and suggest that the γ-asymmetry softness increases with the neutron number for neutron-rich ruthenium isotopes.

Development of a new SARA/IGISOL technique for the study of short-lived products from heavy-ion-induced fusion—evaporation reactions

Abstract A new ion guide chamber has been designed for heavy-ion (HI) induced fusion—evaporation reactions. Its principle is based on the beam projectiles-evaporation residues separation which is achieved by taking advantage of their very different angular distributions after passing a thick target. In this work it is proved that the IGISOL technique can be applied with an overall efficiency > 10 −3 for the study of mass-separated exotic nuclei produced in (HI, x n) reactions.

Beta decay half-lives of neutron rich Ti–Co isotopes around N=40

Abstract The neutron-rich 57 – 59 Ti, 59 – 62 V, 61 – 64 Cr, 63 – 66 Mn, 65 – 68 Fe, 67 – 70 Co have been produced at GANIL via interactions of a 60.4 MeV/u 86 Kr 34+ with a 58 Ni target. They have been separated by the doubly achromatic spectrometer LISE3. Beta-decay half-lives have been determined for all produced nuclei, and subsequent γ -rays have been observed for the most efficiently produced nuclei. The measured half-lives of vanadium and chromium isotopes are compared to QRPA calculations using ground states deformations from the FRDM or ETFSI models. In an astrophysical context, the short half-lives of 58 Ti and 64 Cr indicate that these nuclei are potential r-process progenitors, after β -decay, of 58 Fe and 64 Ni in certain inclusions of meteorites.

Erratum to “Beta decay half-lives of neutron rich Ti–Co isotopes around N=40” [Nucl. Phys. A 660 (1999) 3–19]

Abstract The neutron-rich 57−59 Ti, 59−62 V, 61−64 Cr, 63−66 Mn, 65−68 Fe, 67−70 Co have been produced at GANIL via interactions of a 60.4 MeV/u 86 Kr 34+ with a 58 Ni target. They have been separated by the doubly achromatic spectrometer LISE3. Beta-decay half-lives have been determined for all produced nuclei, and subsequent γ -rays have been observed for the most efficiently produced nuclei. The measured half-lives of vanadium and chromium isotopes are compared to QRPA calculations using ground states deformations from the FRDM or ETFSI models. In an astrophysical context, the short half-lives of 58 Ti and 64 Cr indicate that these nuclei are potential r-process progenitors, after β -decay, of 58 Fe and 64 Ni in certain inclusions of meteorites.

Improved ion guide for heavy-ion fusion–evaporation reactions

The ion guide for heavy-ion-induced reactions developed originally for the SARA facility in Grenoble has been implemented at the Jyvaskyla IGISOL facility. For the Cd-116(Ar-40, 6n)Dy-150 reaction an efficiency of 0.5% relative to the number of reaction products entering the stopping chamber was obtained. This is 3.5 times higher than previously obtained at SARA and corresponds to a yield of about 100 ions/(p mu C mb). Mass-separated yields for the Ar-36 + Mo-92 and Ar-36 + Mo-94 reactions were measured

Shape Coexistence In Light Krypton Isotopes

Coexisting states of prolate and oblate shapes were studied via Coulomb excitation of radioactive 74Kr and 76Kr beams at safe energies at GANIL. The results for the transitional E2 matrix elements for several yrast transitions in both isotopes are in contradiction with the B(E2) values extracted from the lifetimes that are found in the literature. This motivated a new lifetime measurement which showed strong deviations from the previously published values, but is consistent with the results from Coulomb excitation. Having resolved these discrepancies and knowing the B(E2) values with high precision allows to extract the diagonal matrix elements from the Coulomb excitation data. The results confirm the proposed shape coexistence scenario.

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.

The beta-decay of Al-22

Abstract.In an experiment performed at the LISE3 facility of GANIL, we studied the decay of 22Al produced by the fragmentation of a 36Ar primary beam. A β-decay half-life of T1/2 = 91.1±0.5ms was measured. The β-delayed one- and two-proton emission as well as β-α and β-delayed γ-decays were measured and allowed us to establish a partial decay scheme for this nucleus. New levels were determined in the daughter nucleus 22Mg. The comparison with model calculations strongly favours a spin-parity of Iπ = 4+ for the ground state of 22Al.

The β-decay of 22 Al

Abstract.In an experiment performed at the LISE3 facility of GANIL, we studied the decay of 22Al produced by the fragmentation of a 36Ar primary beam. A β-decay half-life of T1/2 = 91.1±0.5ms was measured. The β-delayed one- and two-proton emission as well as β-α and β-delayed γ-decays were measured and allowed us to establish a partial decay scheme for this nucleus. New levels were determined in the daughter nucleus 22Mg. The comparison with model calculations strongly favours a spin-parity of Iπ = 4+ for the ground state of 22Al.

Studying exotic nuclides close to the N = Z line at the HIGISOL facility

The ion guide [1, 2] for heavy-ion fusion-evaporation reactions (HIGISOL) which was developed by Beraud et al. [3] has been implemented at the IGISOL facility in Jyvaskyla [4]. This system was modified over the past 5 years. Figure 1 shows the present set-up. The HIGISOL takes advantage of the different angular distributions of primary beam and reaction products: the primary beam is stopped in front of the stopping chamber and the reaction products enter the stopping chamber through a thin foil passing the beam stop. This so called “shadow” method removes the plasma effect since the primary beam is not ionising the stopping gas. In order to improve ion optical properties, mainly to reduce the energy spread, the normal skimmer system was replaced by a sextupole ion guide, SPIG. The mass resolving power (MRP) for a 219Rn ion beam was measured to be 1100, independent of the helium pressure and SPIG DC voltage level relative to the stopping chamber [6]. The MRP measured earlier with the skimmer was 250 for 219Xe [4].