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An improved high-resolution study of the beta decay of Ti-41, produced in the Ca-40(He-3,2n) reaction at 40 MeV, has been performed at the Ion Guide Isotope Separator On-Line (IGISOL) facility. The beta-delayed radiation was detected by a low-energy charged-particle detector and a large Ge detector for gamma rays. The experimental beta-decay strength and its distribution, extracted from delayed-proton data, are compared with results of shell-model calculations in the sdfp space. The lowest J(pi) 3(+)/2, T = 3/2 state in (41) Sc, the isobaric analogue state of the Ti-41 ground state, is estimated to contain 10% isospin impurity. (C) 1997 Elsevier Science B.V.

In-beam γ-ray transitions in 181Hg, the lightest odd-A Hg isotope known thus far, have been identified from fragment mass-γ and γ-γ coincidence measurements. Five prolate deformed rotational bands were placed in the level scheme. A decoupled band built on the strongly prolate deformed 1/2-[521] ground state was observed up to 29/2-. A 5/2-[512] configuration is suggested for a pair of strongly coupled bands displaying no signature splitting. The other two bands are also signature partner bands. They are populated with the largest intensity and exhibit splitting. They have been associated with the mixed neutron i13/2 orbitals and are proposed to decay to an i13/2 isomeric state associated with an oblate state.

The beta-delayed gamma decay of Nb-108 has been studied using the on-line mass-separator technique. The measured beta-decay half-life 0.20+/-0.03 s agrees with the previous measurement based on beta-delayed neutron detection. The lifetime of the first 2(+) stale in Mo-108 was measured to be 0.5+/-0.3 ns, which is consistent with a deformation beta approximate to 0.4. Spin and parity of 2(+) are suggested for the ground state of Nb-108.

The beta decay of the very-neutron-rich nucleus Y-103 has been studied at the isotope separator IGISOL, allowing for the first time the observation of nonyrast levels in its daughter Zr-103(40)63. The level structure is similar to that of its isotones Sr-101 and Mo-105, suggesting a targe ground-state deformation of beta similar or equal to 0.4. Level systematics allows for new level assignments in both Zr-103 and Mo-105.

The decays of the 9/2(+) and of the three-quasiparticle high spin isomer in Y-97 have been investigated following on-line mass separation with the ion-guide technique. Spins and parities for several of the lowest-lying levels in the daughter nucleus Zr-97 are revised and configurations are proposed. In particular, the 2264 keV level is identified as the h(11/2) single-neutron level. The population of a cascade on top of the h(11/2) level provides evidence for Gamow-Teller beta decay of the high-spin Y-97 isomer. Levels and transition rates are qualitatively well reproduced by regarding Zr-97 as a single-neutron nucleus with respect to the doubly closed Zr-96 core.

Independent and cumulative yields in nearly symmetric fission have been measured for the first time by bombarding U-238 with 20-MeV protons and with 18-, 25-, and 41-MeV deuterons. Isobaric charge dispersion has been determined in the A = 110, A = 112, and A = 114 mass chains and, from asymmetric fission, in the A = 80 mass chain. The average isobaric charges in the p + U reaction were 44.01 +/- 0.20 (A = 110), 45.15 +/- 0.15 (A = 112), and 45.74 +/- 0.15 (A = 114). The widths (standard deviations) of the charge dispersion curves were 0.82 +/- 0.08 (A = 112) and 0.54 +/- 0.08 (A = 114). The average charges are roughly 0.3 unit higher than those calculated on the basis of the unchanged charge distribution model. The ground-state branch in the beta decay of 80Ge was determined to be 65%. Altogether some 15 new neutron-rich isotopes have been found, the newest one being 114Ru with a half-life of 0.53 +/- 0.06 s. An ion guide facility was used to separate the isobaric chains on-line from other fission products. Typical cumulative yields in a mass chain were on the order of 1000 atoms/mu-C, but for new isotopes independent yields as low as a few atoms/mu-C could be observed.

Neutron-rich nuclides Ru-110 and Ru-112 produced in symmetric fission of U-238 by 20 MeV protons have been studied at the IGISOL facility by means of beta-ray, gamma-ray and conversion electron spectroscopy. A total of 12 and 6 gamma-transitions were observed in the decays of Ru-110 and Ru-112, respectively. Multipolarities were determined for a few transitions. The beta decay half-life was determined to be 11.6 +/- 0.6 s for Ru-110 and 1.75 +/- 0.07 s for Ru-112. As a side product, a new value of 2.1 +/- 0.3 s for the beta half-life of the Rh-112 1+ state was obtained. The decay energy measured with the plastic scintillator was 2.81 +/- 0.05 MeV for Ru-110 and 4.52 +/- 0.08 MeV for Ru-112. The beta decay schemes of Ru-110 and Ru-112 isotopes indicate that the main fraction of their beta strength resides in two 0+ --> 1+ spin-flip transitions with their log f t values between 4.4 and 4.7. The decay energies and the energies of the 1+ GT states are compared with the macroscopic-microscopic model calculations. The observed GT-strengths are discussed in the framework of the deformed single-particle model.

In this paper we wish to report on the first observation of the beta decay of the very neutron-rich nucleus 117Rh. It was produced via 23 MeV proton-induced fission of U-238 using the ion guide setup of the LISOL separator. A beta half-life to 0.44 +/- 0.04 s was measured for this nucleus from the decay of the beta-coincident K x rays of Pd. The half-lives of neutron-rich Rh isotopes are compared with the newest model calculations. Three gamma rays of 34.6, 131.7, and 481.6 keV were found to be associated with the decay of 117Rh. Its proposed beta-decay scheme and the decay of the recently discovered 19 ms isomer in 117Pd imply spin and parity of 11-/2 for the isomer fed directly in fission.

Comment on deliverable D5

The low-lying level structure of the neutron-deficient isotope Rn202 has been studied for the first time, using the Ta181(27Al,6n) and Pt192(16O,6n) reactions. Gamma-ray transitions between excited states in Rn202 were identified by mass tagging using a recoil mass separator, the Argonne Fragment Mass Analyzer, and by observation of coincident x rays. Transitions in Rn203 were also identified. The level scheme deduced from these data is consistent with the systematics of light radon isotopes below the N=126 shell closure and with theoretical calculations indicating that the ground-state shape should not be strongly deformed at N=116.

International audience; Excited states in the mirror nuclei 31P and 31S were populated in the 1p and 1n exit channels of the reaction 20Ne + 12C, at a beam energy of 33 MeV. The 20Ne beam was delivered for the first time by the Piave-Alpi accelerator of the Laboratori Nazionali di Legnaro. Angular correlations of coincident γ-rays and Doppler-shift attenuation lifetime measurements were performed using the multi-detector array GASP in conjunction with the EUCLIDES charged particle detector. In the observed B(E1) strengths, the isoscalar component, amounting to 24% of the isovector one, provides strong evidence for breaking of the isospin symmetry in the A=31 mass region. Self-consistent beyond mean field calculations using Equation of Motion method based on a chiral potential and including two- and three-body forces reproduce well the experimental B(E1) strengths, reinforcing our conclusion. Coherent mixing from higher-lying states involving the Giant Isovector Monopole Resonance accounts well for the effect observed. The breaking of the isospin symmetry originates from the violation of the charge symmetry of the two- and three-body parts of the potential, only related to the Coulomb interaction.