[en] High-spin states in the N=Z nucleus ⁷²Kr were populated using the ⁴⁰Ca(³⁶Ar,2p2n) reaction at a beam energy of 145 MeV. The yrast band has been observed up to a tentative spin of 20ℎ. Nonyrast rotational structures have also been observed for the first time. The alignment of g_9/2 protons and neutrons in the yrast band is observed to be significantly delayed relative to the heavier even-even Kr isotopes. Exact deformed cranked shell model calculations suggest that this could be due to the combined effect of isovector (T=1) and isoscalar (T=0) neutron-proton pairing correlations

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[en] High-spin states have been studied in ¹²⁸Ce, produced in the ¹⁰⁰Mo(³²S,4n) reaction, using the EUROBALL γ-ray spectrometer. A quadruples analysis (γ⁴) of the data has extended several bands to high spin. Systematics of quasiparticle alignments in cerium isotopes and relevant isotonic chains are discussed and compared to Woods-Saxon cranking calculations

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No abstract available

[en] The study of the β decay of some N=Z nuclei in the A=70 mass range have been performed using the GANIL and CERN/ISOLDE facilities. The fast decays of three T_z=0 odd-odd nuclei have been measured for the first time which extend the number of superallowed transitions. Information has been obtained on the Gamow Teller strength distribution in the β+-EC decay of two even-even N=Z isotopes ⁷⁶Sr and ⁷²Kr. Results are compared with theoretical predictions giving indication about the shape of the ground state of the parent nucleus

[en] Lifetimes of states in a rotational-like M1 band in ¹¹⁰Cd have been determined through a Doppler-shift attenuation method measurement performed with the Gammasphere array. The deduced B(M1) values, which agree well with the predictions of the tilted axis cranking model, clearly confirm that it has the character of a shears band. Using a semiclassical scheme of the coupling of two long j vectors we deduce information on the strength and form of the effective interaction between the constituent nucleons. These results are the first definitive evidence of the shears mechanism and magnetic rotation' in this mass region. copyright 1999 The American Physical Society

[en] The mechanical design of the EUROBALL neutron wall and neutron detectors, and their performance measured with a ^246,248Cm fission source are described. The array consists of 15 pseudohexaconical detector units subdivided into three, 149 mm high, hermetically separated segments and a smaller central pentagonal unit subdivided into five segments. The detectors are filled with Bicron BC501A liquid scintillator. Each section of the hexaconical detectors is viewed by a 130 mm diameter Philips XP4512PA photomultiplier while the sections of pentagonal detectors are viewed by Philips XP4312B PMTs. The tests of n-γ discrimination performed by zero-crossing and time-of-flight methods show a full separation of γ- and neutron events down to 50 keV recoil electron energy. These tests demonstrate the excellent timing properties of the detectors and an average time resolution of 1.56 ns. The factors determining the efficiency of neutron detectors are discussed. The total efficiency for the full array for a symmetric fusion-evaporation reaction is predicted to be 0.30. (Copyright (c) 1999 Elsevier Science B.V., Amsterdam. All rights reserved.)

[en] High-spin states were populated in ¹⁰⁸Cd using the ⁹⁶Zr(¹⁶O,4n) reaction at a beam energy of 72 MeV. Two magnetic dipole bands have been observed, both of which contain weak E2 crossover transitions. Lifetimes for the stronger of the two bands were measured via the Doppler shift attenuation method. The configuration assignment for this band has been determined from comparison with tilted axis cranking model calculations to be π[g_9/2^-3g_7/2](multiply-in-circle sign)ν[h_11/2(g_7/2d_5/2)¹] and π[g_9/2^-3g_7/2](multiply-in-circle sign)ν[h_11/2³(g_7/2d_5/2)¹], before and after the νh_11/2² band crossing, respectively. The deduced B(M1) strengths decrease rapidly with increasing spin after the νh_11/2² alignment, which is a characteristic behavior of a shears band. (c) 2000 The American Physical Society

[en] The heavy odd-odd N=Z nuclei ⁷⁸Y,⁸²Nb,⁸⁶Tc have been produced at GANIL by fragmentation of a 60 MeV/u ⁹²Mo beam on a natural nickel target. Their lifetime have been measured for the first time, using the identification-implantation and subsequent time correlated β counting technique at the LISE spectrometer. The obtained half-lives for ⁷⁸Y,⁸²Nb,⁸⁶Tc are consistent with the microscopic predictions. These nuclei are good candidates to extend the mass range for the V_ud matrix element evaluation and our experimental results highlight the interest of further investigation of their excited states and β decay schemes as a function of isospin. copyright 1998 American Institute of Physics