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High-spin states up to ( -+) and ( -) in As have been studied via the Ni(' F,n2p) reaction at 62 MeV using in-beam p-ray spectroscopic techniques. Based on a particle-p coincidence measurement a new decay sequence of negative parity has been assigned to As. Lifetimes for some E2 transitions were extracted from Doppler-shifted line shapes observed in coincidence mode, and experimental transition quadrupole moments were determined. They indicate a moderate to high collectivity in both the positive-parity yrast band and the new negative-parity decay sequence at high spins. Total Routhian surfaces calculated for states of both parities reveal strong triaxial shapes at high spins. A noncollective structure of '~and~states is interpreted as a three-quasiparticle excitation.PACS number(s): 21.10. Tg, 23.20.Lv, 27.50.+e

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The high-spin states of " Br were studied via. the Ti( S,apn) Br and the Ni( F,2pn) Br fusion-evaporation reactions at energies of 105 and 62 MeV, respectively, using the Florida State University Tandem LINAC. y-p coincidence arrays were produced using four Compton-suppressed Ge detectors. Two independent groups of p rays were studied one of positive parity and one of negative parity, both of which appear to be based on an isomeric 4 + state. Lifetimes were measured using both the Doppler-shift attenuation and recoil-distance methods. A cranking-model analysis of the bands shows that the kinematic and dynamic moments of inertia for the bands are rather similar and fairly constant for high spins with values of (20 -23)h /MeV. A phase reversal occurs in the signature splitting in the yrast band around spin 9 which is related to the quasiparticle alignments. The lifetimes imply an average axial quadrupole deformation of 0.37 in the yrast band and 0.34 in the negative-parity band. These deformations are close to those predicted by Hartree-Fock-Bogolyubov cranking calculations. up to a probable spin of lib and two other decay sequences to lower spins. Winter et al. reported 4 bands or decay sequences populated in light-ion-induced reactions. The yrast band was observed up to 10h. In a conference proceedings Neumann et al. showed the level scheme for two bands in Br, including one state above the spin (12) member of the yrast band. Neumann et al. also listed the only lifetimes which have been reported in Hr, a set of 8 values measured with the recoildistance method. Most of the lifetimes imply collective electric quadrupole transition strengths [B(E2)] of 50 to 100 single-particle units (W.u. ), which are typical of the well-deformed nuclei in this region. However, a lifetime of 73.3+4.0 ps was reported for the (ll)~(9+) transition, which gives a B(E2) value of 0.74 + O. ll W.u.A band crossing at this frequency (as the anornalously low transition strength was interpreted) would be very interesting.An additional complication in the odd-odd " Br is the existence of a spin-4 isomer 100 -200 keV above the spin (0, 1) ground state. Some uncertainties remain about the parities of these states and about which one the various bands decay into. The available evidence is summarized 43 470 1991 The American Physical Society 43 DEFORMATION AND SIGNATURE SPLITTING IN Br 471 in Sec. IIIA.

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