Deformation and signature splitting inBr74

Abstract

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.

Shape coexistence and high-Kstates in74Se populated following theβdecay ofMcCutchan1, Lister2, Ahn3 et al. 2013Phys. Rev. C10071View full textAdd to dashboardCite

“…The dominant (>90%) β decay in this study is not from the 74 Br ground state but from the T 1/2 = 46 min, 13.8 keV J π =4 (+) isomer. Inbeam spectroscopy indicates this state is the band head for a set of states which are highly deformed and collective in nature with a quadrupole deformation at high spin of β 2 ∼0.4 [18]. The large deformation arises from both of the uncoupled valence particles lying in states of g 9/2 parentage, specifically in the [422]5/2 neutron and [431]3/2 proton Nilsson states.…”

“…Odd-odd 74 Br has J=0 and J=4 β-decaying states so population of almost all the known low-lying levels can be achieved. The higher spin β-decaying state in 74 Br, (J π =4 (+) ) is particularly useful; it has a very unusual structure, being highly prolate-deformed, with a quadrupole moment corresponding to an axial ellipsoid with β 2 ∼ 0.4 and also being a 2-quasi-particle K=4 isomer [17,18]. As β decay is both shape and K-selective, we have an interesting starting point to investigate the overlap with the deformed states in the 74 Se daughter.…”

Nuclear structure of odd-oddY82

“…A careful examination of the positive-parity graphs shows that the phase of the alternations reverses between 95 and 105 for s Y and between 10h and lib for soRb. Such an inversion in the signature splitting has also been seen in "4Br [1], 7sBr [2], and s4Y [24]. Calculations using a 2-qp plus-rotor model [4] have attributed the inversion to a change from excitation modes involving both qp alignment and collective rotation at low spins to rotation only at high spins.…”

“…Among other odd-odd nuclei, they have been reported for 7 Br [1] and can be inferred from intensity tables in papers on 7sBr [2] and 7sRb [26]. In 1-qp bands they have been observed in the N = 41 isotones TsSe [5] and 77Kr [27,28] and interpreted in terms of triaxiality in the particle-rotor model [6].…”

“…Odd-odd nuclei have not been studied as extensively as their neighbors, but recent investigations of nearby odd-odd isotopes, such as 7 Br [1], 7sBr [2], and soRb [3] have shown a similar well developed rotational structure starting above 0.5 MeV excitation energy. Although the pairing of like particles is an important aspect of nuclear structure at low excitation energy and qp alignment has major effects on the behavior of rotational bands, much less is known about the residual proton-neutron interaction.…”