Lifetime measurements in70Se and72Se

Abstract

Mean lives and limits of lifetimes have been determined for some ten mostly yrast states in 7~ by means of the recoil distance Doppler shift technique. The states were excited in the reaction 4~ c~2p) at 115 MeV resp. the reaction 58Ni(14N, pn) at 39 MeV beam energy. The systematic decrease of B(E2) values along the the ground band transitions indicates a band crossing consistent with the ))-ray energies. Effects of continuum feeding times in both reactions are being discussed. The lifetimes of the lowest three yrast transitions in 72Se have been remeasured by means of the reactions 4OCa (36Ar ' 4p) and 6~ (14N, pn).

A new device for combined Coulomb excitation and isomeric conversion electron spectroscopy with fast fragmentation beams

“…A pronounced irregularity is observed for the Se isotopes, which show an unexpected staggering at N = 36 and 38 [26]. However, the relevant lifetimes have been re-measured recently and the data indicate that 70 Se is less collective than previously thought [27].…”

Shape coexistence inSe72investigated following theβdecay ofMcCutchan1, Lister2, Ahn3 et al. 2011Phys. Rev. C212230View full textAdd to dashboardCite

“…The change in intensity of the 380-keV transition has a significant effect on the B(E2; 2 A level at 1876 keV was previously proposed [8] (2,4). In the present work, the 559-keV transition to the 2 + 2 state was confirmed.…”

“…For 72 Se, this corresponds to N reg = 8 and N def = 10 with the deformed configuration based on particles in the g 9/2 orbit. The full Hamiltonian is given by [23,24]Ĥ =Ĥ regPreg +Ĥ defPdef +V mix whereP are projection operators and wherê (2) . Each configuration has the parameters ǫ,κ,χ and e b (where e b is the effective boson charge for the E2 operator).…”

“…Shape coexistence in the light Selenium isotopes has been the subject of intense debate in the last few years, with evidence presented for oblate ground states [1,2], which was challenged [3], supported [4], and once more cast in doubt [5]. Independent of the interpretation of the ground state structure, the dynamic behavior becomes dominated by prolate collective rotation, at modest (∼1 MeV) excitation energy.…”

Coulomb shifts and shape changes in the mass 70 region

“…Shape changes in 70 Se are clear experimentally from the very irregular yrast line and lifetime measurements, which indicated a strong reduction in B(E2) transition strengths near J = 4 [25]. A recent Coulomb excitation measurement favors a prolate shape for the 2 + state consistent with β 2 = 0.25 [7] and is in agreement with a configuration mixing shell model calculation which predicts a ground state band with β 2 = 0.18 crossed by a more deformed band with β 2 = 0.33 near J = 6 [30].…”