Transitional quadrupole moments in83Y

Abstract

Doppler shift attenuation lifetime measurements have been carried out for the 3qp and isomeric rotational bands in S3y using the reaction ~SNi(2Ssi,3p). While the transitional quadrupole moments in the 3qp bands are slightly lower than in the lqp bands, we found evidence for a strong reduction in IQt[ for the isomeric band. PACS :21.60.Ev; 27.50.+e Recent work [1][2][3][4] on the S3y isotope has revealed interesting insights concerning interplay between collective and single particle behavior in the mass 80 region. In the first in-beam study [1] of s3y, several rotational sequences were found. The positive-parity yrast band exhibited a bandcrossing interpreted [4] as being due to g9/2 neutron alignment. The negative parity favored signature sequence forked into two separate bands. The bandcrossing in the yrast band was interpreted as a proton alignment. The second branch of this forking had a rotational structure feeding into the 62 ps lived 17/2~-state. We shall refer to this band as an isomeric band. Between the isomeric band and the yrast negative parity band were seen no cross transitions, in spite of the near degeneracy in energies. G-factor measurements [3] suggested that a complex n-p rotation-aligned configuration was the underlying structure. Lifetime measurements of S3y indicated decreasing [Qt] for the 3qp structure and rather large deformations for the lower spin states in the yrast negative-parity band. But in the isomeric band, except for the 17/2-and 19/2-states, no lifetimes are available.The lifetime measurements have been extended using the Doppler-shift attenuation method. The reaction used was 5SNi(2ssi,3p)SaY at 95. MeV using the Cologne tandem accelerator. The target was an 99.8 % enriched 0.38mg/cm 2 thick 5SNi foil. Six Comptou-supressed detectors were placed in a ring positioned at 900 and one at 0 ~ relative to the beam axis. Doppler shifted lineshapes were obtained, by observing lines in the 0 ~ detector in coincidence with those at 900 .Transitions investigated are shown in the partial level scheme of S3y in Fig. 1. Lineshapes were analyzed with the code GNOMON [2-5]. Side-feeding was treated as in [2,6]. All lifetimes, together with inferred electromagnetic properties are given in Table 1. Because of the doublet structure of many 7-ray lines, some relevant details of the DSA analysis are presented. The effective lifetimes of the (41/2 + ) and (37/2 + ) states were nearly the same (,--0.24 ps) and so an upper limit of 0.10 ps is assigned to the (37/2 +) level. The sidefeeding has the same upper limit. Both cascade-and side-feeding were taken into account in the analysis of the 1340 keV transition. The side-feeding was varied from 0.01 to 0.50 ps; minimum X ~ were found for v,] --0.08,0.31 ps. Since the side-feeding time for the (37/2 + ) level clearly had an upper limit of 0.10 ps, the second minimum (0.31 ps) was excluded since an increase of 0.20 ps in the side-feeding time would be unreasonable [6]. This choice is also consistent with the previous [2] suggestion as to the...

High spin states of the normally deformed bands of Y83

“…12(b), the energies of these configurations are calculated to increase strongly when they approach I max , where the E − E rld curves resemble e.g, the curves of the smooth terminating bands in the A = 110 region [30]. Furthermore, such an energy increase has been observed experimentally in the neighbour nucleus 84 Zr where the ground band has been identified [35] to the maximum spin, I = 34, of the configuration which is assigned [35] to this band, [4,6]. Note especially that the strong increase of the E − E rld was predicted, before it was observed, see e.g.…”

“…Indeed, it is these configurations which are assigned to the observed bands, i.e. [3,6] to the positive parity bands and [2,6] and [4,6] at low and high spin, respectively, for the negative parity bands. With these assignments, experiment and calculations are compared in Fig.…”

“…They can be described as having one hole and two holes, respectively, in a 78 Sr core. All these states are related to the [2,4] configuration in 40 Zr which terminates at I = 20 [35]. Compared with this aligned 20 + state, the 16.5 + state has one less g 9/2 proton, the 21.5 − , 22.5 − states have one more pf hole while the 26.5 + state corresponds to a 2 hole, 1 particle excitation relative to the I = 20 state.…”

“…Therefore several experiments are required to study a single nucleus. For the 83 Y case, the nuclear structure of the first excited states of the yrast band has been previosuly studied by lifetime measurements using different methods [2][3][4]. The Recoil Distance Doppler Shift Attenuation Method (RDSAM) was implemented with the reaction 54 Fe( 32 S,3p) 83 Y at 105 MeV to measure lifetimes of low spin states [3].…”

“…Moreover, the methodology used in Refs. [2][3][4][5] involves the simultaneous measurement of sidefeeding and level lifetimes, i.e., using the same lineshape, possibly introducing non valid correlations between these lifetimes. In the present work that problem is avoided by obtaining lineshapes using both Gates From Above (GFA) and Gates From Below (GFB) the transition of interest, where possible.…”