Nuclear structure of97Y in the interacting boson-fermion model

Pfeiffer

Kratz

et al. 1990

Self Cite

A band with a rotational pattern based on a state at 585.1 keV has been identified in the N= 59 neutron-rich nucleus 97St. Its properties lead to the [422] 3/2 Nilssonorbital assignment for the band head. There is evidence for a second band with the head at 644.7 keV and the configuration [-541] 3/2. Since the ground state and the lowest excited levels are spherical, shape coexistence is established for 97Sr. A deformed nature of several levels at 500-600 keV results also from QRPA-model calculations. The structure of the low-lying spherical levels has been studied in the frame of the IBF model. The results of the present investigations lead to a better understanding of the N= 59 isotones which constitute the link between the spherical and deformed nuclei at A ~ 100 as a species with shape coexistence but without any indications of particular softness.

Section: Spherical Low-lying Levelsmentioning

confidence: 97%

Structure of theN=59 nucleus97Sr: coexistence of spherical and deformed states

Pfeiffer

Kratz

et al. 1990

Self Cite

“…Even the ground--state spin and parity was a long--standing problem, and only recently the 0-assignment has been established [4]. In the light of such a situation, we have attempted to predict the properties of low-lying levels in 98y using the parameters from successful IBFM and IBFFM calculations for 97y [5], 97Sr [6] and 9~V [7]. First we have performed IBFM studies for the negative-parity states in the odd-even isotope 97y with the same boson core of U (5) Then IBFM calculations were performed for the positive parity states in the even-odd isotone 97Sr.…”

mentioning

confidence: 99%

“…In the light of such a situation, we have attempted to predict the properties of low-lying levels in 98y using the parameters from successful IBFM and IBFFM calculations for 97y [5], 97Sr [6] and 9~V [7]. First we have performed IBFM studies for the negative-parity states in the odd-even isotope 97y with the same boson core of U(5) character (96Sr) as in the previous work for the positiveTparity states~ [5]. The BCS occupation probabilities for 7rpl/2, 7~3/~, ~5/2 and ~9/~ are taken as in the calculations for g~Y [7].…”

mentioning

confidence: 99%

IBFFM predictions for low-lying spherical states in the shape-coexisting odd-odd nucleus98Y

Brant

Paar

et al. 1989

Self Cite

Extrapolating the /nteraeting Boson--Model treatment from lighter neighboms to 9sy we predict the properties of low-lying states of spherical nature in IBFFM. This odd--odd nucleus which presents one of the rare cases of coexisting spherical and deformed shapes is of fundamental importance for understanding nuclear phase transitions.The odd-odd nucleus 9sy lies between spherical and deformed isotopes: 96y and 97y exhibit patterns of spherical shell-model states, while ggY and t00y have fully deformed structures with well developed rotational bands. Therefore it is a particularly good candidate for coexistence of spherical and deformed configurations. In fact, the first rotational band found in a non-even--even nucleus of the A, 100 region was the very regular band in 98y with the head at 495keV [1-2], while the lower-lying levels seem to have quasiparticle character [3][4]. In this paper we report the application of the Interacting Boson-Fermion-Fermion approach to the low-lying levels in 98y. We are in a particularly difficult situation since very little is known about the spins. Even the ground--state spin and parity was a long--standing problem, and only recently the 0-assignment has been established [4]. In the light of such a situation, we have attempted to predict the properties of low-lying levels in 98y using the parameters from successful IBFM and IBFFM calculations for 97y [5], 97Sr [6] and 9~V [7]. First we have performed IBFM studies for the negative-parity states in the odd-even isotope 97y with the same boson core of U (5) Then IBFM calculations were performed for the positive parity states in the even-odd isotone 97Sr. We have assumed that the u~/~ configuration is completely occupied and it was omitted from the calculations. The neutron quasiparticle parameters were adjusted to 97Sr: e!~712) -e(~'l/2) = 0;9 MeV, e(~/~)z-e(~'l/2)= 1.2 MeV, v (~'1/2) = 0.5, v2(gT/2)= 0.2, v2(aa/2 ) = 0.15. It is assumed that the 3/21 state at 167.1 keV in 97Sr is not of ~ta/2 structure (see also [7]), but of more complex nature as associated with the I = j -1, j -2 anomaly [10]. The boson-neutron interaction strengths Ao ~ = 0.18 MeV, Po v = 0.5 MeV, ho v = 0.4 MeV were adjusted to the levels of gTSr.In the third step we have carried out the IBFFM studies for the lowest-lying states in ~sy which are associated with a spherical shape, using the same boson core. For the quasiparticle parameters and boson-fermion interaction strengths we used the values from the IBFM calculations for the normal-parity states in gTy and 07Sr. The value of Fo is the same as the one used for 98y [7]. For the spin-spin residual interaction strength we employ the estimate Vaa --20]A = 0.2 MeV. The strength of the surface delta interaction is taken as V6 =-0.22 MeV; this value was obtained by requiring that the diagonal matrix element or the ('rgg/2, ugT]2~configuration of 9sy has the same value as in the calculation for 9~y [7].

“…Typical examples are the works on 91Rb [2] and 97y [3] where not only the excitation energies but also transition probabilities were reproduced satisfactorily. Typical examples are the works on 91Rb [2] and 97y [3] where not only the excitation energies but also transition probabilities were reproduced satisfactorily.…”

Section: Introductionmentioning

confidence: 99%

Nature of93Rb levels studied in IBFM

Brant

Paar

et al. 1989

Self Cite

The structure of the low-lying states with negative parity of 937Rbs6 has been studied in the framework of the Interacting Boson-Fermion Model (IBFM) using the even-even neighbour 94 38Sr56 as a core. A good description of the properties of the levels has been obtained. A sensitive test of the quality of the theoretical studies is the decay pattern of the second excited state at 267 keV with a half-life of 2.0(2) ns. The calculations give tl/2 =2.26 ns and they predict the existence of a 13 keV transition into the first excited state, the existence of which has been confirmed afterwards by experiments.