Decay of three-particle high spin states in85Y

Abstract

High spin states in 85y have been excited in the reaction 72Ge(160, p2n) at 48-60 M eV beam energy. From measurements of n7 and 77 coincidences, excitation functions and angular distributions, the high spin spectrum of 8sy has been established up to 5.4 MeV excitation energy and spin I < 29/2. Lifetimes or limits of lifetimes have been determined for 14 levels via the recoil distance and Doppler shift attenuation method. The g9/2 decoupled proton band is found to backbend at U= 17/2 + as also seen in the reduction of the 17/2+~13/2 + and 21/2+-~17/2 + E2 transition strengths. The lowest (3qp) positive parity band has predominantly a V299/2 X 7~g9/2 structure. The observed negative parity yrast states in the spin range 15/2-<1<29/2-are most probably of (g9/2) 2 x(fs/z,px/2) (3qp) nature as suggested by a comparison of the 84Sr and 85y level structures and electromagnetic transition strengths.

New investigation of83Zr and85Zr beta decay

“…There are, however, a few exceptions from this rule, first, the levels not fed directly in the ,g-decay and then those with very small beta branching (typically less than 0.2%, which are determined with big error). This is obviously the case of the 11/2 + level at 1180 keV, known from the high-spin study, which decays only through the 13/2 + level at 815 keV [9]. The intensity balance for the 794 and 930 keV levels is also consistent with no direct beta feeding.…”

“…Indeed, the results of [9] show that only around 2.5 MeV the 1-qp (g9/2) structures are intersected by, and mix strongly with, 3-qp structures. The parameters of the IBFM-1 calculations for the light (79 to 85) Y isotopes were mainly determined such as to describe well the yrast sequences of positive-parity levels, and it is also of interest to which extent are they able to describe other levels as well.…”

Structure of high spin states in83Y

“…This prominent structure emerges because at large prolate deformation the unpaired proton can occupy Nilsson orbits with low projection numbers f2 onto the axis of largest elongation. Such onequasiparticle bands have been found in sly [3] and 85y [4] as well as in the odd rubidium isotopes 77'79'81'83Rb [5][6][7][8]. In the Br and Rb isotopes bands of this type have given clear evidence for triaxial deformation [2, %7].…”

“…for N > 46, the alignment of two more g9/2 nucleons gives rise to 3 qp yrast bands which intersect the l qp bands around 2.5 MeV excitation and are characterized by their irregular level spacings and reduced E2 transition probabilities. Such 3qp structures of both parities have been extensively discussed for 85y and 83Rb [4,8] in relationship to the corresponding 2qp bands in the neighboring even-even "cores" S/Kr and S4Sr [9][10][11]. The interplay between (near-rigid) rotation and multi-particle alignment effects appears to be best visible in the N = 44 isotones as pointed out in the interpretation of the band structures of 82Sr [12,13].…”

Rotational and single-particle structures in83Zr

“…Nuclei below this line are strongly influenced by the large prolate shell gap at N = Z = 38, as is evidenced by the development of nearrigid rotational bands with large quadrupole moments [1][2][3][4][5][6][7][8]. The isotopes with N > 45 exhibit more spherical shapes and single-particle shell model structures [9][10][11][12]. The simple rotational yrast band [8] of 84Zr gives way to the more complex structure [13] found in 85Zr.…”