High-Spin Multiquasiparticle Yrast Traps inHf176

Abstract

We have identified several high-K four-and six-quasiparticle states between 2 0 5 and 5 MeV excitation in 176 Hf, which are well described by the collective model with axial symmetry,, Isomers with K n = 14", 19 + , and 22" form traps at or near the yrast line. The yrast structure changes from the ground band to a K v = 16 + band at J = 16 and again to a K n =22" state at 7 = 22, providing the first demonstration that intrinsic excitations of a heavy deformed nucleus can become yrast.An etch parameter almost unnoticed previously, etch induction time, has been measured in Kodak Pathe cellulose nitrate track detector films using 4 He, 6 Li, 12 C, 14 N, and le O ions of known low energy per unit mass for calibration. The etch induction time appears to vary with the parameter (dE/dx) w< im /Z* where Z* is the effective ion charge and (dE/ dx) w< 1000 is the restricted energy loss, calculated for a S-ray cutoff energy of 1000 eV.

K-hindered decay of a six-quasiparticle isomer inHf176

“…All transitions reported earlier were confirmed, but no new transitions below the 401 µs isomer were observed. While a rotational band built on this isomer had been observed in the earlier studies up to a 20 − state [7], this band was not reported to be fed by any isomeric state. Here, we present evidence that this band is being fed by an isomer.…”

“…Five isomeric states are known in 176 Hf with halflives ranging from 34 ns to 401 µs [5][6][7]. The present analysis reports on out-of-beam data and transitions above the K π = 14 − isomer (t 1/2 = 401µs) at 2866 keV excitation energy.…”

“…In 176 Hf, 2-, 4-and 6-qp isomers were reported in the earlier studies of K isomerism [5][6][7]. The highest state (22 − ) observed to date in this nucleus to date is a 6-qp isomeric state (t 1/2 = 43µs) at 4864 keV which decays to an intrinsic 20 − state by an allowed E2 transition [7]. Although a number of decay modes with different reduced hindrance factors have been found in the neighboring isotopes [8] and isotones [9,10], there was no new experimental information on 176 Hf since the early studies.…”

“…Isotopes of hafnium, in particular, have been studied extensively over a wide range of spin and excitation energies [4]. In 176 Hf, 2-, 4-and 6-qp isomers were reported in the earlier studies of K isomerism [5][6][7]. The highest state (22 − ) observed to date in this nucleus to date is a 6-qp isomeric state (t 1/2 = 43µs) at 4864 keV which decays to an intrinsic 20 − state by an allowed E2 transition [7].…”

Enhanced mixing of intrinsic states in deformed Hf nuclei

“…The well-deformed Hf nuclei (in particular 172 Hf) are known to possess a set of high K isomers [11][12][13]. This gives good support for axial symmetry in these nuclei and K, the projection of angular momentum onto the symmetry axis, can be considered an approximately good quantum number.…”