High-spin rotational states inHf169from theTb

Abstract

High-spin level. s of the deformed nucleus Hf were deduced from y-ray spectroscopy, both in beam following the heavy-ion reaction 59Tb(~4N, 4ny) 9Hf and out of beam from P decay of 9Ta. The half-l. ife of 9Ta was remeasured as 4.7 + 0.7 m. Three rotational bands were assigned in Hf: & [523] ground band, up to spin 2, 2 [512], 59.1 keVbandhead, up to spin +2, . and g [642], p bandhead at 28.80 keV, up to spin~2 and tentatively up to spin -,. The 2 bandhead of the 2 [642] band is isomeric and decays with a half-life of 82+&5 ns to the ground state. The g factors in the negative parity bands were deduced from the measured angular distributions and branching ratios and compared to the predictions of the Nilsson model. Both this test and the systematics of the moments of inertia confirm the proposed assignments. The z [642] band (originating in the &~3g2 shell-model. state) is strongly perturbed. This band does not backbend although the~@ Hf core does at a lower rotational angular momentum than attained in 9Hf. The consequence of this observation for the explanation of backbending is discussed. The mixing amplitudes in the positive parity band are compared with the predictions of Pyatov's theory. NUCLEAR REACTIONS '"Tb("N 4nq) E =56-92 Mev measured Z, I (6), yy coin, T&g2 of 28.80 keV level.~Hf deduced levels, J, x, K, g, I /2S. RADIOACTIVITY~6 9Ta; measured T&j2, E&, I& 69Hf deduced levels, J, m, K. 1767 1768 I. RE ZANKA et al.surements to avoid counting of the radioactive recoils, from the Al foils, implanted into the next foil in the beam direction. The energy of the beam reaching the target was 116 MeV. Control runs were performed also at lower and higher energies to assure the optimum production of ' Ta. The duration of irradiation was 5 min. Isolation of Ta activityChemical isolation of Ta activity from the Tb target material was accomplished by a method similar to that described by Felber. ' The irradiated target was dissolved in hot 6 V HCl, and the rare earth fluorides were precipitated by using 2-3 drops of concentrated HF. The mixture was centrifuged and the supernatant solution was transferred to a separatory funnel where 3 ml of diisopropylketone was used to extract the Ta activities. This solution was then used as the source for the yand x-ray spectroscopy. The time elapsed between the end of the bombardment and the beginning of the measurement was 3-5 min. y-ray spectraThe y-ray spectra were measured by means of a Ge(Li) detector (volume 40 cm', resolution 2. 1 keV at 1332 keV) in several time intervals for

High spin spectroscopy and lifetime measurements inHf169

“…The resulting level scheme is shown in Fig. 3 [15], was not seen. This absence was also reported recently by the Manchester group [16].…”

“…The positiveand negative-parity bands in ' Hf have been classified [15] as -, ' + [642] and -, ' [523] neutron bands, respectively. The level scheme of ' Hf has been extended significantly in the present work by employing the y-y coincidence technique.…”

“…In the present article, we report on spectroscopic studies and lifetime measurements in ' Hf which is part of our studies of near yrast, high-spin states in heavy hafnium isotopes. The yrast sequence of ' Hf, which was known [15] up to spin 4, '+, where the first backbending just starts to occur, has been extended to spin -", +. Three additional bands were also extended to higher spins.…”

Backbending in theN=96 isotones

“…The intermediate region (Yb, Hf and W isotopes) has also been investigated by this "blocking" technique. It has experimentally been observed that backbending is inhibited in the vi 13/2 mixed positive-parity bands for odd-neutron isotopes of Yb [11,12], Hf [13,14] and W [15,16], but not in bands based on other neutron orbits. For the odd-proton nuclei, experiments show that backbending is inhibited in various 7~h9/2 decoupled bands in 163'165Tm [17,18] 0340-2193/81/0299/0149/$02.60 and 167'169Lu [19,20], but not in bands based on other proton orbits.…”

“…5), we suggest possible reasons why backbending is delaYed for the ~h9/2 proton bands in the odd -Z, N=96 isotones 16STm and 167Lu. The experimental data on the energy levels of the N =96 and 97 isotones which are used in the present paper are extracted from the following references: 164Er [25][26][27]; a65Er [28]; 165Tm [18]; 166yb [29][30][31]; 167yb [32]; 167Lu [19]; 16SHf [29,33,34]; 169Hf [13]; 17~ [35]. The lifetimes of members of the g.s.…”