Electromagnetic Transition Rates inNi58

Abstract

Lifetimes of 15 excited states in 58 Ni and one in 62 Ni have been measured using the Doppler-shift-attenuation method. The levels were excited via inelastic proton scattering at bombarding energies from 7 to 9 MeV. The Doppler shifts of decay 7 rays were measured in a 30-cm 3 Ge(Li) detector in coincidence with particles backscattered near 170°. Theoretical estimates of stopping powers were checked experimentally by Dopplershift-attenuation measurements; excellent agreement was found. The matrix elements extracted from the measured lifetimes are compared with shell-model and vibrational-model predictions. Agreement is, in general, poor. The theoretical analysis indicates that a state-dependent neutron effective charge must be taken into account, and that core excitations play an important role in the determination of transition probabilities.

Lifetimes of Low-Lying Levels inNi57

“…This would imply that this state is not the g 9/2 single-particle level but is instead a state of fairly complicated structure arising perhaps from a coupling of singleparticle levels to the excited states in 56 Ni. It should be noted that the E2 enhancement of the decay of the 2.576-MeV level is close to the value of 10.0 obtained for the enhancement of the first 2 + -to-ground transition in 58 Ni, 10 and might also imply a dominant collective admixture in this state. squared for the forbidden and allowed Ml decays of the first and second excited states, respectively.…”

Identification of significant E0 strength in the 22+→21+ transitions of 58,60,62Ni

“…The newly determined T 1/2 of the 2 + 2 state in 58 Ni (T 1/2 = 0.60 +0. 19 −0.12 ps) is somewhat longer than, but consistent with, that reported previously in (p, p γ) [18]. The T 1/2 of the 2 + 2 state in 60 Ni (T 1/2 = 1.25 +0.76 −0.35 ps) is inconsistent with that determined from the B(E2) value from (e, e ) [19], but is in agreement with the limit determined from a previous (n, n γ) study using reactor neutrons [20].…”

“…For the 826.06 keV 2 + 2 → 2 + 1 transition in 60 Ni minima are found for δ at +0.40 +0.05 −0.04 or +1.01 +0.09 −0.10 from (n, n γ). There is no consistency for this mixing ratio from previously reported values [18,20,[23][24][25][26][27]. In the (p, p γ) data, we obtain a value of +0.63 +0.…”

“…It was not possible to obtain a reliable result from our (p, p γ) study for this transition. This new value is consistent with, but more precise than, the three previously reported values [18,21,22], so it is adopted in this work.…”

“…38 −0.28 ) [10] from (n, n γ) at UK. The other reported values again do not provide a consistent picture [18,20,25,29]. We therefore again report the mean value of the new data in Table 1.…”