Level structure of 184W from the decay of 184gRe and 184mRe

Abstract

The level scheme of 184W has been studied from the decay of 38d 184gRe and 165d 184mRe. Gamma-ray energy and intensity measurements were made using Ge(Li) and Si(Li) detectors; and conversion-electron measurements were made using an iron-free π√2 double-focusing spectrometer. From these data and extensive γ-γ coincidence measurements decay schemes for both 184Re activities have been proposed which incorporate all 42 of the observed γ-ray transitions. Unique spin and parity assignments have been made for all the energy levels observed. Detailed intensity-balance considerations for each energy level have led to improved electron-capture branching ratios and log ft values. In addition to the previously known features of the 184Re decay schemes, it has been established that levels at 1424 and 1431 keV in 184W are weakly populated and that their I π assignments are 3 + and 2 +, respectively. Also, the 4 + → 2 + transition within the γ-vibrational band has been observed, which enables an estimate of the relative magnitudes of the intrinsic quadrupole moments of γ-vibrational and ground-state bands to be made. Within the experimental uncertainties involved (≈ 10%), these two moments are equal. A one-parameter analysis of the E2 transition probabilities between these two bands gives z γ = +0.0408 ±0.0041. Absolute transition probabilities are obtained and discussed for the γ-rays de-exciting the 3 − state at 1221 keV and the 5 − isomeric state at 1284 keV. Evidence for mixing of K π = 2 − and 3 − excitations in the 5 − isomeric state is presented; and a formalism for treating such admixtures, of both collective and two-quasiparticle character, is developed and applied. A close similarity of the M4 γ-decay of 184mRe to that of the 10 − isomeric state in 182Ta is noted.