Level structure of217Rn and221Ra investigated in the alpha-decay225Th ?221Ra ?217Rn

Abstract

The nuclei 22~Ra and 217Rn have been investigated in the e-decay chain 225Th--* 221Ra --->217Rn through 7-ray and conversion-electron studies. The short-lived Z25Th nuclei (T1/z=8 rain) were produced in the 226Ra(e, 5n) reaction, and y-rays and conversion electrons were measured -between the irradiation periods -in coincidence with eparticles. In 221Ra the five lowest levels are interpreted as members of a K=5/2 paritydoublet with AE~= 104 keV. These levels, as well as a higher-lying K~= 3/2 + band, are consistent with an octupole deformation of 2z: Ra, as expected from theoretical considerations. In 217Rn only three excited levels are observed, with a favoured e-decay to a 5/2 + excited level thus establishing positive parity for the ground state of 221Ra.

Studies of pear-shaped nuclei using accelerated radioactive beams

“…For the E2 and E3 matrix elements the measured values are all consistent with the geometric predictions expected from a rotating, deformed distribution of electric charge, although these data do not distinguish whether the negative-parity states arise from the projection of a quadrupole-octupole deformed shape or from an octupole oscillation of a quadrupole shape 32 . The conclusions drawn from the present measurements are also consistent with suggestions from the systematic studies of energy levels 7 (relative alignment of the negative-parity band to the positiveparity band) that the even-even isotopes [218][219][220][221][222] 40 for parity doubling whereas for 221 Ra a parity doublet of states with I=5/2 separated by 103.6 keV has been observed 41 . In the Ba-Nd region with Z~56 and N~88, where the octupole states arise from vibrational coupling to the ground-state band, the evidence for parity doubling of the ground state arising from reflection asymmetry is inconclusive 42,43 self-consistent mean field theory 16 , particularly using the D1M parameterisation 44 .…”

Electron capture decay of 58-minU92229and levels inPa91229

“…Gamma rays in the decay of the α-decay daughter 225 Th (8.72 min) and the granddaughter 221 Ra (28 s) have been reported in Ref. [13]. Gamma rays were assigned to the 229 U EC decay on the basis of their presence in the spectrum of a mass-separated 229 U source, their presence in the spectrum measured in coincidence with…”

“…This γ ray is masked by the Pa K β2 line and hence its intensity was not measured. The electron intensities from all these spectra and conversion coefficients deduced from them are given in [13]. These electron intensities are normalized to the intensity of the 321.35-keV γ ray as 100.…”