Indication of an octupole shape revealed in the (τ, α) population of high-spin states in 225Ra

doi:10.1016/0375-9474(86)90506-3

Nuclear Physics A

Volume 452, Issue 1, 14 April 1986, Pages 30-40

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Abstract

High-spin states in ²²⁵Ra have been populated in the (τ, α) reaction with a 30 MeV³ He beam. Levels associated with the $j_{152}$ intruder orbital are given special attention. The peculiar population pattern observed for such states, located at excitation energies of 274 and 538 keV in ²²⁵Ra, is predicted in a model calculation where an octupole deformation is assumed.

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Cited by (13)

Nuclear Data Sheets for A = 225
2009, Nuclear Data Sheets
Nuclear data sheets for A = 225
1990, Nuclear Data Sheets
Reflection asymmetric and symmetric shapes in 225Ra. polarization effects of the odd particle
1989, Physics Letters B
Measurements of multipolarities in 225Ra
1989, Nuclear Physics, Section A
Multipolarities of 45 transitions in ²²⁵Ra have been established by investigating the radiations associated with the β⁻ decay of ²²⁵Fr. The study includes β⁻, e⁻ and γ-singles spectra, e⁻γ- and γγ-coincidence measurements. The conversion electrons were measured with a mini-orange electron spectrometer, and the γ-spectra with Ge detectors. The multipolarities obtained from the measured conversion coefficients support the assignments of spin-parity doublets thus giving evidence for a stable octupole deformation of this nucleus. The negative parity of the 394.2 keV level established in the present work indicates that this level is a candidate for the parity-doublet partner of the $52^{+}$ state at 236.3 keV.
Intrinsic reflection asymmetry in 225Ra: Additional information from a study of the α-decay scheme of 229Th
1987, Nuclear Physics, Section A
The level structure of ²²⁵Ra has been studied by measuring the radiations associated with the α-decay of ²²⁹Th. These measurements include α- and γ-singles spectra, and αγ-, αe⁻-, and γγ-coincidence measurements. The α-spectra were measured with a high-resolution magnetic spectrometer and Si surface-barrier detectors, the γ-ray spectra with Ge and Ge(Li) semiconductor detectors and the electron spectra with a Si(Li) detector. Chemically purified and isotope-separated sources were used for various experiments. These data provide the energies and intensities for 20 α-branches and for ~87 γ-rays. From this information and previous e⁻ spectrograph measurements, ~81 γ-rays are placed in a level scheme involving 22 excited states below 400 keV. Twenty of these excited states (excluding only tentative levels at 203 and 248 keV) can be assigned as members of four bands having $K^{π} = 12^{+}$ (ground state), $12^{−} (55.1 keV)$ , $32^{+} (149.9 keV)$ and $52^{+} (236.7 keV)$ . It is found necessary to include an additional alternating term (B₁) in the rotational energy formula to adequately fit the energy spacings within the $K = 12$ bands. This approach yields decoupling parameters of opposite sign for these two bands whose absolute values are closer to each other than previously deduced, which has relevance to their interpretation as being a parity doublet. We propose a band structure for the $32^{+}$ band at 149.9 keV that is significantly different from earlier proposals. Under this proposal, the energy-level spacings depart substantially from a simple I(I + 1) pattern. No conclusive evidence has been found for the presence of a $K^{π} = 52^{−}$ band which could be the parity-doublet partner of the well established “favored” $52$ ⁺ band at 236.7 keV. According to the predictions of models which include stable octupole-deformed nuclear shapes, the members of such a $52$ ⁻ band will be fed by α-transitions having relatively small hindrance factors; and they should, consequently, have been observed. Although the existence of reflection-asymmetric shapes in ²²⁵Ra is an open question at present, the bulk of the available evidence on this nuclide can be accounted for, at least qualitatively, by the hypothesis that it possesses a static octupole-deformed shape. However, the nonobservation of the expected $K^{π} = 52^{−}$ band and the large difference in the α-hindrance factors of the spin- $72$ members of the $K^{π} = 12^{+} and 12^{−}$ bands represent potential problems for this interpretation which need to be studied further.
Definition of the actinide region of static quadrupole-octupole deformation
1987, Physics Letters B
Ground state spins of odd-A nuclei in the region just beyond ²⁰⁸Pb are compiled. They are compared with the theoretically predicted spins of an axially symmetric, reflection asymmetric nucleus with octupole deformation ϵ₃ = 0.08 to determine the region of static quadrupole-octupole deformation. Coexistence of different shapes and the corresponding spectra in the same nucleus are predicted in the transition regions.

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^a: Financial support provided by Norges Almenvitenskapelige Forskningsråd.

^b: Financial support provided by the Natural Sciences and Engineering Research Council of Canada.

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Nuclear Physics A

Abstract

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Cited by (13)

Nuclear Data Sheets for A = 225

Nuclear data sheets for A = 225

Reflection asymmetric and symmetric shapes in <sup>225</sup>Ra. polarization effects of the odd particle

Measurements of multipolarities in <sup>225</sup>Ra

Intrinsic reflection asymmetry in <sup>225</sup>Ra: Additional information from a study of the α-decay scheme of <sup>229</sup>Th

Definition of the actinide region of static quadrupole-octupole deformation