Level structure of 225Ac

doi:10.1016/0375-9474(87)90211-9

Nuclear Physics A

Volume 472, Issue 2, 28 September 1987, Pages 285-294

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Abstract

The level scheme of ²²⁵Ac has been deduced from the study of the α-decay of ²²⁹Pa and β⁻ decay of ²²⁵Ra. Sources of ²²⁹Pa were produced by the ²²⁹Th(d, 2n) and ²³⁰Th(d, 3n) reactions, and the ²²⁵Ra activity was obtained by milking a ²²⁹Th sample. Gamma singles spectra of ²²⁹Pa and ²²⁵Ra were measured with high-resolution Ge detectors placed in a very low background shield. Alpha-gamma and γγ-coincidence measurements were made with ²²⁹Pa sources. Using the ratio of the KX-ray and γ-ray intensities obtained from gated γ-ray spectra, we were able to deduce K conversion coefficients of the 115.55 and 120.80 keV transitions which gave M1 multipolarities for these transitions. Four bands were identified: $K π = 32^{−}$ , ground; $32^{+}$ , 40.09 keV; $52^{−}$ , 120.80 keV; and $52^{+}$ , 155.65 keV. The half-life and alpha branching ratio, α/(α+EC), were measured to be 1.50 ± 0.05 d, and (0.48±0.05)%, respectively.

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Cited by (15)

Nuclear Data Sheets for A = 225
2009, Nuclear Data Sheets
Nuclear Data Sheets for A = 229
2008, Nuclear Data Sheets
The evaluators present in this publication spectroscopic data and level schemes from radioactive decay and nuclear reaction studies for all nuclei with mass number A = 229. These nuclei belong to a region of coexisting quadrupole with possible octupole deformations. The latter have been observed in ²²⁹Ra, but in ²²⁹Pa the experimental evidence is inconclusive.
The present evaluation of A = 229, which includes all data received by June 2008, supersedes the 1989 evaluation by Y.A. Akovali, published in Nuclear Data Sheets 58, 555 (1989).
Highlights of this publication are given below:
A comprehensive spectroscopic study of ²²⁹Fr(50.2 s) β- decay using mass-separated sources have provided the first evidence of parity doublets in ²²⁹Ra due to nuclear octupole deformation (1999Fr33).
In ²²⁹Th a level at 7.6 5 eV – the closest level to the ground state ever known – has been confirmed through extremely precise measurements of γ-ray energies from ²³³U α decay (1994He08, 2007Be16). A nuclear level at such low energy may be used for studying a large variety of atomic properties associated to nuclear decay.
The level structure in ²²⁹Pa has been interpreted in terms of the rotational model (1994Le22). Some authors, however, have proposed the existence of parity doublets as evidence of octupole nuclear deformation (1982Ah08). This interpretation has not been confirmed.
Nuclear structure of 229,231Th studied with the 230,232Th(d, t) reactions
2008, Nuclear Physics A
Detailed angular distributions for the ^230,232Th( $d, t$ )^229,231Th reactions were measured with 17 MeV deuterons, using a magnetic spectrograph to analyze the reaction products. Comparisons with distorted wave Born approximation predictions were used to determine ℓ-values and spectroscopic strengths for many levels in both nuclides. These results reconfirm previous assignments for the $3 / 2^{+} [631]$ band in ²²⁹Th, with its bandhead unresolved from the $5 / 2^{+} [633]$ ground state, providing support for the existence of the much-sought “3.5 eV” isomer (for which the latest reported energy is $7.6 \pm 0.5 eV$ ). Although ²³¹Th was previously well studied, many new spin-parity assignments have been made and some changes to adopted model assignments are proposed. There is evidence in both isotopes for appreciable mixing of single-particle orbitals with other configurations, as predicted by the Quasiparticle Phonon Model. Single-nucleon transfer strengths are described much better with earlier values for the Nilsson model parameters κ and μ than later values that have been widely used. An earlier ²³²Th( $d, t$ ) study concluded that serious errors could result in the commonly-used method of predicting cross sections by combining distorted wave Born approximation calculations using spherical form factors with Nilsson wave functions for a deformed potential, but the present work shows this conclusion is not valid because it was based on inadequate knowledge of the ²³¹Th nuclear structure.
Level structure of the odd-odd nucleus 224<inf>89</inf>Ac
1994, Nuclear Physics, Section A
The level structure of the odd-odd nucleus ²²⁴Ac has been studied by measuring radiations associated with the α-decay of the 22 h ²²⁸Pa isotope. The ²²⁸Pa activity was produced by the irradiation of Th metal foils with 45 MeV protons. The Pa fraction was subsequently chemically isolated. Alpha singles as well as αγ-, αe-, αγγ-coincidence measurements were performed with thin sources, and a partial level scheme was deduced for the ²²⁴Ac. Although the spins of the observed levels have not been uniquely determined, the data establish positive- and negative-parity bands which exhibit characteristics of parity doublets. In particular, two bands at 354 and 360 keV appear to be members of a parity doublet. The similarity in the hindrance factors of α-decays to the 354 and 360 keV levels, which have opposite parities, indicates that the wavefunctions of the two states are very similar, which is a signature for octupole deformation.
Intrinsic dipole moments in reflection-asymmetric nuclei
1991, Nuclear Physics, Section A
Low-energy collective E1 moments in nuclei from the Ra-Th and Ba-Sm region are analysed within the shell-correction method based on the reflectio-asymmetric Woods-Saxon model. Extensive systematics of experimental intrinsic dipole moments are presented. Shell effects on the isovector E1 moment explain local quenchings in E1 strength observed experimentally. It is demonstrated that the inclusion of the neutron-skin contribution to the macroscopic dipole moment is crucial for the understanding of experimental trends.
Nuclear data sheets for A = 225
1990, Nuclear Data Sheets

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^†: Deceased.

¹: Permanent address: Japan Atomic Energy Research Institute, Ibaraki-ken, Japan.

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Nuclear Physics A

Abstract

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Cited by (15)

Nuclear Data Sheets for A = 225

Nuclear Data Sheets for A = 229

Nuclear structure of <sup>229,231</sup>Th studied with the <sup>230,232</sup>Th(d, t) reactions

Level structure of the odd-odd nucleus <sup>224</sup><inf>89</inf>Ac

Intrinsic dipole moments in reflection-asymmetric nuclei

Nuclear data sheets for A = 225