Measurement of rates of fast E1 transitions in AcRa nuclei

doi:10.1016/0375-9474(85)90348-3

Nuclear Physics A

Volume 444, Issue 2, 28 October 1985, Pages 237-247

https://doi.org/10.1016/0375-9474(85)90348-3 Get rights and content

Abstract

The half-lives of the 40.0 keV level in ²²⁵Ac, 31.6 keV level in ²²⁵Ra, and 27.4 keV level in ²²⁷Ac have been measured to be 0.72 ± 0.03 ns, 2.1 ± 0.2 ns, and 38.3 ± 0.3 ns, respectively. The three levels decay only by E1 transitions. The lifetimes were measured by delayed coincidence techniques using pure samples. The reduced transition probabilities in ²²⁵Ac and ²²⁵Ra are about two orders of magnitude larger than the values encountered in the mid-actinide nuclei. On the other hand, the transition rate in ²²⁷Ac is similar to the values measured in heavier actinides. Previous studies suggest the presence of octupole deformation in all three nuclei. Our results demonstrate that large enhancements in E1 transition rates can occur for nuclei with octupole deformation. However, the results also indicate that there is no simple relationship between the E1 rate and the octupole deformation. The half-life of the 25.4 keV state in ²²⁵Ra, which decays by a pure rotational E2 transition, has been measured to be 0.88 ± 0.04 ns. This lifetime yields a quadrupole moment of 6.47 ± 0.15 b and a β₂ deformation of 0.17 + 0.004.

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Cited by (27)

Half-life determination of short-lived nuclear levels in 237Np (59.54 keV), 233Pa (86.47 keV) and 227Ac (27.37 keV)
2021, Applied Radiation and Isotopes
Citation Excerpt :
All measurements were made with 231Pa sources. The most recent result from Ishii et al. (1985) was published about 36 years ago. The longest half-life with an uncertainty was reported by Bragança Gil and Petit (1961) and corresponds exactly to the value stated earlier by Teillac et al. (1953).
New half-life values for isomeric states in ²³⁷Np, ²³³Pa and ²²⁷Ac were measured by means of 4πα(LS)-γ coincidence counting with digital data acquisition. A careful assessment of uncertainties was carried out, and the new results are found to be much more precise than any previous measurement result. The half-lives were found to be $T_{1 / 2} ({}^{237}{Np}, E = 59.54 keV) = (67.86 \pm 0.09) ns$ , $T_{1 / 2} ({}^{233}{Pa}, E = 86.47 keV) = (36.44 \pm 0.10) ns$ and $T_{1 / 2} ({}^{227}{Ac}, E = 27.37 keV) = (38.56 \pm 0.15) ns$ , respectively. A comprehensive study of literature data was undertaken for a new data evaluation that includes the results from this work.
Nuclear Data Sheets for A = 227
2016, Nuclear Data Sheets
The evaluated spectroscopic data are presented for ten known nuclides of mass 227 (Po, At, Rn, Fr, Ra, Ac, Th, Pa, U, Np). For ²²⁷Po, ²²⁷At, ²²⁷Rn, ²²⁷Pa, ²²⁷U and ²²⁷Np nuclei, only the ground-state information is available. Their decay characteristics are mostly unknown. Levels in ²²⁷Fr are known only from the decay of ²²⁷Rn to ²²⁷Fr. This decay scheme at present cannot be normalized to deduce γ intensities per 100 decays due to lack of knowledge about multipolarities of many low-energy transitions. The levels in ²²⁷Ra, ²²⁷Ac and ²²⁷Th are known from several decays and reactions, including particle-transfer data for ²²⁷Ra and ²²⁷Ac. The decay scheme of ²²⁷Ra to ²²⁷Ac was last studied in 1971 using small Ge detectors. Improved γ-ray intensity data need to be obtained with a better γ-detection system. The datasets for ²²⁷Ac have undergone extensive revisions, including detailed data for 231Pa α decay from 1986BaYK report, and single-proton transfer data from 1986MaYU thesis. High-spin (J>13/2 or so) structures are known only for 227Th. Level lifetime data are quite scarce for all the nuclides in this mass chain, thus limiting the knowledge of reduced transition probabilities.
Band structures for ²²⁷Fr, ²²⁷Ra, ²²⁷Ac and ²²⁷Th are known in detail, together with evidence of weak octupole deformation and consequent parity-doublet structures.
This evaluation was carried out as part of a joint IAEA-ICTP workshop for Nuclear Structure and Decay Data, organized and hosted by the IAEA, Vienna and ICTP, Trieste, March 24–28, 2014. The evaluation work was coordinated by B. Singh (McMaster). This work supersedes previous A=227 evaluation (2001Br31) published by E. Browne which covered literature before May 2001.
Nuclear Data Sheets for A = 225
2009, Nuclear Data Sheets
Nuclear data sheets for A = 215, 219, 233, 227, 231
2001, Nuclear Data Sheets
The evaluator presents in this publication spectroscopic data and level schemes from radioactive decay and nuclear reaction studies for all nuclei with mass numbers A=215, 219, 223, 227, and 231. Nuclei with mass number A=215 have spherical shape, and their nuclear structure have been interpreted in terms of the shell model. Nuclei with mass number A=219 belong to a transitional region with spherical, quadrupole, and possibly octupole deformations; those with mass numbers A=223 and 227 belong to a newly studied region of coexisting quadrupole with possible octupole deformations; and nuclei with mass number A=231 essentially have quadrupole deformation. Highlights of this publication are given below: A recent study of the ²⁰⁶Pb(¹³C,4nγ) reaction (1998St24) has extended up to Jπ=61/2+ the previously known level scheme from ²⁰⁸Pb(¹³C,6nγ) (1988Fu10,1983Lo16). This study has provided a new interpretation for all the spectroscopic data above the 2247--keV (Jπ=29/2--) level in ²¹⁵Ra. A new isotope, ²¹⁹U (42 μs), which was identified with the recoil separator VASSILISSA (1994Ye08,1994AnZY,1993An07), has been included in this evaluation. The first ²²³Rn β-- decay scheme (1992Ku03) and a significantly improved measurement of ²²⁷Ac α decay (1995Sh03) are presented here. A level scheme of ²²³Fr has been constructed on the basis of these studies, where most of the levels below 600 keV have been assigned to parity doublet bands and interpreted in terms of the reflection--asymmetric rotor model. This evaluation includes the first level structures of ²²⁷Fr and ²²⁷Th. Levels in ²²⁷Fr are from ²²⁷Rn β-- decay (1997Ku20); those in ²²⁷Th, are from ²³¹U α decay, from ²²⁷Pa electron--capture decay, and from ²²⁶Ra(α,3nγ) (1997Mu08,1995Li04,1998Ma83). A study of the β-- decay of a mass--separated source of ²³¹Fr has produced the first level scheme of ²³¹Ra (2001Fr05). The only published data (1994Br36,1996Le01) on the electron--capture decay of ²³¹U have provided much information on the level structure of ²³¹Pa. Studies on ²³²Th(p,2nγ) and Coulomb Excitation of ²³¹Pa (1996Le01,1999Wu05), which have complemented the existing spectroscopic data from these reactions, have suggested the possibility of weak octupole correlations in ²³¹Pa. A new isotope of plutonium, ²³¹Pu (1999La14), has been included in this evaluation.
Search for stable octupole deformation in 225Fr
1997, Nuclear Physics A
Levels in ²²⁵Fr have been studied by γ-ray and conversion-electron spectroscopy following the β-decay of ²²⁵Rn, and by the ²²⁶Ra(t,α)²²⁵Fr single-proton-pickup reaction. Multipolarities were obtained for ∼50 γ-transitions, and a level scheme was established in which definite spin-parity values were determined for over 20 of the 48 levels. Although low-lying rotational bands of both parities exist for $K = 12$ and $K = 32$ , there is no experimental evidence to claim these are parity doublets. E1 strengths connecting the $K^{π} = 32^{±}$ bands are intermediate between those for nuclides which are reflection symmetric and those claimed to be octupole deformed. The (t,α) cross sections are in better agreement with those predicted for the reflection-symmetric case than with those from an octupole-deformed description. These observations may be confirming theoretical predictions that octupole correlations are important in ²²⁵Fr, but that there is no large stable octupole deformation.
Nuclear data sheets for A = 215,219,223,227
1992, Nuclear Data Sheets
This publication presents evaluated spectroscopic data and corresponding level schemes from radioactive decay and nuclear reaction studies for all nuclei with mass numbers A=215, 219, 223, and 227.
Nuclei with mass number A=215 have spherical shape, and their nuclear structure has been interpreted in terms of the shell model. Nuclei with mass number A=219 belong to a transitional region, with spherical, quadrupole, and possibly, octupole deformations, and those with mass numbers A=223 and 227, to newly studied regions of deformations (pure quadrupole coexisting with possible octupole). Because deformations are small in these regions, nuclear states are no longer fully characterized by single Nilsson orbitals. This terminology, however, is used throughout this evaluation to label states rather than to accurately describe their nature.
Highlights of this publication include the emission of ¹⁴C by ²²³Ra, discovered by Rose and Jones (84Ro30), and its fine structure, measured by Brillard et al. (89Br34). This constitutes a new mode of decay and provides additional arguments for configuration assignments. They further include the first set of nuclear levels in ²¹⁵Fr, ²¹⁵Ra, and ²¹⁵Ac, determined from in—beam γ-ray spectroscopic measurements.
Two major publications have been extensively used in this evaluation: the theoretical paper “Reflection—asymmetric Rotor Model of Odd—A ≈219–229 Nuclei” by Leander and Chen (88Le13), which presents a calculation of single—particle state properties by the coupling of shell—model states to a reflection—asymmetric rotor core; and the review paper “Intrinsic States of Deformed Odd—A Nuclei in the Mass Regions (151≤A≤193) and (A≥221)” by Jain et al. (90Ja11), which gives the systematics and assignments of single—particle states in such mass regions.
These evaluations for A=215, 219, 223, and 227 supersede the earlier ones by C. Maples: 77Ma29, Nuclear Data Sheets 22, 207 (1977); 77Ma30, Nuclear Data Sheets 22, 223 (1977); 77Ma31, Nuclear Data Sheets 22, 243 (1977); and 77Ma32, Nuclear Data Sheets 22, 275 (1977).

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^∗: Visitor from Nagoya University, Nagoya, Japan.

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Nuclear Physics A

Abstract

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Cited by (27)

Half-life determination of short-lived nuclear levels in <sup>237</sup>Np (59.54 keV), <sup>233</sup>Pa (86.47 keV) and <sup>227</sup>Ac (27.37 keV)

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Search for stable octupole deformation in <sup>225</sup>Fr

Nuclear data sheets for A = 215,219,223,227