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Direct measurement of the intrinsic electric dipole moment in pear-shaped thorium-228

Chishti, M.M.R, O’Donnell, D., Battaglia, G., Bowry, M., Jaroszynski, D. A., Singh, B. S. Nara, Scheck, M., Spagnoletti, P. and Smith, J. F. (2020) Direct measurement of the intrinsic electric dipole moment in pear-shaped thorium-228 Nature Physics, 16 (8). pp. 853-856.

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Atomic nuclei with certain combinations of proton and neutron numbers can adopt reflection-asymmetric or octupole-deformed shapes at low excitation energy. These nuclei present a promising avenue in the search for a permanent atomic electric dipole moment—the existence of which has implications for physics beyond the Standard Model of particle physics. Theoretical studies have suggested that certain thorium isotopes may have large octupole deformation. However, due to experimental challenges, the extent of the octupole collectivity in the low-energy states in these thorium nuclei has not yet been demonstrated. Here, we report measurements of the lifetimes of low-energy states in 228Th (Z = 90) with a direct electronic fast-timing technique, the mirror symmetric centroid difference method. From lifetime measurements of the low-lying Jπ = 1− and Jπ = 3− states, the E1 transition probability rates and the intrinsic dipole moment are determined. The results are in agreement with those of previous theoretical calculations, allowing us to estimate the extent of the octupole deformation of 228Th. This study indicates that the nuclei 229Th and 229Pa (Z = 91) may be good candidates for the search for a permanent atomic electric dipole moment.

Item Type: Article
Divisions : Faculty of Engineering and Physical Sciences > Physics
Authors :
O’Donnell, D.
Battaglia, G.
Bowry, M.
Jaroszynski, D. A.
Singh, B. S. Nara
Scheck, M.
Spagnoletti, P.
Smith, J. F.
Date : 18 May 2020
Funders : Scottish Funding Council, UK Science and Technology Facilities Council, EPSRC, EC’s LASERLAB-EUROPE, EuCARD-2, EuPRAXIA, ARIES
DOI : 10.1038/s41567-020-0899-4
Grant Title : EPSRC
Copyright Disclaimer : Copyright © 2020, Springer Nature
Additional Information : Embargo OK Metadata OK No Further action
Depositing User : James Marshall
Date Deposited : 26 Aug 2020 14:49
Last Modified : 26 Aug 2020 14:49

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