Evidence for shape coexistence in 52Cr through conversion-electron and pair-conversion spectroscopy

J. T. H. Dowie; T. Kibédi; A. E. Stuchbery; A. Akber; A. Avaa; L. J. Bignell; M. V. Chisapi; B. J. Coombes; T. K. Eriksen; M. S. M. Gerathy; T. J. Gray; T. H. Hoang; E. Ideguchi; P. Jones; M. Kumar Raju; G. J. Lane; B. P. McCormick; A. J. Mitchell; B. P. E. Tee

doi:10.1051/epjconf/202023204004

Proceedings

Open Access

EPJ Web of Conferences 232, 04004 (2020)
https://doi.org/10.1051/epjconf/202023204004

Evidence for shape coexistence in ⁵²Cr through conversion-electron and pair-conversion spectroscopy

J. T. H. Dowie¹^*, T. Kibédi¹, A. E. Stuchbery¹, A. Akber¹, A. Avaa³^,5, L. J. Bignell¹, M. V. Chisapi⁴^,5, B. J. Coombes¹, T. K. Eriksen¹^**, M. S. M. Gerathy¹, T. J. Gray¹, T. H. Hoang², E. Ideguchi², P. Jones⁵, M. Kumar Raju², G. J. Lane¹, B. P. McCormick¹, A. J. Mitchell¹ and B. P. E. Tee¹

¹ Department of Nuclear Physics, Research School of Physics, Australian National University, Canberra ACT 2601, Australia
² Research Center for Nuclear Physics (RCNP), 10-1 Mihogaoka, Ibaraki, Osaka, 567-0047, Japan
³ School of Physics, University of the Witwatersrand, Johannesburg, 2000, South Africa
⁴ Department of Physics, Faculty of science, Stellenbosch University, Private Bag X1, Matieland 7602, Cape Town, South Africa
⁵ Department of Subatomic Physics, iThemba LABS, Old Faure Road, Somerset West 7129, P.O. Box 722, Cape Town, South Africa

^* e-mail: jackson.dowie@anu.edu.au
^** Present Address: Department of Physics, University of Oslo, N-0316 Oslo, Norway

Published online: 6 April 2020

Abstract

Electric monopole (E0) transitions are a highly sensitive probe of the charge distribution of an atomic nucleus. A large E0 transition strength (ρ²(E0)) is a clear indicator of nuclear shape coexistence. In the region between doubly magic ⁴⁰Ca and ⁵⁶Ni, E0 transitions have never been observed in the Ti or Cr isotopes, nor in the heavier iron isotopes (^56,58Fe). We have performed the first measurements of the E0 transitions in ⁵²Cr via conversion-electron and pair-conversion spectroscopy using the Super-e spectrometer at the Australian National University Heavy Ion Accelerator Facility. We present the first spectra obtained for ⁵²Cr, including the first observation of the E0 transition from the first-excited 0⁺ state in ⁵²Cr, in both electron-positron pairs and conversion-electron spectroscopy. The preliminary values for the E0 strength in the 1531keV _2⁺ → _2⁺ transition in ⁵²Cr is ρ²(E0) × 10³ = 470(190), and for the 1728-keV 2_3⁺ → 2_1⁺ transition, it is ρ²(E0) 10³ = 1800(1200). The large E0 strengths observed are consistent with shape coexistence in this region. However, despite the relatively precise observation of the conversion-electron and electron-positron pair intensities, the E0 strengths have large uncertainties. More precise determinations of relevant spectroscopic quantities, such as the state lifetimes and transition mixing ratios for mixed M1 + E2 transitions, are needed to determine the E0 strength more precisely.

© The Authors, published by EDP Sciences, 2020

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