Speaker
Description
The low energy structure of nuclei close to the doubly magic $^{40}$Ca and $^{56}$Ni are driven by collective excitations, including shape coexistence and super-deformation [1]. On the other hand, the N=28 shell closure is also strongly influencing the nuclei between N=Z=20 and 28. Electric monopole, $E$0 transitions are often cited as excellent probes to explore the interactions of collective excitations with different deformations. Strong $E$0 transitions are reported in $^{54}$Fe [2] and in $^{52}$Cr [3], however most of the $E$0 transitions in the region has not been observed. We shall report on a detailed conversion electron and electron-positron pair conversion study of $^{54}$Mn, a N=29, Z=25 nucleus next to $^{52}$Cr and $^{54}$Fe. Excited states up to about 3 MeV energy have been populated using the $^{54}$Cr(p,n)$^{54}$Mn reaction at 5.4 MeV bombarding energy at the ANU HIAS accelerator. Electron and electron-positron pair conversion coefficients have been measured with the Super-e spectrometer [4]. The 1579 keV transition from the 1634 keV 2$^{+}$ state has a conversion coefficient larger than the pure $M$1 or $E$2 value, indicating a significant $E$0 contribution. In this talk we describe the experiments and will present a preliminary interpretation of the results.
[1] K. Hyde and J.L. Wood, Rev. Mod. Phys. 83 (2011) 1467
[2] T.K. Eriksen, PhD thesis, ANU (2018)
[3] J.T.H. Dowie, PhD thesis, ANU (2021)
[4] T.K. Eriksen et al., Phys. Rev. C 102 (2020) 024320
