Speaker
Description
Isospin symmetry implies that the nuclear force acts in the same way between proton-proton, neutron-neutron and proton-neutron pairs in the atomic nucleus. To probe this symmetry, it is possible to study the so-called "mirror nuclei" that have interchanged numbers of protons and neutrons and thus should have analogous structures. Leaving aside the Coulomb interaction, the difference in excitation energy of the states characterised by the same isospin in mirror nuclei, called mirror energy differences (MED), are signatures of isospin symmetry breaking [1].
The proton-rich members of the mirror pairs are challenging to to produce and populate in high-spin states. In a recent experiment performed at the Accelerator Laboratory of the University of Jyväskylä the 3-proton excess nucleus $^{45}$Cr, a $T$=3/2 mirror of $^{45}$Sc, was studied using the MARA separator [2] and the JUROGAM3 spectrometer [3]. $^{45}$Cr was produced in the 3-neutron evaporation channel of the $^{24}$Mg+$^{24}$Mg fusion-evaporation reaction at different beam energies. Although this reaction channel is strongly suppressed in terms of production cross section with respect to the other evaporation channels, the $^{45}$Cr evaporation residues were unambiguously identified at the MARA focal plane by exploiting the characteristic $\beta$-delayed proton emission decay mode of this nucleus [4].
Previous works investigated the mirror energy differences of the $^{45}$Cr-$^{45}$Sc mirror pair produced in two-nucleon knockout up to the $J$=$11/2$ states [5] and carried out a sensitivity study of the MED in positive parity bands [6].
Our work aims at extending the level scheme of $^{45}$Cr and comparing our results with predictions from the shell model calculations. The half-life of the $3/2^+$ isomeric state in $^{45}$Cr could also be measured in our experiment. In addition to that, the experimental 3-neutron evaporation production cross section for $^{45}$Cr was extracted as a function of the excitation energy. The experimental results were compared with the predictions of PACE4 [7] and GEMINI++ [8] fusion-evaporation simulation codes, which produce discordant results that differ for a few orders of magnitude. This result can be particularly useful when planning further experiments in this mass region of the $N$=$Z$ line.
References
[1] M. Bentley and S. M. Lenzi, Progress in Particle and Nuclear Physics,
59, 497 (2007)
[2] J. Sarén et al., Nucl. Instrum. Methods B 266, 4196 (2008)
[3] J. Pakarinen, J. Ojala, P. Ruotsalainen et al., Eur. Phys. J. A 56, 149 (2020)
[4] C. Dossat et al., Nucl. Phys. A 792, 18 (2007)
[5] S. Uthayakumaar, M. A, Bentley, E. C. Simpson et al., Phys. Rev. C 106, 024327 (2022)
[6] W. Satuła, M. A. Bentley, A. Jalili and S. Uthayakumaar, Phys. Rev. C
108, 044315 (2023)
[7] A. Gavron, Phys. Rev. C 21, 230, (1980)
[8] R. J. Charity, Phys. Rev. C 82 014610 (2010)