Speaker
Description
Three experiments were recently performed at the Accelerator Laboratory of the University of Jyväskylä (JYFL-ACCLAB) to produce the $T_\mathrm{z}$=$-3/2$ nuclei $^{29}$S, $^{45}$Cr and $^{37}$Ca that were studied with the MARA [MARA2008] separator and the JUROGAM III [JUROGAM2020] germanium array. These nuclei were produced in the $3$-neutron evaporation channel in $^{20}$Ne+$^{12}$C, $^{24}$Mg+$^{24}$Mg and $^{28}$Si+$^{12}$C fusion reactions, respectively, at different effective beam energies. The evaporation residues of interest were unambiguously identified at the MARA focal plane by exploiting the characteristic $\beta$-delayed proton emission decay mode of these nuclei [Vieira1979] [Dossat2007]. In addition to the new $\gamma$-ray spectroscopy results for these nuclei, the experimental production cross sections could be determined.
These nuclei are particularly important to probe isospin symmetry-breaking effects by exploiting the mirror energy differences (MED) in mirror nuclei. MED are the differences in the excitation energy of the states characterised by the same isospin quantum number in nuclei that have an interchanged number of protons and neutrons [Zuker2002].
However, the proton-rich members of the mirror pairs are challenging to produce experimentally in fusion-evaporation reactions because the production cross sections drop drastically for pure neutron evaporation channels. Moreover, experimental cross-section data for pure neutron evaporation channels are very scarce and fusion-evaporation codes, such as HIVAP [Reisdorf1981] and PACE4 [Gavron1980] tend to overestimate the neutron-evaporation cross sections by few orders of magnitude. For these reasons, choosing the optimal beam energy to maximise the yield of the exotic proton-rich nuclei becomes complicated.
In this presentation, the newly obtained experimental cross-section data points for $^{29}$S, $^{45}$Cr and $^{37}$Ca will be presented and compared to the predictions obtained from the different fusion-evaporation codes. The transmission of the MARA separator, a crucial factor to extract the experimental cross section, will also be discussed.
References
[MARA2008] J. Sarén et al., Nucl. Instrum. Methods B 266, 4196 (2008)
[JUROGAM2020] J. Pakarinen, J. Ojala, P. Ruotsalainen et al., Eur. Phys. J. A 56, 149 (2020)
[Vieira1979] D. J. Vieira, R. A. Gough and J.Cerny, Phys. Rev. C 19, 177 (1979)
[Dossat2007] C. Dossat et al., Nucl. Phys. A 792, 18 (2007)
[Zuker2002] A. P. Zuker, S.M. Lenzi, G. Martinez-Pinedo and A. Poves, Phys. Rev. Lett. 89, 142502 (2002)
[Reisdorf1981] W. Reisdorf, Zeitschrift f{\"u}r Physik A Atoms and Nuclei 300, 227, (1981)
[Gavron1980] A. Gavron, Phys. Rev. C 21, 230, (1980)