Speaker
Description
"Why are the tin isotopes fluffy?" has remained, for nearly a decade, a fundamental open problem in nuclear structure physics: models which reproduce the isoscalar giant monopole resonance (ISGMR) in the “standard" doubly-closed shell nuclei, $^{90}$Zr, $^{208}$Pb, overestimate, by as much as 1 MeV, the ISGMR energies of the open-shell tin and cadmium nuclei [1-4].
To further elucidate this question as also to examine when this “fluffiness" appears in moving away from the doubly-closed nucleus $^{90}$Zr, and how this effect develops, we have carried out measurements of the isoscalar giant resonance strength distributions in a series of molybdenum nuclei. The measurements were performed for $^{94,96,97,98,100}$Mo, using inelastic scattering of 100 MeV/u $\alpha$ particles at the Research Center for Nuclear Physics, Osaka University. The targets, with thicknesses $\sim$ 5 mg/cm$^2$, were enriched to an isotopic purity of approximately 95%. The measurements on all nuclei were performed within the same experiment so as to minimize any systematic effects in the final results. The versatile, high-precision mass spectrometer, Grand Raiden, provided small angle ($0-10^\circ$) spectra virtually free of all instrumental background. The resulting double-differential cross sections can be used to reliably extract ISGMR strength distributions using a multipole decomposition analysis; this procedure is currently in progress. The extracted ISGMR strengths will be presented. It is hoped that these results, in combination with previously published results for the ISGMR strength in $^{90,92}$Zr and $^{92}$Mo [5], will provide important information for possible refinements of theoretical models in describing this mode in open- and closed-shell nuclei alike.
This work has been supported in part by the National Science Foundation (Grant Nos. PHY-1713857 and PHY-1419765), and by the Liu Institute for Asia and Asian Studies, University of Notre Dame.
References:
[1] U. Garg, et al. Nucl. Phys. A, 788, 36. (2007)
[2] J. Piekarewicz, J. Phys. G: Nucl. Part. Phys, 37, 064038. (2010)
[3] L.G. Cao et al. Phys. Rev. C, 86, 054313. (2012)
[4] P. Vesely et al. Phys. Rev. C, 86, 024303. (2012)
[5] Y.K. Gupta et al. Phys. Lett. B, 760, 482. (2016)
