First observation of the fine structure of the Pygmy Dipole Resonance in a nucleus away from stability via the $β^-$ decay of $^{92}$Rb to $^{92}$Sr
Year: 2026
Type: preprint
Abstract: A comprehensive $γ$-ray spectroscopy study of excited states in $^{92}$Sr populated via $β^-$ decay of $^{92}$Rb ($J^π=0^-$, $Q_β=8095(6)$~keV) was performed with the GRIFFIN spectrometer at the Isotope Separator and Accelerator (ISAC) radioactive ion beam facility at TRIUMF. The high $γ$-ray efficiency of the GRIFFIN spectrometer combined with the intense rubidium beams produced allowed for 864 $γ$-ray transitions to be placed in the level scheme with 190 excited levels populated, most of them identified for the first time. The excitation energies of low-spin states in $^{92}$Sr are well reproduced by large-scale Shell Model calculations up to 5~MeV. The $β$-feeding intensities are in very good agreement with results from a recent study employing Modular Total Absorption Spectroscopy, indicating a significant suppression of the Pandemonium effect. The experimental picture reveals the energy level dependence of log~$ft$ values in unprecedented detail. These log~$ft$ values are well reproduced by Multiple-Commutator Model calculations that identify the features in the excited levels' wavefunctions that enable the population of high-lying levels with a low effective Q-value that belong to the Pygmy Dipole Resonance.
Source: arXiv (Cornell University)
Authors: Spagnoletti, P., Ramalho, M., Tahtela, S., Kauppinen, E., Suhonen, J., Andreoiu, C., Scheck, M., Vedia, V., Ahmed, Z., Annen, D., Ball, G. C., Benzoni, G., Bhattacharjee, S. S., Bidaman, H., Bildstein, V., Buck, S., Caballero-Folch, R., Coleman, R. J., Devinyak, S., Dillmann, I., Djianto, I., Garcia, F. H., Garnsworthy, A. B., Garrett, P. E., Greaves, B., Griffin, C. J., Grinyer, G. F., Fuakye, E. G., Hackman, G., Hymers, D., Kalaydjieva, D., Kanungo, R., Kapoor, K., Kasanda, E., Korten, W., Marchini, N., Mashtakov, K., Nannini, A., Ortner, K., Olaizola, B., Natzke, C., Petrache, C. M., Polettini, M., Radich, A., Rocchini, M., Saei, N., Satrazani, M., Siciliano, M., Singh, M., Svensson, C. E., Torres, D. A., Umashankar, R., Wadge, E., Zidar, T., Zielinska, M.
Institutions: Simon Fraser University, University of Jyväskylä, International Center for Advanced Training and Research in Physics, Helmholtz-Zentrum Hereon, TRIUMF, University of Guelph, Istituto Nazionale di Fisica Nucleare, Sezione di Milano, University of Victoria, Lawrence Berkeley National Laboratory, University of Regina, Commissariat à l'Énergie Atomique et aux Énergies Alternatives, Université Paris-Saclay, CEA Paris-Saclay - Etablissement de Saclay, CEA Paris-Saclay, Institut de Recherche sur les Lois Fondamentales de l'Univers, Saint Mary's University, Istituto Nazionale di Fisica Nucleare, Sezione di Firenze, Colorado School of Mines, Centre National de la Recherche Scientifique, Institut National de Physique Nucléaire et de Physique des Particules, Laboratoire de Physique des 2 Infinis Irène Joliot-Curie, University of Milan, University of Liverpool, University of British Columbia
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: U.S. Department of Energy, TRIUMF, Simon Fraser University, China Scholarship Council, Office of Science, Natural Sciences and Engineering Research Council of Canada, National Research Council Canada, British Columbia Knowledge Development Fund, Ontario Ministry of Research and Innovation, Nuclear Physics
OpenAlex ID: W7213913778