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

P. Spagnoletti; M. Ramalho; S. Tahtela; E. Kauppinen; J. Suhonen; C. Andreoiu; M. Scheck; V. Vedia; Z. Ahmed; D. Annen; G. C. Ball; G. Benzoni; S. S. Bhattacharjee; H. Bidaman; V. Bildstein; S. Buck; R. Caballero-Folch; R. J. Coleman; S. Devinyak; I. Dillmann; I. Djianto; F. H. Garcia; A. B. Garnsworthy; P. E. Garrett; B. Greaves; C. J. Griffin; G. F. Grinyer; E. G. Fuakye; G. Hackman; D. Hymers; D. Kalaydjieva; R. Kanungo; K. Kapoor; E. Kasanda; W. Korten; N. Marchini; K. Mashtakov; A. Nannini; K. Ortner; B. Olaizola; C. Natzke; C. M. Petrache; M. Polettini; A. Radich; M. Rocchini; N. Saei; M. Satrazani; M. Siciliano; M. Singh; C. E. Svensson; D. A. Torres; R. Umashankar; E. Wadge; T. Zidar; M. Zielinska

arXiv · 2609.21520

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

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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.

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P. Spagnoletti, M. Ramalho, S. Tahtela, E. Kauppinen, J. Suhonen, C. Andreoiu, M. Scheck, V. Vedia, Z. Ahmed, D. Annen, G. C. Ball, G. Benzoni, S. S. Bhattacharjee, H. Bidaman, V. Bildstein, S. Buck, R. Caballero-Folch, R. J. Coleman, S. Devinyak, I. Dillmann, I. Djianto, F. H. Garcia, A. B. Garnsworthy, P. E. Garrett, B. Greaves, C. J. Griffin, G. F. Grinyer, E. G. Fuakye, G. Hackman, D. Hymers, D. Kalaydjieva, R. Kanungo, K. Kapoor, E. Kasanda, W. Korten, N. Marchini, K. Mashtakov, A. Nannini, K. Ortner, B. Olaizola, C. Natzke, C. M. Petrache, M. Polettini, A. Radich, M. Rocchini, N. Saei, M. Satrazani, M. Siciliano, M. Singh, C. E. Svensson, D. A. Torres, R. Umashankar, E. Wadge, T. Zidar, M. Zielinska. 2026-09-18. 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. https://arxiv.org/abs/2609.21520

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