College 3 Seminar | l-forbidden M1 transitions near N=50 and Z=50 shell closures

J.Benito (benito@lnl.infn.it), G. García De Lorenzo (gagarc06@ucm.es)

In the framework of the nuclear extreme shell model, magnetic dipole (M1) transitions between pure single-particle initial and final states are allowed only when the change in orbital angular momentum is Δl = 0. Consequently, M1 transitions between states with Δl = 2, such as s1/2 ↔ d3/2 and g7/2 ↔ d5/2, are considered l-forbidden. Despite their forbidden nature, such M1 transitions have been experimentally observed. Several explanations for this violation of the Δl = 0 rule have been proposed, including modifications of the M1 operator due to meson-exchange currents [1], or the non-additivity of nucleon moments [2]. Other explanations, while retaining the bare M1 operator, invoke configuration mixing [3] and core-polarization effects [4,5]. Nevertheless, at present there is no consistent description that can account for the hindrance of l-forbidden M1 transitions across isotopes and isotones.

With this aim, the study of l-forbidden transitions in semi-magic nuclei provides an excellent laboratory for investigating this phenomenon. The contribution of configuration-mixing effects is expected to be reduced when approaching closed shells. In this seminar, we will present the experimental results obtained in campaigns carried out both at IDS (ISOLDE), LOHENGRIN and FIPPS (ILL) using fast-timing techniques.

1. L. Spruch et al., Phys. Rev. 103, 365 (1956), URL https://doi.org/10.1103/PhysRev.103.365
2. R. G. Sachs et al., Phys. Rev. 84, 379 (1951), URL https://doi.org/10.1103/PhysRev.84.379.2
3. A. Arima et al., Prog. Theo. Phys. 17, 567 (1957), URL https://doi.org/10.1143/PTP.17.567
4. W. Andrejtscheff et al., Nucl. Phys. A 351, 54 (1981), URL https://doi.org/10.1016/0375-9474(81) 90544-3.
5. A. Arima et al., Prog. Theo. Phys. 12, 623 (1954), URL https://doi.org/10.1143/PTP.12.623.

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Hanno Filter (College 3 Secretary)

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