Investigating the Pygmy Dipole Resonance Using β Decay

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In this contribution it is explored whether γ-ray spectroscopy following β decay with high Q values from mother nuclei with low ground-state spin can be exploited as a probe for the pygmy dipole resonance. The suitability of this approach is demonstrated by a comparison between data from photon scattering, ¹³⁶Xe(γ,γ^'), and ¹³⁶I [J₀^π=(1^-)]→¹³⁶Xe* β-decay data. It is demonstrated that β decay populates 1^- levels associated with the pygmy dipole resonance, but only a fraction of those. The complementary insight into the wave functions probed by β decay is elucidated by calculations within the quasiparticle phonon model. It is demonstrated that β decay dominantly populates complex configurations, which are only weakly excited in inelastic scattering experiments.