Shower of γ rays in the decay of the 49/2+ isomeric state in Gd147

Decay of the $49/{2}^{+}$, $0.51\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{s}$ isomeric state in $^{147}\mathrm{Gd}$ was reinvestigated in the $\ensuremath{\gamma}$-coincidence catcher experiment using the $^{76}\mathrm{Ge}(^{76}\mathrm{Ge},5n$) reaction and the GASP $\ensuremath{\gamma}$ detector array. A previously suggested extraordinary complexity of the decay was confirmed and established down to intensity level better than ${10}^{\ensuremath{-}3}$/decay, involving 400 transitions and 89 levels populated between the isomer and the $^{147}\mathrm{Gd}$ ground state. The earlier measured electron conversion coefficients (ECC) and $\ensuremath{\gamma}$ angular distributions, together with the total ECC extracted presently for low-energy transitions from the intensity balance, allowed to assign spin and parity values to all of the observed levels. Discussion of the level structure is restricted to few important cases clarified by the present investigation in the low-energy part of the decay scheme. Those involved the identification of the new $M2$ and $E2$ branches populating two new levels in the decay of the ${27/2}^{\ensuremath{-}}$ isomer and firm location of positive parity levels arising in the coupling of this isomer with the ${3}^{\ensuremath{-}}$ core excitation. In the upper part it was concluded that the observed complexity of the decay is initiated by fast low-energy $M1$ transitions populating a group of similar structure levels located within 7.8--8.0 MeV excitation energy range. Some statistical features of the observed complex isomeric decay are reviewed and discussed.