Secondary gamma transitions in Gd-159 after neutron capture at isolated resonances

The Gd-158(n,gamma)Gd-159 reaction was studied at 12 isolated neutron reson ances by the TOF method at the IBR-30 Fast Pulse Reactor at JINR Dubna. Tot ally 15 secondary gamma transitions in Gd-159 were recorded in the range fr om 450 keV to 750 keV. Of these, six previously unseen transitions were pla ced on the established Gd-159 level scheme. The depopulation of strongly po pulated levels at 507.7 keV and 558.2 keV (the head and the first excited m embers of band 1/2(-)[521]) was observed for the first time. It was shown t hat the observed 507.7 keV gamma line, masked by the annihilation peak, ori ginates from an unresolved doubler of transitions from the 507.7 keV level to the ground state and from the 558.2 keV level to the level at 50.7 keV. The 507.7 keV level decays exclusively to the ground state, while the 558.2 keV level decays via two transitions with a branching ratio that agrees we ll with the prediction according to Alaga's rule.