Date: 29 May 2012

Alpha-gamma decay studies of 253 No and its daughter products 253 Md , 249 Fm

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Nuclear structure and decay of the isotope 253No and its decay products 249Fm and 253Md were investigated by means of \( \alpha\) -\( \gamma\) spectroscopy. Besides the established strong \( \gamma\) transitions from the \(\ensuremath 9/2^{-}[734]\) Nilsson level in 249Fm , populated predominantly by the \( \alpha\) decay of 253No , into the ground-state (gs) rotational band, a couple of weaker \( \gamma\) lines (58.3, 129.2, 209.3 and 669.5keV) were observed and placed into the 249Fm level scheme. The transition from the \(\ensuremath 7/2^{-}\) level in 249Es , populated by the \( \alpha\) decay of 253Md , into the \(\ensuremath 9/2^{+}\) member of the gs rotational band, so far established for other odd-mass Es isotopes, was observed clearly. GEANT4 simulations were performed to investigate the influence of energy summing between \( \alpha\) particles and conversion electrons (CE) on the shape of the \( \alpha\) spectra at different implantation energies, leading to evidence for a weak \( \alpha\) decay branch of 253No into the gs of 249Fm or the ground-state rotational band, respectively.