Shifted identical bands: A new phenomenon

Abstract

Abstract The levels in 162Gd were identified in spontaneous fission studies. Its transition energies are remarkably similar to those in 160Gd. From that work, an analysis of yrast bands in even-even proton to neutron-rich Ba to Pb nuclei led to the discovery of a new phenomenon, shifted identical bands (SIB). SIBs are yrast bands in neighboring nuclei (a, b) with moments of inertia which are identical when shifted by a constant amount ?, so J 1a (1+?)=J 1b , from 2+ to 8+ and higher to 16+. Out of over 700 comparisons, 55 SIBs were found from stable to the most neutron-rich Ce-W nuclei with $$\left| {\bar k} \right|$$ between 1.5% and 13%, where the spread in ? is less than 1%, and only four identical bands ( $$\bar k \cong 0$$ ). As examples, we found for 158Sm-160Gd, $$\bar k = \left( { - 3.2_{ - 0.2}^{ + 0.1} } \right)\%$$ (where the is the total spread in ? from -3.1 to -3.4); 156Nd-160Gd, (-10.6 -0.2 +0.4 )%; 158Sm-160Sm, (3.4 -0.3 +0.5 )%. The J 1 values were fitted to a variable moment of inertia model with parameters J 0 and C whose values correlate with the SIB J 1 values. The SIBs are not correlated either with deformation or with the N p N n product of the IBA model.