STUDIES OF HIGH-SPIN STATES IN RARE-EARTH NUCLEI USING ANGULAR-MOMENTUM PROJECTION METHOD .2. SIGNATURE INVERSION IN DOUBLY ODD NUCLEI

The signature inversion in doubly odd nuclei is investigated using the angular momentum projection method. The concept of signature in context of spin-projected states is discussed in some detail. We point out two possible mechanisms for the signature inversion, i.e. the one due to the crossing of two bands which have mutually opposite signature dependence, and the other, due to self-inversion which takes place spontaneously in a given band. The latter is a new feature found in the present theory and implies that the zigzag behavior originates in general from more complex physical reasons than what is usually assumed. Agreement of the results with experimental data for Ho-160 and three Tm isotopes is satisfactory. In these nuclei the signature inversion turns out to be due to the first mechanism (band crossing). The particle-rotor model is in conflict with the present theory. It is pointed out that the zigzag amplitude before the signature inversion decreases with increasing proton number in the former, while the opposite is the case in the latter, so that two theories can be distinguished from each other by observing the isotone dependence of experimental data.