A study of γ-decay modes from high angular momentum nuclear states by high order multiplicity measurements

Reactions between ¹⁸O and ¹⁶O ions, with energies well above the Coulomb barrier, and ^{148, 150}Nd target nuclei were used to study the cascades of γ-rays in the residual nuclei ^{161, 162}Er. A multi-counter setup was used in which the γ-rays were detected by a Ge(Li) counter coupled in coincidence with up to 9 NaI(Tl) counters. The γ-multiplicity has been studied for γ-rays cascading through states above and along the yrast line. Higher moments of the multiplicity distributions (shape parameters) were deduced from the data. These moments allow the construction of the spin distribution for the entry states. The difference between these spin distributions from reactions induced by ¹⁶O and ¹⁸O ions was studied. Also the fusion cross section was measured for the two systems as a function of bombarding energy and compared to the multiplicity results at two different excitation energies (E_x = 49.5 and 56.2 MeV). A subtraction technique has been applied in the data analysis with the intention to study the decay of a selected part of the high-spin region, and the results show besides the 4n channel an unexpected large contribution of the 5n channel from this region. The sidefeeding patterns of the multiplicity distributions are extracted and show a significant difference for the ¹⁶O and ¹⁸O induced reactions, especially at the lowest bombarding energies. The results are compared with statistical model calculations.