Intermediate Structure at 19.7 Mev in the OXYGEN+(16) 16)CARBON(12) System (a Heavy Ion Resonance)

The intermediate width structure observed around 19.7 MeV in excitation functions of the system ('16)O+('12)C has been investigated extensively using various techniques. (i) Angular distributions were measured between 19.5 and 21.0 MeV in steps of approximately 125 keV. The elastic scattering angular distributions were investigated with a partial phase-shift analysis. S-matrix elements were determined for a limited number of partial waves at each energy. From the energy dependence of the S-matrix element with partial wave l = 14, it was determined that the 19.7 MeV structure is, in part, due to a resonance with spin J('(pi)) = 14('+), a fact that could not be proven before. (ii) Fine step excitation functions were measured ((DELTA)E = 11 keV) over the 19.7 MeV structure. These measurements revealed that substructure is present within this energy region. It is argued that this substructure is of statistical origin, i.e., due to formation and decay of a compound nucleus. (iii) Angular correlation measurements were performed for the ('12)C(('16)O,('12)C)('16)O(3('-),6.13 MeV) reaction around 19.7 MeV. It was found that the resonant amplitude in this channel is not large enough to dominate the angular correlation function. Therefore, no quantitative analysis was possible and the presence of a resonance could not be shown here. These measurements show that, in principle, nuclear structure information can be obtained from heavy ion reactions. However, the accuracy of the spectroscopic information is not very high, due to the finite precision of the data and due to the presence of statistical fluctuations. The consequences of these limitations are discussed extensively and improvements are suggested.