Reactions 10B+d, 9Be+3He → 3α and excited states in 12C

The main features of the 9Be+3He and 10B+d reactions going to 8Be+α and subsequently to α+α+α , are not inconsistent with a direct mechanism over a wide energy range. However, it was found at low energies that some features of the experimental data were not explained in this context. Some excited states of 12C have been reported in the region between 29 and 31 MeV, attainable also through the reactions mentioned above. Clearly in such case a compound nucleus mechanism and sequential decay should be adequate to describe both reactions. Measurements have been carried out using the van de Graff accelerator at Universite Laval. The experimental technique consisted in the measurement of α-α correlation spectra. The salient feature of the detection system consisted in the particle identification carried out at one of the correlation angles, and also in the determination of the coincidence time spectrum, which permitted an unusually clean operation through a precise selection of the true coincidence region. The accumulation of correlation spectra was effected on-line using a PDP-9 computer with a triple parameter system, the time spectrum being recorded as third parameter. (Auth.)