Bubble chamber studies of nuclear structure

The proton-C12 interaction has been investigated using a twelve-inch propane bubble chamber and the full energy proton beam from the Harwell synchrocyclotron. A series of experiments on the external proton beam led to the establishment of a beam with an energy spread of less than 0.5 MeV; this enabled the bubble chamber to be used at the limit of its resolving power which was then determined by straggling. 2-prong, 3-prong and 4-prong events have been analysed. The quasi-elastic nature of the reaction C12(p, 2p)B11g.s. has been confirmed and its cross-section has been seen to be independent of the proton energy from 50 MeV to 130 MeV and equal to 16 ± 1.5 mb. The energy independence of the cross-section is shown to be explained by the operation of the Pauli principle within the nucleus. The (p, 2p) reaction leading to the low excited states of B11, the 2-prong events with high energy-losses (when reconstructed on the assumption that they are (p, 2p) reactions) the 3-prong events, and the 4-prong events have been analysed with a view to establishing the reactions and the reaction mechanisms giving rise to them. The analysis was facilitated by setting up a reaction model, of the Monte Carlo type, to calculate the energies of final reaction products from various hypothesized reactions. The conclusion reached is that multiple scattering of nucleons within the nucleus is the key to the production of the above-cited events; intranuclear nucleon cascades are set up which lead to reactions of the type C12(p, 2pxn)B11−x, C12(p, 3pxn)Be[illegible]−x and C12(p, 4pxn)Li[illegible]−x, where x = 1, 2, … With the exception of the quasi-elastic (p, 2p) reaction the reactions with x=0 contribute only a small part of the total cross-sections. There is evidence that the production of Be8, or two α-particles, as the final products of cascade and evaporation mechanisms is highly favoured and as an interpretation of this it is suggested that α-particle substructures in C12 are important in influencing the course of the proton-C12 reaction. There is no evidence for a significant proportion of α-particles amongst the reaction products but this could well be due to the fact that the probability of observing an α-particle is zero for α-particles below 16 MeV and only reaches unity at an energy of [illegible] MeV.