Kinematic Calculation of the 16O(γ,4α) Reaction

Abstract

The event distribution over the excitation energy of a system of two α-particles (Ex) is measured for the reaction 16O(γ,4α). It is found that an intermediate excited 8Be nucleus is formed, and the channels of the 8Be nucleus ground state (GS) formation are extracted. After the separation of the GS 8Be nucleus, a broad maximum with a center at ∼ 3 MeV appears in the distribution of Ex, which may correspond to the first excited state of the 8Be nucleus. There are two possible channels for the formation of this state in the reaction - γ + 16O → α1 + 12C* → α1 + α2 + 8Be* →α1 + α2 + α3 + α4 and γ + 16O → 8Be* + 8Be* → (α1 + α2) + (α3 + α4). Each decay mode is reduced to several two-particle systems. For a comprehensive study of the channel for the formation of the first excited state of the 8Be nucleus in the 16O(γ,4α) reaction, a kinematic model for calculating the parameters of α-particles has been developed. The model is based on the assumption of a sequential two-particle decay with the formation of intermediate excited states of 8Be and 12C nuclei. For the kinematic model of the 16O(γ,4α) reaction, a graphical application was created in the Python programming language. The matplotlib library is used for data visualization. To generate random values, a set of functions from the standard random library of the Python programming language is used. Monte Carlo simulations of several distributions for one parameter with a given numerical function were performed. Several excited states of the 12C and 8Be nuclei can contribute to the reaction. The created scheme allows us to choose the relative contribution for each channel of decay, as well as the contribution of a separate level in each channel. To correctly comparison of the experimental data and the results of the kinematic calculation, the α-particles were sorted by energy in such a way that T1sort > T2sort > T3sort > T4sort. As a result of comparing the experimental and calculated data, it was determined that predominantly occurs the process γ + 16O → α1 + 12C* → α1 + α2 + 8Be* → 4α with the formation of the 12C nucleus in states with E0 = 13.3 MeV, E0 = 15.44 MeV, and the 1st excited state of the 8Be nucleus with E0 = 3.04 MeV. The conditions for the identification of α-particles in the experiment for each decay of the stage are determined.

Keywords

• photonuclear reactions
• diffusion chamber
• the excited states of 8Be and 12C nuclei