Development of a monoenergetic neutron source in the 10 MeV region for neutron inelastic scattering experiments

The triple alpha reaction which creates the ¹²C nucleus from three ⁴He nuclei is one of the key reactions to understand the nucleosynthesis in the Universe. It has been pointed out that the triple alpha reaction may be greatly enhanced in the high temprature and high density environment due to the neutron-induced deexcitation of the 0₂⁺ state, that is ,the Hoyle state. This enhancement is directly related to neutron inelastic scattering cross sections for the 0₁⁺ → 0₂⁺ and the 2₁⁺ → 0₂⁺ transitions on ¹²C near threshold energies. However, there are no experimental data for these cross sections, since there is a no conventional monoenergetic neutron source in the 10 MeV region which is close to the threshold energy to excite the 0₂⁺ state from the ground state in ¹²C. Therefore, we developed the monoenergetic 10 MeV neutron source at CYRIC in Tohoku University.

The reaction we adopted is the inverse (p,n) reaction with the light heavy-ion beam. In order to change the neutron energy smoothly, we used the beam-swinger system of CYRIC. Three candidates of the ¹H(¹¹B,n)¹¹C, ¹H(¹³C,n)¹³N, and ¹H(¹⁵N,n)¹⁵O reactions were tested to select the most suitable reaction in CYRIC. In this talk, the setup of the neutron source and the result of the test experiment will be presented.