Development of the solid deuteron target for measuring the gamma-decay probability of the 3^-₁ state in ¹²C with deuteron inelastic scattering

The triple alpha (3α) reaction, which produces ¹²C from three α particles, is one of the most important reactions in nucleosynthesis in the universe. The radiative-decay probabilities of the 3α resonance states are crucial physical quantities that determine the ¹²C production rate. At high temperatures above 10⁹ K, high-lying excited states e.g., 3^-₁ and 2⁺₂ states in ¹²C play an important role.

In this study, we aim to precisely determine the radiative-decay probability of the 3^-₁ state through simultaneous measurement of the scattered ¹²C and the recoil deuteron emitted from the inelastic deuteron scattering under inverse kinematics conditions. We have already conducted a simulation study to search for the optimum experimental condition. We considered utilizing solid deuterium, which offers a high S/N ratio, as a deuteron target. The target should have a certain surface area to avoid backgrounds due to beam halo. Additionally, from the perspective of angular resolution of recoiled deuterons, it is necessary to have a thin target thickness. Therefore, we have undertaken the challenge of developing a thin and large-area solid deuterium target with dimensions of about 15 mm × 15 mm and a thickness of 0.5 mm. Because the solid deuterium might melt due to heating by the beam, we have examined the maximum beam intensity that the solid deuterium target can withstand using the heat conduction equation. In this talk, we will report on the current status of our development efforts.