First direct measurement of the spectrum emitted by the H3(H2,γ)He5 reaction and assessment of the relative yield γ1 to γ0

The spectral $\gamma$ ray emission from the reaction ${}^3\mathrm{H}({}^2\mathrm{H},\gamma ){}^5\mathrm{He}$ has been measured for the first time in a magnetic confinement deuterium-tritium plasma experiment at the Joint European Torus. A custom developed gamma ray spectrometer system based on a $\mathrm{La}{\mathrm{Br}}_3$ scintillator combined to a LiH neutron attenuator and a zero dead time fast digital data acquisition allowed to measure the weak $\gamma$ ray emission under the $\approx {10}^5$ more intense $14\mathrm{MeV}$ neutron field. The $R$-matrix analysis of the ${}^5\mathrm{He}$ nucleus has been used to predict the expected gamma ray spectrum which has been compared with the measurement, but cannot predict the relative intensity of the $\gamma$ lines. The data analysis has identified the energy and width of the known 16.75 MeV $\gamma$ ray emission (${\gamma }_0$), from the second excited state to the ground state of the formed ${}^5\mathrm{He}$ nucleus, and confirmed the presence of a second emission (${\gamma }_1$) at $\approx 14\mathrm{MeV}$ due to the transition from the second to the first excited state. The analysis has shown that the ${\gamma }_1$ emission is broad and has assessed for the first time in a magnetic confinement experiment the relative yield ${\gamma }_1$ to ${\gamma }_0$ equal to $1.09\pm 0.25$.