First direct measurement of the spectrum emitted by the 3 H( 2 H, γ ) 5 He reaction and assessment of the relative yield γ 1 to γ 0 [ First direct measurement of the spectrum emitted by the ³H (²H, γ) ⁵He reaction and assessment of the relative yield γ₁ to γ₀ ]

The spectral γ ray emission from the reaction H3(H2,γ)He5 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 LaBr3 scintillator combined to a LiH neutron attenuator and a zero dead time fast digital data acquisition allowed to measure the weak γ ray emission under the ≈105 more intense 14MeV neutron field. The R-matrix analysis of the He5 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 γ lines. The data analysis has identified the energy and width of the known 16.75 MeV γ ray emission (γ0), from the second excited state to the ground state of the formed He5 nucleus, and confirmed the presence of a second emission (γ1) at ≈14MeV due to the transition from the second to the first excited state. The analysis has shown that the γ1 emission is broad and has assessed for the first time in a magnetic confinement experiment the relative yield γ1 to γ0 equal to 1.09±0.25.