Abstract
Motivated by possible industrial fusion applications of spectroscopy of the gamma rays accompanying d-t collisions we develop the first model calculations of the minor branching ratio of the d + t reaction, d + t-* alpha + n + gamma. The model exploits the most relevant physics feature-spin conservation in electric dipole transitions-which leads to a peculiar mechanism of this reaction: gamma emission via bremsstrahlung from an intermediate alpha-n state. We highlight that, as a consequence of the bremsstrahlung, the gamma spectrum contains nonzero contributions at all energies, thus making inclusive dt gamma cross section measurements sensitive to the low-energy cutoff of the detected gamma events. Comparison of our predictions to existing d + t-* alpha + n + gamma measurements in accelerators, employing cutoffs of 13 and 14 MeV, and inertial confinement fusion facilities, with a low-limit cutoff of 0.4 to 10 MeV, suggests a possible contradiction between results from these two types of experiments. Our predictions agree well with accelerator measurements and corroborate the cutoff dependence observed in inertial confinement experiments. These predictions are sensitive to the wave function details inside the short-range area of the alpha-n interaction, with uncertainty comparable to that of available experimental data, but become model independent below 4-5 MeV. This part of the gamma spectrum features a previously unexpected rise, which below 0.5 MeV surpasses the main 17-MeV gamma peak in strength. The reactivity of the d + t-* alpha + n + gamma branch was found to be proportional to its cross section. It strongly depends on the d-t plasma temperature, which opens the possibility of not only total d + t reactivity measurements but also advanced plasma temperature diagnostics.