We have measured for the first time the cross section of the ${}^2\mathrm{H}$$(n,\gamma )$${}^3\mathrm{H}$ reaction at an energy relevant to big-bang nucleosynthesis by employing a prompt discrete γ-ray detection method. The outgoing photons have been detected by means of anti-Compton NaI(Tl) spectrometers with a large signal-to-noise ratio. The resulting cross sections are $2.23\pm 0.34,1.99\pm 0.25$, and $3.76\pm 0.41\mu$b at $E_n=30.5,54.2$, and 531 keV, respectively. At $E_n=30.5$ keV the cross section differs from the value reported previously by a factor of 2. Based on the present data the reaction rate has been obtained for temperatures in the range ${10}^7-{10}^{10}$ K. The astrophysical impact of the present result is discussed. The obtained cross sections are compared with a theoretical calculation based on the Faddeev approach, which includes meson exchange currents as well as a three-nucleon force.

• Received 24 February 2006

DOI:https://doi.org/10.1103/PhysRevC.74.025804