Using Inertial Fusion Implosions to Measure the $\mathrm{T}+{}^3\mathrm{He}$ Fusion Cross Section at Nucleosynthesis-Relevant Energies

Light nuclei were created during big-bang nucleosynthesis (BBN). Standard BBN theory, using rates inferred from accelerator-beam data, cannot explain high levels of ${}^6\mathrm{Li}$ in low-metallicity stars. Using high-energy-density plasmas we measure the $\mathrm{T}({}^3\mathrm{He},\gamma ){}^6\mathrm{Li}$ reaction rate, a candidate for anomalously high ${}^6\mathrm{Li}$ production; we find that the rate is too low to explain the observations, and different than values used in common BBN models. This is the first data directly relevant to BBN, and also the first use of laboratory plasmas, at comparable conditions to astrophysical systems, to address a problem in nuclear astrophysics.

Figure 1

(a) Cherenkov data from individual implosions with $\mathrm{T}{}^3\mathrm{He}$ or ${\mathrm{T}}_2$ fuel. (b) Average and yield-normalized data for each fuel type. $t=0$ occurs at the signal peak for each curve. In addition to the $\mathrm{T}{}^3\mathrm{He}$-gas-filled implosions (blue), sources of background are measured with ${\mathrm{T}}_2$ (red) or ${}^3\mathrm{He}$ gas-filled (green) implosions. The ${\mathrm{T}}_2$ and $\mathrm{T}{}^3\mathrm{He}$ implosions are normalized by the measured DT-neutron yield produced in each shot.

Figure 2

Cherenkov detector response (100 psi ${\mathrm{CO}}_2$) from a geant4 calculation. Left: Productive electrons and Cherenkov photons detected per incident $\gamma$ (blue and blue dashed curves, respectively). Right: The number of photons detected per productive electron (red curve).

Figure 3

Calculated $\gamma$-ray spectrum (blue, area normalized), detector response (red), and spectrum normalized to sensitivity (magenta).

Figure 4

Astrophysical $S$ factor for the reaction $\mathrm{T}({}^3\mathrm{He},\gamma ){}^6\mathrm{Li}$ measured in this work, compared to previous data [9] and constant values used in BBN theory [3, 7]. The total uncertainty for this measurement (statistical and systematic) is shown. The energy range of interest to BBN, 45–150 keV, is shown by the shaded region.