${}^2\mathrm{H}(p,\gamma ){}^3\mathrm{He}$ cross section measurement using high-energy-density plasmas

An absolute cross section for the radiative capture reaction ${}^2\mathrm{H}(p,\gamma ){}^3\mathrm{He}$ has been measured at the OMEGA laser facility using inertially confined plasmas. These high-temperature plasmas are created by imploding a fuel-containing capsule using laser ablation, and are advantageous in that they better mimic astrophysical systems. We measure an $S$ factor for this reaction of $0.429\pm 0.{026}_{\mathrm{stat}}\pm 0.{072}_{\mathrm{sys}}$ eV b at $E_{c.m.}=16.35\pm 0.40$ keV, which is higher than the adopted evaluations. This reaction is important as a source of nuclear energy in protostars and brown dwarfs. It is also a critical reaction during big-bang nucleosynthesis, and an accurate cross section can be used as a constraint on cosmology.

Figure 1

Schematic of the capsules used in this work, which are $480\mu \mathrm{m}$ radius spherical plastic (CH) shells, $15\mu \mathrm{m}$ thick, filled with a variety of gaseous fuel mixtures of hydrogen (${\mathrm{H}}_2$) and deuterium (${\mathrm{D}}_2$).

Figure 2

Cherenkov detector data from each shot as PMT V per DD-$n$ yield versus time, peak aligned at $t=0$. Different capsule gas fills [mixtures of deuterium (D) and hydrogen (H)] are distinguished by color: ${\mathrm{D}}_2$ (blues), ${\mathrm{H}}_2+{\mathrm{D}}_2$ (reds), and ${\mathrm{H}}_2$ (green). Two shots with 100 psi (absolute) of ${\mathrm{CO}}_2$ (74614 and 74615) instead of 400 psi (absolute) are shown by the dashed curves. The ${\mathrm{H}}_2$ data is normalized to the average DD-$n$ yield on the ${\mathrm{H}}_2+{\mathrm{D}}_2$ experiments since that shot produces no nuclear yield.

Figure 3

Our measurement (red point), compared to previous data from accelerator experiments [10, 11, 12, 13] (black symbols), as well as the evaluated $S$ factors reported [8, 26, 27] (black dashed, blue, and purple curves respectively). The smaller error bar on our measurement is statistical only, while the larger is the combined statistical and systematic.