Figure 1

(a) Model neutron spectrum for the $tt$ reaction, including contributions from the $n+n+{}^4\mathrm{He}$, $n+{}^5\mathrm{He}(\mathrm{GS})$, and $n+{}^5\mathrm{He}(\mathrm{ES})$ channels. This simple analysis neglects interference in the final state and does not include the ${}^5\mathrm{He}$-breakup neutrons as they are below the detection limit for the data discussed in this Letter (contributions from ${}^5\mathrm{He}$ are shown a posteriori to be negligible). (b) Measured $tt$ neutron spectrum from Allen et al. [11] (green triangles) and Wong et al. [12] (blue squares) at c.m. reactant energies of 110 and 250 keV, respectively. The best fits to the two data sets are also shown (solid lines) using the model described above.Reuse & Permissions

Figure 2

(a) MRS measured recoil deuteron spectrum summed over OMEGA shots 55641-55647 (points). The deuteron peak at $\sim 11.6\mathrm{MeV}$ is due to the primary 14 MeV $dt$ neutrons, and the width of this peak is mainly due to the MRS resolution. The $\mathrm{DS}n$ component is observed in the deuteron-energy range of 8–10 MeV. A best fit to the $dt$ and $\mathrm{DS}n$ components (black data points) is shown by the solid black line. The remaining $tt$ neutron signal [gray (red) data points] rises above the $\mathrm{DS}n$ background ($\mathrm{DS}n$ Bkg) below 8 MeV. (b) Modeled neutron spectrum that gives the best fit to the measured $dt$ and $\mathrm{DS}n$ components for the black points discussed in (a).Reuse & Permissions

Figure 3

The $tt$ neutron spectrum averaged over all implosion series spectra. The solid line represents the modeled $n+n+{}^4\mathrm{He}$ channel, while the dashed and dotted lines represent 5% and 20% contributions of the $n+{}^5\mathrm{He}(\mathrm{GS})$ channel, respectively. All three models were convolved with the MRS resolution for direct comparison to the measured data (the neutron energy resolution is 0.55 MeV). As indicated by the spectrum, no $n+{}^5\mathrm{He}(\mathrm{GS})$ reaction channel is observed.Reuse & Permissions

Figure 4

(a) Ratio of the $n+{}^5\mathrm{He}(\mathrm{GS})$ to the total $tt$ reaction yield as a function of c.m. energy. The red circular data point was determined from the neutron spectrum shown in Fig. 3. This measurement is compared to accelerator experiments shown in Fig. 1b. (b) Calculated reactant-energy distribution [gray (red) curve] for the thermonuclear ICF measurement shown in (a). The c.m. energies for the accelerator experiments are indicated by vertical arrows since their widths are negligible on this scale.Reuse & Permissions