Using Inertial Fusion Implosions to Measure theT+He3Fusion Cross Section at Nucleosynthesis-Relevant Energies

Abstract

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 Li in low-metallicity stars. Using highenergy-density plasmas we measure the Tð 3 He; γÞ 6 Li reaction rate, a candidate for anomalously high 6 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. DOI: 10.1103/PhysRevLett.117.035002 While most light nuclei abundances in primordial material are explained well by big-bang nucleosynthesis (BBN) theory [1][2][3], observations of high levels of 6 Li in low-metallicity stars [4,5] disagree with BBN models by 3 orders of magnitude. During BBN several nuclear reactions could produce excess 6 Li, in particular 4 HeðD; γÞ 6 Li and 3 HeðT; γÞ 6 Li. Recent work has ruled out the first reaction [6], while the latter has been hypothesized as a solution to this problem [7], if the rate is much higher than expected, or in nonstandard production models.The nuclear physics of the 3 HeðT; γÞ 6 Li reaction explaining these astrophysical observations is contentious [8] yet still an open question [3]. This is primarily due to the lack of high-quality data for this reaction, with previous experiments being conducted at high energies and with significant inconsistencies between the reported data sets [9]. Only one data set exists at low energy (E cm ≤ 1 MeV) [9], which is still higher than the range where BBN reactions occurred; the fidelity of this data has also been questioned in the literature [3,7]. This strongly motivates additional experiments to determine if this reaction could explain the observed levels of 6 Li in low-metallicity stars via BBN production.In this Letter we report on novel measurements of the Tð 3 He; γÞ 6 Li reaction using high-energy-density plasmas (HEDPs), which were generated by using the OMEGA laser facility [10], to implode gas-filled thin-glass "exploding pusher" [11] capsules. In these experiments, the laser delivered 17 kJ of energy in a 600 ps duration square pulse, illuminating the outer surface of a glass microballoon 960 μm in diameter and 2.5 μm thick, filled with T 2 and 3 He gas with a total pressure of 20 atm and a 30∶70 atomic mixture. Capsules filled with T 2 , 3 He, or a D 2 þ 3 He mixture were used for background measurements and instrument calibration. Ablation pressures on the order of tens of MBar rapidly developed as the laser energy was absorbed in the glass shell's outer surface, launching a strong spherically converging shock into the gas. When this shock reached the center of the capsule and rebounded, it created a high-temperature and high-density plasma in which nuclear reactions occurred [11]. In these implosions, ion temperatures reached ∼20 keV (2.3 × 10 8 K) while ion number densities were ∼4 × 1...

Radiative 3He(2H,γ)5Li Capture at Astrophysical Energy and Its Possible Role in Accumulation of 6Li at the BBN

“…In the same region, a maximum is observed for tritium 3 H, the fraction of which, however, sharply decreases with time. As a result, the conclusions of Zylstra et al (2016) on the minor contribution of this reaction in comparison with (14) are understandable.…”

Development of an inertial confinement fusion platform to study charged-particle-producing nuclear reactions relevant to nuclear astrophysics

“…The use of HED plasmas to study nuclear reactions relevant to SN and BBN has recently begun with implosion experiments at the OMEGA laser 11,12 and a first series of experiments currently underway at the NIF. This work builds on the successful use of plasmas 13 and the HED platform 14,15,16 to probe fundamental nuclear physics problems.…”

“…We conclude that an OMEGA platform to measure charged-particle yields and spectra from reactions relevant to SN and BBN has been successfully developed. The platform has already been exploited to measure the rate of the T 3 He- reaction, ruling this reaction out as an explanation for the 6 Li abundance problem; 11 to measure an energy-dependence of the T(t,2n) reaction at center-of-mass energies from 16 to 50 keV; 34 and for initial studies of the proton spectra from the 3 He( 3 He,2p) and T( 3 He,np) reactions. 12 IV.…”

“…DISCUSSION AND FUTURE DIRECTIONS In this paper, the development of robust HED platforms for probing astrophysically relevant chargedparticle-producing nuclear reactions on OMEGA and the NIF has been described. On OMEGA, the platform is fairly mature, with the first physics results already published 11 and more in the pipeline. 12,34 On the NIF, significant progress has been made, but some further work is required.…”

“…8 The question can also be circumvented by taking the ratio of one reaction branch to another, such as was done for T 3 He- relative to T 3 He-d in Ref. 11. Kinetic effects will also not impact our ability to make spectral measurements (although interpretation of the data could be complicated by kinetic effects, e.g., inasmuch as they impact the inference of plasma conditions such as T ion ).…”