First measurement of the 10B(α,n)13N reaction in an inertial confinement fusion implosion at the National Ignition Facility: Initial steps toward the development of a radiochemistry mix diagnostic

Abstract

We report the first measurement of the [Formula: see text] reaction in a polar-direct-drive exploding pusher (PDXP) at the National Ignition Facility (NIF). This work is motivated by the need to develop alternative mix diagnostics, radiochemistry being the focus here. The target is composed of a 65/35 at. % deuterium–tritium (DT) fill surrounded by a roughly [Formula: see text] thick beryllium ablator. The inner portion of the beryllium ablator is doped with 10 at. % of 10B. Radiation-hydrodynamics calculations were performed in 1D to optimize both the remaining boron rho-R and the DT neutron yield. A charged-particle transport post-processor has been developed to study α-induced reactions on the ablator material. Results indicate a large 13N production from α-induced reactions on 10B, measurable by the radiochemical analysis of a gaseous samples system at the NIF. The PDXP target N201115-001 was successfully fielded on the NIF, and nitrogen from the [Formula: see text] reaction was measured. The 13N production yield, as well as the DT neutron yield, was, however, lower than expected. Some of the reduced yields can be explained by the oblate shape, but the ratios of the various radiochemical signals are not commensurate with expectations based on a simple reduction of the 1D results. Preliminary 2D radiation-hydrodynamics computations are consistent with the experimental measurements, and work is ongoing to extend the radiochemistry analysis into higher dimensions.

Radiochemical capabilities for astrophysics experiments at the national ignition facility

“…The RAGS system can also be used to collect gases other than noble gases. It is routinely used to collect 13 N [12], krypton and xenon fission products, and neutron activation products, such as 41 Ar, either of gases added to the DT fill gas at concentrations less than one atom percent, or of gases trapped in capsules during fabrication.…”

“…In addition, 10 B can be added during the initial sputtering to create an ablator layer with about 10 atomic % that reacts with DT fusion alpha particles (α,n) to make 13 N [12]. Plastic (CH) and HDC capsules have the 12 C isotope that may be mixed into the plasma and react with upscattered deuterons (d*,n) to make 13 N.…”

Threshold effects in the 10B(p,α)7Be, 12C(p,γ)13N and 14N(p,γ)15O reactions

“…The production of 7 Be in a laser driven hot plasma environment can be calculated from the reaction rate and the abundances of 10 B boron and 1 H hydrogen fuel. The difference between observed and predicted number of reaction products will provide the necessary information about the environmental parameters in a plasma environment.…”

“…For a NIF like laser driven plasma study of the reaction, the optimum gas filling of the capsule would be a 10 B 2 H 6 Di-Borane fill gas with number densities of N10 B ≈ 10 20 cm −3 and N1 H ≈ 3 • 10 20 cm −3 , respectively. This would correspond to a rather high density after compression to a hot spot volume of about V HS ≈ 10 -6 cm 3 for the burn width period of Δt ≈ 10 -10 s. From Figure 2, the reaction rate can be estimated to be 〈σv〉10 B(p,α) 7 Be ≈ 10 −20 cm 3 s −1 at a temperature of about kt ≈ 30 keV.…”

“…To explore the value of these facilities for a broader nuclear astrophysics program, it might be appropriate to investigate possible measurements for higher Z isotopes. A first attempt has been made recently to study the 10 B(α, n) 13 N reaction [9] at NIF providing a first glimpse at the challenges such measurements will have to be overcome, both in the collection and in identification of the reactions products [10].…”