  Short-pulse, ultra high-intensity lasers have opened new regimes for studying
fusion plasmas and creating novel ultra-short ion beams and neutron sources.
Diagnosing the plasma in these experiments is important for optimizing the
fusion yield but difficult due to the picosecond time scales, 10s of
micron-cubed volumes and high densities. We propose to use the yields of
photons and neutrons produced by parallel reactions involving the same
reactants to diagnose the plasma conditions and predict the yields of specific
reactions of interest. In this work, we focus on verifying the yield of the
high-interest aneutronic proton-boron fusion reaction
$^{11}{B}(p,2\alpha){}^4{He}$, which is difficult to measure directly due to
the short stopping range of the produced $\alpha$s in most materials. We
identify promising photon-producing reactions for this purpose and compute the
ratios of the photon yield to the $\alpha$ yield as a function of plasma
parameters. In beam fusion experiments, the ${}^{11}{C}$ yield is an
easily-measurable observable to verify the $\alpha$ yield. In light of our
results, improving and extending measurements of the cross sections for these
parallel reactions are important steps to gaining greater control over these
laser-driven fusion plasmas.

Plasma Physics;Nuclear Theory