Nuclear reactions between protons and boron-11 nuclei (p–B fusion) that were used to yield energetic α-particles were initiated in a plasma that was generated by the interaction between a PW-class laser operating at relativistic intensities (~3 × 10¹⁹ W/cm²) and a 0.2-mm thick boron nitride (BN) target. A high p–B fusion reaction rate and hence, a large α-particle flux was generated and measured, thanks to a proton stream accelerated at the target’s front surface. This was the first proof of principle experiment to demonstrate the efficient generation of α-particles (~10¹⁰/sr) through p–B fusion reactions using a PW-class laser in the “in-target” geometry.

In an experiment performed with a high-intensity and high-energy laser system, $\alpha$-particle production in proton-boron reaction by using a laser-driven proton beam was measured. $\alpha$ particles were observed from the front and also from the rear side, even after a 2-mm-thick boron target. The data obtained in this experiment have been analyzed using a sequence of numerical simulations. The simulations clarify the mechanisms of $\alpha$-particle production and transport through the boron targets. $\alpha$-particle energies observed in the experiment and in the simulation reach 10–20 MeV through energy transfer from 20–30 MeV energy incident protons. Despite the lower cross sections for protons with energy above the sub-MeV resonances in the proton-boron reactions, ${10}^8$–${10}^9\alpha$ particles per steradian have been detected.