Explosive Recombination of Compressed Spin-Polarized Hydrogen

Spin-polarized atomic hydrogen gas has been compressed to densities > ${10}^{18}$/${\mathrm{cm}}^3$ with liquid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ at temperatures from 0.24 to 0.67 K in magnetic fields up to 7.5 T. We find that the critical pressure, at which recombination ultimately becomes a thermally triggered explosion, goes through a maximum as a function of temperature. The explosion pressure increases with decreasing sample size and with increasing field and nuclear polarization.