Scintillation of Liquid Helium under Pressure. II.2>T>0.3°K

Abstract

Measurements of the $\alpha$-particle-produced scintillation intensity of liquid ${\mathrm{He}}^4$ under pressure have been performed at temperatures ranging down to 0.3 °K. The data show a strongly temperature-dependent component of the pulse intensity which drops to zero for $T\lesssim 0.75$ °K. The principal pressure dependence of the intensity is in the component remaining below 0.75 °K. A physical interpretation of the results is presented which invokes metastable systems and the superfluidity of He II to explain the temperature dependence, and ionic recombination to explain the pressure dependence.