Compression experiments with spin-polarized atomic hydrogen

Doubly polarized hydrogen has been produced up to densities of 2×{}10¹⁸ cm^-3 with the use of a compression technique. Samples were compressed up to five orders of magnitude into small bubblelike volumes under a column of liquid helium. This technique enabled us to study the volume decay of a bubble at almost constant gas density for minutes. The analysis of the volume decay of such a bubble is discussed. A bulk three-body recombination process was observed with rate constant C₃=[7(2)]×{}10^-39 cm⁶ s^-1, as well as bulk electronic b{→}c relaxation with rate constant Gbcᵛ{↓}=[12(4)]×{}10^-16 cm³ s^-1. The nature of the three-body process is analyzed with a set of extended rate equations. The samples were very delicate and rapid compressions could result in explosions.