Experiments on spin polarized quantum fluids

Recent experimental work in untangling the reaction kinetics and spin relaxation processes which lead to the decay of a low temperature gas of atomic hydrogen in a high magnetic field is reported on. A sample cell equipped with a door opened and closed via the fountain effect of superfluid 4He was used to confine the hydrogen gas to the most homogeneous part of the magnetic field. A 3He melting curve thermometer was used to establish the temperature scale. With the application of microwaves at the resonance frequency between the lowest two hyperfine levels of atomic hydrogen, the population difference between atoms in the two levels could be driven to zero. Using this technique the initial polarization of a decaying gas of atomic hydrogen could be set to zero, making it possible to unambiguously extract the reaction rate and spin relaxation constants from the rate equations. Alternatively, by continuously applyng microwaves, the decay of the hydrogen gas could be modified to simplify the extraction of one of the reaction rate constants. The temperature dependence of the raatio of cross sections for the production of para- and ortho- hydrogen was measured. The two body spin relaxation bottleneck in the hydrogen decay pathway, reported by earlier workers is confirmed. A comparison of the measured rate constants with existing theories is presented. Experiments on the rapid freezing and melting of 3He in 2 and 2.5 T magnetic fields are also reported on. The experiments confirmed the observations of E.A. Shuberth, D.M. Bakalyar and E.D. Adams of the presence of a pressure back-step during fast Pomeranchuk compressions in magnetic fields of the order of 3T