Using magnetization measurements to detect small amounts of plutonium hydride formation in plutonium metal

We report the formation of plutonium hydride in 2 at {\%} Ga-stabilized $\delta $-Pu, with 1 atomic {\%} H charging. We show that magnetization measurements are a sensitive, quantitative measure of ferromagnetic plutonium hydride against the nonmagnetic background of plutonium. It was previously shown that at low hydrogen concentrations, hydrogen forms super-abundant vacancy complexes with plutonium, resulting in a bulk lattice contraction. Here we use magnetization, X-ray and neutron diffraction measurements to show that in addition to forming vacancy complexes, at least 30{\%} of the H atoms bond with Pu to precipitate PuH$_{\mathrm{x}}$, largely on the surface of the sample with x $\sim$ 1.9. We observe magnetic hysteresis loops below 40 K with magnetic remanence, consistent with precipitates of ferromagnetic PuH$_{1.9}$.