ANALYSIS OF DECOMPOSITION OF IMPURITY-HELIUM SOLID-PHASE

The elemental composition of the impurity-helium solid phase (IHSP) gr own by injecting of a gas jet containing Ne, Ar, Kr, and Xe atoms and N-2 molecules into superfluid HeII is studied. The measured stoichiome tric ratios S = N-He/N-Im are much larger than the values predicted by the model of frozen together monolayer helium clusters. The theoretic al possibility of freezing together of two-layered clusters is justifi ed in the continual model of the helium subsystem of IHSP which fills the space between rigid impurity centers. Regularities of decompositio n of ''dry'' samples (extracted from liquid helium) are analyzed in th e temperature range 1.5-12 K under pressures from 10 to 500 torr. Two stages of sample decomposition are discovered: a slow stage accompanie d by cooling and a rapid stage accompanied by heat release. These resu lts suggest the presence of two types of helium in IHSP, viz., weakly bound and strongly bound helium which can be attributed respectively t o the second and first coordination spheres of helium formed around he avy impurity particles. A tendency to elevation of the thermal stabili ty of impurity-helium (IH) samples upon an increase in the mass of imp urity center has been observed. An increase in the helium vapor pressu re above the samples also increases their stability. It is found that the decomposition of IH samples containing nitrogen atoms in the tempe rature range 3-4.5 K is accompanied with luminescence induced by recom bination of atoms. This indicates the possibility of a wide range of c hemical reactions in solidified helium. (C) 1997 American Institute of Physics.