Impurity Systems in Condensed Helium-4.

We reviewed systems formed in liquid and solid helium-4 at high concentrations (1016 cm−3 and higher) of impurity particles. A new explanation for the reversible coagulation of fine hydrogen particles into big flakes observed upon the transition of liquid helium into the superfluid phase is proposed. The importance of nanoclusters presence in helium crystals doped with impurity particle for the metastability of icebergs is discussed. [ABSTRACT FROM AUTHOR]