A REFRIGERATOR WITH A DOUBLE NUCLEAR STAGE FOR RESEARCH ON SUPERFLUID 3He A.I. Ahonen, W.J. Gully, O.V. Lounasmaa et M.C. Veuro J. Phys. Colloques, 39 C6 (1978) C6-1153-C6-1154 DOI: 10.1051/jphyscol:19786510