  We have measured the electrical conductivity of Ge:Ga samples prepared by
neutron-transmutation doping of isotopically enriched 70Ge single crystals in
order to study the metal-insulator transition (MIT) ruling out an ambiguity due
to inhomogeneous distribution of impurities. The critical exponent for the
zero-temperature conductivity is 0.5 in zero magnetic field and 1.1 in magnetic
fields. Variable-range-hopping conduction of the insulating samples and
finite-temperature scaling analysis of the MIT induced by the external magnetic
field are also discussed.
