Possible role of $^3He$ impurities in solid $^4He$

We use a quantum lattice gas model to describe the essential aspects of the motion $^4He$ atoms and of a $^3He$ impurity in solid $^4He$. We find that $^3He$ impurities promote $^4He$ atoms to interstitial sites and this can turn the bosonic quantum crystal into a metastable supersolid. It is suggested that $^3He$ impurity atoms, which produce the interstitial $^4He$ atoms, might have been reabsorbed by pure $^4He$ solid formed during the first stage of a multi-stage solid $^4He$ nucleation process. While we use the ``spin''-wave approximation and low dimensional lattices to illustrate some of the ideas, we argue that the conclusions drawn from these studies may be valid for the real system.