Chiral behaviour of the lattice B-K-parameter with the Wilson and Clover actions at beta=6.0

We present results for the kaon B-parameter BK from a Sample of 200 configurations using the Wilson action and 460 configurations using the SW-Clover action, on a 18(3) x 64 lattice at beta = 6.0. We compare results obtained by renormalizing the relevant operator with different ''boosted'' values of the strong coupling constant alpha(s). In the case of the SW-Clover action, we also use the operator renormalized non-perturbatively. In the Wilson case, we observe a strong dependence of B-K on the prescription adopted for alpha(s), contrary to the results of the Clover case which are almost unaffected by the choice of the coupling, We also find that the matrix element of the operator renormalized non-perturbatively has a better chiral behaviour, This gives us our best estimate of the renormalization group invariant B-parameter, (B) over cap(K)$ = 0.86 +/- 0.15.