  Using the relation between the harmonic oscillator wave function and the
light quark scattering form factor, the expectation values of colour-straight
four-quark operators are evaluated and found to be directly proportional to the
cubic power of the oscillator strength. It is predicted that the ratio
\tau(\Lambda_b)/\tau(B) \approx 0.79(0.84) due to the factorizable
(nonfactorisable) piece, against the experimental 0.79 \pm 0.06.
Notwithstanding the numerical prediction, the present study shows that the
four-quark operators play a role as far the lifetimes of b-flavoured hadrons
are concerned.
