On the Delta I = 1/2 rule in the Lambda N ----> N N reaction

It is shown that the mass dependence of the $Lambda$-lifetime in heavy hypernuclei is sensitive to the ratio of neutron-induced to proton-induced non-mesonic decay rates R_n/R_p. A comparison of the experimental mass dependence of the lifetimes with the calculated ones for different values of R_n/R_p leads to the conclusion that this ratio is larger than 2 on the confidence level of 0.75. This suggests that the phenomenological $Delta$I=1/2 rule might be violated for the nonmesonic decay of the $Lambda$-hyperon.