2 The model and neutron star statistics

We consider a gamma-ray burst model based on a nuclear explosion under the surface of a neutron star. There is a nonequilibrium layer in the crust of the neutron star, consisting of very heavy and neutron overabundant nuclei. After the starquake these nuclei are moved out, and become unstable to fission after several beta-decays. This results in an almost instant explosion and the formation of a GRB (Bisnovatyi-Kogan et al. 1975). The energy resource in the nonequilibrium layer is of the order of 10⁴⁷ ergs. If GRB originates at a distance about 100 pc with the energy release 10³⁶-10⁴⁰ ergs, then each neutron star may give 10⁷-10¹¹ gamma ray bursts. Estimating the total number of neutron stars in the Galaxy as $(2-7)\ 10^8$, and their number inside the sphere with a radius 200 pc as $(3-10)\ 10^4$, we need a recurrence time (100-300) years in old neutron stars to produce an observed GRB every day (Bisnovatyi-Kogan 1992).