We investigate the properties of the collision operator Q associated to the linear Boltzmann equation for dissipative hard-spheres arising in granular gas dynamics. We establish that, as in the case of non-dissipative interactions, the gain collision operator is an integral operator whose kernel is made explicit. One deduces from this result a complete picture of the spectrum of Q in an Hilbert space setting, generalizing results from T. Carleman [6] to granular gases. In the same way, we obtain from this integral representation of Q + that the semigroup in L 1 (R 3 × R 3 , dx ⊗ dv) associated to the linear Boltzmann equation for dissipative hard spheres is honest generalizing known results from [1].