This chapter talks about cascade production occurring at very high defect densities, cascade yield Q c, mean cascade diameter d , number of vacancies N V per cascade, and cascade efficiency η for irradiation at temperature T in Co, Pt and W metal with ions of energy E are tabulated. The average mean cluster diameter can be deduced from transmission electron microscopy (TEM) images. When the size and shape of the clusters and the density of the defects in the cascade are known, the number of defects (generally vacancies) N V can be estimated. N V finally allows to determine the cascade efficiency η which is given by the ratio of the number of defects observed in visible clusters to the number of defects produced in the original cascade. For the calculation of N d, only recoils above the threshold for cascade formation are considered. Mainly under light ion and neutron irradiation the thus calculated numbers are considerably smaller than the total number of atomic defects produced.