Relative ion intensities for cluster ions of the type [M(MX)n]+ and [X(MX)n]− from the SIMS spectra of alkali halides for n<100 are presented. The envelopes of the positive and negative ion spectra are quite similar and can be fit using a random bond-breaking model on the Bethe lattice approximating the bulk crystal structure. Irregularities occur in the vicinity of certain n values with ion intensity enhanced relative to that of the envelope. The greater intensity at these ‘‘magic numbers’’ is consistent with the bond-breaking model if the overall probability of breaking any bond of the bulk crystal is small. However, the reduced ion intensity immediately following the enhancement is only consistent with the subsequent unimolecular cluster ion decomposition. Mass-resolved mass spectra are reported exceeding m/z 25 000 from neutral atom bombardment of alkali iodides.