I was too busy to respond to your original inquiry. High dose irradiation would indeed stop microbial decay, but it would not stop chemistry.
Chemical fixation stops microbial decay and stops chemistry almost completely.
Unfortunately it also causes devastation at the molecular level. Whether the essential elements of memory and identity survive this devastation is not currently known. On the other hand, many individual cells recover spontaneously from cryopreservation protocols similar to ones now used on cryonics patients.