ION-BEAM-INDUCED CHANGES IN DROSOPHILA-MELANOGASTER BRAINS STUDIED WITH STIM

Scanning transmission ion microscopy (STIM) with energy loss contrast has been used to study the effect of ion microbeam irradiation on semi -thick animal tissue specimens. Excised, freeze substituted Drosophila melanogaster brains have been scanned with a 3 MeV proton beam of cur rent 150 pA focused to a spot size of 5 mum for exposures between 0.15 and 2.22 mC/cm2. Sample mass loss, volume loss and specimen deformati on resulting from these irradiations have been observed with STIM usin g a 3 MeV proton beam current of approximately 2000 ions/focused to a spot size of approximately 0.5 mum. The similarity of the sample mass loss and volume loss curves suggests that volume losses are directly l inked with the same beam specimen interactions that give rise to mass loss.