Electric charge of grains and interstellar radioactivity

We investigate the electric potential of high speed interstellar grains trapping radioactive nuclei which are suggested to exist in interstellar medium by the study of meteorite samples and the gamma-ray line observation. These radioactive nuclei, e.g.²²Na,²⁶Al,⁴⁴Ti and⁶⁰Fe bring about a drastic change in grain potential. Grains with larger radius than the critical radiusa_c attain a negative potential when grains are traversing a typical intercloud region.