INTZRNAL EXPOSURE TO ALPHA RADIATION Since alpha particles can be stopped by a few inches of air, or a sheet of paper, or skin, the primary concern is whether the test participants may have received internal doses as a result of inhalation or ingestion of radioactive fallout. The NTPR research effort has found no evidence to date to indicate that significant internal doses of alpha radiation occurred, We have not ruled out the possibility, and we are continuing our search; but available evidence makes the likelihood of significant internal alpha doses appear low for the following reasons: l. A relatively small percentage of the 250,000 DoD participants were in a position where inhalation of alpha particles would have heen possible. 2. Numerous precautions were taken at the time to insure that participants did not inhale or ingest alpha particles. Troops, ships, etc., invariably were positioned or maneuvered upwind; monitoring for alpha activity was done when it was anticipated; face masks were available for those with greatest potential for exposure; rapid evacuation procedures were planned for those who might need them, and other precautions were taken. TAB F