Chemical stability of biological samples subjected to proton-reaction analysis

The kinetic energy of charged particles is rapidly degraded into large amounts of heat in the target; if biological samples are bombarded, chemical decomposition may result. A simple least-squares straight-line fitting procedure was applied to test the chemical stability of freeze-dried, compressed samples of human lung, brain andE. coli, under bombardment with a 0.33–0.48 μA beam of 0.7 MeV protons. The method showed no significant damage in these conditions, and also estimated the meximum length of ‘safe’ bombardment to be approximately 50 min. The samples were being subjected to proton-reaction analysis for ratios¹³C/¹²C and N/C when the least-squares test was performed; however, this method may be easily adapted to check- and roughly predict — sample stability in practically any activation, prompt-reaction, or related analysis based on charged-particle bombardment. Research sponsored by the U.S. Atomic Energy Commission under contract with the Union Carbide Corporation.