LIFETIMES OF CHARMED PARTICLES PRODUCED IN A 20-GEV GAMMA-P EXPERIMENT - ABE, K; BACON, TC; BALLAM, J; BERNY, L; BEVAN, AV; BINGHAM, HH; BRAU, JE; BRICK, D; BUGG, WM; BUTLER, J; CAMERON, W; CARROLL, JT; et al. (PHYSICAL REVIEW LETTERS, 1982)