1. R. D. Sard, University of California Report, UCRL-9353.
2. E. Jenkins, T. Kycia, and L. Marshall, “Report of a feasibility test for a low flux visual profile indicator,” Internal Report, Brookhaven National Laboratory, July 15, 1960, PD-1.
3. Sard (reference 1) inferred from data provided by Polaroid that density 1.5 corresponds to about 6×107 photons∕cm2 of blue light. Assuming that 5×103 photons are emitted per Mev of energy lost in the plastic scintillator, we find that there should have been 3×108 photons emitted per cm2 of plastic by 20 000 π mesons. Sard also found a discrepancy, but only by a factor of 7. It seems reasonable that our result differs from Sard’s because we have made no effort to obtain maximum optical efficiency. It would appear that the sensitivity of the method could be increased by perhaps a factor of five by improving the packaging of the rods and by optimizing the roughening of the surface which faces the film.