Nonuniform Track Shrinkage in Nuclear Emulsions

Abstract

LETTERS TO THE EDITOR 717Our observations can be explained by a theory in which the particles are produced multiply in the initial interaction. 6 The multiplicity apparently does not seem to increase by a large factor through subsequent interactions inside the target nucleus; this is probably because the shower particles do not interact individually inside the nucleus because of their extreme collimation. 1,6,7 The fluctuations from the average behavior as noted above could be the result of large fluctuations in the angular distribution of the shower particles. A few shower particles of the first or possibly the second generation projected at angles considerably greater than the average could be effective in starting independent cascades inside the nucleus, which could increase the observed multiplicity by a considerable factor.We have also noted the occurrence of both high and low energy pairs of charged particles produced by neutral radiation, in observing the passage of the high energy showers through the block of stripped emulsions. The most reasonable assumption is that these pairs are electron-positron pairs produced by photons; though our statistics are too low to draw any definite conclusion, the contribution of bremsstrahlung according to SchifFs theory 8 seems to be too low to account for the low energy pairs.We are indebted to the Aero Medical Field Laboratory, Holloman Air Force Base for their cooperation in obtaining successful balloon flights. We wish to thank Miss Barbara Hull and Miss Katherine Merry for their assistance in scanning the plates. * This research has been supported in part by funds from the Department of the Air Force.i M. F. Kaplon and D. M. Ritson, Phys. Rev. 88, 386 (1952). 2 Stiller, Shapiro, and O'Dell, Phys. Rev. 85, 712 (1952). 3 A lifetime of 3 X10"~1 2 sec in the laboratory system corresponds approximately to a mean life of ~10~1 5 sec in the rest system of the 7r° meson. 4 Daniel, Davies, Mulvey, and Perkins, Phil. Mag. 43, 753 (1952). Recently in this laboratory a proton induced star of about sixty shower particles has also been observed. « E. Fermi, Phys. Rev.

Nucleonics

“…Shrinkage in the emulsion gives rise to a necessary correction in the track length. This shrinkage factor was found by Horan (77) to be a function of the angle of incidence and the usual correction should be restricted to angles of dip of less than 6°if the error of measurement is to be less than 2%. The horizontal -ray ranges alone were found by Poole and Matthews (118) to be usable as a means of determining thorium-uranium concentration ratios.…”