New Photographic Emulsions Showing Improved Tracks of Ionizing Particles

The photographic emulsion method of registering the tracks of ionizing particles suffers from certain disadvantages that are mainly due to the relatively large size of grains forming the tracks and their large spacing. These disadvantages are mostly removed in new emulsions that have been prepared after numerous tests. The tracks of ionizing particles in these emulsions consist of grains of diameter d ~ 0.2 µ, which often form continuous lines.Grain spacing is no longer the main cause of apparent straggling, except below a range of 3 to 4 mm. of air. The standard deviation in determining energy from a single measurement of range is 3.25 to 3.5% for protons of 0.6 to 2.4 Mev., and 1.3 to 1.9% for α-rays of 4 to 8.5 Mev. The latter deviation is one-half to one-quarter that obtained in commercial emulsions. Ease of finding the tracks, especially of protons, is considerably increased. The tracks of fission fragments have a characteristic appearance and are easily found amidst the faint or invisible tracks of ...