Nuclear Emulsion Technique

Abstract

PHOTOGRAPHIC emulsion is merely, as Yagodã~~h as put it, "a cleverly contrived mixture of silver bromide dispersed in an extract of cowhide. " Nuclear emulsions are photographic emulsions of very high silver concentration that are thickly coated on glass backings. Ionizing particles which happen to pass through such emulsions leave behind a number of silver bromide crystals that have been so altered that, upon development, they appear as rows of black grains of colloidal silver and identify the trajectories of thẽ The preparation of this paper was assisted in part by the joint program of the ONR and AKC.particles. The more strongly ionizing the particles, the more numerous are these grains; and the greater their initial energies, the longer the resulting tracks. Relationships exist which connect these quantities very accurately, enabling the identification of the involved particle and its energy under favorable circumstances. More elaborate methods, for example, those making use of the multiple small-angle scattering of light particles, can be used in the event that range and grain density measurements are not adequate in a particular case. Auxiliary techniques, such as those utilizing the deQection of charged particles in an intense magn. etic field, are frequently of value in specialized applications.The first use of photographic emulsions in recording particle tracks was made by Reinganumt (1911), who found that alpha-particles could render developable several of the silver bromide grains along their paths in an emulsion. His work, which occurred at about the same time that C. T. R. Wilson successfully photographed cloud-chamber tracks, was based in part upon the discovery the previous year (Kinoshita, 1910) that alpha-particles could produce developability in individual bromide grains. Michl (1912) performed the first quantitative evaluations of these alpha-particle tracks. It was not until 1925 that proton tracks were observed in an emulsion, this having been accomplished by M. Blau (1925), who, with H. Wambacher, did much of the pioneering research in nuclear emulsions. The early history of the photographic detection of nuclear particles was outlined by Shapiro (1941).Emulsions manufactured especially for these purposes were introduced by Ilford Ltd. , the first being the R1 plates sensitive only to alpha-particles, which were followed by the R2 plates that could record low energy proton tracks (Taylor, 1935) and the even more sensitive "Halftone" emulsions. The performance of the Ilford series was improved upon by Agfa with their K plates (Wambacher, 1939). Eastman Kodak, in collaboration with T. R. Wilkins, produced the "Fine Grain Alpha-Plates" at about this same time.During and since the war enormous advances have been made in nuclear emulsion manufacture and techniques, to a great extent the result of the eBorts of C. F. Powell of the University of Bristol and his coworkers. The development by Kodak Ltd. in 1948 of the NT4 emulsions, sensitive to all charged particles regardless of energy, and the di...

Event-by-event pseudo-rapidity fluctuations in high energy nucleus–nucleus interactions

“…The background tracks can arise due to the decay of radioactive contamination, such as thorium present both in emulsion and in their glass backings [58]. Some of such tracks may also be caused by the cosmic radiations during the time of exposure.…”

Projectile fragmentation of relativistic nuclei in peripheral collisions

“…Systematic uncertainties may also be introduced due to the presence of background tracks in nuclear emulsion detector. The background tracks can arise due to the decay of radioactive contamination, such as thorium present both in emulsion and in their glass backings [44]. Some of such tracks may also be caused by the cosmic radiations during the time of exposure.…”

Photoproduction ofπ0Mesons in Hydrogen

“…40 Pellicles that received a dosage of 300 mr were transparent, while proton tracks up to 70 Mev were clearly visible in them. The highest proton energy of interest was less than 45 Mev.…”