This involved analysing the darkening of photographic plates caused by irradiation with the alpha rays. In 1905 he was using commercially available photographic plates to continue his research into the properties of the recently discovered alpha rays produced in the radioactive decay of some atomic nuclei. History įollowing the 1896 discovery of radioactivity by Henri Becquerel using photographic emulsion, Ernest Rutherford, working first at McGill University in Canada, then at the University of Manchester in England, was one of the first physicists to use that method to study in detail the radiation emitted by radioactive materials. ![]() For an extensive review of the history and wider scientific context of the nuclear emulsion method, refer to the book by Galison. However there remains a continuing use of the method in the study of rare processes and in other branches of science, such as autoradiography in medicine and biology.įor a comprehensive and technically detailed account of the subject refer to the books by Barkas and by Powell, Fowler and Perkins. These disadvantages, coupled with the emergence of new particle detector and particle accelerator technologies, led to a decline in use of nuclear emulsion plates in particle physics towards the end of the 20th century. Finally, the development and scanning of large volumes of emulsion, to obtain useful, 3-dimensional digitised data, is a slow and labour intensive process. The chief disadvantage of nuclear emulsion is that it is a dense and complex material ( silver, bromine, carbon, nitrogen, oxygen) which potentially impedes the flight of particles to other detector components through multiple scattering and ionising energy loss. These features were decisive in enabling the high-altitude, mountain and balloon based studies of cosmic rays that led to the discovery of the pi-meson and parity violation in K-meson decays shedding light on the true nature and extent of the subnuclear " particle zoo", defining a milestone in the development of modern experimental particle physics. It is compact, with no associated read-out cables or electronics, allowing the plates to be installed in very confined spaces and, compared to other detector technologies, is significantly less expensive to manufacture, operate and maintain. In addition, the emulsion plate is an integrating device that can be exposed or irradiated until the desired amount of data has been accumulated. A stack of emulsion plates can record and preserve the interactions of particles so that their trajectories are recorded in 3-dimensional space as a trail of silver-halide grains, which can be viewed from any aspect on a microscopic scale. ![]() It has the advantage of extremely high spatial precision, limited only by the size of the silver halide grains (a few microns), a precision that surpasses even the best of modern particle detectors (observe the scale in the image below, of K-meson decay). The nuclear emulsion plate is a modified form of photographic plate, coated with a thicker photographic emulsion of gelatine containing a higher concentration of very fine silver halide grains the exact composition of the emulsion being optimised for particle detection. After exposing and developing the emulsion, single particle tracks can be observed and measured using a microscope. It is a modified form of photographic plate that can be used to record and investigate fast charged particles like alpha-particles, nucleons, leptons or mesons. A nuclear emulsion plate is a type of particle detector first used in nuclear and particle physics experiments in the early decades of the 20th century.
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