analysing plates exposed at the Sphinx Observatory on the Jungfraujoch in Switzerland, first precise observations of the positive K-meson and its ‘strange’ decays were made by Rosemary Brown, a research student in Cecil Powell’s group at Bristol. Then known as the ‘Tau meson’ in the Tau-theta puzzle, precise measurement of these K-meson decay modes led to the introduction of the quantum concept of Strangeness and to the discovery of Parity violation in the weak interaction. Rosemary Brown called the striking four-track emulsion image, of one 'Tau' decaying to three charged pions, her "K track", thus effectively naming the newly discovered ‘strange’ K-meson. Cecil Powell was awarded the 1950 Nobel Prize in Physics "for his development of the photographic method of studying nuclear processes and his discoveries regarding mesons made with this method". The emergence of new particle detector and particle accelerator technologies, coupled with the disadvantages noted in the introduction, led to a decline in use of Nuclear Emulsion plates in Particle Physics towards the end of the 20th century. However there remained a continuing use of the method in the study of rare interactions and decay processes. More recently, searches for "Physics beyond the Standard Model", in particular the study of neutrinos and dark matter in their exceedingly rare interactions with normal matter, have led to a revival of the technique. Examples are the OPERA experiment, studying neutrino oscillations at the Gran Sasso Laboratory in Italy, and the FASER experiment at the CERN LHC, which will search for new, light and weakly interacting particles including dark photons. Other applications There exist a number of scientific and technical fields where the ability of nuclear emulsion to accurately record the position, direction and energy of electrically charged particles, or to integrate their effect, has found application. These applications in most cases involve the tracing of implanted radioactive markers by Autoradiography. Examples are: Medical research Biological research Metallurgy Reactive surface chemistry Radiation protection Muon tomography (Muography) Archaeology. References External links Nuclear emulsions by Ilford Particle detectors Nuclear physics