The Study of Neutrino Oscillations with Emulsion Detectors

Abstract

Particle detectors based on nuclear emulsions contributed to the history of physics with fundamental discoveries. The experiments benefited from the unsurpassed spatial and angular resolution of the devices in the measurement of ionizing particle tracks and in their identification. Despite the decline of the technique around the 1970’s caused by the development of the modern electronic particle detectors, emulsions are still alive today thanks to the vigorous rebirth of the technique that took place around the beginning of the 1990’s, in particular due to the needs of neutrino experiments. This progress involved both the emulsion detectors themselves and the automatic microscopes needed for their optical scanning. Nuclear emulsions have marked the study of neutrino physics, notably in relation to neutrino oscillation experiments and to the related first detection of tau-neutrinos. Relevant applications in this field are reviewed here with a focus on the main projects. An outlook is also given trying to address the main directions of the R&D effort currently in progress and the challenging applications to various fields.

Nuclear emulsions for the detection of micrometric-scale fringe patterns: an application to positron interferometry

“…Nuclear emulsions are composed of silver-bromide microcrystals with a diameter of approximately 0.2 µm, embedded in a gelatin matrix. The latent image left by the passage of ionizing particles is developed via a chemical process to silver grains approximately 1 µm in diameter, visible through an optical microscope (see [11] for a review of the technology). The emulsion gel used in this work was produced at the Nagoya University in Japan.…”

Detection of low energy antimatter with emulsions

“…The passage of ionizing radiation across a crystal produces a latent image which, after a chemical development process, leads to the creation of a ∼ 1 µm silver grain visible by means of an optical microscope. A review on the technology can be found in [1].…”

“…A sketch of the experimental setup1 Referring to the emulsions produced by the Fuji company in Japan for the OPERA neutrino experiment with a silver bromide content of ∼30% and a background of ∼3 grains/1000 µm 3 .…”

Extra-large crystal emulsion detectors for future large-scale experiments

“…Emulsion detectors consist of silver halide (AgX) crystals homogeneously dispersed in a gelatin support, whose standard size is about 200 nm. Each crystal acts as an independent charged particle detector and a particle track is made visible after the chemical development under an optical microscope in terms of metallic silver filaments (for a review on the technique, see [1]). Briefly, as far as the emulsion production is concerned, a gel with silver halide crystals is the result of a double decomposition reaction between water-soluble silver salt and water-soluble halide salt to form insoluble AgX grains in an aqueous gelatin solution [12].…”