Development of Nuclear Emulsion Detector for Muon Radiography

Abstract

AbstractMuon radiography is the non-destructive testing technique of large-scale constructions with cosmic ray muon. Cosmic ray muon has high penetrating power and it always comes from the whole sky. In the same way of taking a X-ray photograph, we can obtain integrated density of constructions which thickness are several tens to several hundreds. We had ever applied this technique to nuclear reactors, volcanos, and so on. Nuclear emulsion is three dimensional track detector with micrometric position accuracy. Thanks to high position resolution, Nuclear emulsion has mrad angular resolution. In addition, the features which require no power supply and can observe in a large area suitable for muon radiography. In Nagoya University, we launched emulsion manufacturing equipment at 2010. It has become possible to flexible development of our detector and succeeded to development of high sensitive nuclear emulsion film (Nagoya emulsion). An important factor is the temperature characteristic to withstand the outdoor observation as a detector to be used in the muon radiography. There is a phenomenon of a latent image fading, whichit is well known in the photographic industry, and this phenomenon is known that temperature and water are involved. So we examined temperature and humidity characteristic of latent image fading about Nagoya emulsion. As a result, we found latent image fading is strongly depends on both temperature and humidity. By dehydrating emulsion film in RH8%, over 95% (Grain Density>40) detection efficiency of muon track keeps over 3months in 25degree, for 2months in 35degree. Additionally it was showed in this test that increasing back ground noise “fog”, which may have occurred by sealing emulsion film in a narrow space, is reduced by buffer space in the bag