Progress On Scintillator Research By The Crystal Clear Collaboration
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ABSTRACT A large effort has been undertaken since nearly 2 years by 14 research institutes (the "Crystal Clear" collaboration, CERN RD project 18), in order to develop and investigate new dense, radiation hard and fast inorganic scintillators suitable for very good resolution electromagnetic calorimeters to be built at the new high luminosity accelerators. Other fields of interest like nuclear physics, gamma ray astronomy, medical imaging (PET), safety systems and non destructive industrial applications are also rapidly growing. Progress on cerium fluoride will be reviewed with some comments about mass scale production and cost considerations. The pro's and con's of potentially cheaper solutions based on fluoride glasses or lead compounds will be discussed. Finally some attractive candidates will be mentioned for low energy gamma ray applications.
INTRODUCTION The need for a new generation of scintillators becomes very acute to replace Nal, CsI and BGO crystals in many fields of basic research, like high energy physics, nuclear physics and gamma ray astrophysics. There is also a
growing interest for applications in medical imaging (PET), geological survey (well logging), airport security systems and non destructive industrial inspection systems. Unfortunately the ideal scintillator has not been found yet and the quest for it is still continuing. A few years ago CERN has initiated a large R&D effort in view of preparing the experimental program of the future Large Hadron Collider in Europe (LHC). The Crystal Clear Collaboration [1] is in charge of one of these European research and development activities. The program of the collaboration, carried out in close contact with a large number of companies and research laboratories all over the world, is to investigate new dense, radiation hard and fast inorganic scintillators to be used as the components of very good resolution electromagnetic calorimeters at the new high luminosity accelerators, as well as in the other fields mentioned above. The first task of Crystal Clear was to define the most promising research lines, depending on the application and the required performances. For High Energy Physics, an ideal calorimeter would require a dense, fast and radiation hard scintillator with a light yield comparable to the one of BGO. Cerium fluoride (CeF3) is certainly the best candidate known today in this category. If some compromise can be accepted on the light yield, potentially cheaper 51 Mat. Res. Soc. Symp. Proc. Vol. 348. 01994 Materials Research Society
solutions can be found, based either on very dense materials like lead tungstate (PbWO4) for which a significant volume reduction will be made, or on scintillating glasses for which the production cost is smaller than for crystals. On the other hand all the industrial and medical applications are dealing with low energy y rays and require therefore the maximum possible light yield, with less severe constraints on radiation hardness. Some attractive solutions recently developed by the Crystal Clear collaboratio
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