Status of Cerium Fluoride Performances
- PDF / 419,064 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 116 Downloads / 209 Views
E.AUFFRAY* I. DAFINEI*, P. LECOQ*, M. SCHNEEGANS** *CERN, Geneva, Switzerland **LAPP, Annecy, France
ABSTRACT: Cerium fluoride offers a reasonable compromise between parameters like the density, the light yield, the scintillation characteristics (particularly the decay time) and the radiation hardness, and is considered today as the best candidate for large electromagnetic calorimeters in future High Energy Physics experiments. Details on the performances of large crystals produced by different manufacturers all over the world and measured by the Crystal Clear collaboration will be shown and the usefulness of a good collaboration between the industry and the users will be highlighted by some examples on the light yield and radiation hardness improvement.
INTRODUCTION: Cerium fluoride (CeF 3 ) is currently one of the best candidate for large electromagnetic calorimeters in High Energy Physics experiments. The reasons are its high density (6.16g/cm3), short radiation length (1.68cm), small Moliire radius (2.6cm) and fast luminescence in the near UV [1,2]. Since 1991, the Crystal Clear Collaboration has undertaken a precise evaluation of the properties of CeF 3 [3]. This work was carried out in close collaboration with experts in different fields as well as several crystal growth companies. In few years only, the number of companies involved in this development grew from one (OPTOVAC) to eight, the size of the crystals increased from a few cm3 to more than 150cm3, and the crystal quality has improved dramatically. This paper will give a summary of the CeF 3 properties studied by the Crystal Clear Collaboration on more than 200 crystals with dimensions ranging from 1 to 150cm3. We particularly focus on spectroscopic properties as well as on performance under radiation.
TRANSMISSION PROPERTIES: Thanks to an important effort in the preparation of the raw material (and particularly in the reduction of oxygen contamination), long and scatter free undoped CeF3 crystals are currently available with an initial longitudinal transmission very close to the theoretical transmission. Moreover the very small observed dispersion of less than nmm of the position of the optical absorption edge shows that the quality of crystals is now well controlled all along the crystal (Figla). This homogeneity represents an important improvement as compared to the previous undoped crystals 111 Mat. Res. Soc. Symp. Proc. Vol. 348. 01994 Materials Research Society
where a dispersion of the optical absorption edge was observed along the crystal with a red shift on the seed side (Figlb). This fact has been attributed to the presence of oxygen, difficult to suppress in fluorides. Measurements of concentration of oxygen in different parts of crystals show that it is always higher near the seed (this fact is in agreement with the value of the coefficient segregation of oxygen in CeF 3 , superior to 1). Indeed oxygen in the 02- form favours the creation of fluorine vacancies and the optical absorption edge position is strongly coupled to their densit
Data Loading...
