Annealing of single crystals

Abstract

The invention relates to a process for manufacturing a single crystal comprising a rare-earth halide, having improved machining or cleavage behaviour, comprising heat treatment in a furnace, the atmosphere of which is brought, for at least 1 hour, to between 0.70 times T m and 0.995 times T m of a single crystal comprising a rare-earth halide, T m representing the melting point of said single crystal, the temperature gradient at any point in the atmosphere of the furnace being less than 15 K/cm for said heat treatment. After carrying out the treatment according to the invention, the single crystals may be machined or cleaved without uncontrolled fracture. The single crystals may be used in a medical imaging device, especially a positron emission tomography system or a gamma camera or a CT scanner, for crude oil exploration, for detection and identification of fissile or radioactive materials, for nuclear and high-energy physics, for astrophysics or for industrial control.

1 - 12 . (canceled) 
     
     
         13 . Single crystal comprising a rare-earth halide that comprises a cleaved surface greater than 5 cm 2 . 
     
     
         14 . Single crystal according to  claim 13 , comprising a cleaved surface greater than 12 cm 2 . 
     
     
         15 . Single crystal according to  claim 13 , wherein it has a hexagonal crystal structure with a P6 3 /m space group, the cleaved surface corresponding to the crystallographic planes (10  1 0). 
     
     
         16 . Single crystal according to  claim 13 , wherein the single crystal has a volume greater than 1850 cm 3 . 
     
     
         17 . Single crystal comprising a rare-earth halide that comprises a machined surface greater than 5 cm 2 . 
     
     
         18 . Single crystal according to  claim 17  comprising a machined surface greater than 12 cm 2 . 
     
     
         19 . Single crystal according to  claim 17 , wherein it has a hexagonal crystal structure with a P6 3 /m space group, the cleaved surface corresponding to the crystallographic planes (10  1 0). 
     
     
         20 . Single crystal according to  claim 17 , wherein the single crystal has a volume greater than 1850 cm 3 .