3
64 8 16
2 2 1
3.67
C
Note: Density has been reduced by a factor of 2 to represent a porous 
screen with 50% packing fraction. (i.e. 7.34/2 = 3.67 g/cm^3)

Gadolinium Oxysulfide is used as phosphor in screen-film combinations.
The phosphor is doped with Tb. The density of the crystal is 7.34 g/cm^3.

Report on thickness and coating weight vary:
    100 um thickness:
		(taken from B.A. Arnold, Physical Characteristics 
		of Screen-Film Combinations in AAPM Physics
		of Medical Imaging, 1979). 
    0.14 g/cm^2 coating weight:
		(Yip et al. SPIE 2432, 33-52)
    0.105 g/cm^2 coating weight for Alpha 8:
    0.134 g/cm^2 coating weight for lanex regular:
		( Venema at Radiology 130:765, 1979)
For 100% packing, 100 micron thickness (.01 cm) would have 0.073 g/cm^2.
Thus the above coating weight and thickness information doesn't agree.
Lanex-Regular cut from a cassette and inspected with a loupe looks to
have about a 250 micron thickness which at 100% packing would be .185 g/cm2
which suggests a packing fraction of .73 which is believable.
