Light Collection Enhancement Analysis for Digital X-Ray Detector Using Gd2O2S:Tb and CsI:Tl Phosphors in Nanoscale Treatment - Atomic Nanoscale Technology in the Nuclear Industry - page 70

TABLE 6.1
Phosphor.Data.List.by.Exponential.Functions

Energy
(kVp)

Thickness
(µm;mg/cm 2 )

FWHM
(µm)

MTF
(ExponentialFunction)

(a)Gd 2 O 2 S:Tb
. 25
. 26
. 27

48;.35
46;.34
46;.34
82;.60

20.96
50.54
42.60
92.08

y =0.5084.exp(−0.087800χ)+0.5476exp(−0.087755χ)
y =0.5246.exp(−0.196500χ)+0.5331exp(−0.196400χ)
y =0.5954.exp(−0.166400χ)+0.5251exp(−0.166400χ)
y =0.5160.exp(−0.373300χ)+0.4996exp(−0.372800χ)

. 28
. 30
. 90

40;.29
44;.32
68;.50
68;.50

36.81
27.40
37.58
38.31

y =0.5613.exp(−0.153900χ)+0.5337exp(−0.154000χ)
y =0.4926.exp(−0.084820χ)+0.5579exp(−0.084490χ)
y =0.5111.exp(−0.153400χ)+0.5568exp(−0.153700χ)
y =0.5117.exp(−0.157000χ)+0.5212exp(−0.156800χ)

109;.80 51.48 y =0.4813.exp(−0.212198χ)+0.5314exp(−0.212043χ)

(b)CsI:Tl
. 20 a
. 35 a
. 50 a
. 30

150;.68
150;.68
150;.68
150;.68

24.98
29.79
30.68
38.03

y =0.0995.exp(−0.652700χ)+0.9001exp(−0.094440χ)
y =0.3429.exp(−0.577000χ)+0.6571exp(−0.105000χ)
y =0.2790.exp(−0.535900χ)+0.7207exp(−0.096730χ)
y =0.5691.exp(−1.011000χ)+0.4307exp(−0.119900χ)

200 147;.47

. 299;.135

29.64
41.38

y =0.4726.exp(−0.121500χ)+0.5069exp(−0.121400χ)
y =0.1424.exp(−65.75000 χ )+0.8576exp(−0.143400 χ )

a. 20,.35,.50.are.units.of.keV.

Gd 2 O 2 S..CsI.shows.a.much.narrower.shape.compared.to.Gd 2 O 2 S..The. modu-
lation transfer function .(MTF).is.obtained.by.experimental.data.(Bunch.1997;.
Cavouras.et.al..1998;.Jing.et.al..1999;.Kandarakis.et.al..1997a,.1997b;.Nagarkar.
et.al..1996,.1998;.Sabol.and.Boon.1997;.Yu.et.al..1997)..MTFs.are.formulated.
using. exponential. functions,. which. are. shown. in. Table 6.1.. The. MTF. is.
changed.to.a.line.spread.function.(LSF).using.the.inverse.Fourier.transform.
(Bracewell. 2000). and. the. LSF. is. also. converted. to. a. PSF. using. the. inverse.
Abel. transform. in. Figure 6.4.. Table 6.2. shows. the. full. width. at. half. maxi-
mum.(FWHM).of.PSF..Using.these.properties,.the.light.collection.eficiency.
is.obtained..In.the.calculations,.the.geometries.are.classiied.as.Lambertian.
and.isotropic.methods.(Maidment.and.Yaffe.1995)..So,.this.method.simulates.
how.the.digital.imager.coniguration.collects.light..The.Lambertian.quanta.
are.calculated.by

π

E , 0 ≤ ≤ θ

( ) =

o

2

.. E θ φ , . (6.1)

Lamb

0 , otherwise