FLUORESCENT COMPOSITIONS, X-RAY INTENSIFYING SCREENS, AND PROCESSES FOR MAKING SAME

COMPOSES FLUORESCENTS, ECRANS INTENSIFIANT LES RAYONS X ET METHODE DE FABRICATION DE CES COMPOSES ET ECRANS

English Abstract

Abstract of the Disclosure
An x-ray intensifying screen comprises a support
having thereon a fluorescent composition comprising:
a) from 50 to 90 percent by weight of a substantially
isotropic phosphor which 15 excited by x-rays
and substantially transparent to light emitted
by said phosphor; and
b) from 13 to 50 percent by weight of a polymer
having an index of refraction within .02 of
the index of refraction of said phosphor over
at least 80 percent of the omission spectrum
of said phosphor, said support having an index
of refraction up to or equal to 0.05 units
higher than the index of refraction of said
phosphor and having a reflection optical density
of at least 1.7 to light emitted by said phosphor.
The screen is highly transparent, and further
exhibits improved contrast and resolution. A preferred
fluorescent composition useful in the x-ray intensifying
screen comprises:
a) from 50 to 93 percent by weight of a substantially
isotropic phosphor which is excited by x-rays
and substantially transparent to light emitted by
said phosphor; and
b) from 10 to 50 percent by weight of a polymer
having an index of refraction within .02
of the index of refraction of said phosphor
over at least 80 percent of the emission
spectrum of said phosphor, said polymer com-
prising:
i) from 5 to 99 mole percent of recurring
units having the formula:
<IMG>

wherein:
R1 is H or alkyl; and
R2 is alkyl, cycloalkyl, aryl, aralkyl
or aryl substituted with alkyl, alkoxy
or heterocyclic; and
ii) from 1 to 95 mole percent of recurring units
having the formula:
<IMG>
wherein:
Ar is arylene;
R1 is H or alkyl;
R3 is H, alkyl, aryl, or aralkyl; and
R4 is H, alkyl, alkoxy, amino, halogen,
sulfide, sulfoxide, sulfonate or
heterocyclic.

Claims

-26-
CLAIMS
1. A fluorescent composition comprising:
a) from 50 to 90 percent by weight of a substantially
isotropic phosphor which is excited by x-rays
and substantially transparent to light emitted
by said phosphor; and
b) from 10 to 50 percent by weight of a polymer
having an index of refraction within .02 of
the index of refraction of said phosphor over
at least 80 percent of the emission spectrum of
said phosphor, said polymer comprising:
i) from 5 to 99 mole percent of recurring units
having the formula:
<IMG>
wherein
R1 is H or alkyl; and
R2 is alkyl, cycloalkyl, aryl, aralkyl or
aryl substituted with alkyl, alkoxy, or
heterocyclic; and
ii) from 1 to 95 mole percent of recurring units
having the formula:
<IMG>
wherein:
Ar is arylene;
R1 is H or alkyl;
R3 is H, alkyl, aryl, or aralkyl; and
R4 is H, alkyl, alkoxy, amino, halogen,
sulfide, sulfoxide, sulfonate or heterocyclic.

-27-
2. The fluorescent composition of claim 1 wherein
said phosphor is an alkali metal compound.
3. The fluorescent composition of claim 1 wherein
said phosphor is selected from the group consisting of
RbI:Tl and KI:Tl.
4. A fluorescent coating composition comprising:
a) from 50 to 90 percent by weight of a substan-
tially isotropic phosphor which is excited by x-rays
and substantially transparent to light emitted by
said phosphor; and
b) from 10 to 50 percent by weight of a polymer
having an index of refraction within .02 of the index
of refraction of said phosphor over at least 80 per-
cent of the emission spectrum of said phosphor, said
polymer comprising:
i) from 5 to 99 mole percent of a polymerized co-
polymerizable naphthyl carbinyl methacrylate
monomer; and
ii) from 1 to 95 mole percent of a polymerized co-
polymerizable naphthyl carbinyl thioacrylate
monomer.
5. The fluorescent composition of claim 4 wherein
said phosphor is an alkali metal compound.
6. The fluorescent composition of claim 4 wherein
said phosphor is selected from the group consisting of RbI:Tl
and KI:Tl.
7. A fluorescent composition comprising:
a) from 50 to 90 percent by weight of a substantially
isotropic alkali metal phosphor which is excited
by x-rays and substantially transparent to light
emitted by said phosphor; and
b) from 10 to 50 percent by weight of a polymer
having an index of refraction within .02 of
the index of refraction of said phosphor over
at least 80 percent of the emission spectrum
of said phosphor, said polymer comprising:

-28-
i) from 5 to 99 mole percent of recurring units
having the formula:
<IMG>
; and
ii) from 1 to 95 mole percent of recurring units
having the formula:
<IMG>
8. The fluorescent composition of claim 7 wherein
said phosphor is selected from the group consisting of RbI:Tl
and KI:Tl.
9. In an x-ray intensifying screen comprising a
support having thereon a fluorescent composition comprising at
least one substantially isotropic phosphor which is excited by
x-rays and substantially transparent to light emitted by said
phosphor in a polymer having an index of refraction within .02
of the index of refraction of said phosphor over at least 80
percent of the emission spectrum of said phosphor, and wherein
said support has an index of refraction up to or equal to 0.05
units higher than the index of refraction of said phosphor
and a reflection optical density of at least 1.7 to light
emitted by said phosphor.
10. The x-ray intensifying screen of claim 9 wherein
said phosphor is an alkali metal compound.
11. The x-ray intensifying screen of claim 10 wherein
said phosphor is selected from the group consisting of RbI:.Tl
and KI:Tl.

-29-
12. The x-ray intensifying screen of claim 9
wherein said support comprises a black anodized aluminum
surface.
13. An x-ray intensifying screen comprising a
support having thereon a fluorescent composition comprising:
a) from 50 to 90 percent by weight of a substan-
tially isotropic phosphor which is excited by
x-rays and substantially transparent to the light
emitted by said phosphor; and
b) from 10 to 50 percent by weight of a polymer
having an index of refraction within .02 of the
index of refraction of said phosphor over at
least 80 percent of the emission spectrum of
said phosphor, said polymer comprising:
i) from 5 to 100 mole percent of a polymerized
copolymerizable ethylenically unsaturated
monomer; and
ii) from 0 to 95 mole percent of recurring units
having the formula:
<IMG>
wherein:
Ar is arylene;
R1 is H or alkyl;
R3 is H, alkyl, aryl, or aralkyl; and
R4 is H, alkyl, alkoxy, amino, halogen,
sulfide, sulfoxide, sulfonate or heterocyclic;
said support having an index of refraction equal to or up to
0.05 units higher than the index of refraction of said phosphor,
and having a reflection optical density of at least 1.7 to
light emitted by said phosphor.

-30-
14. The x-ray intensifying screen of claim 13
wherein said phosphor is an alkali metal compound.
15. The x-ray intensifying screen of claim 14
wherein said phosphor is selected from the group consisting
of RbI:Tl and KI:Tl.
16. The x-ray intensifying screen of claim 13
wherein said support comprises a black anodized aluminum
surface.
17. An x-ray intensifying screen comprising a
support having thereon a fluorescent composition comprising:
a) from 50 to 90 percent by weight of a substan-
tially isotropic phosphor which is excited by
x-rays and substantially transparent to the light
emitted by said phosphor; and
b) from 10 to 50 percent by weight of a polymer
having an index of refraction within .02 of
the index of refraction of said phosphor over
at least 80 percent of the emission spectrum
of the phosphor, said polymer comprising:
i) from 5 to 100 mole percent of recurring
units having the formula:
<IMG>
wherein:
R1 is H or alkyl; and
R2 is alkyl, cycloalkyl, aryl, aralkyl-
or aryl substituted with alkyl, alkoxy
or heterocyclic; and
ii) from 0 to 95 mole percent of recurring units
having the formula:
<IMG>

-31-
wherein:
Ar is arylene;
R1 is H or alkyl;
R3 is H, alkyl, aryl, or aralkyl; and
R4 is H, alkyl, alkoxy, amino, halogen,
sulfide, sulfoxide, sulfonate or heterocyclic;
said support having an index of refraction equal to or up to
0.05 units higher than the index of refraction of said phosphor,
and having a reflection optical density of at least 1.7 to
light emitted by said phosphor.
18. The x-ray intensifying screen of claim 17
wherein said phosphor is an alkali metal compound.
19. The x-ray intensifying screen of claim 18
wherein said phosphor is selected from the group consisting of
RbI:Tl and KI:Tl.
20. The x-ray intensifying screen of claim 17
wherein said support comprises a black anodized aluminum surface.
21. An x-ray intensifying screen comprising a
support having thereon a fluorescent composition comprising:
a) from 50 to 90 percent by weight of a substan-
tially isotropic phosphor which is excited by
x-rays and substantially transparent to light
emitted by said phosphor; and
b) from 10 to 50 percent by weight of a polymer
having an index of refraction within .02 of the
index of refraction of said phosphor over at
least 80 percent of the emission spectrum of the
phosphor, said polymer comprising:
i) from 5 to 100 mole percent of polymerzied
co-polymerizable naphthyl carbinyl meth-
acrylate monomer; and
ii) from 0 to 95 mole percent of a polymerized
copolymerizable naphthyl carbinyl thioacrylate
monomer;

-32-
said support having an index of refraction equal to or up
to 0.05 units higher than the index of refraction of said
phosphor and having a reflection optical density of at least
1.7 to light emitted by said phosphor.
22. The x-ray intensifying screen of claim 21
wherein said phosphor is an alkali metal compound.
23. The x-ray intensifying screen of claim 22
wherein said phosphor is selected from the group consisting
of RbI:Tl and KI:Tl.
24. The x-ray intensifying screen of claim 21 wherein
said support comprises a black anodized aluminum surface.
25. An x-ray intensifying screen comprising a
support having thereon a fluorescent composition comprising:
a) from 50 to 90 percent by weight of a substan-
tially isotropic alkali metal phosphor which is
excited by x-rays and substantially transparent
to light emitted by said phosphor; and
b) from 10 to 50 percent by weight of a polymer
having an index of refraction without .02 of
the index of refraction of said phosphor over
at least 80 percent of the emission spectrum
of said phosphor, said polymer comprising:
i) from 5 to 100 mole percent of a polymerized
copolymerizable naphthyl carbinyl meth-
acrylate monomer; and
ii) from 0 to 95 mole percent of a polymerized
copolymerizable naphthyl carbinyl thio-
acrylate monomer;

-33-
said support comprising a black anodized aluminum surface
having an index of refraction equal to or up to 0.05 units
higher than the index of refraction of said phosphor and having
a reflection optical density of at least 1.7 to light emitted
by said phosphor.
26. The x-ray intensifying screen of claim 25 wherein
said phosphor is selected from the group consisting of RbI:Tl
and KI:Tl.
27. The x-ray intensifying screen of claim 25 wherein
said naphthyl carbinyl methacrylate monomer is 1-naphthyl
carbinyl methacrylate and wherein said naphthyl carbinyl
thioacrylate monomer is S-(1-naphthyl carbinyl)-thioacrylate.
28. An x-ray intensifying screen comprising a support
having thereon a fluorescent composition comprising:
a) from 50 to 90 percent by weight of a substantially
isotropic alkali metal phosphor which is excited
by x-rays and substantially transparent to light
emitted by said phosphor, selected from the group
consisting of RbI:Tl and KI:Tl; and
b) from 10 to 50 percent by weight of a polymer
having an index of refraction within .02 of
the index of refraction of said phosphor over
at least 80 percent of the emission spectrum of
said phosphor, said polymer comprising:
i) from 5 to 100 mole percent of polymerized
1-naphthyl carbinyl methacrylate monomer; and
ii) from 0 to 95 mole percent of polymerized
S-(1-naphthyl carbinyl) thioacrylate monomer;
said support comprising a black anodized aluminum surface
having an index of refraction equal to or up to 0.05 units
higher than the index of refraction of said phosphor and having
a reflection optical density of at least 1.7 to light emitted
by said phosphor.

-34-
29. A process for making an x-ray intensifying
screen comprising the steps of:
a) coating a mixture comprising:
i) from 50 to 90 percent by weight of a
substantially isotopic phosphor which is
excited by x-rays and substantially trans-
parent to light emitted by said phosphor;
and
ii) from 10 to 50 percent by weight of at least
one copolymerizable monomer or mixture of
monomers, said monomer or mixture of monomers,
when polymerized, having an index of re-
fraction within .02 of the index of refraction
of said phosphor over at least 80 percent of
the emission spectrum of said phosphor,
on a support having an index of refraction
equal to or up to 0.05 units higher than the
index of refraction of said phosphor and
having a reflection optical density of at least
1.7 to light emitted by said phosphor; and
b) polymerizing said mixture coated on said support
to produce a polymer comprising recurring units
of said monomer or monomer mixture.
30. The process of claim 29 wherein said phosphor
is an alkali metal compound.
31. The process of claim 30 wherein said phosphor
is selected from the group consisting of RbI:Tl and KI:Tl.
32. The process of claim 29 wherein said support
comprises a black anodized aluminum surface.
33. The process of claim 29 wherein said mixture
further comprises from .001 to 1.0 percent of weight of a
photoinitiator.
34. The process of claim 29 wherein said poly-
merization step (b) is effected by irradiation with near-
ultraviolet light.

-35-
35. A process for making an x-ray intensifying
screen comprising the steps of:
a) coating a mixture comprising:
i) from 50 to 90 percent by weight of a
substantially isotropic phosphor which is
excited by x-rays and substantially trans-
parent to light emitted by said phosphor; and
ii) from 10 to 50 percent by weight of at least
one copolymerizable monomer or mixture of
monomers, said monomer or mixture of
monomers, when polymerized, having an
index of refraction within .02 of the
index of refraction of said phosphor
over at least 80 percent of the emission
spectrum of said phosphor, said monomer
or mixture of monomers comprising from 5
to 100 mole percent of a copolymerizable
ethylenically unsaturated monomer, and
from 0 to 95 mole percent of units having
the formula:
<IMG>
wherein:
Ar is arylene;
R1 is H or alkyl;
R3 is H, alkyl, aryl, or aralkyl; and
R4 is X, alkyl, alkoxy, amino, halogen,
sulfide, sulfoxide, sulfonate or hetero-
cyclic,
on a support having an index of refraction equal
to or up to 0.05 units higher than the index of
refraction of said phosphor, and having a
reflection optical density of at least 1.7 to
light emitted by said phosphor; and
b) polymerizing said mixture coated on said support
to produce a polymer comprising recurring units
of said monomeror monomer mixture.

-36-
35. The process of claim 35 wherein said phosphor
is an alkali metal compound.
37. The process of claim 36 wherein said phosphor
is selected from the group consisting of RbI:Tl and KI:Tl.
38. The process of claim 35 wherein said support
comprises a black anodized aluminum surface.
39. The process of claim 35 wherein said poly-
merization step (b) is effected by irradiation with near-
ultraviolet light.
40. The process of claim 35 wherein said mixture
further comprises from .001 to 1.0 percent by weight of a
photoinitiator.
41. A process for making an X-ray intensifying
screen comprising the steps of:
a) coating a mixture comprising:
i) from 50 to 90 percent by weight of a sub-
stantially isotropic phosphor which is
excited by x-rays and substantially trans-
parent to light emitted by said phosphor;
and
ii) from 10 to 50 percent by weight of at least
one copolymerizable monomer or mixture of
monomers, said monomer or mixture of monomers,
when polymerized, having an index of refraction
within .02 of the index of refraction of
said phosphor over at least 80 percent of
the emission spectrum of said phosphor,
said monomer or mixture of monomers comprising
from 5 to 100 mole percent of units having
the formula:
<IMG>
wherein:
R1 is H or alkyl; and
R2 is alkyl, cycloalkyl, aryl, aralkyl,
or aryl substituted with alkyl, alkoxy
or heterocyclic; and from 0 to 95 mole
percent of units having the formula:

-37-
<IMG>
wherein:
Ar is arylene;
R1 is H or alkyl;
R3 is H, alkyl, aryl, or aralkyl; and
R4 is H, alkyl, alkoxy, amino, halogen,
sulfide, sulfoxide, sulfonate or
heterocyclic;
on a support having an index of refraction
equal to or up to 0.05 units higher than the
index of refraction of said phosphor and
having a reflection optical density of at
least 1.7 to light emitted by said phosphor 7
and
b) polymerizing said mixture coated on said
support to produce a polymer comprising
recurring units of said monomers or monomer
mixture.
42. The process of claim 41 wherein said phosphor
is an alkali metal compound.
43. The process of claim, 42 wherein said phosphor
is selected from the group consisting of RbI:Tl and KI:Tl.
44. The process of claim 41 wherein said support
comprises a black anodized aluminum surface.
45. The process of claim 41 wherein said poly-
merization step (b) is effected by irradiation with near-
ultraviolet light.
46. The process of claim 41 wherein said mixture
further comprises from .001 to 1.0 percent by weight of a
photoinitiator.
47. A process for making an x-ray intensifying
screen comprising the steps of:
a) coating a mixture comprising:
i) from 50 to 90 percent by weight of a sub-
stantially isotropic alkali metal phosphor
which is excited by x-rays and substantially
transparent to light emitted by said phosphor;
and

-38-
ii) from 10 to 50 percent by weight of at least
one copolymerizable monomer or mixture of
monomers, said monomer or mixture of monomers,
when polymerized, having an index of refrac-
tion within .02 of the index of refraction
of said phosphor over at least 80 percent of
the emission spectrum of said phosphor, said
monomer or mixture of monomers comprising
from 5 to 100 mole percent of a naphthyl
carbinyl methacrylate monomers and from 0
to 95 mole percent of a naphthyl carbinyl
thioacrylate monomer; and
iii) from .001 to 1.0 percent by weight of a
photoinitiator;
on a support having an index of refraction equal to
or up to 0.05 units higher than the index of
refraction of said phosphor and having a reflection
optical density of at least 1.7 to light emitted
by said phosphor; and
b) irradiating said mixture coated on said support
with near-ultraviolet light.
48. The process of claim 47 wherein said phosphor
is selected from the group consisting of RbI:Tl and XI:Tl.
49. The process of claim 47 wherein said support
comprises a black anodized aluminum surface.
50. The process of claim 47 wherein said naphthyl
carbinyl methacrylate monomer comprises 1-naphthyl carbinyl
methacrylate and said naphthyl carbinyl thioacrylate mono-
mer comprises S-(1-naphthyl carbinyl) thioacrylate.
51. The process of claim 47 wherein said photo-
initiator is 4,4'-bis-chloromethyl benzophenone.
52. A process for making an x-ray intensifying
screen comprising the steps of:
a) coating a mixture comprising:
i) from 50 to 90 percent by weight of a sub-
stantially isotropic alkali metal phosphor
which is excited by x-rays and substantially
transparent to light emitted by said phosphor;
and

-39-
ii) from 10 to 50 percent by weight of at least
one copolymerizable monomer or mixture of
monomers, said monomer or mixture of monomers;
when polymerized, having an index of re-
fraction within .02 of the index of re-
fraction of said phosphor over at least
80 percent of the emission spectrum of said
phosphor, said monomer or mixture Or monomers
comprising from 5 to 100 mole percent of 1-
naphthyl carbinyl methacrylate and from 0 to
95 mole percent of S-(1-naphthyl carbinyl)
thioacrylate; and
iii) from .001 to 1.0 percent by weight of a
photoinitiator,
on a black anodized aluminum support having an
index of refraction equal to or up to 0.05 units
higher than the index of refraction of said
phosphor and having a reflection optical density
of at least 1.7 to light emitted by said phosphor;
and
b) irradiating said mixture coated on said support
with near-ultraviolet light.
53. The process of claim 52 wherein said photo-
initiator is 4,4'-bis-chloromethyl benzophenone.

Description

v~
--1--
FLUORESCENT COM~OSITIONS, X-RAY INTENSIFYING
SCREENS, AND PROCESSES FOR MAKING SAME
.
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to transparent x-ray
intensifying screens and processes for making x-ray intensifying
screens for use in radiography, and to fluorescent compositions
comprising anlsotropic phosphor transparent to x-rays and a
polymeric binder.
10 Description Relative to the Prior Art
Transparent x-ray screens comprising alkali halide,
alkaline earth halide, meta] sulfide, and metal selenide phosphors
have been prepared by various methods. These transparent screens
have been shown to be desirable, because they make moxe efficient
use of impinging x-ray radiation than thick conventional scatter-
ing screens, which ~<waste a material amount of the radiation
in diffusion of the light emitted near the back of the screen
and internal absorption. Thick transparent screens, having a
decreased number of reflections permit this light to reach the
20 front surface of the screen with minimal deflection and to form
a sharper image on the photographic film in contact with the
screen~ A greater proportion of the x ray energy, absorbed by
the phosphor and converted to light, is utilized in producing
images without loss of sharpness.
Thin transparent screens, prepared by vapor-
deposition and containing only a phosphor, have also been made
and exhibit lower speeds than scattering screens with equal
phosphor coverage. Further, lacking a protective binder, these
transparent screens are fragile and highly susceptible to
30 physical damage~ Thicker screens have been made by hot pressing
but other defects in the manufacture of these large plates
render them expensive to prepare.
~$~

U.S. Patent No 3,023,313, issued February 27,
1962 to De La Mater et al discloses the use of a polymeric
binder with a refractive index as close to -that of an alkali
metal halide phosphor as possible in order to produce x-ray
intensifying screens with improved speed. However, because
of substantial differences between the refractive index of
selected binders and the refractive index of the phosphor,
reflecting pigments must be added to the mixture to prevent
blurring of the image and improve resolution. Thus, these
screens are not truly transparent to light, and some decrease
in utilization of absorbed x-rays is observed. The screens of
De La Mater comprise a support preferably having a highly
reflective base coating.
Swank, Applied Optics, 12, 1865-1870 ~1973)
describes the theoretical calculation of modulation transfer
function (MTF), related to resolving power, of x-ray intensifying
screens comprising transparent phosphors and a black backing.
Swank discloses that although the Ml'F :is enhanced when a black
backing is used, 50% of the exposing radiation is absorbed by
the backing. Thus, the speed of the x--ray intensifying screen
is reduced.
Gasper, J. Opt. Soc. Am., 63, 71~-720 (1973)
describes the computation of theoretical efficiencies and MTFs
of various screen-receiver systems, and reports that if a dark
antihalation undercoat is applied to the back surface of a
transparent screen, the MTF is only slightly improved If, on
the other hand, the back surface is made perfectly reflecting,
there is degradation of~MTF, but the efficiency of the screen
is advantageously doubled, as is shown in Figure 8 of Gasper.
Experimental verification of the Gasper
calculations is provided by measuring the MTF of a trans-
pa~ent hot-pressed zinc sulfide sc~een coated with a dyed
gelatin undercoat. Excellent agreement was found between
~1

'7
--3--
the measured and computed MT~s. Gasper concludes that
attempts to improve the MTF of a transparent screen
res~lt in an undesirable loss o~ efficiency. Given a
choice between slight increases in MTF coupled with
undesirable losses in efficiency (with an absorbing under-
coat), and great increases ln efficiency coupled with
only slightly lower MTFs (reflective undercoat), the
high efficiency screen with a reflectlve undercoat is
clearly preferred by Gasper.
It is seen that transparent x-ray intensi-
fying screens providing high resolution, while maintàining
speed and efficiency, and which are resistant to
physical damage and are easily and economically manu-
factured, are extremely desirable.
.
I

SUMMA~Y OF THE INVENTION
_ _ .
An x-ray intensifying screen according to this invention
comprises a support having thereon a fluorescent composition
comprising:.
a) from 50 to 90 percent by weight of a substantially
isotropic phosphor which is excited by x-rays and
substantially transpa.rent to light emitted by said
p~osphor; and
b) from 10 to 50 percent by weig~t of a polymer havi~g
an index of refraction within .02 of the index of
refraction of said phosphor over at least 80 percent
of the emission spectrum of said phosphor;
said support having an index of refraction equal to or up to
0.05 units hI~her than the index of refraction of said phosphor
15 and having a reflection optical, density of at least 1.7 to
light emitted by said phosphor. Using this x-ray intensifying
screen~ high resolution andhigh contrast are obtained, while
maintaining high speed, efficieney and resistance to physical
damage. ~urther, the screens can be easily manufactured and
20 do not require the addition of reflection pigments to prevent
image blurring.
It has also been found that a particularly advantageous
fluorescent composition eomprises:
a) from 50 to 90 percent by weight of a substantially
isotropic phosphor which is exeited by x-rays and
substantially transparent to light emitted by said
phosphor; and
b) from 10 to 50 percent by weight of a polymer having
an index of refraction within .02 of the index of
refraction of said phosphor over at least 80 percent
of the emission spectrum of said phosphor, said
polymer eomprising:
i) from 5 to 99 mole pe~eent of recurring units
having the formuIa:
: 35
~'

(CH2 C)
C=O
O-R2
wherein:.
R is H or alkyl; and
R is alkyl, cycloalkyl, aryl, aralkyl or
aryl substituted with alkyl, alkoxy, or heterocyclic;
and
ii) from l to 95 mole percent of recurring units having the
the for~ula::
,R
( H2 C~
C=o
S-CH-R
i
Ar-R
wherein
Ar is arylene;
R is H or alkyl;
R3 is H, alkyl, aryl, or aralkyl; and
R4 is H, alkyl, alkoxy, amino, halogen,
sulfide, sulfoxide, sulfonate or heterocyclic.
In a further embodiment of the invention, a process -for
making an x-ray intensifying screen comprises the steps of:
a~ coating a mixture comprising:.
i) from 50 to 90 percent by weight of a substan-
tially isotropi~ phosphor which is excited by
x-rays and substantially transparent to light
emitted by said phosphor; and
ii~ from lO to 50 percent by weight of at least
one copolymerizable monomer or mixture of
monome~s, said monomer or mixture o;E monomers,
,

when polymerized, having an index of refxaction
within .02 of the in,dex of refraction of said
phosphor over a-t least 80 percent the emission
spectrum of said phosphor,
on a support having an index of refraction equal to or
up to 0.05 units higher than the index of refraction of
said phosphor and having a reflection optical, density of
a-t least 1.7 to light emitted by said phosphor; and
b) polymerizing said mixture coated on said support to produce
a polymer comprising recurring units of said monomer or
monomer mixture.
DETAILED DESCRIPTION OF'THE'PREFERRED'EMBODIMENTS
A novel x-ray intensifying screen comprises a support
having thereon a fluorescent composition comprising:
a) from 50 to 90 percent by weight of a substantially isotropic
phosphor which is excited by x-rays and substantially
transparent to light emitted by said phosphor; and
b) from 10 to 50 percent by weight of a polymer having an
index of refraction within .02 of the index of refraction
of said phosphor over at least ~0 percent of the emission
spectrum oE said phosphor;
said support having an index of refraction equal to or up to
0.05 units higher than the index of refraction of said phosphor
and having a reflection optical density of at least 1.7 to light
2~ emitted by said phosphor.
Any substantially isotropic phosphor which is excited
by x~-rays and substantially transparent to the light emitted
by the excited phosphor is usefuI in preparing the fluorescent
composition. The term substantially iso-tropic phosphor is
30 used herein to mean a crystalline phosphor having substantially
the same optical properties in all ddrections of the crystal~
and that the crystalline phosphor is substantially free from
defects! such as cracks and inclusion,s, which cause scattering of

--7--
light. Useful phosphors include activated alkali metal
halides, such as KCl:Sb, CsBr:Tl, KI:Tl, KBr:Tlt KCl:Tl,
RbCl:Tl, RbBr:Tl and RbI:Tl; alkaline earth halides such
as BaF2 and Ba~Cl; activated alkaline earth halides such
as Ca~2:Eu, SrC12:Sm, SrF2:Eu, BaFCl:Sr, Eu, BaFCl:Eu
and SrF2:Sm; activated metal silicates such as BaSiO3:Eu,
CaSiO3:Mn and Zn2SiO~:Mn; mixed metal fluorides such as
KCdF3:Mn and CsCdF3:Mn; metal sulfates such as lanthanide-
activated metal sulfates such as BaSO4:Sr, Eu, SrSO4:Eu,
BaSO4:Eu, ZnSO4:Mn and Cs3SO~:Ce; metal gallates such as
ZnGa2O4:Mn; and phosphates such as lanthanide-activated
phosphates such as Ba2P4O7:Eu and Ca3(PO4)2:Ce
examples of phosphors are described in U.S. Patent Nos.
4,100,101, 2,303,g63, 3,163,610, 3~163,603 and 3,506,584
and in R.C. Pastor et al, Mat. Res. Bull., 15 469-475
(1980). Typical transparent phosphors include RbI:Tl;
KI:Tl; BaFCl:Sr, Eu; BaSO4:Sr, Eu; CsCdF3Mn; BaF2;
KCdF3:Mn; and SrF2. Preferred phosphors are RbI:Tl;
KI:Tl~; BaFCl:Sr, Eu; CsCdF3:Mn; BaSO4:Sr, Eu; and BaSO4:Pb.
The above-described phosphors are prepared by
any conventional method for preparing isotropic phos-
phors, such as by introducing the anions and cations
which form the phosphor into a reaction solution,main-
taining an excess of up to 1 molar of an anion or cation
throughout the reaction mixture, preventing local excesses
of cations or anions, and thus slowly growing crystals
of the phosphor to at least 0.5 micron, as described
in U.S. Patent No. 3,668,1l~2 issued June 6, 1972 to
Luckey.
Other methods for preparing isotropic phosphors which
are excited by x-rays and substantially transparent to
the emitted light, include precipitation at elevated
temperatures and super-atmospheric pressures described
in ~uthruff, U.S. Patent No. 2,285,464; precipitation
followed by firing, fusion, and grinding to the desired
particle size; and ignition in the presence of a flux~
The method of U.S. Patent No. 3,668,142 is the preferred
method for preparing the isotropic phosphors.

-7a-
These screens can be modlfied so that they
are useful in the apparatus and methods for producing
images that are described in U.S.3,8599527~ U.S~
4,346,295 and U.S. 4,236,078. In this modification
an essentially isotropic storage phosphor is eoated
in a binder on a support that has the characteristics
described below. The phosphor is excited by a pat-
tern of radiation of a first wavelength. The phos-
phor is then exposed to radia~ion of a second wave
length which causes the said storage medium to emit a
~hird wavelength of radiation having an intensity
pattern representative of ~he stored image. The
binder used in making this screen matches the index
of refraction of the phosphor at th~ second wave-
length and the support for the screen is selected sothat it does not reflect the radiation at the second
wavelength. The index of refraction of ~he binder at
the third wavelength is preferably selected so that
i~ does not match that of the phosphor and the sup-
port of the screen may reflect the radiation at thethird wavelength. Thus, the radiation at the third
wavelength, which is emitted when the phosphor is
irradiated at the second wavelength, is not trapped
by total internal reflection or by the support, but
escapes from the screen and is efficiently collected
by a photomultiplier tube with appropriate optics or
by other photosensors which respond efficien~ly to
the radiation at the third wavelength. Screens of
this type are particularly useful for radiography and
other applications in which a pattern of hi8h energy
radiation is absorbed by the phosphor 9 then released
by scanning the screen wlth a laser beam that has a
wavelength equal to that where the index of refrac
tion of the phosphor and binder are matched and where
. ~

~7~
-7b-
the support of the screen has minimum reflectance.
Ideally, the beam from the laser follows the path of
the high energy radiation 60 that the resolution of
the image from the screen i6 determined by ~he dimen-
sions of the laser beam. The light released from thephosphor by the laser is collected by an appropriate
photosensor, amplified, and the signal displayed on a
cathode ray ~ube or recorded on an image recording
medium to form the imageO Appropriate phosphors com-
prise the barium alkaline earth metal fluorohalidesof U.S. 4,261,854 and U.S. 4,239,968, and other
storage phosphors which have indices of refracti.on
less than about 1.75 in the visible region of the
spectrum.
, ~i

-8-
~ ne phosphor crystals are optionally activated
to obta n the desired speed by any conventlonal method
of activation. One method is the addition o~ a solution
o~ a small amount (about .05 percent by weight) o~ the
activating ion in a solvent, such as isopropanol 9 to a
vigorously stirred solution of the lsotropic host in
a solvent, such as water, at very low temperatures (-30
to ~20C), followed by collection of the precipitated
activated phosphor.
The substantially isotropic phosphors Or the
invention generally have crystalline morphologies which
are cubic or substantially cubic. The substantially
isotropic phosphors of the invention generally have
crystal sizes in the range rrom about 1 to about 50
microns, with the size range from about 10 to about 20
micro~s bein~ preferred.
~ ne novel x-ray ~ntensifying screen includes
an~ polymer having an index of refraction within .02
of the index of refraction of the phosphor over at
least Bo percent of the emission spectrum.
The selection of the polymer for the novel
x-ray intensifying screen is depenclent on the index of
refract~on of the selected substantially isotropic
phosphor at its emission wavelength. The index of
25 refraction of the phosphor is determined by
measuring the transmission spectra of the phosphor mixed
with a series of Cargille liquids~ as described in
"~he Particle Atlas", McCrone, Dra~tz and Delly, Ann
Arbor Science Publishers, Inc., 1967, and determining the
30 wavelength at ~nich the index of refraction of th~ phosphor
and the liquid match. A phosphor dispersion curve is
obtained by plotting the wavelengths o~ maximum transmission
ror the series on the ~amily o~ Cargille dispersion curves
publlshed in "The Particle Atlas" referred to above. The
phosphor dispersion curve thus obtained is used directly
to find the lndex of rerraction required for the polymer
of the novel transparent x-ray intensi~ying screen.

l7~
~ he polymer havin~ the required index of rerrac-
tion, i.e., an index of refraction within .02 of the
refraction of the phosphor over at least 80 percent Or its
emission spectrur,, comprises a single polymerized monomer,
or the polymer comprises a mixture of two or more poly-
merized copolymerizable monomers. Generally, the polymer
comprises two copolymerizable polymerized monomers, one
of which, when polymerized, provides a polymer o~ higher
index of refraction than required, and one which~ when
polymerized, provides a lower index of rerraction than
required. The relative proportions of the two monomers
are advusted to provide the required rerraction index.
Calculated formulations are verified by measuring the
transmission curve ol a sample coating o~ the fluorescent
composition of the novel intensifying screen on a spectro~
photometer. h wavelength of maximum transmission which
is less ~han tha~ of the phosphor er.ission wavelen~th
indicates that the refractive index of the polymeric
b~nder is too low. A wavelength Or maximum transmission
2~ which is greater than that of the phosphor emission wave-
leng~h indicates that the refractive index of the polymer
is too high.
Morlomers which, when polymerized, provide an
index of refraction higher than that o~ the phosphor
selected generally ~rovide an index of refraction above
1.4 3 preferably in the range from 1.40 to 1.75. Examples
of monomers which, when polymerized, provide an index
of refraction higher than that of the pho~phor selected,
and thus can be mixed with monomers having a lower index
of refractlon to become useful herein, include S~
naphthyl carbinyl) thioacrylate, naphthyl acrylate, 1-bromo-
2-nap~hylacrylate and naphthylmethacrylate. The pre~erred
monomer is S-(l-naphthyl carbinyl)thioacrylate.
Monomers which, when polymerized, provide an
index of re~raction lower than that of the pho~phor
generally provide an index of refraction ranging from
about 1.40 to about 1.75, preferably in the range from

--10~
1.40 to 1.60. Examples of monomers which, when poly-
merized, provide ~n index of refrackion lower than that
Or the phosphor selected and thus are useful when mlxed
with monomers having a higher index Or refraction~
include copolymerizable ethylenically unsaturated mono-
mers such as acrylates and methacrylates such as methyl
acrylate~ ethyl acrylate, propyl acrylate, bu~yl acrylate,
butyl methacrylate and cyc]ohexyl methacrylate; vinyl
ester~, amides, nitriles, ketones, halides, ethers,
13 olefins, and diolefins as exemplified by acrylonitrile,
methacrylonitrile, styrene, ~-methyl ~tyrene, acrylamide~
methacrylamide, vinyl chloride, methyl vinyl ketone,
fumaric, maleic and itaconic esters, 2-chloroethylvinyl
ether, dimethylaminoethyl methacrylate, 2-hydroxyethyl
15 methacrylate, N-vinylsuccinamide, N vinylphthalimide,
N-vinylpyrrolidone, butadiene and ethylene. Preferred
monomers are acrylates and methacr~lates, with cyclohexyl
methacrylate being most preferred.
The proportion in which the above-described high-
20 index a~d low-index monomers are mixed varies widely to
prov de a polymer having the required index of refraction.
The polymerized low-index monomer preferably comprises
from 5 to 100 mole percent Or the :resulting polymerg
with the range from 15 to 80 mole percent being most
25 preferred. ~he polymerized high index monomer preferably
comprises from 0 to 95 mole percent of the resulting
polymer, with the range from 20 to 85 mole percent
bein~ most preferred.
In one embodiment, the polymer of the novel
; 30 intensifying screen comprises from 5 to 100 mole percent
of recurring units having the formula:
; p~l
-(CH2-C)-
" C=O
O-R
:-~

~h~rei~:
R- is ~ or alkyl, preferably containing from about
1 to ab3ut 4 carbon atoms, such as methyl, ethyl,
propyl, isopropyl, and butyl; and
R2 is alkyl, prererably containing from about 1 to
about l? carbon atoms, such as methyl, ethyl, propyl and
butyl; cycloalkyl~ such as cyclopentyl and cyclohexyl;
aryï prererably containing from about 6 to about 22 carbon
a+o."s, such as phenyl3 naphthyl, anthracene, perylene,
acena~hthene and rubrene; aralkyl, preferably containing
from about 5 to about 20 carbon atoms, such as benzyl,
phenylethyl, phenylpropyl, phenylbutyl, tolylbutyl and
nh~h~hylme;;nyl; or aryl substituted with alkyl, preferably
containing fro~ about 1 to about 20 carbon atoms, such
as 3_thyl, ethyl9 isopropyl and hexyl; alkoxy, preferably
cor.~aining from about 1 to about 20 carbon atoms, such as
methoxy and ethoxy; or heterocyclic, preferably a 5 to
7-membered ring which may be saturated, such as pyrrolidone,
morpholine, piperidine, tetrahydrofurane, dioxane and
quinaldine, or un~tur~ted, such as pyrrole, ~o~az~le,
imidazole, isothiazole 9 furazan and pyrazoline.
A preferred polymer of the novel x-ray
inter.sifying screen ~urther comprises from 0 to 95 mole
percent of recurring units having the ~ormula:
Rl
--(C~12--C)--
C=O
S-CH-R3
Ar-R
wherein:
Ar is arylene, preferably containing from about 6 to
about 22 carbon atoms, such as phenylene, naphthalene,
anthracene; perylene, acenaphthene and rubrene;
Rl is H or alkyl as described for Rl above;
R3 is H, alkyl, aryl, or aralkyl as described for
R above; and

~ -12-
R is ~;, alkyl, pre~erably contalning ~rom about 1 to
abou~ 23 carbo,. atoms, such as methylg ethyl, isopropyl,
and hexyl; alko~y, preferably containing from about
1 to abolt 20 carbo~ atoms, such as methoxy and ethoxy,
amino; haloger~ such as chloride and bromide; sul~ide;
sulfoxide~ sulfonate; or heterocyclic, preferably a 5 to
7 membered ring which may be saturatedl such as pyrrolidine~
morpholine, ~iperidine, tetrahydrofurane, dioxane and
quinaldine, or unsaturated, ~uch AS pyrrole, isoxazole.
im dazole, isothia7ole, furazan and pyrazoline.
I~is noted that throughout the specification
and clai~.s the terms "alkyl", "aryl" and 1'arylene"
incl~de substituved alkyl, aryl and arylene, such as
methoxy e'hyl, chlorophenyl and bromonaphthyl.
Exa~les of polymers useful for the novel x-ray
intensi~ying screen include:
pGly~l-naph~hyl carbinyl ~ethacrylate-co-S-
(l-na~hthyl carbinyl) thioacrylate];
2r poly~l-naphthyl cPrbinyl methacrylate-co-l-bromo-
2-naphthylacrylate];
poly[S-(l-naph~hyl carbinyl) thioacrylate-co-
benzyl methacrylate~;
poly[S-(2-naphthyl carbinyl) thioacrylate-co-
benzyl ~ethacrylate]; and
poly[t-butyl methacrylate].
In an especially preferred embodiment, the poly-
mer of the novel intensifying screen comprises rro~ 5 to
100 mole percent o~ a polymerlzed co-polymerizable naphthyl
carbinyl methacrylate monomer, and fro~. O to 95 mole
percent of a polymerized copolymerizable naphthyl car-
binyl thioacrylate monomer. In a still further embodiment,
the polymer comprises from 5 to lO0 mole percent Or poly-
merized l-naphthyl carbinyl methacrylate and from 0 to 95
mole percent of polymerized S-(l-naphthyl carbinyl) thio-
acrylate.
The x-ray intensi~ying screen of the in~ention,
comprising a substantially isotropic phosphor,which is
excited by x-rays and substantially transparent to light
emitted by the phosphor, and a polymeric binder carerully

-13
seiected so as to ma~ch, within .02, the index of refraction
Or the phosphor, is highly transparent. The intensifying
screens of the invention generally exhibit a mean free path
for li~h' scatter greater than one millimeter~ pre~erably
greater than 3 millimeters, for phosphor:binder ratios of
2.5 or larger. This highly transparent screen material
allows the use of relatively thick screens wh~ch absorb
more of the incident x-ray beam~ and thus results in
higher speed. Further, the increased absorption of x-rays
decreases quanturi mottle and allows improvement in overall
image quality. Further still~ the polymeric binder pro-
tects the fragile phosphors from physical damage.
~ he support for the x-ray intensifying screen
of the invention includes any material having an index Or
relraction equal to or up to 0.05 units higher than the
index of refraction of the phosphor of the invention, and
ha~r-ng a reflection optical density of at least 1.7 to
light emitted by the phosphor. Suitable support materials
include polymeric mate,ials such as Lucite~ (poly(methyl
methacrylate); Elbite (tourmaline); Formica~ (poly(urea)-
for~,aldehyde res n); polyolefins such as polyethylene and
polypropylene; pclycarbonates; cellulose acetate; cellulose
acetate butyrate; poly(ethylene terephthalate); glass such
as Corning Fotoform~ glass having 80 percent of its area
covered with holes .015 inch deep and .005 inch in diameter;
and metal such as black anodized aluminum.
The required re~lection optical density o~ 1.7
to light emitted by the phosphor is provided by the use
of support materials which are inherently darkly colored,
materials which have been dyed or pigmented during manu~;facture to provide a uni~orm dark color throughout, or
materials which have undergone a sur~ace treatment such
as coating with a dye, pigment or dyed or pigmented
material, anodizing in the case of metals, or a combina-
tion of the above surface treatments.
The support of the invention also has an indexof refraction equal to or up to 0.05 units higher than the
index o~ refraction of the phosphor at its wavelength of

-14-
maximum emissior.. Ir. one embodiment, a preferred support
having botn the required optical densi~y and the required
index of refra^tion comprises a conventional support
materiai having a thin polymeric layer on the surface on
which the fluorescent composition is to be applied. This
thin polymeric layer comprises a polymer havlng an index
of refraction equal to or up to 0.05 units higher than
the index of refraction of` the phosphor at its wavelength
of maxi.mum eDission, and a finely divided pigment such as
carbon in an a~.ount suffjcient to produce an optical
density of 1.7 to light emitted by the phosphor.
The x-ray intensifying screen of the invention
compris~ng a highly transparent screen material having
high speed and a light-absorbing support having the
required reflection optical density, gives high contrast
and resolu'ion. The use of a support which has the same
or ver~- sligh~ly higher (up to 0.05 higher) index of
refraction as that of the phosphor layer decreases the
flare of the ima~e and increases contrast.
Tn another em,bodiment of the invention, a particu-
larly a~vansagQous f'luorescent composition comprises:
a) from 50 to 90 percent ~y weight of a subs~antially
isotropic phosphor which is excited by x-rays
and substantially transparent to light emitted by
said phosphor; and
b) from 10 to 50 percent by weight of a polymer
having an index of ref'raction within .02 of
the index of refraction Or said phosphor over
at least 80 percent of the emission spectrum
of said phosphor, said polymer comprising:
i) from 5 to 99 mole percent of recurring
units having the formula:
r~l
r~
-(CH2-C)-
C=02
0-R

15-
wherein:
Rl and R2 are as described ~or the polymer
of the novel x-ray intensifying screen;
. and
ii) from l to 95 mole percent of recurrin~ uniks
having the formula:
Rl
-(CH2 C)-
C=O
S-CH-R3
Ar-R
wherein:
Ar, Rl, R3 and R are as described for
13 the polymer of the novel x-ray intensirying
screen.
Examples of polymers useful in the novel fluores
cent composition include:
poly[l-naphvhyl carbinyl methacrylate-co-S-~-naphthyl
carbinyl~thioacrylate];
poly[S~ naphthyl carbinyl)thîoacrylate-co-benzyl
methacrylate~, and
poly~S-(2-naphthylcarbinyl)thioacrylate-co-benzyl
methacrylate].
Pre~erred polymers which are useful in the novel
fluorescent composition include polymers comprising from
5 to 99 mole percent of a polymerized co-polymerizable
naphthyl carbinyl methacrylate monomer, and from l to 95
mole percent of a polymerized copolymerizable naphthyl
carbinyl thi0acrylate monomer. ~specially preferred is
a polymer comprising from 5 to 99 mole percent Qf recurring
units having the ~ormula: CH
-(CH2-C)-
C=O
-ÇH2
~ ; and

-16-
~rom 1 to ~5 r..ole percent o~ recurrin~ uni~s having the
formul~:
( ~H2 C~ )
C=O
S-ÇH2
The recurring units ~or the polymer and their
relative pro~ortions are generally selected to achieve
the index ol re~ractior. previously described.
In a further embodiment of the invention, a
process for making an intensifying screen comprises the
steps o~
a) coa+ing a mixture comprising:
i) from 50 to 90 percent by weignt Or â sub-
stantially isotropic phosphor which is
excited b~ x-rays and substantially trans-
parent to light emitted by said phosphor; and
ii) .fror. 10 to 50 percent by wei~ht of at least
one copDlymerizable monomer or mixture Or
mono~ers, sâid monomer or mixture of monomers,
when polymerized~ having an index of refrac-
tion within .02 of the index of refraction
Or said phosphor over at least 8Q percent
of the emission spectrum of said phosphor~
on a support having an index of refraction equal
to or up to 0.05 units higher than the index
Or refraction of said phosphor and havlng a
2~ reflection optical density of at least 1.7 to
light emitted by said phosphor, and
b) polymerizing said mixture coâted on said support
to produce a polymer comprising recurring units
o~ said monomer or monomer mixture~
30 - The mixture comprising the fluorescent compositlon
o~ the novel lntensifying screen is preferably prepared by
combining a substantially isotropic phosphor in the form
Or â free-flowing powder with a polymerizable monomer or

mi~;~ure o~ copolymerizable monomers which, when polymerized,
exhibit the required index of refraction. The useful
phosphGr to monomer ratio varies widely, but prererable
ranges are fro~. 50:50 to 90:10 by weight, and more pre-
~erably in the range ~ro~, 70:30 to 80:20 by ~eight. ~eneral-
ly, the phosphor to monomer ratio is maximized, resulting
in a honey~like, viscous mixture, whlch is capable Or
being poured. The resulting mixture is optionally de-
gassed to remove trapped air bubbles.
- The mixture optionally further comprises from
.001 to 1.0 percent by weight~ preferably ~rom 0.1 to 0.5
percent by weight Or a photoinitiator such as 4,4'-bis-
chloromethyl benzophenone, benzoin methyl ether, and
benzoyl peroxide. It is noted that further additional
components are optionally included in the mixtures of the
novel process. For exam~le, resins, stabilizers, surface
active agen s an~ mold release agents serve to improve ~ilm
formation, coating properties, adhesion of the mixture to
the support, separability of the mixture from non-support
r.aterials, mechanical strength and chemical resistance.
~ he miY.ture of the novel process is coated
onto the support to a pre-determined thickness by
techniques well-known in the art, such as roll coat~ng,
brush coating, solvent coating or x-hopper co~ting. One
method of coating the mixture comprises pouring the mixture
onto the desired support, covering it with a cover shee~,
such as a glass cover sheet~ having appropriate spacers
to produce a predetermined coating thickness, and spread~ng
the mlxture by applying pressure to the cover sheet to the
limit of the spacers.
The optimum coating thickness of the phosphor-
monomer mixture depends upon such ~actors as the use to
which the coating will be put, the speed desired, the
degree o~ image quality deslred, the phosphor selected,
the monomer or monomer mixture employed, the phosphor
to monomer ratio and the nature o~ other components
which may be present in the coating. Useful coating

~:3L7~
th ~X.r.ess^s fcr use in preparing x-ray intenslrying screens
~ - ~ro~J 25 ~G ~5~G microns, with coating thicknesses of
from 400 to 120v ~.icrons being preferred. The preferred
coa~ing coverage likewise varies widely between about
10 g and about 530 g/ft2, with the range from 50 to 200
G/ft being preferred.
The coating, co~.prising a monomer or mixture Or
mono~ers and a phosphor, is preferably polymerized at a
temperature of 20-30C by irradiation with a near-ultra-
1~ violet la~. Other me~hods of polymerization are similarlyused. Such methods include thermal polymerization, poly-
merization by election beam radiation and polymeriz~tion by
high energy ga~-.ia irradiation.
After pclymerization, the polymerized mlxture
is preferably cooled to room temperature or below, and
ar.y cover sheet used to spread the coated mixture and
es a~lish coa~ing th.ickness is re~oved. In some cases,
release ~s gen~ly initiated, by inserting a blade between
the support and the cover sheet to separate the support
from the coated polymerized mixture, until Newton's rings
are observed a~ the initiation site. The cover sheet is
then lifted away, optionally further cooling the cover
sheet briefly, for example, with powdered dry ice. Further
cooling should be carefully undertaken, however, as over-
coolinG the cover sheet is likely to shatter the poly-
merized, coated screen mixture.
The resulting polymer has an index of refraction
within .02 of the index of refraction of the phosphor
over 80 percent of its emission spectrum, thus maintaining
a high degree of trar,sparency to the light emitted by the
exclted phosphor. The polymer protects the phosphor from
mechanical damage, and, if hydrophobic, from damage caused
by moisture.
` The process of the invention thus provides a
highly transparent ~-ray intensifying screen having
satisfactory speed, high contrast and high resolution.
Further the process as described provides a relatively

~7~
--19--
inexpensive and straightforward method of manufacturing
high speed~ high resolution x-ray intensifying screens
without the addition of reflecting pigments.
The following preparations and examples are
lncluded for a furth2r understanding of the invention.
Preparation 1 --
The phosphor RbI:Tl (.0004) was prepared by add-
ing a solution of 0.33 g of thallous acetate ln 500 ml of
isopropanol at a rate of 36 ml/min to a vigorously stirred
solution of 636 g rubidium iodide in 460 g of water. The
temperature of the isopropanol solution was maintained at
-29C, and the temperature of the aqueous solution was
maintained at about 15C. 200 g of the precipitated
rubidium iodide phosphor was collected, carefully remov-
ing all of the gupernatan~ lsopropanol water mixture,
which was reserved for recovery of unprecipitated rubidium
iodide to be used in subsequent preparations. (Any BUp~r-
natan~ isopropanol-water mixture remaining with the pre-
cipitated phosphor can contaminate the precipitated
phosphor with further precipitatlon o~ a phosphor di~fering
in composition, and cause unwanted scattering of light
in the resulting fluorescent composition.) The precipitated
*hallium-activated RbI phosphor, being free Of ~upernatant
isopropanol-water mixture 9 was then washed twice with
isopropanol in a high speed, ~ood-processing blender,
and the precipitate collected on glass filter paper after
each washing. The phosphor was vacuum dried and bottled.
The speed of the RbI:Tl (.0004) thus prepared was about
equal to that of ~ l, and speeds between 6 and 7 times
greater than that o~ DuPont No. 501 commercial CaW04
phosphor were obtained ln the x~ray powder test described
in U.S. Patent No. 3,668,142, previously referred to
hereln.
Preparatlon 2 -
-
The phosphor KI:Tl (.0003) was prepared by
adding a solutlon of 0.4 g thallous acetate ln 1.6 liters
of lsopropanol at -29C to a solution of 800 g potassium
lodlde in 600 g distllled water at 15C with vigorous
stirrlng. The temperature of the ~pernatant solution was

-20-
ma nta~ned av about 14~C. The rate o~ addition was 35
ml/min. The crystals of the precipitated phosphor were
free from defects and had cubic morphology with crystal
sizes in the range from about 10-20 microns. The speed
of the phosphor, measured after precipitation, washing,
and drying, by the method used in U.S. 3,66~9142 was about
seven times that of commercial calclum tungstate.
Preparation 3
A mixture of 66 g of cyclopentadiene and 500 ml
13 o, methylene chloride was stirred with 90 g of acryloyl
chloride at dry ice temperature (-78.5DC) and allowed to
warm slowly to room temperature over 24 hours. The
reaction product was then distilled. The resulting
bicycloheptane carbonyl chloride thus obtained was allowed
to react with l-(naphthylcarbinyl)rnercaptan and rerluxed
in methylene chloride (b.p. 40-41C) while one equivalent
of d isocro~ylethylamine was slowly added to the mixture.
The product was vacuum distilled, using a 250C oil bath,
un~er which conditions the cyclopentad~ene split o~,
giving S~ naphthylcarblnyl)thioacrylate in good yield.
thin-layer chromatograph (50:50 hexane/e'her, silica
gel) of the resulting product indicated an ~f value of
0.59 to 0.72.
Preparation 4
l-naphthyl carbinyl methacr~late was prepared
by catalytic transesterification of an excess quantity of
methyl methacrylate with the alcohol l-naphthyl carbinol.
The by-product, methanol, was conkinuously removed by
azeotropic dist~llation and/or use o~ molecular sleves~
thus pulling the reversible reaction towards completion.
When the reaction was essentially complete, the excess
methyl methacrylate was removed by distillation at
atmospheric pressure. A small amount (~rom 5 to 25%) of
the unreacted higher alcohol l--naphthyl carbinol remained
in the resultlng l-naphthyl carbinyl methacrylate.

~ ,~ ~oe
-21-
Preparation~
In an alternative synthesis o~ l~naphthyl
carbinyl methacrylate, l-~chloromethyl)naphthalene is
treated with one equivalent o~ potassium methacrylate
~n dimethyl sulfoxide. m e pota~sium methacrylate
employed is either previously isolated or formed in
situ from potassium hydroxide and methacrylic acid.
The reaction is continued at 70~C for 30 minutes. The
resulting l-naphthylcarbinyl methacrylate is isolated
in 93-98% yield, virtually ~ree from c~ntaminants.
Preparation 6
Aluminum plates were anodized in 12-15 percent
H2S04 at 70~ and 12-14 amperes/ft2. The porous deposit
was treated with aluminum Black B ~ dye (a registered
trademark of Sandoz Colors and Chemicals) and then sealed
with hot water or nickel acetate solution. The resulting
support exhibited a~ optical density of 2.34 when over-
coated with a mLxture of rubidium iodide and polymer
havin~ matched indexes of refraction. Al~hough
the index of re~raction o~ anodized aluminum is not pre-
cisely know." it is thought to be about 1.76, which is
less than 0.05 un~ts higher than that of rubidium iodide
at 425 nm, the region of maximu~. emission.
Example 1
A mixture of 100 g of thallium-activated potassium
iod de phosphor (.0003), as prepared in Preparation 2, and
40 g Gf a 4:1 mixture of S~ naphthyl carbinyl) thio-
acrylate, as prepared in Preparation 3, and l-naphthyl
carbinyl methacrylate, as prepared in Preparation 4, con-
3~ taining 0.3 percent by weight of 4,4'-bis-chloromethyl
benzoquinone was degassed under vacuum. A por~ion of the
mixture was photopolymerized between two glass sheets to
~orm an unsupported screen, and released. The unsupported
sçreen was placed ln a Cary ~ 17 spectrophotometer and
its optical density was measured using an unsupported
screen containlng only photopolymerized polymer (lacking
the phosphor) as a reference. The optical density of the

-22~ 7
unsupported screen was used to calculate the mean ~ree
~ath of light through the screen. The mean free path
was calculated to be at least 2.3 mm.
Another portion of the mixture was coated at
di~erent thicknesses on a black anodized aluminum support
as prepared in Preparation ~ and photopolymerized under
glass cover shee's. Radiographs were made by exposing
Lo-Dose~ film in contact with these experimental supported
screens as back screens wlth 70 kVp x-rays. A control
radiograph was ~ade by likewise exposing Lo-Dose~ film
in contac-~ with a DuPont~ Par Speed Inténsifying screen
in order to obtain the relative speeds of the experimental
screens. The di~ference in speed was calculated through
the known density vs. lo~ exposure curve ~or Lo~Dose~
film ~rom the densities which resulted on the exposed
and developed rilms. The following results were obtained.
Screen ~^Xness Screer C~verage Relative Speed 10 micron lead
(mi ron~? (g/~t ) PAR = 100* bar test o~ect
Resolution
20 405 61 17~ 3.15 lp/m.r,
7~0 113 26~ 2.24-2.5
1115 15Q 325 2.0
*~ont~ ~r $~ee~ Intens~yi~ Screen
Example 2
. . .
A mixture of 35.5 g o~ the thallium-activated
rubidium iodide phosphor (.0004) as prepared in Prepara-
tion 1 and 10 g o~ a 60:40 mixture of l-naphthyl carbinyl
methacrylate and l-bromo-2-naphthylacrylate containing
0.3 percent 4,4'-bis-chloromethyl benzophenone was spread
on a black anodized aluminum support and covered with a
glass sheet while being photopolymerized. When polymeri-
zation was complete, the glass sheet was released. The
resulting transparent screen was 500 microns thick and
had a coverage o~ 89 g of phosphor per square foot.
Radiographs made with this screen as a back screen with
Lo-Dos Film at 70 kVp gave a relatlve radiographic speed
tcalculated as in Example 1) of 255 compared to 285 ror a
DuPont Hi-Plus~ Screen with Lo-Dose~ Film. When a bone

and bead test object was employed in -the same comparison,
better image quality was obtained with the transparent screen.
_ample 3
A mixture of 250 g of the thallium-activated rubidium
iodide and 65 g of a 3:1 mixture of l-naphthyl carbinyl
methacrylate and S-(l-naphthyl carbinyl) thioacr~la-te which
also contained 0.3 percent by weight of 4,4'-bis-chloromethyl
benzophenone was degassed under vacuum and then coated three
ways: (1) on black anodized aluminum support, (2) on reflective
aluminum support on an optically flat surface, and (3) on no
support (self-supporting film). All three coatings were of
equal thickness and were photopolymerized. Radiographs were
made with these three screens, along with the DuPont Hi-Plus~
screen, using Lo~Dose~ Film, 70 k~p x-rays and a 20 ,u lead bar
test object. The resolution of the radiographs was as follows:
Hi-Plus~ Screen 4.0 lp/mm
Black Aluminum Support 4.0 lp/mm
Reflective Aluminum
Support 1.8 lp/mm
Unsupported 1.8 lp/mm
The resolution of the screen having a black support showed
a dramatic increase both over the resolution of the screen
having a reflective support and over that of the unsupported
screen.
Example 4
A mixture of 136.8 g of thallium-activated rubidium
iodide (.0004), 40.0 g of a 3:1 mixture of l-naphthyl
carbinyl methacrylate containing up to 25 percent l-naphthyl
carbinol and S~ naphthyl carbinyl) thioacrylate, and
0.3 percent by weight o~ 4,4'-bis-chloromethyl benzophenone
was degassed under vacuum. The mixture was then coated on
a support consisting of inlaid strips of black polished
Formica~, black anodized aluminuzn, black Corning FotoEor
glass having 80 percent of its area covered with holes,
.005 inch in diameter and .015 inch deep, and dark blue

~.~'7~6~
-2~
tourmaline in a matrix of black Lucite~ plastic. The mixture
was spread evenly across the support so thai the different
types of support were coated with an equal thickness of the
mi~ture. A glass cover sheet was placed on the mixture, and
the mixture was photopolymerized. The cover sheet was removed,
and the reflection optical densities of the dif~erent areas
were measured. A 70 kVp radiograph of a 10 micron lead bar
resolution test ob~ect was made using the screen as a back
screen with DuPont Lo-Dos ~ film. The radiograph made using
this transparent screen was compared with a control radiograph
made with Lo-Dose~ film and using an opaque Hi-Plu ~ screen.
Radiographic speed was determined as in Example 1. The results
obtained were as follows:
Refrac-tive Reflection Radiographic Resolution
i5 Support Index nd_ optical Density Speed (lp/mn)
Lucite~ 1.49 2.25 315 2.5-2.8
Fotofor ~
Glass - 1.87 250 3.15
tourmaline 1.64 2.57 250 3.15
20 Formica~ 1.65 2.17 245 3.15-3.55
Black anodized
Aluminum 1.76 2.34 245 3.55
Hi-Plus~ Screen
Control (opaque) - - 285 3.55
The results indicated that the optimum combination of speed
and resolution were obtained when the fluoxescent composition
mixture was coated on a black anodized aluminum surface for
the particular transparent phosphor-polymer combination
selected. Further, the results showed that the transparent
screen having a black anodized aluminum support exhibited
resolution equal to and radiographic speed nearly equal to
the conYentional opaque control screen; however, the trans-
parent screen of the invention displayed less quantum mottle
than the conventional opaque screen.

-25-
Example 5
A mixture of 180 g of finely powdered Ba
Sr 06FCl:Eu (.006) phosphor and 51 g of a blend of
benzyl methacrylate and l~naphthylcarbinyl methacrylate
~approximately 50:50 by weight) was degassed under
vacuum and spread on a black anodized aluminum support.
A glass cover sheet was placed on top of the layer
and the mixture was polymerized by irradiation with an
ultraviolet lamp with substantial emission at 365 nm
through the glass. After the glass was removed, the
area of the layer and the weight were recorded. Coverage
of the screen was calculated as 85 g/ft of phosphor.
The mean free path for 380 nm radiation was measured
spectropho~ometrically as 304 microns.
The screen was used as a back screen with a
58 g/ft Gd202S:Tb (on a highly reflecting support)
front screen tc make 70 kVp radiographs of a standard
"bone and bead" test object with KODAK X-OMAT ~ x-ray film.
The control for the image quality evaluations was made
with both front and back Gd202S:Tb screens. The speed
of the control was 400 and the resolution was 2.24 lp/mm.
The transparen~ back screen gave a speed of 350 and a
resolution of 2,24 lp/mm, The mottle of both radiographs
was judged about equal, but the sharpness and bead visi-
bility were superior in the transparent screen radiograph.
The invention has been described in detail withparticular reference to certain embodiments thereof, but
it will be understood that variations and modifications
can be effected within the spirit and scope of the
invention.