U.S. patent application number 15/449205 was filed with the patent office on 2017-06-22 for method and apparatus for creating coherent bundle of scintillating fibers.
The applicant listed for this patent is Brown University. Invention is credited to Christopher Bull, Avilash Cramer, Rajiv Gupta, Theodore F. Morse, Paul Waltz.
Application Number | 20170176606 15/449205 |
Document ID | / |
Family ID | 54017138 |
Filed Date | 2017-06-22 |
United States Patent
Application |
20170176606 |
Kind Code |
A1 |
Morse; Theodore F. ; et
al. |
June 22, 2017 |
METHOD AND APPARATUS FOR CREATING COHERENT BUNDLE OF SCINTILLATING
FIBERS
Abstract
A method and apparatus to manufacture a coherent bundle of
scintillating fibers is disclosed. In the method and apparatus, a
polymer matrix of a transparent polymer and nanoparticle
scintillators is placed on top of a collimated bundle having a
plurality of capillaries and pressed in a pressure vessel until the
polymer matrix is forced into the capillaries. Pressure is applied
via an anvil on top of the polymer matrix. To prevent fracturing of
the collimated bundle during pressing, back pressure is supplied to
the pressure vessel via a valve, which controls a supply of high
pressure gas. Alternatively, the back pressure may also be supplied
by a press (and or pressure) and support to the collimated bundle
is provided by a high melting point thermoplastic. Heat may be
applied to the polymer matrix via the anvil to speed the pressing
operation due to the viscosity of the polymer.
Inventors: |
Morse; Theodore F.;
(Providence, RI) ; Gupta; Rajiv; (Wayland, MA)
; Cramer; Avilash; (Lynnfield, MA) ; Bull;
Christopher; (Rehoboth, MA) ; Waltz; Paul;
(Seekonk, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Brown University |
Providence |
RI |
US |
|
|
Family ID: |
54017138 |
Appl. No.: |
15/449205 |
Filed: |
March 3, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14640069 |
Mar 6, 2015 |
9611168 |
|
|
15449205 |
|
|
|
|
61949192 |
Mar 6, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01T 1/201 20130101;
B29L 2011/00 20130101; B29K 2505/02 20130101; B29C 43/18 20130101;
B82Y 15/00 20130101; B29K 2027/12 20130101; G01T 1/2033 20130101;
B29K 2105/162 20130101; B29K 2023/12 20130101; G02B 6/04 20130101;
B29C 43/58 20130101; B29K 2077/00 20130101; B29C 2043/5808
20130101; G02B 6/08 20130101; C03B 37/01262 20130101; B29K 2505/08
20130101; C03B 2203/40 20130101; B29D 11/0074 20130101; B29K
2025/06 20130101; B29C 43/003 20130101; B29C 43/00 20130101 |
International
Class: |
G01T 1/20 20060101
G01T001/20; C03B 37/012 20060101 C03B037/012; B29D 11/00 20060101
B29D011/00; B29C 43/58 20060101 B29C043/58; B29C 43/00 20060101
B29C043/00 |
Claims
1-12. (canceled)
13. A coherent bundle of scintillating fibers, comprising: a
collimated bundle comprising a glass preform having a plurality of
capillaries therethrough, the capillaries having a diameter of
about 1-15 microns; the capillaries infused with a polymer matrix
of scintillating nanoparticles and a transparent polymer.
14. The coherent bundle of claim 13, wherein the diameter of the
capillaries is about 1-5 microns.
15. The coherent bundle of claim 13, wherein the capillaries have a
circular dimension.
16. The coherent bundle of claim 13, wherein the capillaries have a
hexagonal dimension.
17. The coherent bundle of claim 13, wherein the scintillating
nanoparticles are selected from the group consisting of LaBr(3):Ce,
LSO:Ce and GdAlO(3):Ce.
18. The coherent bundle of claim 13, wherein the polymer is a
thermoplastic.
19. The coherent bundle of claim 13, wherein the polymer is
selected from the group consisting of polystyrene, nylon and
polypropylene.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to earlier filed U.S.
Provisional Application Ser. No. 61/949,192, filed Mar. 6, 2014,
the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present patent document relates generally to coherent
bundles of scintillating fibers used as detectors for x-rays used
for medical, scientific and engineering imaging applications, and
methods and apparatuses for the creation thereof.
[0004] 2. Background of the Related Art
[0005] Coherent bundles of scintillating fibers are useful for
detecting x-rays and are placed opposed to a CCD or CMOS camera.
Incident x-rays activate the scintillators in individual fibers,
which then emit visible light to the camera, which then generates
an image. Coherent bundles are used extensively in medical,
scientific and engineering applications. Particularly in the
medical imaging field, coherent bundles are instrumental in
creating images later used to diagnose cancer, heart disease and
other ailments. In engineering fields, parts may be imaged to
determine if they have micro-fractures, which may lead to premature
failure of the part, such as turbine blades in a jet engine. In
domestic security, x-ray imaging is used for scanning of packages,
luggage and persons for weapons and contraband.
[0006] Consequently, it is desirable to have high resolution
images. The size of the scintillators is correlated the maximum
resolution that can be imaged. Consequently, it is desirable to
have coherent bundles of fibers with small diameter scintillating
fibers in order to increase resolution in images.
[0007] Therefore, there is a need in the art for coherent bundles
of scintillating fibers that produce higher resolution images.
SUMMARY OF THE INVENTION
[0008] The method of making and coherent bundle described herein
advance the prior art by providing a coherent bundle of
scintillating fibers and method of making that increases the
resolution of x-ray images in to the single-digit micron range by
controlling the pressure during manufacturing of the coherent
bundle. Specifically, the method of manufacturing a coherent bundle
of scintillating fibers, includes providing a collimated bundle
having a glass preform with a plurality of capillaries. A polymer
matrix of a transparent polymer infused with scintillating
nanoparticles is placed on top of the collimated bundle. Pressure
is applied to the polymer matrix, driving it into the capillaries
while a back pressure is applied to the collimated bundle thereby
reducing the risk of failure of the collimated bundle.
[0009] In one embodiment, a pressure vessel is provided that
uniquely provides pressure to force the polymer matrix into the
collimated bundle and back pressure to moderate the tension to the
collimated bundle cause by the pressure. The pressure vessel
includes an inner wall forming a chamber inside the pressure vessel
and top surface defining a first opening into the chamber. An inner
shoulder extends inwardly from the inner wall of the pressure
chamber and forms support for a collimated bundle. A surface
defining a bore and second opening into the chamber below the inner
shoulder is also included. An anvil is configured and arranged to
apply pressure to the pressure chamber of the pressure vessel
through the first opening. A valve connected to the bottom opening
is configured and arranged to supply and control back pressure to
the chamber.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] These and other features, aspects, and advantages of the
present invention will become better understood with reference to
the following description, appended claims, and accompanying
drawings where:
[0011] FIG. 1 is a perspective view of a collimated bundle having a
plurality of capillaries;
[0012] FIG. 2A is an illustration of a collimated bundle with
hexagonal capillaries;
[0013] FIG. 2B is an illustration of a collimated bundle with
circular capillaries;
[0014] FIG. 3 is an illustration of a pressure vessel having a
collimated bundle and polymer matrix loaded and ready for
pressing;
[0015] FIG. 4 is an illustration of a pressure vessel with pressure
being applied to the polymer matrix while back pressure is applied
to the collimated bundle;
[0016] FIG. 5 shows an exploded view of an exemplary pressure
vessel;
[0017] FIG. 6 shows a perspective view of an exemplary pressure
vessel;
[0018] FIG. 7 shows a cross-section view through line 7-7 of FIG.
6;
[0019] FIG. 8 shows a perspective view of an exemplary pressure
vessel with a valve to supply and control back pressure attached
thereto;
[0020] FIG. 9 is a cross-section view through line 9-9 of FIG.
8.
[0021] FIG. 10A is an illustration of an alternative method of
pressing a polymer matrix into a collimated bundle; and
[0022] FIG. 10B is an illustration of an alternative method of
pressing a polymer matrix into a collimated bundle, showing the
polymer matrix being pressed into the capillaries of the collimated
bundle.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0023] Referring to FIGS. 3 and 4, the method and apparatus to
manufacture a coherent bundle of scintillating fibers is shown
generally. As will be described in greater detail below, in the
method and apparatus, a polymer matrix 14 of a transparent polymer
and nanoparticle scintillators is placed on top of a collimated
bundle 10 having a plurality of capillaries and pressed in a
pressure vessel 16 until the polymer matrix 14 is forced into the
capillaries. Pressure is applied via an anvil 18. To prevent
fracturing of the collimated bundle 10 during pressing, back
pressure is supplied to the pressure vessel 16 via a valve 20,
which controls a supply of high pressure gas. Alternatively, as
shown in FIGS. 10A and 10B, the back pressure may also be supplied
by a press and support to the collimated bundle is provided by a
high melting point thermoplastic. Heat may be applied to the
polymer matrix to speed the pressing operation.
[0024] Referring back now to FIG. 1, an illustration of collimated
bundle is shown generally at 10. Collimated bundles 10 are formed
from glass from preforms that are drawn, stacked into bundles, and
redrawn many times. The voids between the drawn glass fibers form
the capillaries 12 with a characteristic dimension as small as 3-15
microns. There may be 6.25.times.10.sup.7 capillaries 12 formed in
the collimated bundle 10. The capillaries have a cross-sectional
shape. FIG. 2A shows a collimated bundle 10 having a plurality of
hexagonal capillaries 12. FIG. 2B shows an illustration of a
collimated bundle 10 having a plurality of circular capillaries 12.
Other profiles or shapes of the capillaries 12 may be formed. The
collimated bundles 10 are formed into round disks and may be about
25 mm in diameter, 2 mm thick with an index of refraction of
1.49-1.53, typically of borosilicate glass. Other diameters and
thicknesses may be used depending on the desired size of the
detector.
[0025] Nanoparticle scintillators are embedded into a transparent
polymer to create a scintillating material, which will subsequently
be force through the capillaries 12 of the collimated bundle 10.
The scintillator infused polymer forms a polymer matrix 14, which
will form the `cores` of our scintillating fibers, and the glass of
the collimated bundle 10 the `cladding` on the fibers. As stated
above, the latter has a refractive index of 1.49-1.53; the polymer
will have a refractive index of at least 1.60 (although since it is
doped with the scintillating nanoparticles, the actual refractive
index of the cores will be much higher). Suitable polymers are
preferably thermoplastics and more preferably polystyrene, nylon
and polypropylene, other transparent polymers that have a
refractive index higher than 1.59 may be suitalble. Suitable
nanoparticle scintillator materials are LaBr(3):Ce, LSO:Ce and
GdAlO (3):Ce. Other nanoparticle scintillator materials may be
used. U.S. Publication 2008/0093557 and U.S. Publication
2010/2072234, incorporated herein by reference, describe
scintillator materials and methods of embedding them in
plastics..
[0026] It is important to note that the resolution limit of the
coherent bundle is almost that of the material itself. Accordingly,
by using scintillating fibers of 3-15 microns, x-rays with a
resolution in the micron range will be detected, a significant
improvement over both computed axial tomography (CAT), which had a
resolution of 150 microns, and current digital x-ray detectors,
which have a resolution of 30 microns.
[0027] The collimated bundle 10 is able to withstand a force
required to push the polymer matrix 14 through the capillaries 12
in the collimated bundle disk, which may be made from borosilicate
glass, which is able to withstand 63-81 GPa in compression (the
lower bound is equivalent to 6.2E4 atmospheres). It is much less
strong in tension, and the glass of the collimated bundle will
crack under the bending load.
[0028] Referring to FIGS. 3 and 4, a successful way to push
scintillating particles into the capillaries 12 of the collimated
bundle 10 is described below. A polymer infused with nanoparticle
scintillators, forming a polymer matrix 14, is forced into the
capillaries 12 of the collimated bundle 10. To avoid damaging the
collimated bundle 10, sufficient back pressure will be applied on
the exit side of the capillaries 12 so that the unbalanced force on
the collimated bundle 10 (i.e. tension) is able to withstand the
critical fracture load of bending.
[0029] FIGS. 5-7 show an exemplary embodiment of a pressure vessel
16 configured to force the polymer matrix 14 into the capillaries
12 of the collimated bundle 10. The pressure vessel 16 is a
cylindrical structure having an inner wall 22 forming a chamber
inside the pressure vessel 16. The pressure vessel includes a top
surface 24, which with the inner wall 22 define a first opening
into the chamber where the collimated bundle 10 and polymer matrix
14 are loaded for pressing. An inner shoulder 26 extends inwardly
from the inner wall of the pressure chamber forming support for a
collimated bundle 10 and polymer matrix 14 stack. A surface
defining a bore 28 and second opening into chamber is below the
inner shoulder 26 and consequently beneath the collimated bundle 10
and polymer matrix 14 stack (when loaded into the pressure vessel
16). An anvil 18 is placed on top of the polymer matrix 14 and
collimated bundle 10 for applying pressure to the pressure chamber
of the pressure vessel through the first opening. During operation,
pressure is applied to the anvil 18, via a press, which presses the
polymer matrix 14, forcing it through the capillaries 12 of the
collimated bundle 10. Optionally, heat may be applied through the
anvil 18 and/or the pressure vessel 16 to the polymer matrix 14 to
soften the polymer matrix 14 and speed the pressing operation.
[0030] Referring to FIGS. 8 and 9, a valve connected to the bottom
opening and is configured to supply and control back pressure to
the chamber. Preferably a high pressure gas is used to supply the
back pressure. The valve may be a needle valve.
[0031] The technique for accomplishing the creation of the coherent
bundle of scintillating fibers is demonstrated in the
following:
[0032] From Poiseuille's law, the volumetric flow rate Q through a
single capillary of radius r and length L1, subject to a pressure
difference .DELTA.P, for a fluid with absolute viscosity is given
as
Q = .pi. r 4 .DELTA. P 8 .eta. L 1 ##EQU00001##
[0033] The pressure distribution is linear along the capillary
length. If we depict the capillaries as comprising a collimated
bundle, the pressure distribution is linear throughout and the same
across each capillary. In the scheme shown there will be no
pressure drop between the collimated bundle and the exit disk
because the pressure drop created by the capillaries is much
greater than that created by the much larger diameter pressure
cell.
.DELTA. P pressure vessel = .DELTA. P ( 1 - L 1 L total )
##EQU00002##
[0034] The total flow rate of the polymer through the disk is given
by the flow through a single capillary times the number of
capillaries, which we calculated here as the ratio of the
collimated bundle area to a single capillary area. The total flow
rate is also equal to the volume of the collimated bundle divided
by the time it takes to fill the capillaries in the collimated
bundle.
Q total = .pi. r 4 .DELTA. P 1 8 .eta. L 1 R 2 r 2 = .pi. R 2 L 1 t
##EQU00003##
[0035] If the exit valve is set at the pressure that the disk
experiences, there will be a constant pressure along the whole of
the coherent bundle. If the valve were sealed, the pressure vessel
would be at the equal to the pressure across the piston. If the
valve were open, the stress of the tension would rupture the
glass.
t .DELTA. P = 8 .eta. 1 - L 1 L total L 1 2 r 2 ##EQU00004##
[0036] We will provide for the pressure drop to be the equivalent
of the flow through a capillary bundle. It is provided for an
adjustment of the valve settings, and it corresponds to the
L.sub.total=L.sub.1+L.sub.valve
[0037] The total resistance shall be given by the sum of the
thickness of the coherent bundle, plus the resistance of the valve
in the outflow.
.DELTA. P 1 = .DELTA. P ( 1 - L 1 L 1 + L valve ) ##EQU00005##
[0038] In a 25 mm collimated bundle the pressure and times may
therefore be calculated. Specifically, R=25 mm, .eta.=200 Pa-s,
L.sub.1=2 mm, r=2.5.times.10.sup.-6
[0039] Consequently, the volume of the collimated bundle is:
.pi.R.sup.2xL.sub.1/2=490.8
[0040] Consequently, flow through the collimated bundle to
infiltrate the capillaries is:
t.DELTA.P.sub.1=1.024.times.10.sup.+9
[0041] The pressure relief valve is equal to the collimated bundle
in the first case sited below: it is equal to the 2 mm thickness.
In the second case, however, it is equal to 18 mm.
A = .DELTA. P 1 = .DELTA. P ( 1 - 2 2 + 2 ) ##EQU00006## B =
.DELTA. P 1 = .DELTA. P ( 1 - 2 2 + 18 ) ##EQU00006.2##
[0042] The Q refers to the mass flow in each of the respective
cases, i.e. 490.8/t.
[0043] The values for a 25 mm disk with 2 mm thickness may be
tabulated as:
TABLE-US-00001 atm Pa t A Q t B Q 1000 1.01E8 20.2 5.05E7 24.25
10.3 9.9E7 43.84 750 7.59E7 27.01 3.78E7 18.77 14.9 6.83E7 32.72
500 5.06E7 40.47 2.79E7 12.87 22.5 4.55E7 21.83 250 2.53E7 81.26
1.26E7 6.01 45.1 2.27E7 10.88
[0044] Referring to FIGS. 10A and 10B, an alternative method of
forming the coherent bundle of scintillating fibers is shown where
a press is configured to apply pressure to the polymer matrix 14
and back pressure to the collimated bundle 10 simultaneously. In
this alternative method, the collimated bundle 10 is supported with
a high melting point thermoplastic 30 such as
polytetrafluoroethylene (i.e. Teflon).
[0045] Therefore, it can be seen that the present invention
provides a unique solution to providing a coherent bundle of
scintillating fibers that has markedly increased resolution than
prior art x-ray detectors, thereby resulting in higher resolution
and more accurate images in medical, engineering and scientific
imaging using CT or CAT scanning technologies. The coherent bundle
of scintillating fibers may also be used in other fields, such as
domestic security and non-destructive testing.
[0046] It would be appreciated by those skilled in the art that
various changes and modifications can be made to the illustrated
embodiments without departing from the spirit of the present
invention. All such modifications and changes are intended to be
within the scope of the present invention except as limited by the
scope of the appended claims.
* * * * *