A gamma ray collimator including a housing having first and second sections is disclosed. The first section encloses a first section of depleted uranium which is disposed for receiving and supporting a radiation emitting component such as cobalt 60. The second section encloses a depleted uranium member which is provided with a conical cut out focusing portion disposed in communication with the radiation emitting element for focusing the emitted radiation to the target

Casanova, Edgar J.

English

NASA Technical Reports Server

NASA CASE NO.
PRINT FIG.
/,4/-3
SSC-O0013-1
#2
NOTICE
The invention disclosed in thisdoGument resulted from
research in aeronautical and space activities performed under
programs of the National Aeronautics and Space
Administration. The invention is owned by NASA and is,
therefore, available for licensing in accordance with the
NASA Patent Licensing Regulation (14 Code of Federal
Regulations 1245.2).
To encourage commercial utilization of NASA-owned inventions,
it is NASA policy to grant licenses to commercial concerns.
Although NASA encourages nonexclusive licensing to promote
competition and achieve the widest possible utilization, NASA
will consider the granting of a limited exclusive license,
pursuant to the NASA Patent Licensing Regulations, when such
a license will provide the necessary incentive to the
licensee to achieve early practical application of the
invention.
Address inquiries and all applications for license for this
invention to NASA/Marshall Space Flight Center, Patent
Counsel, Mail Code CC01, Marshall Space Flight Center, AL
35812. Approved NASA forms for application for nonexclusive
or exclusive license are available from the above address.
Serial Number 07/740675
Filing Date August 6, 1991
NASA/MSFC
(NA<A-Case-SSC-0001]-I) GAMMA RAY
COLLI_ATL, R Patent Ap_;lication (NASA) 18 p
CSCL 140
G3/3s
NgI-B2515
https://ntrs.nasa.gov/search.jsp?R=19910023201 2020-03-17T14:54:17+00:00Z
NASACASENO. _.... ^_ i
TECHNICAL ABSTRACT
The gamma-ray collimator is a device 18 that focuses gamma
rays toward a target specimen 19 while reducing radiation around
the back and sides of the collimator.
5 The collimator includes a housing 28 having a first section
30 which encloses a first sect!on 50 of depleted uranium and a
second section 34 which encloses a second section 48 of depleted
uranium. The first section 50 of depleted uranium houses a
radiation emitting component which emits radiation through a
10central conical focusing portion 52 of the second section 48 of
depleted uranium which focuses and presents backscattering of
the directed radiation.
The gamma-ray collimator has significant impact in the
productivity of non-destructive inspection of thick walled
15 pressure vessels used by NASA by minimizing the down-time
required for testing the integrity of the vessels. Also, the
gamma-ray collimator has direct application in the petrochemical
industry and other industries which utilize pressure vessels
which must be periodically inspected.
Title:
Inventor:
Employer:
Serial No.:
Filing Date:
Gamma Ray Collimator
Edgar J. Casanova
Sverdrup Technology Inc.
07/740675
August 6, 199!
Cas4 toov R /
PA' T
FILING DATE:
SERIAL NO.:
SSC-00013-1
GAMMA RAY COLLIMATOR
August 6, 1991
07/740675
5
ORGTN OF THE INVENTION
The invention described herein was made in the performance
of work under a NASA contract and is subject to the provisions
of Section 305 of the National Aeronautics and Space Act of
1958, Public Law 85-568 (72 Stat. 435; 42 U.S.C. 2457).
BACKGROUND OF_THE INVENTION
Typically, non-destructive radiographic techniques are used
to radiograph the weldments of large diameter high pressure
vessels with thick walls without access to the interior of the
10 vessel. The presunt radiographic procedures demand unacceptably
long exposure times in order to meet the testing standards set
forth by ASME, Section V. Such long exposure times require that
the pressure vessel be kept out of service for a long period of
time. Additionally, the restricted area (surrounding the
15 radiographic procedure) necessary for personnel is 1,257 feet.
This safety requirement impacts the normal operation where the
vessel is located.
The use of radioisotopes to provide the gamma ray source for
radiographic examination presents a problem in that the isotope
20 sources present a severe radiation hazard and when not in actual
use must be handled carefully and stored and locked in shielded
containers. Thus, remote handling of the gamma ray source is
necessary and such remote handling requires that the gamma ray
source (cobalt 60, in the present application) be first moved
-2-
(by remote controls) from the center to the surface of a
shielded container and then to a point some distance away. In
the present application, this point is a collimator mounted
adjacent the pressure vessel to be tested.
5 The collimator of the present invention is designed to
support and shield Co 60 during actual radiographic exposure and
to focus the radiation from the Co 60 onto the weldment of the
pressure vessel. The collimator allows the radiation to be
emitted in a uniform path toward through the point (surface)
i0 being tested toward a film which is used to record the amount of
radiation passing through the tested surface. The collimator is
designed to shield the Co 60 in such a manner as to prevent an
excessive amount of radiation from being emitted in unwanted
directions. An additional benefit provided by the instant
15 collimator is the mitigation of undesirable backscatter
radiation which adversely affects the quality of radiographs
thus, permitting the radiographer to produce radiographs with
excellent quality and sensitivity. Another feature of the
collimator of the present invention is that it reduces the
20 restricted safety area by 95%. Example: safe stand-off distance
61 feet with the collimator of the present invention versus
1,256.7 feet with no collimator. Additionally, the present
collimator greatly reduces the radiographic exposure time of
presently used radiographic equipment when used in conjunction
25with a special technique under development.
It is an object of the present invention therefore, to
provide a gamma-ray collimator for non-destructlve testing of
pressure vessels or the like.
-3-
It is a further object of the present invention to provide
such a collimator for supporting and shielding a radioisotope
source during the non-destructive testing procedure.
It is another object of the present invention to provide
5 such a collimator with means for focusing the radiation in a
predetermined uniform path to the target.
It is yet another object of the present invention to provide
such a collimator which prevents excessive backscattering of
radiation and thus enhances the quality and sensitivity of the
10 radiographs.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a diagrammatic view illustrating the use of
remotely controlled apparatus utilized in practicing the
principles of the present invention.
15 Figure 2 is a longitudinal cross-sectional view of a
collimator assembly of the present invention illustrating a
housing for enclosing the depleted uranium used in the practice
of the invention.
Figure 3 is a side elevational view of the rear housing
20 section for housing one section of the depleted uraniam.
Figure 4 is a sectional view taken along line 4-4 of Figure
.
Figure 5 is a side elevational view of the depleted uranium.
Figure 6 is an end elevational view of the depleted uranium
25 shown in Figure 5.
-4-
Figure 7 is a side elevational view, partially in section,
of the polypropolene filler material shown in the rear housing
section of Figure 2.
Figure 8 is a front elevational view of the filler material
5 shown in Figure 7.
Figure 9 is a forward elevational view of another embodiment
of the present invention.
Figure I0 is a sectional view taken along lines lO-lO of
Figure 9.
I0 DESCRIPTION OF THE PREFERRED EMBODIMENT
Typically, in a radiographic process (Figure i) an isotope
source i0 is housed in a shielded pig 12 which is disposed in a
shield case assembly 14. Shield case assembly 14 includes
switches and elastically actuated mechanisms for "cranking" the
15 radioisotope (Cobalt 60, for example) element out of the shield
case assembly and into a source tube assembly 16 which is in
communication with the collimator assembly 18 of the present
invention. Collimator assembly 18 focuses the radiation on the
weldment of the pressure vessel being tested as shown in Figure
20 I. The mechanism for cranking the cobalt 60 out of the storage
container is well known in the art.
The shield case assembly 14 of Figure 1 has the cranking
mechanism connected to it and the cranking mechanism includes a
reel assembly 20 having a control box 22 thereon and armored
25 cable tubes 24 and 26 which "cranks" the radioactive element out
of the container 14 and through source tube assembly 16 to
-5-
collimator 18. To indicate the status of shield case assembly
14, "on", "stored" and "open" indicator lights are mounted on
the housing thereof. The reel assembly, shield case assembly,
controls, and the source tube assembly form no part of the
5 collimator of the present invention and are well known in the
art.
As seen in Figure 2, the collimator assembly 18 of the
present invention includes a housing assembly 28 having a
forward cylindrical (focussing) section 30 provided with a front
i0 cover plate 32 and a rear section 34 having a rear cover plate
36. Rear section 34 serves to support and shield the
radioisotope element during the testing process. A circular
flange 38 is attached (as by welding, etc.) to the rear portion
40 of forward housing section 30 and a substantially circular
15 flange 42, having a cut-out portion 43 (Figure 3), is attached
(as by welding) at the forward portion 44 of rear section 34 of
the housing. A circular separator plate 46 (typically,
stainless steel) is disposed between flanges 38 and 42 and
serves as a cover plate for the rear section 34 of the housing.
20 It is to be understood that while lead is typically used to
shield radioisotope material, the present invention uses spent
(depleted) uranium. The depleted uranium shield will weigh
considerably less than a lead shield that would provide the same
amount of attenuation and may be easily directly handled by a
25 person. In the collimator of the present invention the depleted
uranium supports and shields the radioisotope (Co 60) in the
housing and focuses the radiation onto the object to be tested.
-6-
As further seen in Figure 2, the depleted uranium is
comprised of two sections 48 and 50. Section 48 is an annular
member (Figure 2) having a central opening 52 and a bevelled
surface 54 which serves to focus the radiation out of the
5 housing. As seen in Figures 2, 5 and 6, the second section 50
of the depleted uranium includes an end portion 49 having a
substantially conical configuration and a second portion 51
having a substantially circular configuration. Section 50
further includes a side portion 53 (Figures 5 and 6) extending
i0 therefrom. This is an "off-the-shelf" item and is available
with the side portion 53 thereon. If desired, the side portion
53 may be machined off the uranium member to provide the section
50 with a substantially circular transverse cross-sectional
configuration which may be housed in a cylindrical housing.
15 However, if the side protrusion is retained the housing may be
provided with a protruding housing addition 55 (Figures 3 and 4)
to enclose the protruding side portion 53 as described
hereinbelow.
In any event, uranium section 50 (Figures 2, 5 and 6) is
20 provided with an opening 56 extending therethrough. Opening 56
includes a straight, axial portion 58 and an angled portion 60.
A tubular member 62 (Figure 2) having a configuration similar to
opening 56 is supported in opening 56. Tubular member 62
includes an extending end portion 64 which extends into a
25 threaded brass _nsert 66. Insert 66 extends through an opening
68 provided in end plate 36 (Figures 1 and 3). A bracket 69 is
secured to end plate 36 and supports the brass insert 66.
-7-
To support uranium sections 48 and 50 in the housing
sections 30 and 34, a plurality of cushioning members are
provided. Typically, the cushioning members are made of
polypropolene. As can be seen in Figure 2, a pair of cushioning
5 members 70 and 72 are respectively provided at the end and
around spent uranium section 48 to support the uranium section
48 and to provide a cushion against impact. Member 70 is
provided with a flat annular configuration and is positioned
between end plate 32 and the end surface 74 of uranium section
i0 48. An opening 76 in cushion member 70 is axially aligned with
an opening 33 of end plate 32. Cushion member 72 is provided
with a cylindrical configuration and is positioned between the
outer surface 78 of uranium section 48 and the inner surface of
cylindrical housing member 30.
15 To support and cushion the uranium member 50 in the rear
housing member 34, a cushioning member 80 is positioned around
the conical end portion 49 of uranium member 50. Cushion member
80 (Figures 2, 7 and 8) is positioned between member 50 and the
inner surface 81 of cylindrical rear housing member 34 and end
20 plate 36 (Figure 2) and is provided with a substantially conical
internal surface 82 which mates against the conical end portion
49 of uranium member 50. Member 80 further includes a cut-out
portion 84 (Figure 8) to support the protruding portion 53
(Figures 5 and 6) of uranium member 50 therein.
25 Figures 9 and I0 illustrate another embodiment of the
present invention wherein like references refer to like parts.
In this embodiment, the uranium section 50 is provided with
-8-
substantially circular portion 51 and substantially conical end
portion 84. No portion of the uranium section 50 protrudes from
the side as previously discussed. Additionally, in this
embodiment the housing is tubular and includes threaded ends.
5 Threaded end plates are secured at the ends of the housing.
As seen in Figure I0, the collimator 18 includes an
encasement cylinder 90 having threaded ends 92 and 94. An end
cap 96 is disposed in threaded relation with end 92 of
encasement cylinder 90. A second end cap 98 is disposed in
i0 threaded relation with end 94 of encasement cylinder 90. The
annular uranium section 48 and the substantially conical uranium
section 50 is mounted in the encasement cylinder 90, and a
separator plate 100 is mounted in the cylindrical housing
between sections 48 and 50. Uranium sections 48 and 50 are
15 constructed as previously described but without the side
I
protrusion 53. Cap 96 is provided with an opening 102 which is
slightly larger in diameter than the tapered opening 54 of
uranium section 48. Opening 56 is provided with the tubular
member 62 therein and includes extending end portion 64 which
20 extends through an opening 104 provided in the wall 106 of
cylindrical housing 90.
The second uranium section 50 is shown to include the
circular front section 51 and the rear conical portion 49 which
is supported in a bracket 107. Bracket 107 is provided an
25 ogival shaped interior surface 108 which is similar in
configuration to the rear conical portion 49 of member 50.
Bracket 107 is formed by a plurality of spaced gussets II0 which
-9-
extend from a forward attachment plate 112 which is secured to
end plate 96. The inner surfaces of the curved gussets ll0 are
lined with an open cell sponge rubber pad 114 against which
depleted uranium load 50 rests. An open cell sponge rubber pad
5 116 is secured between the back surface 118 of attachment plate
112 and end cap 96. Externally mounted brackets 120 (Figure 9)
are disposed peripherally around the assembly to secure the
assembly to the pressure vessel to be tested.
In operation, the collimator is placed at the desired
10 location on the vessel (Figure i). The source tube end is
connected to the collimator and the gamma ray source is cranked
out of its protective storage container directly into the
collimator. The exposure is timed and the source returned to
the storage container.
15 As can be seen from the above description the present
collimator focuses the gamma rays toward a target specimen while
reducing the radiation level around the back and sides of the
collimator. In one specific design, the collimator is designed
to house 200 curies of cobalt 60 during actual radiographic
20 exposure with a decrease from 212 CI to .5CI of radiation in
unwanted directions. The design of the collimator also
mitigates undesirable backscatter which improves the quality and
sensitivity of the radiograph.
/0
ABSTRACT OF THE DISCLOSURE
A gamma-ray collimator including a housing having first and
second sections. The first section encloses a first section of
depleted uranium which is disposed for receiving and supporting
a radiation emitting component such as cobalt 60. The second
section encloses a depleted uranium member which is provided
with a conical cut-out focusing portion disposed in
communication with the radiation emitting element for focusing
the emitted radiation to the target.
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Gamma ray collimator

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