U.S. patent application number 16/755532 was filed with the patent office on 2021-07-08 for box-type structure having shielding function.
The applicant listed for this patent is Nippon Light Metal Company, Ltd.. Invention is credited to Hidaka Furuya, Hidenori Ishikawa, Maki Takahashi, Hideaki Usui.
Application Number | 20210210237 16/755532 |
Document ID | / |
Family ID | 1000005508808 |
Filed Date | 2021-07-08 |
United States Patent
Application |
20210210237 |
Kind Code |
A1 |
Usui; Hideaki ; et
al. |
July 8, 2021 |
BOX-TYPE STRUCTURE HAVING SHIELDING FUNCTION
Abstract
A box-type structure includes a structure having neutron beam
shielding performance. It is possible to accommodate an organism to
be irradiated in the structure. The box-type structure includes
shielding plates, which include a lithium-fluoride sintered body
having neutron shielding performance. Edge portions of the
shielding plates are joined by abutting against one another. The
edge portions of the shielding plates have a halving joint
structure, and the halving joint structure has a stepped or
inclined cutout shape. The box-type structure has a plurality of
surfaces, and at least one of the faces may be removable or there
may be an opening portion in part of the surface.
Inventors: |
Usui; Hideaki; (Tokyo,
JP) ; Furuya; Hidaka; (Tokyo, JP) ; Takahashi;
Maki; (Tokyo, JP) ; Ishikawa; Hidenori;
(Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nippon Light Metal Company, Ltd. |
Tokyo |
|
JP |
|
|
Family ID: |
1000005508808 |
Appl. No.: |
16/755532 |
Filed: |
October 11, 2018 |
PCT Filed: |
October 11, 2018 |
PCT NO: |
PCT/JP2018/038005 |
371 Date: |
April 10, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 6/508 20130101;
A61N 2005/109 20130101; A61N 5/1077 20130101; G21F 3/00 20130101;
A61B 6/107 20130101; G21F 1/08 20130101; A61N 2005/1094
20130101 |
International
Class: |
G21F 1/08 20060101
G21F001/08; A61B 6/00 20060101 A61B006/00; A61N 5/10 20060101
A61N005/10; A61B 6/10 20060101 A61B006/10; G21F 3/00 20060101
G21F003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 11, 2017 |
JP |
2017-198061 |
Claims
1. A box-type structure comprising shielding plates made of a
sintered body of lithium fluoride, having neutron-shielding
performance, wherein edge portions of the shielding plates are
abutted and joined to each other.
2. The box-type structure according to claim 1, wherein the edge
portions of the shielding plates have a halving joint structure,
and the halving joint structure has a stepped or inclined cutout
shape.
3. The box-type structure according to claim 1, wherein the
box-type structure has a plurality of faces, and at least one of
the faces is removable.
4. The box-type structure according to claim 1, wherein a part of
the faces of the box-type structure has an opening portion.
5. The box-type structure according to claim 1, wherein the
shielding plates are joined with adhesive tape.
6. The box-type structure according to claim 1, wherein the edge
portions of the shielding plates are joined via an adhesive.
Description
TECHNICAL FIELD
[0001] The present invention relates to a box-type structure having
a neutron-shielding function.
BACKGROUND ART
[0002] In recent years, research and development of boron-neutron
capture therapy (BNCT) is rapidly progressing as a means of cancer
treatment. Boron-neutron capture therapy is radiotherapy which uses
a neutron beam. First, a boron compound that is specifically taken
in by cancer cells is administered to a patient. Subsequently, the
cancer cells in which the boron compound has accumulated are
irradiated with a neutron beam whose energy is controlled within a
predetermined range. When the neutron beam collides with the boron
compound, a rays are generated. The cancer cells are killed by the
a rays.
[0003] Boron-neutron capture therapy is promising as a means of
treating cancer and is moving into the clinical trial phase. The
neutron irradiation apparatus used in boron-neutron capture therapy
brings about therapeutic effects by using a thermal neutron beam or
an epithermal neutron beam. The neutron irradiation environment is
a field where radioactive rays having energies in a certain range
coexist.
[0004] It has been necessary so far to use a nuclear reactor as a
neutron generator for supplying a neutron beam to a neutron
irradiation apparatus. However, in recent years, small neutron
generators to be installed in hospitals are being proposed. In such
a small neutron generator, protons and deuterons accelerated by an
accelerator collide with a beryllium or lithium target. The
generated neutron beam has a higher proportion of thermal neutrons
and epithermal neutrons than those generated in conventional
equipment. The generated neutron beam is then decelerated by a
moderator to provide a neutron beam irradiation environment having
little influence on human bodies.
[0005] When neutrons are irradiated in neutron capture therapy, it
is necessary to provide a neutron-shielding means to irradiate a
specific site. In order to examine the effects of neutron capture
therapy, experiments of irradiating small animals, such as mice,
with neutrons have been performed. Patent Document 1 relates to a
case of applying neutron capture therapy using a shielding plate of
lithium fluoride to mammals other than human beings. The object
thereof is to minimize neutrons given to normal tissue when the
target site is deep inside the irradiation object, and to provide
sufficient neutrons to the target located deep inside the
irradiation object by suppressing the reduction in depth and
reachability of neutrons going into the body. [0006] Patent
Document 1: Japanese Unexamined Patent Application, Publication No.
2004-233168
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0007] However, in these shielding methods, the installability and
shielding properties of a shield body may be restricted by the
shape of the organism which is to be an irradiation object, as well
as the size of the irradiation site. Accordingly, there is required
a shielding means that three-dimensionally shields the irradiation
object and separates an irradiation region of the neutron beam from
a non-irradiation region by means of a simple structure.
[0008] Thus, it is an object of the present invention to provide a
box-type structure that has a simple structure having neutron
beam-shielding performance and can accommodate an organism which is
to be an irradiation target.
Means for Solving the Problems
[0009] The present inventors have considered how to solve the
above-described problems. As a result, the present inventors have
found that a box-type structure accommodating an organism can be
easily produced by configuring the box-type structure using
shielding plates made of a specific material and having a
neutron-shielding function, and by making the joining structure at
the edge portions of the shielding plates firm, and thus have
accomplished the present invention. The present invention provides
the following.
[0010] (1) The present invention relates to a box-type structure
including a plurality of shielding plates containing lithium
fluoride and having neutron-shielding performance, wherein edge
portions of the shielding plates are abutted and joined to each
other.
[0011] (2) The present invention relates to the box-type structure
according to aspect (1), wherein the edge portions of the shielding
plates have a halving joint structure, and the halving joint
structure has a stepped or inclined cutout shape.
[0012] (3) The present invention relates to the box-type structure
according to aspect (1) or (2), wherein the box-type structure has
a plurality of faces, and at least one of the faces is
removable.
[0013] (4) The present invention relates to the box-type structure
according to any one of aspects (1) to (3), wherein a part of the
faces of the box-type structure has an opening portion.
[0014] (5) The present invention relates to the box-type structure
according to any one of aspects (1) to (4), wherein the shielding
plates are joined with adhesive tape.
[0015] (6) The present invention relates to the box-type structure
according to any one of aspects (1) to (4), wherein the edge
portions of the shielding plates are joined via an adhesive.
Effects of the Invention
[0016] According to the present invention, in the box-type
structure having neutron-shielding performance, since a plurality
of shielding plates having neutron-shielding performance are joined
in combination, a simple three-dimensional structure can be
obtained. The size of the box-type structure can be freely adjusted
according to the size and the number of the combined shielding
plates.
[0017] In addition, the edge portions of the neutron-shielding
plates can be easily joined to each other by providing stepped or
inclined halving joint structures at the edge portions, and thus an
effect of stabilizing the joining structure can be obtained.
[0018] It is possible to accommodate an organism or the like in a
space shielded from a neutron beam and perform a test in a state in
which not all of the organism or the like is irradiated with a
neutron beam. Furthermore, when the box-type structure has a partly
open structure, a part of the organism or the like can be taken
outside of the shielding region and can be irradiated with a
neutron beam in only that part, broadening the application range of
a neutron beam's irradiation objects and test conditions.
[0019] This box-type structure is suitable for the field of
radiating a neutron beam and examining its action and influence. It
can be used in a test using a small animal such as a mouse, or in
an irradiation test relating to radiotherapy, etc. In addition, a
plurality of irradiation bodies can be simultaneously irradiated by
providing, for example, partitions on the inside of the box-type
structure or by providing a plurality of the box-type structures,
which improves the efficiency of the irradiation test.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a schematic view illustrating a box-type structure
according to an embodiment of the present invention.
[0021] FIG. 2 includes schematic views illustrating a box-type
structure according to another embodiment of the present invention.
(a) is a front view, and (b) is a perspective view.
[0022] FIG. 3 includes schematic views for explaining halving joint
structures at edge portions of shielding plates. (a) is a view
illustrating a halving joint structure composed of edge portions of
shielding plates having stepped concave and convex portions. (b) is
a view illustrating a halving joint structure composed of edge
portions of shielding plates having inclined concave and convex
portions. (c) is a view illustrating a structure composed of flat
edge portions of shielding plates abutted against each other.
[0023] FIG. 4 includes views illustrating an exemplary form of the
edge portion of a shielding plate having a halving joint structure.
(a) is a perspective view, (b) is a plan view, (c) is a
cross-sectional view along the line A-A, and (d) is a
cross-sectional view along the line B-B.
[0024] FIG. 5 includes views illustrating another exemplary form of
the edge portion of a shielding plate having a halving joint
structure. (a) is a perspective view, (b) is a plan view, (c) is a
cross-sectional view along the line A-A, and (d) is a
cross-sectional view along the line B-B.
[0025] FIG. 6 includes views illustrating another exemplary form of
an edge portion of a shielding plate having a halving joint
structure. (a) is a perspective view, (b) is a plan view, (c) is a
cross-sectional view along the line A-A, and (d) is a
cross-sectional view along the line B-B.
[0026] FIG. 7 includes views illustrating another exemplary form of
an edge portion of a shielding plate having a halving joint
structure. (a) is a perspective view, (b) is a plan view, (c) is a
cross-sectional view along the line A-A, and (d) is a
cross-sectional view along the line B-B.
[0027] FIG. 8 includes views illustrating another exemplary form of
an edge portion of a shielding plate having a halving joint
structure. (a) is a perspective view, (b) is a plan view, (c) is a
cross-sectional view along the line A-A, and (d) is a
cross-sectional view along the line B-B.
[0028] FIG. 9 includes views illustrating another exemplary form of
an edge portion of a shielding plate having a halving joint
structure. (a) is a perspective view, (b) is a plan view, (c) is a
cross-sectional view along the line A-A, and (d) is a
cross-sectional view along the line B-B.
[0029] FIG. 10 includes views illustrating another embodiment
related to the box-type structure. (a) is a perspective view, (b)
is a front view, (c) is a right-side view. (d) is a cross-sectional
view along the line A-A, (e) is a cross-sectional view along the
line B-B, (f) is a cross-sectional view along the line C-C, and (g)
is a view illustrating the internal structure.
[0030] FIG. 11 includes views illustrating an embodiment related to
the box-type structure. (a) is a perspective view, (b) is a
perspective view from another direction, (c) is a front view, (d)
is a plan view, (e) is a right-side view. (f) is a cross-sectional
view along the line A-A, (g) is a cross-sectional view along the
line B-B, and (h) is a cross-sectional view along the line C-C.
[0031] FIG. 12 includes views illustrating another embodiment
related to the box-type structure. (a) is a perspective view, and
(b) is a perspective view from another direction.
[0032] FIG. 13 includes views illustrating another embodiment
related to the box-type structure. (a) is a perspective view, and
(b) is a perspective view from another direction.
[0033] FIG. 14 includes views illustrating another embodiment
related to the box-type structure. (a) is a perspective view, and
(b) is a perspective view from another direction.
[0034] FIG. 15 is a perspective view illustrating another
embodiment related to the box-type structure.
[0035] FIG. 16 is a view illustrating another exemplary form of an
edge portion of a shielding plate having a halving joint
structure.
[0036] FIG. 17 includes schematic views illustrating cross-sections
of structures composed of edge portions of shielding plates abutted
against each other. (a) is a view illustrating a structure formed
of stepped concave and convex portions. (b) is a view illustrating
a structure formed of inclined concave and convex portions. (c) is
a view illustrating a structure formed of flat edge portions.
[0037] FIG. 18 is a view for explaining a box-type structure of an
Example.
PREFERRED MODE FOR CARRYING OUT THE INVENTION
[0038] Embodiments of the box-type structure according to the
present invention will now be described. The present invention is
not limited to the following embodiments and can be implemented by
being appropriately modified within a range that does not deviate
from the gist of the present invention.
[0039] (Box-Type Structure)
[0040] The box-type structure includes a plurality of shielding
plates containing lithium fluoride and having neutron-shielding
performance. Edge portions of the shielding plates are abutted and
joined to each other. Here, the term "neutron-shielding
performance" refers to performance of shielding neutron beams. In
the present specification, "neutron-shielding" may be described as
"neutron beam-shielding". The shielding plate according to the
present invention means a neutron-shielding plate. The box-type
structure is composed of a plurality of shielding plates having
neutron-shielding performance assembled into a box-like shape, and
has a simple three-dimensional structure.
[0041] The external appearance of the box-type structure is shown
in FIG. 1. Six shielding plates, e.g., shielding plates 1 and 2,
are assembled to make the box-type structure 10. The edge portion
of the shielding plates are abutted on each other such that the end
faces are closely joined to each other. As the joining means,
adhesive tape or an adhesive can be used. The box-type structure
shown in FIG. 1 is an embodiment in which all outer faces are
surrounded by shielding plates.
[0042] The box-type structure 10 shown by (a) and (b) in FIG. 2 is
another embodiment having an opening 20 provided in a part of the
outer faces. Six shielding plates, e.g., shielding plates, 1, 2, 3,
and 4, are assembled to make the box-type structure. The edge
portions of the shielding plates are abutted on each other such
that the end faces of the shielding plates are closely joined to
each other. As shown by (a) and (b) in FIG. 2, a part of the sides
of the shield 2 is short in length such that the opening 20 is
formed at that part.
[0043] The shielding plates of the box-type structure are made of a
material containing lithium fluoride (LiF), which is excellent in
its neutron-shielding performance. The shielding plates of the
box-type structure prevent the neutron beam radiated from the
outside from passing through. Accordingly, the shielding plates
reduce the neutron beams that reach the inside of the box-type
structure, and thus can make a region (non-irradiation region) that
is not substantially irradiated with the neutron beam in the
box-type structure.
[0044] The box-type structure has a three-dimensional shape, such
as a cube or a rectangular parallelepiped, which forms a
three-dimensional neutron beam-shielding space. The shielding space
can accommodate a small animal, even if it has a certain volume or
more.
[0045] Since the edge portions of the shielding plates are abutted
on and joined to each other, the edge portions form a joining
structure in which the end faces are closely joined to each other.
Accordingly, the neutron beam is sufficiently prevented from
passing through the gap between the edge portions, which can form a
neutron beam-shielding space inside the box-type structure.
[0046] (Shielding Plate)
[0047] The shielding plate has a halving joint structure at the
edge portion. The halving joint structure refers to a structure
which includes a concave portion (hereinafter, referred to as
"concave") or a convex portion (hereinafter, referred to as
"convex") at the edge portions of the shielding plates in such a
manner that the concave and the convex can make a close fit. In the
present specification, the portion having a halving joint structure
in an edge portion of the shielding plate may be also referred to
as the "halving joint portion". The method for forming a halving
joint structure at an edge portion of a shielding plate is referred
to as "halving joint processing".
[0048] The outline of the halving joint structure will be described
using an example shown by (a) and (b) in FIG. 3. (a) in FIG. 3
shows an exemplary form having stepped concave and convex portions
at edge portions of shielding plates. (b) in FIG. 3 shows an
exemplary form having inclined concave and convex portions at edge
portions of shielding plates.
[0049] As shown in (a) of FIG. 3, when the edge portion of one
shielding plate 22 includes a halving joint portion having a
concave (or convex) portion and the edge portion of the other
shielding plate 23 includes a halving joint portion having a convex
(or concave) portion, the concave and convex portions make a close
fit by abutting the edge portions of the shielding plates to give a
joining structure 21 in which the end faces of the shielding plates
22 and 23 are closely joined to each other. In the halving joint
structure of the present embodiment, the concave and convex
portions at the edge portions of the shielding plates preferably
have a stepped cutout shape as shown by (a) in FIG. 3 or an
inclined cutout shape as shown by (b) in FIG. 3. Regarding the
halving joint structure, there are various exemplary forms as shown
in FIGS. 4 to 9.
[0050] As shown by (c) in FIG. 3, when the edge portions are joined
to each other through flat faces and not by a halving joint
structure, the neutron-shielding properties may decrease compared
to the case using halving joint structures such as those shown by
(a) or (b) in FIG. 3. However, supplement firm engagement and
sufficient shielding performance can be made by fixing the joining
faces of the edge portions with an adhesive containing lithium
fluoride. In addition, (a) to (c) in FIG. 17 show exemplary forms
in which these shielding plates are joined for the application to
box-type structures. (a) in FIG. 17 is a view illustrating a
structure composed of stepped concave and convex portions, (b) in
FIG. 17 is a view illustrating a structure composed of inclined
concave and convex portions, and (c) in FIG. 17 is a view
illustrating a structure composed of flat edge portions.
[0051] (a) to (d) in FIG. 4 are views illustrating exemplary forms
in which the edge portions of the shielding plates have halving
joint structures. (a) in FIG. 4 is a perspective view, (b) in FIG.
4 is a plan view, (c) in FIG. 4 is a cross-sectional view along the
line A-A, and (d) in FIG. 4 is a cross-sectional view along the
line B-B. FIGS. 5 to 9 show other exemplary forms of shielding
plates. In each figure, similar to (a) to (d) of FIG. 4, (a) is a
perspective view, (b) is a plan view, (c) is a cross-sectional view
along the line A-A, and (d) is a cross-sectional view along the
line B-B.
[0052] FIG. 4 shows an example in which four sides of a shielding
plate have stepped halving joint structures. As understood from the
cross-sectional views shown by (c) and (d) in FIG. 4, the lengths
of the four sides of the shielding plate on the upper side 31 are
all shorter in length than those of the four sides on the lower
side 32. As a result, as shown by (a) in FIG. 4, this shielding
plate has a shape including steps 33 formed at the edge portions of
four sides.
[0053] FIG. 5 shows another example in which four sides of a
shielding plate have stepped halving joint structures. As
understood from the cross-sectional views shown by (c) and (d) in
FIG. 5, the upper side and the lower side of the shielding plate
differ from each other in the lengths of the four sides. The two
sides 31S among the four sides on the upper side 31 are shorter
than the corresponding two sides on the lower side 32, while the
other two sides 31L on the upper side are longer than the
corresponding two sides on the lower side 32. As a result, as shown
by (a) in FIG. 5, this shielding plate has a shape including steps
33 formed at the edge portions of four sides.
[0054] FIG. 6 shows an example in which three sides of a shielding
plate have stepped halving joint structures. As understood from the
cross-sectional views shown by (c) and (d) in FIG. 6, three sides
among the four sides on the upper side of the shielding plate are
shorter in length than the corresponding three sides on the lower
side. As a result, as shown by (a) in FIG. 6, this shielding plate
has a shape including steps formed at the edge portions of the
three sides.
[0055] FIG. 7 shows an example in which two sides of a shielding
plate have stepped halving joint structures. As understood from the
cross-sectional views shown by (c) and (d) in FIG. 7, two sides
among the four sides on the upper side 31 of the shielding plate
are shorter in length than the corresponding two sides on the lower
side 32. As a result, as shown by (a) in FIG. 7, this shielding
plate has a shape including steps 33 formed at the edge portions of
two sides.
[0056] FIG. 8 shows another example in which two sides of a
shielding plate have stepped halving joint structures. As
understood from the cross-sectional views shown by (c) and (d) in
FIG. 8, the four sides on each of the upper side 31 and the lower
side 32 of the shielding plate have the same length. However, two
sides among the four sides are arranged at different positions from
the corresponding two sides. As a result, as shown by (a) in FIG.
8, this shielding plate has a shape including steps 33 formed at
the edge portions of two sides.
[0057] FIG. 9 shows an example in which one side of a shielding
plate has a stepped halving joint structure. As understood from the
cross-sectional views shown by (c) and (d) in FIG. 9, one side
among the four sides on the upper side 31 of the shielding plate is
shorter in length than the corresponding one side on the lower side
32. As a result, as shown by (a) in FIG. 9, this shielding plate
has a shape including a step 33 formed at the edge portion of one
side.
[0058] The above-described halving joint structures of shielding
plates are not limited to stepped halving joint structures. A
shielding plate having an inclined edge portion as shown by (b) in
FIG. 3 may also similarly have a shape including an inclination
formed at each edge portion of four sides, three sides, two sides,
or one side.
[0059] The planar shapes of the shielding plates shown in FIGS. 4
to 9 are each a square, but the shape is not limited thereto and
may be a rectangle as shown in FIG. 16.
[0060] The end faces of the shielding plates contacts closely with
each other via the above-described halving joint structure to join
the edge portions of the shielding plates. Accordingly, fixing the
abutting portions of the shielding plates are stably fixed to each
other, yielding an effect of enhanced mechanical strength.
[0061] A neutron beam may pass through the gap between the edge
portions of the shielding plates. When the joining portion of the
edge portions of the shielding plates is composed of an even and
flat face, the neutron beam that has entered linearly from the
outside may pass through the joining portion. In contrast, when the
joining portion of the edge portion has a stepped or inclined
halving joint structure as shown in (a) and (b) of FIG. 3 and FIGS.
4 to 9, a neutron beam entering linearly toward the gap between the
edge portions of the shields is blocked by the shielding plate
body, which results in an improved effect of preventing a neutron
beam from entering.
[0062] (Face of Box-Type Structure)
[0063] The box-type structure has a plurality of faces, and at
least one of the faces is preferably removable. The box-type
structure is three-dimensionally configured and therefore has a
plurality of outer faces. These faces have a removable structure.
Accordingly, it is convenient for disassembling the box-type
structure in, for example, preparation for an irradiation test or
withdrawal after the test. In addition, the organism, i.e., an
irradiation object, in the box-type structure can be easily put in
and taken out.
[0064] The box-type structure can be provided with an opening
portion in a part of the faces. Since the outside of the box-type
structure is in an environment under irradiation with a neutron
beam, it is possible to expose a part of the irradiation object to
the outside through the opening portion and to irradiate the part
exclusively. For example, in order to irradiate the leg of a mouse
exclusively for a test with a neutron beam, it is possible to
three-dimensionally cover the mouse body with the box-type
structure and place only the leg of the mouse in the irradiation
environment outside the box-type structure.
[0065] (Joining with Adhesive Tape)
[0066] The shielding plates can be joined with adhesive tape. The
edge portions of the shielding plates are abutted against each
other, and the shielding plate surfaces are then attached to
adhesive tape to fix the shielding plates. Thus, a box-type
structure can be assembled.
[0067] The box-type structure fixed with adhesive tape can be
disassembled by peeling off the adhesive tape after being used in a
necessary test or can be reassembled. The adhesive tape may be any
known product without specific limitation. In order to minimize the
radioactivation rate by irradiation with a neutron beam, it is
preferable to select colorless transparent or translucent tape free
from coloring components and inorganic fillers in the tape base.
The adhesive component adhering to the tape base surface is not
particularly limited and may be, for example, a rubber or acrylic
adhesive agent. The material of the tape base is not particularly
limited and may be, for example, cellophane or acetate.
[0068] (Joining with Adhesive)
[0069] The shielding plates can be joined by adhering the edge
portions with an adhesive. The joining structure of the edge
portions can be strengthened by applying adhesive to a face (end
face) of the edge portions of the shielding plates and abutting the
edge portions against each other. A part of the end faces of the
shielding plates can be temporarily fixed with adhesive tape, and
the part of the end faces can be permanently fixed with an adhesive
afterwards. The temporarily fixed surface can be used as a
removable opening surface.
[0070] The adhesive may be a known product without specific
limitation. An adhesive such as an epoxy resin or a silicone resin
can be used. Since epoxy resin has a low content of elements other
than carbon, hydrogen, and oxygen, the radioactivation rate is low
when irradiated with a neutron beam. Accordingly, it is suitable
for use in medical fields such as radiotherapy. In addition, a
two-liquid curing type epoxy resin is cured by mixing a main agent
and a curing agent. Accordingly, when a powder is added, the main
agent and the curing agent can be separately added to and kneaded
with the powder and can be then mix for reaction and curing. Thus,
the kneading time has a margin, and the workability is improved. It
is possible to select an adhesive having appropriate working time,
curing time and viscosity. If the viscosity is too low, the
adhesive is apt to flow out of the applied gap, and the gap-filling
property is reduced. Accordingly, it is preferable to use an
adhesive having an appropriately high viscosity. A short curing
time is problematic because the time margin for assembling
shielding plates into a desired form is reduced. A long curing time
is problematic because it requires an elongated time for
maintaining the shape of the structure, and therefore, temporary
fixing must be performed for a long time.
[0071] The adhesive used for joining shielding plates may contain a
lithium fluoride powder in an amount of 30 wt % or more. Such an
adhesive functions as a sealant filling the gap between the
shielding plates, as well as glues the shielding plates together.
An adhesive incorporates lithium fluoride containing 6Li, which has
a neutron-shielding function, has the effect of preventing a
neutron beam from entering through the gap between the shielding
plates.
[0072] When the viscosity of the adhesive is low, the adhesive may
contain a lithium fluoride powder in an amount of 40 wt % or more,
50 wt % or more, or 60 wt % or more for adjusting the viscosity to
have appropriate application workability or enhanced
neutron-shielding performance.
[0073] (Embodiment of Box-Type Structure)
[0074] The box-type structure of the present invention can be
provided in various shapes and configurations by combining the
above-described shielding plates. Exemplary forms thereof are shown
in FIGS. 10 to 15.
[0075] (a) to (g) in FIG. 10 show embodiments related to the
box-type structure. (a) in FIG. 10 is a perspective view, (b) in
FIG. 10 is a front view, and (c) in FIG. 10 is a right-side view.
(d) in FIG. 10 is a cross-sectional view along the line A-A, (e) in
FIG. 10 is a cross-sectional view along the line B-B, and (f) in
FIG. 10 is a cross-sectional view along the line C-C. (g) in FIG.
10 is a view illustrating the inside of the box-type structure when
the upper shielding plate 46 is detached. As shown by (a) to (c) in
FIG. 10, it is possible to provide a box-type structure composed of
a combination of six shielding plates 41, 42, 43, 44, 45, and 46
that has a structure in which the shielding plates enclose internal
space completely. The shielding plates 41, 42, 43, 44, 45, and 46
have a structure including the edge portions abutted and joined via
the halving joint portions. On the inside of the box-type
structure, the stepped halving joint structure has a concave on the
inside, as shown by (b) in FIG. 10.
[0076] (a) to (h) in FIG. 11 show another embodiment related to the
box-type structure. (a) in FIG. 11 is a perspective view, (b) in
FIG. 11 is a perspective view from another direction, and (c) in
FIG. 11 is a front view. (d) in FIG. 11 is a plan view, and (e) in
FIG. 11 is a right-side view. (f) in FIG. 11 is a cross-sectional
view along the line A-A, (g) in FIG. 11 is a cross-sectional view
along the line B-B, and (h) in FIG. 11 is a cross-sectional view
along the line C-C. As shown by (a) to (e) in FIG. 11, the box-type
structure is composed of a combination of five shielding plates 41,
42, 43, 44, and 45. As shown by (f) to (h) in FIG. 11, these
shielding plates are abutted and joined to each other via a halving
joint structure formed at the edge portions. One opening is
provided at the upper portion of the box-type structure to give a
structure in which the halving joint portions at the edge portions
of the shielding plates are arranged to protrude outwards along the
periphery of the opening. Accordingly, covering the opening with
another shielding plate makes it possible to give a joining
structure including end faces contacting each other closely. In
addition, it is possible to configure a rectangular parallelepiped
box-type structure by combining the box-type structure with another
box-type structure through connecting the openings to each other. A
shielding plate may be attached to the opening so as to close a
part of the opening.
[0077] (a) and (b) in FIG. 12 show another embodiment related to
the box-type structure. (a) in FIG. 12 is a perspective view, and
(b) in FIG. 12 is a perspective view from another direction. As
shown by (a) and (b) in FIG. 12, this is an example including an
opening provided at each of the upper side and the lower side of
the box-type opening portion. Similar to the box-type structure in
FIG. 10, there is provided a structure in which the halving joint
portions at the end portions of the shielding plates are arranged
to protrude outward along the peripheries of the openings. Except
the above, similar to the box-type structure in FIG. 10, the
shielding plates 41, 42, 43, and 44 have a structure including the
edge portions abutted and joined via the halving joint
portions.
[0078] (a) and (b) in FIG. 13 are views illustrating another
embodiment related to the box-type structure. (a) in FIG. 13 is a
perspective view, and (b) in FIG. 13 is a perspective view from
another direction. As shown by (a) and (b) in FIG. 13, this is an
example including an opening provided at each of the upper side and
the lower side of the box-type opening portion. Similar to the
box-type structure in FIG. 11, there is provided a structure in
which the halving joint portions at the end portions of the
shielding plates are arranged to face inward along the peripheries
of the openings. Except for the above, similar to the box-type
structure in FIG. 10, the shielding plates 41, 42, 43, and 44 have
a structure including the edge portions abutted and joined via the
halving joint portions.
[0079] (a) and (b) in FIG. 14 show another embodiment related to
the box-type structure. (a) in FIG. 14 is a perspective view, and
(b) in FIG. 14 is a perspective view from another direction. As
shown by (a) and (b) in FIG. 14, this is an example including an
opening provided at each of the upper side and the lower side of
the box-type opening portion. Similar to the box-type structure in
FIG. 10, there is provided a structure in which the halving joint
portions at the edge portions of the shielding plates are arranged
to protrude outward along the periphery of the opening at the upper
side. Similar to the box-type structure in FIG. 11, there is
provided a structure in which the halving joint portions at the
edge portions of the shielding plates are arranged to face inward
along the periphery of the opening at the lower side. Except for
the above, similar to the box-type structure in FIG. 10, the
shielding plates 41, 42, 43, and 44 have a structure including the
edge portions abutted and joined via the halving joint
portions.
[0080] The shielding plates shown in FIGS. 10 to 14 each have a
square plane shape, but the shape is not limited thereto and may be
a rectangle as shown in FIG. 15.
[0081] (Regarding Lithium Fluoride Powder Material and a Lithium
Fluoride Sintered Body)
[0082] Regarding a material containing lithium fluoride (LiF), Li
includes two stable isotopes .sup.6Li and .sup.7Li. The natural
abundance ratios of .sup.7Li and .sup.6Li are 92.5 atom % and 7.5
atom %, respectively. Since .sup.6Li contributes to the shielding
of a neutron beam, the neutron beam can be more efficiently
shielded by using .sup.6LiF containing .sup.6Li. The shielding
plate made of a lithium fluoride-containing material is preferably
a lithium fluoride sintered body prepared by shaping and sintering
a lithium fluoride powder to obtain an edge portion structure
having a predetermined shape. For the material of the shielding
plate according to the present embodiment, the content of .sup.6Li
can be adjusted according to the necessary neutron-shielding
performance. For example, when high neutron shielding performance
is required, it is possible to select a lithium fluoride powder
material having a .sup.6Li content of 95 atom % and a LiF purity of
99% or more. Alternatively, it is also possible to use lithium
fluoride having an appropriately adjusted content ratio of .sup.6Li
and .sup.7Li.
[0083] A lithium fluoride sintered body including .sup.6LiF can be
obtained without adding a sintering agent or other inorganic
compound to form a composite material. Accordingly, the shielding
plate made of lithium fluoride according to the present embodiment
can have excellent neutron-shielding performance due to the high
purity of the lithium fluoride itself.
[0084] For the lithium fluoride-containing material according to
the present embodiment, the purity of LiF is preferably 99 wt % or
more. If the shield material contains a large amount of impurities,
such as metal components (elements), the impurities irradiated with
a neutron beam might be radioactivated to emit gamma rays. LiF
itself is not radioactivated even if irradiated with a neutron
beam. Accordingly, regarding the lithium fluoride-containing
material according to the present embodiment, if the purity of the
lithium fluoride itself is low or a sintering agent or other
inorganic compound, i.e., a composite material, is mixed, such
impurities or mixed components may be radioactivated and emit gamma
rays. Thus, the use of lithium fluoride having a high purity is
desirable.
[0085] Examples of methods for manufacturing a lithium fluoride
product include a single crystal growth method, a solidifying
method from a melt, and a sintering method. However, the sintering
method is preferable because this method makes it possible to
supply a stable-quality product at a low cost.
[0086] The single crystal growth method requires high control
accuracy during manufacturing, resulting in low quality stability
and a significantly high product price. In addition, the resulting
single-crystal body has problems such as a high cost for processing
into a predetermined shape, cleavability, and the easy occurrence
of cracks during processing. The solidifying method from a melt
requires strict temperature control during cooling and requires
cooling for a long time, resulting in difficulty in obtaining a
solid substance having a relatively large size and is homogeneous
and defect-fee throughout the substance.
[0087] The sintered body of lithium fluoride (hereinafter may be
also referred to as "LiF sintered body") preferably has a relative
density of 86% or more and 92% or less. In the present embodiment,
the relative density is a value obtained by dividing the density of
a sintered body by the theoretical density of LiF (2.64 g/cm.sup.3)
and multiplying the result by 100. The lithium fluoride sintered
body having a relative density within the above range has the
advantage that swelling and the occurrence of voids and cracks
during sintering are suppressed to provide excellent machinability.
The LiF sintered body is not highly-densified, resulting in the
advantage of excellent machinability.
[0088] If the relative density is too low, there is a risk that the
LiF sintered body does not have sufficient neutron-shielding
performance. In addition, if the relative density is too low, there
is a concern that the ratio of voids inside the sintered body is
high, resulting in an inferior mechanical strength.
[0089] In contrast, if the relative density is too high, the LiF
sintered body has sufficient neutron-shielding performance.
However, there is a concern that the sintered body is highly
densified such that the processing of the sintered body may cause
cracks or the like due to a released residual stress inside the
material.
[0090] The thickness of the LiF sintered body is not particularly
limited as long as a neutron beam can be suitably blocked.
Specifically, the thickness of the LiF sintered body is preferably
2 mm or more and more preferably 3 mm or more from the viewpoint of
the mechanical strength of the sintered body and the workability
during the halving joint processing.
[0091] The upper limit of the thickness of the LiF sintered body is
not particularly limited. From the viewpoint of reducing the size
and weight of the shielding plate, a thinner LiF sintered body is
preferred within a range capable of suitably shielding a neutron
beam. Specifically, the thickness of the LiF sintered body is
preferably 8 mm or less and more preferably 5 mm or less.
[0092] (Method for Manufacturing LiF Sintered Body)
[0093] The method for manufacturing the LiF sintered body according
to the present embodiment includes a pressing step of pressing a
LiF composition containing a LiF powder and an organic shaping
agent to prepare a pressed body, and a firing step of firing the
pressed body at 630.degree. C. or more and 830.degree. C. or less.
Prior to the firing step, for example, a preliminary firing step
for degreasing the organic shaping agent may be performed.
EXAMPLES
[0094] The present invention will now be described in more detail
using examples. The present invention is not limited to these
descriptions.
[0095] (Manufacturing of Box-Type Structure)
[0096] Base plates of a lithium fluoride (LiF) sintered body having
a length of 80 mm, a width of 40 mm, and a thickness of 5 mm were
produced. This sintered body had a relative density within a range
of 88.9% to 91.3%. A shielding plate 1A and a shielding plate 2A
each having a halving joint structure with a predetermined shape
were produced by performing halving joint processing for forming a
step having a length of about 2.5 mm along the peripheries of the
base plates. The shielding plates 1A and 2A were each provided with
a step at each of three peripheral edges. In addition, base plates
having a length of 80 mm, a width of 40 mm, and a thickness of 5 mm
were produced and subjected to halving joint processing for forming
a step having a length of about 2.5 mm at each of the four
peripheral edges to produce shielding plates 3A and 3B. Similarly,
a base plate having a length of 80 mm, a width of 45 mm, and a
thickness of 5 mm was produced and subjected to halving joint
processing for forming a step having a length of about 2.5 mm at
each of the four edges to produce a shielding plate 4A.
Furthermore, a base plate having a length of 80 mm, a width of 25
mm, and a thickness of 5 mm was similarly produced and subjected to
halving joint processing for forming a step having a length of
about 2.5 mm at each of the three edges to produce a shielding
plate 4B.
[0097] Subsequently, the shielding plate 1A and the shielding plate
2A were abutted against each other such that two were joined to
each other at the edge portions of side faces where no halving
joint was provided in the longitudinal direction, to produce a
shielding plate 1B and a shielding plate 2B each having a length of
80 mm and a width of 80 mm. In the abutting and joining, a
two-liquid curing type epoxy adhesive Araldite (registered
trademark) Rapid (manufactured by Huntsman Japan KK) was used. 100
mg of a lithium fluoride powder having a 6Li content of 95 atm %
and a LiF purity of 99% or more was added to each of 100 mg of the
main agent and 100 mg of the curing agent, followed by uniformly
mixing to prepare a main agent mixture and a curing agent mixture
each containing 50 wt % of the lithium fluoride powder.
Subsequently, both agents were uniformly mixed to make an adhesive
containing lithium fluoride in an amount of 50 wt % of the whole
adhesive. A part thereof was applied to the edge portions of the
shielding plates and cured to fix the plates. These shielding
plates 1B, 2B, 3A, 3B, 4A, and 4B were combined to assemble a
box-type structure as shown in FIG. 18.
EXPLANATION OF REFERENCE NUMERALS
[0098] 1, 2, 3, 4, 5 shielding plate [0099] 10 box-type structure
[0100] 20 opening [0101] 21 joining structure [0102] 22, 23, 24,
25, 26, 27 shielding plate [0103] 31 upper side of shielding plate
[0104] 32 lower side of shielding plate [0105] 33 step [0106] 41,
42, 43, 44, 45, 46 shielding plate [0107] 51, 52, 53, 54, 55, 56
shielding plate
* * * * *