U.S. patent application number 15/783242 was filed with the patent office on 2018-02-15 for charge stripping film for ion beam.
This patent application is currently assigned to Kaneka Corporation. The applicant listed for this patent is Kaneka Corporation. Invention is credited to Mutsuaki Murakami, Masamitsu Tachibana, Atsushi Tatami.
Application Number | 20180049306 15/783242 |
Document ID | / |
Family ID | 57127098 |
Filed Date | 2018-02-15 |
United States Patent
Application |
20180049306 |
Kind Code |
A1 |
Murakami; Mutsuaki ; et
al. |
February 15, 2018 |
CHARGE STRIPPING FILM FOR ION BEAM
Abstract
A charge stripping film for an ion beam includes a single layer
body of a graphitic film having a carbon component of at least 96
at % and a thermal conductivity in a film surface direction at
25.degree. C. of at least 800 W/mK, or a laminated body of the
graphitic film. The charge stripping film has a thickness of 100 nm
to 10 .mu.m, a tensile strength in a film surface direction of at
least 5 MPa, a coefficient of thermal expansion in the film surface
direction of at least 1.times.10.sup.-5/K, and an area of at least
4 cm.sup.2.
Inventors: |
Murakami; Mutsuaki; (Osaka,
JP) ; Tachibana; Masamitsu; (Osaka, JP) ;
Tatami; Atsushi; (Osaka, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kaneka Corporation |
Osaka |
|
JP |
|
|
Assignee: |
Kaneka Corporation
Osaka
JP
|
Family ID: |
57127098 |
Appl. No.: |
15/783242 |
Filed: |
October 13, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2016/061983 |
Apr 14, 2016 |
|
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15783242 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H05H 2007/005 20130101;
B32B 27/281 20130101; C01B 32/20 20170801; B32B 2307/54 20130101;
H05H 13/04 20130101; H05H 7/08 20130101; B32B 9/007 20130101; C08J
5/18 20130101; H05H 2007/088 20130101; C01B 32/205 20170801; B32B
2307/302 20130101; G21K 1/14 20130101; H05H 7/10 20130101 |
International
Class: |
H05H 7/10 20060101
H05H007/10; B32B 27/28 20060101 B32B027/28; C08J 5/18 20060101
C08J005/18; B32B 9/00 20060101 B32B009/00; H05H 13/04 20060101
H05H013/04; G21K 1/14 20060101 G21K001/14 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 15, 2015 |
JP |
2015-083716 |
Claims
1. A charge stripping film for an ion beam, comprising: a single
layer body of a graphitic film having a carbon component of at
least 96 at % and a thermal conductivity in a film surface
direction at 25.degree. C. of at least 800 W/mK; or a laminated
body of the graphitic film, wherein the charge stripping film has a
thickness of 100 nm to 10 .mu.m, a tensile strength in a film
surface direction of at least 5 MPa, a coefficient of thermal
expansion in the film surface direction of at least
1.times.10.sup.-5/K, and an area of at least 4 cm.sup.2.
2. A charge stripping film for an ion beam of negative hydrogen,
hydrogen or carbon, comprising: a single layer body of a graphitic
film having a carbon component of at least 98 at % and a thermal
conductivity in a film surface direction at 25.degree. C. of at
least 1000 W/mK; or a laminated body of the graphitic film, wherein
the charge stripping film has a thickness of 100 nm to 5 m, a
tensile strength in a film surface direction of at least 5 MPa, a
coefficient of thermal expansion in the film surface direction of
at least 1.times.10.sup.-5/K, and an area of at least 4
cm.sup.2.
3. The charge stripping film according to claim 1, wherein the
charge stripping film is obtained by heat-treating a polymer film
at a temperature of at least 2400.degree. C. in an inert gas
atmosphere, and wherein the polymer film comprises at least one
selected from the group consisting of polyamide, polyimide,
polyquinoxaline, polyparaphenylene, polyoxadiazole,
polybenzimidazole, polybenzoxazole, polybenzothiazole,
polyquinazolinedione, polybenzoxazinone, polyquinazolone,
benzimidazobenzophenanthroline ladder polymer, and derivatives
thereof.
4. The charge stripping film according to claim 3, wherein the
polymer film comprises aromatic polyimide.
5. The charge stripping film for an ion beam according to claim 1,
wherein the tensile strength is at least 20 MPa.
6. The charge stripping film according to claim 1, wherein the
charge stripping film is obtained by heat-treating a polymer film
at a temperature of at least 2800.degree. C. in an inert gas
atmosphere.
7. The charge stripping film according to claim 3, wherein the
polymer film has a thickness of 200 nm to 25 .mu.m.
8. The charge stripping film according to claim 2, wherein the
tensile strength is at least 20 MPa.
9. The charge stripping film for an ion beam according to claim 2,
wherein the charge stripping film is obtained by heat-treating a
polymer film at a temperature of at least 2400.degree. C. in an
inert gas atmosphere, and wherein the polymer film comprises at
least one selected from the group consisting of polyamide,
polyimide, polyquinoxaline, polyparaphenylene, polyoxadiazole,
polybenzimidazole, polybenzoxazole, polybenzothiazole,
polyquinazolinedione, polybenzoxazinone, polyquinazolone,
benzimidazobenzophenanthroline ladder polymer, and derivatives
thereof.
10. The charge stripping film according to claim 2, wherein the
charge stripping film is obtained by heat-treating a polymer film
at a temperature of at least 2800.degree. C. in an inert gas
atmosphere.
11. The charge stripping film according to claim 9, wherein the
polymer film has a thickness of at least 200 nm to 25 .mu.m.
12. The charge stripping film according to claim 9, wherein the
polymer film comprises aromatic polyimide.
Description
TECHNICAL FIELD
[0001] One or more embodiments of the present invention relate to a
charge stripping film that is used for converting charge of an ion
beam, and more specifically to a charge stripping film for an ion
beam for generating an ion beam with higher charge state by
irradiating the film with an ion beam to remove electrons from
ions. One or more embodiments of the present invention relate to a
charge stripping film for an ion beam with very high durability
under high intensity beam irradiation.
BACKGROUND
[0002] A high intensity ion beam made by an accelerator plays an
important role for elucidating phenomena in life-science and
particle physics, and researches and developments for use of high
intensity beams are actively performed all over the world
(Non-Patent Document 1).
[0003] One of the most frequently used high intensity beams is a
positron beam. A positron beam is composed of a large number of
"proton" that is an atomic nucleus of hydrogen and accelerating up
to approximately the speed of light. As for the positron beam, an
H.sup.- beam that is accelerated by a linear accelerator undergoes
charge stripping to become an H.sup.+ beam by a charge stripping
film installed in an injection part of a small synchrotron, and
followed by acceleration in a small synchrotron then a large
synchrotron to become a positron beam with high intensity. This
proton beam is used for various experiments such as neutrino
experiments, structure analysis experiments, and medical treatments
(positron therapy).
[0004] Since the charge stripping film for an ion beam of atom is
exposed both an injection and an orbital beams, the film is
deformed or broken by beam irradiation or heat generation by the
beam irradiation (not less than 1500 K). The durability (life time)
of the charge stripping film is an important determining factor for
the continuous operation of the beam line. Since the charge
stripping film is radioactivated by irradiation with a high
intensity beam, the operator could be exposed to the radiation
during the replacement of the charge stripping film. Therefore,
development of a charge stripping film with high charge stripping
efficiency, excellent durability, no radiation under high intensity
beam irradiation is required (Non-Patent Document 2).
[0005] A charge stripping film for an ion beam, a carbonaceous film
is widely used. When a carbonaceous film is used as a charge
stripping film for an ion beam, a desired range of thickness of the
carbon film is predetermined by the charge state of the original
beam and after charge stripping, and the kind of the beam so as to
obtain a desired charge conversion efficiency. The film thickness,
which is out of the desired range, influences on both the charge
distribution and the charge stripping efficiency of the ion beam
(Non-Patent Document 1). The specific weight per unit area of
carbon is required for converting the high intensity beam to have a
desired charge state. For example, a required carbon weight for
charge stripping of carbon ion (carbon beam) is not less than 0.02
mg/cm.sup.2 and not more than 2.0 mg/cm.sup.2 per unit area. A
biased charge state distribution of ion beam occurs using a carbon
film, which is out of the range. Thus, the film thickness within
the range of not less than 0.02 mg/cm.sup.2 and not more than 2.0
mg/cm.sup.2 of the carbon film and controlling the film thickness
freely are both important for the high conversion efficiency of the
carbonaceous charge stripping film.
[0006] The density of the carbon film used as a charge stripping
film for an ion beam with an atomic number smaller than oxygen
(atomic number 8) may be not less than 1.6 g/cm.sup.3 and not more
than 2.26 g/cm.sup.3. For example, when the density is 2.0
g/cm.sup.3, the thickness of the film may be not less than 100 nm
and less than 10 m so as to satisfy a specific range of weight per
unit area. For example, in the case of a proton beam, it is
considered that the carbon film having a thickness of about 1.5 m
is ideal for making the conversion rate from H.sup.- to
H.sup.+99.7%. Thus, there has been demanded a carbon film for a
charge stripping film capable of responding to the demand of
various beam lines, and adapting to various thicknesses and having
sufficient durability.
[0007] As such charge stripping films, a carbon film prepared by
vapor-deposition method such as arc discharge (Patent Document 1)
and a charge stripping film comprising a hybrid of carbon and boron
(Patent Document 2) have been reported. However, the carbon films
break in a very short time by high intensity proton beam
irradiation.
[0008] Meanwhile, the carbon-boron hybrid type charge stripping
film has significantly longer life time compared to a conventional
carbon film, however, the life time of the films are still
insufficient. For this reason, a replacing a lot of charge
stripping films enables continuous ion beam operation for a year
without breaking the vacuum. Further the physical strength of the
carbon-boron hybrid film is weak, and sodium impurities which is
contained in the reagent during film fabrication process are
radioactivated after an ion beam irradiation. (Non-Patent Document
2).
[0009] An attempt to improve the properties of the charge stripping
film has been made, and one of such an attempt is a carbon nanotube
(CNT) composite film (Patent Document 3). Although this composite
film has high mechanical strength, it can be damaged after a
long-time operation due to its poor heat resistance. Thus, it is
necessary to suspend the operation of the accelerator every time
such damage occurs (Non-Patent Document 3). A CNT composite film
which containing iron and silicon impurities is easily
radioactivated after beam irradiation and several months are
required for the charge stripping film to be transferable from the
radiation controlled area. From these points of view, it has been
urgent to develop a charge stripping film for an ion beam formed of
high purity carbon, having high quality and high heat resistance
for a charge stripping film and no radioactivation.
[0010] As a method for improving the heat resistance of the carbon
film, use of a graphite film is promising. As a candidate for such
a film, a graphite film utilizing natural graphite has been
proposed (Patent Document 4). This graphite film is produced by
washed expanded graphite (obtained by thermal expanding of natural
graphite using an intercalation compound such as acid), followed by
pressing (hereinafter, described as expanded graphite film).
Therefore, the mechanical strength of the film is weak, and it is
difficult to produce or control a thin film of not more than 20
.mu.m.
[0011] As previously described, for the purpose of charge stripping
of an ion beam, an optimum thickness for the individual ion beam is
known. For example, a thin film of less than 10 .mu.m is required
for a smaller atomic number than oxygen, it is difficult to use or
make an expanded graphite film with the thickness of not more than
20 .mu.m. Further, the strength of the film is weak, the film
breaks easily in the vacuumed casing and leading the fear of
scattering of the broken pieces of graphite which is not desired.
Therefore, an expanded graphite film is not able to be used for
satisfying the above purpose.
PATENT DOCUMENTS
[0012] [Patent Document 1] JPB1342226 [0013] [Patent Document 2]
JPB5309320 [0014] [Patent Document 3] JPB4821011 [0015] [Patent
Document 4] JPB4299261
Non Patent Documents
[0015] [0016] [Non Paten Document 1] 27th International Conference
of the International Nuclear Target Development Society
(INTDS-2014) Tokyo, Japan, August, 2014. [0017] [Non Patent
Document 2] Y. Yamazaki et al., Journal of Radioanalytical and
Nuclear Chemistry vol. 305, 2015, pp. 859-864, Proceedings of the
27.sup.th World Conference of the International Nuclear Target
Development Society State-of-the-art technologies for Nuclear
Target and Charge Stripper. [0018] [Non Patent Document 3] Hasebe
H. et al Journal of Radioanalytical and Nuclear Chemistry, 2014,
299, 1013-1018.
SUMMARY
[0019] One or more embodiments of the present invention provide a
charge stripping film for an ion beam that is unlikely to be
damaged or radioactivated even under high intensity beam
irradiation with high durability, heat resistance, and that makes
it easy to control film thickness to be less than 10 .mu.m, and a
charge stripping film for an ion beam may exhibit excellent
mechanical strength.
[0020] One or more embodiments of the present invention provide a
charge stripping film (1) for ion beam, comprising a single layer
body of a graphitic film having a carbon component of not less than
96 at % and a thermal conductivity in a film surface direction at
25.degree. C. of not less than 800 W/mK, or a laminated body of the
graphitic film, wherein the charge stripping film has a thickness
of not less than 100 nm and less than 10 .mu.m.
[0021] One or more embodiments of the present invention also
include a charge stripping film (2) for ion beam of negative
hydrogen, hydrogen or carbon, comprising a single layer body of a
graphitic film having a carbon component of not less than 98 at %
and a thermal conductivity in a film surface direction at
25.degree. C. of not less than 1000 W/mK, or a laminated body of
the graphitic film, wherein the charge stripping film has a
thickness of not less than 100 nm and not more than 5 m.
[0022] In (1) or (2), (3) the charge stripping film for an ion beam
may have a tensile strength in a film surface direction of not less
than 5 MPa, and a coefficient of thermal expansion in the film
surface direction of not more than 1.times.10.sup.-5/K, and (4) an
area of the charge stripping film for an ion beam may be not less
than 4 cm.sup.2.
[0023] (5) The charge stripping film for an ion beam according to
any one of (1) to (4) may be obtained by heat-treating a polymer
film at a temperature of not less than 2400.degree. C. in an inert
gas atmosphere. (6) The polymer film may be at least one selected
from polyamide, polyimide, polyquinoxaline, polyparaphenylene,
polyoxadiazole, polybenzimidazole, polybenzoxazole,
polybenzothiazole, polyquinazolinedione, polybenzoxazinone,
polyquinazolone, benzimidazobenzophenanthroline ladder polymer, and
derivatives thereof. (7) In one or more embodiments of the present
invention, the polymer film may be an aromatic polyimide.
[0024] (8) The aromatic polyimide in (7) may be obtained by using
either or both of pyromellitic anhydride, and
3,3',4,4'-biphenyltetracarboxylic dianhydride as a raw material.
(9) The aromatic polyimide in (7) or (8) may be obtained by using
either or both of 4,4'-diaminodiphenylether, and p-phenylene
diamine as a raw material.
[0025] One or more embodiments the present invention also include a
charge stripping film (10) for ion beam, wherein one or more
carbonaceous layers formed by vapor deposition or sputtering are
laminated on the charge stripping film for an ion beam according to
any one of (1) to (9).
[0026] Further, one or more embodiments of the present invention
include a process for producing the charge stripping film for an
ion beam according to any one of (1) to (9), the production process
is concretely a process for producing the charge stripping film for
an ion beam, wherein a polymer film is heat-treated at a
temperature of not less than 2400.degree. C. in an inert gas
atmosphere.
[0027] In one or more embodiments of the present invention, the
charge stripping film for an ion beam of has excellent heat
resistance because it is a graphitic film, and the film is unlikely
to be damaged under long-time high intensity beam irradiation and
the film has excellent durability because the thermal conductivity
in the film surface direction is not less than 800 W/mK. Since it
has high carbon purity, there is little fear of radioactivation by
an ion beam irradiation, and there is no fear of outgassing even in
high vacuum. Further, the charge stripping film as described herein
enables to create the uniform thickness less than 10 .mu.m, and the
film has sufficient physical strength, thus the charge stripping
film is capable of processing or handling easily.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a schematic perspective view of a fixing jig for
evaluation of durability of a charge stripping film for an ion beam
according to one or more embodiments of the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0029] According to one or more embodiments of the invention, the
charge stripping film for an ion beam is a graphitized film
(graphitic film) among other carbon films, and has a thermal
conductivity in the film surface direction of not less than 800
W/mK. Therefore, the charge stripping film achieves high charge
stripping efficiency even with a thickness of not less than 100 nm
and less than 10 .mu.m, and is not deformed or damaged under
irradiation with a high intensity beam, and has excellent
durability. Further, since the carbon component is not less than 96
at %, radioactivation is controlled. That is, the charge stripping
film for an ion beam as described herein could achieve significant
improvement of durability, reduction in damage, and reduction in
radioactivation as compared with a conventional carbonaceous charge
stripping film or a carbon-boron hybrid film. Further, in one or
more embodiments of the present invention satisfying the
requirements as described above, it is possible to make the tensile
strength in the film surface direction not less than 5 MPa, and the
coefficient of thermal expansion in the film surface direction not
more than 1.times.10.sup.5/K, and also from these points, it can be
said that the damage is suppressed, and durability is improved.
[0030] The merit of employing a graphitic film as a charge
stripping film for an ion beam lies in improvement in the heat
resistance. This is attributed that the graphite has thermally the
most stable structure among carbon crystal systems. By employing a
graphitic film, it is possible to increase the thermal
conductivity. As the thermal conductivity increases, it is possible
to increase the heat releasing effect, and prevent the temperature
of the film from rising due to the heat accumulated in the film.
The thermal conductivity in the film surface direction at a
temperature of 25.degree. C. of the charge stripping film for an
ion beam according to one or more embodiments of the present
invention is not less than 800 W/mK. The higher the heat
diffusivity is, the higher the capability to diffuse the heat that
is locally generated, and the film can withstand the long-time
irradiation with a high intensity beam. Therefore, the thermal
conductivity may be not less than 1000 W/mK, or not less than 1400
W/mK, or not less than 1600 W/mK. The thermal conductivity may be,
for example, not more than 2500 W/mK, and may be not more than 2300
W/mK. The reason of very low durability of the conventional carbon
films as recited in the foregoing Patent Documents 1 and 2 is
considered that the carbon film is in a state approximate to the
amorphous state, and is short of heat resistance, and has low
thermal conductivity for releasing the heat.
[0031] The thickness of the charge stripping film for an ion beam
according to one or more embodiments of the present invention is
not less than 100 nm and less than 10 .mu.m. While the kind of the
atom of the ion beam for which charge stripping is conducted by the
charge stripping film as described herein is not particularly
limited, the aforementioned thickness of the film may be used, in
particular, for charge stripping of ion beams of atoms having an
atomic number of not more than 8 (light atom having an atomic
number of not more than that of oxygen). Among these, for the
purpose of generating a carbon beam by charge stripping of carbon
ions, a thickness within such a range may be used. The thickness of
the charge stripping film may be not more than 5 .mu.m. In one or
more embodiments of the present invention, the range of thickness
of the film for charge stripping is not less than 100 nm and less
than 10 .mu.m, and the thickness of the charge stripping film for
an ion beam may be adjusted depending on the kind and intensity of
the beam for use, and the conversion efficiency to an intended
charge state.
[0032] The carbon purity of the charge stripping film for an ion
beam according to one or more embodiments of the present invention
is not less than 96 at %. The higher the carbon purity, the more
the radioactivation under the long-time irradiation with a high
intensity beam can be prevented. Therefore, the carbon purity may
be not less than 97 at %, or not less than 98 at %, or not less
than 99 at %. Particularly, metallic impurities such as aluminum,
iron, sodium, potassium, cobalt, titanium and nickel that can be a
cause of radioactivation are desirably not more than detection
limits. In one or more embodiments of the present invention, the
raw material of the charge stripping film for an ion beam is a
polymer film as will be described later, and there is no chance
that the charge stripping film is contaminated by impurities
including metal during the production process thereof. Also, by
annealing at a temperature of not less than 2400.degree. C. as will
be described later, nitrogen, oxygen and hydrogen in the polymer
are eliminated and only pure carbon remains. Therefore, the method
according to one or more embodiments of the present invention is a
very excellent method for forming a film composed exclusively of
pure carbon, and has a feature of being unlikely to have
contaminants other than carbon.
[0033] Among use applications of the charge stripping film for an
ion beam, as a charge stripping film especially for ion beam of a
negative hydrogen, hydrogen or carbon, the charge stripping film
for an ion beam may have a thickness of not less than 100 nm and
not more than 5 .mu.m, a carbon component of not less than 98 at %,
and a thermal conductivity in the film surface direction of not
less than 1000 W/mK. Since ion beams of negative hydrogen, hydrogen
and carbon are beams having very high energy, the characteristics
required for the charge stripping film are stricter. The reason why
a thinner graphitic film may be used in the use application for an
ion beam of negative hydrogen, hydrogen or carbon, in which higher
properties are required, is considered as follows. As will be
described later, the charge stripping film according to one or more
embodiments of the present invention is produced by a polymer
annealing method, and in the polymer annealing method,
graphitization reaction is considered to proceed in the following
manner. First, a graphitization reaction starts from the outermost
layer of the polymer carbonized film, and the graphite structure
grows toward inside the film. As the film thickness of the carbon
film increases, the graphite structure becomes more disordered and
a cavity or a defect is more likely to arise toward inside the
carbon film at the time of graphitization. Contrarily, as the film
thickness decreases, the graphitization proceeds to inside in the
condition that the graphite layer structure of the film surface is
well-ordered, resulting that a graphite structure that is
well-ordered all over the film is likely to be formed. Thus, it is
supposed that a film having higher thermal conductivity is obtained
as the film thickness is smaller because the graphite layer
structure is well-ordered, and the film can be used also for a beam
of high energy. For example, it has been confirmed that when
aromatic polyimide (film thickness 8 .mu.m) is used as a raw
material, the thickness of the graphitic film obtained by a
treatment at 2400.degree. C. for 30 minutes is 4 .mu.m, and the
carbon component is not less than 98 at %, and the thermal
conductivity in the film surface direction is not less than 1000
W/mK. In short, it is understood that a graphitic film having a
higher carbon purity and higher thermal conductivity can be
obtained by employing a smaller film thickness.
[0034] In one or more embodiments of the present invention, the
charge stripping film for an ion beam may have mechanical strength,
and small coefficient of thermal expansion by heating and cooling.
When the charge stripping film for an ion beam is a graphitic film,
it is possible to reduce the coefficient of thermal expansion of
the film, and thus strain by thermal expansion can be reduced, so
that mechanical damage can be controlled. According to one or more
embodiments of the present invention, the coefficient of thermal
expansion in the film surface direction of the graphitic film may
be not more than 1.times.10.sup.-5/K, or not more than
7.times.10.sup.-6/K, or not more than 5.times.10.sup.-6/K. The
lower limit of the coefficient of thermal expansion is not
particularly limited, but is normally about
5.times.10.sup.-7/K.
[0035] The tensile strength in the film direction of the charge
stripping film for an ion beam as described herein may be not less
than 5 MPa. The tensile strength may be not less than 10 MPa, or
not less than 20 MPa, or not less than 30 MPa. While the upper
limit of the tensile strength is not particularly limited, it may
be, for example, 100 MPa. Regarding the graphitic film produced by
the expansion method as described above, it was difficult to form a
film having a thickness of less than 10 .mu.m, and its tensile
strength was not more than 0.2 kgf/cm.sup.2 (namely, 0.02 MPa) in
Patent Document 4, and was about 4 MPa in Comparative Example as
will be described later. In contrast, in one or more embodiments of
the present invention, the charge stripping film for an ion beam
produced in Example as will be described later has a tensile
strength of 40 MPa, and it is apparent that the graphitic film
produced by the expansion method cannot be used for one or more
embodiments of the present invention also from the view point of
the tensile strength. Further, the mechanical strength of the
amorphous carbon film and the carbon-boron hybrid film that have
been conventionally used as charge stripping films is not more than
1 MPa, and this would be one factor of deterioration in the
durability of the hybrid film.
[0036] In one or more embodiments of the present invention, the
density of the charge stripping film for an ion beam as described
herein may be not less than 1.6 g/cm.sup.3. Generally, a highly
heat conductive carbon film has a very dense structure lacking a
defect or a cavity in the film, however, when a defect or a cavity
enters inside the carbon film, the density decreases and the
thermal conductivity tends to decrease. It is considered that heat
is likely to be trapped in the cavity part, and the carbon film
having low density is susceptible to deterioration by the heat.
Thus, the density of the graphitic film may be large, for example,
may be not less than 1.8 g/cm.sup.3, or not less than 2.0
g/cm.sup.3. The upper limit of the density is not more than 2.26
g/cm.sup.3 which is a theoretical value for the graphite single
crystal.
[0037] The area of the charge stripping film for an ion beam as
described herein may be not less than 4 cm.sup.2. From the view
point that the larger the area is, the more the thermal diffusivity
improves and the charge stripping film can withstand the high
intensity beam over a long period of time, the area may be not less
than 9 cm.sup.2, or not less than 16 cm.sup.2, or not less than 25
cm.sup.2. The larger the area is, the more the heat-release
property improves, and the effect of releasing heat from the high
intensity beam is high. Contrarily, when the case where an area is
too small, it may be difficult to fix the film to a jig or a heat
sink, and the heat radiation efficiency may be impaired. While the
upper limit of the area is not particularly limited, it is normally
about 900 cm.sup.2.
[0038] As previously described, in order to convert a high
intensity beam to have an intended charge state, carbon of a
specific weight per unit area is required, and in the charge
stripping film of carbon (carbon beam), carbon may be not less than
0.02 mg/cm.sup.2 and not more than 2.0 mg/cm.sup.2, or not less
than 0.1 mg/cm.sup.2 and not more than 2.0 mg/cm.sup.2, or not less
than 0.4 mg/cm.sup.2 and not more than 2.0 mg/cm.sup.2. For
example, for the purpose of charge stripping of carbon (carbon
beam), it is important that the film thickness of the carbon film
can be controlled freely so that the carbon is not less than 0.02
mg/cm.sup.2 and not more than 2.0 mg/cm.sup.2. In one or more
embodiments of the present invention, as will be described later,
the thickness of the charge stripping film for an ion beam can be
freely varied by controlling the film thickness of the polymer film
that is a raw material, and the area and the shape of the charge
stripping film can also be varied easily.
[0039] In one or more embodiments of the present invention, the
charge stripping film for an ion beam as described herein may be
adjusted to have an intended thickness. In such embodiments, the
charge stripping film may be used alone (single layer body). It is
also envisioned that two or more films may be laminated to adjust
into an intended thickness (laminated body). Consideration of one
or more embodiments of the present invention revealed that the
charge stripping film for an ion beam as described herein
sufficiently functions as a charge stripping film even when a
plurality of charge stripping films are laminated, and this is also
a great advantage of one or more embodiments of the present
invention. By using the charge stripping film for an ion beam as
described herein, it is possible to easily produce films with
various thicknesses that are optimum for the desired beam charge
state only by changing the combination of the charge stripping
films for ion beam having different thicknesses.
[0040] In each case of the single layer body and the laminated
body, the body is used as a charge stripping film having a
thickness of not less than 100 nm and less than 10 m. When two or
more charge stripping films for an ion beam as described herein are
used, the charge stripping films may be closely adhered, or may be
arranged one by one independently at an interval in the travel
direction of the ion beam. In the case of arranging the charge
stripping films one by one independently, if the interval is too
small, heat is likely to be trapped between the charge stripping
films at the time of irradiation with a beam, and the possibility
of damage arises. Therefore, in laminating two or more films, the
films may be closely adhered.
[0041] In the case of using the charge stripping film for an ion
beam as described herein as a charge stripping film, a different
kind of carbon film may be laminated on the charge stripping film
for an ion beam. In particular, for finely controlling the ion
charge state of the beam, the thickness of the charge stripping
film may be finely controlled. In such a case, the thickness can be
finely controlled by making a carbon film (carbonaceous film) on
the charge stripping film for an ion beam as described herein by
vapor deposition, sputtering or the like. The carbon film
(carbonaceous film) obtained by vapor deposition, sputtering or the
like normally has a thermal conductivity in the film surface
direction at 25.degree. C. of less than 800 W/mK. Since the charge
stripping film for an ion beam according to one or more embodiments
of the present invention is excellent in physical strength, no
problem arises even when a composite carbon film is produced by
such a technique.
[0042] While the kind of the atom of the ion beam for which charge
stripping is conducted by the charge stripping film as described
herein is not particularly limited, the charge stripping film may
be used for, in particular, an ion beam of an atom having an atomic
number of not more than 8, such as a proton, a carbon beam or the
like. The graphitic charge stripping film as described herein may
be used not only in a large-size accelerator, but also in a medical
accelerator such as an accelerator for cancer therapy and in a
relatively small-size accelerator for industrial use or the
like.
[0043] In one or more embodiments of the present invention, the
charge stripping film for an ion beam is high thermal conductive
film, and has high carbon purity, so that it is chemically stable
without the fear of radioactivation after irradiation with a high
intensity beam, and has very high heat resistance, and lacks the
fear of outgassing in high vacuum under high temperature. Also, the
charge stripping film can be obtained as a large area film, and is
featured by excellent mechanical strength.
[0044] Next, a method for producing the charge stripping film
according to one or more embodiments of the present invention will
be described. The charge stripping film as described herein can be
produced by using a predetermined polymer material, and
graphitizing the polymer material by conducting a heat treatment at
not less than 2400.degree. C. in an inert gas atmosphere.
<Polymer Raw Material>
[0045] The polymer raw material that may be used in the production
of a graphitic charge stripping film as described herein is an
aromatic polymer, and the aromatic polymer may be at least one
selected from the group consisting of polyamide, polyimide,
polyquinoxaline, polyparaphenylene vinylene, polyoxadiazole,
polybenzimidazole, polybenzoxazole, polybenzothiazole,
polyquinazolinedione, polybenzoxazinone, polyquinazolone,
benzimidazobenzophenanthroline ladder polymer, and derivatives
thereof. The film formed of such a polymer raw material can be
produced by a known production process. Examples of the polymer raw
material may include aromatic polyimide, polyparaphenylene
vinylene, and polyparaphenylene oxadiazole. In one or more
embodiments of the present invention, aromatic polyimide that is
produced from acid dianhydride (particularly, aromatic acid
dianhydride) and diamine (particularly, aromatic diamine) described
below via polyamic acid may be used as a polymer raw material for
producing a graphitic charge stripping film as described
herein.
[0046] Examples of the acid dianhydride used in synthesis of the
aromatic polyimide include pyromellitic anhydride,
2,3,6,7-naphthalenetetracarboxylic dianhydride,
3,3',4,4'-biphenyltetracarboxylic dianhydride,
1,2,5,6-naphthalenetetracarboxylic dianhydride,
2,2',3,3'-biphenyltetracarboxylic dianhydride,
3,3',4,4'-benzophenone tetracarboxylic dianhydride,
2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 3,4,9,10-perylene
tetracarboxylic dianhydride, bis(3,4-dicarboxyphenyl)propane
dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride,
1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride,
bis(2,3-dicarboxyphenyl)methane dianhydride,
bis(3,4-dicarboxyphenyl)ethane dianhydride, oxydiphthalic
dianhydride, bis(3,4-dicarboxyphenyl)sulfone dianhydride,
p-phenylene bis(trimellitic monoester acid anhydride), ethylene
bis(trimellitic monoester acid anhydride), bisphenol A
bis(trimellitic monoester acid anhydride), and analogues thereof,
and these can be used solely or a mixture of any desired ratio. In
particular, for the reason that the polyimide film having a polymer
architecture having a very rigid structure has higher orientation,
and from the view point of the availability, pyromellitic
anhydride, and 3,3',4,4'-biphenyltetracarboxylic dianhydride may be
used.
[0047] Examples of the diamine used in synthesis of the aromatic
polyimide include 4,4'-diaminodiphenylether, p-phenylenediamine,
4,4'-diaminodiphenylpropane, 4,4'-diaminodiphenylmethane,
benzidine, 3,3'-dichlorobenzidine, 4,4'-diaminodiphenylsulfide,
3,3'-diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfone,
4,4'-diaminodiphenylether, 3,3'-diaminodiphenylether,
3,4'-diaminodiphenylether, 1,5-diaminonaphthalene,
4,4'-diaminodiphenyldiethylsilane, 4,4'-diaminodiphenylsilane,
4,4'-diaminodiphenylethylphosphine oxide, 4,4'-diaminodiphenyl
N-methylamine, 4,4'-diaminodiphenyl N-phenylamine,
1,4-diaminobenzene(p-phenylenediamine), 1,3-diaminobenzene,
1,2-diaminobenzene and analogues thereof, and these can be used
solely or a mixture of any desired ratio. Further, from the view
point of improving the orientation of the polyimide film, and the
availability, the aromatic polyimide may be synthesized by using
4,4'-diaminodiphenylether, or p-phenylenediamine as a raw
material.
[0048] For the preparation of polyamic acid from acid dianhydride
and diamine, a known method can be used, and normally, at least one
kind of aromatic acid dianhydride and at least one kind of diamine
are dissolved in an organic solvent, and the obtained solution of
polyamic acid in organic solvent is stirred under a controlled
temperature condition until polymerization between the acid
dianhydride and the diamine completes. These polyamic acid
solutions may be obtained normally in a concentration of 5 to 35 wt
%, or in a concentration of 10 to 30 wt %. When the concentration
falls within this range, an appropriate molecular weight and
solution viscosity can be obtained. In one or more embodiments of
the present invention, acid dianhydride and diamine in the raw
material solution may be substantially equivalent molar amounts,
and the molar ratio may be, for example, 1.5:1 to 1:1.5, or 1.2:1
to 1:1.2, or 1.1:1 to 1:1.1.
<Synthesis of Polymer Raw Material, Film Formation>
[0049] The polymer film can be produced from the polymer raw
material or the synthetic material thereof by various known
techniques. As a method for producing polyimide, a heat curing
method in which a polyamic acid as a precursor is converted into
imide by heating, and a chemical curing method in which a polyamic
acid is converted into imide by using a dehydrating agent typified
by acid anhydride such as acetic anhydride, or tertiary amines such
as picoline, quinoline, isoquinoline, and pyridine as an
imidization promoting agent are known, and any of these methods can
be used. A chemical curing method may be used from the view point
that the obtained film has a small coefficient of linear expansion,
and high modulus of elasticity, and tends to have large
birefringence index, and is not damaged under a tension during
annealing of the film, and a carbon film having excellent quality
is obtained. The chemical curing method is excellent also in the
aspect of improvement in the thermal conductivity of the carbon
film.
[0050] The polyimide film is produced by casting a solution of
polyamic acid which is the aforementioned polyimide precursor in an
organic solvent, on a support such as an endless belt or a
stainless drum, and drying to allow imidization. Specifically, the
production process of the film by chemical curing is as follows.
First, in the aforementioned polyamic acid solution, not less than
a stoichiometric quantity of a dehydrating agent, and a catalytic
amount of an imidization promoting agent are added, and the
solution is casted or applied on a support plate or an organic film
of PET or the like, or a support such as a drum or an endless belt,
to give a film form, and the organic solvent is evaporated to give
a film having self-supportability. Subsequently, the film is
imidized while it is further heated and dried to obtain a polyimide
film. The temperature in heating may be in the range of 150.degree.
C. to 550.degree. C. Further, the production process of the
polyimide may include the step of fixing or elongating the film so
as to prevent it from contracting. This is based on the fact that
conversion into the carbon film proceeds more easily by using a
film in which molecular structure and its high order structure are
controlled. That is, in order to make the graphitization reaction
proceed smoothly, it is necessary to rearrange the carbon molecules
in the graphite precursor. It is supposed that conversion to
graphite is easy to proceed even at low temperature because only
minimum rearrangement is required in polyimide having excellent
orientation.
[0051] The charge stripping film for an ion beam of as described
herein has a thickness within the range of not less than 100 nm and
less than 10 .mu.m, and for obtaining a carbon film of such a
range, the thickness of the polymer film as a raw material may be
in the range of 200 nm to 25 m in the case of aromatic polyimide.
This is because the thickness of the finally obtained carbon film
generally depends on the thickness of the starting polymer film,
and the thickness of the charge stripping film for an ion beam
obtained in the process of carbonization and graphitization by the
heat treatment at not less than 2400.degree. C. becomes about 1/2
of the thickness of the polymer as a raw material. As described
above, it is important that the thickness of the charge stripping
film can be freely varied depending on the charge of the original
beam, the charge of the beam after charge stripping, and the kind
of the beam. According to the polymer annealing method, it is
possible to freely vary the thickness of the obtainable charge
stripping film for an ion beam by controlling the film thickness of
the polymer film as a raw material, and it is possible to easily
vary the area or the shape. Thus, the polymer firing method is very
suitable process for producing a charge stripping film.
<Carbonization, Graphitization>
[0052] Next, the technique of carbonization and graphitization of
the polymer film typified by polyimide will be described. In one or
more embodiments of the present invention, a polymer film as a raw
material is preheated in an inert gas or in a vacuum to be
carbonized. As the inert gas, nitrogen, argon or a mixed gas of
argon and nitrogen may be used. The preheating is generally
conducted at about 1000.degree. C. The heating rate to the
preheating temperature is not particularly limited, but can be, for
example, 5 to 15.degree. C./minute. In the preheating stage, it is
effective to apply a pressure in the vertical direction on a film
surface to such an extent that breakage of the film does not occur
so as to prevent the orientation of the starting polymer film from
being lost.
[0053] The film carbonized by the method as described above is set
in a high temperature furnace, and a graphitized. The carbonized
film may be set in such a manner that it is sandwiched between CIP
materials or glassy carbon substrates. Graphitization is conducted
at not less than 2400.degree. C. In this manner, it is possible to
make the thermal conductivity in the film surface direction of the
obtainable charge stripping film for an ion beam not less than 800
W/mK. Graphitization is conducted at high temperatures which may be
not less than 2600.degree. C., or not less than 2800.degree. C., or
not less than 3000.degree. C. The treatment temperature may be the
highest temperature in the graphitization process, and the obtained
charge stripping film can be heat-treated again in the form of
annealing. In order to produce such a high temperature, generally,
a current is directly applied to a graphite heater, and heating is
conducted by utilizing the Joule heat. While the graphitization is
conducted in an inert gas, argon is most appropriate as an inert
gas, and a small amount of helium may be added to argon. The higher
the treatment temperature is, the higher quality of graphite is
obtained by conversion, however, an excellent charge stripping film
for an ion beam is obtained even when the treatment temperature is,
for example, not more than 3700.degree. C., particularly, not more
than 3600.degree. C., or not more than 3500.degree. C.
[0054] The heating rate from the preheating temperature to the heat
treatment temperature can be, for example, 1 to 25.degree.
C./minute. The retention time at the treatment temperature is, for
example, not less than 10 minutes, or may be not less than 30
minutes, and may be not less than 1 hour. An upper limit of the
retention time is not particularly limited, but may be generally,
not more than 10 hours, in particular, about not more than 5 hours.
When the heat treatment is conducted at a temperature of not less
than 3000.degree. C. to graphitize, the atmosphere in the
high-temperature furnace may be pressurized by the inert gas. When
the heat treatment temperature is high, carbon starts sublimating
from the film surface, and deterioration phenomena such as
expansion of holes and cracks on the graphite film surface, and
thinning occur. However, by pressurization, such deterioration
phenomena can be prevented, and an excellent graphite film can be
obtained. The pressure (gauge pressure) of atmosphere in the
high-temperature furnace by the inert gas is, for example, not less
than 0.05 MPa, or may be not less than 0.10 MPa, or not less than
0.14 MPa. While the upper limit of the pressure of atmosphere is
not particularly limited, it may be, for example, not more than 2
MPa, in particular, about not more than 1.8 MPa. After the heat
treatment, the temperature can be lowered at a rate of, for
example, 30 to 50.degree. C./minute.
<Evaluation of Charge Stripping Film for an Ion Beam>
[0055] For the film obtained through the carbonization and
graphitization treatments as described above, whether the film is
carbonaceous or graphitic can be evaluated by a laser Raman
measurement. For example, in the case of laser Raman spectroscopy,
a band (RG) based on a graphite structure appears at 1575 to 1600
cm.sup.-1, and a band (RC) based on an amorphous carbon structure
appears at 1350 to 1360 cm.sup.-1. Therefore, by conducting Raman
measurement for the graphite film surface, and measuring a relative
intensity ratio RG/RC of these two bands, whether the obtained film
is an amorphous carbonaceous film or a graphitic charge stripping
film for an ion beam can be determined. The relative intensity
ratio RG/RC is called Raman intensity ratio R. In the case of one
or more embodiments of the present invention, Raman measurement is
conducted for a graphite film surface, and the graphite film
showing the intensity of the band based on the graphite structure
higher than the intensity of the band based on the amorphous carbon
structure by 5 times or more (namely, Raman intensity ratio
R.gtoreq.5) is defined as a graphitic charge stripping film for an
ion beam.
[0056] As an index for determining whether the obtained film is a
charge stripping film for an ion beam or a carbonaceous film,
physical properties of thermal conductivity of the film can be
used. When an aromatic polyimide (trade name: Kapton) was used as a
raw material and a thickness of the film as a raw material was 25
.mu.m (therefore, the thickness of the obtained film was about 10
.mu.m), the thermal conductivity of the film obtained by the heat
treatment was 50 W/mK at 2000.degree. C., 200 W/mK at 2200.degree.
C., 800 W/mK at 2400.degree. C., 1200 W/mK at 2600.degree. C., 1600
W/mK at 3000.degree. C. At this time, the Raman intensity ratio R
was R=1 for the treatment at 2200.degree. C., R=5 for the treatment
at 2400.degree. C., R=6 for the treatment at 2600.degree. C., and
R>99 for the treatment at 3000.degree. C. At the temperatures of
not less than 2400.degree. C. where the Raman intensity rapidly
increases and the graphitization proceeds, the value of thermal
conductivity also rapidly increases, revealing that these values
can also be good indexes for determining the graphitization.
[0057] The present application claims the benefit of priority based
on Japanese Patent Application No. 2015-083716 filed on Apr. 15,
2015. The entirety of description of Japanese Patent Application
No. 2015-083716 filed on Apr. 15, 2015 is incorporated in the
present application for reference.
EXAMPLES
[0058] Hereinafter, one or more embodiments of the present
invention will be described more specifically by way of Examples.
Of course, it goes without saying that the present invention is not
limited by these Examples, and various forms can be made for the
details.
(Evaluation Method of Physical Property)
<Film Thickness>
[0059] The thickness of the polymer film which is a raw material,
and the thickness of the produced charge stripping film include an
error of about .+-.5 to 10%. Therefore, the mean of thicknesses
measured at different 10 points in the polymer film as a raw
material or the obtained charge stripping film was adopted as the
thickness of the sample in one or more embodiments of the present
invention. When the film thickness of the produced charge stripping
film is not more than 0.5 .mu.m, the film section was observed at
an accelerating voltage of 5 kV by using a scanning electron
microscope (SU8000) manufactured by Hitachi High-Technologies
Corporation, and the thickness was calculated.
<Density>
[0060] A volume was calculated after measurement of the dimension
of the film and the film thickness, and a mass was separately
measured, and density of the produced charge stripping film was
calculated from the formula: density (g/cm.sup.3)=mass (g)/volume
(cm.sup.3). It was impossible to measure the density of a film
having a thickness of not more than 200 nm by this method because
the error was too large. Thus, in calculating thermal conductivity
from thermal diffusivity of a film having a thickness of not more
than 200 nm, the calculation was conducted assuming that the
density was 2.1.
<Thermal Conductivity>
[0061] The thermal diffusivity of the charge stripping film was
measured at 25.degree. C. in vacuum (about 10.sup.-2 Pa), at a
frequency of 10 Hz using a thermal diffusivity measuring apparatus
based on the periodic heating method ("LaserPit" apparatus,
available from ULVAC-RIKO, Inc.). In this measuring method, a
thermocouple is attached at a point apart by a certain distance
from a point irradiated with a laser to be heated, and the
temperature change of the thermocouple is measured. The thermal
conductivity (W/mK) was calculated by multiplying thermal
diffusivity (m.sup.2/s), density (kg/m.sup.3), and specific heat
(798 kJ/(kg. K)). However, when the thickness of the graphite sheet
is not more than 1 m, the measurement error is too large, and
accurate measurement was impossible.
[0062] Thus, as a second measuring method, measurement was
conducted by using a periodical heating radiant temperature
measuring (Thermo Analyzer TA3 manufactured by BETHEL Co., Ltd.).
This is an apparatus that conducts periodical heating by a laser,
and measures the temperature by a radiation thermometer. Since the
non-contact measurement was carried out using this apparatus, a
graphite sheet with the thickness of not more than 1 .mu.m was able
to be measured. For confirming the reliability of the measured
values by both methods, several graphite films were measured by
both methods and both measured values were confirmed to be
identical.
[0063] The frequency of periodical heating using BETHEL apparatus
can be varied up to 800 Hz. The features of this apparatus are
non-contact temperature measurement using a radiation-thermometer
instead of conventional contact temperature measurement method with
thermocouple and, the measurement frequency can be varied.
Principally, thermal diffusivity results should be same even when
the frequency is varied, the measurement using this apparatus,
measurement was conducted at varied frequencies. When measurement
was conducted with a sample having a thickness of not more than 1
.mu.m at 10 Hz or 20 Hz, the measured values were often varied,
whereas, the measured values were almost constant in the range
between 70 Hz and 800 Hz. Thus, the numerical value that is
constant regardless of the frequency (between 70 Hz and 800 Hz) is
determined as thermal diffusivity.
<Tensile Strength>
[0064] The tensile strength of a film was measured according to the
method of ASTM-D882.
<Coefficient of Thermal Expansion>
[0065] The coefficient of thermal expansion of a charge stripping
film for an ion beam was determined by TMA measurement according to
JIS K7197. The measurement temperature range was from 0.degree. C.
to 600.degree. C.
<Determination of Carbon Purity>
[0066] The carbon purity of the produced charge stripping film for
an ion beam was measured by a scanning electron microscope (SU8000)
manufactured by Hitachi High-Technologies Corporation, and a
large-diameter SDD detector (hereinafter, EDX-XMax) manufactured by
HORIBA, Ltd. Elemental analysis of the carbon film was conducted at
an accelerating voltage of 20 kV, and based on the atomic
concentration (%) of each elements calculated after the analysis by
attached software, the carbon purity was calculated by the
following formula (1):
Carbon purity (%)=atomic concentration of carbon (%)/[atomic
concentration of carbon (%)+atomic concentration of elements other
than carbon (%)].times.100 (1)
<Durability Test of Charge Stripping Film>
[0067] FIG. 1 is a schematic perspective view of a fixing jig for
use in a durability evaluation test of a charge stripping film. A
plurality of SiC fibers 12 are set on an aluminum member 11, and on
the SiC fibers 12, a produced charge stripping film 10 is pasted
together. Durability was evaluated by irradiating a substantially
center part 13 of the charge stripping film with a
.sup.20Ne.sup.+DC beam of 3.2 MeV, 2.5.+-.0.5 .mu.A having a beam
spot diameter of 3.5 mm from a Van de Graaff accelerator. When the
film withstood for irradiation of an ion beam after 48 hours or
more, the film was determined as passing the durability test, and
when the film broke within 48 hours, the test was interrupted.
(Production of Polymer Films)
[0068] A hardener comprising 20 g of acetic anhydride and 10 g of
isoquinoline was mixed to 100 g of an 18 wt % DMF solution of a
polyamic acid synthesized from pyromellitic acid anhydride and
4,4'-diaminodiphenyl ether in a proportion of 1/1 in terms of the
mole ratio to be stirred, and after being centrifuged to be
degassed, the liquid was cast and applied on a aluminum foil. The
process from stirring to defoaming was conducted at 0.degree. C.
After heating the resultant laminate of the aluminum foil and the
polyamic acid solution for 150 seconds at 120.degree. C., and every
30 seconds at 300.degree. C., 400.degree. C., and 500.degree. C.
respectively. Then the aluminum foil was removed to produce
polyimide films (polymer sample A) having different thicknesses. In
a similar way for sample A, polyimide films (polymer sample B) were
produced by using pyromellitic anhydride and p-phenylene diamine as
raw materials, and polyimide films (polymer sample C) were produced
by using 3,3',4,4'-biphenyltetracarboxylic dianhydride and
p-phenylene diamine as raw materials. Regarding the thickness of
the polyimide film, several kinds of films having different
thicknesses ranging from 200 nm to 25 .mu.m were produced by
adjusting the casting speed.
Production Examples 1 to 7 of Charge Stripping Films
[0069] Seven polymer films (sample A) having different thicknesses
(ranging from 0.4 to 25 .mu.m) were heated up to 1000.degree. C. at
a rate of 10.degree. C./minute in nitrogen gas using an electric
furnace, and they were retained at 1000.degree. C. for 1 hour to
conduct a pre-treatment. Then the obtained carbonized films were
set inside a cylindrical carbon heater, and heated up to
3000.degree. C. at a heating rate of 20.degree. C./minute to
conduct a heat treatment. The films were retained at this
temperature for 30 minutes, and then the temperature was lowered at
a rate of 40.degree. C./minute, to produce charge stripping films 1
to 7. The treatment was conducted in an argon atmosphere under
pressurizing at 0.1 MPa.
Production Examples 8, 9 of Charge Stripping Films
[0070] Each of a polymer film having a thickness of 10 .mu.m
(sample B), and a polymer film having a thickness of 7.0 .mu.m
(sample C) were heated up to 1000.degree. C. at a rate of
10.degree. C./minute in nitrogen gas using an electric furnace, and
they were retained at 1000.degree. C. for 1 hour, to conduct a
pre-treatment. Then the obtained carbonized films were set inside a
cylindrical carbon heater, and heated up to 3000.degree. C. at a
heating rate of 20.degree. C./minute to conduct a heat treatment.
The films were retained at this temperature for 30 minutes, and
then the temperature was lowered at a rate of 40.degree. C./minute,
to produce charge stripping films 8, 9. The treatment was conducted
in an argon atmosphere under pressurizing at 0.1 MPa.
Production Examples 10 to 13 of Charge Stripping Films
[0071] Polyimide films of polymer sample A having a thickness of
3.2 .mu.m were heated up to 1000.degree. C. at a rate of 10.degree.
C./minute in nitrogen gas using an electric furnace, and the films
were retained at 1000.degree. C. for 1 hour, to conduct a
pre-treatment. Then the obtained carbonized films were set inside a
cylindrical carbon film heater, and charge stripping film 10
(2800.degree. C.), charge stripping film 11 (2600.degree. C.),
charge stripping film 12 (2400.degree. C.), and charge stripping
film 13 (2200.degree. C.) were heated to the respective highest
temperatures at a heating rate of 20.degree. C./minute. The films
were retained at these temperatures for 30 minutes, and then the
temperature was lowered at a rate of 40.degree. C./minute, to
produce charge stripping films 10 to 13. The treatment was
conducted in an argon atmosphere under pressurizing at 0.1 MPa.
Production Examples 14, 15 of Charge Stripping Films
[0072] Polyimide films of polymer sample A having a thickness of
0.2 m were heated up to 1000.degree. C. at a rate of 10.degree.
C./minute in nitrogen gas using an electric furnace, and the films
were retained at 1000.degree. C. for 1 hour, to conduct a
pre-treatment. Then the obtained carbonized films were set inside a
cylindrical carbon film heater, and heated up to 2600.degree. C.,
and 3000.degree. C., respectively at a heating rate of 20.degree.
C./minute. The films were retained at these temperatures for 30
minutes, and then the temperature was lowered at a rate of
40.degree. C./minute, to produce charge stripping films 14, 15. The
treatment was conducted in an argon atmosphere under pressurizing
at 0.1 MPa.
Production Examples 16, 17 of Charge Stripping Films
[0073] Polyimide films of polymer sample A having a thickness of 25
m were heated up to 1000.degree. C. at a rate of 10.degree.
C./minute in nitrogen gas using an electric furnace, and the films
were retained at 1000.degree. C. for 1 hour to conduct a
pre-treatment. Then the obtained carbonized films were set inside a
cylindrical carbon film heater, and heated up to 2200.degree. C.,
and 2600.degree. C., respectively at a heating rate of 20.degree.
C./minute. The films were retained at these temperatures for 30
minutes, and then the temperature was lowered at a rate of
40.degree. C./minute, to produce charge stripping films 16, 17. The
treatment was conducted in an argon atmosphere under pressurizing
at 0.1 MPa.
[0074] For these charge stripping films 1 to 17, measurement
results of film thickness, thermal conductivity, density, tensile
strength and carbon purity are shown in Table 1.
[0075] Regarding Raman intensity ratios of the charge stripping
films from 1 to 9 and 15 that were treated at 3000.degree. C., a
peak derived from amorphous carbon could not be observed, and Raman
intensity ratio R was not less than 99. The Rs of charge stripping
films 13, 16 were 1 indicating that they were composed of amorphous
carbonaceous. The R of the charge stripping film 12 treated at
2400.degree. C. was 5 and the Rs of the charge stripping films 11,
14, 17 treated at 2600.degree. C. were 6, and the R of the charge
stripping film 10 treated at 2800.degree. C. was 20. These results
suggested that heating temperature at not less than 2400.degree. C.
is required for converting into the graphitic charge stripping
film.
TABLE-US-00001 TABLE 1 Thickness Kind of of Charge Weight Ratio of
Charge Highest Polymer Stripping Thermal Tensile Carbon per Unit
Raman Stripping Temp. Sample Film Conductivity Density Strength
Purity Area Intensity Film (.degree. C.) (Polyimide) (.mu.m) (W/mK)
(g/cm.sup.3) (MPa) (at % (mg/cm.sup.2) (R) 1 3000 A 9.6 1900 2.05
40 >99 1.97 >99 2 3000 A 4.7 1950 2.07 44 >99 0.97 >99
3 3000 A 2.1 2000 2.11 50 >99 0.44 >99 4 3000 A 1.2 2000 2.22
60 >99 0.27 >99 5 3000 A 0.72 1950 2.22 48 >99 0.16 >99
6 3000 A 0.31 1980 2.20 40 >99 0.07 >99 7 3000 A 0.14 1920
2.21 44 >99 0.03 >99 8 3000 B 4.3 1960 2.15 40 >99 0.92
>99 9 3000 C 3.4 1980 2.20 40 >99 0.75 >99 10 2800 A 2.1
1600 2.00 40 99.0 0.42 20 11 2600 A 2.2 1200 1.90 40 98.6 0.42 6 12
2400 A 2.2 800 1.82 40 98.0 0.40 5 13 2200 A 2.3 200 1.67 40 96.8
0.38 1 14 2600 A 0.08 1000 -- 10 99.0 0.02 6 15 3000 A 0.06 1860 --
10 >99 0.01 >99 16 2200 A 12.2 140 1.62 40 96.7 1.98 1 17
2600 A 10.5 700 2.05 46 98.7 2.15 6
[0076] These results show that charge stripping films 1 to 12
obtained by heat treating the polyimide films as raw materials at
temperatures of not less than 2400.degree. C. have a carbon purity
of not less than 96 at %, and are graphitic, and have a thermal
conductivity in the film surface direction of not less than 800
W/mK. On the other hand, the charge stripping film 13 for which
heat treatment temperature was 2200.degree. C. had a thermal
conductivity of 200 W/mK, and could not satisfy the requirement of
the thermal conductivity of one or more embodiments of the present
invention. That is, by the heat treatment at not less than
2400.degree. C., charge stripping films for ion beam satisfying the
requirement of one or more embodiments of the present invention are
obtained. While the charge stripping film 13 heat-treated at
2200.degree. C. had a carbon purity of 96.8 at %, any of the charge
stripping films 1 to 12 heat-treated at not less than 2400.degree.
C. may realize a carbon purity of not less than 97 at %.
[0077] Further, the coefficient of thermal expansion of the film
depends on the treatment temperature in the thickness range of one
or more embodiments of the present invention (not less than 100 nm
and less than 10 .mu.m), and the coefficients of thermal expansion
were 4.times.10.sup.-6/K (sample treated at 2400.degree. C.,
namely, the charge stripping film 12), 2.times.10.sup.-6/K (sample
treated at 2600.degree. C., namely, the charge stripping film 11),
1.times.10.sup.-6/K (sample treated at 2800.degree. C., namely, the
charge stripping film 10), 9.times.10.sup.-7/K (sample treated at
3000.degree. C., namely, the charge stripping films 1 to 9),
respectively. In one or more embodiments of the present invention,
the coefficients of thermal expansion of charge stripping films for
an ion beam were determined to be not more than
1.times.10.sup.-5/K.
[0078] Table 1 also shows weight per unit area calculated from film
thickness and density. As described above, a carbon weight per unit
area of charge stripping film for carbon (carbon beam) for desired
efficiency is for example, not less than 0.02 mg/cm.sup.2 and not
more than 2.0 mg/cm.sup.2. All of the charge stripping films from 1
to 12 could satisfy the aforementioned range, and excellent charge
stripping efficiency.
[0079] Concerning radioactivation, a higher carbon purity provides
lower radioactivation. The charge stripping films from 1 to 12,
radioactivation is sufficiently controlled due to a carbon purity
of not less than 96 at %.
Examples 1 to 12
[0080] For the produced charge stripping films 1 to 12, a 48-hour
durability test was conducted, and breakage or damage of the charge
stripping films was not observed. A film thickness of not more than
1 .mu.m, elongation of the film and slight deformation due to
sublimation after irradiation were observed, however, a hole, a
crack was not observed in the film.
Comparative Examples 1 to 4
[0081] Three kinds of expanded graphite sheets having different
thicknesses [respectively having a film thickness of 20 .mu.m
(Comparative Example 1), 30 .mu.m (Comparative Example 2), and 50
.mu.m (Comparative Example 3)], and a carbon film having a
thickness of 1 .mu.m (Comparative Example 4) formed by sputtering
were produced, and durability tests were conducted. As results, in
any Comparative Example, the film was broken by irradiation within
2 hours. Examples 1 to 12 have excellent durability compared with
these Comparative Examples. The tensile strength of the expanded
graphite sheet was about 4 MPa, which is significantly smaller than
that of Examples 1 to 12, revealing that the graphite film produced
by the expansion method was unsuitable for one or more embodiments
of the present invention.
Comparative Examples 5 to 9
[0082] A durability test was conducted for the charge stripping
films 13, 14, 15, 16, 17. The film 13 ruptured at 8 hours, the film
14 ruptured at 24 hours, and the film 15 ruptured at 30 hours. It
is inferred that these films are very thin (respectively, having a
film thickness of 80 nm, 60 nm), and have sufficient thermal
conductivity. However, they could not withstand the 48-hour
durability tests owing to the low heat-release property and
mechanical strength due to the thickness. The carbon film ruptured
at 24 hours for the film 16, and at 28 hours for the film 17. It is
inferred that the film 16 and the film 17 have sufficient
characteristics as the tensile strength of the film, but they
ruptured due to the deformation of the film caused by further
graphitization proceeded by the heat during the long-time ion beam
irradiation.
[0083] According to one or more embodiments of the present
invention, it is possible to easily provide a charge stripping film
for an ion beam, which can be used for long-time irradiation a high
intensity beam. Since the charge stripping film has high carbon
purity, there is little fear of radioactivation after a beam
irradiation. The charge stripping film as described herein is a
graphitic film, and the film has sufficient heat resistance and
mechanical strength even with a thickness of less than 10 m that
enables to work or handle easily. Since the weight per unit area
can be made higher, charge stripping efficiency will be higher than
that of the carbon film of other kind with the same thickness.
Further, the density of the films should be less than 1.6
g/cm.sup.3 and not more than 2.26 g/cm.sup.3 indicating that the
carbon film contains less cavity, and heat generation by a beam
irradiation can be controlled correspondingly, and durability to a
beam irradiation can be improved. Thus, the charge stripping film
must be an optimum material for the charge stripping film for an
ion beam as described herein.
DESCRIPTION OF REFERENCE SIGNS
[0084] 10 charge stripping film [0085] 11 aluminum member [0086] 12
SiC fiber
[0087] Although the disclosure has been described with respect to
only a limited number of embodiments, those skilled in the art,
having benefit of this disclosure, will appreciate that various
other embodiments may be devised without departing from the scope
of the present invention. Accordingly, the scope of the present
invention should be limited only by the attached claims.
* * * * *