CROSS-REFERENCES TO RELATED APPLICATIONS
The present application includes subject matter related to subject matter disclosed in U.S.
Patent Application No. 12/435,903 entiUed "ISOTOPE PRODUCTION SYSTEM AND
CYCLOTRON"; Application No. 12/435,949 entitled "ISOTOPE PRODUCTION
SYSTEM AND CYCLOTRON HAVING A MAGNET YOKE WITH A PUMP
ACCEPTANCE CAVITY"; Application No. 12/435,931 entitled "ISOTOPE
PRODUCTION SYSTEM AND CYCLOTRON HAVING REDUCED MAGNETIC
STRAY FIELDS"; all of which were filed on May 5, 2009 and all of which are
incorporated by reference in their entirety.
BACKGROUND OF THE INVENTION
Embodiments of the invention described herein relate generally to isotope production
systems, and more particularly to isotope production systems that may be safely used in
relatively confined spaces, such as hospital rooms.
Radioisotopes (also called radionuclides) have several applications in medical therapy,
imaging, and research, as well as other applications that are not medically related.
Systems that produce radioisotopes typically include a particle accelerator, such as a
cyclotron, that has a magnet yoke that surrounds an acceleration chamber. The
acceleration chamber may include opposing pole tops that are spaced apart from each
other. Electrical and magnetic fields may be generated within the acceleration chamber
to accelerate and guide charged particles along a spiral-like orbit between the poles. To
produce the radioisotopes, the cyclotron forms a beam of the charged particles and directs
the particle beam out of the acceleration chamber and toward a target system having a
target material. The particle beam is incident upon the target material thereby generating
radioisotopes.
2
During operation of an isotope production system, large amounts of radiation (i.e.,
unhealthy levels of radiation for individuals nearby) may be generated within the target
system and, separately, within the cyclotron. For example, with respect to the target
system, radiation from neutrons and gamma rays may be generated when the beam is
incident upon the target material. With respect to the cyclotron, ions within the
acceleration chamber may collide with gas particles therein and become neutral particles
that are no longer affected by the electrical and magnetic fields within the acceleration
chamber. These neutral particles, in turn, may collide with the walls of the acceleration
chamber and produce secondary gamma radiation. To protect nearby individuals from
the radiation (e.g., employees or patients of a hospital), isotope production systems may
use shields to attenuate or block the radiation.
In some conventional isotope production systems, radiation leakage has been addressed
by adding a large amount of shielding that surrounds both the cyclotron and the target
system. However, the large amounts of shielding may be costly and too heavy for the
rooms where the isotope production system are to be located. Alternatively or in addition
to the large amounts of shielding, isotope production systems may be located within a
specially designed room or rooms. For example, the cyclotron and the target system may
be in separate rooms or have large walls separating the two. However, designing specific
rooms for isotope production systems raises new challenges, especially for pre-existing
rooms that were not originally intended for radioisotope production.
Yet another challenge presented by radiation leakage is how to remove the isotope
production system when, for example, it is replaced or moved to another location.
Decommissioning an isotope production system includes safely disassembling the system
and removing and storing the radioactive parts and materials. Another concern is
decontaminating the room where the isotope production system was located. In some
instances, original support structures of the room, such as floors, ceilings, and walls, must
be removed because the support structures have been contaminated by radioactivity.
3
Such decommissioning and decontaminating procedures can be costly and timeconsuming.
Accordingly, there is a need for methods, cyclotrons, and isotope production systems that
reduce radiation exposure to individuals in the room or nearby area. Furthermore, there
is a need for isotope production systems that may be more easily decommissioned than
known systems.
BRIEF DESCRIPTION OF THE INVENTION
In accordance with one embodiment, an isotope production system that includes a
cyclotron having a magnet yoke that surrounds an acceleration chamber is provided. The
cyclotron is configured to direct a particle beam from the acceleration chamber through
the magnet yoke. The isotope production system also includes a target system that is
located proximate to the magnet yoke. The target system is configured to hold a target
material and includes a radiation shield that extends between the magnet yoke and the
target location. The radiation shield is sized and shaped to attenuate ganuna and neutron
rays emitted from the target material toward the magnet yoke. The isotope production
system also includes a beam passage that extends from the acceleration chamber to the
target location. The beam passage is at least partially formed by the magnet yoke and the
radiation shield of the target system.
In accordance with another embodiment, an isotope production system is provided that
includes a cyclotron that has a base supported on a platform. The cyclotron includes a
magnet yoke that surrounds an acceleration chamber. The cyclotron is configured to
direct a particle beam from the acceleration chamber through the magnet yoke. The
isotope production system also includes a target system that is located on the platform
and adjacent to the magnet yoke. The target system is configured to hold a target
material at a target location. The particle beam is incident upon the target material. The
isotope production system also includes a beam passage that extends from the
acceleration chamber to the target location. The beam passage is at least partially formed
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by the magnet yoke and the target system. The beam passage extends along a beam axis
that intersects the platform.
In yet another embodiment, a method of decommissioning an isotope production system
located in a room of a facility is provided. The method includes providing an isotope
production system that has a cyclotron having a base supported on a platform. The
platform is supported by a floor of the room. The cyclotron is configured to direct a
particle beam along a beam passage to a target system. The target system is located on
the platform adjacent to the magnet yoke. The beam passage extends along a beam axis
that intersects the platform. The method also includes removing the target system from
the platform and removing the platform from the floor of the facility.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a block diagram of an isotope production system formed in accordance with
one embodiment.
Figure 2 is a schematic side view of an isotope production system in accordance with one
embodiment.
Figure 3 is a plan view from above the isotope production system shown in Figure 2.
Figure 4 is a perspective view of a magnet yoke formed in accordance with one
embodiment.
Figure 5 is a side view of a cyclotron formed in accordance with one embodiment.
Figure 6 is an enlarged side view of a portion of the cyclotron shown in Figure 5.
Figure 7 is a schematic side view of a target region used with the isotope production
system of Figure 2.
Figure 8 is a perspective view of an isotope production system formed in accordance with
one embodiment having a housing in a closed position.
s
Figure 9 is a perspective of the isotope production system of Figiire 8 when the housing is
in an open position.
Figure 10 is a side view of a cyclotron formed in accordance with another embodiment
that may be used with the isotope production system shown in Figure 8.
Figure II is a schematic side view of an isotope production system formed in accordance
with an alternative embodiment.
Figure 12 is a block diagram of a method for decommissioning an isotope production
system in accordance with one embodiment.
DETAILED DESCRIPTION OF THE INVENTION
Figure 1 is a block diagram of an isotope production system 100 formed in accordance
with one embodiment. The system 100 includes a cyclotron 102 that has several subsystems
including an ion source system 104, an electrical field system 106, a magnetic
field system 108, and a vacuum system 110. During use of the cyclotron 102, charged
particles are placed within or injected into the cyclotron 102 through the ion source
system 104. The magnetic field system 108 and electrical field system 106 generate
respective fields that cooperate with one another in producing a particle beam 112 of the
charged particles.
Also shown in Figure 1, the system 100 has an extraction system 115 and a target system
114 that includes a target material 116. The target system 114 may be positioned
adjacent to the cyclotron 102. To generate isotopes, the particle beam 112 is directed by
the cyclotron 102 through the extraction system 115 along a beam transport path or beam
passage 117 and into the target system 114 so that the particle beam 112 is incident upon
the target material 116 located at a corresponding target location 120. When the target
material 116 is irradiated with the particle beam 112, radiation fix>m neutrons and gamma
rays may be generated.
c
The system 100 may have multiple target locations 120A-C where separate target
materials 116A-C are located. A shifting device or system (not shown) may be used to
shift the target locations 120A-C with respect to the particle beam 112 so that the particle
beam 112 is incident upon a different target material 116. A vacuum may be maintained
during the shifting process as well. Alternatively, the cyclotron 102 and the extraction
system 1 IS may not direct the particle beam 112 along only one path, but may direct the
particle beam 112 along a unique path for each different target location 120A-C.
Furthermore, the beam passage 117 may be substantially linear from the cyclotron 102 to
the target location 120 or, alternatively, the beam passage 117 may curve or turn at one or
more points therealong. For example, magnets positioned alongside the beam passage
117 may be configured to redirect the particle beam 112 along a different path.
Examples of isotope production systems and/or cyclotrons having one or more of the subsystems
described above are described in U.S. Patent Nos. 6,392,246; 6,417,634;
6.433,495; and 7,122,966 and in U.S. Patent Application Publication No. 2005/0283199,
all of which are incorporated by reference in their entirety. Additional examples are also
provided in U.S. Patent Nos. 5,521,469; 6,057,655; and in U.S. Patent Application
Publication Nos. 2008/0067413 and 2008/0258653, all of which are incorporated by
reference in their entirety. Furthermore, isotope production systems and/or cyclotrons
that may be used with embodiments described herein are also described in copending
U.S. Patent Application Nos. 12/435,903; 12/435,949; and 12/435,931 all of which are
incorporated by reference in their entirety.
The system 100 is configured to produce radioisotopes (also called radionuclides) that
may be used in medical imaging, research, and therapy, but also for other applications
that are not medically related, such as scientific research or analysis. When used for
medical purposes, such as in Nuclear Medicine (NM) imaging or Positron Emission
Tomography (PET) imaging, die radioisotopes may also be called tracers. By way of
example, the system 100 may generate protons to make '*F isotopes in liquid form, "C
isotopes as CO2, and ' ^ isotopes as NH3. The target material 116 used to make these
7
isotopes may be enriched "O water, natural ''*N2 gas, "O-water, and ' ^2 gas. The
system 100 may also generate protons or deuterons in order to produce '^O gases
(oxygen, carbon dioxide, and carbon monoxide) and '^O labeled water.
In some embodiments, the system 100 uses 'H" technology and brings the charged
particles to a low energy (e.g., about 7.8 MeV) widi a beam current of approximately 10-
30^A. In such embodiments, the negative hydrogen ions are accelerated and guided
through the cyclotron 102 and into the extraction system IIS. The negative hydrogen
ions may then hit a stripping foil (not shown) of the extraction system IIS thereby
removing the pair of electrons and making the particle a positive ion, 'H^. However, in
alternative embodiments, the charged particles may be positive ions, such as 'H*, ^H^
and ^He'*'. In such alternative embodiments, the extraction system US may include an
electrostatic deflector that creates an electric field that guides the particle beam toward
the target material 116.
The system 100 may include a cooling system 122 that transports a cooling or working
fluid to various components of the different systems in order to absorb heat generated by
the respective components. The system 100 may also include a control system 118 that
may be used by a technician to control the operation of the various systems and
components. The control system 118 may include one or more user-interfaces that are
located proximate to or remotely from the cyclotron 102 and the target system 114.
Although not shown in Figure 1, the system 100 may also include one or more radiation
and/or magnetic shields for die cyclotron 102 and the target system 114.
The system 100 may produce the isotopes in predetermined amounts or batches, such as
individual doses for use in medical imaging or therapy. A production capacity for the
system 100 for the exemplary isotope forms listed above may be SO mCi in less than
about ten minutes at 20jiA for " F ; and 300 mCi in about thirty minutes at SOjiA for
"CO2.
Also, the system 100 may use a reduced amount of space with respect to known isotope
production systems such that the system 100 has a size, shape, and weight that would
allow the system 100 to be held within a confined space. For exanple, the system 100
may fit within pre-existing rooms that were not originally built for particle accelerators,
such as in a hospital or clinical setting. As such, the cyclotron 102, the extraction system
1 IS, the target system 114, and one or more components of the cooling system 122 may
be held within a common housing 124 that is sized and shaped to be fitted into a confined
space. As one example, the total volume used by the housing 124 may be 2m^. Possible
dimensions of the housing 124 may include a maximum width of approximately 2.2m, a
maximum height of approximately 1.7m, and a maximum depth of approximately 1.2m.
The combined weight of the housing and systems therein may be approximately 10000
kg. However, embodiments described herein are not limited to the size and weight noted
above and may have greater sizes and weights. The housing 124 may be fabricated fi-om
polyethylene (PE) and lead (Pb) and have a thickness configured to attenuate neutron flux
and gamma rays from the cyclotron 102. For example, the housing 124 may have a
thickness (measured between an inner surface that SUTTOUIKIS the cyclotron 102 and an
outer surface of the housing 124) of at least about 10 mm along predetermined portions
of the housing 124 that attenuate the neutron and gamma flux.
The system 100 may be configured to accelerate the charged particles to a predetermined
energy level. For example, some embodiments described herein accelerate the charged
particles to an energy of approximately 18 MeV or less. In other embodiments, the
system 100 accelerates the charged particles to an energy of approximately 16.S MeV or
less. In particular embodiments, the system 100 accelerates the charged particles to an
energy of approximately 9.6 MeV or less. In more particular embodiments, the system
100 accelerates the charged particles to an energy of approximately 7.8 MeV or less.
Figures 2 and 3 are a schematic side view and a schematic top plan view, respectively, of
an isotope production (IP) system 300 formed in accordance with one embodiment The
IP system 300 includes a cyclotron 200 having a magnet yoke 202 and also includes a
9
target system 302 that incliides a radiation shield 306 and a target region 308 located
within the radiation shield 306. The magnet yoke 202 includes an acceleration chamber
206 where a particle beam 312 is generated and directed through the magnet yoke 202
and toward the target region 308 along a beam passage 314. The beam passage 314 is at
least partially formed by the magnet yoke 202 and the radiation shield 306. Although not
shown, the IP system 300 may include an extraction system to facilitate removing and
directing the particle beam 312 from the cyclotron 200.
Also shown, the cyclotron 200 and the target system 302 may be enclosed within a
common housing 305. In some embodiments, the IP system 300 also includes a separate
platform 220 (Figure 2) that rests upon a floor or ground 313 of the area in which the IP
system 300 is located. The cyclotron 200, the target system 302, and the housing 305
may rest upon the platform 220. For example, the cyclotron 200 may include a base 315
that is at least partially supported on the platform 220. The base 315 may be formed from
the magnet yoke 202 or may be a portion of the housing 305. The base 315 may also
include a vacuum pump 276 that is positioned between the magnet yoke 202 and the
platform 220. The vacuum pump 276 may be configured to maintain an evacuated state
within the acceleration chamber 206, the beam passage 314, and within the target region
308.
Embodiments described herein include separated shielding systems where radiation
generated within the cyclotron 200 is at least partially attenuated by the magnet yoke 202
and where radiation generated within the target region 308 is at least partially attenuated
by the radiation shield 306. When the charged particles are accelerated and guided along
a predetermined path within the acceleration chamber 206, ions within the acceleration
chamber 206 may collide with gas particles therein and become neutral particles that are
no longer affected by the electrical and magnetic fields. The neutral particles may be
sprayed along a mid plane 232 (Figiu^ 4) of the magnet yoke 202 and around a periphery
of the acceleration chamber 206 therein. Interception panels (not shown) may be
(b
positioned within the acceleration chamber 206 to facilitate capturing the neutral
particles.
Figures 2 and 3 illustrate several points XRI where particles may collide with the magnet
yoke 202 and generate neutron and gamma radiation. The gamma rays emit firom the
corresponding points XRI in an isotropic manner (i.e., away from the corresponding point
XRI in a spherical manner). The dimensions of the magnet yoke 202 may be sized to
attenuate the radiation of the gamma rays within the acceleration chamber 206. For
example, dimensions of conventional magnet yokes are typically determined by the
desired magnetic field needed to form the particle beam within the acceleration chamber.
However, dimensions of the magnet yoke 202 may be thicker than what is required to
form the desired magnetic field. The additional thickness of the magnet yoke 202 may
facilitate attenuating the radiation emitting ftom the acceleration chamber 206.
Furthermore, the cyclotron 200 may be operated at a low energy that produces a
relatively low amount of neutral particles. For exan^le, the IP system 300 may bring the
charged particles to an energy level of approximately 9.6 MeV or, more specifically, 7.8
MeV or less.
With respect to the target system 302, the target region 308 includes a target location 340
(shown in Figure 7) where a target material is located. When the particle beam 312 is
incident upon the target material, radiation from gamma rays and neutrons may be
generated and emitted from the target material and from ancillary components that are
proximate to the target material. Furthermore, the emitted neutrons may also generate
gamma rays when the neutrons interact with matter within the target system 302. As
such, the radiation shield 306 is configured to attenuate the radiation.
The target region 308 may be located proximate to a geometric center of the radiation
shield 306. By way of one example, the target region 308 may be located in a
predetermined location within the radiation shield 306 so that an exterior boimdary 301
of the IP system 300 has a dose rate of less than a desired value (e.g., less than about 4
jiSv/h or less than about 2 (iSv/h). An "exterior boundary" includes an exterior surface of
II
the IP system 300 that may be touched by a user when the IP system 300 is in normal
operation. For example, the exterior boundary 301 is shown as an exterior surface 301 of
the housing 305 in Figure 3. However, in alternative embodiments, the exterior boundary
301 may be the exterior surface 304 of the radiation shield 306 or the exterior surface 205
of the cyclotron 200. As such, the dose rate may be measured from the exterior surface
301 if there is a housing 305 or, alternatively, from the exterior surfaces 205 and 304 if
there is no housing.
The magnet yoke 202 and the radiation shield 306 may comprise different material
compositions that are configured to attenuate the radiation emitting from the
corresponding area. For example, the magnet yoke 202 may be formed from iron.
Dimensions of the material that forms the magnet yoke 202 may be increased in order to
attenuate the radiation emitting from within the acceleration chamber 206. The radiation
shield 306, on the other hand, may have a different material composition including
separate layers or structures of different materials. For example, the radiation shield 306
may comprise a first or inner shielding structure 320 and a second or outer shieldmg
structure 322 that surrounds the fu^t shielding structure 320. The fust shielding structure
320 may immediately surroimd the target region 308 and be configured to attenuate the
gamma radiation emitting from therein. In one example, the first shielding structure 320
includes a cage that is formed from mostly lead (Pb) or nearly pure lead (Pb). However,
other materials configured to attenuate the gamma radiation may be used with the first
shielding structure 320.
The second shielding structure 322 may surround the first shielding structure 320 and be
configured to attenuate the neutrons and also the gamma rays emitting from the target
region 308 and also to attenuate gamma rays generated by neutron capture. The second
shielding structure 322 may have a spherical shape. A majority of the material
composition comprising the second shielding structure 322 may include polyethylene.
Other material may include lead (Pb) and boron in smaller amounts. In one particular
embodiment, the second shielding structure 322 includes about 80% polyethylene
(including 3% boron) and about 20% lead (Pb). However, other elements or materials
may be included in the material composition of the first and second shielding structures
320 and 322.
Also shown in Figures 2 and 3, the target system 302 may be located adjacent to the
magnet yoke 202. As used herein, the target system 302 and the magnet yoke 202 are
"adjacent to" one another when the target system 302 and the magnet yoke 202 are
proximate to or near each other without a substantial distance or spacing between the
two. For example, in the illustrated en^diment, a portion of the radiation shield 306 is
shaped to fit within a shield-acceptance cut-out or recess 262 (shown in Figure 4). More
specifically, a portion of the radiation shield 306 may be shaped to conform to a shape of
the shield-acceptance recess 262. Furdiermore, the exterior surfaces 304 and 205 may
directly abut each other. However, in other embodiments where the target system 302 is
adjacent to the magnet yoke 202, the exterior surface 205 may not form a shieldacceptance
recess 262. Instead, the exterior surfaces 304 and 205 may still directly abut
each other along, for example, planar portions of the exterior surfaces 304 and 205.
In alternative embodiments, the target system 302 and the magnet yoke 202 may be
adjacent to one another having only a small spacing between the exterior surfaces 304
and 205 (e.g., less than about 25 centimeters or less than about 10 centimeters).
However, in alternative embodiments, the target system 302 and the magnet yoke 202 are
not adjacent to each other but may be, for example, separated by half a meter or more
meters.
Also shown in Figure 2, the radiation shield 306 may have a radial thickness TR
extending from the target region 308 to the exterior surface 304. The radial thickness TR
may be configured so that the exterior surface 304 experiences at most a limited dose
rate. As shovm, the radial thickness TR may have a varying length or dimension. For
example, the radial thickness TR may have a reduced portion 325 that extends between
the target region 308 and the platform 220 or ground 313. The remaining portion(s) of
the radiation shield 306 may have a substantially equal radial thickness TR. The reduced
13
portion 325 of the radiation shield 306 may be used, for example, where the target system
302 rests upon the platform 220 or, alternatively, directly upon the groimd 313. The
platform 220 may comprise a material (e.g., concrete) and have a thickness Tc that is
configured to absorb radiation leakage from at least one of the cyclotron 200 and the
target system 302.
The beam passage 314 is at least partially formed by the magnet yoke 202 and the
radiation shield 306 of the target system 302. In the illustrated embodiment, the beam
passage 314 may be substantially linear as shown in Figures 2 and 3. Altematively, the
beam passage 314 may have curves or abrupt turns therealong. For example, in
alternative embodiments, magnets may be positioned alongside the beam passage and
configured to direct or redirect the particle beam 312 along a different path. Furthermore,
the beam passage may have a cross-sectional diameter DBP and a distance or length L.
The diameter DBP and the length L are sized and shaped to reduce an amount of neutrons
emanating from the target material and into the beam passage 314 in order to
significantly reduce or eliminate any neutrons re-entering the acceleration chamber 206.
The length L may be measured form an interior surface of die acceleration chamber 206
to the target location 340 (Figure 7). In some embodiments, the length L is between
about .5 meters and about l.S meters. Also, although not shown, the beam passage 314
may be formed from a pipe or conduit that is formed from a material other than the
material that forms the magnet yoke 202 and the radiation shield 306.
With respect to Figure 2, the particle beam 312 and the beam passage 314 may extend
along a beam axis 330. The beam axis 330 may be directed at least partially downward,
i.e., toward the ground or floor 313. In some embodiments, the beam axis 330 may
intersect the platform 220. In such embodiments, when the IP system 300 is to be
decommissioned and when the room of the facility where the IP system 300 is located is
to be decontaminated, the housing 305, the cyclotron 200, and the target system 302 may
be removed from the platform 220. The platform 220 may then be removed from the
facility in a controlled manner (i.e., according to safety standards with respect to the
removal of radioactive material). As such, the platform 220 may protect or otherwise
prevent the removal of pre-existing support structures within the room. For example, by
using the platform 220, other support structures, such as ceilings, floors, and walls, may
be kept within the room.
Figures 4-7 describe the IP system 300 and its components in greater detail. Figure 4 is a
perspective view of the magnet yoke 202 formed in accordance with one embodiment.
The magnet yoke 202 is oriented with respect to X, Y, and Z-axes. In some
embodiments, the magnet yoke 202 is oriented vertically with respect to the gravitational
force Fg. The ntjagnct yoke 202 has a yoke body 204 that may be substantially circular
about a central axis 236 that extends through a center of the yoke body 204 parallel to the
Z-axis. The yoke body 204 may be manufactured from iron and/or another ferromagnetic
material and may be sized and shaped to produce a desired magnetic field.
The yoke body 204 has a radial portion 222 that curves circumferentially about the
centml axis 236. The radial portion 222 has an outer radial surface 223 that extends a
width Wi. The width Wi of the radial surfece 223 may extend in an axial direction along
the central axis 236. When the yoke body 204 is oriented vertically, the radial portion
222 may have top and bottom ends 212 and 214 with a diameter Dy of the yoke body 204
extending therebetweea The yoke body 204 may also have opposite sides 208 and 210
that are separated by a thickness Ti of the yoke body 204. Each side 208 and 210 has a
corresponding side surface 209 and 211, respectively (side surface 209 is shown in Figure
5). The side siufaces 209 and 211 may extend substantially parallel to each other and
may be substantially planar (i.e., along a plane formed by the X and Y axes). The radial
portion 222 is connected to the sides 208 and 210 through comers or transition regions
216 and 218 that have comer surfaces 217 and 219, respectively. (The transition region
218 and the comer surface 219 are shown in Figure S.) The comer surfaces 217 and 219
extend from the radial surface 223 away from each other and toward the central axis 236
to corresponding side surfaces 211 and 209. The radial surface 223, the side surfaces 209
and 211, and the comer surfaces 217 and 219 collectively fonn an exterior surface 205
(Figure 5) of the yoke body 204.
The yoke body 204 may have several cut-outs, recesses, or passages that lead into the
yoke body 204. For example, the exterior surface 205 of the yoke body 204 may form a
shield-acceptance recess 262 that is sized and shaped to receive a radiation shield 306
fiom a target system 302 (Figure 2). As shown, the shield-acceptance recess 262 has a
width W2 that extends along the central axis 236. In the illustrated embodiment, the
shield-acceptance recess 262 curves inward into the radial portion 222 and toward the
central axis 236 through the thickness T|. Although not shown in Figure 4, the beam
passage 314 may extend through the radial portion 222 proximate to the shieldacceptance
recess 262. As such, the width W| is less than the width W2. Also, the
shield-acceptance recess 262 may have a radius of curvature having a center (indicated as
a point C) that is outside of the exterior surface 205. The point C may represent an
approximate location of the target location 340 (Figure 7). In alternative embodiments,
the shield-acceptance recess 262 may have other dimensions that are configured to
receive the radiation shield. Furthermore, in other embodiments, the yoke body 204 may
not have a shield-acceptance recess 262 but may be positioned proximate to the radiation
shield. Also shown, the yoke body 204 may form a pump acceptance (PA) cavity 282
that is sized and shaped to receive a vacuum pump 276 (Figure 2).
Figure 5 is a side view of a cyclotron 200 formed in accordance with one embodiment.
The cyclotron 200 includes the magnet yoke 202 described above with respect to Figures
2-4. As shown in Figure 5, the yoke body 204 may be divided into opposing yoke
sections 228 and 230 that define the acceleration chamber 206 therebetween. The yoke
sections 228 and 230 are configured to be positioned adjacent to one another along a midplane
232 of the magnet yoke 202. The cyclotron 200 may rest on a platform 220 that is
configured to support the weight of the cyclotron 200. The platform 220 may be, for
example, a floor of a room or an additional slab of material (e.g., of cement) that is
supported by the floor. The central axis 236 extends perpendicular to the mid-plane 232
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through a center of the yoke body 204 between the side surfaces 209 and 211. The
acceleration chamber 206 has a central region 238 located at an intersection of the midplane
232 and the central axis 236. In some embodiments, the central region 238 is at a
geometric center of the acceleration chamber 206. Also shown, the magnet yoke 202
includes an upper portion 231 extending above the central axis 236 and a lower portion
233 extending below the central axis 236,
The yoke sections 228 and 230 include poles 248 and 250, respectively, that oppose each
other across the mid-plane 232 within the acceleration chamber 206. The poles 248 and
250 may be separated from each other by a pole gap G. The pole gap G is sized and
shaped to produce a desired magnetic field when the cyclotron 200 is in operation.
Furthermore, the pole gap G may be sized and shaped based upon a desired conductance
for removing particles within the acceleration chamber. As an example, in some
embodiments, the pole gap G may be 3 cm.
The pole 248 includes a pole top 252 and the pole 250 inchides a pole top 254 that faces
the pole top 252. In the illustrated embodiment, the cyclotron 200 is an isochronous
cyclotron where the pole tops 252 and 254 each form an arrangement of sectors of hills
and valleys (not shown). The hills and the valleys interact with each other to produce a
magnetic field for focusing the path of the charged particles. The yoke sections 228 or
230 may also include radio firequency (RF) electrodes (not shown) that include hollow
dees located within the corresponding valleys. The RF electrodes cooperate with each
other and form a resonant system that includes inductive and capacitive elements tuned to
a predetermined frequency (e.g., 100 MHz). The RF electrode system may have a high
frequency power generator (not shown) that may include a frequency oscillator in
communication with one or more amplifiers. The RF electrode system creates an
alternating electrical potential between the RF electrodes and ground.
The cyclotron 200 also includes a magnet assembly 260 located within or proximate the
acceleration chamber 206. The magnet assembly 260 is configured to facilitate
producing the magnetic field with the poles 248 and 250 to direct charged particles along
17
a desired path. The magnet assembly 260 includes an opposmg pair of magnet coils 264
and 266 that are spaced apart from each other across the mid-plane 232 at a distance Di.
The magnet coils 264 and 266 may be, for example, copper alloy resistive coils.
Alternatively, the magnet coils 264 and 266 may be an aluminum alloy. The magnet
coils may be substantially circular and extend about the central axis 236. The yoke
sections 228 and 230 may form magnet coil cavities 268 and 270, respectively, that are
sized and shaped to receive the corresponding magnet coils 264 and 266, respectively.
Also shown in Figure 5, the cyclotron 200 may include chamber walls 272 and 274 that
separate the magnet coils 264 and 266 from the acceleration chamber 206 and facilitate
holding the magnet coils 264 and 266 in position.
The acceleration chamber 206 is configured to allow charged particles, such as 'H' ions,
to be accelerated therein along a predetermined curved path that wr^s in a spiral manner
about the central axis 236 and remains substantially along the mid-plane 232. The
charged particles are initially positioned proximate to the central region 238. When the
cyclotron 200 is activated, the path of the charged particles may orbit around the central
axis 236. In the illustrated embodiment, the cyclotron 200 is an isochrcMious cyclotron
and, as such, the oibit of the charged particles has portions that curve about the central
axis 236 and portions that are more linear. However, embodiments described herein are
not limited to isochronous cyclotrons, but also includes odier types of cyclotrons and
particle accelerators. As shown in Figure 5, when the charged particles orbit around the
central axis 236, the charged particles may project out of the page in the upper portion
231 of the acceleration chamber 206 and extend into the page in the lower portion 233 of
the acceleration chamber 206. As die charged particles orbit around the central axis 236,
a radius R that extends between the orbit of the charged particles and the central region
238 increases. When the charged particles reach a predetermined location along the
orbit, the charged particles are directed into or through an extraction system (not shown)
and out of the cyclotron 200.
The acceleration chamber 206 may be in an evacuated state before and during the
forming of the particle beam 312 (Figure 2). For example, before the particle beam is
created, a pressure of the acceleration chamber 206 may be approximately 1x10'^
millibars. When the particle beam is activated and Ha gas is flowing through an ion
source (not shown) located at the central region 238, the pressure of the acceleration
chamber 206 may be approximately 2x10'^ millibar. The vacuum pump 276 may include
a portion that projects radially outward from the end 214 of the yoke body 204.
In some embodiments, the yoke sections 228 and 230 may be moveable toward and away
from each other so that the acceleration chamber 206 may be accessed (e.g., for repair or
maintenance). For example, the yoke sections 228 and 230 may be joined by a hinge (not
shown) that extends alongside the yoke sections 228 and 230. Either or both of the yoke
sections 228 and 230 may be opened by pivoting the corresponding yoke section(s) about
an axis of the hinge. As another example, the yoke sections 228 and 230 may be
separated from each other by laterally moving one of the yoke sections linearly away
from the other. However, in alternative embodiments, the yoke sections 228 and 230
may be integrally formed or remain sealed together when the acceleration chamber 206 is
accessed (e.g., through a hole or opening of the magnet yoke 202 that leads into the
acceleration chamber 206). In alternative embodiments, the yoke body 204 may have
sections that are not evenly divided aod/or may include more than two sections. For
example, the yoke body may have three sections as shown in Figure 10 with respect to
the magnet yoke 504.
The acceleration chamber 206 may have a shape that extends along and is substantially
symmetrical about the mid-plane 232. For instance, the acceleration chamber 206 may
be surrounded by an interior radial or wall surface 223 that extends around the central
axis 236 such the acceleration chamber 206 is substantially disc-shaped. The
acceleration chamber 206 may include inner and outer spatial regions 241 and 243. The
inner spatial region 241 may be defined between the pole tops 252 and 254, and the outer
spatial region 243 may be defined between the chamber walls 272 and 274. The spatial
region 243 extends around the central axis 236 surrounding the spatial region 241. The
orbit of the charged particles during operation of the cyclotron 200 may be within the
spatial region 241. As such, the acceleration chamber 206 is at least partially defined
widthwise by the pole tops 252 and 254 and the chamber walls 272 and 274. An outer
periphery of the acceleration chamber 206 may be defined by the interior radial surface
225. The acceleration chamber 206 may also include passages diat lead radially outward
away from the spatial region 243, such as a passage that leads toward the vacuum pump
276 and the beam passage 314 (Figure 2).
The exterior surface 205 defines an envelope 207 of the yoke body 204. The envelope
207 has a shape that is about equivalent to a general shape of the yoke body 204 defmed
by the exterior surface 205 without small cavities, cut-outs, or recesses. (For illustrative
purposes only, the envelope 207 is shown in Figure 5 as being slightly larger than the
yoke body 204.) As shown in Figure 5, a cross-section of the envelope 207 is an eightsided
polygon defined by die exterior radial surface 223, the side siufaces 209 and 211,
and the comer surfaces 217 and 219. The yoke body 204 may form passages, cut-outs,
recesses, cavities, and the like that allow component or devices to penetrate into the
envelope 207. The shield-acceptance recess 262 (Figure 4) and the PA cavity 282 are
examples of such recesses and cavities.
Figure 6 is a side view of the upper portion 231 illustrating radiation being emitted during
operation of the cyclotron 200 (Figure 3). The cyclotron 200 may be separately
configured to attenuate radiation emitted fix)m the acceleration chamber 206 (Figure 5).
However, the cyclotron 200 may also be configured to attenuate radiation and to reduce
the strength of the stray fields as described in U.S. Patent Application No. 12/435,931,
which is incorporated by reference in the entirety. As discussed above, one type of
radiation is from neutron flux. In a particular embodiment, the cyclotron 200 is operated
at a low energy such that radiation fi'om the neutron flux does not exceed a predetermined
amount outside of the yoke body. For example, the cyclotron may be operated to
accelerate the particles to an energy level of approximately 9.6 MeV or less. More
specifically, the cyclotron may be operated to accelerate the particles to an energy level
of approximately 7.8 MeV or less.
The second type of radiation, ganmia rays, is produced when neutrons or protons collide
with the yoke body 204. Figure 6 illustrates several points XRI where particles generally
collide with the yoke body 204 when the cyclotron 200 is in operation. The gamma rays
emit from the corresponding points XRI in an isotropic manner (i.e., away from the
corresponding point XRI m a spherical manner). The dimensions of the yoke body 204
may be sized to attenuate the radiation of the gamma rays. For example, Figure 6 shows
the thicknesses T4, Ts, and Ti that extend through a radial portion 222, a transition region
218, and a portion of the yoke body 204 that extends from a coil cavity 270 to the side
208, respectively. The thicknesses T4, Ts, and T^ may be sized so that the dose rate
within a desired distance from the exterior surface 205 (or at the exterior surface 205) is
below a predetermined amount. Distances D7-D9 represent predetermined distances away
from the exterior surface 205 in which the radiation sustained is below a desired dose
rate. Each distance D7-D9 from the exterior surface 205 may be a shortest distance to the
exterior surface 507 from a point outside of flie yoke body 204,
Accordingly, the thicknesses T4, T5, and Ts may be sized so that the dose rate outside of
the yoke body 204 does not exceed a desired amount within a desired distance when the
target current operates at a predetermined current. By way of example, the thicknesses
T4, Ts, and Tg may be sized so that the dose rate does not exceed 2 }iSv/h at a distance of
less than about 1 meter from the corresponding surface at a target current from about 20
to about 30 ^A. Furthermore, the thicknesses T4, Ts, and Ts may be sized so that the dose
rate does not exceed 2 ^Sv/h at a point along the corresponding surface (i.e., D4, Ds, and
D( equal approximately zero) at a target current from about 20 to about 30 ^A. However,
the dose rate may be directly proportional to the target current. For example, the dose
rate may be 1 ^Sv/h at a point along the corresponding surface when the target current is
10-15 fiA.
The dose rate may be determined by using known methods or devices. For example an
ion chamber or Geiger MuUer (GM) tube based gamma survey meter could be used to
detect the gammas. The neutrons may be detected using a dedicated neutron monitor
usually based on detectable ganunas coming from the neutrons interacting with a suitable
material (e.g., plastic) aroimd an ion chamber or GM tube.
In accordance with one embodiment, the dimensions of the yoke body 204 are configured
to limit or reduce magnetic stray fields around the yoke body 204 and to reduce the
radiation emitted from the cyclotron 200. A maximum magnetic flow (B) that can be
achieved by the cyclotron 200 with respect to the magnetic fields through the yoke body
204 may be based upon (or significantly determined by) the least cross-sectional area of
the yoke body 204 found along the thickness Ts. As such, the size of other crosssectional
areas within the yoke body 204, such as cross-sectional areas associated with
the thicknesses T4 and Tg, may be determined based upon the cross-sectional area with
the transition region 218. For example, in order to reduce the weight of the magnet yoke,
conventional cyclotrons typically reduce the cross-sectional areas T4 and Tg until any
further reduction would substantially affect the maximum magnetic flow (B) of the
cyclotron.
However, the thicknesses T4, Ts, and Tt may be based upon not only a desired noagnetic
flow (B) through the yoke body 204 but also a desired attenuation of the radiation. As
such, some portions of the yoke body 204 may have excess material with respect to an
amount of material necessary to achieve a desired average magnetic flow (B) through the
yoke body 204. For example, the cross-sectional area of the yoke body 204 associated
with the thickness Te may have an excess thickness of material (indicated as ATi). The
cross-sectional area of the yoke body 204 associated with the thickness T4 may have an
excess thickness of material (indicated as AT2). Accordingly, embodiments described
herein may have a thickness, such as the thickness T5, that is defined to maintain
magnetic flow (B) below an upper limit and another thickness, such as the thicknesses T^
and T4, that is defined to attenuate die gamma rays that are emitted firom within the
acceleration chamber.
Fiirthermore, dimensions of the yoke body 204 may be based upon the type of particles
used within the acceleration chamber and the type of material within the acceleration
chamber 206 that the particles collide with. Furthermore, dimensions of the yoke body
204 may be based upon the material that comprises the yoke body. Also, in alternative
embodiments, an outer shield may be used in conjunction with the dimensions of the
yoke body 204 to attenuate both the magnetic stray fields and the radiation emitting fk)m
within the yoke body 204.
Figure 7 is an enlarged side view of the target region 308. As shown, the target region
308 includes the first or inner shielding structure 320, a collimator 338, a target holder
342 that holds the target media within target locations 340A-340C, and a rotating
mechanism 344 that movably couples the target holder 342 to the collimator 338 (or the
beam passage 314). The particle beam 312 is directed along the beam passage 314 and is
narrowed or focused by the collimator 338 before the particle beam 312 impinges or
collides with the target material at the corresponding target location 340. The rotating
mechanism 344 may be selectively controlled to move or rotate the holder 342 so that the
target locations 340A-340C are moved with respect to the particle beam 312. More
specifically, an operator of the IP system 300 (Figure 2) may select a target material to
make a desired radioisotope. The rotating mechanism 344 may then rotate about a pivot
point 348 to move the target locations 340A-340C so that the desired target material
collides with the particle beam 312. In alternative embodiments, the rotating mechanism
344 may rotate the holder 342 about the beam axis 330 (Figure 2). Furthermore,
although three target locations 340A-340C are shown, fewer or more target locations may
be used.
As shown, the first shielding structure 320 immediately surrounds the target locations
340A-340C. The first shielding structure 320 may consist essentially of lead (Pb) and be
shaped to attenuate the prompt gamma radiation generated at the target location 340. In
2^
some embodiments, a space or void within the first shielding structure 320 is sized and
shaped to allow the holder 342 to move into various positions. As such, a size and shape
of the first shielding structure 320 may be determined by the space used by the holder
342 to move the target locations 340. Also shown, the first shielding structure 320 may
have a thickness T?. The thickness T? is configured to attenuate the prompt gamma
radiation so that the exterior boundary 301 has less than a maximum dose rate. In such
embodiments where the first shielding structure 320 immediately surrotmds the target
location(s) 340, the isotope production system 300 (Figure 2) may use less lead (Pb) than
conventional isotope production systems that have lead (Pb) surrounding most or all of
the cyclotron and target system.
Figures 8 and 9 are perspective views of an isotope production (IP) system 500 formed in
accordance with one embodiment while in a closed or operational position and an open or
accessible position, respectively. As shown, the IP system 500 may include a housing
524 that encloses a cyclotron 502 (Figure 9) and a target system 514 (Figure 9). With
reference to Figure 9, the IP system 500 is configured to be used within a hospital or
clinical setting and may include similar components and systems as described with the IP
system 100 (Figure 1) and the IP system 300 (Figure 2). The cyclotiwn 502 and target
system 514 may manufacture radioisotopes for use with a patient. The cyclotron 502
defmes an acceleration chamber 506 where charged particles move along a
predetermined path when the cyclotron 502 is activated. When in use, the cyclotron 502
accelerates charged particles along a predetermined or desired beam path 536 and directs
the particles toward a target region 532 of the target system 514. The beam path 536
(indicated as a hashed-line) extends fi'om the acceleration chamber 506 into the target
system 514,
Figure 10 is a cross-section of the cyclotron 502. As shown, the cyclotron 502 has
similar features and components as the cyclotron 200 (Figure 2). However, the cyclotron
502 includes a magnet yoke 504 that may comprise three sections 528-530 sandwiched
together. More specifically, the cyclotron 502 includes a ring section 529 that is located
2-V
between yoke sections 528 and 530. When the ring and yoke sections 528-530 are
stacked together as shown, the yoke sections 528 and 530 face each other across a midplane
534 and define the acceleration chamber 506 of the magnet yoke 504 therein. As
shown, the ring section 529 may define a passage Pj that leads to a port 578 of a vacuum
pump 576. The vacuum pump 576 may be a fluidless pump and have similar features as
described in U.S. Patent Application Nos. 12/435,931 and 12/435,949, which are
incorporated by reference in the entirety. For example, the vacuum pump 576 may be a
turbomolecular pump.
Also shown, the housing 524 may have a thickness Ts and an exterior surface 525. The
housing 524 may be fabricated from polyethylene (PE) and lead (Pb) and the thickness Ts
may be configured to attenuate neutron flux from the cyclotron 502. In other
embodiments, the housing 524 is substantially free of lead (Pb). The exterior surface 525
may represent an exterior boundary of the isotope production system 500. In addition to
the other dimensions of the magnet yoke 504, the housing 524 may be sized and shaped
to achieve desired attenuation of radiation and a desired reduction in stray fields. For
example, the dimensions of the magnet yoke 504 and the dimensions of the housing 524
(e.g., the thickness Ts) may be configured so that the dose rate does not exceed 2 iiSv/h at
a distance of less than about 1 meter from the exterior surface 525 and, more specifically,
at a distance of 0 meters. Also, the magnet yoke 504 and the dimensions of the housing
524 may be sized and shaped such that the stray fields do not exceed 5 Gauss at a
distance of 1 meter from the exterior surface 525 or, more specifically, at a distance of .2
meters.
Returning to Figure 9, the housing 524 may provide access to the acceleration chamber
506 and the target region 532. For example, the housing 524 may include moveable
partitions 552 and 554 that provide access to the acceleration chamber 506 and the target
region 532, respectively. As shown in Figure 9, both of the partitions 552 and 554 are in
an open position. The partition 554 may be opened separately so that the target region
and a user interface 584 of the target system 514 may be accessed without opening the
2^
partition 552. When closed, the partition 554 may COVCT the target region 532 and the
user interface 584 of the target system 514. The partition 552 may cover the cyclotron
502 when closed.
The partition 554 may include a portion of a radiation shield, such as the radiation shield
306. The partition 554 may comprise a first section 555 of the radiation shield and a
main body 557 of the IP system 500 may include a second section 557 of the radiation
shield. Accordingly, when the partition 554 is closed, the radiation shield of the target
system 514 may be comprised of the first and second sections 555 and 557 and may have
similar dimensions and features as described above with respect to the radiation shield
306.
Also shown, the yoke section 528 of the cyclotron 502 may be moveable between open
and closed positions. (Figure 9 illustrates an open position and Figure 10 illustrates a
closed position.) The yoke section 528 may be attached to a hinge (not shown) that
allows the yoke section 528 to swing open like a door or a lid and provide access to the
acceleration chamber 506. The yoke section 530 (Figure 10) may also be moveable
between open and closed positions or may be sealed to or integrally formed with the ring
section 529 (Figure 10).
Furthermore, the vacuum pump 576 may be located within a pump-acceptance chamber
562 of the ring section 529 and the housing 524. The pump-acceptance chamber 562
may be accessed when the partition 552 is in the open position. As shown, the vacuiun
pump 576 is located below a central region 538 of the acceleration chamber 506 such that
a vertical axis extending through a center of the port 578 &om a horizontal support 520
would intersect the central region 538. Also shown, the yoke section 528 and ring
section 529 may have a shield-acceptance recess 560. The beam path 536 extends
through the shield-acceptance recess 560 to the target region 532.
Figure 11 is a schematic side view of an isotope production (IP) system 600 formed m
accordance with an alternative embodiment. The IP system 600 includes a cyclotron 602
1(.
and a target system 604 that may have similar features as the cyclotrons and target
systems described above. The IP system 600 may be supported by a platform 610 and be
enclosed within a housing 605. As shown, the cyclotron 602 is configured to provide a
particle beam 612 that extends along a beam passage 614 fi'om an acceleration chamber
606 of the cyclotron 602 to a target region 608 of the target system 604. As shown, the
cyclotron 602 may rest upon and be supported by a radiation shield 616 of the target
system 604. The particle beam 612 and the beam passage 614 may extend along a beam
axis 630 such that the beam axis 630 intersects the platform 610.
The IP system 600 may also include a vacuum pump 676. Conventional cyclotrons and
isotope production systems have vacuiun pumps (e.g., difRision pump) that use a working
fluid (e.g., oil) to generate the required pressure for evacuating the acceleration chamber.
However, the vacuum pump 676 in the cyclotron 602 may be a fluidless pimip (e.g.,
turbomolecular pimip) that is fluidicly coupled to the acceleration chamber 606 of the
cyclotron 602. The vacuiun pump 676 may be oriented along a longitudinal axis 640 that
forms an angle 6 with respect to a gravitational force direction FQ. The angle 9 may be,
as shown, approximately 90 degrees. However, in alternative embodiments, the angle 6
may be any angle greater than 10 degrees with respect to the gravitational force FG. By
way of one example, the vacuum pump 676 may be a turbomolecular pump having a fan
678 that rotates about the longitudinal axis 640. Accordingly, in such embodiments
where the vacuum pump 676 is a fluidless vacutmi pump, the vacuimi pump 676 may
have different orientations without concern for oil or another fluid spilling into the
acceleration chamber 606.
Figure 12 shows a method 700 for decommissioning an isotope production (IP) system,
such as the IP systems 100,300,500, and 600 described above. The method 700 includes
providing an IP system at 702 that includes a cyclotron and a target system. The
cyclotron and the target system may be supported on a platform. The platform, in turn,
may be supported by a floor of a room in a facility. As described above, the cyclotron
may be configured to direct a particle beam along a beam passage toward the target
2-7
system. The target system may be located on the platform adjacent to the magnet yoke.
Furthermore, the beam passage may extend along a beam axis that intersects the
platform. The beam passage may be directed toward the platform such that accumulated
radioactivity m walls or ceilings of the room do not exceed a threshold level. The
method 700 also includes at 704 removing the cyclotron and, at 706, removing the target
system from the platform.
The method 700 also includes at 708 removing the platform from the floor of the facility
in a controlled manner (i.e., in accordance with established safety standards with respect
to handling radioactive material). The method 700 also includes at 710 disposing of the
platform in a controlled manner. In some embodiments, the method 700 does not include
removing an original support structure from the room. The original support structure
may be at least a portion of one of a ceiling, the floor, and a wall.
Embodiments described herein are not intended to be limited to generating radioisotopes
for medical uses, but may also generate other isotopes and use other target materials..
Furthermore, in the illustrated embodiment the cyclotrons are vertically-oriented
isochronous cyclotrons. However, alternative embodiments may include other kinds of
cyclotrons and other orientations (e.g., horizontal). Furthermore, embodiments described
herein include methods of manufacturing the IP systems, target systems, and cyclotrons
as described above.
It is to be understood that the above description is intended to be illustrative, and not
restrictive. For example, the above-described embodiments (and/or aspects thereof) may
be used in combination with each other. In addition, many modifications may be made to
ad^t a particular situation or material to the teachings of the invention without departing
from its scope. While the dimensions and types of materials described herein are
intended to defme the parameters of the invention, they are by no means limiting and are
exemplary embodiments. Many other embodiments will be apparent to those of skill in
the art upon reviewing the above description. The scope of the invention should,
therefore, be determined with reference to the appended claims, along with the full scope
2g^
of equivalents to which such claims are entitled. In the appended claims, the terms
"including" and "in which" are used as the plain-English equivalents of the respective
terms "comprising" and "wherein." Moreover, in the following claims, the terms "first,"
"second," and "third," etc. are used merely as labels, and are not intended to impose
numerical requirements on their objects. Further, the limitations of the following claims
are not written in means-plus-fimction format and are not intended to be interpreted based
on 35 U.S.C. § 112, sixth paragraph, unless and until such claim limitations expressly use
the phrase "means for" followed by a statement of function void of further structure.
This written description uses examples to disclose the invention, including the best mode,
and also to enable any person skilled in the art to practice the invention, including making
and using any devices or systems and performing any incorporated methods. The
patentable scope of the invention is defined by the claims, and may include otiier
examples that occur to those skilled in the art. Such other examples are intended to be
within the scope of the clainos if they have structural elements that do not differ from the
literal language of the claims, or if they include equivalent structural elements with
insubstantial differences from the literal languages of the claims.

WE CLAIM :
1. An isotope production system comprising:
a cyclotron including a magnet yoke that surrounds an acceleration chamber, the
cyclotron configured to direct a particle beam fi'om the acceleration chamber through the
magnet yoke; and
a target system located adjacent to the magnet yoke, the target system configured to hold
a target material and including a radiation shield that extends between the magnet yoke
and the target region, wherein the radiation shield is sized and shaped to attenuate
neutrons that are emitted fit>m the target material toward the magnet yoke; and
a beam passage extending fit>m the acceleration chamber to the target region, the beam
passage being at least partially formed by the magnet yoke and the radiation shield of the
target system.
2. The isotope production system in accordance with claim 1 wherein the beam passage
has a length and a cross-sectional diameter, the length and the diameter of the beam
passage being configured to substantially reduce neutrons that are emitted from the target
region into the magnet yoke.
3. The isotope production system in accordance with claim 1 wherein an exterior surface
of the radiation shield directly abuts the magnet yoke.
4. The isotope production system in accordance with claim 1 further conqirising a
common housing that contains the cyclotron and the target system.
5. The isotope production system in accordance with claim 4 wherein the housing
provides access to the acceleration chamber of the cyclotron and the target system.
6. The isotope production system in accordance with claim 1 wherein the radiation shield
comprises a material composition configured to attenuate radiation emitting from the
30
target material and the magnet yoke comprises a different material composition
configured to attenuate radiation emitting from the acceleration chamber.
7. The isotope production system in accordance with claim I wherein the magnet yoke
has an exterior surface that forms a shield-acceptance recess, the beam passage extending
through the magnet yoke from the acceleration chamber and into the shield-acceptance
recess, wherein a portion of the radiation shield is shaped to fit within the shieldacceptance
recess of the magnet yoke.
8. The isotope production system in accordance with claim 7 wherein the radiation shield
has a shape that substantially conforms to a shape of the recess.
9. The isotope production system in accordance with claim 1 wherein the target system
comprises a first shielding structure that immediately surrounds the target region, the fust
shielding structure comprising a first material composition that is configured to attenuate
gamma rays that emit fix)m the target material.
10. The isotope production system in accordance with claim 9 wherein the target system
further comprises a second shielding structure that surrounds the first shielding structure,
the second shielding structure comprising a different second material conqrasition that is
configured to attenuate neutrons emitting fit>m the target material.
11. The isotope production system in accordance with claim 10 wherein the second
material composition is configured to attenuate gamma rays emitting from the target
material and generated by neutron capture.
12. The isotope production system in accordance with claim 1 wherein the particle beam
travels a distance from an interior siuface of the acceleration chamber to the target
material, the distance being from about O.S meters to about l.S meters.
13. The isotope production system in accordance with claim 1 wherein the magnet yoke
has a geometric center located within the acceleration chamber, wherein an exterior
31
boundary of the cyclotron has a dose rate of less than about 4 jiSv/h at a distance of less
than about 1 meter from the geometric center and an exterior boundary of the target
system has a dose rate of less than about 4 {iSv/h at a distance of less than about 1 meter
from the target material, wherein the target material experiences a beam current of
between about 20 ^A and 30nA.
14. An isotope production system comprising:
a cyclotron supported by a platform, the cyclotron including a magnet yoke that
surrounds an acceleration chamber, the cyclotron configured to direct a particle beam
from the acceleration chamber through the magnet yoke; and
a target system located on the platform and adjacent to the magnet yoke, the target system
configured to hold a target material at a target region, the particle beam being incident
upon the target material; and
a beam passage extending from the acceleration chamber to the target region, the beam
passage being at least partially formed by the magnet yoke and the target system, the
beam passage extending along a beam axis that intersects the platform.
15. The isotope production system in accordance with claim 14 wherein the target system
includes a radiation shield configiu'ed to attenuate at least one of gamma rays and
neutrons that emit from the target material, the radiation shield extending between the
target region and the magnet yoke.
16. The isotope production system in accordance with claim 15 wherein the radiation
shield has a radial thickness measured from the target region, an exterior surface of the
radiation shield defining a reduce portion of the radial thickness, the radiation shield
being supported by the platform along the exterior siuface of the reduced portion.
17. The isotope production system in accordance with claim 15 wherein the radiation
shield has an exterior surface that abuts the magnet yoke.
S2-
18. The isotope production system in accordance with claim 14 wherein the beam
passage is substantially linear.
19. The isotope production system in accordance with claim 14 further comprising a
fluidless pump that is fluidicly coupled to the acceleration chamber of the magnet yoke,
the fluidless pump being oriented along a longitudinal axis that forms an angle with
respect to a gravitational force direction, the angle being greater than 10 degrees.
20. The isotope production system in accordance with claim 19 wherein the fluidless
vacuum pump is a turbomolecular pump.
21. The isotope production system in accordance with claim 14 further comprising the
platform, the platform resting upon a floor and having a thickness configured to absorb
radiation leakage from at least one of the cyclotron and the target system.
22. A method of decommissioning an isotope production system located in a room of a
facility, the method comprising:
providing an isotope production system that includes a cyclotron supported on a platform,
the platform being supported by a floor of the room, the cyclotron configured to direct a
particle beam along a beam passage to a target system, the target system being located on
the platform adjacent to the magnet yoke, wherein the beam passage extends along a
beam axis that intersects the platform;
removing the target system fix>m the platform; and
removing the platform from the floor of the facility.
23. The method in accordance with claim 22 wherein the beam passage is directed
toward the platform such that accumulated radioactivity in walls or ceilings of the room
do not exceed a threshold level.
33
24. The method in accordance with claim 22 further comprising disposing of the
platform in a controlled manner.
25. The method in accordance with claim 22 wherein the room has an original support
structure, the method not including removmg the original support structure widiin the
room due to accumulated radioactivity.
26. The method in accordance with claim 25 wherein the original support structure is at
least a portion of one of a ceiling, the floor, and a wall.