Patent Application
20200029421
The present disclosure concerns a cyclotron capable of extracting a spiralling beam of accelerated charged particles out of its spiral path at different energies and steering it towards a target, e.g., for producing specific radioisotopes. In particular, it concerns a cyclotron provided with an energy specific extraction kit for changing the extraction settings of the cyclotron such that particles can be extracted by stripping at a specific energy, Ei, or at a different energy, Ej, and can reach a target.
A cyclotron is a type of circular particle accelerator in which negatively or positively charged particles accelerate outwards from the center of the cyclotron along a spiral path up to energies of several MeV. There are various types of cyclotrons. In isochronous cyclotrons, the particle beam runs each successive cycle or cycle fraction of the spiral path in the same time. Cyclotrons are used in various fields, for example in nuclear physics, in medical treatment such as proton-therapy, or in nuclear medicine, e.g., for producing specific radioisotopes.
A cyclotron comprises several elements including an injection system, a radiofrequency (RF) accelerating system for accelerating the charged particles, a magnetic system for guiding the accelerated particles along a precise path, an extraction system for collecting the thus accelerated particles, and a vacuum system for creating and maintaining a vacuum in the cyclotron.
An energy specific extraction kit comprises a stripper assembly for extracting charged particles at the specific energy, Ej, and an insert for orienting the target to intersect the extraction path, Sj, followed by the particle beam after crossing the stripper. The energy specific extraction kit allows an easy change of the extraction settings of the cyclotron for hitting a target with particles of different energies. The energy specific extraction kit is cost-effective and comprises no articulated or otherwise delicate parts.
The present disclosure concerns a cyclotron for accelerating a beam of charged particles, comprising H−, D−, HH+, over an outward spiral path until the beam of charged particles reaches a desired energy, and for extracting the beam to hit a target, the cyclotron comprising:
The present disclosure also concerns a method for hitting a target with a particle beam of second energy, Ej, comprising the steps of:
For a fuller understanding of the nature of the present disclosure, reference is made to the following detailed description taken in conjunction with the accompanying drawings in which:
The present disclosure concerns accelerated particle beam extraction systems for extracting out of the acceleration gap of a cyclotron a beam of charged particles such as H−, D−, HH+, at a first energy, Ei, and steering the extracted beam towards a target, for the production of radioisotopes. The energy, Ei, of the extracted particle beam can be between 5 and 30 MeV, or, in alternative embodiments, between 10 and 24 MeV, or between 11 and 20 MeV. The cyclotron can be an isochronous cyclotron or a synchrocyclotron. The target (20t) can be solid, liquid, or gaseous.
With reference to
The magnetic system generates a magnetic field that guides and focuses the beam of charged particles along the spiral path (5) until reaching its target energy, Ei. The magnetic field is generated in the acceleration gap (7) defined, e.g., between two magnet poles (2), by one or more solenoid main coils (9) wound around these magnet poles, as illustrated in
The main coils (9) are enclosed within a flux return, which restricts the magnetic field within the cyclotron. Vacuum is extracted from a vacuum chamber defined by the acceleration gap (7) and a peripheral wall (8) sealing the acceleration gap (7). The peripheral wall is provided with at least one opening (8o) for allowing extraction of the beam out of the gap.
When the particle beam reaches its target energy, Ei, the extraction system extracts it from the cyclotron at a point of extraction and guides it towards an extraction channel through the opening (8o) in the peripheral wall. Several extraction systems exist and are known to a person of ordinary skill in the art.
In the present disclosure the extraction system comprises a stripper (13) consisting of a thin sheet, e.g., made of graphite, capable of extracting charges from particles impacting the stripper, thus changing the charge of the particles, and changing their path leading them out of the cyclotron through the opening and along an extraction channel. A stripper is generally part of a stripper assembly (10i) comprising a bracket (12i) for holding the stripper at a specific distance, ri, from a rotating axle (11). The rotating axle is rotatably mounted within the acceleration gap (7) and can be rotated to bring the stripper in and out of a colliding position, Pi, with a beam of accelerated particles of energy, Ei, as described e.g., in U.S. Pat. No. 8,653,762. As described in EP2129193, more than one stripper can be mounted on a single rotating axle, for bringing a new stripper in colliding position in case of damage of the stripper in place.
After stripping of one or more charges, the particle beam is steered by the magnetic field in the vacuum chamber along an extraction path, Si, of opposite curvature to the spiralling path, leading it through the opening (8o), along a tubular channel (20c) of a target support element (20), and onto a target (20t) held within or at an end of the tubular channel. For the production of radioisotopes, the target (20t) can be solid, liquid or gaseous. A person of ordinary skill in the art knows how a target can be held in irradiating position depending on whether it is solid, liquid or gaseous.
The production of a specific radioisotope for imaging and other diagnostic methods, or for biomedical research, by irradiating a given target material with a beam of accelerated particles depends on the energy of the particle beam. As illustrated in
Most cyclotrons are designed for extracting a particle beam at a single value of energy. A stripper located at a first stripping position, Pi, is crossed by particles of first energy, Ei, and does not intercept particles of second energy, Ej≠Ei, travelling at a different radial orbit in the spiral path. For intercepting particles of second energy, Ej, the stripper is moved to a second stripping position, Pj≠Pi. A stripper can be mounted on a moving element, e.g., on a rail or a telescopic arm, to move the stripper from a first radial stripping position, Pi, to any second radial stripping position. When the stripper is moved to the second stripping position, Pj, the extraction path of the stripped particles of second energy, Ej, is deviated with bending magnets at the crossover point of the extraction path of the beam of first energy, Ei, to reach their target. Such systems are available on the market and operational, but they increase the complexity and cost of a cyclotron.
The position of the target (20t) intercepts the extraction path, Si, Sj, of the particle beam. As discussed above, the extraction path of the particle beam can be deviated with bending magnets, but they render the system more complex. For production of radioisotopes for biomedical research and diagnostic medicine, typically imaging, it is preferred to locate the target (20t) close to the opening (8o) and position the target at an intersecting position with the particle beam without requiring any additional steering means for deviating the beam towards the target.
Variable energy cyclotrons are available on the market, equipped with an articulated multi-holder target support. It is believed that bending magnets are required to steer the particle beam towards a given holder. Such articulated multi-holder target supports are bulky and complex to handle. Handling the position of a target to make it intercept a high energy particle beam can be not only cumbersome, but dangerous, with a risk of damaging equipment and, possibly, injuring an operator.
There therefore remains a need for a cyclotron which can be operated for extracting a particle beam at two or more different values of energies, Ei, Ej, for the production of radioisotopes, which is of simple and economical design compared with single energy cyclotrons, which is fool-proof, and requiring no additional bending magnets. The present disclosure proposes a cyclotron provided with an energy specific extraction kit allowing an easy change of the extraction settings of the cyclotron for hitting a target with particles of different energies.
As illustrated in
A cyclotron comprises one or more main coils coiled around the first and second magnet poles, for generating a main magnetic field in the acceleration gap and outwardly guiding the accelerated charged particles along the spiral path (5) (cf.
As shown in
For extracting a particle beam out of the spiralling path (5) it follows in the acceleration gap (7), and steering it towards the target (20t), the stripper (13) is positioned at a first stripping position, Pi, intersecting the particle beam at a first radial distance, Ri, from the central axis, Z, corresponding to the desired beam first energy, Ei. A stripper generally consists of a carbon stripping foil capable of extracting one or more electrons from the charged particles of energy, Ei, crossing it. For example, a negative ion, 1H− can be accelerated to a first energy, Ei. Upon crossing the stripper, a pair of electrons is removed (stripped), making the particle a positive ion, 1H+. The stripped particle deviates from the spiralling path (5), is steered along the extraction path, Si, exits through the opening (8o) and reaches the target (20t). The extraction path, Si, depends on the local value of the magnetic field, B, and on the charge, q, of the stripped particle (assuming a constant velocity, vi, and mass, m).
A stripper can be mounted on a bracket (12i) by means known to a person of ordinary skill in the art. The stripper is held by the bracket (12i) such that an outer edge of the stripper most remote from the rotating axle is held at a distance, ri, from a rotating axle (11). The distance, ri, is the distance from the outer edge of the exposed surface of stripper to the rotating axle (11). The rotating axle (11) is mounted in the gap, near a peripheral edge of the magnet poles, parallel to the central axis, Z, such that the stripper (13) can rotate about the rotating axle in and out of the first stripping position, Pi, intercepting the beam of charged particles at the first energy, Ei.
As illustrated by dashed lines in
The extraction settings, including the positions of the stripper (13), of the outlet (8o) and of the target (20t), are selected such as to steer the extraction path, Si, followed by the particle beam after stripping through the opening (8o), along the tubular channel (20c) of the target support element (20) and onto the target (20t) held in the target holder. A person of ordinary skill in the art can calculate the extraction settings for steering a particle beam of first energy, Ei, towards the target. For fine tuning and optimizing the relative position of the extraction path, Si, with respect to the target (20t), the stripping point, Pi, can be slightly displaced by minute rotations of the stripper (13) about the rotational axle, as discussed earlier with respect to
A cyclotron is generally designed for extracting charged particles at a single first energy, Ei, because changing the extraction settings for extracting a particle beam at a second energy, Ej, is quite complex. Cyclotrons allowing extraction of particle beams at different energies are available on the market, but they are very complex with, on the one hand, specific devices for changing the position of the stripper and, on the other hand, additional devices either for bending the extraction path after stripping with bending magnets to steer it towards the target, or for moving the target in an articulated target support element. The drawback with these cyclotrons is that they are complex, expensive, and delicate. Furthermore, there is no automatic coupling of the position of the stripper with the bent extraction path, nor the position of the target. When fine tuning of the intersecting point of the extraction path with the target is allowed for an optimal use of the cyclotron, experimenting with a new extraction path, without any accurate knowledge of the resulting extraction path of a 10 to 30 MeV particle beam, is dangerous for the equipment and for the operators. Such cyclotrons are therefore not fool-proof, and a handling error while changing the extraction settings can have dire consequences.
The present disclosure provides one or more energy specific extraction kits for extracting a particle beam at a second or additional energies, Ej, from a same cyclotron designed for extracting a particle beam at a first energy, Ei. With reference to
The second stripper assembly (10j) comprises: a second rotating axle (11) provided with one or more second brackets (12j) each for holding a second stripper (13) centered at a second distance, rj, from the second rotating axle.
The second stripper assembly (10j) is such that the second stripper (13) can rotate about the second rotating axle (11) to a second stripping position, Pj, intercepting the beam of charged particles at the second energy, Ej. The particle beam of second energy, Ej, crossing the stripper is depleted of some electrons and is steered by the magnetic field in the gap along a second modified path, Sj, through the opening (8o) in the peripheral wall.
As shown in
The first stripper assembly (12i) in
The relation between ri−rj, Ri−Rj, and Ei−Ej discussed earlier is visible by comparing
The first and second energies, Ei and Ej, may be between 5 and 30 MeV, or, in alternative embodiments, between 10 and 24 MeV, or between 11 and 20 MeV. They may differ from one another by at least 2 MeV (|Ei−Ej|≥2 MeV), or at least 4 MeV (|Ei−Ej|≥4 MeV). For example, if Ei=18 MeV, then the second energy, Ej, may be 12 to 16 MeV. The second energy, Ej, may also be between 20 and 25 MeV, but for the reasons explained earlier, that the first stripping position, Pi, is generally near the periphery of the magnet poles, the second energy, Ej, is generally smaller than the first energy, Ei.
A beam of particles of charge qj after stripping is deviated at a velocity, vj, by a magnetic field, B(r), along a curve with radius of curvature, ρj=m vj/(qj B(r,θ)), wherein r and θ are the cylindrical coordinates of the position of a particle on the median plane, P. At the periphery of the magnet poles (at r>Rj), the magnetic field, B(r), strongly varies and drops with increasing values of the radial distance, r. The extraction path therefore straightens with larger values of the radius of curvature, ρj, as the particle beam moves towards the opening (8o). The calculation of an extraction path, Sj, from an extraction position, Pj, such that it crosses the opening (8o) is not straightforward, but can be carried out by a person of ordinary skill in the art. Beyond the peripheral wall, the magnetic field, B(r), is quite low, and the extraction path can have quite a large radius of curvature, ρj, of at least 5 m, or, in alternative embodiments, at least 10 m and higher.
The second stripping position, Pj, is carefully positioned to ensure that the second extraction path, Sj, crosses through the opening. As shown in
As shown in
Assuming the cyclotron was designed for extracting a particle beam of first energy, Ei, a first insert (21i) is not necessary, and is not represented in
The solutions proposed in other cyclotrons for ensuring that a particle beam of second energy, Ej, intercepts the target (20t), include either the use of bending magnets for bending the second extraction path, Sj, and forcing it to intercept the target (20t) or the use of moving means for displacing the target to intercept the second extraction path, Sj. Both options require tuning the positions of the bending magnets or of the target holder to match the second extraction path, which can be a delicate and risky operation, as discussed earlier.
The present disclosure proposes a third solution: the use of an insert (21j) to be sandwiched between the downstream end of the opening (8o) and the target support element (20) for modifying an orientation of the tubular channel to match the second extraction path, Sj, such that the modified charged particles of second energy, Ej, intercept the target held in the target holder. The insert (21j) forms a pair with the second stripper assembly (10j) and both are used in combination.
When the insert is mounted on the cyclotron, the insert channel is in fluid communication with both opening (8o) and tubular channel (20c) of the target support element (20). As can be seen in
The energy specific extraction kit of the present disclosure comprises two elements: a stripper assembly (10j) and an insert (21j). The two elements are used in combination, and define a unique ready-to-use kit allowing a particle beam of second energy, Ej, to be extracted and to hit a target (20t) using a cyclotron initially designed for extracting a particle beam of first energy, Ei. Apart from fine tuning for the optimization of the extraction path, the installation of the energy specific extraction kit requires no lengthy and delicate determination of the extraction settings required for the extraction of a beam of second energy, Ej.
The installation of an energy specific extraction kit is simple, in that the angular orientation of the stripper assembly can be reproducibly controlled by providing a rotation axle (11) with a portion which is not of revolution as discussed earlier. As there is only one way of mounting the insert, no error can occur.
It is clear that more than one energy specific extraction kit may be used for a same cyclotron. For example, the first energy, Ei, may be the highest beam energy extractable with a given cyclotron, and the second energy, Ej, the lowest beam energy to be extracted with the cyclotron. Any number of third, fourth, or more energy specific extraction kits can be provided for extracting and hitting a target with particle beams at third, fourth, etc. energies, Ek, El, Em, wherein Ej<Ek<El<Em<Ei.
The second stripper assembly (10j) ensures that the particle beam (5) is stripped at the second energy, Ej, and that the second extraction path, Sj, exits through the opening (8o). The insert (21j) ensures that the tubular channel (20c) becomes coaxial with the portion of the second extraction path, Sj, downstream of the opening (8o), and that the second extraction path intercepts the target held in the target holder. Using a first stripper (10i) with an insert (21j) is therefore avoided. The two elements of a second energy specific extraction kit belong to a pair. For example, a color code or an alpha-numerical code may be used to identify the two elements of a second energy specific extraction kit.
With the present disclosure, solid, liquid, or gaseous targets (20t) such as 68Zn, 124Te, 123Te, 89Y, may be irradiated with a single cyclotron with particle beams of various energies, Ei or Ej, allowing the production of different radioisotopes, nX, mX, with a same target as illustrated in
The cyclotron may be an isochronous cyclotron, or a synchro-cyclotron. As illustrated in
As shown in
Hitting a Target with Particle Beams of Different Energies, Ei, Ej
The present disclosure concerns hitting a target (20t) with particle beams of first energy, Ei, and of second energy, Ej, and any other energy between Ei and Ej, using a single cyclotron, originally designed for extracting particle beams at the first energy, Ei, only. This can be achieved with a method comprising the following steps:
There is one way only to mount the second stripper assembly (10j) and insert (21j), and the calculated second extraction path, Sj, necessarily intersects the target position, without requiring any further changes in the extraction settings. The position of the stripper (13) can be fine-tuned by minute rotations of the rotating axle (11), to optimize a hitting point on the target by the particle beam. This fine-tuning may optimize the extraction path as a function of the actual second extraction path of the stripped particle beam which may differ slightly from the calculated extraction path. The present disclosure needs neither a bending magnet for bending the second extraction path, nor articulated target support for moving the target (20t) to intersect the second extraction path, Sj, with the target.
The present disclosure therefore opens new horizons in the multiple applications a cyclotron can be used for.
Additionally, the first and second energies, Ei, Ej, can be between 5 and 30 MeV, or, in alternative embodiments, between 10 and 24 MeV, or between 11 and 20 MeV, and they can differ from one another, for example, by at least 2 MeV (|Ei−Ej|≥2 MeV), or, in alternative embodiments, at least 4 MeV (|Ei−Ej|≥4 MeV). Such cyclotrons may be used for the production of radioisotopes by irradiation with the accelerated particle beam of a target material selected among 68Zn, 124Te, 123Te, 89Y, and the like.
A second energy specific extraction kit according to the present disclosure comprises a stripper assembly and an insert. The one or more first and second brackets of the first and second stripper assemblies may comprise a frame-like structure for fastening the first or second stripper, and an arm or plate for keeping the fastened first or second stripper at an accurate distance, ri, rj, from the first or second rotating axle The first and/or second stripper assemblies may comprise more than one frame azimuthally distributed about the first or second rotating axle, each holding a stripper foil.
The insert may comprise a first coupling surface for coupling to the downstream end of the opening, and a second coupling surface for coupling to the target support element. The first and second coupling surfaces are not parallel to one another and form an angle, α, between 1° and 45°, or, in alternative embodiments, between 3° and 35°, or between 5° and 20°.
The cyclotron may comprise a first insert to be used with the first stripping assembly, comprising a first coupling surface for coupling to the downstream end of the opening, and a second coupling surface for coupling to the target support element, and wherein the first and second coupling surfaces are parallel to one another. Such first insert is optional and serves only to move the target along the first extraction path, Si, to a position more remote from the central axis, Z.
Because they are used in combination, the second stripper assembly and the insert of a second energy specific extraction kit may be identified by a color code or an alpha-numerical code as forming a pair. This should avoid mixing by error a first stripper assembly with an insert designed for a second energy, Ej.
The present disclosure may be implemented in synchro-cyclotrons as well as isochronous cyclotrons. Each of the first and second magnet poles of the cyclotron may comprise at least N=3 hill sectors having an upper surface defined by upper surface edges, and a same number of valley sectors comprising a bottom surface. The hill sectors and valley sectors are alternatively distributed around the central axis, Z. A gap separating the first and second magnet poles thus comprises hill gap portions and valley gap portions. The hill gap portions are defined between the upper surfaces of two opposite hill sectors and have an average gap height, Gh, measured along the central axis, Z. The valley gap portions are defined between the bottom surfaces of two opposite valley sectors and have an average valley gap height, Gv, measured along the central axis, Z, with Gv>Gh. In such cyclotrons, the first or second rotating axle of the first or second stripper assemblies may be positioned at a hill gap portion, adjacent to an upper surface edge located downstream with respect to the spiral path. The term “downstream” is defined with respect to the flow direction of particles.
In alternative embodiments, the position of the second stripper can be fine-tuned by minute rotations of the second rotating axle to optimize a hitting point on the target by the particle beam.
| Number | Date | Country | Kind |
|---|---|---|---|
| 17209226.4 | Dec 2017 | EP | regional |
