Liquid Target System

Abstract

A liquid target system (1) for the production of radioisotopes, the liquid target system (1) comprising a boiling chamber (2) for containing a liquid, which is water or penta-deuterium water, from which radioisotopes can be produced using irradiation, and a basic chemical, which is a salt having a positive enthalpy relative to water, the boiling chamber (2) allowing the liquid and the basic chemical to be irradiated and comprising an irradiation window for evaporating the liquid into a vapor, the liquid target system being configured such that superheating of the liquid target (8) is controlled by the thermodynamics of the evaporation process.

Description

Technical Field

[0001] The present invention relates to the field of radioisotopes. More specifically, the present invention relates to liquid target systems for the production of radioisotopes, as well as their use and corresponding methods.

Background Art

[0002] For the production of radioisotopes, generally, solid targets are used for their respective high yields in state-of-the-art systems, and for solid targets, a large density of the parent nuclide, which is the source of the radioisotope, can be easily achieved. In practice, the drawback of using liquid targets is the limited solubility in water of most parent nuclide compounds at room temperature (typically used as liquid solvents). For example, the salt of Ra-226, which can be used as a basic chemical substance to provide a parent nuclide for producing the radioisotope Ra-225 that can decay to the radioisotope Ac-225, has limited solubility in water. By way of illustration, the radium nitrate salt Ra(NO3)2 has a solubility of 13.9 g per 100 g of H2O at 20°C.

[0003] However, one advantage of using a liquid target instead of a solid target is that in the chemical process for separating the radioisotope from the target, there are fewer (or no) required conversions from liquid to solid and from solid to liquid. Such steps in such chemical processes typically have a high risk of (uncontrolled) losses in the production of radioisotopes and radioactive waste. Such conversions are not necessary for liquid targets and are a significant advantage of such targets.

[0004] Furthermore, it is necessary to correctly grasp the potential drawbacks of the low concentration of nucleophilic species in the liquid target. As an example, consider the production of Ra-225 from Ra-226 via a photonuclear reaction. The production of Ra-225 as a function of time can depend on the electron beam current (mA), electron energy (MeV), converter design, and target design. Here, the converter is designed to stop high-energy electrons and produce the high-energy bremsstrahlung photons required for the photonuclear reaction. The more high-energy photons are produced and the more Ra-226 is in the direct path of the photon beam, the more Ra-225 will be formed. However, assuming about 50% conversion of electrons to bremsstrahlung photons, about half of the electron energy can still be deposited in the converter. The very high energy deposition in a small converter volume associated with energy deposition can easily limit the production capacity and thus reduce the yield of high-energy bremsstrahlung photons.

[0005] One way to address this is to have multiple slices of converter material separated by cooling means and, in addition, rasterize the electron beam over a larger surface area of the converter. However, it is inevitable that a larger surface area will have an adverse effect on the production rate. The result of a larger converter surface area is that the Ra should be spread over the entire surface area where high-energy gammas are present, but the highest yield is obtained by placing the Ra as close to the converter as possible. This means that the current density of the converter is a limiting factor (e.g., 0.125 - 0.25 mA / cm 2 ) and, when it is necessary to increase the surface area to volume ratio, any type of solid target can be considered a drawback because the achievable high density (e.g., 3 - 5 g / cc) cannot be optimally utilized.

[0006] US2014 / 0362964A1 describes an isotope production system configured to irradiate a feed liquid with a particle beam to generate a radioisotope and convert a portion of the feed liquid to vapor.

[0007] Accordingly, there are several drawbacks associated with solid targets. Nevertheless, the efficiency and yield of liquid targets are generally very low, so in the state of the art, the focus remains on solid targets. Accordingly, there is still a need in the art for devices and methods that can improve the efficiency and yield of liquid target systems.

Summary of the Invention

[0008] An object of the present invention is to provide a good liquid target system. A further object of the present invention is to provide a good method for producing radioisotopes.

[0009] The above object is achieved by a method and apparatus according to the present invention.

[0010] An advantage of embodiments of the present invention is that the yield and production of radioisotopes can be comparable to those of solid targets. A further advantage of embodiments of the present invention is that the amount of parent nuclide material required to obtain a certain amount of radioisotope is limited. Yet another advantage of embodiments of the present invention is that a liquid target is provided that enables the production of radioisotopes with less generation of radioactive waste.

[0011] An advantage of embodiments of the present invention is that the liquid target system can be cooled continuously and efficiently, thereby preventing overheating of the liquid target. A further advantage of embodiments of the present invention is that the liquid target system enables heat to be discharged continuously and reliably in a steady state.

[0012] Advantages of embodiments of the present invention are that, since the liquid target can have a large total volume, for example, the adverse effects expected from losses due to hydrogen formation or non-condensable water can be limited. A further advantage of embodiments of the present invention is that the liquid target system can operate safely. Yet a further advantage of embodiments of the present invention is that the operation of the liquid target can be monitored, for example, by accurately tracking temperature and / or pressure, which is often difficult for solid targets.

[0013] In a first aspect, the present invention relates to a liquid target system for the production of radioisotopes. The liquid target system comprises a boiling chamber for containing a liquid and a basic chemical substance, wherein the radioisotope can be produced using irradiation. The boiling chamber comprises an irradiation window that enables the liquid and the basic chemical substance to be irradiated and that evaporates the liquid into vapor. The liquid target system is configured such that overheating of the liquid target is controlled by the thermodynamics of the evaporation process.

[0014] When referring to an irradiation window in an embodiment of the present invention, reference is made to a region of the wall of the boiling chamber that enables the radiation necessary to irradiate the basic chemical substance capable of producing the radioisotope to enter the boiling chamber. The type of irradiation window used can depend on the type of irradiation. For example, when using gamma rays, the wall can be permeable to any radiation, for example.

[0015] In an embodiment, a liquid target system configured such that overheating of the liquid target is controlled by the thermodynamics of the evaporation process can include that the liquid target system is configured to use the evaporation of the liquid, preferably, to control the temperature of the liquid target, in order to prevent such overheating. Overheating of the liquid target can result in evaporation of substantially all of the liquid within the liquid target, which in turn boils and dries the basic chemical substance.

[0016] Advantages of embodiments of the present invention are that the liquid target can be prevented from overheating, so that the liquid target system can avoid the release of non-condensable gases from chemical material, enable avoidance of sintering of the chemical material, and / or enable avoidance of the formation of insoluble chemical material. Such overheating can result from a large amount of irradiation energy deposited on the liquid target. In particular, so-called pair production reactions contribute to heating of the liquid target. In pair production reactions, high-energy photons in the presence of a high-Z nucleus (e.g., the parent nuclide Ra-226) are converted into electrons and positrons with remaining kinetic energy. Charged particles, namely electrons and positrons, release their respective kinetic energies into the liquid target as they decelerate (and in the case of positrons, annihilate), which is converted into heat.

[0017] Advantages of embodiments of the present invention are that a cooling circuit for a liquid target system, controlled by a pump, in which a liquid and a basic chemical are pumped within the cooling circuit, may not be required. A further advantage of embodiments of the present invention is that a large heat exchanger that requires a large contact area with the liquid target can be avoided, and as a result, the amount of liquid target required can be limited.

[0018] Advantages of embodiments of the present invention are that the system enables in-operation up-concentrating. More specifically, the initial concentration of the basic chemical used to produce the radioisotope in the liquid at the starting temperature can be limited due to solubility in a solvent (e.g., water), and a higher concentration at this starting temperature would result in precipitation, but an advantage of embodiments of the present invention is that the concentration can be increased during heating of the liquid target as the solubility of the basic chemical in the solvent (e.g., water) increases. The latter is established by evaporation of the solvent, but the basic chemical is retained in the irradiated area.

[0019] In an embodiment, the evaporated water can be stored in the system as steam or as a liquid.

[0020] In an embodiment, the liquid target system further includes a condensation region disposed above the boiling chamber, the condensation region having a wall for condensing vapor into a liquid condensate, and the liquid condensate can be systematically returned or provided to the boiling chamber. Such a wall can also be referred to as a cooling surface. In an embodiment, the liquid target system is configured to systematically return the liquid condensate into the boiling chamber, for example, by a direct fluid connection between the condensation region and the boiling chamber or by systematically dripping the liquid condensate from the condensation region into the boiling chamber (e.g., by gravity).

[0021] In an embodiment, thus, at least one condensate collection region can be disposed on the wall for condensing vapor and can include a dripping mechanism for systematically returning the condensate to the boiling chamber.

[0022] In a preferred embodiment, the liquid target system comprises at least one condensate collection region for collecting liquid condensate, wherein at least one condensate collection region is disposed outside the boiling chamber (i.e., at least one condensate collection region and the boiling chamber are separated from each other), and further comprises at least one condensate collection region, and at least one condensate collection region and the boiling chamber are interconnected so as to function as a communicating vessel. In an embodiment, at least one condensate collection region and the boiling chamber are configured such that the ratio of the volume of the liquid condensate (i.e., liquid) present in at least one condensate collection region to the volume of the liquid present in the boiling chamber is at least 0.5, preferably at least 1, more preferably at least 2. In an embodiment, the ratio of the area of the horizontal cross-section of at least one condensate collection region to the area of the horizontal cross-section of the boiling chamber is at least 0.5, preferably at least 1, more preferably at least 2. The dimensions of the system can be selected to obtain an enrichment factor of 2. The advantage of these embodiments is that the basic chemical substance can be concentrated in the boiling chamber and may not be present in at least one condensate collection region, so that during the operation of the liquid target system, the increased concentration of the basic chemical substance in the boiling chamber is at least 50%, preferably at least 100%, preferably at least 200% higher than the initial concentration of the basic chemical substance present in all liquids, including any liquid present in at least one condensate collection region.

[0023] In an embodiment, the volume of the boiling chamber is 5 mL to 500 mL. In an embodiment, the total volume of at least one condensate collection region is 5 mL to 500 mL.

[0024] In an embodiment, the interconnection between the boiling chamber and at least one condensate collection region includes a gap or a pipe. In an embodiment, the inlet of the interconnection for introducing liquid into the boiling chamber is located near the bottom of the boiling chamber, for example, on the wall or the bottom. Preferably, the inlet is located at a height within the boiling chamber that is less than 25% of the height of the boiling chamber, preferably less than 10% of the height of the boiling chamber, and more preferably substantially at the bottom of the boiling chamber. In an embodiment, the cross-sectional area of the interconnection perpendicular to the nominal flow direction within the interconnection is at most 10%, preferably at most 5%, and more preferably at most 2% of at least one (e.g., both) of the vertical or horizontal cross-sectional areas of the boiling chamber.

[0025] By way of example, and not limitation, embodiments will be described below. For example, a target that receives 1200 W having 50% of the energy efficiently used to convert a liquid to steam, and a single opening of 0.2 cm (corresponding to a radius of the circular opening of about 2.5 mm). 2 In the case of, the liquid would move at a velocity of 1.33 cm / s. The smaller the opening, the greater the velocity. By using a small cross-section for the interconnection, backflow from the irradiation chamber towards the condensate chamber is avoided. By selecting a sufficiently small cross-section, the liquid flows uniformly in one direction at a sufficiently high velocity. The length and / or diameter of the interconnection can be designed to create a pressure drop that creates a liquid level difference. In some embodiments, the design is such that it stores condensate above the irradiation level of the irradiation chamber. This ensures that when irradiation and boiling are complete, most of the condensate returns to the irradiation chamber. In this way, precipitation is avoided when the chemical is diluted and the solution cools.

[0026] In an alternative example, the inlet can be located at the top of the system and can operate via dripping.

[0027] The advantages of these embodiments are that heat dissipation (and thus prevention of overheating) in the liquid target system is ensured by the boiling and condensation processes of the liquid. The condensation region can be cooled by a secondary system containing a coolant fluid that does not contain radioactive material. In an embodiment, the liquid target system further comprises a coolant fluid bath and / or a coolant fluid circulation secondary system for cooling the condensation region. In a preferred embodiment, the condensation region and at least one condensate collection region are at least partially surrounded by a coolant fluid circulation secondary system.

[0028] An advantage of embodiments of the present invention is that the liquid target system can function automatically as a concentrator, such that the concentration of basic chemical substances increases in the irradiated volume during the heating process and subsequent liquid evaporation caused by irradiation. Further, since the solubility of basic chemical substances in the liquid typically increases with temperature, the liquid target can contain a high concentration of basic chemical substances without precipitation, enabling efficient production of radioisotopes. In practice, since the solubility of the basic chemical substance material from which the radioisotope is produced is relatively low at room temperature, it is advantageous that the concentration can increase during the heating process caused by irradiation, taking advantage of the higher solubility of the basic chemical substance material in the liquid at higher temperatures.

[0029] In an embodiment, the system further comprises an irradiation beam generator configured to irradiate the liquid and the basic chemical substance. Here, the irradiation beam generator is typically located outside the boiling chamber and is configured to irradiate the liquid and the basic chemical substance through an irradiation window. In an embodiment, the irradiation beam generator is selected from an electron beam gun, a gamma beam gun, a proton beam gun, and a neutron beam gun. In an embodiment comprising an electron beam gun or a proton beam gun, the irradiation beam generator may further comprise a converter for converting a charged particle beam (i.e., an electron beam or a proton beam) into high-energy bremsstrahlung photons forming the irradiation beam.

[0030] In embodiments including at least one condensate collection region, the irradiation beam generator may be configured such that the irradiation beam propagates from the irradiation beam generator located outside the boiling chamber, through the irradiation window, into the boiling chamber without passing through the at least one condensate collection region. An advantage of embodiments of the present invention is that any liquid within the at least one condensate collection region does not boil, thereby converting the liquid within the at least one condensate collection region to vapor. This can result in an elevated concentration of basic chemical substances present in the at least one condensate collection region, which can result in a decrease in the concentration of basic chemical substances within the boiling chamber. A further advantage of these embodiments is that there is no risk of the irradiation beam being attenuated by absorption by liquid condensate within the at least one condensate collection region.

[0031] In embodiments, the liquid target system comprises a pressurization unit for pressurizing the system to control the bubble size and boiling temperature of the liquid. In these embodiments, the system may further comprise a pressure sensor for measuring the pressure of the boiling chamber or the system.

[0032] In embodiments, the boiling chamber, the condensation region, and the at least one condensate collection region form a system having a cylindrical design. An advantage of embodiments of the present invention is that the number of welds in the cylindrical design is typically limited, thereby making the system pressure-resistant.

[0033] In embodiments, the boiling chamber includes an inlet and an outlet for generating a flow of inert gas (e.g., argon, helium, or nitrogen, preferably helium) through the boiling chamber. The loss of non-condensable water (humidity) exiting the liquid target system at the same flow rate as the inert gas can be compensated for by exposing the inert gas to water (humidity) prior to adding it to the target system. In this way, the mass balance of water can be kept constant (excluding hydrogen gas exiting the system).

[0034] The advantages of these embodiments are that good pressure control can be achieved. It is a further advantage that an inert gas stream can be used to remove any gaseous material formed in the boiling chamber from the boiling chamber and collect the gaseous material (e.g., Rn when the nucleophile contains Ra-226). In an embodiment, the boiling chamber includes an inlet for introducing and / or removing a liquid target, i.e., a liquid and a basic chemical substance, from the boiling chamber.

[0035] In an embodiment, the basic chemical substance comprises or consists of a salt containing a radionuclide for forming a radioisotope when exposed to irradiation. The radionuclide is typically a cation, and the salt further includes an anion. In an embodiment, the liquid is water or heavy water, and the basic chemical substance is a salt having a positive enthalpy with respect to water. In an embodiment, the basic chemical substance is any one or a combination of Ra(NO3)2, RaCl2, and Ba(NO3)2. Although embodiments of the present invention often refer to the production of Ac-225, it should be noted that the embodiments are not limited thereto, and liquid target systems for the production of other isotopes are also envisioned. The advantage of the embodiments of the present invention is that these salts have sufficient solubility in water. In an embodiment, the salt includes one of a Ca salt that can be used for the production of Sc-47, a Zn salt that can be used for the production of Cu-67, a Ba salt that can be used for the production of Cs-131, and a Dy salt that can be used for the production of Tb-155. In an embodiment, the liquid target system is adapted to produce Sc-47, Cu-67, Cs-131, Tb-155, Ra-225, or Ac-225, preferably Ac-225.

[0036] Any feature of any embodiment of the first aspect can be standalone as appropriately described for any embodiment of any other aspect of the present invention.

[0037] In a second aspect, the present invention relates to a method for producing a radioisotope. The method includes irradiating a liquid target containing a liquid and a basic chemical substance, where the radioisotope can be produced using irradiation, and evaporating the liquid to vapor. Here, the thermodynamics of the evaporation process is used to control the superheating of the liquid target.

[0038] In an embodiment, the method can be carried out using a liquid target system according to an embodiment of the first aspect of the present invention.

[0039] In an embodiment, the method includes collecting the radioisotope from the liquid target after the irradiation.

[0040] In an embodiment, the irradiation is carried out using, for example, 1.5 kW of power incident on the liquid target, for example, 0.5 kW to 10 kW (for example, 0.5 kW to 5 kW, for example, 0.5 kW to 3 kW). In an embodiment, the irradiation step is carried out at a pressure of vacuum to 60 bar, for example, 0.5 bar to 10 bar. It should be noted that, in principle, higher pressures can also be used.

[0041] In a preferred embodiment, the liquid target has a concentration of the basic chemical substance that is, at the location of irradiation, preferably at least 20% higher, more preferably at least 50% higher, even more preferably at least 100% higher, even more preferably at least 200% higher than the solubility of the basic chemical substance in the liquid (i.e., the maximum concentration before precipitation occurs) at a temperature of 25 °C and a pressure of 1 atmosphere. Typically, any further basic chemical substance does not dissolve in the liquid, and for example, precipitates from the liquid, so the maximum concentration that can be achieved is equal to the solubility of the basic chemical substance.

[0042] Any feature of any embodiment of the second aspect can be standalone as appropriately described for any embodiment of any other aspect of the present invention.

[0043] In a third aspect, the present invention relates to the use of a liquid target system according to an embodiment of the first aspect for generating a radioisotope.

[0044] Any feature of any embodiment of the third aspect may be standalone, as would be appropriately described for any embodiment of any other aspect of the present invention.

[0045] Certain preferred aspects of the present invention are set out in the appended independent and dependent claims. Features from the dependent patent claims may be combined with the features of the independent claims and the features of other dependent claims, as required, not merely as explicitly set out in the claims.

[0046] Although there have been continuous improvements, changes and evolutions of devices in this field, this concept represents a substantial new and innovative improvement, including a departure from conventional practices, and is believed to result in the provision of more efficient, stable and reliable devices of this nature.

[0047] The above and other characteristics, features and advantages of the present invention will become apparent from the following detailed description in conjunction with the accompanying drawings, which illustrate the principles of the invention by way of example only. This description is given for illustration only and does not limit the scope of the present invention. The reference figures cited below refer to the accompanying drawings.

Brief Description of the Drawings

[0048]

Fig. 1A

Fig. 1B

Fig. 2

Fig. 3

Fig. 4

Fig. 5

[0049] In different drawings, the same reference numerals refer to the same or similar elements.

DETAILED DESCRIPTION OF THE INVENTION

[0050] The present invention is described with reference to specific drawings with respect to specific embodiments, but the present invention is not limited thereto and is limited only by the claims. The drawings described are merely schematic and non-limiting. In the drawings, the sizes of some of the elements may be exaggerated for illustrative purposes and may not be drawn to scale. The dimensions and relative dimensions do not correspond to the actual implementation of the present invention.

[0051] Furthermore, the terms first, second, third, etc. in the description and claims are used to distinguish similar elements and are not necessarily used to describe an order in any temporal, spatial, ranking, or any other manner. The terms used in this way are interchangeable under appropriate circumstances, and it should be understood that the embodiments of the present invention described herein can operate in an order other than that described or illustrated herein.

[0052] Furthermore, the terms upper, lower, top, bottom, etc. in the description and claims are used for illustrative purposes and are not necessarily used to describe a relative position. The terms used in this way are interchangeable under appropriate circumstances, and it should be understood that the embodiments of the present invention described herein can operate in an orientation other than that described or illustrated herein.

[0053] It should be noted that the term "comprising" as used in the claims should not be construed as being limited to the means recited thereafter. This does not exclude other elements or steps. Thus, it should be construed as identifying the presence of the described features, integers, steps or components as such, but not as precluding the presence or addition of one or more other features, elements, steps or components, or groups thereof. Thus, the term "comprising" encompasses both situations where only the described features are present and situations where these features and one or more other features are present. Thus, the term "comprising" according to the present invention, as an embodiment, also includes the case where no further components exist. Thus, the scope of the expression "a device comprising means A and B" should not be construed as being limited to a device consisting only of components A and B. This means, with respect to the present invention, that the only relevant components of the device are A and B.

[0054] Similarly, it should be noted that the term "coupled" should not be construed as being limited to direct connection only. The terms "coupled" and "connected" may be used with their derivatives. It should be understood that these terms are not intended to be synonyms of each other. Thus, the scope of the expression "device A coupled to device B" should not be limited to a device or system in which the output of device A is directly connected to the input of device B. This means that there is a path between the output of A and the input of B, which may be a path including other devices or means. "Coupled" can mean that two or more elements are in direct physical or electrical contact with each other, or that two or more elements are not in direct contact with each other but still cooperate or interact with each other.

[0055] References to "one embodiment" or "an embodiment" throughout this specification mean that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, although they may. Further, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments, as will be apparent to those skilled in the art from the present disclosure.

[0056] Similarly, in the description of exemplary embodiments of the present invention, it should be understood that various features of the present invention may be grouped together in a single embodiment, drawing, or description thereof in order to simplify the disclosure and assist in understanding one or more aspects of the various inventions. However, this method of disclosure should not be construed as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as reflected by the following claims, aspects of the invention are less than all of the features of the single foregoing disclosed embodiment. Thus, the claims following the detailed description are expressly incorporated into this detailed description, and each claim stands on its own as a separate embodiment of the present invention.

[0057] Furthermore, some embodiments described herein include some but not other features that are included in other embodiments, while combinations of features of different embodiments are within the scope of the present invention and are intended to form different embodiments, as will be understood by those skilled in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

[0058] Furthermore, some embodiments are described herein as a method, or a combination of elements of a method, that can be implemented by a processor of a computer system or by other means for performing a function. Accordingly, a processor having instructions necessary to implement such a method or elements of a method forms means for implementing the method or elements of the method. Further, the elements described herein of an apparatus embodiment are an example of means for performing the functions implemented by the elements for the purpose of implementing the present invention.

[0059] In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the present invention may be practiced without these specific details. In other instances, well-known methods, structures, and techniques have not been shown in detail so as not to obscure the understanding of this description.

[0060] Here, the present invention will be described by way of a detailed description of some embodiments of the present invention. It is apparent that other embodiments of the present invention can be configured according to the knowledge of those skilled in the art without departing from the technical teachings of the present invention, and the present invention is limited only by the conditions of the appended claims.

[0061] In a first aspect, the present invention relates to a liquid target system for the production of radioisotopes. The liquid target system comprises a boiling chamber for containing a liquid and a basic chemical substance, wherein the radioisotope can be produced using irradiation. The boiling chamber comprises an irradiation window that enables the liquid and the basic chemical substance to be irradiated and evaporates the liquid into vapor. The liquid target system is configured such that the superheat of the liquid target is controlled by the thermodynamics of the evaporation / condensation process.

[0062] In a second aspect, the present invention relates to a method for producing a radioisotope. The method comprises irradiating a liquid target comprising a liquid and a basic chemical substance, wherein the radioisotope can be produced using irradiation, and evaporating the liquid into vapor. Here, the thermodynamics of the evaporation process is used to control the superheat of the liquid target.

[0063] In a third aspect, the present invention relates to the use of a liquid target system according to an embodiment of the first aspect for generating a radioisotope.

[0064] Reference is made to FIG. 1A, which is a schematic exploded view of at least a part of the liquid target system 10 according to an embodiment of the present invention. At the same time, reference is made to FIG. 1B, which is a schematic vertical cross-sectional view of at least a part of the liquid target system 10. In this example, the liquid target system for the production of radioisotopes comprises a boiling chamber 2 for containing a liquid target 8 consisting of a liquid and a basic chemical substance capable of producing radioisotopes using irradiation. In this example, an irradiation window 23, which is a part of the wall of the boiling chamber 2, through which the irradiation can propagate, is included in the wall of the boiling chamber 2. In this example, the liquid contained in the liquid target 8 in the boiling chamber 2 is water, and the basic chemical substance dissolved in the water is a salt containing the parent nuclide Ra-226 (for example, (Ra-226)(NO3)2), but the present invention is not limited thereto. Therefore, in this example, the liquid target 8 consists of a liquid and a salt containing Ra-226.

[0065] The liquid target 8 is continuously irradiated by a high-energy photon beam through the irradiation window 23. As a result, the liquid target 8 boils under the continuous irradiation, thereby converting the liquid into vapor, i.e., water vapor (white arrows). The water vapor is then condensed in a condensation region 3 located above the boiling chamber 2, thereby converting the vapor into a liquid condensate. At least the condensation region 3, optionally the condensate collection region 4, and optionally the boiling chamber 2 can also be cooled by a water coolant fluid bath and / or a forced coolant fluid water circulation secondary system 32.

[0066] In this example, the liquid target system further comprises two condensate collection regions 4, which are different from the boiling chamber 2 and, in this example, are separated from each other by a separation wall 21. The two condensate collection regions 4 are located on both sides of the boiling chamber 2 and are separated by the separation wall 21 each time. The liquid target system is configured such that the condensate formed within the condensation region 3 moves, for example, drops (horizontal striped arrow) into the condensate collection region 4. This is achieved, in this example, because the wall of the condensate collection region 4 is connected to the wall of the condensation region 3, so that the liquid condensed on the wall of the condensation region 3 can move, for example, downward through the wall into the condensate collection region 4. Further, in this example, the liquid target system comprises a condensate steering element 5 that guides any condensate away from the boiling chamber into the condensate collection region 4 (which may also be referred to as a condensate collection chamber).

[0067] The condensate collection region 4 is fluidly coupled to the boiling chamber 2, for example, via an opening 24 in the separation wall 21. For example, as in this example, at least a portion of the separation wall 21 may be separated from the bottom of the boiling chamber 2 by a gap 24, through which liquid can move between the condensate collection region 4 and the boiling chamber 2. Alternatively, for example, piping may be used to effect such fluid coupling. Thereby, the liquid condensate 41 collected in the condensate collection region 4 can flow into the boiling chamber 2 (black arrow).

[0068] Therefore, in this example, the condensate collection region 4 and the boiling chamber 2 can be regarded as functioning as three communicating vessels. The liquid target 8 in the boiling chamber 2 is placed directly in the high-energy photon beam and is boiling, while the condensate is collected in the condensate collection region 4 and is not boiling due to the lower energy deposition in the condensate collection region 4. In fact, the condensate, i.e., the liquid, in the condensate collection region 4 may not contain a significant amount of Ra-226 for absorbing irradiation, for the continuous effective liquid flow (black arrow) from the condensate collection region 4 through the gap to the boiling chamber 2 to compensate for the vapor flow (white arrow) and the condensate flow (hatched arrow) through the condensation region 3. In the steady state, the velocities of each of these three flows may be substantially equal. The condensate 41 is at a significantly low irradiation level. Furthermore, due to the absence of Ra, the heat absorption is lower and the condensate is not boiled. In other words, since the condensate collection region 4 and the boiling chamber 2 are essentially communicating vessels, the continuous loss of the water mass in the boiling chamber 2 due to the boiling is compensated by the continuous water flow from the condensate collection region 4 through the holes at the bottom of the target to the boiling chamber 2. The size of the gap (or alternatively, the diameter of the pipe) is preferably optimized such that a continuous flow of condensate (i.e., liquid) exists towards the boiling chamber 2, and as a result, substantially no Ra-226 moves into it in the opposite direction, i.e., from the boiling chamber 2 towards the condensate collection region 4. Therefore, the opening should be neither too narrow nor too large. Preferably, the liquid flow rate into the boiling chamber through the opening is 0.1 cm / s to 20 cm / s, preferably 0.5 cm / s to 5 cm / s, for example 1 cm / s. Preferably, the liquid flow rate results almost entirely from the loss of liquid in the boiling chamber 2 due to boiling by irradiation and the gain of liquid in the condensate collection region 4 due to the subsequent collection of condensate in the condensate collection region 4. The continuous countercurrent flow of the condensate (i.e., liquid) to the liquid target in the boiling chamber 2 prevents the liquid target from boiling and drying out and prevents overheating.

[0069] In this example, the irradiation of the liquid target 8 results in the production of Ac-225 by the photonuclear reaction Ra-226(γ,n)Ra-225(β-)Ac-225. Any Ac-225 formed is preferably separable from the liquid target 8. In this example, the liquid target system includes an opening 22 at the bottom of the boiling chamber 2, which functions as an inlet and / or outlet for the liquid target 8, for example, before and after irradiation, but preferably does not function during irradiation. Thereby, after irradiation, the liquid target 8 may be moved through the opening 22, for example, to a hot cell facility for chemical separation and purification of Ac-225. After the separation, the liquid target may be returned to the boiling chamber 2 through the opening 22. To avoid crystallization and losses in any flow path (e.g., piping) interconnecting the boiling chamber 2 and the hot cell facility, preferably, immediately after transferring the liquid target 8 through the flow path, a certain rinse volume of liquid, for example, dilute nitric acid, is used. This may further dilute the basic chemicals in the liquid target 8 and, thus, may reduce the yield by the excess volume introduced by the rinse volume. The excess volume may be removed by boiling the liquid target 8 in the boiling chamber 2 while establishing a flow of inert gas (e.g., helium or N2) from the opening 22 to the opening 31, thereby removing any excess vapor. However, with an appropriate design of the target (the ratio of the volume of the boiling chamber 2 to the volume of the condensate chamber 4), this excess volume may not be a problem. In practice, the volume ratio between the liquid in the boiling chamber 2, i.e., the liquid irradiated by the beam, and the liquid in the condensate collection chamber 4 can be optimized, and the concentration of Ra in the boiling chamber can increase. For example, in the case of a 1 / 1 volume ratio, the concentration of Ra in the beam can be doubled during operation, i.e., during irradiation of the liquid target 8, compared to a design without a condensate collection chamber 4. As a result, the production yield is also doubled. The advantage of such an increased concentration is that a small amount of the parent nuclide (e.g., Ra-226) may be required for the gamma production route to obtain a high isotopic yield of Ra-225. Such an increased concentration may not be a problem regarding the maximum value of the radium solubility during irradiation.This is because the liquid target can be strongly heated, for example, up to 100°C which is the boiling temperature of water at standard pressure, or above 100°C when the pressure exceeds the standard pressure, so that the solubility can be further increased.

[0070] In this example, at least a part of the liquid target system 10, namely, the boiling chamber 2, the condensation region 3, and the condensate collection region 4, form a cylindrical shape so as to limit the amount of welding, which enhances the strength of this part of the liquid target system that can operate at high pressure. The higher pressure can be used to raise the boiling point of water and can affect the thermodynamics of the evaporation process. In practice, when operating this liquid target 8 within the beam, any heat generation should be discharged in a safe and reliable manner during steady operation. The boiling liquid target 8 is preferred because it is an efficient and convenient way to remove excess heat from the solution, i.e., the liquid target 8. Due to the relatively small size of the liquid target 8, pressurization may be highly preferred to control the bubble size within the boiling liquid target 8. The higher the pressure, the smaller the bubbles may be and the better the boiling performance may be. The pressure and the steady-state temperature can be controlled to optimize the thermal-hydraulic performance of the liquid target 8.

[0071] (Ra-226)(NO3)2 has a relatively high solubility in water compared to other Ra-226 salts and is thus well-suited for use in embodiments of the present invention. The solubility of the compound in water at 20 °C and standard pressure is 13.9 g / 100 g (see Erbacher, O. Loslichkeits-Bestimmungen einiger Radiumsaltze; Berichte der deutschen chemischen Gesellschaft, 1930; Vol. 63: 141-156). However, alternatively, other compounds such as (Ra-226)Cl2 can also be used. The solubility of (Ra-226)(NO3)2 increases significantly at higher temperatures. To estimate the solubility of (Ra-226)(NO3)2 at high temperatures, the solubility of barium nitrate can be considered as an accurate estimate due to the similar behavior of the alkaline earth metals Ra and Ba or the atoms of Group 2 (however, the solubility of Ba(NO3)2 is slightly lower than the solubility of Ra(NO3)2). Reference is made to Figure 2, which is a plot of the solubility in grams of salt per 100 mL of H2O as a function of temperature (degrees Celsius). Data for Ba(NO3)2 over the temperature range of 0 °C to 100 °C (from http: / / periodic-table-of-elements.org / SOLUBILITY / barium_nitrate), represented by black dots connected by a dotted curve, and data for Ra(NO3)2 (only data at 20 °C) are shown. At 100 °C, it can be observed that the solubility of Ba(NO3)2 increases by a factor of 3 compared to its solubility at 20 °C. Therefore, the solubility at 100 °C is expected to be approximately 3 times higher for Ra(NO3)2 as well. Above 100 °C, even higher solubilities are expected. In practice, the boiling point of water can rise first due to the presence of the salt dissolved therein and second due to an increase in pressure.

[0072] The pressure dependence of Ra(NO3)2 can also be derived by comparison with Ba(NO3)2. The water solubility of Ba(NO3)2 increases from 0.394 to 0.841 ± 0.005 mol / kg (13.79 to 29.435 ± 0.175 g / 100 g H2O) when the pressure is increased from standard pressure to 200 MPa. (B.R. Churagulov, S.L. Lyubimov, A.N. Baranov, A.A. Burukhin. Influence of Pressures up to 300 MPa on the Water Solubilities of Poorly Soluble Salts. September 1999. Russian Journal of Inorganic Chemistry 44(9):1489-1493). Therefore, it is not expected that the high pressure in the boiling chamber can have an adverse effect (decrease) on the solubility of Ra(NO3)2 in the water of the liquid target.

[0073] Here, proceed with a quantitative example. Referring back to FIGS. 1A and 1B, as an example, a volume of 25 cm 3It may be considered to have a liquid target 8, and it is not preferable to exceed the solubility in water at room temperature (13.9 g / 100 g). In practice, the liquid target 8 should typically be pumped from within the boiling chamber 2 at room temperature, that is, between the boiling chamber 2 and the hot cell facility. Therefore, a higher concentration can result in precipitation in the flow path connecting the boiling chamber 2 to the hot cell facility. For this reason, at room temperature, the liquid target can contain only about 2 grams of Ra-226. However, the goal is to have 6 grams of the basic chemical substance in the boiling chamber 2 in order to increase the efficiency and yield of the liquid target system. Therefore, instead, a target of 6 grams of Ra-226 dissolved in 125 ml may be assumed, and the volume ratio between the liquid in the boiling chamber 2 and the condensate collection chamber 4 is equal to 1 / 4. Therefore, initially, 100 mL of the liquid target is present in the condensate collection chamber 4 and 25 mL is present in the boiling chamber 2. At the start of irradiation, the Ra-226 is evenly divided between the compartments. When the boiling chamber 2 begins to boil under the influence of the irradiation by the above mechanism, the Ra-226 from the condensate collection chamber 4 flows towards the boiling chamber 2 and remains there during irradiation. Therefore, over time, the Ra-226 depletes in the condensate collection chamber 4 such that the condensate collection chamber 2 contains only the liquid, that is, the condensate 41. Further, 25 cm 3 The boiling chamber 2 containing the liquid target of 25 cm contains all the remaining Ra-226 (that is, the amount obtained by subtracting from 6 grams the amount that reacted to form Ra-225 or Ac-225). That is, only the boiling chamber 2 efficiently contains the liquid target 8. As the water is heated to, for example, 80 °C or 100 °C, the concentration of the basic chemical substance in the liquid target 8 still remains below the dissolution limit of Ra(NO3)2.

[0074] In addition to heating by irradiation, forced heating (not due to irradiation) of the boiling chamber 2 can be performed until a steady state is achieved. It is advantageous that the steady state, in which thermodynamics is continuous and predictable, can be achieved rapidly. Further, when cooling the liquid target 8 after the irradiation, slow cooling may be preferred in order to avoid any precipitation of Ra(NO3)2. One way to achieve this can be, for example, to immerse the cylinder or target vessel, and then at least the boiling chamber 2 and the condensate collection region 4, in a water bath operating at 70 - 80 °C. Alternatively, a purge gas that causes forced mixing can be introduced, for example, through the opening 22 and exit through a further opening 31 located above the boiling chamber 2.

[0075] Reference is made to FIG. 3, which is a schematic diagram of a liquid target system 1 according to an embodiment of the invention, which may include at least a part of the liquid target system 10 of FIGS. 1A and 1B. The boiling chamber included in at least a part of the liquid target system 10 can be irradiated by an irradiation beam 26 generated from an irradiation beam generator 25. In this example, the opening 22 at the bottom of the boiling chamber can be coupled to a buffer container 6 via a valve V3. The buffer container 6 is coupled to a hot cell facility 61 via a valve V8. The buffer container 6 is further connected to an inlet for introducing demineralized water 62 via a valve V5. The inlet for introducing demineralized water 62 is further connected to a further opening 31 via a valve V7. In this example, a compressed gas, for example, N2 or He, can be introduced from a compressed gas source 63, for example, a compressed gas cylinder, through the opening 22 via the valve V4, the buffer container 6, and the valve V3, or through the further opening 31 via the valve V2. Further, a vacuum can be introduced from a vacuum source 64, for example, a pump, through the opening 22 via the valve V6, the buffer container 6, and the valve V3, or alternatively, through the further opening 31 through the valves V6, V4, and V2. The further opening 31 can be coupled to a chimney 7 via a volume containing activated carbon 71, or any other system for capturing radioactive non - condensable gases.

[0076] In the initial state, all valves V1 - V8 are closed. The buffer container 6 can then be filled with the liquid target by opening valves V6 and V8 such that the vacuum draws the liquid target from the hot cell facility 61.

[0077] Thereafter, the liquid target is moved from the buffer container 6 to the boiling chamber and the condensate collection region by introducing a gas stream (e.g., He or N2) through the buffer container 6, through the boiling chamber, into at least a portion of the liquid target system 10, and then through the activated carbon 71 into the chimney 7, by opening valves V4, V3, and V1. The fluid connection connecting the boiling chamber to the buffer container 6 can be flushed with demineralized water by first opening only valve V5, then closing V5, opening valve V4, and opening valve V3, and introducing demineralized water 62 from an inlet for introducing demineralized water to fill the buffer container 6 with demineralized water initially. Alternatively, the flushing can be performed by opening valve V7. This can introduce additional liquid into the boiling chamber, but in the present invention, this cannot be a problem due to a potential increased concentration of basic chemicals in the boiling chamber. Further, in the next step, the excess liquid in the boiling chamber can be removed from the boiling chamber by evaporation by a gas stream from the compressed gas source 63 through the boiling chamber into the chimney 7, thereby reducing the volume of the liquid in the boiling chamber.

[0078] In the next step, valve V1 is opened and the liquid target in the boiling chamber is boiled by using the low-power irradiation beam 26 generated from the irradiation beam generator 25. During irradiation, compressed gas (e.g., Ar, He, or N2) is introduced into at least a part of the liquid target system 10, and the valve may not be opened, or alternatively, only valves V4 and V3 may be opened, or V1 may be slightly opened, so as to obtain a preferable, for example, high pressure in at least a part of the liquid target system 10. The flow rate can be controlled via the flow rate controller 631 and the pressure regulator 632. The increased pressure in the boiling chamber can enable the liquid in the boiling chamber to reach a temperature higher than the atmospheric pressure, which can improve the solubility of the basic chemical substance. Further, for example, when the basic chemical substance contains Ra-226, a small gas flow rate can be maintained so as to remove and collect any gas formed in the boiling chamber, e.g., Rn. An advantage of the embodiment of the present invention is that the liquid target system is compatible with Rn collection.

[0079] After the photonuclear reaction in the boiling chamber, all the radioisotopes formed in the boiling chamber can be collected. For this purpose, all the valves can be closed to move the liquid target containing the radioisotope from the boiling chamber to the buffer container 6 by means of a gas flow, and then valves V2 and V3 can be opened. In some cases, subsequently, the pipe connecting the boiling chamber to the buffer container 6 can be flushed with demineralized water by opening valve V7. Finally, the content of the buffer container 6 can be sent to the hot cell facility 61 by closing all the valves, then opening valves V8 and V4, and subsequently opening valve V5 slightly for a while to flush with demineralized water.

[0080] Although at least a part of the liquid target system 10 in the above description is assumed to be an example embodiment related to FIGS. 1A and 1B, at least a part of the liquid target system 10 may alternatively be an example embodiment of the subsequent examples, or may include the features of both examples.

[0081] Reference is made to FIG. 4, which is a schematic diagram of a further example of a liquid target system according to an embodiment of the present invention. The boiling chamber 2 includes a liquid target 8 containing a liquid and a basic chemical substance capable of producing a radioisotope. Irradiation 26 incident on the liquid target 8 causes heating of the liquid target 8 such that the liquid evaporates to form vapor in the volume 9 above the boiling chamber 2. The walls of the volume are thermally insulated by a thermal insulation material 91 so that a high temperature of the vapor in the volume can be achieved. Thereby, a high concentration of vapor in the volume can be achieved, allowing the pressure to increase. In other words, the volume 9 can contain a large amount of liquid in the vapor phase, i.e., in the vapor. In an embodiment, the ratio between the volume of the gas vapor in the volume 9 and the volume of the liquid target 8 in the boiling chamber 9 is at least 2, preferably at least 5.

[0082] In other words, instead of directly condensing the formed vapor, alternatively, thus, the volume above the boiling chamber can be used to store the evaporated solvent as vapor.

[0083] Reference is made to FIG. 5. As a result of evaporation by irradiation and the large amount of vapor formed, the volume of the liquid target 8 decreases. Thereby, the concentration of the basic chemical substance therein increases, and for forming a radioisotope, the efficiency and yield of a nuclear reaction of the basic chemical substance, for example, a photonuclear reaction, can be enhanced. In an embodiment, the irradiation is adapted to produce a pressure within the volume 9 of up to 20 bar, for example, up to 10 bar. The upper limit of the pressure is typically limited by the pressure that the walls of the liquid target system can withstand. The high pressure used can improve the solubility of the basic chemical substance in the liquid target 8 in order to raise the boiling temperature, and then enable more liquid to evaporate without causing precipitation of the basic chemical substance from the liquid target 8. During irradiation of the liquid target 8, the concentration of the basic chemical substance in the liquid is preferably higher than, for example, the solubility of the basic chemical substance in the liquid at room temperature without irradiation. In this example, high irradiation can thus result in a high yield due to both the high irradiation and the increased concentration of the basic chemical substance in the liquid target 8. Further, overheating can be prevented by finding a balance between the irradiation output and the power loss due to evaporation of the liquid from the liquid target 8.

[0084] It should be noted that in embodiments of the present invention, the operating conditions and additional measures can be selected so as to limit or prevent radiolysis or reverse it by recombination of oxygen with hydrogen. Such measures are well known in the art. Examples of technical solutions are provided by https: / / link.springer.com / article / 10.1007 / BF02387473.

[0085] Although preferred embodiments, specific structures and configurations, and materials have been discussed herein for the devices according to the present invention, it is to be understood that various changes or modifications of form and detail can be made without departing from the scope of the present invention. Steps can be added or removed to the methods described within the scope of the present invention.

Claims

1. A liquid target system (1) for the production of radioactive isotopes, wherein the liquid target system (1) comprises: - A boiling chamber (2) for containing a liquid and a basic chemical substance, wherein the radioactive isotope can be produced using irradiation, and the boiling chamber (2) enables the liquid and the basic chemical substance to be irradiated and is provided with an irradiation window for evaporating the liquid into vapor. Comprising: The liquid target system (1) is configured such that the superheating of the liquid target (8) is controlled by the thermodynamics of the evaporation process. The liquid is water or heavy water, and the basic chemical substance is a salt having a positive enthalpy with respect to water. The liquid target system (1) further comprises: - A condensation region (3) disposed above the boiling chamber (2), and the condensation region (3) has a wall for condensing the vapor into a liquid condensate. Further comprising: The liquid target system (1) in which the liquid condensate can be systematically returned or provided to the boiling chamber (2).

2. The liquid target system (1) according to claim 1, wherein the evaporated water is stored as steam or as a liquid.

3. The liquid target system (1) further comprises: - At least one condensate collection region (4) for collecting the liquid condensate, and the at least one condensate collection region (4) is disposed outside the boiling chamber (2). The liquid target system (1) according to claim 1.

4. The liquid target system (1) according to claim 3, wherein the at least one condensate collection region (4) and the boiling chamber (2) are interconnected so as to function as a communicating vessel.

5. The liquid target system (1) according to claim 3, wherein the at least one condensate collection region (4) is disposed on the wall for condensing the vapor and is provided with a dripping mechanism for systematically returning the condensate to the boiling chamber.

6. The boiling chamber (2), the condensation region (3) and the at least one condensate collection region (4) form a system having a cylindrical design and / or The liquid target system (1) according to any one of claims 3 to 5, further comprising an adjustment fluid bath and / or an adjustment fluid circulation secondary system (32) for insulating or controlling the temperature of the condensation region (3).

7. The liquid target system (1) according to claim 6, wherein the outer walls of the boiling chamber (2), the condensation region (3) and the at least one condensate collection region (4) are at least partially surrounded by a coolant fluid bath and / or a coolant fluid circulation secondary system (32).

8. The liquid target system (1) further comprises an irradiation beam generator (25) configured to irradiate the liquid and the basic chemical substance, and / or The liquid target system (1) according to any one of claims 1 to 7, further comprising a pressurizing unit for pressurizing the boiling chamber to control the bubble size and boiling temperature of the liquid.

9. The liquid target system (1) according to claim 8, further comprising a pressure sensor for measuring the pressure in the boiling chamber (2).

10. The basic chemical is Ra(NO ３ ) ２ The liquid target system (1) according to any one of claims 1 to 9, wherein the liquid target is either or a combination of:

11. The liquid target system (1) according to any one of claims 1 to 10, adapted to produce Sc-47, Cu-67, Cs-131, Tb-155, or Ac-225, preferably Ac-225.

12. The liquid target system (1) according to any one of claims 1 to 11, used for producing radioisotopes.

13. A method for producing a radioisotope, the method comprising: irradiating a liquid target (8) containing a liquid and a basic chemical substance, wherein the radioisotope can be produced using irradiation, and evaporating the liquid into vapor; comprising the thermodynamics of the evaporation process being used to control the superheat of the liquid target (8); wherein the liquid is water or heavy water, and the basic chemical substance is a salt having a positive enthalpy with respect to water; the method further comprising condensing the vapor into a liquid condensate and systematically returning the liquid condensate or providing it to the liquid target (8).

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