Liquid target system

Abstract

A liquid target system (1) for producing radioactive isotopes, the liquid target system (1) comprising a boiling chamber (2) for containing a liquid and a base chemical by which a radioactive isotope can be produced by radiation, the boiling chamber (2) comprising a radiation window for effecting radiation on the liquid and the base chemical, causing the liquid to evaporate into vapor, wherein the liquid target system is configured such that the superheating of the liquid target (8) is controlled by the thermodynamics of the evaporation process, wherein the liquid is water or heavy water, and the base chemical is a salt having a positive enthalpy with respect to water.

Description

Technical Field

[0001] The present invention relates to the field of radioactive isotopes. More specifically, the present invention relates to liquid target systems for producing radioactive isotopes, their use, and corresponding methods. Background Art

[0002] Generally speaking, in order to produce radioactive isotopes, due to their high production rates in existing technology systems (for solid targets, a high density of parent nuclides), radioactive isotopes can be easily achieved thereby. In fact, the disadvantage of using liquid targets is that at room temperature, most parent nuclide compounds have limited solubility in water (which is usually used as a liquid solvent). For example, salts of Ra-226 have limited solubility in water (which can be used as a basic chemical to provide the parent nuclide for the production of the radioactive isotope Ra-225 that can decay into the radioactive isotope Ac-225). For instance, at 20 °C, the solubility of the radium nitrate salt Ra(NO3)2 is 13.9 g per 100 g of H2O.

[0003] However, one advantage of using liquid targets instead of solid targets is that in the chemical process of separating the radioactive isotope from the target, fewer (or no) liquid-solid and solid-liquid phase transitions are required. This chemical process step usually has a large (uncontrolled) risk of radioactive isotope loss and the generation of radioactive waste. For liquid targets, such phase transitions are not required, which is a significant advantage for such targets.

[0004] In addition, the potential disadvantage of the low concentration of parent nuclides in liquid targets must be properly considered. For example, consider the production of Ra-225 from Ra-226 via a photonuclear reaction. The production of Ra-225 as a function of time may 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 generate the high-energy bremsstrahlung photons required for the photonuclear reaction. The more high-energy photons are generated and the more Ra-226 is directly in front of the photon beam, the more Ra-225 will be formed. However, assuming an electron-bremsstrahlung photon conversion ratio of about 50%, about half of the electron energy will still be deposited in the converter. The very high energy deposition in the associated small-volume converter will easily limit the production capacity, thus reducing the yield of high-energy bremsstrahlung photons.

[0005] One solution to this is to have multiple converter material sheets separated by a cooling device and, in addition, rasterize the electron beam over a larger surface area of the converter. However, the larger surface area will inevitably have a negative impact on the production rate. The result of the larger converter surface area is that the Ra should be distributed over the entire surface area where high-energy gamma is present, while the highest yield is obtained by placing the Ra as close as possible to the converter. This can be regarded as a defect of any type of solid target because when the current density of the converter is the limiting factor (e.g., 0.125 - 0.25 mA / cm 2 ), and when an increase in the surface-volume ratio is required, the achievable high density (e.g., 3 - 5 g / cc) cannot be optimally utilized.

[0006] The isotope production system described in US2014 / 0362964 A1 is configured to irradiate a starting liquid with a particle beam to produce a radioactive isotope and convert a portion of the starting liquid into vapor.

[0007] Therefore, there are some defects associated with solid targets. However, the efficiency and yield of liquid targets are generally very low, so in the prior art, the focus remains on solid targets. Therefore, 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] The object of the present invention is to provide a good liquid target system. Another object of the present invention is to provide a good method for producing radioactive isotopes.

[0009] The above objects are achieved by the method and device according to the present invention.

[0010] The advantages of the embodiments of the present invention are that the yield and production of radioactive isotopes can be comparable to those of solid targets. Another advantage of the embodiments of the present invention is that the amount of parent nuclide required to obtain a certain amount of radioactive isotope is limited. Another advantage of the embodiments of the present invention is that the provided liquid target can produce radioactive isotopes with low generation of radioactive waste.

[0011] The advantages of the embodiments of the present invention are that the liquid target system can be continuously and efficiently cooled, thus preventing overheating of the liquid target. Another advantage of the embodiments of the present invention is that the liquid target can dissipate heat in a steady-state, continuous and reliable manner.

[0012] Advantages of embodiments of the present invention are that the liquid target can have a large overall volume, so that the adverse effects expected from losses due to, for example, hydrogen formation or uncondensed water may be limited. Another advantage of embodiments of the present invention is that the liquid target system can be operated safely. Another advantage of embodiments of the present invention is that the operation of the liquid target can be monitored by, for example, precisely tracking the temperature and / or pressure, which is usually difficult for solid targets.

[0013] In a first aspect, the present invention relates to a liquid target system for producing radioactive isotopes. The liquid target system includes a boiling chamber for containing a liquid and basic chemicals, whereby radioactive isotopes can be produced by radiation. The boiling chamber includes a radiation window for enabling radiation of the liquid and basic chemicals, causing the liquid to evaporate into vapor. The liquid target system is configured such that the overheating of the liquid target is controlled by the thermodynamics of the evaporation process.

[0014] In the case of embodiments of the present invention referring to the radiation window, reference is made to such a region in the wall of the boiling chamber that allows the radiation required for radiating the basic chemicals and thereby producing radioactive isotopes to enter the boiling chamber. The type of radiation window used can depend on the type of radiation. For example, in the case of using gamma radiation, the wall can be transparent to the radiation in any way. In an embodiment, the liquid target system configured to control the overheating of the liquid target by the thermodynamics of the evaporation process can include: the liquid target system is configured to use the evaporation of the liquid to prevent the overheating, preferably to control the temperature of the liquid target. The overheating of the liquid target may cause substantially all of the liquid in the liquid target to evaporate, so that the basic chemicals are boiled dry.

[0015] Advantages of embodiments of the present invention are that, since the overheating of the liquid target can be prevented, the liquid target system can avoid releasing non-condensable gases from the chemical material, can avoid sintering of the chemical material and / or can avoid forming insoluble chemical materials. The overheating may occur as a result of a large amount of radiation energy deposited in the liquid target. Specifically, so-called pair production reactions contribute to the heating of the liquid target. In pair production reactions, in the presence of high-Z nuclides (e.g., the parent nuclide Ra-226), high-energy photons are converted into electrons and positrons with residual kinetic energy. As the charged particles (i.e., electrons and positrons) slow down (and in the case of positrons, annihilation occurs), they release their kinetic energy inside the liquid target, which is converted into heat.

[0016] Advantages of embodiments of the present invention are that a cooling circuit for a liquid target system that does not require pump control (wherein a liquid and a base chemical are pumped in the cooling circuit) can be dispensed with. Another advantage of embodiments of the present invention is that a heat exchanger that requires a large contact area with the liquid target can be avoided, thereby limiting the amount of liquid target required.

[0017] Advantages of embodiments of the present invention are that the system achieves up - concentration during operation. More specifically, although the initial concentration of the base chemical for producing a radioisotope in a liquid at an initial temperature may be limited due to solubility in a solvent (e.g., water) (and a higher concentration at this initial temperature would cause precipitation), embodiments of the present invention have the advantage that the concentration increases during heating of the liquid target, in line with the increased solubility of the base chemical in the solvent (e.g., water). The latter is established by evaporation of the solvent, while the base chemical remains in the irradiated area.

[0018] In an embodiment, the water that has evaporated can be stored in the system as vapor or liquid.

[0019] In an embodiment, the liquid target system further includes a condensation region located above the boiling chamber, the condensation region having a wall for condensing liquid vapor into liquid condensate, wherein the liquid condensate can be systematically returned or supplied 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 to the boiling chamber, for example, through a direct fluid connection between the condensation region and the boiling chamber, or by allowing the liquid condensate to drip (e.g., by gravity) from the condensation region into the boiling chamber.

[0020] Thus, in an embodiment, the at least one condensation collection region can be placed at the wall such that vapor condenses and a dripping mechanism can be provided for systematically returning the condensate to the boiling chamber.

[0021] In a preferred embodiment, the liquid target system further includes at least one condensate collection area for collecting liquid condensate, and the at least one condensate collection area is located outside the boiling chamber (i.e., the at least one condensate collection area and the boiling chamber are separated from each other), wherein the at least one condensate collection area is interconnected with the boiling chamber so as to act as a communicating vessel. In an embodiment, the at least one condensate collection area and the boiling chamber are configured such that the ratio of the volume of the liquid condensate (i.e., liquid) present in the at least one condensate collection area 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 the at least one condensate collection area 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 scale of the system can be selected to obtain a positive concentration factor of 2. The advantage of these embodiments is that since the base chemical can be concentrated in the boiling chamber and may not be present in the at least one condensate collection area, during the operation of the liquid target system, the base chemical can be positively concentrated in the boiling chamber to reach at least 50%, preferably at least 100%, more preferably at least 200% higher than the initial concentration of the base chemical when it is present in all the liquid (including any liquid present in the at least one condensate collection area).

[0022] In an embodiment, the volume of the boiling chamber is 5 mL to 500 mL. In an embodiment, the total volume of the at least one condensate collection area is 5 mL to 500 mL.

[0023] In an embodiment, the interconnection between the boiling chamber and the at least one condensate collection area includes a gap or a pipe. In an embodiment, the inlet of the interconnection for allowing liquid to enter the boiling chamber is located near the bottom of the boiling chamber, such as in the wall or in the bottom. Preferably, the height in the boiling chamber where the inlet is located is lower than 25% of the height of the boiling chamber, preferably lower 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 in the interconnection is at most 10%, preferably at most 5%, more preferably at most 2% of at least one (e.g., both) of the longitudinal or horizontal cross-sectional areas of the boiling chamber.

[0024] For example (the embodiment is not limited thereto), examples are discussed below. For a target receiving, for example, 1200 W, 50% of the energy is effectively utilized to convert the liquid into vapor, and the single opening is 0.2 cm 2(corresponding to a radius of approximately 2.5 mm in the circular opening), the liquid will move at a speed of 1.33 cm / s. The smaller the opening, the greater the speed. By using small cross-sections in connection with each other, the backflow from the radiation chamber towards the condensation chamber is avoided. By choosing a cross-section small enough, the liquid flows uniformly in one direction at a high enough speed. The length and / or diameter of the connection can be designed to create a pressure drop that will create a liquid level difference. In some embodiments, it is designed such that the condensate is stored above the radiation level of the radiation chamber. This ensures that when radiation occurs and thus the top boils, most of the condensate will return to the radiation chamber. In this way, chemical dilution and precipitation when the solution cools are avoided.

[0025] In an alternative example, the position of the inlet can be at the top of the system and operate via dripping.

[0026] The advantages of these embodiments are that, through the boiling and condensation processes of the liquid, heat dissipation in the liquid target system is ensured (and thus overheating is prevented). The condensation area can be cooled by a secondary system containing a cooling fluid (which does not contain corrosive materials). In an embodiment, the liquid target system further includes a coolant fluid bath and / or a coolant fluid circulation secondary system for cooling the condensation area. In a preferred embodiment, the condensation area and the at least one condensate collection area are at least partially surrounded by the coolant fluid circulation secondary system.

[0027] The advantages of the embodiments of the present invention are that the liquid target system can automatically act as a concentrator, so that the concentration of the base chemical in the irradiated volume can be increased during the heating process caused by radiation (and subsequent evaporation of the liquid). In addition, since the solubility of the base chemical in the liquid generally increases with temperature, the liquid target can contain a high concentration of the base chemical without precipitation, enabling the efficient production of radioisotopes. In fact, since the solubility of the base chemical material for generating radioisotopes is low at room temperature, it can be advantageous to increase the concentration during the heating process caused by radiation, taking advantage of the higher solubility of the base chemical material in the liquid at higher temperatures.

[0028] In an embodiment, the system further includes a radiation beam generator configured to irradiate the liquid and the base chemical. Here, the radiation beam generator is generally located outside the boiling chamber and is configured to irradiate the liquid and the base chemical through a radiation window. In an embodiment, the radiation beam generator is selected from: an electron beam gun; a gamma beam gun; a proton beam gun; and a neutron beam gun. In embodiments including an electron beam gun or a proton beam gun, the radiation beam generator may further include a converter for converting a charged particle beam (i.e., an electron beam or a proton beam) into high-energy bremsstrahlung photons forming a radiation beam.

[0029] In embodiments that include the at least one condensate collection region, the radiation beam generator can be configured such that the radiation beam propagates from a radiation beam generator located outside the boiling chamber through a radiation 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 no liquid in the at least one condensate collection region boils (thereby converting the liquid in the at least one condensate collection region into vapor). This can result in a positive concentration of the base chemical in the at least one condensate collection region, which can lead to a decrease in the concentration of the base chemical in the boiling chamber. Another advantage of these embodiments is that there can be no attenuation of the radiation beam due to absorption of liquid condensate in the at least one condensate collection region.

[0030] In embodiments, the liquid target system includes a pressurization unit for pressurizing the system to control the bubble size and boiling temperature of the liquid. In these embodiments, the system can also include a pressure sensor to measure the pressure of the boiling chamber or the system.

[0031] 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 a cylindrical design is typically limited, which can render the system pressure-resistant. In embodiments, the boiling chamber includes an inlet and an outlet for generating a flow of an inert gas (e.g., argon, helium, or nitrogen, preferably helium) through the boiling chamber. The loss of non-condensable water (humidity) leaving the liquid target system at the same flow rate as the inert gas can be compensated by exposing the inert gas to water (humidity) before addition to the target system. In this way, the water mass balance can be kept constant (with the exception of hydrogen leaving the system).

[0032] Advantages of these embodiments are that good pressure control can be achieved. Another advantage is that the inert gas flow can be used to remove any gaseous material formed in the boiling chamber outside the boiling chamber for collection of the gaseous material (e.g., Rn when the parent nuclide contains Ra-226). In embodiments, the boiling chamber includes an inlet for introducing and / or removing the liquid target (i.e., the liquid and the base chemical) from the boiling chamber.

[0033] In an embodiment, the base chemical includes, or consists of, a salt of a radionuclide that includes a radionuclide for forming a radioisotope when exposed to radiation. The radionuclide is typically a cation, and the salt also includes an anion. In an embodiment, the liquid is water or heavy water, and the base chemical is a salt that has a positive enthalpy of solution in water. In an embodiment, the base chemical is any one or combination of Ra(NO3)2, RaCl2, and Ba(NO3)2. It is to be understood that although the embodiments of the present invention generally refer to the production of Ac-225, the embodiments are not limited thereto and liquid target systems for the production of other isotopes are also contemplated. An 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 the following: a Ca salt, which can be used for Sc-47 production; a Zn salt, which can be used for Cu-67 production; a Ba salt, which can be used for Cs-131 production; and a Dy salt, which can be used for Tb-155 production. In an embodiment, the liquid target system is suitable for the production of Sc-47, Cu-67, Cs-131, Tb-155, Ra-225, or Ac-225, preferably Ac-225.

[0034] Any feature of any embodiment of the first aspect can independently correspond to be described for any embodiment of any other aspect of the present invention.

[0035] In a second aspect, the present invention relates to a method for producing a radioisotope. The method includes irradiating a liquid target that includes a liquid and a base chemical (whereby a radioisotope can be produced by radiation), causing the liquid to evaporate into a vapor. Here, the thermodynamics of the evaporation process is used to control the overheating of the liquid target.

[0036] In an embodiment, the method can be performed using the liquid target system according to the embodiment of the first aspect of the present invention.

[0037] In an embodiment, the method includes, after the irradiation, a step of collecting the radioisotope from the liquid target.

[0038] In an embodiment, the irradiation is performed using, for example, an incident power on the liquid target of 1.5 kW (for example, a power of 0.5 kW to 10 kW, for example, 0.5 kW to 5 kW, for example, 0.5 kW to 3 kW). During the irradiation, the irradiation step is performed at a pressure from 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.

[0039] In a preferred embodiment, at least during part of said irradiation, the concentration of the base chemical in the liquid target (e.g., at the irradiation location) is higher than the solubility of the base chemical in the liquid at a temperature of 25 °C and a pressure of 1 atm (i.e., the maximum concentration before precipitation occurs), preferably at least 20% higher, more preferably at least 50% higher, even more preferably at least 100% higher, and still more preferably at least 200% higher. Generally speaking, the maximum concentration that can be achieved is equal to the solubility of the base chemical, because any further base chemical will not dissolve in the liquid, e.g., precipitation occurs from the liquid.

[0040] Any feature of any embodiment of the second aspect may independently correspond to any embodiment described for any other aspect of the present invention.

[0041] 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 producing radioisotopes.

[0042] Any feature of any embodiment of the third aspect may independently correspond to any embodiment described for any other aspect of the present invention.

[0043] The specific and preferred aspects of the present invention are listed in the appended independent claims and dependent claims. The features in the dependent claims may be appropriately combined with the features in the independent claims and the features in other dependent claims, not limited only to the situations explicitly described in the claims.

[0044] Although there have always been improvements, changes, and developments of devices in the art, it is believed that the concept of the present invention represents a sufficiently new and novel improvement, including changing existing practices, resulting in the provision of a more effective, stable, and reliable device with such properties.

[0045] Through the following detailed description, in conjunction with the drawings that illustrate the principles of the present invention by way of examples, the above and other characteristics, features, and advantages of the present invention will be obvious. The description provided is only for illustration and does not limit the scope of the present invention. The reference figures cited below refer to the drawings. Brief Description of the Drawings

[0046] Figure 1A is at least a partially exploded schematic view of a liquid target system according to an embodiment of the present invention.

[0047] Figure 1B is according to an embodiment of the present invention Figure 1A at least a partially longitudinal cross-sectional schematic view of the liquid target system.

[0048] Figure 2It is a graph of the solubility (in grams of salt per 100 mL of H2O) of Ba(NO3)2 and Ra(NO3)2 dependent on temperature (in degrees Celsius).

[0049] Figure 3 It is a schematic diagram of a liquid target system according to an embodiment of the present invention.

[0050] Figure 4 It is a schematic longitudinal cross-sectional view of a liquid target system according to an embodiment of the present invention.

[0051] Figure 5 It is after heating the liquid target by irradiating the liquid target Figure 4 schematic longitudinal cross-sectional view of the liquid target system.

[0052] In different figures, the same reference numerals denote the same or similar elements. Detailed Embodiments

[0053] The present invention will be described with reference to specific embodiments and certain drawings, but the present invention is not limited thereto and is only limited by the claims. The described drawings are illustrative and non-limiting. In the drawings, for illustrative purposes, the sizes of some elements may be exaggerated and not drawn to scale. The sizes and relative sizes do not correspond to the actual reduction of the present invention when put into practice.

[0054] Furthermore, the terms "first", "second", "third", etc. in the specification and claims are used to distinguish similar elements and are not necessarily used to describe a hierarchical order in time or space or any other order. It should be understood that, where appropriate, such terms may be used interchangeably, and the embodiments of the present invention described herein can be operated in an order other than the order described or illustrated herein.

[0055] In addition, in the specification and claims, terms such as top, bottom, above, and below are used for descriptive purposes and are not necessarily used to describe relative position. It should be understood that, where appropriate, such terms may be used interchangeably, and the embodiments of the present invention described herein can be operated in a direction other than the direction described or illustrated herein.

[0056] It should be noted that the term "comprising" used in the claims should not be construed as being limited to the parts listed thereafter, and it does not exclude other elements or steps. Therefore, it should be understood as indicating the presence of the recited features, integers, steps or components, but this does not exclude the presence or addition of one or more other features, integers, steps or components or combinations thereof. Thus, the term "comprising" covers both the case where only the stated features are present and the case where these features and one or more other features are present. Therefore, in the context of the present invention, the term "comprising" also includes an embodiment where no other components are present. Thus, the scope of the expression "a device comprising devices A and B" should not be construed as being limited to a device consisting only of components A and B. It means that, for the purposes of the present invention, the only relevant components of the device are A and B.

[0057] Similarly, it should be noted that the term "connected" should not be construed as being strictly limited to a direct connection only. The terms "connected" and "coupled" may be used, as well as their derivatives. It should be understood that these terms are not used as synonyms for each other. Thus, the scope of the expression "device A connected 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. It means that there is a path between the output of A and the input of B, and the path may be a path including other devices or components. "Connected" may mean that two or more elements have direct physical or electrical contact, or that two or more elements do not have direct contact with each other but still operate together or interact with each other.

[0058] The phrase "in one embodiment" or "in an embodiment" as used in the specification means that the specific features, structures, or characteristics described in connection with the embodiment are included in at least one embodiment of the present invention. Thus, the phrase "in one embodiment" or "in an embodiment" that appears throughout the specification does not necessarily all refer to the same embodiment, but may all refer to the same embodiment. In addition, the specific features, structures, or characteristics may be combined in any suitable manner in one or more embodiments, which will be apparent to those of ordinary skill in the art.

[0059] Similarly, it should be understood that in the description of the exemplary embodiments of the present invention, for the purpose of simplifying the description and facilitating the understanding of one or more aspects of the various inventive aspects, the various features of the present invention are sometimes combined in a single embodiment, drawing, or description thereof. However, this method of presentation should not be construed as reflecting an intention that the present invention requires more features than are expressly recited in each claim. On the contrary, as reflected in the appended claims, the inventive aspects may include fewer features than all of the features of a single foregoing disclosed embodiment. Thus, the claims that precede the detailed description are expressly incorporated into this detailed description, where each claim stands alone as a separate embodiment of the present invention.

[0060] In addition, those skilled in the art should understand that although some of the embodiments described herein include some features included in other embodiments but not others, combinations of features of different embodiments are intended to be within the scope of the present invention and form different embodiments. For example, in the following claims, any of the embodiments claimed can be used in any combination.

[0061] In addition, some embodiments are described herein as methods or combinations of method elements that can be implemented by a processor of a computer system or other means for implementing the functions. Accordingly, a processor having the necessary instructions for implementing such a method or method elements forms a means for implementing the method or method elements. In addition, the elements of the device embodiments described herein are examples of means for implementing the functions performed by the elements for the purpose of implementing the present invention.

[0062] Numerous specific details are set forth in the description herein. It should be understood, however, that the practice of embodiments of the present invention may not employ these specific details. In other instances, well-known methods, structures, and techniques have not been described in detail so as not to obscure the description of the present invention.

[0063] The present invention will now be described by way of a detailed description of several embodiments of the present invention. It is obvious that other embodiments of the present invention can be constructed based on the knowledge of those skilled in the art without departing from the technical teachings of the present invention, and the present invention is only limited by the terms of the appended claims.

[0064] In a first aspect, the present invention relates to a liquid target system for producing radioactive isotopes. The liquid target system includes a boiling chamber for containing a liquid and basic chemicals, whereby radioactive isotopes can be produced by radiation. The boiling chamber includes a radiation window for irradiating the liquid and basic chemicals, causing the liquid to evaporate into vapor. The liquid target system is configured such that the overheating of the liquid target is controlled by the thermodynamics of the evaporation / condensation process.

[0065] In a second aspect, the present invention relates to a method for producing radioactive isotopes. The method includes irradiating a liquid target containing a liquid and basic chemicals (whereby radioactive isotopes can be produced by radiation), causing the liquid to evaporate into vapor. Here, the thermodynamics of the evaporation process is used to control the overheating of the liquid target.

[0066] In a third aspect, the present invention relates to using the liquid target system according to the embodiments of the first aspect to produce radioactive isotopes.

[0067] Reference Figure 1A is a schematic, at least partially exploded view of a liquid target system 10 according to an embodiment of the present invention. Also refer to Figure 1B, which is a schematic longitudinal cross-sectional view of at least a portion of the liquid target system 10. In this example, the liquid target system for producing radioactive isotopes includes: a boiling chamber 2 for containing a liquid target 8 (which is composed of a liquid and basic chemicals, and thus radioactive isotopes can be produced by radiation). A radiation window 23 is included in the wall of the boiling chamber 2, which is in this example a part of the wall of the boiling chamber 2, and the radiation can propagate through the radiation window 23. In this example, the liquid contained in the liquid target 8 in the boiling chamber 2 is water, and the basic chemical 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. Thus, in this example, the liquid target 8 is composed of a liquid and a salt containing Ra-226.

[0068] The liquid target 8 is continuously irradiated with a high-energy photon beam passing through the radiation window 23. As a result, the liquid target 8 will boil under the continuous irradiation, thereby converting the liquid into vapor (i.e., water vapor, white arrows). Subsequently, the water vapor condenses in the condensation region located above the boiling chamber 2, thereby converting the vapor into a liquid condensate. The condensation region 3 can be cooled at least by a water coolant fluid bath and / or a forced coolant fluid circulation secondary system 32, but it is also possible to cool the condensate collection region 4 and also possibly the boiling chamber 2.

[0069] In this example, the liquid target system further includes two condensate collection regions 4 different from the boiling chamber 2, and in this example, they are separated from each other by a partition wall 21. These two condensate collection regions 4 are located on opposite sides of the boiling chamber 2, separated by the partition wall 21 each time. The liquid target system is configured such that the condensate formed in the condensation region 3 moves (for example, drips) into the condensate collection region 4 (arrows filled with horizontal stripes). In this example, this is achieved 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 on the wall) into the condensate collection region 4. In addition, in this example, the liquid target system includes a condensate guiding element 5, which guides any condensate away from the boiling chamber to the condensate collection region 4 (which can also be referred to as the condensate collection chamber).

[0070] The condensate collection region 4 is fluidly connected to the boiling chamber 2, for example, via an opening 24 in the partition wall 21. For example, in this example, at least a portion of the partition wall 21 can be separated from the bottom of the boiling chamber 2 via a gap 24, whereby the liquid can move between the condensate collection region 4 and the boiling chamber 2. Alternatively, for example, a pipe can be used to perform the fluid connection. Thus, the liquid condensate 41 collected in the condensate collection region 4 can flow into the boiling chamber 2 (black arrows).

[0071] Thus, in this example, the condensate collection region 4 and the boiling chamber 2 can be considered to function as three communicating vessels, where the liquid target 8 in the boiling chamber 2 boils while being directly in the high-energy photon beam, and the condensate is collected in the condensate collection region 4, which does not boil 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 Ra-226 in a significant amount to absorb radiation, since there is a continuous and effective liquid flow (black arrow) from the condensate collection region 4 through the gap into the boiling chamber 2, which compensates for the flow of vapor (white arrow) and the flow of condensate (arrow with horizontal stripes) through the condensation region 3. At steady state, the rate of each of these three flows can be substantially the same. The condensate 41 would be at a significantly lower radiation level. Additionally, since there is no Ra, the lower heat absorption results in the condensate not boiling. In other words, since the condensate collection region 4 and the boiling chamber 2 are substantially communicating vessels, the continuous loss of the water substance in the boiling chamber 2 due to the boiling is compensated by the continuous water flow from the condensate collection region 4 (entering the boiling chamber 2 through the holes at the bottom of the target). The size of the gap (or, alternatively, the diameter of the pipe) is preferably optimized in such a way that there is a continuous flow of condensate (i.e., the liquid) towards the boiling chamber 2, so that substantially no Ra-226 moves in the opposite direction (i.e., from the boiling chamber 2 towards and into the condensate collection region 4). Thus, the opening should not be too narrow nor too large. Preferably, the liquid flow velocity towards the boiling chamber through the opening is from 0.1 cm / s to 20 cm / s, preferably from 0.5 cm / s to 5 cm / s, such as 1 cm / s. Preferably, the fluid flow velocity substantially entirely originates from the liquid loss in the boiling chamber 2 due to boiling caused by radiation and the liquid increase in the condensate collection region 4 due to subsequent condensate collection therein. Due to the continuous reflux of the condensate (i.e., the liquid reaching the liquid target in the boiling chamber 2), the liquid target can not be boiled dry and overheating is prevented.

[0072] In this example, irradiating the liquid target 8 produces Ac-225 via the photonuclear reaction Ra-226(γ,n)Ra-225(β-)Ac-225. Preferably, any Ac-225 formed can be separated from the liquid target 8. In this example, the liquid target system includes an opening 22 in the bottom of the boiling chamber 2 that functions as an inlet and / or outlet for the liquid target 8 (e.g., before and after irradiation, but preferably not during irradiation). Thereby, the liquid target 8 can be moved through the opening 22 after irradiation to, for example, a hot cell facility for chemical separation and purification of Ac-225. After the separation, the liquid target can be moved back into the boiling chamber 2 through the opening 22. To avoid crystallization and losses in any fluid path (e.g., the piping connecting the boiling chamber 2 and the hot cell facility), it is preferred to immediately use a certain cleaning volume of liquid (e.g., dilute nitric acid) after transferring the liquid target 8 through the fluid path. This may further dilute the base chemicals in the liquid target 8 and thereby reduce the yield due to the excess volume introduced by the cleaning volume. The excess volume can 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, by appropriate design of the target (the volume ratio of the boiling chamber 2 to the condensate chamber 4), this excess volume may not be a problem. In fact, the volume ratio between the liquid in the boiling chamber 2 (i.e., those irradiated by the beam) and the liquid in the condensate collection chamber 4 can be optimized, and the Ra concentration in the boiling chamber can be increased. For example, in the case of a 1 / 1 volume ratio, the Ra concentration in the beam can be doubled during operation (i.e., during irradiation of the liquid target 8) compared to a design without the condensate collection chamber 4. As a result, the yield is also doubled. This positive concentration is advantageous in that a small amount of the parent nuclide (e.g., Ra-226) may be required for the gamma production path to obtain a high isotopic yield of Ra-225. For the maximum solubility of radium, this increase in concentration during irradiation may not be a problem because the liquid target can be strongly heated, e.g., heated to 100 °C (the boiling temperature of water at standard pressure) or even above 100 °C (when the pressure is above standard pressure), thereby further increasing the solubility.

[0073] In this example, at least a portion of the liquid target system 10 (i.e., the boiling chamber 2, the condensation region 3, and the condensate collection region 4) forms a cylindrical shape, thereby limiting the amount of welding and increasing the strength of this portion of the liquid target system that can operate at elevated pressures. The higher pressure can be used to increase the boiling point of water and can affect the thermodynamics of the evaporation process. In fact, when operating this liquid target 8 in the beam, any heat generated should be removed in a safe and reliable steady-state operation manner. The boiling liquid target 8 is preferred because this is an efficient and convenient way to remove excess heat from the solution (i.e., the liquid target 8). Due to the small size of the liquid target 8, pressurization may be highly preferred to control the bubble size in the boiling liquid target 8. The higher the pressure, the smaller the bubbles can be and the better the boiling performance may be. The pressure and the steady-state temperature can be controlled to optimize the hydrothermal performance of the liquid target 8.

[0074] (Ra-226)(NO3)2 is well-suited for embodiments of the present invention because it has a relatively high solubility in water compared to other Ra-226 salts. The compound is soluble at 20 °C and standard pressure (13.6 g / 100 g water) (see Erbacher, O's -Bestimmungen einiger Radiumsaltze; Berichte der deutschen chemischen Gesellschaft (Solubility determinations of some radium salts; Reports of the German Chemical Society), 1930; Volume 63, pages 141-156). However, other compounds (e.g., (Ra-226)Cl2) can also be used as an alternative. The solubility of (Ra-226)(NO3)2 increases significantly at higher temperatures. To approximately obtain the solubility of (Ra-226)(NO3)2 at elevated temperatures, the solubility of barium nitrate can be selected as a good approximation because of the very similar behavior of the alkaline earth metals Ra and Ba or Group 2 atoms (although the solubility of Ba(NO3)2 is slightly lower than that of Ra(NO3)2). Refer to Figure 2 , which is a graph of solubility (in grams of salt per 100 mL of H2O) as a function of temperature (in degrees Celsius). The data shown (from

[0075] http: / / periodic-table-of-elements.org / SOLUBILITY / barium_nitrate): Ba(NO3)2, the dark points are connected by dashed lines, over the temperature range from 0 °C to 100 °C, while for Ra(NO3)2, only data at 20 °C are available. It can be observed that at 100 °C, the solubility of Ba(NO3)2 is increased by a factor of 3 compared to its solubility at 20 °C. Thus, it is expected that for Ra(NO3)2, the solubility at 100 °C is also approximately 3 times higher. Even higher solubilities are expected at temperatures above 100 °C. In an embodiment, the boiling point of water can be increased first by the presence of salts dissolved therein and second by an increase in pressure.

[0076] The pressure dependence of Ra(NO3)2 can also be obtained by comparison with Ba(NO3)2. When the pressure is increased from standard pressure up to 200 MPa, the aqueous solubility of Ba(NO3)2 increases from 0.394 to 0.841 ± 0.005 mol / kg (from 13.79 to 29.435 ± 0.175 g / 100 g H2O). (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). Thus, it is expected that an increase in pressure in the boiling chamber is unlikely to have a negative impact (decrease in solubility) on the solubility of Ra(NO3)2 in the water of the liquid target.

[0077] Now for a quantitative example. Refer back to Figure 1A and 1B , as an example, consider having 25 cm 3a liquid target 8 of volume, and an excessive solubility at room temperature (13.9 g / 100 g water) is not preferred. In fact, the liquid target 8 should be pumped into and out of the boiling chamber 2, i.e., between the boiling chamber 2 and the hot cell facility (which is typically approximately at room temperature). Thus, a higher concentration may cause precipitation in the fluid path connecting the boiling chamber 2 and the hot cell facility. Thereby, when at room temperature, the liquid target may contain only about 2 grams of Ra-226. However, the goal is to have 6 grams of the base chemical in the boiling chamber 2, thereby increasing the efficiency and yield of the liquid target system. Thereby, as an alternative, it may be considered to dissolve 6 grams of the Ra-226 target in 125 mL, and the volume ratio between the liquid in the boiling chamber 2 and the condensate collection chamber 4 is equal to 1 / 4. Thereby, initially, there is 100 mL of the liquid target in the condensate collection chamber 4, and 25 mL in the boiling chamber 2. At the start of the radiation, the Ra-226 is evenly distributed in the compartments. When the boiling chamber 2 starts to boil under the influence of the said radiation, due to the mechanism explained above, the Ra-226 from the condensate collection chamber 4 will flow towards the boiling chamber 2 and remain there during the radiation event. Thereby, over the event time, the Ra-226 in the condensate collection chamber 4 will be consumed, so that the condensate collection chamber 2 only contains liquid (i.e., the condensate 41). In addition, containing 25 cm 3 The boiling chamber 2 of the liquid target contains all the remaining Ra-226 (i.e., 6 grams minus those that react to form Ra-225 or Ac-225). That is to say, in fact, only the boiling chamber 2 contains the liquid target 8. As the water is heated to 80 °C or 100 °C, the concentration of the base chemical in the liquid target 8 is still below the solubility limit of Ra(NO3)2.

[0078] In addition to the heating due to radiation, forced heating (not from radiation) of the boiling chamber 2 can also be carried out until a steady state is achieved. It is advantageous that the steady state (where the thermodynamics is continuous and predictable) can be achieved quickly. In addition, when cooling the liquid target 8 after the said radiation, slow cooling is preferably carried out to avoid any Ra(NO3)2 precipitation. One way to achieve this can be to immerse the cylinder or the target container (and thus at least the boiling chamber 2 and the condensate collection area 4) in a water bath operating at, for example, 70 - 80 °C. Alternatively, a purge gas causing forced mixing can be introduced, for example, through the opening 22, and exit through another opening 31 located above the boiling chamber 2.

[0079] First refer to Figure 3 , which is a schematic diagram of a liquid target system 1 according to an embodiment of the present invention, and may include Figure 1A and 1BAt least a portion of the liquid target system 10. The boiling chamber included in at least a portion of the liquid target system 10 can be irradiated by the radiation beam 26 from the radiation beam generator 25. In this example, the opening 22 in the bottom of the boiling chamber 2 can be connected to the buffer container 6 via the valve V3. The buffer container 6 is connected to the hot cell facility 61 via the valve V8. The buffer container 6 is further connected to the inlet for introducing demineralized water 62 via the valve V5. The inlet for introducing demineralized water 62 is further connected to the other opening 31 via the valve V7. In this example, compressed gas (e.g., N2 or He) can be introduced from the compressed gas source 63 (e.g., compressed gas cylinder) through the opening 22 (via the valve V4), the buffer container 6 and the valve V3 or through the other opening 31 through the valve V2. In addition, vacuum can be introduced from the vacuum source 64 (e.g., pump) through the opening (via the valve V6), the buffer container 6 and the valve V3 or alternatively through the other opening 31 through the valves V6, V4 and V2. The other opening 31 can be connected to the chimney 7 via a volume containing activated carbon 71 or any other system for capturing radioactive non-condensable gases.

[0080] In the initial state, all the valves V1-8 are closed. Subsequently, the buffer container can be filled with the liquid target by opening the valves V6 and V8, so that the vacuum sucks the liquid target from the hot cell facility 61.

[0081] Subsequently, by opening the valves V4, V3 and V1, the liquid target can be moved to the boiling chamber and the condensate collection area, an air flow (e.g., He or N2) can be introduced through the buffer container 6 via the boiling chamber in at least a portion of the liquid target system 10, and then through the activated carbon 71 and reach the chimney 7, so that the liquid target moves from the buffer container 6 to the boiling chamber. The fluid connection connecting the boiling chamber and the buffer container 6 can be flushed with the mechanical energy of the demineralized water from the inlet for introducing demineralized water 62. First, the buffer container 6 is filled with demineralized water by only opening the valve V5, then V5 is closed, the valve V4 is opened, and the valve V3 is opened. Alternatively, it can be flushed by opening the valve V7. This may result in additional liquid in the boiling chamber, but in the present invention, due to the potential positive concentration of the basic chemicals in the boiling chamber, this may not be a problem. In addition, in the next step, the excess liquid in the boiling chamber can be evaporated and removed from the boiling chamber by the air flow from the compressed gas source 63 through the boiling chamber and reaching the chimney 7, thereby reducing the liquid volume in the boiling chamber.

[0082] In the next step, valve V1 is opened, and the liquid target in the boiling chamber is boiled by using the low-power radiation beam 26 from the radiation beam generator 25. Then, radiation is carried out (with no valve open; or only valves V4 and V3, and V1 slightly open) so as to introduce compressed gas (e.g., Ar, He or N2) into at least a part of the liquid target system 10, and thus a preferred (e.g., high) pressure is obtained in at least a part of the liquid target system 10. The flow can be controlled by the flow controller 631 and the pressure regulator 632. The increase in pressure in the boiling chamber can enable the liquid in the boiling chamber to be at an increased temperature compared to the atmospheric pressure, which can improve the solubility of the base chemicals. In addition, for example, when the base chemical includes Ra-226, a small gas flow can be maintained to remove and collect any gas (e.g., Rn) formed in the boiling chamber. An advantage of the embodiments of the present invention is that the liquid target system is compatible with Rn collection.

[0083] After the photonuclear reaction in the boiling chamber, any radioactive isotopes formed in the boiling chamber can be collected. For this purpose, all valves can be closed, and then valves V2 and V3 can be opened so that the liquid target containing the radioactive isotope is moved from the boiling chamber to the buffer container 6 by means of an air flow. If possible, after that, the pipeline connecting the boiling chamber and the buffer container 6 can be rinsed with demineralized water by opening valve V7. Finally, by closing all valves and then opening valves V8 and V4, and subsequently briefly opening valve V5 to rinse with demineralized water, the buffer container 6 can be emptied into the hot cell facility 61.

[0084] Although in the above explanation, at least a part of the liquid target 10 is assumed to relate to Figure 1A and Figure 1B the example embodiments, at least a part of the liquid target 10 can be replaced by the embodiments of the subsequent examples or can include the features of both examples.

[0085] Reference Figure 4 , which is a schematic representative diagram of another example of a liquid target system according to an embodiment of the present invention. The boiling chamber 2 contains a liquid target 8, which includes a liquid and a base chemical that can produce radioactive isotopes. The radiation 26 incident on the liquid target 8 causes heating of the liquid target 8, so 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 the thermal insulation material 91, so that a high-temperature vapor can be achieved in the volume. Thus, a higher concentration of vapor in the volume can be achieved, realizing pressure accumulation. In other words, the volume 9 can include a large amount of gas-phase liquid (i.e., vapor). In the embodiment, the ratio of the volume of the gas vapor in the volume 9 to the volume of the liquid target 8 in the boiling chamber 9 is at least 2, preferably at least 5.

[0086] In other words, instead of the vapor formed by direct condensation, the volume above the boiling chamber can be used to store the evaporated solvent as vapor.

[0087] See Figure 5 . As a result of evaporation due to radiation and the formation of a large amount of vapor, the volume of the liquid target 8 decreases. Thereby, the concentration of the basic chemical therein increases, which can increase the efficiency and yield of the nuclear reaction (e.g., photonuclear reaction) of the basic chemical to form a radioisotope. In an embodiment, radiation is used to generate a pressure of up to 20 bar (e.g., up to 10 bar) in the volume 9. The upper limit of the pressure is generally limited by the pressure that the wall of the liquid target system can withstand. Using a high pressure can improve the solubility of the basic chemical in the liquid target 8 because this increases the boiling temperature, thereby enabling more liquid to evaporate without causing precipitation of the basic chemical from the liquid target 8. During the radiation of the liquid target 8, the concentration of the basic chemical in the liquid is preferably higher than the solubility of the basic chemical in the liquid at room temperature (e.g., in the absence of radiation). Thus, in this example, high radiation can result in a high yield due to both the high radiation and the positive concentration of the basic chemical in the liquid target 8. In addition, overheating can be prevented by seeking a balance between the radiation power and the power loss due to the evaporation of the liquid from the liquid target 8.

[0088] It should be noted that in the embodiments of the present invention, the operating conditions and additional measures can be selected to limit or prevent radiolysis, or reversed by the recombination of oxygen and hydrogen. Such measures are known in the art. https: / / link.springer.com / article / 10.1007 / BF02387473 gives an example of a technical solution.

[0089] It is to be understood that although the preferred embodiments, specific structures and configurations, and materials of the device of the present invention have been discussed herein, various changes or modifications can be made to the form and details without departing from the scope of the present invention. Steps can be added to or removed from the method without departing from the scope of the present invention.

Claims

1. A liquid target system (1) for producing radioactive isotopes, said liquid target system (1) comprising: - A boiling chamber (2) for containing a liquid and a base chemical by which radioactive isotopes can be produced by radiation, said boiling chamber (2) comprising a radiation window for effecting radiation on the liquid and the base chemical, causing the liquid to evaporate into vapor, wherein the liquid target system is configured such that the superheat of the liquid target (8) is controlled by the thermodynamics of the evaporation process, wherein the liquid is water or heavy water, characterized in that the base chemical is a salt having a positive enthalpy with respect to water. The liquid target system (1) further comprises: - A condensation region (3) located above the boiling chamber (2), said condensation region (3) having a wall for condensing the vapor into a liquid condensate. wherein the liquid condensate can be systematically returned to or supplied to the boiling chamber (2); and - At least one condensate collection region (4) for collecting the liquid condensate, said at least one condensate collection region (4) being located outside 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) according to claim 1, wherein, The at least one condensate collection region (4) and the boiling chamber (2) are interconnected to act as communicating vessels.

4. The liquid target system (1) according to claim 1, wherein, The at least one condensate collection region (4) is placed at a wall such that the vapor condenses and provides a dripping mechanism for systematically returning the condensate to the boiling chamber.

5. The liquid target system (1) according to any one of claims 1 to 4, wherein, 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 wherein the liquid target system (1) further comprises a regulating fluid bath and / or a regulating fluid circulation secondary system (32) for insulating or controlling the temperature of the condensation region (3).

6. The liquid target system (1) according to claim 5, wherein, The outer wall 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 regulating fluid bath and / or a regulating fluid circulation secondary system (32).

7. The liquid target system (1) according to any one of claims 1 to 4, the system further comprising a radiation beam generator (25) configured to radiate the liquid and the base chemical, and / or Among them, The system further comprises a pressurizing unit for pressurizing the boiling chamber to control the bubble size and the boiling temperature of the liquid.

8. The liquid target system (1) according to claim 7, wherein, The system (1) further comprises a pressure sensor for measuring the pressure in the boiling chamber (2).

9. The liquid target system (1) according to any one of claims 1 to 4, wherein, The base chemical is any one or a combination of Ra(NO3)2, RaCl2 and RaBr2.

10. The liquid target system (1) according to any one of claims 1 to 4, wherein, The liquid target system (1) is suitable for producing Sc-47, Cu-67, Cs-131, Tb-155 or Ac-225.

11. Use of the liquid target system (1) according to any one of claims 1 to 10 for producing radioactive isotopes.

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