Liquid Targeting 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 to a liquid target system for the production of radioisotopes, as well as its uses and corresponding methods. [Background technology]

[0002] For the production of radioisotopes, solid targets are generally used due to their high yield in state-of-the-art systems, for which a large density of the parent nuclide, from which the radioisotope is derived, can be easily achieved. In fact, a drawback of using liquid targets is the limited solubility in water (typically used as the liquid solvent) of most parent nuclide compounds at room temperature. For example, salts of Ra-226, which can be used as basic chemicals to provide the parent nuclide for producing the radioisotope Ra-225, which can decay to the radioisotope Ac-225, have limited solubility in water. As an illustration, the radium nitrate salt Ra(NO3)2 has a solubility of 13.9 g per 100 g H2O at 20°C.

[0003] However, one advantage of using a liquid target rather than a solid target is that fewer (or no) liquid-to-solid and solid-to-liquid conversions are required in the chemical process to separate the radioisotopes from the target. Such chemical process steps typically carry a large risk of (uncontrolled) loss of the radioisotopes and the production of radioactive waste. Such conversions are not necessary with liquid targets, which is a major advantage of such targets.

[0004] Furthermore, the potential drawbacks of low parent nuclide concentrations in the liquid target need to be appreciated. As an example, consider the production of Ra-225 from Ra-226 via a photonuclear reaction. The production of Ra-225 in 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 intercept high-energy electrons and produce the high-energy bremsstrahlung photons required for the photonuclear reaction. The more high-energy photons produced and the more Ra-226 directly in front of the photon beam, the more Ra-225 is formed. However, assuming a conversion of about 50% electrons to bremsstrahlung photons, about half of the energy of the electrons can still be deposited in the converter. The very high energy deposition in the small converter volume associated with the 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, plus raster the electron beam over a larger surface area of ​​the converter. However, a larger surface area inevitably has a negative effect on production rate. The consequence of a larger converter surface area is that Ra should be divided over the entire surface area where the high energy gamma is present, but the best yield is obtained by placing Ra as close to the converter as possible. This means that the converter current density becomes a limiting factor (e.g., 0.125-0.25 mA / cm). 2 ) and can be considered a drawback for any kind of solid target, since if the surface-to-volume ratio needs to be increased, the high densities that can be achieved (e.g., 3-5 g / cc) cannot be optimally utilized.

[0006] US2014 / 0362964A1 describes an isotope production system configured to irradiate a source liquid with a particle beam for producing radioisotopes and converting a portion of the source liquid into steam.

[0007] Thus, there are several drawbacks associated with solid targets. Nevertheless, the state of the art remains focused on solid targets, since the efficiency and yield of liquid targets are generally very low. Thus, there remains 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] It is an object of the present invention to provide a good liquid target system.It is a further object of the present invention to provide a good method for producing radioisotopes.

[0009] The above objectives are 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 that of solid targets. A further advantage of embodiments of the present invention is that the amount of parent nuclide material required to obtain a given amount of radioisotope is limited. A still further advantage of embodiments of the present invention is that a liquid target is provided, which allows for the production of radioisotopes with less generation of radioactive waste.

[0011] An advantage of embodiments of the present invention is that a liquid target system can be continuously and efficiently cooled, thereby preventing overheating of the liquid target. A further advantage of embodiments of the present invention is that the liquid target system allows for a continuous and reliable extraction of heat at steady state.

[0012] An advantage of embodiments of the present invention is that liquid targets can have a large total volume, so that potential adverse effects from, for example, hydrogen formation or losses due to non-condensable water can be limited. A further advantage of embodiments of the present invention is that liquid target systems can be operated safely. A still further advantage of embodiments of the present invention is that operation of liquid targets 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 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 from which a radioisotope can be produced using irradiation. The boiling chamber comprises an irradiation window for allowing the liquid and the basic chemical to be irradiated and for evaporating the liquid into a vapor. The liquid target system is configured such that superheating 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, it refers to an area of ​​the boiling chamber wall that allows the radiation necessary to irradiate the basic chemical capable of producing the radioisotope to enter the boiling chamber. The type of irradiation window used may depend on the type of irradiation. For example, when using gamma radiation, the wall may be transparent to any radiation, for example.

[0015] In embodiments, a liquid target system configured such that overheating of the liquid target is controlled by the thermodynamics of the evaporation process may include the liquid target system configured to use the evaporation of the liquid to prevent such overheating, preferably to control the temperature of the liquid target. Overheating of the liquid target may result in evaporation of substantially all of the liquid within the liquid target, resulting in boiling off the basic chemicals to dryness.

[0016] An advantage of the embodiments of the present invention is that the liquid target system can avoid the emission of non-condensable gas from the chemical material, can avoid sintering of the chemical material, and / or can avoid the formation of insoluble chemical materials, since overheating of the liquid target can be prevented. Such overheating can occur as a result of a large amount of irradiation energy deposited on the liquid target. In particular, so-called pair production reactions contribute to the heating of the liquid target. In pair production reactions, high-energy photons in the presence of high-Z nuclei (e.g., parent nuclide Ra-226) are converted into electrons and positrons with remaining kinetic energy. As the charged particles, i.e., electrons and positrons, slow down (and, in the case of positrons, anneal), they release their respective kinetic energy into the liquid target, which is converted into heat.

[0017] An advantage of embodiments of the present invention is that a pump-controlled cooling circuit for the liquid target system, in which liquid and basic chemicals are pumped through the cooling circuit, may not be required. A further advantage of embodiments of the present invention is that large heat exchangers requiring a large contact area with the liquid target can be avoided, so that the amount of liquid target required may be limited.

[0018] An advantage of an embodiment of the present invention is that the system allows for up-concentrating during operation. More specifically, while the initial concentration of the basic chemical used to produce the radioisotope in the liquid at the starting temperature may be limited due to its solubility in the solvent (e.g., water) and a higher concentration at this starting temperature would result in precipitation, an advantage of an embodiment of the present invention is that the concentration can be increased during heating of the liquid target according to the increase in the solubility of the basic chemical in the solvent (e.g., water). The latter is established by the evaporation of the solvent, while the basic chemical is retained in the irradiated area.

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

[0020] In an embodiment, the liquid target system further comprises a condensation region disposed above the boiling chamber, the condensation region having a wall for condensing the vapor into a liquid condensate, which may be systematically returned or provided to the boiling chamber. Such a wall may 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, by a direct fluid connection between the condensation region and the boiling chamber, or by systematically dripping the liquid condensate from the condensation region (e.g., by gravity) into the boiling chamber.

[0021] In an embodiment, therefore, at least one condensate collection area may be disposed in the wall for condensing the vapor and may include a dripping mechanism for systematically returning the condensate to the boiling chamber.

[0022] In a preferred embodiment, the liquid target system further comprises at least one condensate collecting area for collecting liquid condensate, the at least one condensate collecting area being located outside the boiling chamber (i.e., the at least one condensate collecting area and the boiling chamber are separated from each other), and the at least one condensate collecting area and the boiling chamber are interconnected to function as a communicating vessel. In an embodiment, the at least one condensate collecting area and the boiling chamber are configured such that the ratio between the volume of liquid condensate (i.e., liquid) present in the at least one condensate collecting area and the volume of 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 between the area of ​​a horizontal cross section of the at least one condensate collecting area and the area of ​​a 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 may be selected to obtain an increased concentration by a factor of 2. An advantage of these embodiments is that because the basic chemical may become concentrated in the boiling chamber and may not be present in the at least one condensate collection area, during functioning of the liquid target system, the elevated concentration of the basic chemical in the boiling chamber can be at least 50%, preferably at least 100%, preferably at least 200% higher than the initial concentration of the basic chemical when present in all liquids, including any liquid present in the at least one condensate collection area.

[0023] In an embodiment, the volume of the boiling chamber is between 5 mL and 500 mL. In an embodiment, the total volume of the at least one condensate collecting area is between 5 mL and 500 mL.

[0024] In an embodiment, the interconnect between the boiling chamber and at least one condensate collection area comprises a gap or piping. In an embodiment, the inlet of the interconnect for admitting liquid into the boiling chamber is located near the bottom of the boiling chamber, e.g., in the wall or bottom. Preferably, the inlet is located in the boiling chamber at a height less than 25% of the height of the boiling chamber, preferably less than 10% of the height of the boiling chamber, more preferably substantially at the bottom of the boiling chamber. In an embodiment, the cross-sectional area of ​​the interconnect perpendicular to the nominal flow direction in the interconnect is at most 10%, preferably at most 5%, more preferably at most 2% of at least one (e.g., both) of the vertical or horizontal cross-sectional area of ​​the boiling chamber.

[0025] By way of illustration, and not limitation, embodiments, examples are described below. For example, a target receiving 1200 W has 50% of the energy effectively used to convert liquid to steam, and a 0.2 cm diameter (corresponding to a circular aperture radius of about 2.5 mm) 2 For a single opening of 1.33 cm / s, the liquid will move with a velocity of 1.33 cm / s. The smaller the opening, the higher the velocity. By using a small cross section for the interconnect, backflow from the irradiation chamber towards the condensate chamber is avoided. By choosing a sufficiently small cross section, the liquid flows uniformly in one direction at a sufficiently high velocity. The length and / or diameter of the interconnect can be designed to create a pressure drop that creates a liquid level difference. In some embodiments, the design is made to store the condensate above the irradiation level of the irradiation chamber. This ensures that when irradiation and boiling are completed, most of the condensate returns to the irradiation chamber. In this way the chemical is diluted and precipitation is avoided when the solution cools down.

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

[0027] An advantage of these embodiments is that heat dissipation (and therefore prevention of overheating) in the liquid target system is ensured by the boiling and condensation process of the liquid. The condensation region can be cooled by a secondary system containing a cooling fluid that does not contain radioactive materials. 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 collecting 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 automatically act as a concentrator, resulting in an increase in the concentration of the basic chemical in the irradiated volume during the heating process and subsequent liquid evaporation induced by irradiation. Furthermore, since the solubility of the basic chemical in liquids typically increases with temperature, the liquid target can contain a high concentration of the basic chemical without precipitation, allowing for efficient production of radioisotopes. In fact, since the solubility of the basic chemical material from which the radioisotopes are produced is relatively low at room temperature, it is an advantage that the concentration can be increased during the heating process induced by irradiation by taking advantage of the higher solubility of the basic chemical material in liquids at higher temperatures.

[0029] In an embodiment, the system further comprises an irradiation beam generator configured to irradiate the liquid and the basic chemical, where the irradiation beam generator is typically located outside the boiling chamber and configured to irradiate the liquid and the basic chemical 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 that form the irradiation beam.

[0030] In embodiments including at least one condensate collecting 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 an irradiation window into the boiling chamber without passing through the at least one condensate collecting region. An advantage of embodiments of the invention is that any liquid in the at least one condensate collecting region does not boil, thereby converting the liquid in the at least one condensate collecting region to vapor. This may result in an increased concentration of basic chemicals present in the at least one condensate collecting region, which may result in a decreased concentration of basic chemicals in the boiling chamber. A further advantage of these embodiments is that the irradiation beam is not attenuated by absorption by liquid condensate in the at least one condensate collecting region.

[0031] In embodiments, the liquid target system comprises a pressurizing 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 in the boiling chamber or the system.

[0032] In an embodiment, the boiling chamber, the condensation region, and the at least one condensate collection region form a system having a cylindrical design. An advantage of an embodiment of the present invention is that the number of welds in a cylindrical design is typically limited, which can make the system pressure-tight.

[0033] In an embodiment, 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-condensed 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) before adding it to the target system. In this way, the mass balance of the water can be kept constant (excluding hydrogen gas exiting the system).

[0034] An advantage of these embodiments is that good pressure control can be achieved. A further advantage is that an inert gas flow 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, if the parent nuclide includes Ra-226). In an embodiment, the boiling chamber includes an inlet for introducing and / or removing the liquid target, i.e., the liquid and the basic chemical, from the boiling chamber.

[0035] In an embodiment, the basic chemical 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 comprises an anion. In an embodiment, the liquid is water or heavy water and the basic chemical is a salt with a positive enthalpy with respect to water. In an embodiment, the basic chemical is any one or combination of Ra(NO3)2, RaCl2, and Ba(NO3)2. It should be noted that while the embodiments of the present invention often refer to the production of Ac-225, the embodiments are not so limited and liquid target systems for the production of other isotopes are also envisioned. An advantage of the embodiments of the present invention is that these salts have sufficient solubility in water. In an embodiment, the salt comprises one of a Ca salt that can be used to produce Sc-47, a Zn salt that can be used to produce Cu-67, a Ba salt that can be used to produce Cs-131, and a Dy salt that can be used to produce 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 may stand alone, as correspondingly described for any embodiment of any of the other aspects of the invention.

[0037] In a second aspect, the present invention relates to a method for producing radioisotopes, the method comprising irradiating a liquid target comprising a liquid and a basic chemical from which the radioisotope can be produced using irradiation to vaporize the liquid into a vapor, where the thermodynamics of the evaporation process are used to control the overheating of the liquid target.

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

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

[0040] In an embodiment, the irradiation is carried out using a power incident on the liquid target of, for example, 1.5 kW, 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 between vacuum and 60 bar, for example, 0.5 bar to 10 bar. It should also 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 that is preferably at least 20% higher, more preferably at least 50% higher, even more preferably at least 100% higher, and even more preferably at least 200% higher than the solubility of the basic chemical in the liquid (i.e., the maximum concentration before precipitation occurs) at a temperature of 25° C. and 1 atmosphere, e.g., at the location of irradiation and during at least a portion of said irradiation. Typically, the maximum concentration that can be achieved is equal to the solubility of the basic chemical, since any additional basic chemical will not dissolve in the liquid and will, e.g., precipitate from the liquid.

[0042] Any feature of any embodiment of the second aspect may stand alone as correspondingly described for any embodiment of any of the other aspects of the 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 producing a radioisotope.

[0044] Any feature of any embodiment of the third aspect may stand alone as correspondingly described for any embodiment of any of the other aspects of the invention.

[0045] Particular and preferred aspects of the invention are set out in the accompanying independent and dependent claims. Features from the dependent claims may be combined with features of the independent claims and with features of other dependent claims as appropriate and not merely as explicitly set out in the claims.

[0046] While there have been constant improvements, changes and evolutions of devices in this field, it is believed that the present concepts represent substantial new and novel improvements which involve departures from conventional practice and 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, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. This description is given for the purposes of illustration only, without limiting the scope of the invention. The reference figures quoted below refer to the attached drawings. [Brief description of the drawings]

[0048] [Figure 1A] 1 is a schematic exploded view of at least a portion of a liquid target system, in accordance with an embodiment of the present invention. [Figure 1B] 1B is a schematic cross-sectional side view of at least a portion of the liquid target system of FIG. 1A, in accordance with an embodiment of the present invention. [Diagram 2] 1 is a plot of solubility (grams of salt per 100 mL of H2O) as a function of temperature (in degrees Celsius) for Ba(NO3)2 and Ra(NO3)2. [Diagram 3] FIG. 1 is a schematic diagram of a liquid target system according to an embodiment of the present invention. [Figure 4] 1 is a schematic cross-sectional side view of a liquid target system according to an embodiment of the present invention. [Diagram 5] 5 is a schematic cross-sectional side view of the liquid target system of FIG. 4 after heating of the liquid target by irradiation of the liquid target.

[0049] In the different drawings, the same reference signs refer to the same or similar elements. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0051] Moreover, terms such as first, second, third, etc. in the description and claims are used to distinguish between similar elements and not necessarily to describe an order either temporally, spatially, in ranking, or in any other manner, It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operating in orders other than those described or illustrated herein.

[0052] Moreover, terms such as top, bottom, upper, lower, etc. in the description and claims are used for descriptive purposes and not necessarily to describe relative positions, and it is to be understood that the terms so used are interchangeable under appropriate circumstances, and that the embodiments of the invention described herein are capable of operation in orientations other than those described or illustrated herein.

[0053] It should be noted that the term "comprising" used in the claims should not be interpreted as being limited to the means recited thereafter. It does not exclude other elements or steps. It should therefore be interpreted as specifying the presence of the recited features, integers, steps or components as referred to, but without excluding the presence or addition of one or more other features, elements, steps or components, or groups thereof. The term "comprising" therefore encompasses the situation where only the recited features are present, as well as the situation where these features and one or more other features are present. The term "comprising" according to the present invention therefore also includes, as an embodiment, the absence of further components. Thus, the scope of the expression "a device comprising means A and B" should not be interpreted as being limited to a device consisting of only components A and B. This means that, in the context of the present invention, the only relevant components of the device are A and B.

[0054] Similarly, it should be noted that the term "coupled" should not be interpreted as being limited to only direct connections. The terms "coupled" and "connected" may be used along with their derivatives. It should be understood that these terms are not intended as synonyms for each other. Thus, the scope of the phrase "device A coupled to device B" should not be limited to devices or systems 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 that includes other devices or means. "Coupled" may mean that two or more elements are in direct physical or electrical contact, or that two or more elements are not in direct contact with each other, but still cooperate or interact with each other.

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

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

[0057] Moreover, while some embodiments described herein include some features that are included in other embodiments but not others, combinations of features of different embodiments are intended to form different embodiments within the scope of the invention, as would be understood by one of ordinary skill in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

[0058] Furthermore, some of the embodiments are described herein as methods or combinations of elements of methods that may be implemented by a processor of a computer system or other means for performing functions. Thus, a processor with the necessary instructions for performing such a method or element of a method forms a means for performing the method or element of a method. Furthermore, a described element of an apparatus embodiment herein is an example of a means for performing the functions performed by the element for implementing the invention.

[0059] In the description provided herein, numerous specific details are set forth. However, it will be 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 in order not to obscure an understanding of this description.

[0060] Hereinafter, the present invention will be described by detailed descriptions of some embodiments of the present invention. Other embodiments of the present invention can be constructed according to the knowledge of those skilled in the art without departing from the technical teachings of the present invention, and it is clear that the present invention is limited only by the terms of the appended claims.

[0061] In a first aspect, the 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 from which a radioisotope can be produced using irradiation. The boiling chamber comprises an irradiation window for allowing the liquid and the basic chemical to be irradiated and for evaporating the liquid into a vapor. The liquid target system is configured such that superheating 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 radioisotopes, the method comprising irradiating a liquid target comprising a liquid and a basic chemical from which the radioisotope can be produced using irradiation to vaporize the liquid into a vapor, where the thermodynamics of the evaporation process are used to control the overheating 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 producing a radioisotope.

[0064] Reference is now made to FIG. 1A, which is a schematic exploded view of at least a portion of a liquid target system 10 according to an embodiment of the present invention. Reference is now also made to FIG. 1B, which is a schematic vertical cross-sectional view of at least a portion of the liquid target system 10. In this example, the liquid target system, which is intended for the production of radioisotopes, comprises a boiling chamber 2 for containing a liquid target 8 consisting of a liquid capable of producing radioisotopes using irradiation and a basic chemical. An irradiation window 23, which is in this example a part of the wall of the boiling chamber 2, is included in the wall of the boiling chamber 2 through which the irradiation can propagate. 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 (e.g., (Ra-226)(NO3)2), although the present invention is not so limited. Thus, 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 said continuous irradiation, thereby converting the liquid into vapor, i.e. water vapor (white arrow). The water vapor is then condensed in a condensation region 3 located above the boiling chamber 2, thereby converting the vapor into liquid condensate. At least the condensation region 3, possibly the condensate collection region 4, and possibly also the boiling chamber 2 may 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 collecting areas 4, different from the boiling chamber 2, in this example separated from each other by a separation wall 21. The two condensate collecting areas 4 are located on either side of the boiling chamber 2 and are separated each time by a separation wall 21. The liquid target system is configured in such a way that the condensate formed in the condensation area 3 moves, for example falls (arrow with horizontal stripes), to the condensate collecting area 4. This is achieved in this example, since the walls of the condensation collecting area 4 are connected to the walls of the condensation area 3, so that liquid condensed on the walls of the condensation area 3 can move, for example over the walls and downwards, to the condensate collecting area 4. Furthermore, in this example, the liquid target system comprises a condensate steering element 5, which directs any condensate leaving the boiling chamber to the condensate collecting area 4 (which may also be called the condensate collecting chamber).

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

[0068] Thus, the condensate collection area 4 and the boiling chamber 2 may be considered to function as three communicating vessels in this example, where the liquid target 8 in the boiling chamber 2 is placed directly in the high energy photon beam and boils, but the condensate is collected in the condensate collection area 4 and is not boiling due to the lower energy deposition in the condensate collection area 4. In fact, the condensate, i.e., the liquid in the condensate collection area 4, may not contain a significant amount of Ra-226 to absorb the irradiation, due to the continuous effective liquid flow (black arrow) from the condensate collection area 4 through the gap to the boiling chamber 2, which compensates for the flow of vapor (white arrow) and the flow of condensate (horizontally striped arrow) through the condensation area 3. At steady state, the rate of each of these three flows may be substantially equal. The condensate liquid 41 is at a significantly lower irradiation level. Furthermore, due to the absence of Ra, the heat absorption is lower and does not boil the condensate. In other words, the condensate collecting area 4 and the boiling chamber 2 are essentially communicating vessels, so that the continuous loss of water mass in the boiling chamber 2 due to the boiling is compensated by a continuous water flow from the condensate collecting area 4 through the holes in the bottom of the target to the boiling chamber 2. The size of the gap (or alternatively the diameter of the piping) is preferably optimized so that there is a continuous flow of condensate (i.e. 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 the condensate collecting area 4. The opening should therefore be neither too narrow nor too large. Preferably, the liquid flow rate through the opening to the boiling chamber is between 0.1 cm / s and 20 cm / s, preferably between 0.5 cm / s and 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 subsequent gain of liquid in the condensate collecting area 4 due to the collection of condensate therein. The continuous backflow of condensate (ie, liquid) into the liquid target in the boiling chamber 2 ensures that the liquid target cannot be boiled dry and overheating is prevented.

[0069] In this example, irradiation of the liquid target 8 leads to the production of Ac-225 by the photonuclear reaction Ra-226(γ,n)Ra-225(β-)Ac-225. Any Ac-225 formed can preferably be separated 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 serves 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, the liquid target 8 may be transferred through the opening 22 after irradiation, for example, to a hot cell facility for chemical separation and purification of Ac-225. After said separation, the liquid target may be returned through said opening 22 to the boiling chamber 2. In order to avoid crystallization and losses in any flow paths (e.g., piping) interconnecting the boiling chamber 2 and the hot cell facility, a certain rinsing volume of liquid, for example, dilute nitric acid, is preferably used immediately after transferring the liquid target 8 through said paths. This may further dilute the basic chemicals in the liquid target 8 and therefore reduce the yield, i.e. due to the excess volume introduced by the rinsing 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 a proper design of the target (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 fact, 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 may be optimized and the concentration of Ra in the boiling chamber may be increased. For example, in the case of a volume ratio of 1 / 1, the concentration of Ra in the beam may be doubled in operation, i.e. during irradiation of the liquid target 8, compared to a design without the 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 needed in the gamma production route to obtain a high isotopic yield of Ra-225. Such an increased concentration may not be a problem with respect to the maximum radium solubility during irradiation.This is because the liquid target can be strongly heated, for example to 100° C., which is the boiling temperature of water at standard pressure, or even above 100° C. if the pressure is above standard pressure, so that the solubility can be increased further.

[0070] 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, form a cylindrical shape to limit the amount of welding, which increases the strength of this portion of the liquid target system that can operate at high pressure. The higher pressure can be used to increase the boiling point of water, which can affect the thermodynamics of the evaporation process. In fact, when operating this liquid target 8 in the beam, any heat generation should be evacuated in a manner that is safe and reliable for steady-state 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 in the boiling liquid target 8. The higher the pressure, the smaller the bubbles and the better the boiling performance. The pressure and steady-state temperature may 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, making it well suited for use in embodiments of the present invention. The compound has a solubility in water of 13.9 g / 100 g at 20° C. and standard pressure (see Erbacher, O. Loslichkeits-Bestimmungen einiger Radiumsaltze; Berichte der deutschen chemischen Gesellschaft, 1930; Vol. 63:141-156). However, other compounds, such as (Ra-226)Cl2, may also be used instead. 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 approximation due to the very similar behavior of the alkaline earth metals Ra and Ba or atoms of group 2 (although the solubility of Ba(NO3)2 is slightly lower than that 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 depending on temperature (degrees Celsius). Shown are data for Ba(NO3)2 over the temperature range 0°C to 100°C (from http: / / periodic-table-of-elements.org / SOLUBILITY / barium_nitrate) and data for Ra(NO3)2 (only data at 20°C), black points connected by a dotted curve. At 100°C, it can be observed that the solubility of Ba(NO3)2 increases by a factor of three compared to the solubility at 20°C. So the solubility at 100° C. is expected to be about three times higher for Ra(NO3)2. Above 100° C., even higher solubility is expected. In fact, the boiling point of water can be increased, firstly, by the presence of salts dissolved in it, and secondly, by increasing pressure.

[0072] The pressure dependence of Ra(NO3)2 can also be derived by comparing it 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 increasing the pressure from standard pressure to 200 MPa. (BRChuragulov, SL Lyubimov, AN Baranov, AA 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 adversely affect (reduce) the solubility of Ra(NO3)2 in the liquid target water.

[0073] A quantitative example will now be presented. Referring back to FIG. 1A and FIG. 1B, as an example, a 25 cm 3A liquid target 8 having a Ra-226 concentration of 1.0 g / 100 g may be considered, preferably not exceeding its 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, i.e. between the boiling chamber 2 and the hot cell facility. Higher concentrations may therefore result in precipitation in the flow paths connecting the boiling chamber 2 with the hot cell facility. So, at room temperature, the liquid target may contain only about 2 grams of Ra-226. However, the goal is to have 6 grams of basic chemicals in the boiling chamber 2 to increase the efficiency and yield of the liquid target system. So, instead, a target of 6 grams of Ra-226 dissolved in 125 ml may be envisaged, with a volume ratio between the liquid in the boiling chamber 2 and the condensate collection chamber 4 being equal to 1 / 4. So, initially, 100 mL of the liquid target is present in the condensate collection chamber 4 and 25 mL in the boiling chamber 2. At the start of the irradiation, the Ra-226 is evenly divided between the compartments. When the boiling chamber 2 starts to boil under the effect of said irradiation by the mechanism described above, Ra-226 from the condensate collection chamber 4 flows towards the boiling chamber 2 and remains there during the irradiation. Thus, over time, Ra-226 is depleted in the condensate collection chamber 4 such that the condensate collection chamber 2 contains only liquid, i.e., condensate 41. Furthermore, within 25 cm 3 The boiling chamber 2, which contains the liquid target, contains all the remaining Ra-226 (i.e., 6 grams minus that which reacted to form Ra-225 or Ac-225). That is, only the boiling chamber 2 effectively contains the liquid target 8. As the water is heated, for example to 80° C. or 100° C., the concentration of basic chemicals in the liquid target 8 remains below the solubility limit of Ra(NO3)2.

[0074] In addition to the heating by irradiation, forced heating (not due to irradiation) of the boiling chamber 2 can be carried out until a steady state is reached. It is an advantage that a steady state can be reached quickly, at which the thermodynamics are continuous and predictable. Furthermore, when cooling the liquid target 8 after said irradiation, a slow cooling may be preferred to avoid any precipitation of Ra(NO3)2. One of the ways to achieve this can be to submerge the cylinder or target vessel, then at least the boiling chamber 2 and the condensate collecting area 4, for example in a water bath operating at 70-80°C. Alternatively, a purge gas causing 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 now made to FIG. 3, which is a schematic diagram of a liquid target system 1 according to an embodiment of the present invention, which may include at least a part of the liquid target system 10 of FIGS. 1A and 1B. A boiling chamber included in at least a part of the liquid target system 10 may be irradiated by an irradiation beam 26 originating from an irradiation beam generator 25. In this example, an opening 22 at the bottom of the boiling chamber may be coupled to a buffer vessel 6 via a valve V3. The buffer vessel 6 is coupled to a hot cell facility 61 via a valve V8. The buffer vessel 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, may be introduced from a compressed gas source 63, for example a compressed gas cylinder, via a valve V4, the buffer vessel 6, and a valve V3 through the opening 22 or via a valve V2 through the further opening 31. Further, a vacuum may be introduced from a vacuum source 64, e.g. a pump, via valve V6, buffer vessel 6 and valve V3 through opening 22, or alternatively through valves V6, V4 and V2 through a further opening 31. The further opening 31 may be coupled to the chimney 7 through a volume containing activated charcoal 71 or any other system for capturing radioactive non-condensable gases.

[0076] Initially, all valves V1 to V8 are closed. The buffer vessel 6 can then be filled with the liquid target by opening valves V6 and V8 so that the vacuum draws the liquid target out of the hot cell facility 61.

[0077] The liquid target can then be moved to the boiling chamber and condensate collection area by opening valves V4, V3 and V1 to introduce a gas flow (e.g. He or N2) through the buffer vessel 6, via the boiling chamber, into at least a part of the liquid target system 10, then through activated carbon 71 into the chimney 7, thereby moving the liquid target from the buffer vessel 6 to the boiling chamber. The fluid connection connecting the boiling chamber with the buffer vessel 6 can be flushed with demineralized water from an inlet for introducing demineralized water 62 by first filling the buffer vessel 6 with demineralized water by first only opening valve V5, then closing V5, opening valve V4 and opening valve V3. Alternatively, flushing can be performed by opening valve V7. This may result in additional liquid in the boiling chamber, but in the present invention this may not be a problem due to the potential increased concentration of basic chemicals in the boiling chamber. Furthermore, in a next step, excess liquid in the boiling chamber can be evaporated and removed from the boiling chamber by gas flow from the compressed gas source 63 through the boiling chamber to the chimney 7, thereby reducing the volume of 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 a 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 portion of the liquid target system 10, and no valves are opened, or alternatively, only valves V4 and V3 may be opened and V1 may be opened slightly to obtain a preferred, e.g., high, pressure in at least a portion of the liquid target system 10. The flow rate may be controlled via flow controller 631 and pressure regulator 632. The increased pressure in the boiling chamber may allow the liquid in the boiling chamber to be at an elevated temperature compared to atmospheric pressure, which may improve the solubility of basic chemicals. Furthermore, for example, if the basic chemical includes Ra-226, a low gas flow rate may be kept to remove and collect any gas, e.g., Rn, formed in the boiling chamber. An advantage of an 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, all valves can be closed and then valves V2 and V3 can be opened in order to move the liquid target containing the radioisotopes from the boiling chamber to the buffer vessel 6 by a gas flow. Optionally, the piping connecting the boiling chamber to the buffer vessel 6 can then be flushed with demineralized water by opening valve V7. Finally, the contents of the buffer vessel 6 can be discharged to the hot cell facility 61 by closing all valves and then opening valves V8 and V4, followed by briefly opening valve V5 for flushing with demineralized water.

[0080] Although at least a portion of the liquid target system 10 in the above description is assumed to be an embodiment of the example related to Figures 1A and 1B, at least a portion of the liquid target system 10 may instead be an embodiment of the subsequent example, or may include 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, which includes a liquid capable of producing radioisotopes and a basic chemical. Irradiation 26 incident on the liquid target 8 results in heating of the liquid target 8, such that the liquid evaporates to form steam in a volume 9 above the boiling chamber 2. The walls of the volume are thermally insulated by a thermal insulating material 91, so that a high temperature of the steam in the volume can be achieved. Thereby, a high concentration of steam in the volume can be achieved, allowing the pressure to build up. In other words, the volume 9 can include a large amount of liquid in the vapor phase, i.e. in the vapor. In an embodiment, the ratio between the volume of 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, apart from directly condensing the vapors formed, it is possible alternatively therefore to use the volume above the boiling chamber to store the evaporated solvent as vapor.

[0083] Referring to FIG. 5 , as a result of evaporation due to irradiation and the large amount of vapor formed, the volume of the liquid target 8 decreases. This increases the concentration of the basic chemical therein, which can increase the efficiency and yield of the nuclear reaction, e.g., photonuclear reaction, of the basic chemical to form radioisotopes. In an embodiment, the irradiation is adapted to produce a pressure in the volume 9 of up to 20 bar, e.g. up to 10 bar. The upper pressure limit 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 in the liquid target 8, since it increases the boiling temperature, which in turn allows more liquid to evaporate without resulting in the precipitation of the basic chemical from the liquid target 8. During irradiation 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., without irradiation. In this example, a high irradiation can therefore result in a high yield, both due to the high irradiation and the increased concentration of the basic chemical in the liquid target 8. Furthermore, by finding a balance between radiation output and power losses due to evaporation of liquid from the liquid target 8, overheating can be prevented.

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

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

Claims

1. A liquid target system (1) for the production of radioisotopes, said liquid target system (1) comprising: a boiling chamber (2) for containing a liquid and a basic chemical from which said radioisotope can be produced using irradiation, said boiling chamber (2) comprising an irradiation window allowing said liquid and basic chemical to be irradiated and for evaporating said liquid into a vapor, the liquid target system is configured such that the superheating of the liquid target (8) is controlled by the thermodynamics of an evaporation process; A liquid target system (1), characterized in that the liquid is water or heavy water and the basic chemical is a salt having a positive enthalpy with respect to water.

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

3. The liquid target system (1), - a condensation zone (3) arranged above the boiling chamber (2), the condensation zone (3) having walls for condensing the vapor into a liquid condensate, 10. The liquid target system (1) according to any one of the preceding claims, wherein the liquid condensate can be systematically returned or provided to the boiling chamber (2).

4. The liquid target system (1), The liquid target system (1) of claim 3, further comprising at least one condensate collecting area (4) for collecting the liquid condensate, the at least one condensate collecting area (4) being arranged outside the boiling chamber (2).

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

6. 5. The liquid target system (1) of claim 4, wherein the at least one condensate collecting area (4) is arranged on the wall for condensing the vapor and is provided with a dripping mechanism for systematically returning the condensate to the boiling chamber.

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

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

9. the system further comprises an irradiation beam generator (25) configured to irradiate the liquid and the basic chemical; and / or 10. The liquid target system (1) according to any one of the preceding claims, wherein the system further comprises a pressurization unit for pressurizing the boiling chamber to control bubble size and boiling temperature of the liquid.

10. The liquid target system (1) of claim 9, wherein the system (1) further comprises a pressure sensor for measuring a pressure in the boiling chamber (2).

11. The basic chemical is Ra(NO ３ ) ２ , RaCl ２ , and RaBr ２ 10. The liquid target system (1) according to any one of the preceding claims, wherein the liquid target system (1) is a liquid target system having a liquid concentration of 10 ...

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

13. 1. A method for producing a radioisotope, comprising: irradiating a liquid target (8) containing a liquid and a basic chemical, from which the radioisotope can be produced using irradiation and vaporizing the liquid into a vapor; The thermodynamics of the evaporation process is used to control the heating of the liquid target (8), 4. The method of claim 3, wherein the liquid is water or heavy water and the basic chemical is a salt having a positive enthalpy with respect to water.

14. Use of a liquid target system (1) according to any one of claims 1 to 12 for producing radioisotopes.

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