MXPA97003381A

MXPA97003381A - Production of radioisotopes by isotop conversion

Info

Publication number: MXPA97003381A
Application number: MXPA/A/1997/003381A
Authority: MX
Inventors: Lawrence M Lidsky; Richard Lanza
Original assignee: Massachusetts Institute Of Technology
Priority date: 1995-09-08
Filing date: 1997-05-08
Publication date: 1997-08-01

Abstract

An apparatus and method for producing a specific high activity of a radioisotope in an individual increment of target material (12), or sequentially within serial increments of target material (38, 40, 42), is disclosed by exposing a selected isotope in the target material to a beam of high energy photons (20) to convert the selected isotope isotopically. In particular, this invention is used to produce a specific high activity of Mo99, of at least 1.0 Ci / gram or preferably at least about 10.0 Ci / gram, of Mo1

Description

PRODOCCIOH RADIOISÓTOPOS BY CONVBRBIOM ISOtOPICA ftnteceti'gntgg d invention The radioactive isotopes are widely used in industry, medicine and living science. The utility and commercial value of a radioisotope are determined based on the specific activity, having greater utility and value with a high specific activity. Normally, the isdtopos are produced by electron beams, ion beams, and nuclear reactors. Electron beams are currently used to produce short-lived isotopes near the site of use. Ion beams and reactors are generally used to produce longer-lived isotopes in central facilities. Some of the isotopes are sensitive to production by all three techniques. These include isotopes prepared by both the addition and removal of a neutron from a selected isotope that occurs naturally. Normally, the ion beam has been the method of choice for the elimination of neutrons due to its relatively high energy efficiency. However, the ion beam process is unfavorable because of its high initial cost, complexity of operation, and limited capacity to be scaled up to higher production rates. Additionally, the relatively heavy mass of the ions makes it very difficult to generate high current density beams. In addition, since the ion energy is deposited in a very short distance, thereby causing intense local heating of the object, the beam can not focus sharply without destroying the object. This limits the average specific activity achievable by ion beams. The electron beams have significantly longer stopping distances than the ion beams, however, the electron beams must - generate photons inside the object before radioisotopes can be formed. In addition, the high power density of the electron beam required to generate the intensity of the photon needed to produce a high specific activity of radioisotope will typically impose unacceptably high thermal loads on an object material resulting in the melting of the object. Fission reactors compete with beam sources in the production of isotopes through neutron absorption processes and also have a unique role in the production of separate isotopes of fission products. Fission reactors are the method of choice for the addition of neutrons due to their ability to produce large quantities of the product. However, nuclear reactors are extremely expensive, have very high operating costs and are subject to excessively strict location and operating limits under Federal regulations. Therefore, there is a need for less expensive and less complex means to produce specific high activities of radioactive isotopes of longer life.

SUMMARY OF THE INVENTION This invention relates to an apparatus and method for producing a specific high activity of a radioisotope in a single increment of target material, or sequentially within serial increments of target material. In particular, this invention relates to an apparatus and method for producing a specific high activity of molybdenum-99 (Mo99) by exposing Mo100 to a high-energy, high-intensity photon beam, typically with an intensity of about 50 microns. / cm2 or more. In the production of a high specific activity of Ma ", the product of f'R is at least 2.2? 10 ~ 8 ≤ g" 1, where f is the isotope fractionation of Ho100 in the object and R is the length of the path of the photons per unit volume per unit of energy, weighted by the cross section of the photoneutron over the energy. An average specific activity of Mo "of at least 1.0 curie / gram can be obtained in mollbdeno objects up to 7.5 cm thick.For molybdenum objects up to 0.5 cm thick, an average specific activity of 10.0 curies / gram can be obtained, one embodiment of the apparatus of this invention includes an electron accelerator, a converter for converting an electron beam in a high energy photon beam, and a selected isotope that is contained in the target material, Optionally, the converter includes at least two separate converter plates, where the converter plates have different thicknesses, and coolant arranged between adjacent converter plates to cool the converter plates to remove the heat generated by the electron beam In preferred embodiments of the invention, a concentration of at least one isotope product is produced sequentially within serial increments. of object material.An object set contains increments of object material that include the object isotope. next to the beam source is the radioisotope-removable from the object set, while additional object material for the production of radioisotopes comes out. This apparatus may additionally include means for moving increments in series toward the source of the photon beam as the near increment of the object set is eliminated. Optionally, this apparatus also includes means for inserting an increment of additional target material in the object set separate from the source of the photon beam. A material object of the present invention can be a solid mass or selected from the group consisting of a liquid, a suspension or particles. In one embodiment of the apparatus, each increment of the subject material is contained separately within a container. The method of the invention for producing a high specific activity of a radioisotope, preferably Mo ", in an object material containing a selected isotope, such as M01DO, includes exposing the target material to a high energy photon beam to form an activity. specific high inside the target material Typically, the intensity of the photon beam is 50 microamperes / cm2 or more.In addition, in the production of a high specific activity of Mo ", the product f R eß at least 2.2 x 10 ~ 8 sec. "1. In one embodiment, the thickness of the target material is approximately 7.5 centimeters, or less, and the converter is a tungsten converter, where the electron beam power density is approximately 35,000. watts / crn3 In another embodiment of the method of this invention, the method optionally includes directing the photon beam from a photon beam source through the increments of the target material, where the increments are in series with respect to said photon beam. This method optionally includes the step of advancing the increments of object material in series towards the source of the photon beam. This method can additionally include the step of eliminating an increase in target material from the photon beam, where the increase is close to the photon beam source. The advantages of this invention include the highly efficient production of radioisotopes using a high energy electron beam to produce a specific, desirable level of activity of a radioisotope within an increase of an object material. As the desired specific activity occurs in an increase of the target material near the source of the electron beam, other increments of material object in series with respect to the next increment are sequentially pre-irradiated by the photon beam to begin the formation of the specific activity level of the radioisotope within each increment. Therefore, the period of time in which an increase is radiated, while being close to the source of the electron beam to produce a desired specific activity level. of a radioisotope has been reduced by pre-irradiating the increase. This invention also has the advantage that each increment of the target material can be eliminated to pick up radioisotopes without significantly affecting the overall production of specific high activities in other serial increments of target material. An additional benefit of the present invention is that the subject material is a source of intense neutron radiation. Neutron radiation can be used for the generation of additional isotope by absorption of neutrons or other medical or industrial uses, such as image formation. In addition, photons not absorbed by the target material can be used in the sterilization and treatment of materials.BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a graph of specific activity generated with a) a beam of photons of relatively higher intensity and b) a beam of photons of relatively lower intensity at different thicknesses within a subject material. . Figure 2 is a sectional view of an embodiment of an apparatus and method of this invention for producing a high specific activity of a radioisotope product. Figure 3 is a sectional view of an alternative embodiment of a converter used in an apparatus, and method of this invention. Figure 4 is a sectional view of still another embodiment of a converter used in an apparatus and method of this invention; - Figure 5 is a sectional view of an embodiment of an apparatus and method of this invention for producing a specific activity high of radioisotope product in sequential objects. Figure 6 is a sectional view of an alternative embodiment of an object assembly used in an apparatus and method of this invention. Figure 7 is a sectional view of still another embodiment of an object assembly used in an apparatus and method of this invention. Figure 8 is a theoretical graph of a) total curies removed per day from an object set and b) specific activity within an object, with respect to the time in which each object is irradiated, measured in the object segments eliminated by days of an object. object set. Figure 9 is a graph of a) activity of the center point and b) semi-width of the activated region, with respect to the depth in a molybdenum object of example 1.

DETAILED DECRIPTION OF THE INVENTION The features and other details of the apparatus and method of the invention will now be described more particularly with reference to the accompanying drawings and as indicated in the claims. The same number present in different figures represents the same element. It will be understood that the particular embodiments of the invention are shown by way of illustration and not by limitations of the invention. The main features of this invention can be employed in various embodiments without departing from the scope of the present invention. The specific activity of a radioisotope, within a volume of target material, is the number of radioactive decays per second of radioisotope nuclides (in curies (Ci)) measured per gram of the radioisotope element, including all isotopes of the element, within of the volume of the object material. The specific activity provides an indication of the concentration of the radioisotope within the volume of the target material. Typically, the specific activity is not uniform across a volume of target material, but is averaged across the volume of the target material. The level of specific activity that constitutes a specific high activity depends on the radioisotope and its use. For example, where the radioisotope is olibdene-99 (Mo99), which subsequently decays to the descendant product tecneoio-99 (Ta99), a specific activity high for Mo "is typically a specific activity average of about 0.5 Ci / gram of molybdenum , or more Preferably, the specific activity of Mo "is about 1.0 Ci / gram or more. More preferably, a specific high activity of Mo "is about 5 Ci / grams or more, Even more preferably, a high specific activity of Mo" eß about 10 Ci / grams or more. A radioisotope can be generated in an object-material using high energy photons from a beam of photons in at least one isotopic conversion reaction. An object material is a material that consists of or contains an object isotope, which when exposed to high energy photons, forms a radioisotope as a product. Typically, a selected isotope has a high atomic number (Z), for example, a 2 of about 30 or more. A radioisotope product can be a final product, such as cadmium-115 or Tantalum-179. Alternatively, a radioisotope product, such as Cadmium-109 or Oßmium-191 may be an intermediate which decays poorly to form a desired down-product. Preferably, a radioisotope product is longer lived. A long-lived radioisotope, as defined here, is a radioisotope with an adequate i-life to allow the transport and subsequent use of the radioisotope or a downstream product, after generating the radioisotope. Typically, a longer isotope of life has a half-life of approximately 12 hours or more. Preferably the ε emi-life is approximately 48 hours or more. More preferably, the half-life is about 60 hours or more. More preferably, the radioisotope product is Mo. "Suitable isotopic conversion reactions include, for example, reactions (?, N), (?, 2n), (?, P) and an appropriate energy level for a high energy photon. is a level of energy that is at least equal to the energy level (minimum) threshold of the Giant Resonance region of the cross section with respect to the energy curve for the desired isotope conversion reaction, required to produce the reaction between a photon and the selected isotope The specific activity of a radioisotope generated by photon beam, within a volume of an object material, depends on several variables, including the intensity (photon energy per unit area per unit time) of High-energy photons in the photon beam and the thickness of the target material As shown in Figure 1, the peak-specific activity level for a beam of photons of any intensity is in the surface of the target material irradiated by the photon beam. A beam of photons with a higher intensity of high-energy photoneß, irradiating the same target material, typically generates a peak-specific activity higher than that of a photon beam with a lower intensity of high-energy photoneß. A high intensity of high energy photons is a sufficient intensity to generate a high specific activity of a radioisotope. Typically, an adequate intensity of high energy photons is at least 50 microamperes / em2 (μa / cm2). Preferably, the intensity of high energy photons is at least 500 μa / am2. More preferably, the high energy photoneß intensity is at the enoß of 1,000 μa / sra2. In addition, as also shown in Figure 1, the levels of specific activity within the subject material decrease exponentially as the depth increases along the thickness of the subject material. The thickness of the target material is the distance from the irradiated side of the target material to the opposite side. Therefore, the average specific activity of a radioisotope within a volume of target material increases as the thickness of the target material decreases. The maximum specific activity (saturation activity) achievable by isotopic conversion in a volume of target material varies linearly with the production rate of the radioisotope. Typically, saturation activity is only achieved after periods of irradiation that are significantly longer than the half-life of the radioisotope. The saturation activity (S) is calculated by the following equation: S - 1.62 X 1013 f-R / A where f is the fraction of the isotope of the target element which is the selected isotope and A is the atomic weight of the selected element, R, which eß indicative of the intensity of high energy photons, is the path length of the photon per unit of volume and per unit of energy (N? (E) **) weighted by the photon cross section ("s (E)"), integrated over all photon energy levels. The specific formula to calculate the value of R is as follows: The energy values of the photon included in the calculation of R can be limited to those in the Giant Resonance range, since the photons of lower energy or are effective. Specifically, lower energy photons do not result in photonuclear conversion of Mo100 to Mo. "An embodiment of the apparatus for producing a high specific activity of a radioisotope product in a volume of target material, is illustrated in Figure 2. The apparatus 10 includes target material 12, converter 14 and electron accelerator 16. The target material 12 contains a charge of a selected isotope that can be established based on the intended isotope conversion reaction and the desired radioisotope product concentration. Specific isotopic conversion rates that occur within the target material 12 typically depend on the desired isotope product and on the availability of nuclei of the selected isotope within the subject material 12. In one embodiment, the loading of a selected isotope in the target material is 12. is at levels that occur naturally, preferably the material obj Eto 12 contains enriched levels of the selected isotope. The selected isotope may be in elemental form, in at least one compound (e.g., a salt or oxide), and / or complexed. The selected isotope within the subject material can be in any physical state, for example, in particles, a liquid, in solution, in a suspension, or in a larger solid mass. Examples of other components optionally contained in the subject material 12 include materials in IOB that the selected isotope is retained, such as a metallic or ceramic material, or materials in which the selected isotope is dispersed such as in a liquid (e.g. water or oils) or in particles. The apparatus 10 additionally includes electron beam 18 and photon beam 20. The electron beam 18 is generated by the electron accelerator 16 and is directed to the converter 14, where it generates the ha of photons 20, which includes high energy photons . The beam of photons 20 radiates from the converter 14 into the target material 12. Typically, the beam of photons 20 is a beam of energently collimated high energy photons. A suitable converter contains at least one high Z material, for example tungsten or platinum, which is refractory under the conditions of the method of the invention. A high Z material is used to improve the conversion efficiency within the converter 14 of high energy electrons from the electron beam 18 in high energy photons to form the beam of photons 20. The total extent of the converter 14 in the direction of the electron beam path l should be sufficient to absorb a significant portion of the energy of the electron beam 18, while the photoneß radiation is transmitted in a suitable energy range for the desired isotopic conversion reaction. Concurrently with the transformation of the energy of the electron beam 18 into high energy photons in the beam of. photons 20, the converter 14 also protects the target material 13 against any significant residual electron beam ». If the converter 14 is too thick, the photons emitted from the converter 14 will degrade in energy due to the passage through the material of the converter 14. If the converter 14 is too thin, significant levels of electrons will pass through the converter 14 and will then impact against the target material 12. The preferred thickness of the converter 14, to obtain optimal product isotope performance, depends on the energy of the electron beam, the composition of the converter 14 and the threshold energy of the Giant Resonance region of the converter isotope. An example of an optimal converter is a converter containing approximately six 5 mm thick aggregate tungsten alloy plates separated by cooling ducts for water cooling. The intensity of high energy photons generated in the converter 14 is proportional to the power density (PD) of the electron beam 18 in the converter 14. Therefore, the specific activity of a radioisotope within a volume of target material is 12. it is also proportional to the power density. The power density within the converter 14 can be calculated by the following equation J PD - E X i / V where E is the energy of the electron beam 14, i is the current of the electron beam 18 and v β the volume of the converter 14 through which the electron beam 18 passes. The power density used in this invention is limited by the thermal elimination capacity of the converter 14. In another embodiment illustrated in Figure 3, the converter 14 is composed of two or more plates 22 of high material z, such as tungsten, instead of a single solid converter to allow the best heat removal from the converter 14 and, therefore, higher power densities of the electron beam 18 in the interior. Laß placaa 22 can be manufactured from the same material or from different material. The plates are typically enclosed by outer cover 24, which maintains the geometry of the converter 14 and also retain any optional refrigerant within the converter 14. In a preferred embodiment, the plates 22 have no equal thickness. The eßpeßoreßß of the plates ße vary to equalize the thermal loads on the plates. The thermal load ßobre on each plate is derived from the energy transferred to the plate by electron beam 18 and by generated photons that pass through each plate. Typically, the thermal loads on the plate β distant from the electron accelerator 16 are larger than the thermal loads on the adjacent plates as the electron beam 18 deposits energy on a plate after the electrons are ralsened by previous plates. . In addition, the photons generated in the nearby plates can also deposit energy in subsequent distant plates. Therefore, in a more preferred embodiment, the plates 22 close to the electroneß accelerator 16 ßon are thicker than the plates 22 which are distant from the accelerator of the elstro-nßs 16 to better equalize the generation of heat in each plate 22. The plates 22 and the cooling channels 26 in the converter 14 do not need to be perpendicular to the direction of the electron beam 18. Preferably, the cross-sectional areas of the converter 14, or plates 22, are perpendicular to the beam path. electrons 18. Optionally, means are provided for removing heat from at least one portion of the converter 14. The removal of heat is carried out by typical means, such as radiation, conduction and / or convection. The heat removal means are disposed around and / or through the converter 14. Examples of suitable heat removal means include coolant channels 26 which are disposed within the converter forming the material 14 (eg, where the converting material is a honeycomb), pickling along the surface of the converter 14, etched on the surface of the plates 22 and / or are disposed between the plates 22. Alternatively, the converter 14 includes porous material in the form of glass porous where the refrigerant flows through the interstiaios into the porous glass for heat removal. The heat removal means also include the converter 2 input and the output of the converter 30 which are arranged in the cover 24 of the converter 14. Preferably, the heat generated within the converter 14, or within each plate 27. of the converter 14 , is removed by flow of fluid refrigerant in the converter 14 through the inlet of the converter 28 by means of the refrigerant channel 26 and out of the converter 14 through the outlet of the converter 30. Suitable fluid coolant flow means include yen, for example, one-step fluid flow, natural circulation and forced recirculation. Typically, outside the converter 14, the refrigerant is then cooled, such that it is directed through the heat exchanger 32A. Suitable fluid coolants include liquids, such as water or liquid gallium and gases such as helium.For very high power densities within the converter 14, such as greater than about 3,000 watts / cm 3 or more, it is preferred that the converter 14 is a porous metallic glass which is cooled by fluid refrigerant flowing at high pressure through the pores, or interstices, inside the porous glass. In the embodiment where the converter 14 is tungsten and the target isotope is Mo100, the optimal yield of an isotope product of Mo "ee is obtained when the plates 22 of the converter 14 have a combined thickness slightly smaller than the stopping distance. for an electron in the electron beam 18. When the plates 22 have a combined thickness -n less than the electron stopping distance, the reinforcement 34 is disposed between the converter 14 and the target material 12 to capture the electrons without degrading significantly the energy of the photon beam The materials suitable for the reinforcement 34 include lower Z metals such as co or aluminum.

Typically, the high energy photon beam is directed through the reinforcement 34 at or near the center of the reinforcement 34. Furthermore, the cross-sectional area of the reinforcement 34 is preferably equal to or greater than the width of the high photon beam. IB energy. Optionally, the reinforcement 34 can be cooled by heat-removing means, not shown, such as heat transfer to a cooling medium (eg, water). In still another embodiment illustrated in Figure 4, the converter 14 consists of high molten or liquefied material Z which is recirculated from the inlet of the converter 28, through the converter 14, out of the outlet of the converter 30, through of the heat exchanger 32B, and subsequently back to the input of the converter 28. The heat generated in the converter material 33 inside the converter 14 by the electron beam is then dissipated, or eliminated by suitable means, such as the heat exchanger 32B , while the converter material is outside the converter. Figure 5 illustrates an alternative embodiment of the apparatus of this invention where separate or separable increases of target material 12 are irradiated in series thereby producing a high specific activity of radioisotopes in the first increment and pre-irradiating the second increment to begin the formation of the radioisotope concentration within the increment. The apparatus 100 includes the object set 36, the converter 14 and the electron accelerator 16. The electron beam 18 is generated by the electron accelerator 16 and is directed to the converter 14, where the photon beam 20 including photons is generated. high energy The photon beam 20 extends from the converter 14 to the object assembly 36.

The object assembly 36 includes an object material that is separate or detachable in at least two increments, with the first increment of target material 38 located next to the converter 14 and a second increment of target material 40 located adjacent to the first increment of target material. 38 and separated from the converter 14. The increments of target material 42 are arranged, in series, behind the second increment of target material 40. An increase of an object material is a quantity of target material that is separate or separable from the subject material. within the object set 12. Each increment of subject material, such as the first increment of material object 38, the second increment of material 40 and the additional object material inset 42, contains a charge of a selected isotope within the subject material of the object. Typically, where the selected isotope is contained within a large solid mass, the first increment of target material and the second increment of target material 40 consist of separate sections of target material. The object set 36 also includes the input 44A and the output 46 ?. The inlet 44A is disposed at or near the end of the object assembly 36 remote from the container 14. The inlet 44a is provided as a means for directing the additional objects 21 in the object assembly 36 ßon the distant side of the second increment of the target material 40. The outlet 46A is disposed at or near the end of the object assembly 36 that is proximate to the converter 14. The output 46A is provided as a means for separating an increase in distant target material from its increase in adjacent target material (e.g., separating the first increment of object material 38 of the second material material increase (40) directing the - - increase of distant object material outside the object assembly 36 through the outlet 46A Preferably, the object assembly 36 also includes means, such as a push rod 48, for transporting increments of material object through the object assembly 36 to the converter 14, and then outside the object assembly 36. Alt ernatively, other known means of non-destructively conveying object material can also be used to transport objects or object material through the object assembly 36. Examples of other suitable transport means include, for example, conveyor belts, screws, pistons or pumps . The object assembly 36 may include additionally reflector of photons 50. The photoneß reflector 50 is disposed around a portion of the object assembly 36 around the body. The photon reflector 50 is typically composed of high metaleß Z (e.g. of about 30 or more) such as olibden-98, uranium, tantalum, tungsten, lead and other heavy metals. The photon reflector 50 reflects at least a portion of high energy photoneß that strike the reflecting material (eg, from the photon beam input or scattered from the increments of the serial object material) in the target material within the set Object 36. Optionally, the object assembly 36 includes neutron protection 52 which is disposed at least partially around the photon reflector 38. Neutral protection types include protection with a high hydrogen content such as a plastic or water. , which thermally and / or captures at least a portion of the neutrons emitted during an isotope conversion reaction. The depth of the target material 12 through which the photoneß beam 20 passes within the aggregate of increments of material object in series, disposed within the object set 36 is determined based on the loading of the selected isotopes within each increment, the desired concentration of product isotopes within each increment, the energy level of the photon beam 20 and the irradiation period. Preferably, the target material, contained in the increments of mass material object, has a thickness of aggregate that results in the capture of all of a photon-emitting, high-energy photoness in the beam of photons 20 striking the target material. and na ße scatter out of the object material. For example, where the selected isotope is Mo100 and the desired product is Mo ", the thickness of the aggregate of the objects is typically between about 6 cm to about 10 cm for a photoneß beam produced by a tungsten converter exposed to a beam of electrons of 30-40 Hßv The cross-sectional area of the target material 12 within the object assembly 36 perpendicular to the beam of photons 20 may vary depending on the focal area of the photon beam 20 ßon the increase of target material 38 and the expected extension of the beam of photons 20 along the path of the beam of photons 20 through the target material 12. The cross-sectional area of the target material 12 is normally approximately equal to or greater than the focal area of the beam of photons 20. In an alternative embodiment illustrated in Figure 6, the subject material 12 is in the form of a particle, liquid, suspension or any other synthetic form. e no increase in target material 12 is contained in an individual solid mass. Therefore, the increments of the subject material 12 are not separated, but can be separated. The object assembly 36 - includes means containing target material 12 within the object assembly 36, such as the cylinder 54 that is disposed within the object assembly 36. Suitable container means include containers for solids and / or liquids, which are refractory, such co or titanium. The composition of the material and the structural design of the container should not result in a significant reduction in the energy of the photon beam 20 or a significant increase in the scattering of the photons from the photon beam 20. The cylinder 54 includes diverters 55 which control the flow in cylinder 54 to ensure generally uniform irradiation. The object assembly 36 also includes means for directing increments of target material 12 through the cylinder 54. Medium address bins include the inlet 44B and the outlet 46B. The inlet 44B is disposed at or near the end of the cylinder 54 remote from the converter 14. The outlet 46B is disposed at or near the end of the cylinder 54 which is close to the converter 14. In this embodiment, the target material 12, which is typically in liquid form, in suspension or in particles, is directed in the cylinder 54 through the inlet 44H, moves towards the proximal end of the cylinder 54, and then exits the cylinder 54 through the of exit 46B. The movement (eg, flow) of the target material 12 through the cylinder 54 may be continuous or intermittent. Suitable means for directing the flow of target material 12 include, for example, pumps, pistons and gravity feed. The flow of the target material 12 through the cylinder 54 can be controlled, for example, by a valve or clamp located in a suitable position to interrupt the flow (for example, in the inlet 44B or outlet 46B) and / or by controlling the means of flow direction (for example, starting and stopping a pump).

In another embodiment illustrated in Figure 7, where the increments of the target material 12 are separated, but not solid masses, the object set 36 includes additional means for separately containing each increment of target material 12. Typically, the material object 12 eßtá in a particle form, liquid or in suspension. Suitable container means, such as container 56, include containers that can contain a solid and / or a liquid, where the container is refractory according to the method of this invention. The composition of the material and the structural design of the container should not result in a significant reduction in the energy of the photon beam 20 or a significant increase in the scattering of photons from the photon beam 20. An example of a container material suitable is titanium. In this embodiment, the containers 56 enter the far end of the object assembly 36 through the inlet 44B, ß direct towards the proximal end of the object assembly 36 while being irradiated at the same time by the photoneß beam 20, and then they leave the object set 36 through the exit 6B. Next, the operation of the embodiment of FIG. 2 will be described to produce a high specific activity of a radioisotope. The electron accelerator 16 generates electron beam 18 which is directed to the converter 14. At least a portion of the electron beam electrons 18 ßon captured in a reaction (electron?) By the high Z material of the converter 14 to generate photons , including high energy photons in the photon beam 20. Typically, most of the electrons are captured and most of the photons pass through the converter 14. Typically, the electron accelerator 16 generates an electron beam 18 with an electron beam. average energy level of about 25 MeV or more, preferably between about 30 MeV and about 50 MßV. The total power of the electron beam 18 is limited by the design of the electron accelerator 16 and by the design, thickness and heat removal capacity of the converter 14. If the beam energy is too low, there will not be enough photons in the beam. Giant Resonance region to produce a specific high activity of the radioisotope and the electron range in the converter 14 will be so short that it will make it very difficult to remove heat from the converter 14. If the beam energy is too high, many photons will have energies per above the optimum range, the direct heating of the electrons of the target material 12 will be a problem and the electron accelerator 16 will be relatively expensive. In addition, increased production of impurities, such as niobium, may result for other isotopic conversion reactions. The photon beam 20 is directed from the converter 14 and focused on the target material 12. The target material 12 is typically placed in close proximity to the converter 14 and in alignment with the output of the photon beam 20 from the converter 14. it can leave a sufficient distance between the converter 14 and the target material 12 to attenuate the electromagnetic fields to deflect the electron beam 18 or to interpose material to modify the photoneß spectrum of the beam of photons 20, but this distance is minimized with the purpose of using a beam of photons at high intensity. If attenuation is not required, the target material 12 may be in contact with the converter 14. Within the target material 12, at least a portion of the high energy photons of the beam of photons 20 react with the selected isotope to form a - concentration of a radioisotope within the subject material by an isotopic conversion reaction, such as by the reaction (y., ti). (?, 2n), (?, P) or (?, Pn). Preferably, a significant number of photons in the beam of photons 20 ßon high energy photons having an energy level falling within the range of energy levels included in the Giant Resonance region of the cross section with respect to the curve of energy for the desired isotope conversion reaction. More preferably, a significant portion of photons in the photoneß 20 beam have energy levels approximately equal to the peak energy level of the Giant Resonance region. For heavier materials, the energy levels that correspond to the Giant Resonance region are relatively lower, while for lighter materials, the energy levels are relatively higher. Preferably, the energy of the array of lights 18 should be about 2 haß about 3 times the peak energy level of the Giant Resonance region of the selected isotope. For example, in the isotope conversion (?, N) of Mo100 in Mo ", it is preferred that at least a significant portion of the photons in the photon beam 20 have energy levels that fall within the Giant Resonance region for this reaction, specifically between the threshold energy level of approximately 10 MeV and the high energy limit of approximately 19 MeV.More preferably, the energy levels of photons are approximately 15 MeV, which is the peak of the Giant Resonance region. Electron beam energy for this isotopic conversion is typically between about 25 MßV haß about 50 MeV, with a preferred energy range of about 35 MeV to about 40 MeV.The energy level of a photon generated directly depends on the energy level of the photon. beam of electrons 18, the peak energy level of photons being generated equal to approximately the energy level of the electron beam trones 18, Typically, most of the photons generated have energy levels less than half the peak energy. Therefore, the energy level of at least a portion of the electrons in the electron beam 18 at a minimum must be equal to the energy level (minimum) threshold required to produce the desired isotopic conversion reaction between a generated photon and the selective isotope. Preferably, the energy level of the electron beam 18 is within or above the resonance region Giant of the desired isotopic conversion reaction. In a preferred embodiment, where the selected isotope is olybdenum-ioo (Mo100), which is isotopically converted to molybdenum-99 (Mo99), which then decays to the desired descending product technet-99 (Te99), the beam of photons produced includes radiation? at an energy level of approximately 8 Mev or more. Preferably, a substantial amount of radiation? produced is at energy levels between approximately 8 MeV and approximately 16 MeV. The attainment of an average specific activity of Mo "of about 1.0 ci / grams of Mo in solid molybdenum requires a relatively high energy density in the converter 14. Specifically, in the equation of saturation activity, the product fR must have a value greater than approximately 2.0 x 10"8 sec." 1. This value of R is difficult to achieve due to technical limitations on the energy density of the electron beam and the removal of heat from the converter. Thus, the volume at which the average specific activity of 1.0 Ci / gram can be maintained is typically limited to volumes of target material having relatively small thicknesses.In the determination of the maximum volume of the subject matter, the cross-sectional area of the The object material should normally be equal to or less than the focal area of the photon beam 20. Therefore, the volume of the subject material is often limited to a few centimeters. cubic meters to less. For example, for a natural molybdenum object containing approximately 10% Mo100, an electron beam of 35 MeV of a 1.0 milliamp current focused on an object object of 1.0 cm radius, with an optimal converter, produces an average specific activity of about 1.0 Ci / gram for a thickness of the target material of approximately 0.5 s. The power density in the active regions of the converter should be approximately 35,000 watts / cm3. Higher specific activities can be achieved by isotopic enrichment of the target material. An object material enriched up to 100% Mo100 would produce a specific activity in excess of 10 Ci / grams up to a material thickness of approximately 0.5 c for the same conditions. It is possible to obtain thicknesses of the molybdenum object greater than 0.5 cm, which have an average specific activity of at least 1.0 Ci / grams, varying the isotopic enrichment of Mo100 in the target material and / or varying the energy levels of photoneß in the photon beam, provided that the product value fR is at least 2.2 x 10"ß sec.-1 For a coarse object, the activity produced in the first 0.5 cm depth of the object is only 28% of the total generated in the object, however, the other 72% of the desired isotope product is diluted with non-converted object material of low commercial interest, on the other hand, the irradiation of a single object of 0, 5 cm thick or less results in loss of photon energy The thick object portion with minus of threshold activity represents a potentially valuable resource, unusable if it is not improved.Therefore, providing an object increases as in Figure 5 , only that p The object that has been irradiated to an average specific activity above a given threshold value is removed for processing. Additional portions of the object, irradiated less than the threshold value, can be sequentially irradiated up to the threshold value in this manner to optimize the combination of specific activity of individual target elements and the total radioisotope production rate. Preferably, each object increase is 0.5 cm in thickness or less. At least within the first increment of target material 38 and the second increment of target material 40, a portion of the high energy photons of the photon beam 20 reacts with the selected isotope to form a high specific activity in the first increment of target material 38 and the second increment of pre-irradiated object material 40, and possibly in increments of additional target material 42, to begin the formation of the specific activity of the radioisotope within these increments. This method also includes moving the first increment of material object 38 and the second increment of the object material 40 towards the exit 6A, and closer to the converter 14, by the action of the push bar 48 applying force to the distant side of the second increment of material object 40 through increments of additional object material 42. Alternatively, the objects can be moved by any automatic or non-automatic means. In addition, the movement of objects can be continuous, concurrent, sequential or staggered. Finally, the first increment of the target material 38 is pushed through the outlet 46A and eß withdrawn out of the object assembly 36. The second increment of additional target material 40 is pushed to the original position of the first increment of target material 38, after which the beam of photons 20 is then focused on the second increment of target material 40 to complete the production of a high specific activity in the interior. The additional object material increments 42 can add serially subtracted from the second increment of target material 40 through the input 44A. In this method, the ratio of the eispecific activity of the radioisotope product in each increment to the amount of isotope product removed per unit time can be optimized depending on the need for a high rate of radioisotope product discharge or a high specific activity of radioisotope product. The concentration of the radioisotope product generated by the isotopic conversion reaction is dependent on the intensity of the high energy photons in the 2D photon beam, the volume of irradiated target material 12, the radioactive sera of the isotope product, and the amount of material object 12 that is irradiated. The intensity of photons is only partially dependent on the level of the electron beam current 18 for the same focal area, with higher currents generating more high energy photons per unit of time, which are then directed into the target material to react with isotope more selected per unit of time. The volume of target material 12 irradiated by photon beam 20 depends on the focal area of the photon beam 20, on the target material 12 and on the amount of scattering of the photoneß within the target material. Typically, the focal area of the photon beam 20 is a function of the high energy photon emission angle from the converter 14. Higher energy photons, which have an energy level that falls within the Giant Resonance region for the desired isotopic conversion reaction, are emitted in a narrow cone whose axis is aligned along the direction of an extended axis of the electron beam 19- The intensity of the photons of higher energy, which are emitted at an angle with respect to The cone axis decreases rapidly as the angle increases from the cone. For example, at an angle of approximately 5 degrees from the axis of the cone, the intensity of peak photons is approximately one fifth of the intensity of the peak photons emitted over the center of the cone. In addition, the intensity of the highest energy photons, which have approximately half a peak of photon energy, is less about two orders of magnitude at an angle of 25 degrees from the axis of the cone greater than the intensity along the axis of the coho Therefore, the ha2 of photons 20 reaches the highest point strongly in the forward direction along an extended axis of the electron beam IB. Therefore, the focal area of the photon beam 20 is determined by the focal area of the electron beam 18 on the converter 14. With increasing energies of the electron beam, the focal area of the beam of photons 20 is smaller with a minimum area having the size of the focal area of the electron beam 18 on the converter 14. Therefore, with increasing energies of the photon beam, the area of the photon beam is further limited. the transverse ssccidn of the object material 12.

To optimize the specific activity of the radioisotope product in each increment of target material, when removed from the target set, the focal width of the photon beam 20 is minimized to produce a higher concentration of radioisotope product near the center of the first increment of material object 38 with lower concentrations near the edges of the object. As the photon beam 20 travels through the target material and propagates, such as by scattering, the concentration εe reduces near the center of the target material and increases closer to the edges of the target material 12. Thus, after passing through the first increment of target material 38, the beam of photons 20 will pre-irradiate the second insor-ment of target material 40 and the additional object material increases 42 to produce lower levels of isotope product through these incremental objects. ntals (for example, near the centers and at the edges). Preferably, the focal area of the electron beam 18 is minimized to achieve higher concentrations of isotope product near the centers of the objßtoß. The lower limit on the electron beam focal area 18 on the converter 14 is dependent on the heat dissipation capacity of the converter 14. The electron beam focal area 18 should not be so small as to create a high power density in the affected portion of the converter 14 leading to localized melting, destruction and / or loss of function of the converter material. The amount of. time that an object is radiated may depend on the speed of movement of the increments of material object in series, while it is in the beam of photons 20, to the output 46. The increments of material object ßon entered, moved and charge-two to a speed such that the combination of the thickness of segment and velocity of discharge provides a product of the desired specific activity of isotope product. A high discharge velocity of objects will result in the recovery of a larger fraction of the generated radioisotope, but the specific activity of the discharged material will not be as high as it would be, with all factorels remaining unchanged at a low discharge rate. of the increase of object material. Figure 8 further illustrates the calculated effect on production speed and product specific activity by varying the flow velocity of target material within the photosene beam. Figure 8 is based on an electron beam energy of 35 MeV, an electron beam current of 1.10 ma, and cylindrical object segments of Mo100 that are 2.0 cm in radius and 0.5 c in thickness. The method of this invention can also be used to produce stable isotope concentrations. The invention will now be described further and specifically by the following examples.

Example 1 Production of Mo "by Mo100 Photonuclear Transmutation A molybdenum cylinder (4 inches in diameter), which has a natural isotopic abundance, ss cut into planes perpendicular to the length of the cylinder in folio and molybdenum tiles. By a separate tile, each sheet had a thickness of approximately 0.01 inch (0.25 mm), while each tile had a thickness between approximately 0.75 inches and approximately 1.5 inches. specific activity of Mo "at different points within the Thicken aggregate of the folios and tiles. In the object, the six folio / aldose units were placed in series, with the tiles closest to the beam source? which has narrower widths. Each folio or tile was touching the folio or adjacent tile. A tungsten tile 4.3 m thick, 2 inches in diameter, used as a converter plate, was placed between the source of the beam? and the object. The converter was also touching the first page of the object. An electron beam of 28 MeV, which has a current of 1.84 icroampe ioß. { μa) and a beam width of 1.5 cm, was directed substantially perpendicular to the side of the converter close to the source of the electron beam. A beam? Was generated, subsegmentally perpendicular to the distant side of the converter. The beam? It was directed inside the object. The object exp exposed for 4.6 hours to the beam? generated. Twenty-six hours after radiation, the total activity of technetium-99 (Te99) and the half-width of the Giant Resonance beam were then measured for each folio using a calibrated intrinsic germ crystal, measuring the amount of e that they have. a specific energy decay of Te99 (for example, 140,1 JceV) that were emitted at the center point of each folio, and measuring the radial distance from the center of the folio on which the activity is halved to show the beam scattering. The results of the measurements of the activity of the central point for the sequential sheets are given in Figure 9. As shown here, the activity of Te99 measured at the center point of the first page, located on the ß surface of the object ( depth -0), was 30.3 microeurie (μCi). Point activities Central to deeper folioß in the object declined nonlinearly as a function of their relative depths within the object. This shows that the intensity of the photon flux in the energy range Giant Resonance decreases rapidly with the distance in the target material. The measurements of the emi-width for the six folios ße cuencia cuencia cuencia cuencia cuencia cuencia proporcionan proporcionan proporcionan proporcionan proporcionan proporcionan proporcionan proporcionan proporcionan also provide in Figure 9. The half-width of the first folio (depth = 0) was 1.5 c. The smallest measured widths for folioß in the object showed some increase with depth, for example the semi-width for a folio at a depth of approximately 6 cm was approximately 3.3 o. These measurements of the ßmi-widths show that the radiation beam?, Through the propagation of the? -dispersion within the object, remained sufficiently collimated to support the production of Mo99 through a cross-section of the object without a loss significant radiation energy? from the object material.

EQUIVALENTS Those skilled in the art will recognize, or will be able to ascertain, using routine experimentation, many equivalents to specific embodiments of the invention specifically described herein, it is intended that such equivalents be included within the framework of the following claims.

Claims

The claimed invention is: 1. Apparatus for producing a specific high activity of molybdenum-99 from an olybdenum-ioo object, by means of an isotopic conversion reaction, comprising: a) an electron accelerator, b) a converter to convert an electron beam into a beam of high intensity high energy photons; and c) a molybdenum-ioo object.
2. The apparatus of claim 1, wherein the converter includes a) at least two separate converter plates, arranged in parallel, where the convolver plates have different thicknesses, and b) refrigerant channels disposed between adjacent converter plates for cooling The converter plates to eliminate heat generated.
3. Apparatus of claim 1, wherein the intensity of the photoneß beam is at least 50 microamp-rivers / cm2.
4. Apparatus of claim 1, wherein f-R > 2.2 x 10"° sec» '-? where f is the molybdenum-100 isotopic fraction in the molybdenum-100 object, and R is the path length of the photoneys per unit volume per unit of energy, weighted by the cross section of the integrated photoneutron over energy.
The apparatus of claim 4, wherein the average specific activity of molybdenum-99 in the molybdenum-100 object is at least 1.0 curie / gram.
6. Apparatus of claim 5, wherein the molybdenum-100 e-molybdenum object having a natural abundance of molybdenum-ioo, said object having a thickness of 0.5 cm or less.
The apparatus of claim 5, wherein the molybdenum-100 eß-molybdenum-enriched object having a thickness of 7.5 cm or less.
8. Apparatus of claim 4, wherein: a) the molybdenum-100 molded molybdenum-100 object having a thickness of 0.5 cm or less, and b) the average molybdenum-99 specific activity in said object TS at least 10.0 curies / gram.
9. Apparatus for sequentially producing a concentration of at least one isotope product within increments in series of target material, by means of an isotope conversion reaction, comprising: a) a beam source for generating a high-energy, high-energy photon beam density, and b) an object set containing increments of target material, where said increments include a isotopic islet that becomes the isotope product with irradiation by the photon beam, with an increase of the target material close to the beam source being separable of the object set with isotope product, leaving at the same time material object for additional irradiation by the photon beam.
10. Apparatus of claim 9, wherein the intensity of the photoneß beam is at least 50 microampe- 11.
Apparatus of claim 9, wherein f-R 2.2 x? o ~ B sec. "1 where f is the molybdenum-ioo isotopic fraction in the object of mollbdßno-100, and R is the path length of the photons per unit volume per unit of energy, weighted by the cross-section of photoneutron integrated into the energy.
The apparatus of claim 11, further comprising a means for moving increments of target material, in series, towards the photoneß beam source as the next object increase, containing isotope product, is eliminated from the object set .
The apparatus of claim 12 further comprising a means for inserting an increment of additional target material within the distant target array with respect to the photon beam generating means.
14. Apparatus of claim 11, wherein the subject material is in a solid mass.
15. Apparatus of claim 11, wherein the subject material is in a form selected from the group consisting of a liquid, suspension or particles.
16. Apparatus of claim 15, wherein each increment of the target material has separate contents within a container.
17. Apparatus of claim 11, wherein the beam source includes: a) an electron accelerator, and b) a converter to convert an electron beam into the high energy photon beam.
18. Apparatus of claim 17, wherein the converter includes at least one separate inverter plates disposed within the converter, where the converter plates have different thicknesses.
The apparatus of claim 18, further comprising means for cooling the converter, wherein said cooling means includes coolant channels disposed between adjacent converter plates.
20. Apparatus for sequentially producing a concentration of at least one iStope product within objects in series, by an isotopic conversion reaction, comprising: a) an electron accelerator, b) a converter for converting an electron beam into a beam of high-density high-energy photons, c) at least two objects for the high-energy photoneß beam, where said objects are located in series with respect to said photon beam, d) a selected isotope that is contained in each object , and e) means to move the objects, in series, towards the converter.
21. The apparatus of claim 20, wherein the intensity of the photoneß beam at least 50 microamp-
22, Apparatus of claim 20, wherein where f is the isotope moiety of molybdenum loo in the molybdenum-100 object, and R is the path length of photoneß per unit volume per unit of energy, weighted by the transverse section of the integrated photonutrient ßon energy.
23. Apparatus for high power density conversion of a high energy electron beam of an electron accelerator into a high energy photon beam, comprising: a) a converter containing at least two separate converter plates, arranged in parallel, where the converter plates have different thicknesses, and b) coolant channels disposed between adjacent converter plates, to cool the converter plates to remove heat generated by the electron beam.
24, A method for producing a high epspelfish activity of molybdenum-99 by isotopic conversion of mslibdene-1 0 into an object, comprising the step of exposing the object to a high density high energy photon beam, thus forming a specific high activity of molybdenum-99 within the object.
25. The method of claim 21, wherein: a) the thickness of the target material is about 7.5 centimeters, or less, and b) the high energy photon beam is generated by an electron beam incident on a tungsten converter , where the power density of the electron beam inside the converter is approximately 35,000 watt / cm3.
26. The method of claim 25, wherein: a) the natural molybdenum object material, and b) the specific activity of molybdenum-99 in the subject material is at menoßi, or curies / gram.
The method of claim 25, wherein: a) the target material is enriched molybdenum, and b) the specific activity of molybdenum-99 in the subject material is at least 10.0 curies / gram.
28. The method of claim 24, wherein the intensity of the photon beam is at least 50 miaroampe-rios / cm2.
29. The method of claim 24, wherein: a) the object is molybdenum, and b) r R > 2.2 x 10"s sec." 1, where f is the isotopic function of raolibdene-100 in the molybdenum object, and R is the path length of the photons per unit volume per unit of energy, weighted by the cross-section of the integrated photonutron ßon energy.
The method of claim 29, wherein a) the molybdenum object is molybdenum having a natural abundance of molybdenum 100, said object having a thickness of 0.5 cm or less, and b) the average specific activity of molybdenum-99 in said object is 1.0 curie / gram or more.
31. The method of claim 29, wherein the molybdenum object is molybdenum-enriched.
32. The method of claim 31, wherein: a) the thickness of the molybdenum object is 7.5 cm or less, and b) the average specific activity of molybpt-mo-99 in said object is 1.0 curie / gram or more .
33. The method of claim 29, wherein: a) the thickness of the molybdenum object is 0.5 cm or less, and b) the specific activity of molybdenum-99 in said object is 10.0 curies / gram or more.
34. The method of claim 24, wherein the high energy photoneß beam is generated by an electron beam incident on a converter.
35. The method of claim 34, wherein the converter includes at least two separate converter plates, disposed within the converter having different thicknesses.
36. The method of claim 35, further including the step of cooling the converter.
37, Method for sequentially producing a concentration of at least one isotope product within serial increments of an object material, by means of an isotope conversion reaction, comprising the steps of a) directing a high density high energy photon beam from a photon beam source through increments of target material, where the increments are in serious with respect to the photon beam, by which an isotope of object contained within the increments eß exposed to said photon beam, thus forming the product isotope within increments of target material, b) eliminating a first increment of target material outside the photon beam, where the first increment of target material is the near increase with respect to the source of the photon beam , and c) advancing the material material increments in seríes towards the source of the photon beam, 38, method of claim 37, wherein: a) The object is molybdenum, and b) f R = 2.2 X 10 ~ ß sec. -1, where f is the isotope function of molybdenum-100 in the molybdenum object, and R is the path length of the photons per unit volume per unit of energy, weighted by the cross section of the integrated photoneutron ßobre energy. 39. The method of claim 37, wherein the intensity of the photon beam is at least 50 icroampe-40, a composition comprising -nolibone-99, wherein molybdenum-99 has a high specific activity, produced by exposing molybdenum-ioo to a beam of high energy photons. 41. A composition of claim 40, wherein the specific activity is at least about 1.0 curie / gram. 42. A composition of claim 41, wherein the specific activity is at least about 10.0 curies / gram.