RU2716280C1 - Porous low density iridium - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention relates to a radiation source. Radiation source contains porous or microporous iridium.

EFFECT: density of active insert is in range of 30–85 % relative to pure iridium with 100-percent density.

20 cl, 10 dwg

Description

BACKGROUND OF THE INVENTION

This application is a partial continuation of PCT / US2017 / 033508, entitled "Low Density Spherical Iridium", filed May 19, 2017, which claims priority according to 119 (e) Section 35 of the Code of the US laws on provisional application for US patent No. 62 / 378,881, filed August 24, 2016, and by provisional patent application US No. 62 / 340,777, filed May 24, 2016, the contents of which are hereby incorporated by reference for all purposes and in their entirety.

FIELD OF THE INVENTION

The invention relates to a gamma radiation source, usually containing iridium microspheres or alloys, low density iridium compounds or composites and their encapsulated porous variants, and methods for their production.

State of the art

Various types of radiation sources for medical, industrial and other processes are well known in the prior art. However, the search for further improvements continues, in particular with regard to the manufacturing economy and product characteristics.

A method of manufacturing a gamma radiation source in the prior art is disclosed in PCT / NL2004 / 000401 (also published as WO 2004109716 A2) in the Bakker class. This method includes the steps of neutron irradiation of iridium or cobalt disks and stacking the disks with columns to form a cylinder. Similarly, PCT / US2015 / 029806 (also published as WO 2015175326 Al) under the name "Device and Method for Enhanced Iridum Gamma Radiation Sources"; German patent document DE 19824689 Cl with the translated title "Iridium-Containing Molding useful as a Gamma Radiation Source e.g., For Weld Seam Radiography and Cancer Treatment"; and document PCT / US2015 / 029806 entitled "Device and Method for Enhanced Iridium Gamma Radiation Sources."

[0005] Additionally, the prior art relating to the production of metal spheres contains US patent No. 2,394,727 entitled "Method for Making Small Metallic Spheres", issued February 12, 1946, by Taylor, and information on this can be found on the following sites:

http://www.orau.org/ptp/collection/sources/3mdisk.htm; and

http://www.nrc.gov/docs/ML0415/ML041550720.pdf.

Methods for producing porous iridium can be found in The Metallurgical Integrity of the Frit Vent Assembly Diffusion Bond, by G. B. Ulrich, June 1994, Y / DV-1321, Oak Ridge Y-12 Plant, Martin Marietta Energy Systems, Inc.

OBJECTS AND SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to provide improvements to radioactive sources used for medical and industrial applications. Embodiments of the invention can solve many of the following problems compared to the previous level: reduced manufacturing costs, reduced focal sizes (in particular, in relation to sources with natural iridium disks with cylindrical geometry), increased activation yield, increased output (more Curie output / mg, due to the reduced density), a softer emission spectrum due to the reduced density (i.e., significantly lower energy emission) and almost spherical or quasispherical geometry (resulting in resulting in improved image quality), but generally comprising planar lateral sides around its circumference to avoid excessively sharp tangential component of the cover. Additionally, in embodiments of this invention, powder handling may be reduced or eliminated.

It is contemplated that embodiments of the present invention can increase the output efficiency of iridium-192, probably in the range of 11-17 percent, in particular if the sources can be manufactured using iridium with a 50-65 percent density with spherical geometry. This can additionally lead to a decrease in the content of iridium-192 in the source by 11-17 percent and a decrease in its annual consumption. Additionally, a softer output spectrum in combination with an almost spherical focal size can result in image quality approaching that of cylindrical sources with enriched iridium-192. Additionally, it is assumed that this could potentially lead to an activation yield increased by 7–11 percent, leading to a total efficiency gain of 18–28 percent.

Alternatively, flat-sided disks of low density iridium or compound, alloy, composite, or a porous variant thereof can be activated to obtain disks containing iridium-192. After activation, the disks can be stacked on top of each other to form a cylinder, and in this form can be used to make traditional cylindrical sources with focal geometry, or they can be compressed, compressed, or deformed after activation to create more spherical or quasispherical focal geometries.

Discs made of low density iridium or compound, alloy, composite, or a porous version thereof, having curved, domed, or otherwise shaped ends can be made so as to be thicker in the middle than at the periphery. Some practical examples are shown in FIG. 4. They can be activated to receive disks containing iridium-192. After activation, such disks can be stacked in a column and then compressed, compressed, or deformed to obtain spherical or quasispherical focal geometries. Discs that are molded in this way can easily be converted to spherical or quasispherical focal geometry by compression, compression, or deformation, as shown in FIG. 5, which gives manufacturing advantages.

The use of spherical or quasispherical iridium-192 low density or compound, alloy, composite or its porous version can achieve output and gains in overall efficiency similar to those achieved with ring iridium, but without disadvantages in terms of image quality or focal size inherent in ring sources laid in a cylindrical configuration.

Alternatively, low density spherical or quasispherical iridium-192 or a compound, alloy, composite, or porous version thereof can also be made using random (or almost random) stacked microspheres in a spherical or quasispherical cavity of the source. Porous microgranules can be compressed, compressed or deformed to obtain spherical or quasispherical focal geometries.

It should be noted that the pore size within the porous iridium or compound, alloy, composite, or porous variant thereof can vary and range from sub-micrometric sizes (sometimes referred to as microporosity) to approximately sub-millimeter sizes (sometimes referred to as porosity).

Porous iridium or compound, alloy, composite or their porous version can be produced in several different ways. One way is to heat the microspheres or microbeads at a temperature usually above 1000 ^° C, but more often above 1300 ° C for a time long enough to initiate long-term binding and fusion of them at the contact points.

Microporous iridium or compound, alloy, composite, or a porous version thereof can also be made by partially sintering finely ground powder at a temperature usually above 1000 ° C, but more often above 1300 ° C for a time long enough to initiate long-term bonding between particles and fusing them at contact points, but not so long as to lead to a process of complete compaction. Such a microporous product will have a density of less than one hundredth of a percent of the theoretical density of iridium due to bubbles, pockets or channels formed inside the iridium or alloy, compound or composite iridium.

The isotopically enriched iridium-191 powder can be used as a raw material for the manufacture of porous low-density iridium or compound, alloy, composite, or a porous variant thereof. This form of iridium can be produced by isotopic enrichment in a gas centrifuge of gaseous natural isotopically excess iridium hexafluoride or iridium tetrafluoride, reducing the amount of enriched process gases to obtain a highly amorphous form of elemental enriched iridium-191, often referred to as "black" iridium-black. Iridium obtained through such processes loses crystallinity, has a very small average particle size (usually subnanometric), has a very high internal surface area and is porous.

It has been found that such an amorphous (or substantially amorphous) iridium powder can be cold compressed to form compacts having a 30-50 percent density from the theoretical density of iridium. They can be partially densified, bonded and fused by sintering at an unexpectedly low temperature, well below the temperature typical of crystalline materials. High surface energy due to the large internal surface area and high energy of the amorphous crystal lattice can trigger compaction, crystallization, grain growth and fusion between particles at lower than expected temperatures.

It has been found that a partial compaction of a substantially amorphous pure iridium powder, such as material produced in a gas enrichment process using a centrifuge, can be achieved at temperatures below 1300 ° C. Moreover, the addition of certain sintering additives that are non-activating, weakly activating, or co-activating (that is, producing minimally interfering gamma radiation) and have a lower melting point compared to iridium, can form alloys, intermetallic compounds, or combinations thereof with iridium . Such additives include, but are not limited to, aluminum, vanadium, boron-11, silicon, phosphorus, sulfur, carbon, beryllium, titanium, nickel, tungsten or their alloys and intermetallic compounds that further lower the sintering temperature and can enhance the partial compaction process and / or to improve ductility in order to achieve excellent bonding with improved mechanical properties at a lower temperature and less time.

The finely ground amorphous or substantially amorphous iridium powder having a natural isotopic composition can also be partially densified and bonded in a similar manner.

Partially sealed, bonded, porous, low-density iridium components can be shaped into discs, cylinders, wire, granules or microspheres. They can be stacked on top of each other or otherwise assembled together and then compressed, compacted or mechanically deformed to create a spherical or quasispherical focal geometry that is optimal both for the production of x-ray sources and for the quality of the x-ray image.

The focal size of spherical or quasispherical iridium-192 low density can usually be no larger than the diagonal of the traditional geometry of a cylindrical source with disks stacked on top of each other with a 100 percent density.

The resulting sources can emit gamma rays with less energy, resulting in improved image contrast and resolution.

Brief Description of the Drawings

Additional objectives and advantages of the invention will become apparent from the following description and accompanying drawings, in which:

FIG. 1 is a flowchart of a typical embodiment of a manufacturing process in accordance with the proposed invention with the proposed variations.

FIG. 2 is a calculated spectral redundancy of gamma energy as a function of iridium density in accordance with an embodiment of the invention.

FIG. 3 - volumetric ratios of cylindrical stackings depending on spheres having the same focal size, and a typical increase in emissivity and the result of irradiation achieved using an embodiment of the proposed invention.

FIG. 4A is a side view of the design options of the disks corresponding to the proposed invention.

FIG. 4B is a side view of a prior art disc structure.

FIG. 5A is a side view of a preferred embodiment of a disc assembly before being compressed, squeezed, or deformed to produce a sphere or quasisphere.

FIG. 5B is a side view of a preferred embodiment of a disc assembly after compression, compression, or deformation, thereby producing a sphere or quasisphere.

FIG. 6 - assembly of disks without compression, squeezing or deformation, installed in spherical / quasispherical geometry, using end sections in the form of half-disks.

FIG. 7 is a cross-sectional view of a disk containing bonded microspheres and binders.

FIG. 8A and 8B are shyloid and void forms, respectively, as defined by the applicants.

FIG. 9 is a view of an embodiment of a disc in accordance with the invention.

FIG. 10 is a cross-sectional view along the plane 10-10 of FIG. nine.

Detailed Description of Preferred Embodiments

Turning now to the detailed drawings, where in FIG. 1 shows a general diagram of a typical process 100 underlying the proposed invention. Natural iridium is provided at steps 102, 102 'or 102ʺ. Natural iridium at step 102 is provided directly to step 110 of manufacturing discs or microgranules. Natural iridium in step 102 'forms an alloy or is provided with sintered additives in step 108 and then transferred to step 110 of manufacturing disks or microgranules. Natural iridium in step 102 ″ is fed to a gas enrichment step 104 using a centrifuge, enriched iridium step 106 and, alternatively, is fused or sintered by additives in step 108 before being transferred to step 110 for manufacturing disks or microgranules. Microbeads or beads in many embodiments typically have a diameter of 0.25-0.60 mm, preferably 0.40 mm. Alternatively, microcylinders with a diameter of 0.20-0.50 mm, preferably 0.30 mm, can be used in many embodiments. These microcylinders can be formed by cutting off the iridium wire of the desired diameter before or after activation.

Iridium in the form of disks or microgranules from step 110, regardless of origin (102, 102 'or 102ʺ), is alternatively fed to step 112 for partial compaction, for example, by sintering or some other technology. Iridium is hereinafter optionally supplied to step 114 of laser surface compaction and then to activation and measurement steps 116, 118, respectively. As shown in the upper branch of the circuit, the iridium from the measurement step 118 may be loaded into the capsule at step 120, alternatively, compressed, compacted, or deformed to be loaded into the capsule at step 122 and then the source is brewed at step 128. Alternatively, as shown in the lower branch of the circuit, the iridium from the measurement step 118 may first be stacked in step 124 and compressed, compacted or deformed before loading into the capsule in step 126 (similar to step 120), and then the source is brewed in step 128.

In FIG. 2 is a typical gamma-energy spectrum showing the calculated spectral redundancies as a function of iridium density for reduced density iridium in accordance with the type of processes summarized in FIG. 1.

Similarly, in FIG. 3, you can see a typical increase in emissivity and radiation yield compared to the 100 percent iridium density in the prior art and a proportionally higher emission at lower energies. Note, for example, that a sphere with a 53 percent density of a given diameter "d" (such as, but not limited to 3.82 mm) has 85 percent more volume than a straight cylinder with a 100 percent density with a diagonal "d" "3.82 mm. Such a straight cylinder has a height and diameter of 2.7 mm (3.82 mm divided by the square root of 2.0). These sizes are completely typical for the active sizes of standard cylindrical sources with iridium-192, having 100 Curie and containing natural iridium-192. However, the sphere or quasisphere used for reference has the same focal size and an estimated eleven to seventeen percent higher yield than the straight cylinder (note that the relative increase in output depends on the direction of emission and is measured in axial, radial, 4π or other directions). Therefore, low density spherical or quasispherical iridium-192 is expected to increase the source output efficiency in the range of about 11-17 percent. With the expected increase in reactor yield in the range of 7-11 percent, it is assumed that the combined increase in reactor yield and output efficiency will be about 18-28 percent.

In FIG. 4A shows examples of compressible, sealed, or deformable disk profiles that can be implemented in accordance with the type of processes summarized in FIG. 1. In contrast to that shown in FIG. 4B, a prior art design in which a conventional flat disc profile is created by a hatched cylindrical shape, disc 10 in FIG. 4A is approximated by rotating the ellipse around a minor axis (see also Figs. 9 and 10 with a somewhat similar shape). Alternative disk profiles are selected from the various profiles shown 11 (a flat central region in cross section with sharp directed edges at the periphery), 12 (a flat central region in cross section with blunt directed edges at the periphery), 13 (a flat narrow central region in cross section with blunt directed edges on the periphery), 14 (a flat narrow central region in cross section with slightly rounded edges on the periphery), 15 (disk or ellipsoid shape with partially rounded edges on periphery), 16 (thinned disk or ellipsoid shape with partially rounded edges on the periphery), 17 (disk or ellipsoid shape with partially rounded edges on the periphery and a central portion 18 that extends upward in the orientation shown in Fig. 4A, so that to ensure the alignment characteristic of the stacked discs, so that a plurality of stacked discs 17 can interlock with each other in series). These discs usually have a thickness of 0.1-0.7 mm and, as a rule, do not exceed 0.75 mm in thickness.

In FIG. 5A shows a pack of disks 10 (or, alternatively, any of 11-17) prepared for compression, compaction, or deformation (see steps 122 and 124 in FIG. 1) to form a spherical or hemispherical source 90 shown in FIG. 5B.

An alternative embodiment of the radiation source 90 shown in FIG. 6, contains iridium-191 in the form of a metal, alloy, compound, composite or porous variant with the above optimal range of iridium density in the active insert (selected from 30-85 percent, 40-70 percent or 50-65 percent), in which 22, 24 half-disk, semi-ellipsoid or with rounded edges are located at each end of the stack of flat discs 26. Disks 26 can optimally have a thickness of approximately 0.25 mm or higher to a maximum of 0.5 mm to maximize activation efficiency and minimize self-shielding Maintenance of neutrons during the activation time. The curved end portions 22, 24 may optimally have a thickness of about 0.5 mm in the center or up to a maximum of 0.75 mm in the center to maximize activation efficiency and minimize self-shielding from neutrons during activation. This forms a cylinder with curved (or rounded) edges (similar to a dome-shaped void or schiltoid shape).

A shiltoid, the name of which was invented by the applicants and as shown in FIG. 8A is formed by rotating an octagon around its vertical axis. Similarly, the name of the invented by the applicants and as shown in FIG. 8B is formed by inscribing the octagon into a circle, preserving the alternating walls of the octagon forming the apex, bottom, and vertical sides, while maintaining circular sections for the remaining sections, and subsequently rotating the resulting shape around its vertical axis. Although the geometry shown in FIG. 6 is less spherical in shape than the preferred form; it may have other advantages. It may be possible to perform conventional disk irradiations using the traditional geometry of the irradiation target.

An additional alternative comprises the use of porous iridium, possibly containing an non-activated, low-activated or co-activated sintering additive or binder, such as, but not limited to, aluminum, vanadium, boron-10, silicon, phosphorus, sulfur, carbon, beryllium, titanium , nickel, tungsten or any of their alloys, such as DOP26 alloy and their intermetallic compounds. Additionally, some products, such as platinum-192 and osmium-192, can be created in situ as the β-decay product of iridium-192. Depending on the specific proportions of the elements or physical conditions of the composite, compound or alloy, varying degrees of ductility and adhesion can be achieved. Reduced ductility configurations can be brittle, resulting in a kink due to stress. Higher ductility configurations may allow the composite, compound or alloy to contract, compact, or deform to the desired shape, such as, for example, but not limited to, a sphere or quasisphere.

Additionally, under certain circumstances, grinding with sufficient physical impact may allow iridium and additives such as aluminum or vanadium to bind or be bound in the alloy (i.e., the alloy is formed in the intermediate regions of mutual intersection between the iridium particles and the additive particles). Cold pressed iridium with an aluminum or vanadium additive can result in a product with an iridium density of less than 100 percent (due to the presence of the additive and / or porosity).

Moreover, liquid sintering can be carried out using a liquid additive, such as, but not limited to, aluminum heated above its melting point, which can melt in situ, or be poured into the volume of iridium microspheres, resulting in a product with a lower iridium density 100 percent (due to the presence of the additive). The liquid additive hardens at low temperature and holds iridium microspheres in place. In some embodiments, the microspheres or microspheres can be provided in a single layer bonded to aluminum or vanadium or other compatible low density binder to form a disk 18 from the associated low density microspheres or microspheres 40 (see FIG. 7) that can be activated using traditional targets for irradiating discs stacked on top of each other after activation and then compressible, compacted or otherwise deformed to form a spherical or quasisphere insert nical source.

Additional embodiments comprise compressing iridium in the form of nanoparticles (sometimes referred to as “iridium black”), resulting in an amorphous (non-crystalline product with an iridium density in the range of 30-50%, but more typically about 35 percent compared to with traditional solid iridium Similarly, iridium and aluminum, both in the form of nanoparticles, can be mixed and heated to obtain the adhesion effect between the particles, and then pressed into a disk.

A domed (disk-shaped) disk for alloys, compounds or other iridium composites containing porous iridium can facilitate compression, compaction or deformation into quasispheres inside the active insert, as shown in FIG. 4A, 5A and 5B.

In cases where partially sintered or pressed low-density porous iridium is excessively brittle to handle without risk of fracture or surface erosion, discs can be bonded together using soft film metals (such as, but not limited to, aluminum, titanium or vanadium or other generally non-activated or low-activated alloys). Other options may include laser melting, sintering or bonding of the surfaces of the disks, similar to the laser engraving of a solid circle, which can seal and harden the surface of the disk. These dome-shaped (disk-shaped) disks can subsequently be compressed, compressed or deformed into spherical or quasispherical shapes for use in an active insert, as shown in FIG. 5A and 5B.

Additional embodiments of reduced density iridium can be obtained by 3D printing using a reservoir or bed for iridium powder, an iridium alloy, composite particles and / or a binder. Such a process may further comprise subsequent burning of the binder.

Thus, several of the above objectives and advantages are achieved in the most efficient manner. Although preferred embodiments of the invention have been disclosed and described in detail here, it should be understood that the present invention is in no way limited to this.

Claims (20)

1. A radiation source containing iridium, wherein at least a portion of the iridium is porous or microporous iridium, the density of the active insert containing iridium being in the range of 30-85 percent relative to pure iridium with a 100 percent density. 2. The radiation source according to claim 1, in which iridium has a density in the range of 40-70 percent relative to pure iridium with a 100 percent density. 3. The radiation source according to claim 1, in which iridium has a density in the range of 50-65 percent relative to pure iridium with a 100 percent density. 4. The radiation source according to claim 1, in which the pores inside the porous or microporous iridium contain a metal, alloy, compound or composite of a low density non-activated, low-activated or co-activated additive. 5. The radiation source according to claim 1, in which the iridium before irradiation with neutrons has the form of a metal, alloy, compound or composite. 6. The radiation source according to claim 1, wherein the iridium is iridium-192 contained within a metal, alloy, compound or composite and is molded in the form of a sphere or quasisphere. 7. The radiation source according to claim 1, in which the iridium has the form of thin porous or microporous disks of a metal, alloy, compound or composite of low density. 8. The radiation source according to claim 7, in which the iridium disks have a thickness of 0.1-0.7 mm 9. The radiation source according to claim 1, in which iridium is iridium-192 contained inside a metal, alloy, compound or composite, in the form of disks having flat, curved or pointed ends that are thicker in the middle than on the periphery that are laid each other, compressed or otherwise formed into a sphere or quasisphere. 10. The radiation source of claim 9, wherein the iridium disks have a thickness of 0.1-0.7 mm. 11. The radiation source according to claim 9, in which iridium-192 is contained inside a metal, alloy, compound or composite material and is molded or has the shape of a sphere or quasisphere using the method of physical compression, compaction or deformation. 12. The radiation source according to claim 1, in which, before irradiation with neutrons, the metal, alloy, compound or composite of iridium is in the form of microspheres or microspheres with a diameter of approximately 0.4 mm or microcylinders with a diameter of approximately 0.3 mm containing porous iridium-191. 13. The radiation source according to claim 1, in which, before irradiation with neutrons, the metal, alloy, compound or composite of iridium has the form of microspheres or microgranules with a diameter of 0.25-0.60 mm or microcylinders with a diameter of 0.20-0.50 mm containing porous iridium-191. 14. The radiation source according to claim 1, in which, before irradiation with neutrons, the metal, alloy, compound or composite of iridium has the form of a wire with a diameter of approximately 0.3 mm containing porous iridium-191, which is then cut after activation to form microcylinders. 15. The radiation source according to claim 9, wherein the microspheres, microspheres, or microcylinders of metal, alloy, compound, or iridium-191 composite are in a random or partially random packaging configuration. 16. The radiation source according to claim 1, in which the iridium before irradiation with neutrons contains iridium-191 in the form of a metal, alloy, compound or composite, which is molded in the form of a disk, semi-ellipse or other thin flat shape with a thickness of less than 0.75 mm 17. The radiation source according to claim 1, further comprising a spherical or quasispherical cavity of the source, which contains iridium. 18. The radiation source according to claim 1, wherein the radiation source consists of a plurality of iridium disks with flat or curved ends in the form of a metal, alloy, compound or composite. 19. The radiation source according to claim 1, in which the pores inside the porous or microporous iridium contain a metal, alloy, compound or composite of a low density non-activated, low-activated or co-activated additive, which promotes sintering, compression or deformation, while the additive or additives selected from a group containing aluminum, vanadium, boron-11, silicon, phosphorus, sulfur, carbon, beryllium, titanium, nickel, tungsten or their alloys or intermetallic compounds. 20. The radiation source according to claim 2, in which the iridium before irradiation with neutrons is in the form of a metal, alloy, compound or composite, the additive or additives selected from the group consisting of aluminum, vanadium, boron-11, silicon, phosphorus, sulfur, carbon , beryllium, titanium, nickel, tungsten or their alloys or intermetallic compounds.

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