Patent Publication Number: US-11387011-B2

Title: Compact radioisotope generator

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a divisional of U.S. patent application Ser. No. 12/887,933, filed Sep. 22, 2010, the contents of which are incorporated by reference. 
    
    
     FIELD OF INVENTION 
     This application is directed toward production and use of radioactive isotopes, or radioisotopes. 
     BACKGROUND 
     Radioactive isotopes have many beneficial uses. As one example, positron-emitting copper isotopes, such as copper-64 ( 64 Cu) and copper-60 ( 60 Cu) have a number of uses in clinical and pre-clinical nuclear medicine. These uses include, but are not limited to, the labeling of compounds and the creation of phantom objects suitable for localization and coregistration of multimodality imaging systems, such as those which combine magnetic resonance and positron-emission (MR-PET) imaging. In some instances these radioisotopes are used for oncology imaging and oncological therapy. 
     The production of radioisotopes is one of the factors that limit their use. Production may involve expensive starting materials, such as isotopically enriched substances, and expensive and time-consuming procedures using large, unmovable, and scarce equipment. If a desired radioisotope has a very short half-life it must be used very soon after it is made. This may not be possible unless the radioisotope is made at, or very close to, the location where it is to be used. It may not be economically or physically feasible, however, to have the necessary equipment at or near that location. 
     As an example,  64 Cu is produced using either a cyclotron or a nuclear reactor, both of these being large, immobile machines with relatively high operating expenses. A starting material used is Nickel-64 ( 64 Ni), which is a rare isotope requiring expensive enrichment before being transformed into  64 Cu. For the particular case of  64 Cu, two methods are known for producing this isotope. In one method,  64 Ni is bombarded with protons from a particle accelerator. A  64 Ni nucleus absorbs a proton and emits a neutron and is thereby transmuted into a  64 Cu nucleus. This series of reactions, also referred to as a channel, is designated  64 Ni(p,n) 64 Cu. In a second method, naturally occurring copper is bombarded with neutrons. A  63 Cu nucleus absorbs a neutron and is thereby transmuted into  64 Cu nucleus. The nucleus is created with excess energy, which it reduces by emitting gamma radiation immediately after the transmutation. This channel is designated  63 Cu(n,γ) 64 Cu. 
     In a variation known as the Szilard-Chalmers effect, a particular atom is a constituent of a molecule dissolved in a liquid. A nuclear reaction involving the nucleus of such atoms results in the nucleus emitting one or more gamma rays, causing a recoil effect in which the atoms, now each transformed into a radioisotope, are ejected from the molecules and into solution in the liquid. The radioisotope atoms may then be chemically or electrolytically extracted from the liquid. 
     SUMMARY 
     Disclosed are method and apparatus for making a radioisotope using a portable neutron source. A material comprising a particular isotope is obtained and exposed to neutrons from a portable neutron source, the particular isotope reacting with a neutron and transforming into the radioisotope. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a method for producing a radioisotope including a portable neutron source. 
         FIG. 2  shows an embodiment of an apparatus for producing a radioisotope including a portable neutron source. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a method of making a radioisotope. A material is obtained which includes a particular isotope which will be transformed into the radioisotope  110 . The particular isotope may be present in its natural concentration—the method described here may not require initial enrichment. As an example, naturally occurring copper comprises 69% copper-63 ( 63 Cu) and 31% copper-65 ( 65 Cu). The particular isotope  63 Cu, in this naturally occurring abundance, may be transformed, without being enriched, into  64 Cu, as described below. The material may be a bulk solid or powdered solid containing the particular isotope. The material may be a pure liquid or a mixture of liquids containing the particular isotope. The material may be a solution of a compound containing the particular isotope, the compound being dissolved in a liquid, solid, or gas. The material may be a gas or vapor including the particular isotope or a mixture of gasses, at least one of which includes the particular isotope. The particular isotope may be a nucleus of a single atom or a nucleus of an atom bound in a molecule. Other appropriate configurations of matter may be considered by one of ordinary skill in the art without departing from the scope of the claims. 
     The material is exposed to neutrons from a portable neutron source  120 . A portable neutron source is to be understood as a neutron source that is easily moved between different locations and that occupies a relatively small space, as distinct from, for example, a cyclotron or a nuclear reactor. Examples of known, commercially available portable neutron sources include plutonium-beryllium sources, americium-beryllium sources, deuterium-tritium neutron sources, and californium 252 ( 252 Cf) sources. In a deuterium-tritium source, deuterium gas is ionized, accelerated in an electrostatic field, and allowed to impact on a sealed tritium target, creating neutrons as a result of the t(d,n) 4 He nuclear reaction. In an americium-beryllium source, alpha particles emitted by the americium react with beryllium nuclei, resulting in the emission of neutrons. A plutonium-beryllium source works in similar fashion with plutonium emitting the alpha particles.  252 Cf undergoes spontaneous fission with the emission of a neutron.  252 Cf neutron sources are available that emit a total flux of 10 11  neutrons per second. Neutron sources can be fabricated in a large range of sizes including portable sizes as described above. For example,  252 Cf neutron sources shaped as cylinders, including ones with outer diameter 5.5 mm and outside length 25 mm, are available from Frontier Technology Corporation, Xenia, Ohio. 
     The portable neutron source may be situated within the material. The portable neutron source may be completely surrounded by the material. Alternatively, at least a portion of the portable neutron source may be situated outside the material. Nuclei of the particular isotope react with neutrons from the portable neutron source  120  resulting in the particular isotope transforming into the desired radioisotope. The transformation may occur through any of several different reaction paths, or channels, such as those described below. 
     After the material has been exposed to the neutrons  120  for a time sufficient to produce a desired quantity of the radioisotope, the radioisotope may be extracted from the material  130 . Extraction  130  may be carried out by, for example, chemical methods known to those of ordinary skill in the art for the particular element in question. Alternatively, the radioisotope may be left within the material. The material may then be used as a source of the radiation emitted by the radioisotope. 
       FIG. 2  shows an embodiment of an apparatus  200  for producing a radioisotope using a portable neutron source  240  in proximity to a container  220 . Container  220  contains a material  210  which includes a particular isotope  250 . Portable neutron source  240  is shown completely surrounded by material  210 . Alternatively, at least a portion of portable neutron source  240  may be situated outside material  210 . Portable neutron source  240  emits neutrons  260  into material  210 . Neutrons  260  emerging from portable neutron source  240  may have energies in excess of thermal energy of material  210 , as depicted by thick arrows. These neutrons  260  are known as fast neutrons. Within a short distance of portable neutron source  240 , several centimeters for example, fast neutrons  260  may slow down and come into thermal equilibrium with material  210  after undergoing many collisions with atoms or molecules in material  210 . These slower neutrons  230 , depicted by thin arrows, are known as thermalized neutrons or thermal neutrons. 
     Neutrons from portable neutron source  240 , either fast neutrons  260  or thermal neutrons  230 , may then react with the nuclei of a particular isotope  250 , represented by filled-in circles, included in material  210 . As a result, the nuclei of particular isotope  250  are transformed into nuclei of a desired radioisotope  270 , represented by unfilled circles. Depending on neutron cross-sections and neutron reaction dynamics for particular isotope  250 , either fast neutrons  260  or thermal neutrons  230  or both may contribute significantly to formation of radioisotope  270 . 
     Material  210  may be a bulk solid or powdered solid containing particular isotope  250 . Material  210  may be a pure liquid or a mixture of liquids containing particular isotope  250 . Material  210  may be a solution of a compound, the compound containing particular isotope  250 . The compound may be dissolved in a liquid, in a solid, or in a gas. Material  210  may be a gas or vapor including particular isotope  250  or a mixture of gasses, at least one of which includes particular isotope  250 . Particular isotope  250  may be a nucleus of a single atom or a nucleus of an atom bound in a molecule. A portion of material  210  may act as a moderator that reduces energy of neutrons emitted from portable neutron source  240 . Such moderated neutrons may be slowed down to energies less than energies with which they are emitted. The neutrons may be thermalized in this way. For example, if particular isotope  250  is in a water solution, the water may act as a moderator. Thus, portable neutron source  240  may be completely surrounded by both particular isotope  250  and by a moderator. This geometry is shown in the embodiment illustrated in  FIG. 2 . Other appropriate states of matter and other geometrical configurations may be considered by one of ordinary skill in the art without departing from the scope of the claims. 
     Once a desired amount of particular isotope  250  has been transformed into radioisotope  270 , the latter may be separated from material  210  by, for example, chemical or physical methods known to those of ordinary skill in the art. As an example, if radioisotope  270  can be ionized in solution it may be separated by electroplating. Alternatively, the separation may be carried out using separate extraction apparatus known as a chemistry kit (not shown). The chemistry kit may be integral with apparatus  200 . Alternatively, radioisotope  270  may be left within the material. The material may then be used as a source of the radiation emitted by the radioisotope. 
     As examples not to be considered limiting, the method, apparatus, and composition of matter described above may be applied to the production of the copper isotope  64 Cu. In a particular embodiment, portable neutron source  240  may be a plutonium-beryllium (Pu—Be) source, an americium-beryllium (Am—Be) source, a deuterium-tritium (D—T) source, a  252 Cf source, or another portable neutron source. Material  210  may be an aqueous solution of a copper-containing compound such as copper phthalocyanine, or copper salicylaldehyde o-phenylene diamine. The compound may contain copper isotopes in their natural abundances, which are 69%  63 Cu and 31%  65 Cu. The  63 Cu may serve as particular isotope  250 . Thermal neutrons  230  may react with the  63 Cu particular isotopes  250  which transform into  64 Cu as an example of formed radioisotope  270 . In this embodiment the  64 Cu radioisotope is produced by the  63 Cu(n, γ) 64 Cu reaction, in which a  63 Cu nucleus absorbs a neutron to become  64 Cu, emitting a γ photon in the process. Experiments in which a copper-containing solid was bombarded with thermal neutrons have yielded about 50 nanoCuries of  64 Cu. By using a stronger portable neutron source and a geometry such as that shown in  FIG. 2 , it is estimated that 100-1000 times as much  64 Cu—that is to say a large number of microCuries—may be generated in this manner. 
     Materials including radioisotopes made using the method and apparatus described above may be shaped into objects with geometrical shapes such as markers, arrows, right-left designating shapes, text, and numbers. Such objects may be used in medical imaging for image registration, aligning, testing, and labeling. In particular, objects that include the positron-emitting isotope  64 Cu may be useful in positron-emission tomography (PET) imaging. 
     Compared with currently known technologies for making radioisotopes, the method, apparatus, and composition of matter described above, making use of a portable neutron source, present possibilities for making radioisotopes less expensively with equipment taking up much less space. Also presented is the possibility of making radioisotopes with short half lives at the location where they are needed, such as a hospital. In this way, a larger number of useful radioisotopes may become available to a practitioner, such as a physician. 
     While the preceding description refers to certain embodiments, it should be recognized that the description is not limited to those embodiments. Rather, many modifications and variations may occur to a person of ordinary skill in the art which would not depart from the scope and spirit defined in the appended claims.