System and method for collecting and isolating radiosotopes

Abstract

A method for obtaining .sup.225AC from .sup.225Ra having the steps of assembling a column having an inorganic stationary phase; priming the column to immobilize .sup.226Ra .sup.225Ra and natural decay products therefrom; immobilizing the .sup.226Ra, .sup.225Ra, .sup.224Ra, and natural decay products therefrom onto a stationary phase within the column; and eluting the column containing the .sup.225Ra with an aqueous sulfate solution to obtain a milking effluent that contains .sup.225AC. Also provided is a method for obtaining pure .sup.225AC from its isotope parents, the method comprising assembling a column having a stationary phase comprising an inorganic material; priming the column with the isotope parents to immobilize .sup.225Ac, and natural decay products of .sup.225AC; immobilizing the .sup.225Ac, and natural decay products therefrom onto the stationary phase within the column .sup.226Ra, .sup.225Ra, .sup.224Ra; and eluting the column containing the .sup.225AC to obtain an effluent that contains the isotope parents.

Claims

1. A method for obtaining .sup.225Ac from its isotope parents, the method comprising: a) assembling a column having a stationary phase comprising an inorganic material; b) priming the column with the isotope parents; c) immobilizing the .sup.225Ac, and natural decay products therefrom onto the stationary phase within the column; and d) eluting the column containing the .sup.225Ac to obtain an effluent that contains the isotope parents wherein the priming step further comprises eluting an aqueous solution containing free hydroxide ions until the effluent of the column is basic.

2. The method as recited in claim 1 wherein the eluting step comprises contacting the column with a mineral acid selected from the group consisting of hydrochloric acid, nitric acid, sulfuric acid, perchloric acid, and combinations thereof.

3. The method as recited in claim 1 wherein the .sup.225Ac, immobilized on the column remains on the column after step d).

4. The method as recited in claim 1 wherein the inorganic material is a compound selected from the group consisting of alumina, zirconate, titanate, niobate, and combinations thereof.

5. A method for obtaining .sup.225Ac from its isotope parents, the method comprising: a) assembling a column having a stationary phase comprising an inorganic material; b) priming the column with the isotope parents; c) immobilizing the .sup.225Ac, and natural decay products therefrom onto the stationary phase within the column; and d) eluting the column containing the .sup.225Ac to obtain an effluent that contains the isotope parents wherein the immobilizing step further comprises: e) eluting an aqueous solution containing .sup.226Ra, .sup.225Ra, .sup.224Ra, and natural decay products therefrom through the column; f) eluting a dilute solution of H.sub.2SO.sub.4 through the column; and g) eluting water through the column until the effluent has neutral pH.

6. The method as recited in claim 5 wherein the eluting step comprises contacting the column with a mineral acid selected from the group consisting of hydrochloric acid, nitric acid, sulfuric acid, perchloric acid, and combinations thereof.

7. The method as recited in claim 5 wherein the .sup.225Ac, immobilized on the column remains on the column after step d).

8. The method as recited in claim 5 wherein the inorganic material is a compound selected from the group consisting of alumina, zirconate, titanate, niobate, and combinations thereof.

Description

BRIEF DESCRIPTION OF DRAWING

(1) The invention together with the above and other objects and advantages will be best understood from the following detailed description of the preferred embodiment of the invention shown in the accompanying drawings, wherein:

(2) FIG. 1 is a schematic of a method for immobilizing .sup.225Ra on a column, and milking desired products therefrom, in accordance with the features of the present invention;

(3) FIG. 2 is a schematic depiction of a method for immobilizing .sup.225Ac on a column, and eluting undesired parent isotopes therefrom, in accordance with the features of the present invention;

(4) FIG. 3 is a schematic detailing the loading, milking, and recycling steps of the invented method, in accordance with the features of the present invention;

(5) FIGS. 4A-D are γ spectra taken of effluent solutions in an example of the invented method, in accordance with the features of the present invention;

(6) FIG. 5 is a graph of a High Purity Germanium spectrum of isolated actinium-228, in accordance with features of the present invention; and

(7) FIG. 6 is a plot of the activity of isolated actinium isotope showing its purity, in accordance with features of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(8) The foregoing summary, as well as the following detailed description of certain embodiments of the present invention, will be better understood when read in conjunction with the appended drawings.

(9) All numeric values are herein assumed to be modified by the term “about”, whether or not explicitly indicated. The term “about” generally refers to a range of numbers that one of skill in the art would consider equivalent to the recited value (e.g., having the same function or result). In many instances, the terms “about” may include numbers that are rounded to the nearest significant figure.

(10) The recitation of numerical ranges by endpoints includes all numbers within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5).

(11) The following detailed description should be read with reference to the drawings in which similar elements in different drawings are numbered the same. The drawings, which are not necessarily to scale, depict illustrative embodiments and are not intended to limit the scope of the invention.

(12) As used herein, an element or step recited in the singular and preceded with the word “a” or “an” should be understood as not excluding plural said elements or steps, unless such exclusion is explicitly stated. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.

(13) Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments “comprising” or “having” an element or a plurality of elements having a particular property may include additional such elements not having that property.

(14) The invention generally provides a system and method to produce a radium/actinium generator that can be milked for .sup.225Ac and its daughter isotopes. FIG. 1 depicts a general schematic of the method as numeral 10. The first step 12 of the method 10 comprises irradiating .sup.226Ra targets 14 with low energy (e.g., less than 50 MeV) bremsstrahlung photons 16 from a LINAC to generate .sup.225Ra via equation 1 below. Some .sup.224Ra will also be generated from the irradiating step via equation 4. In the second step 18, the irradiated targets 20 are dissolved in water or dilute acid to create a target liquor 21. In the third step 22, a column 24 is loaded with .sup.226Ra, .sup.225Ra, and .sup.224Ra contained in the target liquor. .sup.225Ra decays into .sup.225Ac via equation 2 below. In the fourth step 26, the column is periodically milked to selectively elute .sup.225Ac and its daughter isotopes that results from this decay while the .sup.226Ra, .sup.225Ra, and .sup.224Ra remain in the column. In the fifth step 28, the column is washed to elute remaining .sup.226Ra from the column that can be used to start the method 10 over again.
.sup.226Ra+γ.fwdarw..sup.225Ra+.sup.1n  Equation 1
.sup.225Ra.fwdarw..sup.225Ac+β+decay products  Equation 2
.sup.224Ra.fwdarw..sup.220Rn+α+decay products  Equation 3
.sup.226Ra.fwdarw..sup.224Ra+2.sup.1n+decay products  Equation 4

Generation of .SUP.225.Ra Parent Isotope Detail

(15) As stated above and shown in FIG. 1, the instant method uses a LINAC to irradiate .sup.226Ra targets in order to generate .sup.225Ra within the targets. An exemplary LINAC that may be used in the current method is at Argonne National Laboratory in Lemont, Ill. Argonne's LINAC has a maximum energy of approximately 55 MeV, a power of approximately 25 kW at 25-35 MeV, and a peak current of approximately 2.5 A. Though Argonne's LINAC is the envisioned LINAC to be used in conjunction with this method, any LINAC or alternative method for delivering bremsstrahlung photons to .sup.226Ra targets to generate .sup.225Ra via equation 1 is suitable. The LINAC should have an energy level of between approximately 5 MeV and approximately 50 MeV, a power level of between approximately 5 kW and approximately 30 kW, and run at an exemplary current of approximately 0.5 mA. The targets comprise radium salts. Suitable and exemplary radium salts are radium nitrate, radium chloride, and combinations thereof.

(16) After irradiation, the irradiated targets are dissolved in aqueous solution. Exemplary aqueous solutions include H.sub.2O, dilute HCl (pH of 1 at the lowest), dilute HNO.sub.3 (pH of 1 at the lowest), NaCl, NaNO.sub.3 and combinations thereof.

(17) In the third step 22 of the invented method, dissolved .sup.226Ra, .sup.225Ra, and .sup.224Ra are loaded onto a column to remain there while generated, desired isotopes are selectively eluted from the column.

(18) FIG. 2 depicts a reverse paradigm than what FIG. 1 presents. As in the first protocol, a target liquor 21 is loaded onto a column 24. But then, mineral acids such as nitric or hydrochloric is added in a parent isotopes elution step 25 to remove .sup.226Ra, .sup.225Ra, and .sup.224Ra.

(19) Lastly, sulfuric acid is added in a second elution step 27 to remove the actinium and bismuth.

Column Detail

(20) The inventors have discovered that inorganic stationary phases are robust when used along with the radionuclides present throughout the instant method and do not have the disadvantage of prior art resins. Exemplary inorganic resins include alumina, titanates, niobates, zirconates, and combinations thereof. Titania particles produced by ZirChrom Separations, LLC of Anoka, Minn. sold under the brand name SACHTOPORE® have been identified as a suitable, commercially available stationary phase for use with this invention. This exemplary phase has an average particle diameter of about 110 μm and average pore sizes of about 60 Å.

(21) In practice, the size of the column and amount of sorbent used can be customized to suit the amount of .sup.226Ra, .sup.225Ra, and .sup.224Ra to be initially loaded on the column. To prepare this column, approximately 1 to approximately 3 grams of titania sorbent stationary phase (SACHTOPORE®) are loaded into a column and washed with distilled water until the effluent is clear. The column is then washed with HCl (of pH 1 or higher) followed by H.sub.2SO.sub.4 (having a pH of 1 or higher).

(22) A salient feature of the invention is the priming of the column with hydroxide after washing with HCl and H.sub.2SO.sub.4 and before loading the column with .sup.226Ra, .sup.225Ra, and .sup.224Ra. The hydroxide priming step comprises eluting the column with an aqueous hydroxide solution ranging in hydroxide concentration between approximately 0.01 M and approximately 0.1 M until the effluent is basic. Any hydroxide solution in this concentration range is suitable. Exemplary, suitable hydroxide solutions are NaOH, KOH, LiOH, NH.sub.4OH, and combinations thereof. Surprisingly and unexpectedly, this hydroxide priming step causes strong adsorption of the .sup.226Ra, .sup.225Ra, and .sup.224Ra onto the titania stationary phase during the loading step 22 below.

Column Loading, Elution, and Recycling Protocol Detail

(23) FIG. 3 is a schematic labelled as numeral 30 that provides more detail of the loading step 22, milking step 26, and .sup.226Ra recycling step 28 shown generally in FIG. 1. After the column is assembled and primed according to protocol detailed above, .sup.226Ra, .sup.225Ra, and .sup.224Ra contained in the target liquor 21 are loaded onto the column. The loading step 22 comprises running the solution containing the dissolved targets through the hydroxide primed column. With this loading step, the .sup.226Ra, .sup.225Ra, and .sup.224Ra dissolved in the target liquor adsorbs onto the titania stationary phase as hydrolyzed species (likely Ra(OH).sub.2 and Ac(OH).sub.3). After loading, the column is rinsed with a H.sub.2SO.sub.4 (approximately 0.01 M to approximately 0.05 M in concentration). This H.sub.2SO.sub.4 solution may also contain (NH.sub.4).sub.2SO.sub.4. This rinse will likely contain .sup.225AC and daughter isotopes generated subsequent to the initial radiation of the .sup.226Ra targets in the initial step shown in FIG. 1 above. As such, the effluent from the H.sub.2SO.sub.4 wash should be subjected to testing to determine whether there is sufficient .sup.225AC to be isolated.

(24) Upon loading and washing a column as described above, the loaded column can be milked 26 for .sup.225AC and desired daughter isotopes. In an embodiment, the column is milked once a week after loading. The milking step 26 comprises eluting the column with 20 to 40 mL of approximately 0.01 M to approximately 0.05 M H.sub.2SO.sub.4 or a solution containing a combination of H.sub.2SO.sub.4 and (NH.sub.4).sub.2SO.sub.4 resulting in a sulfate ion concentration similar or equivalent to the aforementioned concentration range of H.sub.2SO.sub.4 by itself. This milking step creates Ra, Ac and Bi sulfates. The Ac and Bi sulfates are soluble in the aqueous H.sub.2SO.sub.4 solution and exit the column. The Ra sulfates, however, are insoluble and remain in the column.

(25) Effluent from this step will contain any .sup.225AC and desired daughter isotopes that have been generated by decay of .sup.226Ra, .sup.225Ra, and .sup.224Ra immobilized on the column. Protocols to separate .sup.225AC from its daughter isotopes include eluting the eluent from the milking step above through an anion exchange column 27 packed with AG® MP-1 strong anion exchange resin produced by BIO-RAD of Hercules, Calif. A suitable separation protocol can be found in F. Nelson, K. A. Kraus, J. Am. Chem. Soc., 1954, Vol 76, page 5916-5920, the entirety of which is hereby incorporated by reference.

(26) After the last milking, any .sup.226Ra, .sup.225Ra, and .sup.224Ra are removed from the column in a recycling step 28. In this step, the column is contacted with excess carbonate solution, the contact maintained for approximately 8 to approximately 24 hours. Suitable carbonate solutions include saturated solutions of (NH.sub.4).sub.2CO.sub.3, saturated Na.sub.2CO.sub.3, and combinations thereof. During the contacting of the column with carbonate solution, radium sulfate is converted to radium carbonate according to equation 5 below. The insoluble radium carbonate remains on the column.
RaSO.sub.4+CO.sub.3.sup.2−.fwdarw.RaCO.sub.3+SO.sub.4.sup.2−  Equation 5

(27) After the carbonate solution, the column is contacted with a dilute solution of HNO.sub.3 (between approximately 1 M to approximately 5 M in concentration). With this nitric acid wash, the insoluble radium carbonate converts to soluble radium nitrate via equation 6 below and elutes from the column. The effluent, resulting from the nitric acid wash, will contain most of the .sup.226Ra (and non-decayed .sup.225Ra and .sup.224Ra) that remain in the column. Recovered .sup.226Ra may be recycled and used again in the instant method.
RaCO.sub.3+2HNO.sub.3.fwdarw.Ra(NO.sub.3).sub.2+CO.sub.2+H.sub.2O  Equation 6

(28) The above described processes for actinide milking can be adapted in the paradigm depicted in FIG. 2 in appropriate places for parent isotope elution, and final target isotope extraction. Generally, the protocol depicted in FIG. 2 will comprise the following steps:

(29) 1) Dissolving radium targets;

(30) 2) Adjusting pH to somewhere between 1 and 5 with a dilute mineral acid;

(31) 3) Feeding the slurry through the pre-equilibrated column;

(32) 4) Subsequent column washing steps; and

(33) 5) Eluting the desired actinium from the column with a dilute mineral acid.

Example 1

(34) The instant method was performed using 226Ra and its natural decay products. To begin, a column was prepared with approximately 1-3 grams of titania particles (SACHTOPORE®). The column was first washed with water until the effluent was clear. Subsequently, the column was washed with approximately 8 M HCl, followed by 1 M H.sub.2SO.sub.4. Following the H.sub.2SO.sub.4 wash, the column was washed with 3 bed volumes of water. The column was then activated through elution of NaOH aliquots varying in concentration between approximately 0.1 M and approximately 1 M until the effluent was basic. To load the column, approximately 1 nCi of .sup.226Ra was dissolved in 10 mL in H.sub.2O to generate a target liquor. FIG. 4A shows a γ spectrum of that target liquor. This spectrum shows the presence of .sup.226Ra and its natural decay products .sup.214Pb and .sup.214Bi.

(35) The target liquor was then eluted through the column. A γ spectrum was also taken of the target liquor after elution through the column which is shown as FIG. 4B. As shown in FIG. 4B, the .sup.226Ra and its natural decay products were retained by the column. After elution of the target liquor, the column was washed with approximately 2 mL 0.1 M H.sub.2SO.sub.4 followed by approximately 2 mL of water until the effluent was pH neutral.

(36) Decay products of .sup.226Ra were milked from the loaded column through elution of approximately 2 mL of 6M HCl with approximately 0.001 M NaHSO.sub.4. A γ spectrum was taken of the milking effluent. That spectrum is shown as FIG. 4C. Looking to FIG. 4C, the spectrum indicates the presence of the .sup.214Pb and .sup.214Bi natural decay products of .sup.226Ra. Notably, there is no peak for .sup.226Ra in the milking effluent. Such a peak would be expected at about 186 keV. This indicates that the column retains the .sup.226Ra during milkings.

(37) To demonstrate the recoverability of the .sup.226Ra in the invented method, after the last milking of the column tested in this example, the column was contacted overnight with a saturated, stagnant solution of Na.sub.2CO.sub.3. The Na.sub.2CO.sub.3 solution was then decanted and the column contacted with 5 M HNO.sub.3 until bubbling from the column ceased. This solution was removed and counted (the γ spectrum of this solution shown as FIG. 4D). As shown in FIG. 4D, the recycling protocol used here removed a significant portion of the .sup.226Ra remaining on the column.

Example 2

(38) Elution of Ac off a column loaded with immobilized Ra was simulated using barium and europium. Approximately 1 gram of SACHTOPORE® normal phase resin was loaded into a column support (1.3 cm×2 cm). The resin was washed with water followed by 0.1 M NaOH until the effluent was basic (determined by pH paper). A 4 mL solution containing 100 mg of BaCl.sub.2 and 4000 Bq of Eu-152 in pH 6 was fed into the column by gravity. The solution exited the column at approximately 1 drip/second. The eluent showed no signs of Eu-152. The loaded resin was then washed with 2 mL of 0.1M H.sub.2SO.sub.4. Gamma-analysis showed that over 95% of the Eu-152 was recovered in this step. No barium was observed in this solution; qualitatively determined by sulfate precipitates.

Example 3

(39) A stock of Ra-228/Ac-228 was prepared from an aged batch of thorium nitrate (estimated 30-40 years) using solvent extraction and ion exchange. The final pH of the solution was approximately three according to pH indicator. The purity was confirmed by the consistent decay of Ra-224 (Th-228). The solution was allowed to age for one month before use.

(40) Titania resin (Sachtopore) was packed into a 1×10 cm column support, washed with de-ionized water followed by approximately 10 bed volumes of 0.1M NaOH. Using gravity flow, the Ra-228/Ac-228 stock was fed through the column and washed with water. Neither the eluent nor the wash fractions contained activity of Ra-228 or Ac-228. The column was then contacted with 8 mL of 0.1M sulfuric acid to elute pure Ac-228.

(41) FIG. 5 is a graph of a High Purity Germanium spectrum of the isolated actinium, in accordance with features of the present invention. (An HPGe detector converts gamma rays into electrical impulses which can be used, with suitable signal processing, to determine their energy and intensity.) FIG. 5 shows photo-peaks at 338 and 911 keV, indicative of the presence of Ac-228.

(42) Using the photopeaks at 338 and 911 keV in FIG. 5, a series of measurements were carried out over 15 hours and are plotted below.

(43) FIG. 6 represents this plot, which is a measure of AC-228 activity over a period of about 18 hours. The solid circles and triangles represent the experimental data, while the solid lines represent a half-life of 6.1 hours.

(44) It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. While the dimensions and types of materials described herein are intended to define the parameters of the invention, they are by no means limiting, but are instead exemplary embodiments. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the terms “comprising” and “wherein.” Moreover, in the following claims, the terms “first,” “second,” and “third,” are used merely as labels, and are not intended to impose numerical requirements on their objects. Further, the limitations of the following claims are not written in means-plus-function format and are not intended to be interpreted based on 35 U.S.C. § 112, sixth paragraph, unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further structure.

(45) As will be understood by one skilled in the art, for any and all purposes, particularly in terms of providing a written description, all ranges disclosed herein also encompass any and all possible subranges and combinations of subranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as “up to,” “at least,” “greater than,” “less than,” “more than” and the like include the number recited and refer to ranges which can be subsequently broken down into subranges as discussed above. In the same manner, all ratios disclosed herein also include all subratios falling within the broader ratio.