CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of U.S. Provisional Patent Application Serial No. 62/857,681 filed June 5, 201 9, entitled “Separation of Radiu m from Lead, Bismuth, and Thoriu m for Medical Isotope Production Applications”, the entirety of which is incorporated by reference herein.

STATEM ENT AS TO RIGHTS TO DISCLOSU RES MAD E UN DER FEDERALLY-SPONSORED RES EARCH AN D DEVELOPM ENT

This disclosure was made with Government support under Contract DE-AC0576RL01 830 awarded by the U.S. Department of Energy. The Government has certain rights in the invention.

TECHN ICAL FI ELD

The disclosure generally relates to nuclear medicine and more particularly to methods for obtaining materials and performing separations for generating such materials.

BACKG ROUN D

In the field of nuclear medicine separations of materials and preparation of materials for inclusion in various treatments face a nu mber of obstacles. Availability, cost, timing, and limited shelf-life coupled with the need to perform many activities in specialized safe facilities create a number of obstacles. The existing method of ²¹² Pb/ ²¹² Bi generator preparation requires two steps : first ²²⁴ Ra must be isolated from a ²²⁸ Th stock solution ; second the ²²⁴ Ra must be loaded onto a cation exchange (CatlX) resin (which becomes the ²¹² Pb/ ²¹² Bi generator colu mn), the performance of which can expose staff to a high radiological dose. The dose is largely caused by the short-lived progeny below ²¹² Po. In addition, this method is cu mbersome and labor intensive and can requires multiple colu mns and boildown steps to achieve the desired ends.

What are needed are more and more improved methods for simplifying these processes, increasing the yields and addressing the various barriers to use. The following description provides various examples and advances in this regard.

SUMMARY

Systems for separating Ra from a mixtu re comprising at least Ra, Pb, Bi, and Th are provided. The systems can include: a first vessel housing a first media and either Pb or Bi and/or Th; and a second vessel in fluid communication with the first vessel, the second vessel housing a second media and Ra, wherein the first media is different from the second media.

Systems for separating Ra from a mixtu re comprising at least Ra, Pb, Bi, and Th are also provided that can include a first vessel housing a first media and Th and/or Bi ; and a second vessel in fluid communication with the first vessel, the second vessel housing a first media and Pb, wherein the first media is different from the second media.

Additional systems for separating Ra from a mixtu re comprising at least Ra, Pb, Bi, and Th can include: a first vessel housing a first media and Th or Bi; a second vessel in fluid commu nication with the first vessel, the second vessel housing a second media and Pb; and a third vessel in fluid communication with the second vessel, the third vessel housing a third media and Ra, wherein at least one of the first, second, or third medias are different from the other medias.

Methods for separating Ra from Pb, Bi, and Th are provided, the methods can include : providing a first mixtu re comprising Ra, Pb, Bi, and/or Th ; providing a system that includes: a first vessel housing a first media; and a second vessel in fluid communication with the first vessel, the second vessel housing a second media; exposing the first mixture to the first media within the first vessel to separate the Th and Bi from the Ra and Pb; then, through the fluid communication , exposing the remaining mixture to the second media in the second vessel to associate the Pb or Ra with the second media.

Methods for separating Ra from Pb, Bi, and Th can also provide for providing a first mixture comprising Ra, Pb, Bi , and/or Th; providing a system that can include: a first vessel housing a first media; a second vessel in fluid communication with the first vessel, the second vessel housing a second media; and a third vessel in fluid commu nication with the second vessel , the third vessel housing a third media; and exposing the first mixture to the first media within the first vessel then, through the fluid commu nication, exposing the first remainder to the second media in the second vessel, then, through fluid communication, exposing the next remainder to the third media in the third vessel, the exposing separating the Th and Bi from the Ra and Pb, and the Ra from the Pb.

Methods for separating Ra from being associated with a media are also provided. The methods can include : exposing the Ra and media to a chelating agent to form a mixtu re comprising the Ra complexed with the chelating agent.

Methods for separating Ra from Pb, Bi, and Th are also provided that can include : providing a first mixture comprising Ra and at least Bi and/or Th ; separating one or more of Bi and/or Th from the Ra, the separating associating the Bi and/or Th with a first media; and disassociating the Bi and/or Th from the first media to form a mixture comprising the Bi and Th and transferring the mixture to a vessel housing at least Ra and additional Bi and/or Th.

DRAWINGS

Embodiments of the disclosure are described below with reference to the following accompanying drawings. Fig. 1 depicts an example modified triple-colu mn ²²⁴ Ra isolation scheme; green cells indicate active flow paths at each step A through E. (A) Load and wash “a” to adsorb Th, Pb, and Ra on C1 -C3, respectively; (B) Secondary wash “b” for C2-C3; (C) Water rinse through C3 to remove H ⁺ ions; (D) Ra elution from C3; and (E) Elution of Th from C1 for reuse.

Fig. 2 is a depiction of Step A: Initial 3-colu mn load of ²²⁸ Th stock + wash“a”.

Fig. 3 depicts gamma spectra obtained following triple-colu mn load/wash routine (see path A in Fig. 2). The ²²⁸ Th/progeny sample is loaded (a) and washed (b) through all three colu mns using 6 M FINO3; no activity is observed to break through the three-colu mn stack (c) Following load and wash steps, the An lXpoiy media (C1 ) shows ²²⁸ Th, ²¹² Bi, and ²⁰⁸ TI adsorbed on the resin beads. Fig. 4 depicts gamma spectrum showing a prominent ²²⁴ Ra emission in a fraction collected immediately downstream of C2 during the wash“a” sequence. Traces of ²¹² Bi / ²⁰⁸ TI, likely generated by the ²¹² Pb adsorbed on C2, are likewise observed.

Fig. 5 depicts Step B: C2 + C3 wash“b”. Fig. 6 depicts (a) Resin capacity factors (/c') for Group I I divalent cations in nitric acid on Sr Resin (b) Sr Resin effluent fraction elution profiles for u nretained ²¹² Bi and slightly retained ²²⁴ Ra in 2 M HNO3.

Fig. 7 depicts gamma spectra obtained following double-colu mn load/wash routine (see path B in Fig. 5). (a) The ²¹² Pb and ²²⁴ Ra are washed through C2/C3 using 2 M HNO3; no activity is observed to break through the two-column stack, as ²¹² Pb is retained on the Sr Resin column (C2) and ²²⁴ Ra is retained on the Ra-01 Resin colu mn (C3). (b) Spectrum taken of the Sr Resin colu mn (C2) at the conclusion of the wash“b” step shows pure ²¹² Pb. Fig. 8 is Step C : C3 water rinse.

Fig. 9 depicts (a) Elution of residual ²¹² Pb from the ²²⁴ Ra-loaded C3 using water (b) Decay rate of the water wash fractions indicated little to no ²²⁴ Ra loss during the water wash step. Fig. 1 0 is Step D : C3 elution of isolated ²²⁴ Ra.

Fig. 11 depicts (a) Assembled radiochromatogram of ²²⁴ Ra elute fractions (b) Monitoring the isolated ²²⁴ Ra fraction activity over the theoretical decay rate as a function of time shows that it is radionuclidically pure. Fig. 1 2 is Step E : C1 elution of ²²⁸ Th stock with HCI.

Fig. 13 is (a) Elution of ²²⁸ Th, ²¹² Bi, and ²⁰⁸ TI from the An lXpoiy resin M1 using 8 M HCI. (b) Spectrum of the An lXpoiy M1 following the HCI elution cycle indicates incomplete ²²⁸ Th elution.

Fig. 14 is fluidic layout schematic of automated triple-colu mn based ²²⁴ Ra purification system according to an embodiment of the disclosure.

Fig. 1 5 depicts (a) stepper motor driven syringe pu mp for ²²⁸ Th stock solution loading operations (b) solenoid-based fluid routing system to drive the triple-column ²²⁴ Ra isolation procedure according to embodiments of the disclosure.

Fig. 1 6 is gamma spectra of ²²⁸ Th elution fractions (A) and elution chromatogram (B) using 1 M HCI on M P-1 M resin (M1 ). ²²⁸ Th elution fractions (C) and elution chromatogram (D) using 8 M HCI on same. Dashed line at 10 mL indicates the beginning of an applied strip solution of EDTA.

Fig. 1 7 depicts (A) Load and wash“a” fractions collected from 1 cc TEVA resin effluents in 6 M HNO3. Arrow indicates the location of the absent ²²⁸ Th X-ray. ²¹² Pb, ²¹² Bi and ²⁰⁸ TI photon peaks are observed to break through the media (the ²²⁴ Ra emission is hidden u nder the ²¹² Pb peak at ~240 keV). (B) Analysis of the TEVA resin effluents over time indicate a decay rate consistent with that of ²²⁴ Ra; this indicates that ²²⁸ Th was well adsorbed on the media during the load/wash“a” steps.

Fig. 18 depicts gamma spectra of ²²⁸ Th elution fractions (A) and elution chromatogram (B) using 1 M HCI on TEVA resin (M 1 ). ²²⁸ Th elution fractions (C) and elution chromatogram (D) using 8 M HCI on same. Dashed line at 1 0 mL indicates the beginning of an applied strip solution of EDTA.

Fig. 1 9 depicts (A) ²²⁸ Th activity fractions as a fu nction of 1 M HCI elution volu me from TEVA resins of different internal volu mes. (B) Cumulative ²²⁸ Th activity yield for same.

Fig. 20 depicts observed activity decay rate of TEVA resin load fraction (combined loads) for a 1 cc (A) vs. 0.25 cc (B) vessel volu me. Dashed line is the theoretical decay rate for ²²⁴ Ra. Positive deviation from the ²²⁴ Ra cu rve indicates the presence of ²²⁸ Th as TEVA resin column breakthrough.

Fig. 21 depicts observed activity decay rate of TEVA cartridge ²²⁸ Th load fraction (combined loads) for a 2 cc (a), a 1 cc (b), 0.4 cc HML (half-milliliter)(c), and 0.2 cc QML(quarter milliliter) cartridge (d). Black and grey dashed lines are the theoretical decay rate curves for ²²⁴ Ra and ²²⁸ Th, respectively. Positive deviation from the ²²⁴ Ra curve indicates the presence of ²²⁸ Th.

Fig. 22 (a) depicts observed activity decay rate of TEVA colu mn ²²⁸ Th load fraction for a 1 cc hand-packed TEVA resin SPE column (b) depicts cumulative ²²⁸ Th activity fractions as a fu nction of 1 M HCI elution volu me from same.

Fig. 23 depicts cu mulative ²²⁸ Th activity fractions as a function of 1 M HCI elution volu me from machine-packed TEVA resin cartridges of decreasing internal resin volu me. Cartridge are (a) 2 cc, (b) 1 cc, (c) HML, and (d) QML.

Fig. 24 is HML (0.41 cc) and QML (0.25 cc) cartridges that were evaluated for ²¹² Pb removal in the C2 position. Fig. 25 is gamma spectra of ²²⁸ Th/ ²²⁴ Ra solution effluent fractions from C1 + C2 during the load + wash“a” steps in 6 M HNO3. C2 volume was varied between 0.41 cc (A) and 0.25 cc (B) of Sr Resin bed. Colored arrows indicate radionuclides observable in the fractions: blue = ²²⁸ Th (absent); grey = ²¹² Bi; yellow = ²¹² Pb; green = ²²⁴ Ra; orange = ²⁰⁸ TI.

Fig. 26 depicts (A) load + wash“a” effluent fractions from a 0.25 cc Ra-01 resin showing the elution of ²²⁸ Th (arrow), some ²¹² Pb, and ²¹² Bi/ ²⁰⁸ TI . (B) effluent fractions from wash“b” showing no observable ²²⁸ Th X-rays (arrow). ²¹² Bi/ ²⁰⁸ TI are observed to wash from the media. Fig. 27 is Load / wash“a” colu mn effluent fractions showing ²²⁴ Ra elution profile through C1 + C2, wherein C2 is a (a) HML cartridge or a (b) QML cartridge packed with Sr Resin.

Fig. 28 depicts water wash fractions from the C3 step 3 that was inserted before the ²²⁴ Ra elution step. (A) gamma spectra of effluent fractions collected during water wash show ²¹² Pb removal. (B) the activity decay rate observed from water wash effluents; it matches the decay rate of ²¹² Pb. Data indicates that ²²⁴ Ra remains adsorbed to the media during water wash.

Fig. 29 depicts observed activity decay rate of the primary ²²⁴ Ra elution fraction from a Ra-01 resin colu mn (C3) loaded with a ²²⁸ Th/ ²²⁴ Ra solution. Dashed line is the theoretical ²²⁴ Ra decay rate.

Fig. 30 is a speciation diagram for Ra(l l) in 0.05 M EDTA across a range of pH. Fig. 31 is a schematic showing the process for loading the ²²⁴ Ra product fraction from the triple-colu mn method onto a CatlX-based generator column. The pu rified ²²⁴ Ra/E DTA product solution is acidified by adding a small volu me of concentrated HCI (other mineral acids such as HNO3 are acceptable as well), which dissociates the ²²⁴ Ra/EDTA complex. Next, the acidified ²²⁴ Ra ⁺⁺ solution is loaded onto the generator column.

Fig. 32 depicts results from loading the HCI-acidif ied ²²⁴ Ra ⁺⁺ product onto a strong cation exchange colu mn. ²²⁴ Ra load fraction (a) and wash fractions (b) plotted vs. elapsed time. Legend indicates the collected fractions (1 mL each) of wash solution delivered through the vessel. The decay rates indicate that all ²²⁴ Ra was adsorbed onto the column du ring load/wash steps (c) Direct counts of the ²²⁴ Ra-loaded cation exchange colu mn vs. elapsed time indicates the decay rate of ²²⁴ Ra beyond the ~ 1 .6 day period wherein progeny equilibrium first occurs.

Fig. 33 is a schematic of a Ra-complex reaction system according to an embodiment of the disclosu re.

DESCRI PTION

The present disclosure will be described with reference to Figs. 1 -33. Referring first to Fig. 1 , a series of configu rations (A-E) of vessels (C1 -C3) in fluid commu nication with one another is depicted.

The present disclosure provides systems and methods for the separation of materials that can be used for the acquisition of targets for alpha radiation when performing targeted radioimmunotherapy applications. In one example the ²¹² Pb/ ²¹² Bi isotope pair shows good promise. The parent isotope, ²²⁴ Ra, must be periodically purified from ²²⁸ Th via radiochemical separation. The purified ²²⁴ Ra can then be used to prepare ²²⁴ Ra/ ²¹² Pb/ ²¹² Bi generators. The present disclosu re provides a ²²⁴ Ra purification method that can be safer and more efficient than existing prior art methods resulting in reduced personnel dose; and may be fully, but at least partially, automated using laboratory fluidics.

With reference to Fig. 1 , the present disclosure provides systems and/or methods for separating Ra from a mixture comprising at least Ra, Pb, Bi, and Th. As can be seen in Fig. 1 , there are three vessels (C1 , C2, and C3), but there can be at least two. These vessels can house media. For example, C1 can house media M 1 , C2 can house media M2, and C3 can house media M3. One or all three of these vessels can be in fluid communication via conduits for example. Each of the conduits can be controlled via a valve or valves for example. Referring to Fig. 2, in accordance with an example implementation, a mixture (Th/Ra+ (“+” subsequent progeny can be present) in FINO3) that can provide Ra, Pb, Bi, and Th, can be exposed to vessels C1 -C3 and thereby M1 -M3. Each of the Media can be different from one another.

Accordingly, the media can be (in fluidic introduction order, and as shown in Table 1 ) An lX-M1 (AG M P-1 M, Bio-Rad, or TEVA resin, Eichrom) ; 18-crown-6-M2 (Sr Resin, Eichrom); M3 (Ra-01 resin, IBC Advanced Technologies). In accordance with example implementations, a ²²⁸ Th / ²²⁴ Ra / ²¹² Pb / ²¹² Bi / etc. mixture can be passed through all three vessels in strong HNO3 (³6M, however concentrations as low as 2M FINO3 can be utilized as well); a 3-colu mn wash (strong FINO3) can be delivered, and Th + Bi retains in C1 ; Pb retains in C2; Ra retains in C3 (the system configuration of which is shown in Fig. 2 as (A).

Accordingly, systems of the present disclosure can include a first vessel housing a first media and either Pb or Bi and/or Th (C1 or C2) ; and a second vessel in fluid communication with the first vessel, the second vessel housing a second media and Ra (C3), wherein the first media is different from the second media. Additionally, systems of the present disclosure can include a first vessel housing a first media and Th and/or Bi (C1 ) ; and a second vessel in fluid commu nication with the first vessel, the second vessel housing a second media and Pb (C2), wherein the first media is different from the second media. Embodiments, of the present disclosure can also include systems having a first vessel housing a first media and Th or Bi (C 1 ) ; a second vessel in fluid communication with the first vessel, the second vessel housing a second media and Pb (C2) ; and a third vessel in fluid communication with the second vessel, the third vessel housing a third media and Ra (C3), wherein at least one of the first, second, or third medias are different from the other medias.

Methods are also provided that can include providing a mixture having Ra, Pb, Bi, and/or Th ; providing the described system having vessel (C1 ) housing the media (M1 ), and vessel (C2 or C3) in fluid communication with vessel (C1 ), with vessel (C2 or C3) housing media (M2 or M3) ; exposing the mixture to media (M1 ) within vessel (C1 ) to separate the Th and Bi from the Ra and Pb; then, through the fluid communication, exposing the remaining mixture to media (M2 or M3) in vessel (C2 or C3) to associate the Pb or Ra with the M2 or M3 media. In accordance with example implementations, Th (with Bi) of C1 can be eluted from M1 in strong HCI for dry-down and storage for re-use as desired.

Additionally, as shown and described, vessel (C3) can be in fluid communication with vessel (C2), and vessel (C3) and house a media (M3). The methods can include exposing the mixture to media (M 1 ) within the vessel (C1 ) then, through the fluid commu nication, exposing the first remainder (that which passes through C1 or is washed through C1 ) to media (M2) in vessel (C2), then, through fluid commu nication, exposing the next remainder (that which passes through C2 or is washed through C2) to media (M3) in vessel (C3), the exposing separating the Th and Bi from the Ra and Pb, and the Ra from the Pb to sequester the Th and Bi in one vessel, the Pb in another vessel, and the Ra in still another vessel.

Upon distributing the materials within the system, and with reference to configuration B of Fig. 1 , vessels C2 and C3 are washed with less strong or weaker HNO3 (< 7M, between 2M and 7M, or about 6M). In accordance with example implementations, M3 can then be washed with water to remove H ⁺ /excess Pb in configuration C. In configu ration D, Ra can be eluted from M3 (to which it was associated) with dilute EDTA solution (pH adjusted to >7), or a chelating solution with a bonding constant that is higher than that of Ra-01 resin. For example, Per Fig. 30, the Ra is EDTA bound -1 00% at a pH of -6, and is -50% EDTA bound at pH -5.3. Accordingly, methods of the present disclosure provide for separating Ra from being associated with a media by exposing the Ra and media to a chelating agent to form a mixture comprising the Ra complexed with the chelating agent.

The Ra/EDTA product solution is not compatible with loading onto a CatlX-based generator column. Adding enough HCI to the Ra/EDTA solution to drop the pH below -2 (Per Fig. 30, Ra is freed from EDTA at pH -4. By pH -2, the EDTA is rendered insoluble and precipitates out, leaving Ra in supernate) can decouple or disassociate the Ra from the EDTA (thereby producing free Ra ⁺⁺ ions in solution). The weakly acidified Ra ⁺⁺ solution can then be adsorbed onto the CatlX-based generator column.

The systems and methods of the present disclosure can provide purified ²²⁴ Ra product that can be loaded onto the CatlX generator column. Embodiments of the disclosure can be performed without boil- down or acid transposition steps. The purified Ra (without ²¹² Pb and ²¹² Bi progeny) can be handled in a low-dose state for several hours. This can allow for packing the generator colu mn, removing the colu mn from containment, and packing it for shipping before the dosage becomes an issue. Additionally, the present disclosure also provides fluidic systems to perform the methods. This can provide a fluidic platform. Table 1 . Commercial resins evaluated for the triple-colu mn process to isolate ²²⁴ Ra from ²²⁸ Th.

a. Functional group: Quaternary amine on macroporous polystyrene

divinylbenzene copolymer.

b. Functional group: Aliquat 336, an organic quaternary amine salt on

Amberchrom CG-71 polymer support.

c. Functional group: 18-crown-6 and 1-octanol on Amberchrom CG-71 polymer support.

d. Functional group: Presumed to be a 21-crown-7 on silica support.

An example overall fluidic protocol for the modified triple-column method is shown in Tables 2 and 3.

Table 2. Protocol for modified triple-column purification of ²²⁴ Ra from ²²⁸ Th. Example resins and column volu mes are included. ^a

a. C 1 = 1 cc TEVA resin ; C2 = 0.25 cc Sr Resin; C3 = 0.25 cc

Ra-01 resin.

b. ²²⁸ Th in equilibrium with ²²⁴ Ra and progeny.

c. pH was adjusted to ~ 11 . Table 3. Description of Steps for the Schematic of Fig. 1 .

Step Description

A Load and wash“a” to adsorb Th, Pb, and Ra on Col. 1 -3, respectively. _

B Secondary wash“b” for Col. 2-3 to assure complete transport of Ra between _ Col. 2 and 3. _

C Water rinse through Col. 3 to remove nitric acid. _

D Ra elution from Col. 3 via transchelation with EDTA solution. _

E Elution of Th from Col. 1 for recovery and eventual reuse.

During Step A, the prepared ²²⁸ Th/progeny stock solution (in 6 M H NO3) can be passed through three colu mns, each fluidically interlinked. The 6 M H NO3 concentration can provide high affinity of Th on the An IX media (1 ) and high affinity of Pb on the Sr media (M2). Du ring the load step, Th (and Bi/TI daughters) are adsorbed on M1 , Pb is adsorbed on M2, and Ra is adsorbed on M3.

Following up the load solution is wash“a”, comprising 6 M H NO3. This can provide for complete fluid transport of the load solution through the three tandem columns.

The Step A process efficacy is demonstrated by gamma spectra in Fig. 3. In this instance, M1 was an An lXpoiy. Solutions can be delivered to the three colu mns at 1 mL/min. The ²²⁸ Th/progeny load (a) and initial“wash a” solution (b) triple-column effluent fractions can be collected in test tubes and counted by gamma spectrometer. It was observed that no activity was present from the fractions that has passed through all three columns during the load and wash“a” steps; all activity was adsorbed onto the colu mns. Additionally, a direct gamma count of the C1 immediately after the completion of the load/wash“a” steps shows the presence of ²²⁸ Th, ²¹² Bi, and ²⁰⁸ TI (Fig. 3C). No ²¹² Pb or ²²⁴ Ra gamma peaks are observed on M1 , as these radionuclides have been adsorbed onto M2 and M3, respectively. The passage of ²²⁴ Ra out of C1 and C2 can be confirmed by evaluating a wash“a” effluent fraction that was diverted away from C3. In Fig. 4, rather pure ²²⁴ Ra in the C2 effluent can be observed, along with a trace of ²¹² Bi and ²⁰⁸ TI. The absence of ²¹² Pb spectral lines indicates the good collection efficiency of Pb on the Sr Resin (C2). Any freshly ingrown ²¹² Bi and ²⁰⁸ TI daughters of the C2-bound ²¹² Pb would likely not be retained on M2 during this step, but would rather be swept from C2 and pass through C3 to waste.

The role of M2 is to adsorb ²¹² Pb from the ²¹² Pb / ²²⁴ Ra mixture that passes through C1 . The 1 8-crown-6 ether extracting agent on the Sr Resin has strong affinity for Pb(l l) ions, and low affinity for Ra(l l) ions and Bi(l l l) ions in multi-Molar concentrations of HNO3 (see Fig. 5 and Fig. 6). Consequently, ²²⁴ Ra can pass through the Sr Resin and thereby collect onto M3. Any ²¹² Bi generated by ²¹² Pb on the M2 is u nretained and will pass out of C2 along with ²²⁴ Ra to C3. As the ²¹² Bi is likewise unretained on M3, it will pass to waste while ²²⁴ Ra is being loaded.

In Step B, C1 can be disconnected from the chain of vessels and remain static u ntil the end of the method, when the adsorbed ²²⁸ Th is recovered via a separate elution step. By disconnecting, the fluid communication is simply blocked off, but the conduit associated C1 and C2 can remain.

Wash“b”, comprising 2 M FINO3, can be passed through C2 and C3 to assu re quantitative transfer of Ra from C2 to C3. The Pb is strongly bound onto M2 and remains there. 2 M HNO3 can be used in this step because it provides the high level of affinity of Pb on the Sr Resin.

The Ra has a low level of affinity for the Sr Resin (M2) at 2 M FINO3 {k ~ 2, Fig. 6). This is evident by the slight retardation of Ra during the load / wash“b” step shown in Fig. 6 (b) . Flere, the ²¹² Bi trace represents an u nretained ion (k of <0.4) passing through the vessel ahead of the ²²⁴ Ra passage. Because of this slight Ra / resin affinity, wash “b” can require a volu me of ~ 10 ml_ to assu re complete Ra passage through the Sr Resin colu mn.

The wash “b” process data is demonstrated in Fig. 7 (a). The C2/C3 effluent fractions show no indication of ²¹² Pb or ²²⁴ Ra breakthrough from the columns. Once wash“b” is complete, Fig. 7 (b) demonstrates that a pure ²¹² Pb spectru m is observed on the Sr Resin column (C2).

Referring next to Fig. 8, in step C, C2 can be disconnected from C3, as M3 now contains the isolated ²²⁴ Ra fraction. Again, the disconnection does not remove the conduit connecting vessels C2 and C3, it simply prohibits fluid flow through the conduit.

Water can be flushed through the C3 in order to remove the HNO3 from the system. Ra remains strongly bou nd to M3 during the water flush as Ra affinity for Ra-01 resin increases as HNO3 concentration drops. Additionally, the water wash through C3 can result in removal of ²¹² Pb that may reside on the colu mn. This ²¹² Pb could be from C2 breakthrough or freshly ingrown ²¹² Pb produced by the M3-bound ²²⁴ Ra. A series of five 1 ml_ water effluent fractions were collected and analyzed by gamma spectroscopy. The removal of ²¹² Pb from C3 du ring the water wash is shown in Fig. 9 (a). By evaluating the water fraction decay rate over time, it was confirmed that the water fractions did not contain ²²⁴ Ra. The rate of activity loss was in agreement with the ²¹² Pb decay factor (Fig. 9 (b)). This indicates that no ²²⁴ Ra was co-eluted with ²¹² Pb du ring the water wash.

As ²²⁸ Th, ²¹² Bi, and ²⁰⁸ TI are locked onto M 1 of the now- disconnected C1 vessel and ²¹² Pb is locked onto M2 of the now- disconnected C2, and traces of ²¹² Pb on M3 were removed during the water rinse, the isolated ²²⁴ Ra that is bou nd onto M3 has a low associated dose rate. This is temporary, as progeny ingrowth quickly escalates dose on M3. Referring next to Fig. 10, in Step D, the ²²⁴ Ra on M3 was eluted using 5 mL of 0.05 M EDTA that had been adjusted to pH 11 using NaOH. Column effluent fractions were collected, and gamma spectrometry was performed. The resulting radiochromatogram is shown in Fig. 11 . In this ²²⁴ Ra elution, four milliliters contained the vast majority of the ²²⁴ Ra activity (it is contemplated that higher concentrations of E DTA, or a stronger chelating agent, or a smaller column volu me, would result in sharper 224Ra elution peaks.).

The series of ²²⁴ Ra elution fractions was cou nted repeatedly over the cou rse of -35 days in order to gauge the decay rate and assess the radionuclidic purity of the ²²⁴ Ra. Fig. 11 (B) shows that the rate of activity diminishment of the C3 elution product tracks with the theoretical ²²⁴ Ra rate of decay across several orders of magnitude. Importantly, the decay rate data indicates that no ²²⁸ Th is present in the ²²⁴ Ra product fraction, at least down to -0.1 % activity fraction.

Referring next to Fig. 1 2, the recovery of ²²⁸ Th from M 1 of C1 can be performed. In accordance with example implementations, methods for separating Ra from Pb, Bi, and Th can include separating one or more of Bi and/or Th from the Ra. The separating can associate the Bi and/or Th with a media (M 1 ). The method can further include disassociating the Bi and/or Th from the media (M 1 ) to form a mixture comprising the Bi and Th and transferring the mixture to a vessel housing at least Ra and additional Bi and/or Th. This vessel can be considered a“cow” that through decay generates additional Ra which can be used to initiate step A.

Th was eluted from the An lXpoiy media (M1 ) using 5 mL 8 M HCI. (Th can be eluted from 1 M to 1 2M). About 8M will be sufficient if the concentration is sufficient to elute the Bi and/or Th. Fig. 1 3 (a) shows the resulting spectra from these Th elute fractions. The first and second elutions showed most of the recovered Th. Additionally, it was observed that ²¹² Bi and ²⁰⁸ TI were eluted co-eluted with ²²⁸ Th, primarily in the first elute fraction. Complete ²²⁸ Th recovery from the An lXpoiy media (M1 ) was not possible in a 5 ml_ delivery of 8 M HCI. A direct count of C1 post-elution indicated that some fraction of Th remained on the column Fig. 1 3 (b). Subsequent to this ²²⁸ Th retention observation, 5 mL of 0.05 M EDTA (pH -3.5) was passed through C1 . This secondary elution treatment can provide improved Th removal from the M 1 .

Referring next to Figs. 14 and 15, fluidic systems capable of performing the methods of the present disclosure in a fully automated fashion are provided. The fluidic system architecture is presented as a schematic in Fig. 14. The system was designed with an eye towards operation remotely or in a shielded facility. Two digital syringe pumps (SP1 , SP2) are responsible for reagent delivery to the vessels (C1 , C2, and C3) ; these pumps can be located outside of the shielded zone to minimize chances of radiolytic degradation.

Within the shielded zone can be a third syringe pu mp (SP3). This pu mp can include a stepper motor and a disposable plastic syringe, for example. A role of SP3 is to withdraw the ²²⁸ Th“cow” solution (the first mixture, for example) into the sample injection loop indicated at the top of Fig. 14 and in Fig.15 (b) (upper left of image). Once the cow is loaded into the loop, the digital syringe pu mps located outside of the shielded zone can access the cow solution in the loop and direct it through the colu mns.

As the stepper motor can drive the syringe pu mp from voltage signals originating outside the shielded zone, and the stepper motor has no integrated circuits within it, the chances of radiolytic degradation of this component is small. For example, two of these stepper motors can be irradiated using a 208 R/hr ¹³⁷ Cs source within a hot cell. The motors received a total dose of -33,700 R over the course of 6.75 days. After removal of the motors from the hot cell, each was tested for functionality; both remained functional.

The fluids can be routed through a multitude of pathways using Teflon FEP tubing and solenoid-actuated valves that feature fluoropolymer wetted surfaces (Fig. 16 (b)). As the solenoids are electromagnetically actuated by voltages applied from outside the shielded zone, the potential for radiation-based component failure are low. The fluidic system can be routinely utilized in a fume hood (Or in a shielded location using multi-mCi levels of 228Th/224Ra) using ²²⁸ Th/ ²²⁴ Ra spiked solutions.

²²⁸ Th elution performance between 1 M and 8 M HCI were compared. The results are shown in Figs. 1 6 and 1 7.

As shown, the 8 M HCI demonstrated better ²²⁸ Th elution performance than in 1 M HCI. TEVA resin is an extraction chromatographic resin loaded with Aliquat 336, an organic quaternary ammonium salt. The load / wash“a” / elute performance of ²²⁸ Th on 1 cc TEVA resin colu mns was evaluated. Load / wash “a” was again performed using 6 M HNO3, and elution was performed at 1 M and 8 M HCI.

The ²²⁸ Th load / wash“a” performance from C1 (1 cc TEVA resin) is shown in Fig. 1 8. No discernable break-through of ²²⁸ Th was observed. As with M P-1 M resin, ²¹² Bi and ²⁰⁸ TI had low retention; they began breaking through the colu mn at the third load / wash“a” fraction.

The subsequent C1 ²²⁸ Th elutions with 1 M (Fig. 1 8 A) and 8 M HCI (Fig. 1 8 C, D) are shown. Flere, the reduced HCI concentration results in improved ²²⁸ Th recovery relative to that obtained from the stronger HCI concentration eluent. The use of lower concentration HCI is advantageous in a shielded environment, as less corrosion to the containment and equipment would be anticipated.

The 1 cc colu mn elution recovery fractions for ²²⁸ Th from Fig. 16 (MP-1 M) and Fig. 18 (TEVA resin) for 1 M ((A)/(B)) and 8 M ((C)/(D)) HCI eluents are provided in Table 4. From this table, it can be concluded that the optimal ²²⁸ Th elution recovery is obtained from a TEVA resin column, using 1 M HCI as the eluting solution. Table 4. ²²⁸ Th colu mn yields (%) for MP-1 M and TEVA resin columns (1 cc) as a fu nction of - 1 mL elution fraction volumes in 1 M and 8 M HCI. Primary recovery fractions are shaded grey

a. Cumulative activity fraction from a 5 mL 0.05 M EDTA (pH 3.5) strip, applied at the conclusion of the HCI elution.

As shown in Table 4, TEVA resin and MP-1 M can have a roughly equivalent ability to adsorb ²²⁸ Th from a load solution in a 6 M HNO3 matrix. 8 M HCI provides better (but incomplete) ²²⁸ Th elution from M P- 1 M relative to 1 M HCI. TEVA resin can provide improved ²²⁸ Th elution profiles relative to M P-1 M in both 1 M and 8 M HCI. ²²⁸ Th elution profiles from TEVA resin are better in 1 M HCI vs. 8 M HCI.

Other column geometries and volumes may be utilized as well. For example, the 1 cc SPE column geometry described above (0.56 x 4.5 cm) as well as 0.61 x 0.865 cm (0.25 cc volume, QML cartridge).

The results of the evaluation are shown in Fig. 19 (A), where the 2 ²⁸ Th elution profile is plotted (fractions were aged 32 days to allow 2 ²⁸ Th progeny ingrowth). The smaller-volume column resulted in earlier 2 ²⁸ Th release; ²²⁸ Th yield reached -96% after a 3 mL elution (Fig. 19 (B)). In comparison, the 1 cc column began its elution at the 2nd 1 mL fraction, and recovery reached -94% after a 3 mL elution. These recoveries are within experimental uncertainty of each other. Parallel column evaluations were performed with identical ²²⁸ Th load solutions (6 M HNO3) through a 1 cc and a 0.25 cc column of TEVA resin. The load effluents, which contain ²²⁴ Ra, were collected and aged over a ~ 1 month period. The decay rate of the ²²⁴ Ra-bearing TEVA effluent fraction can be used to determine its degree of purity from ²²⁸ Th. The results are shown in Fig. 20 (a) for a 1 cc and in Fig. 20 (b) for a 0.25 cc TEVA media. There can be a divergence of the ²²⁴ Ra- bearing fraction decay rate from the theoretical ²²⁴ Ra decay rate lay beyond ~28 d for the 1 cc column and beyond ~ 1 2 d for the 0.25 cc column. The 0.25 cc column can exhibit significantly greater ²²⁸ Th breakthrough du ring the load step than the 1 cc column.

Table 5. TEVA resin cartridges and colu mn evaluated for ²²⁸ Th sorption, desorption, and breakthrough. a

a. Some column chambers are slightly tapered cylinders; reported volumes based on a conical frustum.

b. Normalized value, relative to the 1 cc SPE column

c. Transit time for non-retained species in the resin bed.

d. HML =“half-milliliter”

QML =“quarter-milliliter

In both cases, the colu mn effluent fractions were aged a minimum of 40 days to allow for complete ²²⁸ Th progeny ingrowth. The resulting ²²⁸ Th + progeny gamma spectra was used to quantify the ²²⁸ Th activity in each fraction. The four TEVA resin cartridges and the TEVA resin S PE column listed in Table 5 received identical ²²⁸ Th-spiked solutions in 6 M HNO3. Delivered flow rate was 1 mL/min. C1 effluents were collected and aged for up to two months. Du ring this time, the decay rate of each ²²⁴ Ra- bearing TEVA load / wash “a” effluent fractions were tracked to determine its degree of purity over ²²⁸ Th. The results are shown in Fig. 21 for the four machine-packed cartridges and Fig. 22 (a) for the hand- packed 1 cc SPE tube.

Accordingly, a 1 cc and 0.25 cc TEVA resin provided roughly equivalent ²²⁸ Th elution yields after a 3 ml_ elution volume in 1 M HCI (Fig. 1 9). The 1 cc TEVA resin retained a greater fraction of ²²⁸ Th during the load / wash “a” step than the 0.25 cc colu mn volu me, as some ²²⁸ Th breakthrough was observed (Fig. 20). The 1 cc TEVA resin therefore provides a higher pu rity ²²⁴ Ra fraction passing into the remaining fluidic system.

The measured column load fraction activity values can begin to deviate from the theoretical ²²⁴ Ra decay curve at progressively earlier elapsed times as the cartridge bed volu me decreases. These observed decay curve deviations can be related to increasing levels of ²²⁸ Th in the ²²⁴ Ra-bearing colu mn load fractions. Next, the ²²⁸ Th decay profile can be fitted atop the data points that lay beyond 40 elapsed days. Extrapolation of the curve to the y-intercept provided an estimate of the ²²⁸ Th activity fraction present in the ²²⁴ Ra-bearing column load effluents. It is observed that the calculated ²²⁸ Th activity fraction increases as the TEVA cartridge volume decreases (Fig. 21 , grey dashed lines).

These calculated ²²⁸ Th activity fractions are presented in Table 6. From these, ²²⁸ Th decontamination factors ( DF) in the ²²⁴ Ra-bearing TEVA colu mn load fractions can be obtained. The QML cartridge (the smallest TEVA resin bed volume evaluated) had a surprisingly high calculated ²²⁸ Th load / wash“a” breakthrough of ~ 1 .6% {DF = 61 ). This breakthrough fraction can be reduced to 0.018% for the largest bed volume (2 ml_) cartridge (DF = 548).

Table 6. Observed performance of TEVA resin columns / cartridges of the resin bed geometries listed in Table 5 : ²²⁸ Th decontamination factors ( DF) in the ²²⁴ Ra elution fraction, and ²²⁸ Th yields from the load / wash / elute process.

a. Values based on ²²⁸ Th“load” fraction decay profiles.

b. Obtained from the inverse of ²²⁸ Th activity fraction

c. Values based on sum of column load / wash / elute fractions (see cumulative yield traces in Figure 22 and Figure 23).

d. FiML =“half-milliliter”

e. QML =“quarter-milliliter”

It is interesting to note that the ²²⁸ Th activity fractions for the four Eichrom TEVA resin cartridge type load / wash “a” effluents follow a negative power fu nction when modeled against each cartridge’s resin bed volume (provided in Table 5). The modeled curve is y = 0.00268x ^{_ 1 1 1 1 2} (R ² = 0.9797), and, the 1 cc SPE tube activity fraction does not fit this curve.

It is noted that the data presented may indicate that the hand- packed 1 cc SPE tube provided the highest ²²⁸ Th decontamination factor (even higher than the 2 cc TEVA cartridge).

The second cartridge / column performance evaluation was to assess the quality of the ²²⁸ Th elution profile. After the load / wash“a” solution had been delivered to each of the TEVA cartridges shown in Table 6, the ²²⁸ Th was eluted with 1 0 ml_ of 1 M HCI, delivered at 1 mL/min. Approximately 1 ml_ fractions were collected. The cumulative ²²⁸ Th fraction yields are shown for the four TEVA resin cartridge types in Fig. 23.

The ²²⁸ Th elution profiles are consistent with the anticipated peak broadening associated with increasing TEVA resin bed volu mes. However, even for the largest (2 mL) TEVA cartridge, the ²²⁸ Th recovery was virtually complete after the third fraction. The ²²⁸ Th cumulative yield for the 1 cc SPE tube is shown in Fig. 22 (b) its yield is likewise virtually complete after 3 mL of eluent. The ²²⁸ Th elution yields, calculated from the su m of all load / wash / elute fractions, is shown in Table 6. ²²⁸ Th elution yields between 94% and 98% were observed, and this spread is within experimental uncertainty.

The machine-packed / commercially available TEVA cartridges exhibited ²²⁸ Th breakthrough levels that increased with decreasing cartridge bed volu me. The hand-packed 1 cc SPE tube provided the least degree of ²²⁸ Th breakthrough vs. the cartridges. The TEVA SP E vessel and cartridges exhibited nearly complete ²²⁸ Th elutions after 3 mL of 1 M HCI eluent had been delivered at 1 mL/min. Overall, the hand-packed 1 cc SPE TEVA colu mn provided a higher-purity ²²⁴ Ra fraction relative to the machine-packed TEVA cartridges.

Regarding Media M2, the 18-crown-6 ether extracting agent on the Sr Resin column has strong affinity for Pb(l l) ions, and low affinity for Ra(l l) ions and Bi(l l l) ions in HNO3. Consequently, ²²⁴ Ra is able to pass through the Sr Resin colu mn be collected onto C3, Ra-01 resin). The ²¹² Bi, which passed with ²²⁴ Ra through the C2, is likewise u nretained on Col. 3 - so this dose-causing radionuclide is sent to waste while ²²⁴ Ra is being loaded. The ²¹² Pb removal by C2, and the transference to waste of ²¹² Bi following C3 can reduce the radiological dose imparted by ²²⁴ Ra progeny.

The HML (0.41 cc) and QML (0.25 cc) both from Eichrom, as shown in Fig. 24 may be used for M2. The Sr Resin-bearing cartridges were loaded into the triple-column system in the C2 slot, and the C1 slot was configured with 1 cc TEVA resin columns. No C3 was installed. C1 C2 effluent fractions were collected du ring the ²²⁸ Th/ ²²⁴ Ra colu mn load + wash“a” steps.

The results for the 0.41 cc HML and the 0.25 cc QML cartridge effluents are shown in Fig. 25 (A) and Fig. 25 (B), respectively. The gamma spectra (Fig. 25) are virtually the same; in both cases, ²¹² Pb was successfully scrubbed from the ²²⁴ Ra-bearing stream. The cartridges are between 0.41 cc and 0.25 cc in volume, and each of these performed virtually the same at removing ²¹² Pb from the ²²⁴ Ra- bearing load stream.

In accordance with another example implementation, ²²⁸ Th/ ²²⁴ Ra can be provided as a solution directly through C3, and C3 effluent fractions collected throughout the process.

The load + wash“a” fraction gamma spectra are shown in Fig. 26 (A), and the wash“b” fractions are shown in Fig. 26 (B). ²²⁸ Th can be eliminated from the Ra-01 column du ring the wash“a” steps. During the wash “b” steps, no ²²⁸ Th is apparent; the ²²⁸ Th has been largely eliminated from C3. This data indicates that any ²²⁸ Th that may break through C1 and into the downstream fluidic system during the load / wash“a” step would pass, u nretained, through the Ra-01 resin.

The spectra above also indicates that ²¹² Bi/ ²⁰⁸ TI is largely u nretained on the Ra-01 . There is an obvious absence of ²¹² Pb in the Ra-01 effluent fractions; ²¹² Pb may be retained on Ra-01 resin (which is why C2 (Sr Resin) is upstream to the Ra-01 resin column to strip it out).

In accordance with example implementations, a water wash can be placed between wash “b” and the ²²⁴ Ra elution step. The water would be used to remove residual H ⁺ ions from the column prior to the introduction of the pH ~ 11 ²²⁴ Ra eluent solution. The impact of the water wash through the Ra-01 resin is shown in Fig. 28 (A). ²¹² Pb (retained on the Ra-01 colu mn due to the lack of C2 upstream in this experiment) is removed from the vessel in water. An evaluation of the decay rate of these colu mn effluent fractions indicated that ²²⁴ Ra was not present (Fig. 28 (B)). Therefore, indications were that the water wash could be employed to eliminate excess H ⁺ ions (preventing EDTA precipitation) and fu rther remove ²¹² Pb from the Ra-01 resin (thus reducing ²²⁴ Ra product dose) without impacting ²²⁴ Ra elution yield.

It is preferable that the wash “a” volume is sufficient to assure passage of ²²⁴ Ra through C1 and onto C2/C3 (Step A), and the wash “b” volu me is sufficient to assure passage of ²²⁴ Ra through C2 and onto C3 (Step B). The load / wash“a” volumes shown in Fig. 27 are therefore more than adequate to accomplish the Step A objective.

Following the water wash, the Ra-01 resin contained isolated ²²⁴ Ra. The ²²⁴ Ra was eluted using the EDTA solution, and the eluent fraction’s decay rate was monitored to evaluate its radionuclidic purity.

The results presented in Fig. 28 indicate that the addition of a water wash between wash“a” and the ²²⁴ Ra elution serves to eliminate H ⁺ ions from the column, which in turn eliminates acidification of the basic EDTA-based ²²⁴ Ra eluent. Additionally, the water wash was observed to remove ²¹² Pb from the column, while ²²⁴ Ra was retained.

The results presented in Fig. 29 indicate that the single-colu mn (C3) separation of ²²⁴ Ra from ²²⁸ Th with the Ra-01 resin is capable of a >1000-fold decontamination factor (decontamination factor determination was limited by dynamic range of the analysis method). In other words, <0.1 % of any ²²⁸ Th that manages to break through C1 during the load / wash“a” step (the two steps wherein all three colu mns are inter-connected) would be expected to be fou nd in the ²²⁴ Ra elute. It is believed that the C1 ²²⁸ Th retention factor is at least 1000. If this is so, then the approximate ²²⁸ Th decontamination factor across the entire triple-colu mn method is >1 x1 0 ⁶ .

While the radionuclidic pu rity of ²²⁴ Ra is essential in providing a robust isotope product, it is just as important that the output of the triple-colu mn method be amenable to existing and future ²²⁴ Ra/ ²¹² Pb generators.

For the existing ²²⁴ Ra/ ²¹² Pb generator design, the ²²⁴ Ra source is loaded onto a CatlX resin column (using AG MP-50 resin beads). Therefore, the Ra output from the triple-colu mn method should be amenable to direct loading onto CatlX resin. Unfortunately, the purified Ra product, delivered in dilute EDTA solution (pH adjusted to > 7), will not bind to CatlX resin as a free divalent cation ; according to the speciation plots for Ra/EDTA mixtures (Fig. 30), Ra is completely bound to EDTA above pH 7. The chelated complex likely progresses from NaRa(EDTA) to Na2Ra(EDTA) as the pH increases above 7. However, at pH values near 5, the Ra/EDTA complex is -50%, and at pH values < 4, the Ra ⁺⁺ cation is completely dissociated from the EDTA complex.

The information presented above indicates that lowering the ²²⁴ Ra/EDTA product solution pH to < 4 will result in free Ra ⁺⁺ cation in solution. The schematic shown in Fig. 31 provides a pathway to binding free Ra ⁺⁺ onto a generator column packed with AG MP-50 CatlX resin.

One milliliter of the isolated ²²⁴ Ra product (5 ml_) resulting from the triple-column separation can be acidified using 21 .7 mI_ of concentrated HCI (0.26 mmoles H ⁺ added). Next, the acidified solution can be delivered to a MP-50 resin at 0.5 mL/min. The data in Fig. 32 (a) shows the activity observed in the colu mn load effluent fraction as a fu nction of elapsed days. Virtually no activity is present in the colu mn effluent solution. Subsequent to media load, the media can be washed with five 1 ml_ fractions of dilute HCI solution (Fig. 32 (b)). An elution of a short-lived daughter isotope is observed immediately after the fractions were collected; the isotope decays away within the first -0.18 days (~4 h), and this shows now bleed-through of ²²⁴ Ra during the wash. Continuous counting of the CatlX column over -7 days shows the characteristic decay rate of ²²⁴ Ra beyond - 1 .6 days (Fig. 32 (c)).

The results in Fig. 32 indicate that acidification of the isolated ²²⁴ Ra product fraction can provide for quantitative loading of the ²²⁴ Ra onto a CatlX column. Therefore, the triple-column method appears to be well suited to the subsequent ²²⁴ Ra/ ²¹² Pb generator colu mn preparation via a simple solution acidification step.

As can be seen in Fig. 33, at least one schematic depiction of the preparation of the Ra ⁺⁺ is shown. The chemical modification chamber can receive the ²²⁴ Ra eluent directly from the triple-colu mn method Step D. Within this chamber, acid can be injected to reduce the solution pH to a point in which the Ra/EDTA complex is eliminated, thereby producing free ²²⁴ Ra ⁺⁺ ions in solution (per Fig. 30). A stir bar ensures efficient mixing of acid into the ²²⁴ Ra eluent.

If the solution is acidified to -pH 2, not only does the ²²⁴ Ra ⁺⁺ dissociate from the Ra/EDTA complex, but the EDTA precipitates from the solution. Once the precipitate is fully formed, the supernate can be withdrawn from the base of the chemical modification chamber, through a hydrophobic polyethylene frit for example, thereby removing the EDTA from the ²²⁴ Ra ⁺⁺ solution.

Table 7. Syringe pu mp distribution valve port and descriptions of system illustrated in Fig. 33.