RU2538398C1 - Method of producing strontium-82 radioisotope - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: method includes irradiating a target on a proton accelerator and separating ⁸²Sr without a carrier from the irradiated target. The target used is the ⁸⁴Sr isotope; the target is irradiated with a beam of protons; during irradiation, as a result of a threshold nuclear reaction ⁸⁴Sr(p, 3n)⁸²Y, ⁸²Y is produced in the target and extracted from the target using a radiochemical technique, wherein the decay product of ⁸²Y, which is the desired ⁸²Sr (without carrier) isotope, is further separated using a radiochemical technique. The object of the invention is to produce ⁸²Sr without a carrier in the proton energy range of E_p≤30-40 MeV, using standard cyclotrons with E_p≤30-40 MeV to produce ⁸²Sr, increasing the integrated yield of ⁸²Sr in a production scheme based on the reaction Rb(p, xn)⁸²Sr on accelerators with E_p=70-100 MeV for producing ⁸²Sr.

EFFECT: solving the set task.

2 cl, 1 dwg

Description

The invention relates to a technology for producing radioisotopes for nuclear medicine on charged particle accelerators.

At present, one of the most promising and dynamically developing areas of nuclear medicine is cardiac diagnostics based on the method of positron emission tomography (PET).

Recently, mainly in the USA, PET technology has been developed based on the use of ⁸² Sr- ⁸² Rb isotope generators.

In our country, in connection with the planned construction of PET centers, the indicated isotope generator should also find wide application.

Obtained in the isotopic generator of rubidium, being a physiological analogue of potassium, when introduced into the patient's body, it is mainly localized in the myocardium.

The specified generator is compact, can be easily delivered to any clinic, including over long distances, and can be used for quite a long time. At the same time, there is no need to have and operate a cyclotron in the clinic (bulky and expensive equipment that requires special facilities and maintenance personnel).

The present invention can be used for the production of ⁸² Sr radioisotope in practically significant quantities on standard, relatively inexpensive to operate and fairly widespread proton accelerators of medium energies (E _p ≤30 ÷ 40 MeV). (At present, ⁸² Sr is produced at high-energy accelerators (E _p ≈100 ÷ 800 MeV), intended for basic research.)

Traditional methods for producing cyclotron radioisotopes involve the use of a sequence of technological operations in each production cycle, usually carried out in manual mode: manufacturing and mounting a disposable target on the accelerator’s ion duct, dismantling the irradiated target, opening the target mechanically, dissolving the active substance. All these operations are quite time-consuming, expensive and must be carried out in special conditions. Unlike traditional methods, the proposed method for producing ⁸² Sr allows one to quite easily automate the process of extracting ⁸² Sr from the target in a continuous mode during operating time, eliminating the laborious and expensive radiochemical redistribution operations characteristic of other methods from the procedure for strontium extraction.

State of the art

At present, ⁸² Sr are produced by proton irradiation (E _p ≈100–800 MeV) of solid targets from molybdenum, metallic rubidium, or its compounds at high-energy accelerators.

A known method of producing ⁸² Sr by the reaction of Mo (p, spallation) (Thomas KE Strontium-82 Production at Los Alamos National Laboratory. - Applied Radiation and Isotopes, 1987, v. 38, No. 3, pp175-180). Targets made of metal molybdenum with a diameter of 1.9–6.4 cm and a thickness of 1.25–1.9 cm were irradiated with proton beams with an energy of 800 MeV. As a result of the cleavage reaction, ⁸² Sr. was formed. The duration of irradiation of various targets ranged from 2 to 30 days. The nominal current of the proton beam is 500 μA. Then the targets were dissolved in a mixture of nitric and phosphoric acid in the presence of hydrogen peroxide. After that, ⁸² Sr. was isolated by a multi-stage chemical redistribution

This method has significant disadvantages, which are as follows:

- To obtain ⁸² Sr, a unique and expensive installation is used, mainly intended for basic research: the meson factory of the Los Alamos National Laboratory of the USA;

- the technology is based on the use of a disposable target;

- along with ⁸² Sr, a large amount of radioactive impurities is formed in the target;

- the release of ⁸² Sr is associated with the need for multi-stage radiochemical redistribution of the target and the disposal of a large amount of radioactive waste;

- high content in the target product of the main interfering impurity ⁸⁵ Sr, the activity of which is comparable to the activity of the target product.

It is known that one of the significant factors determining the quality of ⁸² Sr is its radionuclide purity. The main radionuclide impurities are ⁸³ Sr and ⁸⁵ Sr. The activity of ⁸³ Sr can be significantly reduced by the exposure of the irradiated target (T _{1 | 2} = 32.4 hours for ⁸³ Sr). As for the long-lived ⁸⁵ Sr (T _{1 | 2} = 64.73 days), its presence in ⁸² Sr significantly increases the dose load on the patient and the medical staff and complicates the PET studies (with partial “breakthrough” of strontium in the ⁸² Sr- ⁸² separation column Rb of the isotope generator), since ⁸⁵ Sr has an intense line E _γ = 514 keV, close to the annihilation line ⁸² Rb (E _γ = 511 keV). In addition, the presence of ⁸⁵ Sr substantially increases the radiation protection requirements of the ⁸² Sr- ⁸² Rb isotope generator and reduces its service life before recharging.

A known method of producing ⁸² Sr by the reaction of Rb (p, xn) on targets from metal rubidium (Zhuikov B. L., Kokhanyuk V. M., Glushenko V. N. and others. Obtaining strontium-82 from a target metal rubidium in a proton beam with an energy of 100 MeV. - Radiochemistry, 1994, Volume 36, pp. 494-498). The targets made of metal rubidium were disks with a diameter of 30 mm and a thickness of 11 mm, enclosed in sealed stainless steel shells. The thickness of the entrance window of the shell was 0.13-0.2 mm. The shells were charged with metallic rubidium in a box in an inert atmosphere. To do this, rubidium in an ampoule was heated by an electric furnace to 80-90 ° C, taking liquid rubidium with a medical syringe, liquid metal was introduced through a nozzle into the shell. Target irradiation was carried out on a linear accelerator with a proton beam with an energy of 100 MeV at beam currents of 6–10 μA. The exposure time reached 10 days. The technology for processing the target included mechanical opening of the cartridge and dissolution of the target in isobutanol, destruction of the rubidium isobutonolate formed during dissolution of the target and separation of the organic phase by distillation, separation of strontium isotopes from rubidium on an ion-exchange column.

The disadvantages of this method, as in the previous example, include:

- use for the production of ⁸² Sr of an expensive high-energy accelerator (linear accelerator of the INR RAS, Troitsk);

- rather complicated procedure for manufacturing the target;

- the technology is based on the use of a disposable target;

- the allocation of ⁸² Sr is associated with the need for multi-stage radiochemical redistribution of the target;

- high content in the target product of the main interfering impurity ⁸⁵ Sr, the activity of which is comparable to the activity of the target product.

In addition, a significant disadvantage of this method should be considered a high potential explosion hazard due to the use of metallic rubidium.

A known method of producing ⁸² Sr in the reactions Kr (α, xn) and Kr (3He, xn) when irradiated with accelerated beams of α particles or 3He targets from natural krypton (Tarkanyi F., Qaim SM, Stocklin G. Excitation Functions of ³ He- and α-Particle Induced Nuclear Reactions on Natural Krypton: Production of ⁸² Sr at a Compact Cyclotron. - Applied Radiation and Isotopes, 1988, v. 39, No. 2, pp135-143). When using natural krypton and accelerated α particles or 3He with an initial energy of 60–80 MeV as a target, the production of ⁸² Sr is possible on all Kr isotopes except ⁷⁸ Kr. However, the ⁸² Sr production time on each of the isotopes using natural krypton is not optimal, since the cross sections for nuclear reactions leading to the formation of ⁸² Sr on each of the krypton isotopes vary over a wide range (from 0 to σ _max ) in the energy range of drag in the target charged particles.

The disadvantages of this method include:

- a relatively low yield of ⁸² Sr in the target from natural krypton;

- high content in the target product of the main interfering impurity ⁸⁵ Sr, the activity of which is comparable to the activity of the target product.

A known method of producing a radioisotope ⁸² Sr by the reactions of ^{80.82.83.84.86} Kr (α, xn) ⁸² Sr or ^{80.82.83.84.86} Kr (3Не, xn) ⁸² Sr (Zagryadsky V.A., Latushkin S.T., Novikov V.I., Ogloblin A.A., Unezhev V.N., Chuvilin D.Yu., Shatrov A.V., Yartsev D.I .; Patent No. 2441290 of January 27, 2012 . "A method of obtaining a radioisotope of strontium-82"). The method includes irradiating at the cyclotron or linear accelerator with a beam of α particles or 3H nuclei a cascade target consisting of modules with krypton isotopes arranged in series, in decreasing order of their atomic masses in the direction of the accelerated particle beam, and accumulating in it one or several threshold particles nuclear reactions ^{80.82.83.84.86} Kr (α, xn) ⁸² Sr or, respectively, one or more threshold nuclear reactions ^{80.82.83.84.86} Kr (3He, xn) ⁸² Sr of the target radioisotope ⁸² Sr .

The disadvantages of this method include the operational limitations of the ⁸² Sr optimal cascade target, consisting in the need for tight matching of the length of the modules with krypton isotopes with the beam current and gas pressure in them. The need for this coordination is associated with the appearance of a gas density gradient in the target under the action of a beam of charged particles and, as a result, a change in the optimal path lengths in the modules of the cascade target.

As a prototype, a method for producing ⁸² Sr by the reaction of Rb (p, xn) on targets from rubidium chloride (Mausner LF, Prach T., Srivastava SC Production of ⁸² Sr by Proton Irradiation of RbCl. - Applied Radiation and Isotopes, 1987, v .38, No. 3, pp181-184). For the purpose of dehydration, rubidium chloride was kept in vacuum for 48 hours, then a tablet of 0.81 cm thick and 4.44 cm in diameter was pressed with a force of 75 tons in 35 g. A rubidium chloride tablet was placed in a stainless steel capsule and sealed in a vacuum with an electron beam. Then, the capsule with rubidium chloride was irradiated with protons at the accelerator of the Brookhaven National Laboratory, which allows accelerating protons to an energy of 200 MeV. The proton beam current was 45 μA. After irradiation, the capsule was transported in a protective container to a hot laboratory and after 6 days the extracts were opened. Then rubidium chloride was dissolved in 100 ml of 0.1 M NH ₄ OH: 0.1 M NH ₄ Cl and ⁸² Sr. was isolated after multistage radiochemical redistribution.

The disadvantages of this method include:

- the use to obtain ⁸² Sr of an expensive high-energy accelerator;

- rather complicated procedure for manufacturing the target;

- the technology is based on the use of a disposable target;

- due to the poor thermal conductivity of rubidium chloride at currents above a few μA, overheating in the center of the target and sublimation of rubidium chloride is possible, which leads to a decrease in the effective thickness of the target and, accordingly, the yield of the target product;

- the allocation of ⁸² Sr is associated with the need for multi-stage radiochemical redistribution of the target;

- high content in the target product of the main interfering impurity ⁸⁵ Sr, the activity of which is comparable to the activity of the target product.

Disclosure of invention

Technical results are:

1) The ability to produce ⁸² Sr in a fundamentally different (different from the traditional) range of proton energies (E _p ≤30 ÷ 40 MeV), which allows the use of a fundamentally different class of plants for the production of ⁸² Sr: standard, relatively cheap to operate, and quite widespread in world cyclotrons with E _p ≤30 ÷ 40 MeV.

2) The ability to significantly increase the integral yield of ⁸² Sr using the well-known operating time for the reaction Rb (p, xn) ⁸² Sr in accelerators with E _p = 70 ÷ 100 MeV due to the additional use of protons with E _p <40 MeV (reaction threshold Rb ( p, xn) ⁸² Sr) to produce ⁸² Sr by the reaction ⁸⁴ Sr (p, 3n) ⁸² Y → ⁸² Sr (cascade target).

3) The use of a reusable target, eliminating the cost of manufacturing new targets for each new irradiation cycle.

4) The ability to relatively easily automate the allocation of ⁸² Sr, abandoning the classical technological operations implemented during radiochemical redistribution of the target, and carried out, as a rule, in manual mode.

5) A significant decrease compared with the prototype of the main interfering activity of ⁸⁵ Sr.

To achieve these results, a method for producing a ⁸² Sr radioisotope is proposed, which involves irradiating the target with protons and isolating ⁸² Sr from the irradiated target, while the ⁸⁴ Sr isotope is taken as the target, during the irradiation of which as a result of a threshold nuclear reaction ⁸⁴ Sr (p, 3n) ⁸² Y in the target is produced and simultaneously, by the radiochemical method, ⁸² Y is continuously extracted from the target, the decay product of which, the target radioisotope ⁸² Sr without carrier, is then isolated by the radiochemical method.

In this case, the ⁸⁴ Sr isotope is a part of a chemical compound, the aqueous solution of which in a closed circuit circulates through the proton irradiation zone and through a centrifugal extractor, in which the ⁸² Y generated by the extraction method is separated from the strontium of the target.

The figure illustrates a schematic diagram of the implementation of the method of production and allocation of ⁸² Sr.

1. The target.

2. Extractor.

3. Reextractor.

4. The contour of the aqueous phase.

5. The contour of the organic phase.

6. The contour of the aqueous phase.

7. The pump.

p - Proton beam with Ep≤30 ÷ 40 MeV.

The method is as follows.

An aqueous solution of the strontium compound enriched in the ⁸⁴ Sr isotope is taken and placed in a closed loop in which the solution is forcedly circulated through the proton 1 irradiation zone (see drawing) and centrifugal extractor 2. In the irradiation zone 1, according to the ⁸⁴ Sr reaction (p, 3n) ⁸² Y produces ⁸² Y having a half-life of 10 minutes. ⁸² Y along circuit 4 is sent to a centrifugal extractor 2, where it is extracted into the organic phase, which is forcibly circulated in circuit 5. At the same time, the strontium of the target remains in circuit 4. Then ⁸² Y along circuit 5 is sent to centrifugal reextractor 3, where it is forcedly extracted into the aqueous phase circulating in circuit 6. In circuit 6, ⁸² Y and ⁸² Sr decay product are accumulated during proton irradiation time of the target. The total time of movement ⁸² Y along circuit 4 from the irradiation zone 1 to extractor 2, extraction from the aqueous phase to the organic phase, movement along circuit 5 from extractor 2 to reextractor 3 and reextraction from the organic phase of circuit 5 to the aqueous phase of circuit 6 is about 1 minute . After several hours of exposure after irradiation ( ⁸² Y decay), ⁸² Sr without a carrier from circuit 6 is sent for further purification by the sorption method (not shown in the figure).

The proposed method for producing a radioisotope ⁸² Sr has significant advantages compared to analogues and prototype described in the literature:

- The method can be implemented on relatively inexpensive to operate and widely used in the world accelerators of medium energies (E _p ≤30 ÷ 40 MeV).

- The target device can be used repeatedly.

- The yield of ⁸² Sr is acceptable for practical use.

- Isolation of ⁸² Sr from the target is easy to automate and is not associated with the need for its destruction and multistage radiochemical redistribution.

- The activity of the main interfering impurity ⁸⁵ Sr when using strontium enriched in the ⁸⁴ Sr isotope can be reduced by an order of magnitude compared to the prototype.

An example embodiment of the invention

The target device, which is a compact copper cylinder with an inner cylindrical cavity h × d = 10 × 15 (mm) with an end window of 50 μm thick Mo foil, was mounted on a proton beam with Е _р = 32 MeV of the U-150 cyclotron of the Kurchatov Institute Research Center ". An aqueous solution of SrCl ₂ (Sr of natural isotopic composition) in 0.1 M HCl (aqueous phase) was pumped through a target device 1 (see the drawing) and through a centrifugal extractor 2 in a closed loop 4 using a pump. At the same time, in circuit 5, a pump was used to circulate a 50% solution of D2-ethylhexylphosphoric acid in toluene, and in circuit 6 to circulate an aqueous solution of 3 M HCl.

Under the action of the proton beam at the target device ⁸⁴ by the reaction of Sr (p, 3n) accumulating Y ^{82 82 82} Y Y. Then, the flow of the aqueous phase over the contour 4 transported to the centrifugal extractor where it was extracted with 50% sodium D2-etilgeksilfosfornoj acid in toluene ( organic phase). After this, the ⁸² Y stream of organic phase was transported along circuit 5 to a centrifugal reextractor 3, where ⁸² Y was reextracted with 3 M HCl into the aqueous phase of circuit 6. ⁸² Y and its decomposition product ⁸² Sr were accumulated in circuit 6 (without carrier). After the end of irradiation and exposure (for the decay of ⁸² Y) for 2 hours, ⁸² Sr was sent for further purification by the sorption method. The total time of movement ⁸² Y along circuit 4 from the irradiation zone 1 to extractor 2, extraction from the aqueous phase to the organic phase, movement along circuit 5 from extractor 2 to reextractor 3 and reextraction from the organic phase of circuit 5 to the aqueous phase of circuit 6 was about 1 minute .

The separation coefficient of yttrium and strontium by centrifugal extractor 2 amounted to 10 ⁶ . The yield of ⁸² Sr at a concentration of SrCl ₂ in solution of 0.6 g / ml (taking into account reduction to ⁸⁴ Sr isotope enrichment to 100%) was 112 μCi / μA hour.

Claims (2)

1. A method of producing a ⁸² Sr radioisotope, comprising irradiating the target with protons and isolating ⁸² Sr from the irradiated target, characterized in that the ⁸⁴ Sr isotope is taken as the target, during the irradiation of which, as a result of a threshold nuclear reaction, ⁸⁴ Sr (p, 3n) ⁸² Y ⁸² Y is produced in the target and at the same time, by the radiochemical method, ⁸² Y is continuously extracted from the target, the decay product of which, the target radioisotope ⁸² Sr without carrier, is then isolated by the radiochemical method. 2. The method according to claim 1, characterized in that the ⁸² Sr isotope is part of a chemical compound, the aqueous solution of which in a closed circuit circulates through the proton irradiation zone and through a centrifugal extractor, in which the produced ⁸² Y is separated from the strontium by the extraction method.

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