RU2598089C1 - Method of producing strontium-82 radionuclide - Google Patents

Abstract

FIELD: nuclear physics; chemistry.

SUBSTANCE: invention relates to physical-chemical separation of radionuclides, particularly to a method of producing strontium-82 radionuclide, and can be used in nuclear medicine. Method involves irradiating with an accelerated proton beam with energy 70 MeV a container with rubidium chloride or rubidium metal target, evaporating target substance in a ballast volume in high vacuum at temperature of 900-950 °C, evaporating strontium-82 radionuclide remaining on inner surface of container at temperature 1,500-1,900 °C and simultaneous deposition thereof onto a cooled collector, from which it is subsequently washed off with hydrochloric or nitric acid solution.

EFFECT: invention simplifies production of strontium-82 radionuclide and provides high output of end product.

1 cl, 4 dwg

Description

The invention relates to the field of physico-chemical separation of radionuclides, in particular to methods for producing strontium radionuclides. The invention can be used in nuclear medicine for the production of a radioisotope generator of strontium-82 radionuclide. The invention relates to a technology for producing radioisotopes for nuclear medicine on charged particle accelerators.

Currently, one of the most promising and dynamically developing diagnostic areas of nuclear medicine is the method of positron emission tomography (PET), using radionuclides emitting positrons. Nowadays, short-lived β ⁺ emitters — ¹¹ C, ¹³ N, ¹⁵ O, and ¹⁸ F radionuclides — are mainly used for PET diagnostics. The use of these short-lived radionuclides with half-lives of minutes-hours suggests the presence of cyclotrons with incident particles in the range of 10 in the corresponding PET centers -20 MeV. The need to use a cyclotron significantly complicates the use of the PET diagnostic method in small PET centers, since it requires additional significant costs for its operation.

The method of radioisotope generators allows you to overcome these difficulties. This method is currently widely used in developed countries, in particular, PET technology based on the use of an isotope generator based on strontium-82, which is the mother nucleus (generator) of the rubidium-82 β ⁺ emitter, has been widely developed.

The specified radionuclide pair has the following nuclear physical characteristics:

Sr-82: T _{1 | 2} = 25.55 days; ε ⁺ (100%); no accompanying gamma quanta.

Rb-82: T _{1 | 2} = 1.27 min; β ⁺ (95%), ε ⁺ (5%), γ-quanta: annihilation E _γ = 511 keV and E _γ = 776 keV.

The properties of this radionuclide pair provide unique opportunities for use in the diagnosis of PET by the method. The generator charged with strontium-82 can be easily delivered to a clinic located in any remote corner of the globe and operated for a fairly long time (about two months). In this case, the need for a cyclotron naturally disappears.

A known method of producing Sr-82 in the reaction of irradiation of molybdenum with protons with an energy of 800 MeV: "Thomas KE Strontium-82 Production at Los Alamos National Laboratory. - Applied Radiation and Isotopes, 1987, v. 38, No. 3, p. 175-180" [one]. The targets made of metal molybdenum in the form of thin foils are irradiated with a proton beam with an energy of 800 MeV and a current of up to 500 μA. In the deep cleavage reaction, Sr-82, other strontium isotopes, and many other radionuclides with Z≤42 are formed. After ten days of exposure, the targets are dissolved in a mixture of nitric and phosphoric acids and hydrogen peroxide. Then, as a result of multistage chemical isolation, strontium isotopes are obtained, including Sr-82.

This method has the following disadvantages:

- a large amount of impurities of other radionuclides with Z≤42 is formed in the target, which affects the purity of isolation of the target product;

- Sr-82 isolation technique is associated with the need for a multi-stage radiochemical process for target processing (wet radiochemistry) and the disposal of a large amount of radioactive waste associated with "wet radiochemistry" (the complexity and complexity of the process);

- when molybdenum is irradiated, the obtained sources contain the main interfering impurity Sr-85, the activity of which is comparable with the activity of the target product of strontium-82.

A known method of producing Sr-82 in the reaction Rb (p, xn) upon irradiation of a target from metal rubidium: Zhuikov B.L., Kokhanyuk V.M., Glushchenko V.N. et al. Obtaining strontium-82 from a metal rubidium target on a proton beam with an energy of 100 MeV. - Radiochemistry, 1994, Volume 36, pp. 494-498 [2]. Rubidium metal targets placed in sealed stainless steel containers were irradiated with a linear accelerator with a beam with proton energies of 100-150 MeV at beam currents of up to 100 μA. Processing of the irradiated target included mechanical opening of the container and dissolution of the target in isobutanol, destruction of 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 disadvantage of this method is that the isolation of Sr-82 is also associated with the need for a multi-stage radiochemical process for processing the target (wet radiochemistry) and the disposal of a large amount of radioactive waste associated with "wet radiochemistry".

As a prototype, a method for producing strontium ⁸² Sr radionuclide is considered (B. L. Zhuykov, V. M. Kokhanyuk, J. Vincent, patent No. 2356113, priority 03/27/2008) [3]. The method of producing radiostrontium-82 is as follows. A target containing metallic rubidium (target substance) inside the target shell is irradiated with a stream of accelerated charged particles. After irradiation, rubidium is melted inside the target shell. Extraction of radiostrontium from liquid rubidium is carried out by sorption. Sorption is carried out at a temperature of the sorbing surface of 275-350 ° C, and the inner surface of the shell of the irradiated target is used as the sorbing surface. After sorption, the radiostrontium of rubidium is removed from the target shell, and then the radiostrontium is washed off with solvents from the inner surface of the target shell. The removal of rubidium metal is carried out by pumping from the target. It is proposed to extract sorbed radiostrontium by transferring it to a solution by pouring various solvents into the target, for example, organic alcohols, water and / or aqueous solutions of mineral acids, etc. The output of radiostrontium is 96 ± 4%

The disadvantage of this method, as well as analogues, is the need to transport the irradiated target of large radioactivity (as described in the prototype), filled with the target substance, in a hot box, followed by a multi-stage process of melting rubidium and extracting the formed radiostrontium from rubidium by sorption on the surface of various materials followed by their washing and purification from the target substance. Those. “wet radiochemistry” and the disposal of a sufficiently large amount of radioactive waste accompanying “wet radiochemistry” are also present.

In addition, due to the explosion hazard, all procedures for the extraction of ⁸² Sr from the target substance should be carried out in an atmosphere of some inert gas. Thus, we can definitely say that the process is time-consuming, complex, associated with work in conditions of high radioactivity.

The technical result of the claimed invention is to simplify the production of strontium-82 radionuclide while maintaining a high yield of the final product.

The task is to conduct the process of obtaining the strontium-82 radionuclide, bypassing the multi-stage operations associated with the use of "wet radiochemistry" and eliminating the explosion hazard.

The problem is achieved in that in the known method for producing strontium-82 radionuclide, which includes irradiating an accelerated proton beam with an energy of 70 MeV of a container with a target from rubidium chloride or rubidium metal, the separation of strontium-82 radionuclide (with concomitant isotopes) from the target substance is new that the separation of the strontium-82 radionuclide from the target substance is carried out by evaporation of the target substance into the ballast volume in high vacuum at a temperature of 900-950 ° C, and the strontium-82 radionuclide remaining and the inner surface of the container is evaporated at a temperature in the range of 1500-1900 ° C with simultaneous planting of it on a cooled collector, from which it is then washed with a solution of hydrochloric or nitric acid.

This set of operations eliminates the multi-stage radiochemical process of processing the target. This will avoid the receipt of a large amount of liquid radioactive waste associated with this process, and reduce the activity of samples obtained for processing in hot chambers by 5–6 times while maintaining the activity of accumulated strontium-82.

This is due to the fact that the separation of strontium radionuclides from the target container is carried out at the site of irradiation of the container with an efficiency of about 95%. The efficiency of separation of strontium radionuclides from the target substance is better than 99.9%. In contrast to the prototype, a different approach to the separation of the target substance from the radioisotope of strontium-82 (target product) and other strontium isotopes, namely due to different heating temperatures, was performed. In this case, the target product remains completely inside the container without the target substance. Then carry out its complete evaporation from the inner surface of the container and complete deposition on a cold collector. This is confirmed by the experimental results given below in the corresponding figures. Thus, there is no need to transport the irradiated target of large radioactivity, filled with the target substance, in a hot box, followed by a multi-stage process of melting rubidium and extracting the formed radiostrontium from rubidium by sorption on the surface of various materials, as is done in the prototype, which is complex and explosive operations.

In the inventive method, all operations for the separation of the target substance and the target product are carried out in a single enclosed space - the site of irradiation of the target. Therefore, the multi-stage isolation of the product using an irradiated target of high radioactivity is excluded. The proposed method allows you to work with the already selected fraction of strontium radionuclides, whose activity is 5-6 times less than the activity of the irradiated target.

In FIG. Figure 1 shows the experimentally obtained gamma spectra of irradiated rubidium chloride, where the gamma lines of rubidium-83 (552 keV) and rubidium-82 (776 keV), the daughter nucleus of strontium-82, are present. These are the spectra of the capsule with the target substance before it is heated and after it is heated at low (less than 800 ° C). It can be seen from the spectrum that, at temperatures below 800 ° C, neither the target substance nor strontium fly out of the target capsule.

In FIG. Figure 2 shows the experimentally obtained gamma spectra of irradiated rubidium chloride, where the gamma lines of rubidium-83 (552 keV) and rubidium-82 (776 keV), the daughter nucleus of strontium-82, are present. These are the spectra of the capsule with the target substance before and after its heating at a temperature of 900-950 ° C. It can be seen from the spectrum that, in this temperature range, the target substance completely flew out of the target capsule (container), and strontium did not fly out of the target capsule.

In FIG. Figure 3 shows the experimentally obtained spectrum of strontium-82 isolated on a cooled tantalum collector and washed off the collector with a 10% hydrochloric acid solution.

In FIG. Figure 4 shows the experimentally obtained gamma spectra of irradiated metal rubidium with the same gamma lines. It can be seen from the spectrum that, with 90% evaporation of the target substance (metallic rubidium), strontium-82 almost all remains in the target. Incomplete evaporation of the target substance is explained by the short evaporation time of the target substance (60 min.).

According to calculations, the time required for complete evaporation will be 5-6 hours, and can be determined experimentally in preliminary measurements with low activity

The method is as follows. A target in the form of a container of a sufficiently refractory material with the target substance in the container in the form of rubidium chloride or metal rubidium in high vacuum is irradiated with energy protons of 70-80 MeV. When a target substance is irradiated in it, strontium-strontium-82, 83, 85 radioisotopes are formed with high cross sections in the reaction (p, xn). The ⁸² Sr radionuclide is used in diagnostic procedures as an isotope generating the daughter radionuclide Rb-82, decaying beta plus decay and used in PET diagnostics. The isolation of strontium radioisotopes from the target substance is as follows. After completion of irradiation and exposure for 5-10 days, the target container is first heated in high vacuum at 900–950 ° C for the target substance (RbCl or rubidium metal) to radiate cooling the target and decay the short-lived strontium-83 in ballast volume. The measured efficiency of collecting the target substance in the ballast volume is more than 95%. In this case, the atoms of the radioactive isotopes of strontium, which has a much higher boiling point than the target substance (RbCl, or metallic rubidium) remain with a probability close to 100% on the inner surface of the target container. The next time the target container is heated at a temperature of 1900-1950 ° C, the atoms of the radioactive isotopes of strontium Sr-82 and Sr-85 evaporate from the target and land on a cooled collector. The collector in the form of molybdenum, niobium or tantalum foil with the strontium radionuclides deposited is transported to a hot box, where they are washed off with a solution of hydrochloric or nitric acid. The washing efficiency is about 100%. The acid solution obtained in the amount of several cm containing strontium radioisotopes has a high radiochemical purity and, if necessary, can be subjected to additional chemical purification. The yield of the target product of strontium-82 is (95 ± 5)%

Thus, all of the above confirms that in the claimed method, all operations for the separation of the target substance and the target product are carried out in a single enclosed space - the site of irradiation of the target in the volume of the vacuum target device where the irradiated target is located. Therefore, the multi-stage isolation of the product using an irradiated target of high radioactivity is excluded. The proposed method allows you to work with the already selected fraction of strontium radionuclides, whose activity is 5-6 times less than the activity of the irradiated target.

The proposed method for producing Sr-82 makes it possible to exclude the operation of radiochemical "wet" processing of a target from the procedure for isolating strontium from a target irradiated with a cyclotron beam, as is done using purely radiochemical extraction methods. This allows you to minimize the amount of liquid radioactive waste, the processing of which is quite time-consuming and highly costly. Sr-82 obtained by this method can have a higher, if necessary, radionuclide purity compared to existing analogues, since the obtained sources without a carrier with strontium isotopes extracted from the target can undergo additional purification.

The present invention can be used to obtain a generator radionuclide Sr-82 on proton cyclotrons of medium energy (E _p = 65-80 MeV).

Literature

1. Thomas K.E. Strontium-82 Production at Los Alamos National Laboratory. - Applied Radiation and Isotopes, 1987, v. 38, No. 3, p. 175-180.

2. Zhuykov B.L., Kokhanyuk B.M., Glushenko B.H. et al. Obtaining strontium-82 from a metal rubidium target on a proton beam with an energy of 100 MeV. - Radiochemistry, 1994, Volume 36, pp. 494-498.

3. B.L. Zhuykov, V.M. Kokhanyuk, J. Vincent, RF patent No. 2356113, priority 03/27/2008, IPC G21G 1/10. METHOD FOR PRODUCING RADIOSTRONTIUM (OPTIONS) - prototype.

Claims (1)

A method of producing a strontium-82 radionuclide, comprising irradiating with an accelerated proton beam of 70 MeV energy a container with a target from rubidium chloride or metallic rubidium, isolating strontium-82 radionuclide from a target substance, characterized in that the strontium-82 radionuclide is extracted from the target substance by evaporation of the target substances into the ballast volume in high vacuum at a temperature of 900-950 ° C, and the strontium-82 radionuclide remaining on the inner surface of the container is evaporated at a temperature in the range of 1500-1900 ° C with by simultaneously planting it on a cooled collector, from which it is subsequently washed off with a solution of hydrochloric or nitric acid.

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