Method to produce radioisotope strontium-82

FIELD: power engineering.

SUBSTANCE: method to produce radioisotope strontium-82 includes radiation of α-particles or 3He target from krypton by accelerated beams. The target is one isotope or cascade from several isotopes of crypton, every of which represents crypton enriched by i isotope to concentration that exceeds concentration of i isotope in natural mix of crypton isotopes, and simultaneously exceeding concentration of any other isotope in mixture of crypton isotopes, at the same time crypton isotopes in the cascade are arranged in series in direction of the accelerated particle beam in the decreasing order of atomic masses of isotopes having maximum concentration in the mixture of crypton isotopes, and in process of one or more threshold nuclear reactions ^{80,82,83,84,86}Kr(α,xn)⁸²Sr or accordingly one or more threshold nuclear reactions ^{80,82,83,84,86}Kr(3He,xn)⁸²Sr, the target radioisotope ⁸²Sr is accumulated in the target.

EFFECT: invention makes it possible to increase yield of target radioisotope ⁸²Sr and provides for control and minimisation of the value of accompanying activities of the main interfering admixtures ⁸⁵Sr and ⁸³Sr.

2 cl, 1 dwg

The invention relates to a technology for production of radioisotopes for nuclear medicine on the accelerator.

Currently one of the most promising and dynamically developing directions of nuclear medicine heart conditions ' diagnosis is based on the method of positron emission tomography (PET).

The most PET centers are now based on the use of ultra short-lived β⁺-emitting radionuclides (¹¹C,¹³N¹⁵Oh,¹⁸F) and assumes PAT the centre of two mandatory components: positron emission tomography and the particles with E_p<20 MeV for production of the above radioisotopes. Condition binding to the cyclotron, of course, inhibits the proliferation of PET method, because not every hospital can afford to own and operate the cyclotron. Known more rational approach to solving this problem.

In recent years, mainly in the United States, has been the development of PET technology based on the use of⁸²Sr-⁸²Rb isotope generators.

Below are some of the nuclear-physical characteristics of this isotope pairs:

⁸²Sr: T_1/2=25.3; EZ (100%); no related γ-quanta.

⁸²Rb: T_1/2=1.27 min; β⁺(95%), EZ (5%), the main associated γ-rays: E_γ=511 Kev (189%) and E_{γ =776.9 Kev (12.5%).}

_{Get in isotope generator rubidium, being a physiological analogue of potassium, when introduced into the patient's body is mainly localized in the myocardium.}

_{These physical and physiological properties of this radioisotope pairs make this generator is very convenient for use in PET method. This generator is compact, can be easily delivered to any clinic, including over long distances, and be used for quite a long time. This eliminates the need to have and operate in a clinic cyclotron (bulky and expensive equipment requiring special facilities and staff).}

_{The present invention can be used to produce a radioisotope⁸²Sr are relatively cheap to operate the accelerators medium energy (Eα,3He≤60 MeV). The proposed method of obtaining⁸²Sr allows to exclude from allocation of strontium from the cyclotron target time-consuming and costly operation radiochemical processing targets inherent in other methods. Obtained in this way⁸²Sr will have a higher radionuclide purity in comparison with existing analogues as cascading layout krypton gas target in this way will allow you to adjust and optimizarea the ü the composition and quantity of radionuclide impurities in the final product.}

Prior art

Currently,⁸²Sr is produced by irradiation by protons (E_p≈100÷800 MeV) solid targets of molybdenum, a metal rubidium or its compounds in high energy accelerators.

A method of obtaining⁸²Sr by the reaction of Mo (p, spallation) (Thomas K.E. Strontium-82 Production at Los Alamos National Laboratory. - Applied Radiation and Isotopes, 1987, v.38, №3, p.175-180). The target of metallic molybdenum with a diameter of 1.9-6.4 cm, thickness 1.25-1.9 cm was irradiated with a proton beam energy of 800 MeV. In the reaction of cleavage formed⁸²Sr. The duration of irradiation of different targets ranged from 2 to 30 days. The rated current of the proton beam is 500 µa. Then the target was dissolved in a mixture of nitric and phosphoric acids in the presence of hydrogen peroxide. Then a multi-stage chemical redistribution allocated⁸²Sr.

This method has significant disadvantages, which are as follows:

- for⁸²Sr uses a unique expensive to install, primarily intended for fundamental research: meson factory Los Adamoski national laboratory of the U.S.;

the technology is based on the use of disposable targets;

along with the⁸²Sr in the target produce large quantities of radioactive impurities;

- selection⁸²Sr is associated with the need for many who stupenchatogo radiochemical redistribution target and disposal of large quantities of radioactive waste;

- high content of the target product main interfering impurities⁸⁵Sr activity, which is comparable with the activity of the target product.

It is known that one of the essential factors that determine the quality of⁸²Sr is its radionuclide purity. Basic radionuclide impurities -⁸³Sr and⁸⁵Sr. Activity⁸³Sr can be significantly reduced by exposure of the irradiated target (T_1/2=32.4 hours for⁸³Sr). As for long-lived⁸⁵Sr(T_1/2=64.73 day), its presence in⁸²Sr significantly increases the dose burden to the patient and the medical staff and complicates research PET method (when partial "breakthrough" of strontium in the separation column⁸²Sr-⁸²Rb isotope generator), as⁸⁵Sr has an intensive line of E_γ=514 Kev, close to annihilation line⁸²Rb(E_γ=511 Kev). In addition, the presence of⁸⁵Sr significantly increases the requirements for radiation protection⁸²Sr-⁸²Rb isotope generator and reduces its service life to recharge.

A method of obtaining⁸²Sr by the reaction of Rb(p,xn) on the target of rubidium chloride (Mausner, L.F., Prach T., Srivastava S.C. Production of⁸²Sr by Proton Irradiation of RbCl. - Applied Radiation and Isotopes, 1987, v.38, №3, p.181-184). The purpose of dehydration rubidium chloride was kept in vacuum for 48 hours, then p is has assouli with a force of 75 tons per 35 g tablet 0.81 cm thick and 4.44 cm in diameter. Tablet of rubidium chloride were placed in a capsule made of stainless steel and brew in vacuum electron beam. Then the capsule with rubidium chloride was irradiated by a proton accelerator at Brookhaven national laboratory to accelerate protons to an energy of 200 MeV. Current proton beam was 45 μa. After irradiation capsule was transported in a protective container in the hot laboratory, and after 6 days of exposure was opened. Then the rubidium chloride was dissolved in 100 ml of 0.1 M NH₄OH:0.1 M NH₄Cl and after the multi-step radiochemical redistribution allocated⁸²Sr.

The disadvantages of this method include:

- use for⁸²Sr costly high energy accelerator;

is quite a complicated procedure of manufacturing a target.

the technology is based on the use of disposable targets;

- due to the poor thermal conductivity of rubidium chloride for currents above a few µa possible overheating in the center of the target and the sublimation of rubidium chloride, which reduces the effective thickness of the target and, consequently, the output of the target product;

- selection⁸²Sr is associated with the need for multi-step radiochemical redistribution target;

as in the previous example, the high content in the target product main interfering impurities⁸⁵Sr activity is comparable with the activity of the target product.

A method of obtaining⁸²Sr by the reaction of Rb(p,xn) on a target of metallic rubidium (started B.L., Kokhanok V.M., V. Glushchenko. and other Receiving strontium-82 from the target metal rubidium beam of protons with an energy of 100 MeV. - Radiochemistry, 1994, volume 36, str-498). The target of metallic rubidium was a disk with a diameter of 30 mm and a thickness of 11 mm, enclosed in a sealed envelope made of stainless steel. The thickness of the entrance window of the shell was 0.13-0.2 mm Shell was charged metal rubidium in the box in an inert atmosphere. To do this, rubidium vials were warmed up the oven up to 80-90°C, selecting a liquid rubidium using a medical syringe, injected liquid metal through the nozzle into the shell. For target irradiation was performed on a linear accelerator beam energy of 100 MeV protons at beam currents 6-10 mA. The duration of exposure was 10 days. Technology of processing of the target consisted of the mechanical opening of the cassette and the dissolution of the target in Isobutanol, the destruction formed by dissolving the target of Isobutanol rubidium and separation of the organic phase by distillation, the separation of isotopes of strontium from rubidium ion-exchange column.

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

- use for⁸²Sr costly high energy accelerator;

DOS is enough complicated procedure of manufacturing the target;

the technology is based on the use of disposable targets;

- selection⁸²Sr is associated with the need for multi-step radiochemical redistribution target;

- high content of the target product main interfering impurities⁸⁵Sr activity, which is comparable with the activity of the target product.

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

As a prototype the selected method of obtaining⁸²Sr in reactions of Kr(α,xn) and Kr(3He,xn) upon irradiation with accelerated beam of α-particles or 3He target of natural krypton (F. Tarkanyi, S.M. Qaim, Stocklin G. Excitation Functions of³He - and α - Particle Induced Nuclear Reactions on Natural Krypton: Production of⁸²Sr at a Compact Cyclotron. - Applied Radiation and Isotopes, 1988, v.39, No.2, p.135-143). When using as a target of natural krypton and accelerated α particles or 3He with initial energy 60-80 MeV life⁸²Sr possible at all isotopes of Kr with the exception of⁷⁸Kr. However, time⁸²Sr on each of the isotopes in the use of natural krypton is not optimal, because of the magnitude of the cross sections of nuclear reactions leading to the formation of⁸²Sr on each of the isotopes of krypton, vary over a wide range (from 0 to σ_max) in the energy interval inhibition in the target charged particles.

the relatively low yield⁸²Sr in the target of natural krypton;

- high content of the target product main interfering impurities⁸⁵Sr activity, which is comparable with the activity of the target product.

Disclosure of inventions

The technical result is to increase the yield of the desired radioisotope⁸²Sr and the ability to regulate and minimize the magnitude of related activities the main interfering impurities:⁸³Sr and⁸⁵Sr.

This method for obtaining the radioisotope strontium-82, including irradiation by beams of accelerated α particles or 3He targets from krypton, and as a target take one isotope or a cascade of several isotopes of krypton, each of which represents a krypton enriched by the i-th isotope concentrations in excess of the concentration of the i-th isotope in the natural mixture of isotopes of krypton, and, at the same time, in excess of the concentration of any other isotope in a mixture of isotopes of krypton, and the isotopes of krypton in the cascade feature consistently in the direction of the beam of accelerated particles in descending order of atomic masses of the isotopes with in a mixture of isotopes of krypton maximum concentration, and in the process one or more threshold nuclear reactions^{80,82,83,84,86}Kr(α,xn) ⁸²Sr or, respectively, one or more threshold nuclear reactions^{80,82,83,84,86}Kr(3He,xn)⁸²Sr accumulate in target target radioisotope⁸²Sr.

In addition, as a source of accelerated particles using a cyclotron or a linear accelerator.

The figure shows the dependence of the threshold cross sections of nuclear reactions^80,82,83Kr(α,xn)⁸²Sr energy of accelerated particles in the energy range from threshold reactions up to 60 MeV.

The method is as follows.

Since each point of the target on the beam axis corresponds to a specific energy of accelerated particles, the modular layout of the target isotopes of krypton allows for each isotope to choose energy range (and the corresponding place in the cascade so that the time between⁸²Sr on each isotope of krypton is carried out in the energy field to its maximum efficiency. In other words, the time between⁸²Sr carried out where the reaction cross section education⁸²Sr on this particular isotope of krypton higher than any other isotope. The selection of the appropriate energy ranges is carried out using the energy dependences of the cross sections for reactions^{80,82,83,84,86}Kr(α,xn)⁸²Sr and^{80,82,83,84,86}Kr(3He,xn)⁸²Sr, leading to the formation of⁸²Sr. The choice of specific isotopes of krypton and their number on what I experience ⁸²Sr depends on the initial energy of the charged particles. The higher the initial energy of the charged particles, the higher the atomic number of an isotope of krypton, which will go a threshold reaction with the formation of⁸²Sr. The energy threshold of nuclear reactions leading to the formation of⁸²Sr increases with increasing atomic number of the isotope of krypton. This method allows you to get the maximum yield⁸²Sr for each fixed set of isotopes of krypton and fixed initial energy of the charged particles. The absolute maximum output⁸²Sr in krypton targets (for a fixed initial energy of charged particles) obtained using this method isotopes of krypton maximum possible enrichment.

In addition to optimizing output⁸²Sr modular layout cascading targets allows to minimize the main interfering impurities:⁸³Sr and⁸⁵Sr. The minimization procedure is the same as in the case of optimization outlet⁸²Sr. The only difference is that the time between⁸³Sr and⁸⁵Sr on each isotope of krypton is carried out in the energy fields of its minimal effectiveness. In other words, the time between⁸³Sr and⁸⁵Sr will be implemented where the reaction cross section education⁸³Sr and⁸⁵Sr on this particular isotope of krypton lower than any other isotope. the ri that the selection of the appropriate energy ranges is carried out using the energy dependences of the cross sections for reactions ^{80,82,83,84,86}Kr(α,xn)⁸³Sr^82,83,84,86Kr(α,xn)⁸⁵Sr^82,83,84,86Kr(3He,xn)⁸³Sr and^83,84,86Kr(3He,xn)⁸⁵Sr, leading to the formation of⁸³Sr and⁸⁵Sr.

In practice, the conditions optimization outlet⁸²Sr and minimize the impurity content of activities⁸³Sr and⁸⁵Sr can contradict each other. In this case, taking into account the consumer requirements for the target product, implement a compromise layout cascading krypton targets.

The proposed method of producing radioisotope⁸²Sr has significant advantages in comparison with those described in literature analogues:

The method can be implemented on relatively cheap to operate the accelerators medium energy (E_α,3He≤60-70 MeV).

- Target device may be used multiple times.

- Selection⁸²Sr from the target does not involve its destruction and carrying out multi-step radiochemical processing.

In this method, the main activity of interfering impurities⁸⁵Sr can be reduced by an order in comparison with analogues.

The proposed method of producing radioisotope⁸²Sr has significant advantages compared with prototype:

Output⁸²Sr in cascade target isotopes of krypton can be raised several times in comparison with the output targets of natural krypton./p>

The main activity of interfering impurities⁸⁵Sr in this way can be reduced by an order in comparison with the prototype.

An example of carrying out the invention

The target, representing the cascade of two consecutive aluminum modules with highly enriched isotopes of krypton⁸⁰Kr and⁸²Kr (enrichment >99.9%, a pressure of 300 kPa), was installed on the beam of α-particles with energy of 60 MeV and in the process threshold nuclear reactions^80,82Kr(α,xn)⁸²Sr accumulated in her target radioisotope⁸²Sr. On the basis of previously obtained by the authors of the experimental values of the cross sections for reactions^80,82,83Kr(α,xn)⁸²Sr (see figure) and to ensure maximum yield⁸²Sr in the field of E_α≤60 MeV cascade krypton target made of two modules with highly enriched isotopes of krypton:⁸⁰Kr and⁸²Kr, and geometric border between modules with⁸⁰Kr and⁸²Kr, in the form of Al foil with a thickness of 100 μm, was installed at a distance of 12 cm (in the region where E_α≈50 MeV) from an input beam of α-particles in the first module with⁸²Kr. The length of the second module⁸⁰Kr equal to 29 cm, provided complete inhibition of α-particles with E_α≈50 MeV⁸⁰Kr. Used layout cascading targets resulted in the maximum number of⁸²Sr in the energy region of α-cha is a TIC in the range 60-50 MeV (isotope ⁸²Kg) and the maximum number of⁸²Sr in the energy of α-particles in the range from threshold⁸⁰Kr(α,xn)⁸²Sr reactions up to 50 MeV (isotope⁸⁰Kr). In addition, in the module with⁸⁰Kr has gained⁸²Sr, devoid of impurity activity⁸⁵Sr, as the reaction initiated by α-particles, with the formation of⁸⁵Sr⁸⁰Kr no. After exposure and prior to the extraction procedure⁸²Sr cascade target was kept in for 3 days to give to decay of short-lived activities and reducing the corresponding radiation doses to personnel. Then cascade the target transported in a special protective box, which was connected to the communications gotowkowego radiochemical stand. Krypton was removed from the cascade modules of the target, for example, a method of cryogenic freezing in a special gas traps (each isotope of krypton in his own trap)at the temperature of liquid nitrogen. After removal of krypton in the volume of modules cascading targets through special channels were introduced nozzle, through which the pressure within a few seconds was injected a solution of NH₄Cl, washing the walls with cascading target activity isotopes of rubidium and strontium. A solution of NH₄Cl collected by gravity in a special pit. Then use the pump active RA the solution through a filter was applied to ion-exchange column, where shared activity isotopes of rubidium and strontium.

Thus, the invention allows an increase in the number of times output⁸²Sr compared with output⁸²Sr in the target of natural krypton. The main activity of interfering impurities⁸⁵Sr⁸²Sr can be reduced in this way by an order in comparison with the prototype and are considered equivalents. The method can be implemented on relatively cheap to operate the accelerators medium energy (E_α3He≤60-70 MeV).

Selection⁸²Sr from the target does not involve its destruction and carrying out multi-step radiochemical processing.

The totality of these circumstances, allows to expect that this method will have a commercial perspective and will provide a broader introduction of diagnostic PET method in our country.

1. The method of producing the radioisotope strontium-82, including irradiation with accelerated beam of α-particles or 3He targets from krypton, characterized in that as a target take one isotope or a cascade of several isotopes of krypton, each of which represents a krypton enriched by the i-th isotope concentrations in excess of the concentration of the i-th isotope in the natural mixture of isotopes of krypton, and at the same time in excess of the concentration of any other isotope in a mixture of isotopes of krypton while the isotopes of krypton in the cascade feature consistently in the direction of the beam of accelerated particles in descending order of atomic masses of the isotopes, with a mixture of isotopes of krypton maximum concentration, and in the process one or more threshold nuclear reactions^{80,82,83,84,86}Kr(α,xn)⁸²Sr respectively one or more threshold nuclear reactions^{80,82,83,84,86}Kr(3He,xn)⁸²Sr accumulate in target target radioisotope⁸²Sr.

2. The method according to claim 1, characterized in that as a source of accelerated particles using a cyclotron or linear accelerator.