RU2756917C1 - Method for obtaining an i-123 radioisotope - Google Patents

Abstract

FIELD: radiation.

SUBSTANCE: invention relates to a method for obtaining a ¹²³I radioisotope by the reaction ¹²⁴Xe(p,2n)¹²³Cs→¹²³Xe→¹²³I and(or) by the reaction ¹²⁴Xe(p,pn)¹²³Xe→¹²³I. The method includes irradiation with protons of a target with a ¹²⁴Xe isotope, extraction of the starting ¹²⁴Xe with the accumulated ¹²³Xe from the target after irradiation, exposure of ¹²³Xe for decay thereof into ¹²³I. Hydrogen is therein added to the target with the ¹²⁴Xe isotope, a gas mixture of the ¹²⁴Xe isotope and hydrogen is irradiated with protons, ¹²³I is additionally extracted from the target after irradiation as part of hydrogen iodide H¹²³I by one of the known approaches.

EFFECT: significant (by 2 to 3 times) increase in the technological yield of ¹²³I without change in the primary operating conditions and increase in the temporary load of the cyclotron due to the additional, compared to the prototype, extraction of ¹²³I formed in the target during irradiation as a result of the decay of ¹²³Xe from the target.

3 cl, 1 dwg

Description

Technology area

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

State of the art

Currently, one of the most popular diagnostic radioisotopes in medicine is ¹²³ I. Due to extremely convenient nuclear-physical properties, such as a high yield of low-energy photons (83%, 159 keV), emitted after 100% electron capture, a half-life of 13.2 hours , ¹²³ I is an almost ideal radionuclide for single-photon computed tomography and, accordingly, is widely used for the diagnosis of thyroid diseases, in cardiology, neurology, and oncology. Radioisotope ¹²³ I is also widely used for multifunctional in- = vivo studies. The great advantage of ¹²³ I is its low radiation load on the human body and the high quality of the image showing the distribution of the radionuclide in the body. These properties of iodine-123 provide it with priority use in the diagnosis of diseases in pediatric patients.

There are two known approaches to the preparation of iodine-123. The first approach includes methods based on the use of reactions in which iodine-123 is the primary product. In these methods, iodine-123 is obtained by irradiating targets made of antimony with ⁴ He ( ³ He) nuclei or by irradiating targets with tellurium isotopes of high proton (deuteron) enrichment. The main disadvantage of these methods is the presence in the target radioisotope I-123 of an admixture of long-lived I-124 (T _1/2 = 4.15 days), which impairs the resolution of the resulting image and increases the radiation load on the patient.

The second approach is based on the use of reactions in which I-123 is a secondary product and is produced as a result of the decomposition of the precursor ¹²³ Xe (T _1/2 = 2.08 hours). This approach allows one to obtain a more pure product and can be realized, for example, by the reaction ¹²⁷ I (p, 5n) ¹²³ Xe. Sometimes a similar reaction is used for ¹²⁷ I (d, 6n) ¹²³ Xe deuterons at higher energies of accelerated particles. Solid NaI or KI targets are irradiated. This approach can also be implemented using the reaction ¹²⁴ Xe (γ, n) ¹²³ Xe, or by the method based on irradiation of ¹²⁴ Xe with protons according to the reaction ¹²⁴ Xe (p, 2n) ¹²³ Cs → ¹²³ Xe → ¹²³ I and according to the reaction ¹²⁴ Xe (p, pn) ¹²³ Xe → ¹²³ I. When using a gas target with ¹²⁴ Xe, the radioisotope ¹²³ I is extracted from the target, as a rule, in two ways. In the first method, ¹²³ Xe decays into ¹²³ I directly in the target. Then, after removal of the target Xe-124 from the walls of the target ¹²³ is rinsed with an alkaline solution I. Because the amount of target gas ~ 100 cm ³ or more, a filling and flushing of the target solution ¹²³ I can be prepared in solution and low volumetric activity for practical use of such the solution may require a technological operation of concentration (evaporation). After removing ¹²³ I, bringing the target to its original state will require the use of additional technological operations of washing, drying, and degassing. As a result, all this complicates both the design of the target and the technological process of obtaining ¹²³ I.

In the second method, after irradiation, Xe-124 and the Xe-123 produced by the cryogenic method are pumped into a "decay" balloon. After disintegration of Xe-123 and accumulation of 1-123 Xe-124 is removed from the "decay" cylinder into a reservoir for storage and subsequent reuse, and the "decay" cylinder with 1-123 is handed over to the customer for further use. This method is simpler in implementation, it is not associated with the need to carry out technological operations of "wet" chemistry when removing I-123 from the target. The main disadvantage of this method is that due to the short half-life of ¹²³ Xe (T _1/2 = 2.08 hours) during the irradiation time, a significant fraction of ¹²³ Xe has time to decay into the radioisotope ¹²³ I, which is not extracted from the target within the framework of this method. ... On the basis of this method, the production of iodine-123 was organized at the U-150 cyclotron of the Kurchatov Institute. At present, the NRC "Kurchatov Institute" is the only manufacturer of this radioisotope for clinics in the Moscow region.

As analogs for the present invention, indirect (through the decay of ¹²³ Xe) methods of obtaining I-123 on gas targets with the isotope ¹²⁴ Xe should be considered.

A known method of obtaining I-123 by the reaction ¹²⁴ Xe (γ, n) ¹²³ Xe followed by the decay of ¹²³ Xe ^{nuclei into 123} I (G.N. Flerov, Yu.G. Oganesyan, A.G. Belov, G.Ya. Starodub “Obtaining a short-lived isotope ¹²³ I at the MT-22 microtron”, JINR Preprint No. 18-85-750, 1985). The source of γ-quanta was an electron beam of the MT-22 microtron (Joint Institute for Nuclear Research, Dubna) with an energy of 22-25 MeV, which was converted into γ-radiation upon deceleration in the target. We used a target made of gaseous xenon of natural composition in a tantalum cylindrical vessel with a volume of 7 cm ³ at a pressure of 150 atm. Irradiation with an electron beam was carried out at a current of 5 μA for 2-8 hours. The wall of a vessel 2.5 cm thick served as an electron converter. After the end of irradiation and 6.5 hours of exposure (for the decay of ¹²³ Xe into ¹²³ I), the gas at a temperature of minus 100 ° C was passed into the intermediate volume. Then the vessel was opened, iodine was washed off the walls with Na ₂ S ₂ O ₃ × 5H ₂ O.

The main disadvantages of this method are:

- the use of a target in the form of a high-pressure vessel, which carries a potential hazard and increases the risk of accidents;

- the need to carry out procedures for mechanical opening of a highly active target and flushing ¹²³ I directly from the target. This prevents the same target from being used multiple times;

- not a high yield of obtaining the target product.

In the work (B.V. Zhuravlev, S.P. Ivanova, N.N. Krasnov, Yu.N. Shubin, "On the possibility of producing ¹²³ I by irradiation of ¹²⁴ Xe with protons with an energy of 20-30 MeV", Atomic energy, vol. 60, Issue 5, May 1986, pp. 337-340.) Two methods of extracting ¹²³ I from a gas target with the ¹²⁴ Xe isotope irradiated by a proton beam with an energy of 20-30 MeV are considered. In the first method, immediately after the end of the irradiation, radioactive ¹²³ Xe with stable ¹²⁴ Xe is passed through a filter to freeze into a trap and maintain the time required for ¹²³ Xe ^{to decay into 123} I. After that, the trap temperature is set above the xenon condensation temperature, but below iodine. Then ¹²⁴ Xe is pumped back into the target for subsequent irradiation. In the second method, after the end of the irradiation, it is proposed to hold the exposure required for the decay of ¹²³ Xe into ¹²³ I directly in the target. Iodine is deposited on the walls of the target by cooling it to the condensation temperature of iodine. ¹²⁴ Xe is pumped into another volume, and ¹²³ I is washed off the target walls with an appropriate solvent.

The main disadvantages of the first method are:

- incomplete extraction of ¹²³ I from the target; the radioisotope ¹²³ I formed in the target as a result of the decay of ¹²³ Xe during the irradiation is not extracted from the target;

- inexpediency of irradiation for more than 3 half-lives of ¹²³ Xe.

The main disadvantages of the second method should be considered:

- the use of "wet" chemistry ^{in the 123 I extraction procedure,}

inevitably complicating the design of the target;

- washout from the walls of the target together with ¹²³ I of the accompanying long-lived radioisotope ¹²¹ Te and the need for subsequent purification of ¹²³ I from it.

A known method of obtaining I-123 by reaction ¹²⁴ Xe (p, 2n) ¹²³ Cs → ¹²³ Xe → ¹²³ I and by reaction ¹²⁴ Xe (p, pn) ¹²³ Xe → ¹²³ I (N.I. Venikov, A.A. Sebyakin , "Method for producing iodine-123" Patent SU 1661842. Bulletin No. 25 dated 07.07.1991). The aim of the invention was to increase the integral yield of iodine-123 at high proton beam currents. To implement the method, helium in an amount of 15-25 mol% was added to a gas target filled with an enriched (more than 99.9%) isotope of xenon-124. The gas mixture was irradiated with a 15-45 MeV proton beam, pumped cryogenically into a "decay" balloon, and after accumulation of iodine-123, xenon was removed into the storage tank, and iodine-123 was washed off the walls of the "decay" balloon with an alkaline solution. It is noted that an increase in the integral yield of iodine-123 has been achieved by 15-25% while maintaining the high purity of the product. In this case, irradiation was carried out at a proton beam current above 17 μA.

Proposed in the patent for the USSR Inventor's Certificate No. SU 1661842. The method in terms of extracting iodine-123 repeats the above methods. It does not solve the problem of extracting from the target the iodine-123 formed in the target during the irradiation as a result of the decay of ¹²³ Xe. An attempt was made by adding helium to the target to improve the heat removal and thereby increase the yield with an increase in the proton beam current. The result of an increase of 15-25% most likely fell short of expectations.

As a prototype, a method was chosen that is currently being implemented on the U-150 cyclotron of the National Research Center "Kurchatov Institute" (N.I. Venikov, O.A. Vorobiev, V.I. Novikov, A.A. Sebyakin, A.Yu. , DI Fomichev, VA Shabrov - "Development of the target irradiation technology for the production of high-purity radionuclide ¹²³ I at the cyclotron", Preprint of IAE-4934/14, M., 1989), including exposure for ~ 6 hours protons of the target with the isotope ¹²⁴ Xe, the production of the radioisotope ¹²³ Xe in the target by the reactions ¹²⁴ Xe (p, 2n) ¹²³ Cs → ¹²³ Xe and ¹²⁴ Xe (p, pn) ¹²³ Xe, extraction (pumping) from the target immediately after cryogenic irradiation ¹²⁴ Xe and ¹²³ Xe into a "decay" cylinder, holding ¹²³ Xe in a "decay" cylinder for ~ 6 hours to accumulate ¹²³ I, transferring from a "decay" cylinder by cryogenic method ¹²⁴ Xe to a tank for storage and reuse. Thus, in this method, I-123 is removed only from the "decay" cylinder.

The method currently being implemented at the NRC "Kurchatov Institute" does not allow the extraction of ¹²³ I formed in the target during irradiation as a result of the decay of ¹²³ Xe from the target. In the preprint IAE-4934/14 it is noted that the greatest losses of ¹²³ I are inherent in this particular method. But at the same time, the choice of this method was at one time justified from the point of view of costs, organizational efforts and the established time frame for obtaining the product in the required volumes.

Disclosure of invention

The technical problem to be solved by the claimed invention is a significant increase in comparison with the prototype of the technological output ¹²³ I without changing the basic operating conditions and increasing the time load of the cyclotron due to additional extraction directly from the target ¹²³ I formed in the target during irradiation as a result of decay ¹²³ Heh.

The technical result of the claimed invention is to increase the integral technological output of I-123 without increasing the time loading of the cyclotron, due to the implementation of the production method within the framework of the second approach on a gas target with the Xe-124 isotope.

The technical result of the claimed invention is achieved by the fact that the proposed method for producing a radioisotope ¹²³ I by the reaction ¹²⁴ Xe (p, 2n) ¹²³ Cs → ¹²³ Xe → ¹²³ I and (or) by the reaction ¹²⁴ Xe (p, pn) ¹²³ Xe → ¹²³ I, including the irradiation of the target with the ¹²⁴ Xe isotope by protons, the extraction after irradiation of the starting ¹²⁴ Xe with the generated ¹²³ Xe from the target, the exposure of ¹²³ Xe to decay it into ¹²³ I, while hydrogen is added to the target with the ¹²⁴ Xe isotope, the protons of the gas mixture of the isotope ^{124 are irradiated} Xe and hydrogen are extracted after irradiation from the target with additional ¹²³ I in the composition of hydrogen iodide (H ¹²³ I) by one of the known methods.

Options for extracting hydrogen iodide H ¹²³ I from the target:

by contacting a gas mixture of hydrogen, xenon and hydrogen iodide (H ¹²³ I) with water or an alkali solution;

extraction from the target by cryogenic method.

The combination of the above essential features leads to the fact that the method makes it possible to produce and extract from the target both 1-123 formed in the target as a result of the decay of Xe-123 during the irradiation, and I-123 accumulated in the “decay” cylinder and, as as a result, it makes it possible to multiply the technological yield of I-123 in comparison with the prototype.

Brief Description of Drawings

The figure shows the dependence on the irradiation time of the ratio of the number of ¹²³ I nuclei produced in the target during the irradiation to the number of ¹²³ I nuclei that are formed as a result of the decay of ¹²³ Xe extracted from the target after irradiation and 6.6 hours of exposure τ.

Implementation and examples of implementation of the invention

The method proposed in the present invention is implemented within the framework of the second approach on a gas target with the Xe-124 isotope. It allows accumulating and extracting from the target both I-123, formed in the target as a result of Xe-123 decay during irradiation, and I-123, accumulated in the “decay” cylinder as a result of decay extracted from the target after Xe-123 irradiation. Additional extraction of I-123, formed in the target during irradiation, makes it possible to multiply the integral technological yield of I-123 without increasing the time load of the cyclotron. The method is realized due to the fact that ^{hydrogen is added to the target with the 124} Xe isotope, the gas mixture of the ¹²⁴ Xe isotope and hydrogen is irradiated with protons, and after irradiation, both ¹²³ Xe (with the subsequent production of I-123 after the decay of ¹²³ Xe) and additionally ¹²³ I in the composition of hydrogen iodide (H ¹²³ I) immediately after irradiation.

The proposed method allows you to accumulate and extract from the target, both I-123, formed in the target as a result of the decay of Xe-123 during the irradiation, and I-123, accumulated in the "decay" cylinder as a result of the decay of Xe-123 extracted from the target after irradiation ...

To achieve this result, a method for producing a radioisotope ¹²³ I is proposed. The method is carried out as follows. Hydrogen is added to the gas target of the cyclotron filled with the isotope ^{124 Xe.} The gas mixture is irradiated with 30-32 MeV protons with a current of ~ 10-20 μA for ~ 6 hours. As a result of irradiation, according to the reactions ¹²⁴ Xe (p, 2n) ¹²³ Cs → ¹²³ Xe and ¹²⁴ Xe (p, pn) ¹²³ Xe, the radioisotope ^{123 Xe is produced in the target, which partially decays in 123} I during the irradiation of the target.

According to a calculated estimate based on a heat transfer model (M.A. Mikheev, I.M. Mikheeva, "Fundamentals of heat transfer", Moscow: Energiya, 1977), when the target is irradiated with a proton beam with a current of 10-20 μA with an energy of 30-32 MeV , the hydrogen-xenon mixture in the beam region is heated up to temperatures of 800-1000 ° K, which is sufficient for the reaction of formation of hydrogen iodide from ¹²³ I, which is formed as a result of the decay produced by ¹²³ Xe, during the irradiation of the hydrogen-xenon mixture.

Atomic ¹²³ I (hereinafter I), formed in the target as a result of the decay of ¹²³ Xe, can enter into radical reactions, which are summarized as

между исходными веществами и продуктами реакций быстро устанавливается термодинамическое равновесие. Причем вероятность реакции (1) низка из-за малой концентрации атомарного йода и может для наших оценок не приниматься во внимание (этот вывод подтверждается и при ее явном учете). Оценим концентрацию водорода, достаточную для существенного смещения равновесных концентраций реакции (2) в сторону образования HI. (В качестве существенного смещения равновесных концентраций принимаем смещение, при котором отношение концентрации HI к концентрации I составляет ≥10²). Согласно закону действующих масс при постоянной температуре отношение произведения равновесных концентраций продуктов реакции в степенях, равных их коэффициентам, к произведению равновесных концентраций исходных веществ, в степенях, равных их коэффициентам, есть величина постоянная, называемая константой равновесия. Для уравнения (2) закон действующих масс принимает видAt temperatures

thermodynamic equilibrium is rapidly established between the starting materials and reaction products. Moreover, the probability of reaction (1) is low due to the low concentration of atomic iodine and may not be taken into account for our estimates (this conclusion is also confirmed when it is explicitly taken into account). Let us estimate the hydrogen concentration sufficient for a significant shift of the equilibrium concentrations of reaction (2) towards the formation of HI. (As a significant shift in the equilibrium concentrations, we take the shift at which the ratio of the HI concentration to the I concentration is ≥10 ² ). According to the law of mass action at constant temperature, the ratio of the product of the equilibrium concentrations of the reaction products in powers equal to their coefficients to the product of the equilibrium concentrations of the initial substances, in powers equal to their coefficients, is a constant value called the equilibrium constant. For equation (2), the mass action law takes the form

Here K is the equilibrium constant of reaction (2) [cm ³ ];

n (HI) - concentration of HI molecules [cm ^-3 ];

n (I) is the concentration of atoms I [cm ^-3 ];

n (Н ₂ ) - concentration of hydrogen molecules [cm ^-3 ].

An expression for the equilibrium constant K, calculated according to the rules of statistical mechanics (see L.D. Landau, E.M. Lifshits, Statistical Physics. Part I, Moscow: FIZMAT LIT, 2002) taking into account the known parameters of molecules (see, for example , A.A. Radtsig, B.M.Smirnov, Handbook of Atomic and Molecular Physics, Moscow: Atomizdat, 1980) can be represented as:

For our estimates, we take the temperature of the gas mixture in the target equal to T = 1000 ° K. Then the equilibrium constant of reaction (2) according to (4) will be the value

Let us estimate the hydrogen concentration required for the implementation of the invention and providing a significant shift in the equilibrium concentrations of reaction (2) towards the formation of HI for a gas mixture temperature of 1000 ° K. Substituting in (3) the ratio [n (HI)] / [n (I)] = 10 ² and K = 8.9 × 10 ^-14 [cm ³ ] we obtain

n (H ₂ ) = [n (HI)] ² / [n (I)] ² × K = {[n (HI)] / [n (I)]} ² / K = 10 ⁴ / 8.9 × 10 ^-14 = 1,12 × October ¹⁷ [cm ^-3] H ₂ molecules, which is equivalent to the pressure of ~ 0.4 kPa at STP The addition of such an amount of hydrogen to the target will not affect either the proton range in the target or the physical yield of ¹²³ Xe and, at the same time, will provide conditions under which the ¹²³ I accumulated in the target at the end of irradiation will be in the form of hydrogen iodide.

Let us estimate the dependence on the irradiation time of the ratio of the number of ¹²³ I nuclei that are produced in the target during the irradiation to the number of ¹²³ I nuclei that are formed as a result of the decay of ¹²³ Xe extracted from the target after irradiation in accordance with the prototype. For simplicity, we neglect the decay time of ¹²³ Cs (T _1/2 = 5.88 min) in the reaction ¹²⁴ Xe (p, 2n) ¹²³ Cs → ¹²³ Xe → ¹²³ I. Expressions for the number of ¹²³ I nuclei that are produced in the target during the time irradiation of N ₁ and which are formed as a result of the decay of ¹²³ Xe extracted from the target after irradiation with N ₂ can be written as follows

Here

λ ₁ and λ ₂ - decay constants, respectively, ¹²³ Xe and ¹²³ I [hour ^-1 ];

t - target irradiation time [hour ^-1 ];

τ is the holding time of ¹²³ Xe after irradiation and extraction from the target [hour ^-1 ];

q is the total yield in saturation of ¹²³ Xe in the reactions ¹²⁴ Xe (p, 2n) ¹²³ Cs → ¹²³ Xe and

¹²⁴ Xe (p, pn) ¹²³ Xe [Bk].

From (6) it follows that N ₂ reaches a maximum at a holding time

Dividing (5) by (6) and substituting τ = 6.6 hours, we obtain the dependence of N ₁ / N ₂ on the irradiation time, shown in the figure.

Dependence of the ratio of the number of ¹²³ I nuclei produced in the target during irradiation to the number of ¹²³ I nuclei formed as a result of the decay of ¹²³ Xe extracted from the target after irradiation and 6.6 hours of exposure τ.

It follows from the figure that at a 6 hour (currently used) irradiation regime, even for the most optimal holding regime of ¹²³ Xe (6.6 hours), the amount of ¹²³ I, which can be extracted from the target immediately after irradiation in the form of H ¹²³ I, ~ in 1.5 times the amount of ¹²³ I, which is formed as a result of the decay of ¹²³ Xe extracted from the target after irradiation.

After the completion of the irradiation, ¹²³ I in the composition of hydrogen iodide (H ¹²³ I) is extracted from the target by one of the methods (see examples), ¹²³ Xe and starting ¹²⁴ Xe are extracted from the target by a cryogenic method similar to the prototype, ¹²³ Xe is kept until decay into ¹²³ I, and ¹²⁴ Xe, after the decay of ¹²³ Xe, is cryogenically collected in a reserve tank for further use. As a result, the proposed method makes it possible to extract from the target ¹²³ I formed in the target as a result of the decay of ¹²³ Xe during irradiation in the form of hydrogen iodide and additionally ¹²³ I, which is obtained similarly to the prototype after the decay of ¹²³ Xe extracted from the target after irradiation. Hydrogen iodide during or after extraction can be converted into an aqueous solution of HI or react with alkali to form Na ¹²³ I. A gain in the amount of ¹²³ I obtained using the present invention compared to the prototype can be achieved, within the framework of the current regime irradiation and exposure, 2-2.5 times.

Examples of implementation of the invention

Example 1. The target is filled with a gas mixture of ¹²⁴ Xe isotope and hydrogen to a pressure of 600 kPa. The partial pressure of hydrogen in the target is 1 kPa. The target is irradiated with a proton beam with a current of 10 μA with an energy of 30 MeV for 6 hours. We assume that the length of the target and the pressure of the gas in it provide such a range of protons in the gas at which the protons release their energy from the starting 30 MeV to 20 MeV. In this energy range, ¹²³ Xe is produced by the reactions ¹²⁴ Xe (p, 2n) ¹²³ Cs → ¹²³ Xe and ¹²⁴ Xe (p, pn) ¹²³ Xe. After the end of the irradiation, the target volume is connected with the balloon No. 1 containing a thin layer of water until the H ¹²³ I is completely absorbed by the water. The resulting solution containing ¹²³ I is poured into a special container for storage and subsequent use. Connect the volume of the target and the balloon No. 1 with the balloon No. 2, previously evacuated and kept at the temperature of liquid nitrogen. Freeze ¹²³ Xe together with ¹²⁴ Xe into a bottle No. 2. Hydrogen is pumped out of the target and both cylinders. Disconnect balloon # 2 from the target and balloon # 1. Withstand ¹²³ Xe and ¹²⁴ Xe in cylinder # 2 for 6.6 hours to decay ¹²³ Xe into ¹²³ I. Cryogenically extract ¹²⁴ Xe from cylinder # 2 into a special reserve container for storage and subsequent use. Let us evaluate the activity of ¹²³ I, which can be obtained using the technology of the prototype and using the present invention. Taking into account the short half-life of ¹²³ Cs (T _1/2 = 5.88 min), we assume that the yield in saturation of ¹²³ Cs is equal to the reaction rate of formation (and, accordingly, the yield in saturation) of daughter ¹²³ Xe. According to the IAEA data ("Charged particle cross-section database for medical radioisotope production: diagnostic radioisotopes and monitor reactions), IAEA, Vienna, 2001, IAEA-TECDOC-1211, pp 211-220, May 2001) when the target is irradiated from ¹²⁴ X in the proton energy range 20-30 MeV, the yield in saturation of ¹²³ Cs (and, accordingly, of the daughter ¹²³ Xe) in the reaction ¹²⁴ Xe (p, 2n) ¹²³ Cs → ¹²³ Xe is 16.4 GBq / μA, and the yield in saturation is ¹²³ Xe (variant of Tárkányi et al.) in the reaction ¹²⁴ Xe (p, pn) ¹²³ Xe is 2.06 GBq / μA. The total yield of ¹²³ Xe in saturation for 1 μA current for the two reactions is 16.95 GBq / μA.

Substituting into equation (6) the decay constant of ¹²³ Xe λ ₁ = 0.33 h ^-1 , the decay constant of ¹²³ I λ ₂ = 0.0525 h ^-1 , the target irradiation time t = 6 hours, the holding time ¹²³ Xe τ = 6, 6 hours, total yield in saturation of ¹²³ Xe in reactions ¹²⁴ Xe (p, 2n) ¹²³ Cs → ¹²³ Xe and ¹²⁴ Xe (p, pn) ¹²³ Xe for a current of 10 μA, equal to 16.95 GBq / μA × 10 μA = 169 , 5 GEq and, multiplying both sides of equation (6) by λ ₂ , we obtain the activity value of ¹²³ I, corresponding to the prototype. The value of this activity is 16.4 GBq or 0.44 Curie. Substituting the corresponding values of the parameters into Eq. (5), we obtain the activity of ¹²³ I produced in the target at the time of the end of the irradiation. This activity is 26.7 GBq or 1.165 Curie. Thus, for the above-selected irradiation and exposure parameters, the invention makes it possible, in addition to 0.44 Curie ¹²³ I, to obtain 1.165 Curie ¹²³ I, that is, it increases productivity by 2.6 times.

Example 2. The target is filled with a gas mixture of the ¹²⁴ Xe isotope and hydrogen to a pressure of 600 kPa. The partial pressure of hydrogen in the target is 1 kPa. The target is irradiated with a proton beam with a current of 20 μA with an energy of 30 MeV for 6 hours. We assume that the length of the target and the pressure of the gas in it provide such a range of protons in the gas at which the protons release their energy from the starting 30 MeV to 20 MeV. In this energy range, ¹²³ Xe is produced by the reactions ¹²⁴ Xe (p, 2n) ¹²³ Cs → ¹²³ Xe and ¹²⁴ Xe (p, pn) ¹²³ Xe. After completion of the irradiation target is connected via a reduction gear, and an intermediate tank reactor (with 0.5 M NaOH solution, 5 cm high) with a pre-located and evacuated at liquid nitrogen tank 1. Peremorazhivayut from the target ¹²³ with ¹²⁴ Xe Xe cylinder №1, passing gas into cylinder 1 at a low flow rate through a layer of 0.5 M NaOH solution, providing with a special nozzle the size of bubbles with a diameter of ~ 1 mm for complete dissolution of H ¹²³ I with the formation of a Na ¹²³ I solution in the intermediate container. Disconnect the intermediate container with the solution from the target Na ¹²³ I. Hydrogen is pumped out from the volume of the target and cylinder 1. Disconnect balloon 1 from the target. Maintain ¹²³ Xe and ¹²⁴ Xe in balloon 1 for 6.6 hours to decay ¹²³ Xe into ¹²³ I. Cryogenically extract ¹²⁴ Xe from balloon 1 into a special reserve container for storage and subsequent use. Let us evaluate the activity of ¹²³ I, which can be obtained using the technology of the prototype and using the present invention. In example 2, the irradiation mode differs from the irradiation mode in example 1 only by the magnitude of the proton beam current: 20 μA instead of 10 μA. This increases the absolute value of the operating time ¹²³ I, without changing the ratio between the amount of operating time in the prototype and the operating time using the present invention. Assuming that in both examples the complete extraction of H ¹²³ I from the target is carried out, in example 2 the production of ¹²³ I in the prototype will be 0.88 Curie, using the invention of 2.33 Curie.

Example 3. The target is filled with a gas mixture of the ¹²⁴ Xe isotope and hydrogen to a pressure of 600 kPa. The partial pressure of hydrogen in the target is 1 kPa. The target is irradiated with a proton beam with a current of 10 μA with an energy of 30 MeV for 4 hours. We assume that the length of the target and the pressure of the gas in it provide such a range of protons in the gas at which the protons release their energy from the starting 30 MeV to 20 MeV. In this energy range, ¹²³ Xe is produced by the reactions ¹²⁴ Xe (p, 2n) ¹²³ Cs → ¹²³ Xe and ¹²⁴ Xe (p, pn) ¹²³ Xe. After the completion of the irradiation, the target volume is connected with cylinders 1 and 2. Freeze from the ¹²³ Xe target together with ¹²⁴ Xe into the cylinder 1, previously evacuated and cooled with liquid nitrogen to a temperature of ~ 100 ° K. H ¹²³ I and H ₂ remain, while, in the gaseous phase. Freeze from the target and balloon 1 H ¹²³ I into balloon 2, previously evacuated and cooled with liquid nitrogen to a temperature of ~ 77 ° K. Hydrogen is evacuated from the volume of the target and both balloons. Disconnect balloon 2 from the target and balloon 1. Disconnect balloon 1 from the target. Maintain ¹²³ Xe and ¹²⁴ Xe in balloon 1 for 6.6 hours to decay ¹²³ Xe into ¹²³ I. Cryogenically extract ¹²⁴ Xe from balloon 1 into a special reserve container for storage and subsequent use. Let us evaluate the activity of ¹²³ I, which can be obtained using the technology of the prototype and using the present invention. In example 3, the irradiation mode differs from the irradiation mode in example 1 only in the irradiation time. Assuming that the extraction of H ¹²³ I from the target by the cryogenic method is carried out in full, substituting in (5) and (6) t = 4 hours, τ = 6.6 hours, q = 16.95 GBq / μA, the beam current is 10 μA and multiplying the right and left sides of the equations by λ _2, we obtain that in example 3 the operating time of ¹²³ I in the prototype will be 0.38 Curie, using the invention of 0.78 Curie. The productivity with the application of the invention in example 3 exceeds the productivity of the prototype by about 2 times.

Example 4. The target is filled with a gas mixture of ¹²⁴ Xe isotope and hydrogen to a pressure of 600 kPa. The partial pressure of hydrogen in the target is 1 kPa. The target is irradiated with a proton beam with a current of 20 μA with an energy of 30 MeV for 8 hours. We assume that the length of the target and the pressure of the gas in it provide such a range of protons in the gas at which the protons release their energy from the starting 30 MeV to 20 MeV. In this energy range, ¹²³ Xe is produced by the reactions ¹²⁴ Xe (p, 2n) 123Cs → ¹²³ Xe and ¹²⁴ Xe (p, pn) ¹²³ Xe. After the completion of the irradiation, the target volume is connected with cylinders 1 and 2. Freeze from the ¹²³ Xe target together with ¹²⁴ Xe into the cylinder 1, previously evacuated and cooled with liquid nitrogen to a temperature of ~ 100 ° K. H ¹²³ I and H ₂ remain, while, in the gaseous phase. Freeze from the target and balloon 1 H ¹²³ I into balloon 2, previously evacuated and cooled with liquid nitrogen to a temperature of ~ 77 ° K. Hydrogen is evacuated from the volume of the target and both balloons. Disconnect balloon 2 from the target and balloon 1. Disconnect balloon 1 from the target. Keep ¹²³ Xe and ¹²⁴ Xe in balloon 1 for 6.6 hours to decay ¹²³ Xe into ¹²³ I. Cryogenically extract ¹²⁴ Xe from balloon 1 into a special reserve container for storage and subsequent use. Let us evaluate the activity of ¹²³ I, which can be obtained using the technology of the prototype and using the present invention. In example 4, the irradiation mode differs from the irradiation mode in example 3 only by the irradiation time and the magnitude of the proton beam current. Assuming that the extraction of H ¹²³ I from the target by the cryogenic method is carried out in full, substituting in (5) and (6) t = 8 hours, τ = 6.6 hours, q = 16.95 GBq / μA, the beam current is 20 μA and multiplying the right and left sides of the equations by λ _2, we obtain that in example 4 the operating time of ¹²³ I in the prototype will be 0.96 Curie, using the invention of 3.08 Curie. The productivity using the invention in example 4 exceeds the productivity of the prototype by about 3.2 times.

Claims (3)

1. A method of obtaining a radioisotope ¹²³ I by the reaction ¹²⁴ Xe (p, 2n) ¹²³ Cs → ¹²³ Xe → ¹²³ I and (or) by the reaction ¹²⁴ Xe (p, pn) ¹²³ Xe → ¹²³ I, including irradiation of the target with the isotope ¹²⁴ Xe, extraction after irradiation of the starting ¹²⁴ Xe from the target with the accumulated ¹²³ Xe, holding ¹²³ Xe to decay it into ¹²³ I, characterized in that ^{hydrogen is added to the target with the 124} Xe isotope, irradiation with protons of the gas mixture of the ¹²⁴ Xe isotope and hydrogen is carried out, and after irradiation from the target, additionally ¹²³ I in the composition of hydrogen iodide H ¹²³ I is one of the known methods. 2. The method according to claim 1, characterized in that hydrogen iodide H ¹²³ I is extracted from the target by contacting a gas mixture of hydrogen, xenon and hydrogen iodide (H ¹²³ I) with water or an alkali solution. 3. The method according to claim 1, characterized in that hydrogen iodide H ¹²³ I is extracted from the target by a cryogenic method.

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