RU2585004C1 - Method of producing strontium-82 radioisotope - Google Patents

Abstract

FIELD: medicine; physics.

SUBSTANCE: invention relates to technology of producing radioisotopes for nuclear medicine on charged particle accelerators. Method of producing strontium-82 (⁸²Sr) radioisotope by reaction of Rb(p,xn)⁸²Sr includes irradiating target by protons, such as solution or melt of one or more chemical compounds of rubidium or their suspension in liquid carrier, and their circulation in closed circuit through protons irradiation area, gaining in target at reaction ⁸⁵Rb(p,4n)⁸²Sr and (or) reaction ⁸⁷Rb(p,6n)⁸²Sr radioisotope ⁸²Sr, and extraction of ⁸²Sr from irradiated target after irradiation or directly during exposure using radiochemical method.

EFFECT: invention provides low explosion hazard of method, expansion of functionality, possibility to use multiple target device, excluding costs for its production and possibility of automating process.

6 cl, 3 dwg, 9 tbl

Description

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

In connection with the planned development in our country of a network of positron emission tomography (PET) centers, the introduction of ⁸² Sr- ⁸² Rb isotope generators into clinical practice, currently used mainly in the USA to obtain ⁸² Rb used in myocardial PET diagnostics, is becoming relevant . To charge ⁸² Sr- ⁸² Rb isotope generators, ⁸² Sr without a carrier is required. Several methods are known for producing ⁸² Sr. However, a practical application was found for the method of producing ⁸² Sr at proton accelerators with an energy of ≥70 MeV by the reaction Rb (p, xn) ⁸² Sr. The target material used is, as a rule, a metal rubidium or a solid-state target from RbCl. The use of metallic rubidium is associated with a potential explosion hazard of ⁸² Sr production and, with an unfavorable development of events (the “human factor”), can lead to a severe radiation accident. RbCl is more convenient to use. The processing technology of the irradiated RbCl target is relatively simple and safe. However, due to the poor thermal conductivity of RbCl for proton beams with a current above 10 μA, the risk of overheating and melting of the irradiated zone of the target is high. As a result of volume expansion (RbCl expands by about 20% upon melting), the melt can partially leave the irradiation zone, reducing the effective thickness of the target, which leads to a decrease in the yield of ⁸² Sr.

According to (B.L. Zhuikov, V.M. Kokhanyuk, V.N. Glushenko et al. “Obtaining strontium-82 from a target of metallic rubidium on a proton beam with an energy of 100 MeV.” Preprint INR-0810, May 1993) an increase in current to 10 μA leads to a decrease in the yield of ⁸² Sr in the RbCl target in comparison with irradiation of the RbCl target at low currents to 80%.

The present invention avoids the above problems and can be used to produce a ⁸² Sr radioisotope by the Rb (p, xn) ⁸² Sr reaction in commercially significant volumes at accelerators with proton beam currents of up to several hundred microamps.

State of the art

The ⁸² Sr radioisotope can be obtained by irradiation with protons (Е _р 70 ÷ 800 MeV) of solid targets from molybdenum, metallic rubidium, rubidium chloride, or by irradiation with ⁴ He or ³ He nuclei (energies 5 ÷ 100 MeV) of gas targets with natural krypton or isotopes krypton.

A known method of producing ⁸² Sr 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, No. 3, pp 175-180). 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 which ⁸² Sr was isolated by a multi-stage chemical redistribution.

This method has significant disadvantages, which are as follows:

- to obtain Sr, a unique and expensive installation is used, mainly intended for basic research: 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.

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. For this, rubidium in an ampoule was heated by an electric furnace to 80-90 ° C, taking liquid rubidium with a medical syringe, and 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 include:

- 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;

- the main 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 by the reaction of Rb (p, xn) on targets from metallic rubidium (B.L. Zhuykov, V.M. Kokhanyuk, J. Vincent, patent RU 2102808 C1, 1998), including irradiation with a stream of accelerated charged particles of targets from metallic rubidium, melting of rubidium after irradiation and extraction of ⁸² Sr from it by sorption on the surface of various metals or oxides immersed in molten metal rubidium.

The disadvantages of this method include:

- significant losses of ⁸² Sr due to sorption on the inner surface of the target shell: at proton currents of the order of 0.5-1 μA, 10-30% of the formed ⁸² Sr is adsorbed on the inner surface of the target shell, with an increase in current intensity, this fraction reaches 50-70% ;

- rather complicated procedures for manufacturing the target and extracting ⁸² Sr from the target;

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

- the main disadvantage, as in the previous method, should be considered a high potential explosion hazard due to the use of metallic rubidium.

A known method of producing ⁸² Sr by the reaction Rb (p, xn) on targets from metallic rubidium (Ermolaev S.V., Kokhanyuk V.M. Zhuykov B.L. Patent RU 2356113, 2008), including irradiation with a stream of accelerated charged particles of the target, containing metallic rubidium inside the target’s shell, melting rubidium inside the target’s shell after irradiation, extraction of ⁸² Sr from it on the surface of various materials in contact with liquid rubidium, in contrast to the previous example ⁸² Sr is extracted by sorption from liquid metal rubidium directly on the inside the lower surface of the shell of the irradiated target (possible shell materials are stainless steel, tantalum, niobium, tungsten, molybdenum, nickel or noble metals) by keeping the target sealed at a temperature of 275-350 ° C. Then, metal rubidium is pumped out of the target, while 96 ± 4% ⁸² Sr remains sorbed on the inner surface of the target shell. Then ⁸² Sr is transferred into the solution by pouring various solvents into the target, for example, organic alcohols, water and / or aqueous solutions of mineral acids, etc. It is most simple and technologically to wash off first with water, then with mineral acids.

Another embodiment of the technical solution (the same patent) is that liquid rubidium is used as the target working substance, which during irradiation circulates in a closed loop with a trap. ⁸² Sr is recovered by two methods. The first method is its sorption on the surface of materials heated to 220-350 ° C, immersed in liquid rubidium (for example, on the surface of metal rods in a trap made of stainless steel, tantalum, niobium, titanium, zirconium, tungsten, molybdenum, nickel or noble metals), and the temperature of rubidium circulating in the circuit is maintained in the range of 10-220 ° C, and the oxygen content in rubidium does not exceed 3 wt.%. The second method is the extraction of ⁸² Sr adsorbed on ash particles (solid phase) in liquid rubidium using a filter - a porous membrane (for example, made of a metal that does not interact with rubidium), and the oxygen content in the circulating rubidium is maintained in the range 0 , 1-4.0% by weight by adding oxygen or rubidium. In this case, the temperature is selected in the range of 10-38 ° C so as to maintain a certain ratio of solid and liquid phases. Then ⁸² Sr is washed off the surface of the rods or filter with organic alcohols, water and / or aqueous solutions of mineral acids. This option makes it possible to extract ⁸² Sr from rubidium weighing even in kilograms, simultaneously irradiating it with a beam of high-intensity accelerated protons (several hundred μA).

The disadvantages of this method, including all of the above options for the extraction of ⁸² Sr, include:

- the difficulty of extracting ⁸² Sr from the target;

- the presence of risks associated with the potential explosiveness of the method due to the use of metallic rubidium.

A known method for producing ⁸² Sr in the reactions Kr (α, xn) and Kr (3He, xn) when irradiated with accelerated beams of α particles or ³ He 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, pp 135-143). The target was irradiated with α-particles with an energy of 120 MeV and ³ He nuclei with an energy of 90 MeV at the JULIC cyclotron (Germany). Based on the measured cross sections of the reactions were calculated ⁸² Sr Sr ⁸² outputs a thick target for α-particle beams and cores ³ He. Even at such high energies of charged particles, ⁸² Sr yields on targets from natural krypton were only 35 μCi / μAh for ³ He and 52 μCi / μAh for α particles.

It should be emphasized that the yield of ⁸² Sr in the gas target substantially depends on the current of the beam of charged particles. Gas heating in the beam zone leads to a decrease in density, a change in the effective thickness of the target, and, consequently, to a decrease in the yield of ⁸² Sr. According to the work (Appl. Radiat. Isot. Vol. 39, No. 2, pp 135-143, 1988), an increase in the ³ He beam from 1 μA to 10 μA in a gas krypton target leads to a three-fold decrease in the yield of ⁸² Sr.

The disadvantages of this method include:

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

- a strong dependence of the yield on the current of a beam of charged particles, which does not allow ⁸² Sr to be generated in a gas krypton target at high currents of charged particles.

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 (3He, 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 dated January 27, 2012. “A method for producing a radioisotope of strontium-82”). The method includes irradiating at a cyclotron or linear accelerator with a beam of α particles or nuclei of a 3He 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 more threshold 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 yield of ⁸² Sr in this method is significantly higher than that of a target from natural krypton (for the optimal structure of the cascade target, E _α ~ 70 MeV and low current, the yield is ⁸² Sr ~ 95 μCi / μAh). However, the dependence of the ⁸² Sr yield on the current value of the charged-particle beam remains.

The disadvantages of this method include:

- relatively low (compared with solid targets) yield ⁸² Sr;

- the difficulty of achieving an optimal ⁸² Sr output mode of operation of a cascade target, associated with the need to carefully match the module lengths with krypton isotopes and the gas pressure in them with the current of a charged particle beam. The need for this coordination is associated with heating the gas in the beam zone, decreasing its density and, as a result, changing the optimal mean free paths of charged particles in the modules of the cascade target.

A known method of producing ⁸² Sr without a carrier according to the reaction ⁸⁴ Sr (p, 3n) ⁸² Y → ⁸² Sr (Boldyrev P.P., Vereshchagin Yu.I., Latushkin S.T., Erilov P.E., Zagryadsky V.A. ., Novikov V.I., Ogloblin A.A., Unezhev V.N., Chuvilin D.Yu .; Patent No. 2538398 dated July 23, 2013, “Method for the production of the Sr-82 radioisotope”), including irradiation of target protons with the ⁸⁴ Sr isotope, in which, as a result of a threshold nuclear reaction, ⁸⁴ Sr (p, 3n) ⁸² Y is produced and simultaneously (during irradiation) ⁸² Y is continuously extracted by the radiochemical method, the decay product of which the target radioactive isotope ⁸² Sr without carrier is then released chemical method. The practical implementation of the method was carried out as follows. An aqueous solution of the strontium compound enriched in the ⁸⁴ Sr isotope was taken and placed in a closed loop in which the solution was forcedly circulated through the proton irradiation zone and a centrifugal extractor. The irradiation of the reaction zone ⁸⁴ Sr (p, 3n) accumulating Y ^{82 82} Y, having a half-life of 10 min. Then ⁸² Y was sent along the circuit to a centrifugal extractor, where it was extracted into the organic phase of the second circuit. In this case, the strontium of the target remains in the primary circuit. Then, ⁸² Y in the second circuit was sent to a centrifugal reextractor, where it was re-extracted into the aqueous phase, forcibly circulating in the third circuit, in which ⁸² Y and its decay product ⁸² Sr. were accumulated.

The disadvantages of this method include:

- the complexity of the process for producing ⁸² Sr without a carrier from a strontium target, based on two consecutive technological operations (extraction and reextraction of ⁸² Y), which are carried out in a short time (<< T _1/2 = 10 min);

- a very high price for starting raw materials ( ⁸⁴ Sr isotope), which is only 0.56% in the natural mixture and is produced only by the expensive electromagnetic method.

The market value of ⁸⁴ Sr (enrichment of ~ 75%) is currently ~ 60 $ / mg. To obtain ⁸² Sr of acceptable quality by this method, ⁸² Sr of even higher enrichment is required. The use of ⁸⁴ Sr low enrichment, in addition to reducing the yield of ⁸² Sr, leads to the appearance of a large number of undesirable radioactive impurities, and above all ⁸⁵ Sr.

The use of a circulation loop with a solution of the compound of strontium with the ⁸⁴ Sr isotope provides for the presence of at least several grams of the ⁸⁴ Sr isotope in the loop. This means the need for large starting investments and, accordingly, the extension of the payback period when organizing the production of ⁸² Sr in this way.

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, pp 181-184). In order to dehydrate, rubidium chloride was kept in vacuum for 48 hours, then pressed with a force of 75 tons into a 35 g tablet 0.81 cm thick and 4.44 cm in diameter. A rubidium chloride tablet was placed in a stainless steel capsule and sealed under 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. 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 a multi-stage radiochemical redistribution.

The disadvantages of this method include:

- the complexity of the manufacturing process of the target;

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

- a significant decrease in the yield of ⁸² Sr with increasing proton beam current; due to the poor thermal conductivity of rubidium chloride (7.6 W / mK) at currents above several μA, overheating and melting of the irradiated zone of the target is possible; as a result of volume expansion (RbCl expands by about 20% upon melting), the melt can partially leave the irradiation zone, reducing the effective thickness of the target, which leads to a decrease in the yield of ⁸² Sr;

- obtaining ⁸² Sr is associated with the need to carry out a large number of technological operations, carried out, as a rule, in manual mode: manufacturing and mounting a disposable target on the accelerator’s ion duct, dismantling the irradiated target, mechanically opening the target, dissolving the active substance, etc.

Disclosure of invention

The technical results of the proposed method for producing ⁸² Sr produced by the reaction Rb (p, xn) should be considered:

1) Refusal to use metal rubidium as a target material, which is a potentially explosive material, the use of which leads to the risk of a severe radiation accident.

2) The rejection of the use of rubidium compounds in the form of solid targets in which, due to poor thermal conductivity, it is difficult to ensure effective heat removal, which limits the possibility of using large proton beam currents.

2) The ability to use a wide range of rubidium compounds in the composition of the target material, depending on the requirements for the quality and production volume of ⁸² Sr.

3) The ability to provide a yield of ⁸² Sr, comparable with the prototype for some rubidium compounds in the composition of the target material.

4) The ability to produce ⁸² Sr in proton beams with high current (≥100 μA) without reducing the output of ⁸² Sr (unlike the prototype), which makes it possible to produce integral amounts of ⁸² Sr in comparable times, significantly exceeding the corresponding quantities that can be obtained with using the prototype.

5) The use of a reusable target device that eliminates the cost of manufacturing target devices for each new exposure.

6) 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.

To achieve these results, a method for producing a strontium-82 ( ⁸² Sr) radioisotope by the Rb (p, xn) ⁸² Sr reaction is proposed, which involves irradiating the target with protons and isolating ⁸² Sr from the irradiated target, using one or more solution or melt as the target rubidium chemical compounds or their suspension in a liquid carrier and circulate them in a closed loop through the proton irradiation zone, producing ⁸⁵ Rb (p, 4n) ⁸² Sr and / or ⁸⁷ Rb (p, 6n) ⁸² Sr radioisotope ⁸² in the target Sr, which is isolated from the target by a radiochemical Odom.

Besides:

- as a suspension of one or more chemical compounds of rubidium in a liquid carrier, an aqueous or other saturated solution with a precipitate of one or more chemical compounds of rubidium is used;

- the circulation of the target is carried out forcibly;

- circulation of the target is carried out in natural circulation;

- the target is circulated in a closed loop through the proton irradiation zone and the heat exchanger, using the target as a coolant;

- as chemical compounds of rubidium, use is made of compounds selected from the series: RbCl, RbF, Rb ₂ CO ₃ , RbNO ₃ , Rb ₂ SO ₄ , RbBr, RbI, Rb (OH).

The figure 1 shows the General scheme of the method,

figure 2 is a diagram of a target device, where

1 - target device;

2 - pump;

3 - heat exchanger;

4 - capacity to compensate for thermal expansion of the target;

5 - device for selection (extraction) of the irradiated target;

6 - shut-off valves and connecting communications;

7 - body of the target device;

8 - a window of molybdenum foil;

9 - an operating zone of ⁸² Sr;

10 - cooling zone;

p is the proton beam.

Figure 3 shows a cross section for the formation of ⁸² Sr upon irradiation of natural isotopic composition with Rb protons (experimental data and experimental data estimation curve).

The method is as follows.

A target in the form of a solution or melt of one or more rubidium chemical compounds, or their suspension in a liquid carrier, is placed in a closed loop in which either the target is circulated through the proton irradiation zone of target device 1 and the heat exchanger either by natural circulation or by pump 2 3. In the target, while passing through the target device 1 by the reaction ⁸⁵ Rb (p, 4n) ⁸² Sr and (or) the reaction ⁸⁷ Rb (p, 6n) ⁸² Sr, in the operating zone of the target device 9, ⁸² Sr is generated, which is released from the target any known radiochemical method.

The target in the method, in addition to the operating time function ⁸² Sr, also performs the function of a heat carrier: it heats up in the target device 1 (proton irradiation zone) and transfers heat (cools) in the heat exchanger 3. Heat exchanger 3 provides efficient heat removal from the target circulation circuit for all proton beam currents, at which operates the target (all the heat generated in the target, when the target passes through the target device is taken from the target in the heat exchanger 3).

If the target is a melt, a heating system (not shown) is provided in the circulation loop that ensures the temperature of the circuit so that the target in the circulation loop is in the form of a melt. The choice of a particular rubidium compound and type of target (solution, melt or suspension) is based on the following technical and economic indicators: acceptable yield of ⁸² Sr, the required chemical and radionuclide purity of ⁸² Sr, corrosion compatibility of the target with the materials of the circulation circuit. The thickness of the target in the proton irradiation zone ( ⁸² Sr production zone) is taken to be the proton mean free path in the target, corresponding to the deceleration (energy loss) of protons from the initial energy to the reaction energy threshold of ⁸⁵ Rb (p, 4n) ⁸² Sr (for a target with natural rubidium or enriched in the isotope ⁸⁵ Rb). For a target with highly enriched ⁸⁷ Rb, up to the reaction energy threshold of ⁸⁷ Rb (p, 6n) ⁸² Sr. The target flow rate in the circulation circuit is chosen so as to exclude the possibility of boiling of the target in the proton irradiation zone.

The target device is a housing 7, divided by a partition into two parts — a strontium production zone 9 and a cooling zone 10 (the route of cooling the target water device in FIG. 1 is not shown). The proton beam enters the strontium-82 production zone through a window 8 made of molybdenum. The circuit is equipped with valves 6 and a device for selecting (extracting) the irradiated target 5 and a device for compensating the thermal expansion of the target 4.

Examples of carrying out the invention

Example No. 1. Target in the form of an aqueous solution of RbF (with Rb of natural isotopic composition) with a concentration of RbF 3 g / ml (solubility of RbF in water at n.o. according to V.A. Rabinovich, Z.Ya. Khavin, Brief chemical reference book, ed. " Chemistry, 1977, equal to 300 g per 100 ml of water) is placed in a circulation loop with forced circulation of the target (see figure 1).

During irradiation, the average proton beam current is 100 μA. The proton beam at the entrance to the target has a circle shape with a diameter of 20 mm with a constant surface current density. The target device is made of stainless steel and is a cylindrical container with a diameter of 20 mm, divided into two zones by a thin-walled (~ 0.5 mm) partition (figure 2) with an end window of metal molybdenum 8.

Turn on pump 2, providing circulation of the target in the circuit. While moving along the circulation loop while passing through the operating zone 9 of the target device 1, the target is irradiated with 70 MeV protons and ⁸² Sr is produced in it by the reactions ⁸⁵ Rb (p, 4n) ⁸² Sr and ⁸⁷ Rb (p, 6n) ⁸² Sr. Irradiation is carried out during the day. After irradiation, the target using the device for selection (extraction) of the irradiated target 5 through the valve 6 is removed from the circulation circuit and sent for radiochemical processing to isolate ⁸² Sr.

In production zone 9, the proton loses energy from 70 MeV to 35 MeV (close to the physical threshold of the reaction ⁸⁵ Rb (p, 4n) ⁸² Sr). In the partition and in the cooling zone 10, the remaining 35 MeV are distinguished. Based on the initial conditions specified above in example 1, we evaluate the basic conditions for the implementation and productivity of the method. To do this, we calculate:

- the width of the operating zone in the target device, in which the proton discharges energy from 70 MeV to 35 MeV in the target;

- ⁸² Sr yield in the target;

- target consumption during movement in the circulation circuit, ensuring the absence of boiling of the target in the target device;

- the performance of the method (the integral amount of ⁸² Sr produced per day on a proton beam with a current of 100 μA).

1) Estimation of the width of the operating zone.

The width of the operating zone was taken equal to the mean free path of a proton with an initial energy of 70 MeV until it reaches an energy of 35 MeV. The proton mean free path was calculated using the STRIM program (JF Ziegler, JP Biersack “The Stopping and Range of the Ions in Matter”, www.srim.org). The target density used in mileage calculations was determined as the sum of the densities of RbF and water with the weight of their mass fractions in the target in accordance with the additivity rule. The indicated density was 2.92 g / cm ³ . Table 1 shows the results of calculation using the STRJM program of the total path lengths of protons in the target for different initial energies.

From table 1 it follows that the width of the operating zone of the target device, equal to the difference in proton mean free paths for 70 MeV and 35 MeV, is 14.7 mm.

2) Estimation of the target flow rate in the circulation circuit, ensuring the passage of the target through the target device without boiling.

Upon irradiation of the target with protons, when the boiling point of the solution is reached, a vapor phase may appear that reduces the effective thickness of the target and, as a result, leads to a decrease in the yield of the radionuclide. The target concept proposed in the present method makes it possible to exclude boiling of the target in a wide range of proton beam currents. We estimate for the initial conditions (Example 1) the flow rate that ensures the passage of the target through the target device without boiling. We use the well-known relation to estimate the relationship between the energy released in the medium during deceleration of the proton beam and the parameters of the medium:

here:

Q is the energy lost by the proton beam (released in the form of thermal energy) when protons are inhibited in the target;

With _p - specific heat of the target;

m _p is the mass of the target irradiated by the proton beam in the target device;

t ₁ is the target temperature before irradiation (at the entrance to the target device is the proton irradiation zone);

t ₂ is the temperature of the target after irradiation (at the exit from the target device is the proton irradiation zone).

The proton beam current is related to the proton flux by the expression:

where I is the current of the proton beam;

e is the elementary charge;

Ф - proton beam flux.

The energy lost by the proton beam in the target (Q) is:

where E is the energy lost by one proton (released in the form of thermal energy) when the proton is inhibited in the target.

In view of (1) and (2), expression (3) can be rewritten as follows:

For the purposes of this assessment, we take in the calculations t ₂ = 80 ° C and t ₁ = 20 ° C. That is, the heating of the target from the initial (t ₁ = 20 ° C - room temperature) when passing through the target device 1 (operating zone 9 - proton irradiation zone) should not exceed 60 ° C.

The heat transfer to the target from the foil window 8 (due to smallness) and the back wall — the partition, which is additionally cooled, is neglected.

The specific heat of the target is calculated based on the additivity rule:

where C _p is the specific heat of the target (a solution of RbF in water);

C _RbF — specific heat of rubidium fluoride;

C _H2O is the specific heat of water;

M _RbF — mass of rubidium fluoride in solution (solubility);

M _H2O is the mass of water in solution.

(The values of C _H2O = 4.18 [J / g ° C] (25 ° C) from (V.A. Rabinovich, Z.Ya. Khavin, Brief chemical reference book, publishing house “Chemistry”, 1977) were used in C _p calculations. ) and C _RbF = 50.6 [J / mol ° C] from (“Physical quantities”, Handbook. Edited by IS Grigoryev and EZ Meilikhov, M., Energoatomizdat, 1991).

Substituting into the expression (4) the values of the proton beam current I = 100 μA, the proton energy loss E = 35 MeV, the specific heat of the target C _p from (5), equal to 1.408 J / g ° C and the value of the solution heating (t ₂ -t ₁ ) = 60 ° C, we obtain the target mass m _p = 41.4 g. The resulting mass of the target is heated by a proton beam of 100 μA in one second from 20 ° C to 80 ° C. Dividing m _p by the target density equal to 2.92 g / cm ³ , we obtain the target volume equal to 14.2 cm ³ . The target volume obtained by irradiating a proton beam with a current of 100 μA is heated in one second from 20 ° C to 80 ° C.

It follows that if the target flow rate in the target circuit is chosen equal to 14.2 cm ³ / s, then the target, when passing through the target device (proton irradiation zone), will heat up no higher than 80 ° С. Technically, implementing a circulation mode with a specified flow rate is not difficult.

3) Estimation of the yield of ⁸² Sr in the target.

To simplify the estimation of the yield of ⁸² Sr, we make several assumptions:

- neglect the scattering of protons on the thickness of the target (we consider the paths in the target to be the same for all protons);

- neglect the decay of ⁸² Sr during the irradiation time (in the case of prolonged irradiation, a correction must be made);

- we consider the current density (flux) of protons to be uniform on the target surface (achieved by defocusing and scanning the proton beam over the target).

Let a proton beam with a current of 1 μA fall onto an element of the target surface S with an area of 1 cm ² (for reference: 1 μA of the current of the proton beam corresponds to the proton flux Φ = 6.25 × 10 ¹² proton / sec).

The yield of ⁸² Sr was calculated numerically in the 7-group energy approximation for energy ranges of 70–65 MeV; 65 ÷ 60 MeV; 60 ÷ 55 MeV; 55 ÷ 50 MeV; 50 ÷ 45 MeV; 45 ÷ 40 MeV and 40 ÷ 35 MeV according to the formula:

Where

here:

V [Bq / μA × h] - ⁸² Sr yield in the target;

V _i [Bq / μA × h] - ⁸² Sr yield in the i-th energy range;

λ [sec ¹ ] is the decay constant of ⁸² Sr;

T [sec] - time of irradiation of the target;

ρ [cm ^-3 ] is the concentration of rubidium nuclei in the target;

f [cm ^-2 × sec ^-1 ] is the proton flux density;

S = 1 cm ² - according to the initial conditions;

x _i [cm] is the path length of the proton in the i-th energy interval;

σ _i [cm] is the average cross section for the formation of ⁸² Sr for the ith energy interval upon irradiation with rubidium protons of a natural isotopic composition (as a result of the sum of the reactions Rb (p, xn) ⁸² Sr, where x = 4 and 6).

The values of σ _i were obtained from the experimental data estimation graph (Figure 3) given in [PRODUCTION OF LONG LIVED PARENT RADIONUCLIDES FOR GENERATORS: ⁶⁸ Ge, ⁸² Sr, ⁹⁰ Sr AND ¹⁸⁸ W. IAEA RADIOISOTOPES AND RADIOPHARMACEUTICALS SERIES No. 2. INTERNATIONAL ATOMIC ENERGY AGENCY VIENNA, 2010].

As σ _i , the values of the estimated curve corresponding to the midpoints of the i-th energy intervals were taken. The indicated values of σ _i are shown in table 2. Here are the values of x _i calculated using table 1.

Substituting in (6) and (7) the values λ = 3.21 × 10 ^-7 sec ^-1 , T = 3.6 × 10 ³ sec, ρ = 1.539 × 10 ²² cm ^-3 (for a solution with a salt concentration of 3 g / ml and density 2.92 g / cm ³ ), f = 6.25 × 10 ¹² cm ^-2 sec ^-1 S = 1 cm ² , x _i and σ _i from table 2, we obtain V = 9.768 × 10 ⁶ Bq / (μA × h) or 264 μCi / (μA × hour).

4) Evaluation of the performance of the method. We estimate the integral activity (A) of ⁸² Sr, which can be obtained per day in Example 1. Since the irradiation time (1 day) is significantly less than the half-life of ⁸² Sr (T _1/2 = 25 days), correction for decay during irradiation is not necessary taking into account:

here: V - exit ⁸² Sr.

Substituting the value V = 264 [μCi / (μA × h)] in (8), we obtain A = 0.63 Ci.

Example 2. Target in the form of an aqueous solution of RbCl (with Rb of natural isotopic composition) with a concentration of RbCl 0.91 g / ml (solubility of RbCl in water at n.o. according to (VA Rabinovich, Z.Ya. Khavin, Brief chemical reference , published by Chemistry, 1977) is equal to 91.1 g per 100 ml of water) placed in the same circulation circuit as in Example 1, see figure 1.

Turn on pump 2, providing circulation of the target in the circuit. While moving along the circulation loop when passing through the target device 1, the target is irradiated with 70 MeV protons and ⁸² Sr is produced in it by the reactions ⁸⁵ Rb (p, 4n) ⁸² Sr and ⁸⁷ Rb (p, 6n) ⁸² Sr. Irradiation is carried out during the day. After irradiation, the target using the device for selection (extraction) of the irradiated target 5 through the valve 6 is removed from the circulation circuit and sent for radiochemical processing to isolate ⁸² Sr.

The design of the target device, the proton beam current is the same as in Example 1, except for the width of the operating zone in the target device, in which the proton discharges energy from 70 MeV to 35 MeV in the target. Based on the given initial conditions in Example No. 2 (composition and concentration of the rubidium compound), we evaluate the main conditions for the implementation and productivity of the method.

To do this, we calculate:

- the width of the operating zone in the target device, in which the proton discharges energy from 70 MeV to 35 MeV in the target;

- target consumption during movement in the circulation circuit, ensuring the absence of boiling of the target in the target device;

- ⁸² Sr yield in the target;

- the performance of the method (the integral amount of ⁸² Sr produced per day on a proton beam with a current of 100 μA).

1) Estimation of the width of the operating zone. The width of the operating zone was taken equal to the mean free path of a proton with an initial energy of 70 MeV until it reaches an energy of 35 MeV. The proton path lengths were calculated using the STRIM program (see Example 1). The density of the target used in the calculation of mileage was determined in accordance with the additivity rule, as in Example 1. The indicated density was 1.84 g / cm ³ . Table 3 shows the results of calculation using the STRIM program of the total path lengths of protons in the target for different initial energies.

From table 3 it follows that the width of the operating zone of the target device, equal to the difference in proton mean free paths for 70 MeV and 35 MeV, is 20.9 mm.

2) Estimation of the target flow rate in the circulation circuit, ensuring the passage of the target through the target device without boiling.

The algorithm for calculating the flow rate of the target in the circulation loop, ensuring the passage of the target through the target device without boiling, is the same as in Example 1. (In calculations of C _p , the values C _H2O = 4.18 [J / g ° C] (25 ° C) from (V. A. Rabinovich, Z.Ya. Khavin, Brief chemical reference book, publishing house “Chemistry”, 1977) and C _RbCl = 52.3 [J / mol ° С] from (“Physical quantities”, Reference. Ed. I.S. Grigoriev and E.Z. Meilikhova, M., Energoatomizdat, 1991)

Substituting into the expression (4) the values of the proton beam current I = 100 μA, the proton energy loss E = 35 MeV, the specific heat of the target С _p calculated by formula (5) for RbCl, equal to 2.39 J / g ° С and the solution heating value ( t ₂ -t ₁ ) = 60 ° C, we obtain the target mass m _p = 24.4 g. The resulting mass of the target is irradiated with a proton beam of 100 μA current in one second from 20 ° C to 80 ° C. Dividing m _p by the target density equal to 1.84 g / cm ³ , we obtain the target volume equal to 13.3 cm ³ . The target volume obtained by irradiating a proton beam with a current of 100 μA is heated in one second from 20 ° C to 80 ° C.

It follows that if the target flow rate in the target circuit is chosen equal to 13.3 cm ³ / s, then the target, when passing through the target device (proton irradiation zone), will heat up no higher than 80 ° C. Implement the circulation mode with the specified flow rate as well as in Example 1, is not difficult.

3) Estimation of the yield of ^S2 Sr in the target.

The algorithm for calculating the yield of ⁸² Sr in the target is the same as in Example 1. Table 4 shows the values of σ _i . The values of x _i calculated using table 3 are also shown here.

Substituting in (6) and (7) the values λ = 3.21 × 10 ^-7 sec ^-1 , T = 3.6 × 10 ³ sec, ρ = 6.56 × 10 ²¹ cm ^-3 (for a solution with a salt concentration of 0.91 g / ml and density 1.84 g / cm ³ ), f = 6.25 × 10 ¹² cm ^-2 sec ^-1 , S = 1 cm ² , x _i and σ _i from table 4, we obtain V = 5.88 × 10 ⁶ Bq / (μA × hour) or 159 μCi / (μA × hour).

4) Evaluation of the performance of the method.

We estimate the integral activity of (A) ⁸² Sr, which can be accumulated per day in Example 2.

here: V - exit ⁸² Sr.

Substituting the value V = 159 [μCi / (μA × hr)], we obtain A = 0.382 Ci.

Example No. 3. Target in the form of an aqueous solution of Rb ₂ CO ₃ (with Rb of natural isotopic composition) with a concentration of Rb ₂ CO ₃ 2.23 g / ml (solubility of Rb ₂ CO ₃ in water at n.o. according to (V.A. Rabinovich, Z.Ya. . Khavin, Brief chemical reference book, publishing house "Chemistry", 1977) is equal to 223 g per 100 ml of water) are placed in the same circulation circuit as in Example 1, see figure 1.

Turn on the pump, providing circulation of the target in the circuit. While moving along the circulation circuit while passing through the target device, the target is irradiated with 70 MeV protons and ⁸² Sr is produced in it by the reactions ⁸⁵ Rb (p, 4n) ⁸² Sr and ⁸⁷ Rb (p, 6n) ⁸² Sr. Irradiation is carried out during the day. After irradiation, the target, using the device for selecting (extracting) the irradiated target (5) through the valve (6), is removed from the circulation circuit and sent for radiochemical processing to isolate ⁸² Sr.

The design of the target device, the proton beam current is the same as in Example 1, except for the width of the operating zone in the target device, in which the proton discharges energy from 70 MeV to 35 MeV in the target. Based on the given initial conditions in Example 3 (composition and concentration of the rubidium compound), we evaluate the main conditions for the implementation and productivity of the method.

To do this, we calculate:

- the width of the operating zone in the target device, in which the proton discharges energy from 70 MeV to 35 MeV in the target;

- target consumption during movement in the circulation circuit, ensuring the absence of boiling of the target in the target device;

- ⁸² Sr yield in the target;

- the performance of the method (the integral amount of ⁸² Sr produced per day on a proton beam with a current of 100 μA).

1) Estimation of the width of the operating zone.

The width of the operating zone was taken equal to the mean free path of a proton with an initial energy of 70 MeV until it reaches an energy of 35 MeV. The proton path lengths were calculated using the STRIM program (see Example 1). The density of the target used in the calculation of mileage was determined in accordance with the additivity rule, as in Examples 1 and 2. The specified density was 2.71 g / cm ³ . Table 5 shows the results of calculation using the STRIM program of the total path lengths of protons in the target for different initial energies.

From table 5 it follows that the width of the operating zone of the target device, equal to the difference in proton mean free paths for 70 MeV and 35 MeV, is 15.0 mm.

2) Estimation of the target flow rate in the circulation circuit, ensuring the passage of the target through the target device without boiling.

The algorithm for calculating the flow rate of the target in the circulation loop, ensuring the passage of the target through the target device without boiling, is the same as in Examples 1 and 2. In the calculations C _p , the values C _H2O = 4.18 [J / g ° C] (25 ° C) were used from (V.A. Rabinovich, Z.Ya. Khavin, Brief chemical reference book, publishing house “Chemistry”, 1977) and C _Rb2CO3 = 117.6 [J / mol ° С] from (Efimov A.I. et al. “Properties of inorganic compounds.” Handbook, L., Chemistry, 1985).

Substituting the proton beam current I = 100 μA into expression (4), the proton energy loss E = 35 MeV, the specific heat of the target С _p calculated by formula (5) for Rb ₂ CO ₃ , equal to 1.646 J / g ° С, and the solution heating value (t ₂ -t ₁ ) = 60 ° C, we obtain the target mass m _p = 35.4 g. The resulting target mass when heated by a proton beam of 100 μA is heated in one second from 20 ° C to 80 ° C. Dividing m _p by the target density equal to 2.71 g / cm ³ , we obtain the target volume equal to 13.1 cm ³ . The target volume obtained by irradiating a proton beam with a current of 100 μA is heated in one second from 20 ° C to 80 ° C.

The calculated estimate shows that at a proton beam current of 100 μA, the target flow rate in the circulation loop equal to 13.1 cm ³ / s will make it possible to limit the rise in the target temperature during passage of the target device to 80 ° C. It is easy to circulate the target with the indicated flow rate.

3) Estimation of the yield of ⁸² Sr in the target.

The algorithm for calculating the yield of ⁸² Sr in the target is the same as in Examples 1 and 2. Table 6 shows the values of σ _i . The values of x _i calculated using table 5 are also shown here.

Substituting in (6) and (7) the values λ = 3.21 × 10 ^-7 sec ^-1 , T = 3.6 × 10 ³ sec, ρ = 1.25 × 10 ²² cm ^-3 (for a solution with a salt concentration of 2.23 g / ml and a density 2.71 g / cm ³ ), f = 6.25 × 10 ¹² cm ^-2 sec ^-1 , S = 1 cm ² , x _i and σ _i from table 6, we obtain V = 8.07 × 10 ⁶ Bq / (μA × hour) or 218 μCi / (μA × hour).

4) Evaluation of the performance of the method.

We estimate the integral activity of (A) ⁸² Sr, which can be accumulated per day in Example 3.

here: V - exit ⁸² Sr.

Substituting the value V = 218 [μCi / (μA × hour)], we obtain A = 0.523 Ci.

It is known that all inorganic compounds of rubidium are soluble in water or react with water to form soluble compounds. Therefore, in the proposed method, any inorganic rubidium compounds can be used. Variants of the proposed method with different inorganic compounds of rubidium will vary slightly by the width of the operating zone in the target device, the flow rate of the target in the circulation circuit, the output of ⁸² Sr and, accordingly, throughput, but all the options will work. Table 7 additionally shows as examples the most significant technical parameters of several options for implementing the method with the most widespread inorganic compounds of rubidium, calculated using the above algorithms (see Examples 1-3).

Depending on the requirements for the quality and volume of production of ⁸² Sr, within the framework of the proposed method, it is possible to select and optimize rubidium compounds in the target composition. The calculated yield of ⁸² Sr in the prototype (solid-state target from rubidium chloride), obtained using the algorithm used in the above Examples, is 249 μCi / (μ × hour). This is in good agreement with the data of the work (NG Zaitseva et al .: “Cross Sections for the 100 MeV Proton-Induced Nuclear Reactions and Yields of some Radionuclides Used in Nuclear Medicine”, Radiochimica Acta, 57, 57-72 (1991): 260 μCi / (μA × hour) and confirms the quality of the constants and algorithm used in the present calculations. From the results it follows that the ⁸² Sr yield in the target with RbF (264 μCi / (μA × hour; Example 1) practically coincides with the yield in the prototype (249 μCi / [μA × hr]). For rubidium compounds from other examples, the yield of ⁸² Sr is somewhat lower. However, due to the fact that the proposed method allows working at high currents otons (in contrast to the prototype, in which the output decreases significantly with increasing current), its real integral performance for many rubidium compounds can be higher than in the prototype.

The method can also be implemented if the target is a solution of not one, but two or several rubidium compounds at once. There are no fundamental differences in the implementation of the method in this case from the variants of the target with a solution of one rubidium compound.

Conceptually, the use of melts as a target will not differ from the use of solutions, with the only difference being that the circulation circuit must be maintained at temperatures above the melting point of the target.

Example No. 9. A target in the form of a suspension of RbF (a suspension of undissolved RbF particles in a saturated aqueous solution of RbF is 10% of the mass of salt in the solution) with a rubidium of a natural isotopic composition is placed in the same circulation circuit as in Example 1. The pump is turned on, allowing the target to circulate in the circuit . While moving along the circulation circuit while passing through the target device, the target is irradiated with 70 MeV protons and ⁸² Sr is produced in it by the reactions ⁸⁵ Rb (p, 4n) ⁸² Sr and ⁸⁷ Rb (p, 6n) ⁸² Sr. Irradiation is carried out during the day. After irradiation, the target, using the device for selecting (extracting) the irradiated target (5) through the valve (6), is removed from the circulation circuit and sent for radiochemical processing to isolate ⁸² Sr.

During the irradiation time, the average current of the proton beam is 100 μA. The proton beam at the entrance to the target has a circle shape with a diameter of 20 mm with a constant surface current density. The target device is the same as in Example 1. Based on the initial conditions specified above, we will evaluate the same as in Example 1, the basic conditions for the implementation and productivity of the method.

To simplify the estimates, we make the following assumptions:

1. The particle size of the suspension is 100 microns.

2. Particles of the suspension are distributed evenly throughout the volume of the solution.

1) Estimation of the width of the operating zone of the target device.

The width of the production zone was taken equal to the mean free path in the proton target with an initial energy of 70 MeV until it reaches an energy of 35 MeV. To simplify the estimation of the proton mean free path in the target, the heterogeneous structure of the target in the calculations was replaced by a homogeneous structure with an increase in salt concentration by the fraction of solid particles (10%). The target density used in mileage calculations was determined as the sum of the densities of RbF and water with the weight of their mass fractions in the target in accordance with the additivity rule. The indicated density was 2.96 g / cm ³ . Table 8 shows the results of calculation using the STRIM program of the total path lengths of protons in the target for different initial energies.

From table 8 it follows that the width of the operating zone of the target device, equal to the difference in proton mean free paths for 70 MeV and 35 MeV, is 14.6 mm.

2) Estimation of the target flow rate in the circulation circuit, ensuring the passage of the target through the target device without boiling.

Example 1 shows that the target flow rate in the circulation loop, equal to 14.2 cm ³ / s, provides heating of the target during the passage of the target device by no more than 60 ° C, which ensures that the target does not boil. This example differs from Example No. 1 only in the presence of particles of undissolved salt in the solution, the temperature of which may differ from the temperature of the solution. Let us estimate the degree of heating of the suspension particles during the passage of the target device if the target flow rate in the circulation loop is 14.2 cm ³ / s.

For the sake of definiteness of calculations and simplicity of estimation, we make the following assumptions:

- the particles of the suspension are in the form of a cylinder and an overall dimension of 100 microns (the diameter is equal to the height);

- the flow of protons during the movement of particles in the target device is directed perpendicular to the base of the cylinder;

- due to the poor thermal conductivity of the suspension particles, we neglect the heat transfer from the suspension particle to the solution during the time the particle crosses the irradiation zone.

According to the calculated estimate, the proton energy loss in the RbF suspension particle (at a length of 100 microns) near the front wall of the production zone (for protons with an energy of 70 MeV) will be ~ 0.2 MeV. The proton energy loss in a particle of the RbF suspension (at a length of 100 microns) at the back wall of the production zone (for protons with an energy of 35 MeV) will be ~ 0.3 MeV. Let us evaluate the heating of a suspension particle near the front wall of the target device during the passage of a particle of the irradiation zone with a diameter of 20 mm at a proton beam current of 100 μA. The ratio of the area of the base of the cylinder (the surface onto which the proton beam falls) to the area of the irradiation zone (diameter 20 mm) is 2.5 × 10 ^-5 . Therefore, a proton flux of 6.25 × 10 ¹⁴ × 2.5 × 10 ⁻⁵ = 1.56 × 10 ¹⁰ proton / s (1 μA = 6.25 × 10 ¹² proton / s) falls on the particle during motion. The cross-sectional area in the target device is 1.47 cm × 2 cm = 2.94 cm ² (1.47 cm is the width of the operating zone in Example 1; 2 cm is the height of the cross-section of the target device equal to the diameter of the proton beam). Hence, the velocity of the suspension particle through the proton irradiation zone will be 14.2 cm ³ / s / 2.94 cm ² = 4.8 cm / s, here 14.2 cm ³ / s is the flow rate in Example 1. Accordingly, the intersection time of the irradiation zone will be 2 cm / 4.8 cm / s = 0.42 sec. Hence, the number of protons that enters the particle during its movement through the proton irradiation zone will be: 1.56 × 10 ¹⁰ protons / sec × 0.42 sec = 6.55 × 10 ⁹ protons. The mass of the RbF particle at a density of 3.56 g / cm ³ is 1.86 × 10 ^-6 g. Next, transforming expression (4), we obtain formula (9) for the amount of heating (temperature change Δt) during the time the RbF suspension crosses the irradiation zone with protons at a current a proton beam on a target of 100 μA and a target flow rate in the circulation loop of 14.2 cm ³ / s.

Here:

Δt is the change in temperature of the suspension particle;

E is the energy lost by the proton when crossing the suspension particles;

I is the current of the proton beam;

e is the elementary charge;

With _p is the heat capacity of the suspension particles;

m is the mass of the suspension particles.

Taking into account that 1 MeV = 1.6 × 10 ^-13 J, and substituting E = 0.2 MeV × 1.6 × 10 ^-3 J / MeV = 3.2 × 10 ^-14 J in the expression (9); I / e = 6.55 × 10 ⁹ protons; With _p = 0.484 J / g ° C and m = 1.86 × 10 ^-6 g, we obtain Δt = 233 ° C. This means that on the surface of the particles of the suspension, the solution will begin to boil while moving through the irradiation zone. In order for the suspension particles to be heated no higher than 60 ° C (same as the solution in Example 1), it is necessary to increase the target flow rate in the circulation loop by a factor of K, where K = 233 ° C / 60 ° C = 3.9 times. For suspension particles near the rear wall of the production zone, the energy release from proton drag is one and a half times higher than that of the front wall. Therefore, in order to ensure that the solution does not boil on the surface of the suspension particles, it is necessary to increase the target flow rate in the circulation circuit to a value equal to (14.2 cm / s × 3.9 × 1.5) = 83 cm ³ / s. Ensuring the specified flow rate is quite achievable. It should be noted that according to the calculations, a change in the particle size of the suspension while maintaining the remaining initial conditions in Example 19 does not change the desired target flow rate.

3) Estimation of the yield of ⁸² Sr in the target.

To simplify the estimation of the yield of ⁸² Sr in the target, an assumption was made according to which the heterogeneous structure of the target in the calculations was replaced by a homogeneous structure with an increase in the RbF concentration by the fraction of solid particles. The algorithm for calculating the yield of ⁸² Sr in the target is the same as in Example 1. Table 9 shows the values of σ _i . The values of x _i calculated using table 8 are also shown here.

Substituting in (6) and (7) the values λ = 3.21 × 10 ^-7 sec ^-1 , T = 3.6 × 10 ³ sec, ρ = 1.574 × 10 ²² cm ^-3 (for a solution with a salt concentration of 3.3 g / ml and density 2.96 g / cm ³ ), f = 6.25 × 10 ¹² cm ^-2 sec ^-1 , S = 1 cm ² , x _i and σ _i from table 9, we obtain V = 9.91 × 10 ⁶ Bq / (μA × hour) or 268 μCi / (μA × hour).

4) Evaluation of the performance of the method. We estimate the integral activity of (A) ⁸² Sr, which can be accumulated per day in Example 9.

here: V - exit ⁸² Sr.

Substituting the value V = 268 [μCi / (μA × hour)], we obtain A = 0.643 Ci.

Similarly to Example 9, the method can be implemented with suspensions consisting of solutions and solid particles of other rubidium compounds, as well as solutions and solid particles of two or more rubidium compounds.

Implementation of the proposed method in the forced circulation mode is preferable, since it provides freedom of maneuver when operating at high currents of the proton beam. However, it is obvious that it is possible to choose the conditions under which the method can be implemented in the natural circulation mode.

The above examples do not limit the options for performing the method, while proving its feasibility and achieving a technical result.

- The method provides for the abandonment of the use of metallic rubidium as a target material to eliminate the risk of contingencies associated with its potential explosion hazard, which can lead to a severe radiation accident.

- The method provides for the rejection of the use of rubidium compounds in the form of solid targets, in which, due to poor thermal conductivity, it is difficult to provide effective heat removal, which limits the possibility of using large proton beam currents.

- With an output of ⁸² Sr comparable to the prototype (for example, for solutions with RbF or Rb2CO3), the present method allows working on proton beams with a high current (≥100 μA) without reducing the yield (unlike the prototype), which makes it possible for a comparable the time to produce integral amounts of ⁸² Sr, significantly exceeding the corresponding quantities that can be obtained using the prototype.

- Depending on the requirements for the quality and production volume of ⁸² Sr, there is the possibility of choosing and optimizing rubidium compounds in the target composition.

- The target device (in contrast to all solid-state target variants in analogues and prototype) can be used repeatedly, eliminating the need for the cost of manufacturing target devices for each new exposure.

- Removing the target from the target device and separating ⁸² Sr from the target is easy to automate and is not associated with the need to carry out technological operations in manual mode.

Claims (6)

1. A method of obtaining a radioisotope of strontium-82 ( ⁸² Sr) by the reaction Rb (p, xn) ⁸² Sr, comprising irradiating the target with protons and isolating ⁸² Sr from the irradiated target, characterized in that one or more chemical or molten solutions are used as the target rubidium compounds or their suspension in a liquid carrier, and circulate them in a closed loop through the proton irradiation zone, producing a ⁸⁵ Rb (p, 4n) ⁸² Sr and (or) ⁸⁷ Rb (p, 6n) ⁸² Sr radioisotope in the target ⁸² Sr, which after irradiation or directly during irradiation is extracted from mi Sheny one of the radiochemical methods. 2. The method according to p. 1, characterized in that as a suspension of one or more chemical compounds of rubidium in a liquid carrier, an aqueous or other saturated solution with a precipitate of one or more chemical compounds of rubidium is used. 3. The method according to p. 1, characterized in that the circulation of the target is carried out forcibly. 4. The method according to p. 1, characterized in that the circulation of the target is carried out in natural circulation. 5. The method according to p. 1, characterized in that the target is circulated in a closed loop through the proton irradiation zone and the heat exchanger, using the target as a coolant. 6. The method according to p. 1, characterized in that the chemical compounds of rubidium use compounds selected from the series: RbCl, RbF, Rb ₂ CO ₃ , RbNO ₃ , Rb ₂ SO ₄ , RbBr, RbI, Rb (OH).

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