RU2436179C1 - Start target composition on basis of radium, and manufacturing method thereof - Google Patents

Abstract

FIELD: power industry. ^ SUBSTANCE: for using in the technology of obtaining radioactive isotopes the start target composition on the basis of radium includes radium and lead oxide (diluter). Method for obtaining start composition on the basis of radium consists in co-deposition of radium carbonate with lead carbonate from water solutions of their soluble salts with solutions of water-soluble carbonates and calcination of the obtained deposit at temperature of more than 350C. ^ EFFECT: group of inventions allows increasing specific yield of radium activation products. ^ 6 cl, 1 dwg, 1 tbl

Description

The invention relates to the field of radiochemistry and can be used in the technology for the production of radioactive isotopes.

Currently, one of the possible uses of radium-226 is to irradiate it with neutrons, charged particles, or high-energy gamma rays to produce ²²⁷ Ac, ²²⁸ Th, ²²⁹ Th, and ²²⁵ Ac isotopes, which are of considerable interest for use as generators of short-lived alpha-emitting radionuclides medical supplies intended for the treatment of cancer.

When radium is irradiated with neutrons in water-cooled reactors, it is necessary that radium be in a form that is hardly soluble in water. This will avoid the ingress of significant amounts of radium, its daughter decay products and activation products into the coolant (cooling water). In this case, it is necessary that this form of radium be thermally stable, and also allow dissolution of the irradiated material to isolate the products of nuclear transformations. Radium carbonate satisfies these requirements. Radium sulfate and fluoride, although slightly soluble in water and have a high decomposition temperature, but their chemical properties impede the radiochemical isolation of the target components and the regeneration of radium. Sulfur in radium sulfate is also able to be activated by the reactions ³⁴ S (n, γ) ³⁵ S and ³² S (n, p) ³² P. The second reaction leads to the formation of phosphate ions, giving insoluble compounds with radium and its activation products (Ac at irradiation with protons, fast neutrons and gamma rays, Ac and Th when irradiated with thermal neutrons), which further complicates the radiochemical processing of the irradiated target.

Known starting radium composition of the target using radium in the form of bromide (Patent US No. 3459634).

Anhydrous radium bromide can be obtained by dissolving radium carbonate in HBr or by repeatedly treating radium chloride with hydrobromic acid, followed by evaporation and drying at 120-150 ° C [Vdovenko VM, Dubasov Yu.V. Analytical chemistry of radium. Series "Analytical chemistry of elements". Leningrad, Science. 1973. 190 p.].

The disadvantage of this starting material for the target is that radium bromide dissolves well in water and, if the target shell is depressurized, the coolant may be contaminated.

The closest analogue of the invention is the starting radium composition of the target using radium in the form of carbonate (Vdovenko VM, Dubasov Yu.V. Analytical chemistry of radium. Series "Analytical chemistry of elements". Leningrad, Science. 1973. 191 S.).

A method of manufacturing such a starting composition consists in fusing radium sulfate with alkali metal carbonates at high temperatures, dissolving the resulting alloy in water, filtering the precipitate of radium carbonate and annealing it at 700 ° C.

This method has the following disadvantages:

- when using milligram amounts of radium, it is of little use due to the inevitable significant mechanical losses;

- for macro amounts of radium, this method also has significant disadvantages due to a decrease in the yield of target activation products of ²²⁶ Ra due to resonant self-shielding.

Resonant shielding occurs due to the significant contribution of resonance neutron absorption to the process of radium activation, and as a result, a rapid decrease in the neutron flux density occurs with energies corresponding to resonance with a compact arrangement of radium atoms in the target volume.

The objective of the proposed technical solution is to increase the specific yield of radium activation products.

The above problem is achieved in that the starting composition based on radium-226 additionally contains a diluent - lead oxide.

Radium in the starting composition is in the form of radium carbonate or plumbate.

A method of obtaining a starting composition based on radium-226 consists in the coprecipitation of radium carbonate with lead carbonate from aqueous solutions of their salts with solutions of water-soluble carbonates and calcining the resulting precipitate at temperatures above 350 ° C.

Precipitation of radium-lead carbonates is produced from neutral or slightly acidic solutions of radium and lead nitrates.

Precipitation of radium-lead carbonates is made from neutral or slightly acidic solutions of radium and lead acetates.

The use of lead as a diluent for radium has the following advantages:

- reduced mechanical losses when working with milligram quantities of radium;

- there is no decrease in the yield of target products of radium activation due to resonance self-shielding;

- simplified subsequent radiochemical processing of irradiated material;

- Natural lead isotopes are practically not activated upon neutron irradiation and have little effect on the neutron flux density due to low neutron capture cross sections.

Lead ions of Pb ²⁺ and radium Ra ²⁺ , on the one hand, have close ionic radius values, which result in a similar crystalline structure, close solubility of radium and lead (II) compounds, and the ability of radium salts to precipitate isomorphically with lead (II) salts ) If necessary, lead can be easily separated from radium, for example, by precipitation of sparingly soluble chloride or sulfide.

The co-precipitation of carbonates was chosen on the basis that radium co-precipitates well with lead carbonate, the radium and lead carbonates themselves, as well as the products of their thermal decomposition, are insoluble in water, but soluble in nitric acid, traditionally used to dissolve irradiated targets.

Precipitation must be carried out from neutral or slightly acidic solutions of lead salts, since in alkaline solutions lead salts undergo strong hydrolysis, and during deposition from strongly acidic solutions, intense gas evolution is observed, leading to spraying of the solution.

When calcining at temperatures below 350 ° C, the decomposition of lead carbonate will be incomplete, therefore, there is a risk of increasing pressure in the ampoule with the irradiated material during irradiation.

The advantages of the proposed starting composition over the prototype are an increase in the specific yield of radium activation products due to a decrease in the resonance self-screening coefficient and the possibility of using lead, which is part of the starting composition, as a carrier in the precipitation separation of radium from its activation products.

The properties of the claimed composition and the method for its preparation were verified using barium nitrate as a simulator of radium nitrate. Based on the proximity of the chemical properties of radium and barium, including the isomorphism of radium and barium carbonates, the data obtained for barium can be used for radium.

To 12 ml of a solution of Pb (NO ₃ ) ₂ containing 3 g of lead nitrate, 20 mg of Ba and a tag of ¹³³ Ba, 30 ml of a solution of NH ₄ CO ₃ concentration of 62 mg / ml was slowly added through a dropping funnel. The reaction mixture was left for 15 hours to mature the precipitate. The solution was filtered through a blue ribbon paper filter, the precipitate was washed with 10 ml of a 10% solution of NH ₄ HCO ₃ , then 4 times in portions of 5 ml of double-distilled water. The barium concentration was determined radiometrically by the Ba label, and the lead concentration was determined by spectrophotometry with arsenazo III.

Conducted similar experiments using (NH ₄ ) ₂ CO ₃ , Na ₂ CO ₃ and K ₂ CO ₃ .

The results of experiments on the coprecipitation of barium-lead carbonates are shown in table 1.

Table 1 No. Water soluble carbonate The degree of deposition of lead,% The degree of coprecipitation of barium,% one NH ₄ HCO ₃ > 99.9 ~ 88 2 (NH ₄ ) ₂ CO ₃ > 99.9 ~ 92 3 K ₂ CO ₃ > 99.9 > 99.9 four Na ₂ CO ₃ > 99.9 > 99.9

From table 1 it is seen that the best result is achieved when using sodium and potassium carbonates.

The resulting preparations were calcined at various temperatures. The attached drawing shows the thermal decomposition of the starting composition with a ratio of Ba: Pb = 1: 2, obtained by coprecipitation of lead and barium carbonates in an aqueous solution of potassium carbonate.

As can be seen from the drawing, at 410-550 ° C, the mass of the drug reaches a constant level, which indicates the end of the decomposition reaction of lead carbonate and the thermal stability of the resulting starting composition (PbO / BaCO ₃ ). With further heating in an oxygen-containing atmosphere, further decomposition is observed with the formation of barium plumbate.

A general check of the proposed method was carried out experimentally using milligram quantities of radionuclide ²²⁶ Ra. The solution containing radium nitrate was evaporated to dryness, the residue was dissolved in a solution of lead nitrate with a concentration of 0.2 mol / L. An excess of 0.5 mol / L potassium carbonate solution was added to the resulting solution. The precipitate was filtered off. Then it was dried and calcined at 600 ° C. The specified starting composition with a mass of 1 g, containing 2.5 mCi ²²⁶ Ra, was placed in a quartz capsule and irradiated in the neutron trap of the SM-3 reactor for 25 effective (30 calendar) days at a thermal neutron flux density of 1.5 · 10 ¹⁵ cm ^{- 2} s ^-1 . After irradiation and exposure for 17 days, the irradiated target was dissolved in nitric acid. To the resulting solution was added 50 ml of nitric acid with concentrations of 16 mol / L. In this case, precipitation of lead and radium nitrates occurred. The degree of precipitation of radium was 97%, the capture of actinium and thorium by sediment was 8.7 and 11%, respectively. Thus, the precipitation of poorly soluble lead-radium nitrates from a solution of irradiated lead-radium composition with an aqueous solution of nitric acid with a concentration of 11.5 mol / L, followed by reprecipitation, allows the separation of radium and its activation products. The solution after precipitation was analyzed by alpha and gamma spectrometry for a content of ²²⁸ Th. The yield of ²²⁸ Th was 44 Ci / g, which is close to the theoretically calculated for this target (46 Ci / g). Moreover, for the prototype (target made of radium carbonate), taking into account resonant self-screening, the yield of ²²⁸ Th would be only 34 Ci / g.

Claims (6)

1. The starting composition of the target based on radium, containing radium and a diluent, characterized in that the diluent used is lead oxide. 2. The starting composition according to claim 1, characterized in that the radium is in the form of radium carbonate. 3. The starting composition according to claim 1, characterized in that the radium is in the form of a radium plumbate. 4. A method of obtaining a starting composition based on radium, which consists in the coprecipitation of radium carbonate with lead carbonate from aqueous solutions of their soluble salts with solutions of water-soluble carbonates and calcining the resulting precipitate at a temperature of more than 350 ° C. 5. The method according to claim 4, characterized in that the carbonates are precipitated from neutral or slightly acidic solutions of radium and lead nitrates. 6. The method according to claim 4, characterized in that the carbonates are precipitated from neutral or slightly acidic solutions of radium and lead acetates.