RU2344504C1 - Method of obtaining silver radioisotopes without carrier - Google Patents

Abstract

FIELD: technological processes; chemistry.

SUBSTANCE: metal cadmium is used as target substance and irradiated by high-energy protons. Target substance is separated by distillation in hydrogen atmosphere. Nuclear reaction and transformation products are collected on quartz sand surface. Obtained radioactive sample is placed into start zone of quartz thermochromatographic column. The sample undergoes high-temperature chemical processing in the presence of reagent, with transfer of obtained volatile compounds. Volatile compounds are precipitated on the column walls at certain temperatures. Phosphor or arsenic vapours are used as reagent.

EFFECT: enhanced radiochemical purity of silver radioisotopes.

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Description

The invention relates to the field of radiochemistry, in particular to methods for producing radioisotopes. The invention can be used in radiochemistry for the production of silver radioisotopes with a high degree of purity.

To date, 33 silver radioisotopes of silver have been identified [1] (excluding isomers) (Antony MS Nuclide Chart 2002, IReS, 23 rue du Loess, BP 20, Strasburg, France, p.15-16). Most of them have small half-lives T _1/2 - from milliseconds to several hours. 2 neutron-deficient radioisotopes with atomic numbers A equal to 105 and 106, as well as 2 neutron-rich nuclides with A = 110 and 111 are characterized by large values of T _1/2 (more than a day). They are widely used in physical chemistry and electrochemistry (Haissinsky M., Adioff J.-P. Radiochemical Survey of the Elements, Elsevier Publishing Company, Amsterdam / London / New York, 1965, p. 143).

A known method for producing short-lived silver radioisotopes (Bruechle W., Herrmann G. Decay properties neutron-rich silver isotopes. Radiochim. Acta, 1982, Vol.30, N 1, pp.1-10) formed during the irradiation of natural uranium with neutrons with energies of 14 MeV when irradiated with ²⁵² Cf thermal neutrons and cadmium neutrons with an energy of 14 MeV (analogue). After irradiation, a saturated solution of K ₂ Cr ₂ O ₇ in a 2N H ₂ SO ₄ solution was added to nitric acid solutions of uranium and cadmium, then the resulting solution was passed through a thin AgCl layer in which silver radioisotopes were accumulated. The resulting collection was washed, dissolved, filtered and its γ-spectrometry (manually or automatically) was carried out for the content of silver radioisotopes. The disadvantages of the method include its complexity and the complexity of the technological cycles.

A method for producing silver radioisotopes without carriers is described (Eichler B., Domanov V.P. JINR Preprint, P 12-7775, Dubna, 1974), which are isolated in the form of chlorides (prototype). According to the proposed approach, cadmium metal is used as the target material, which is irradiated with accelerated protons with an energy of 660 MeV. During irradiation, neutron-deficient radioisotopes of silver are accumulated in the target material, in particular, ¹⁰⁵ Ag and ¹⁰⁶ Ag, formed by the nuclear reactions Cd (p, 2pxn), as well as related nuclides with serial numbers Z <47. The irradiated material is transferred to the surface of quartz sand placed in a quartz tube, and when heated, the target substance is distilled off in a stream of hydrogen, and quartz sand with the nuclear reaction products adsorbed on its surface is placed in the starting zone of the quartz tube (TCA), which is heated at 1000 ° С in a stream of chlorine - carrier gas and reagent. The resulting volatile chlorides are adsorbed on the walls of TCA at certain temperatures. Under the described conditions, silver chloride (AgCl) precipitates at 620 ° C.

The disadvantages of the method include the presence in the radioactive silver preparations of the radioisotopes of rhodium and palladium, because the volatility of their chlorides is close to the volatility of silver chloride.

An object of the present invention is to obtain silver radioisotopes with high radiochemical purity.

The problem is achieved in that for the separation of silver radioisotopes as a reagent, pairs of phosphorus or arsenic are used. In the first case, silver forms volatile phosphide, which is deposited on the surface of quartz at 660-680 ° C, and in the second, volatile arsenide adsorbed at 620-640 ° C. Radioisotopes accompanying silver with Z <47, in particular, palladium, rhodium, ruthenium, technetium, niobium, zirconium and yttrium, do not form volatile compounds and they remain in the original sample.

A significant difference of the proposed method from the prototype lies in the fact that as the reagent gases use pairs of phosphorus or arsenic.

This essential feature makes it possible to obtain silver radioisotopes with a high degree of purification from extraneous impurities.

The essence of the method is as follows: the cadmium target is irradiated with accelerated protons. When irradiated with cadmium, radioisotopes are formed with Z≤48, in particular ¹⁰⁶ Ag (T _1/2 = 8.3 days) and ¹⁰⁵ Ag (T _1/2 = 41.3 days). After irradiation, the target material is transferred to the surface of quartz sand placed in a quartz tube, and the target material heated to a certain temperature is distilled off in a stream of hydrogen. After distillation and cooling of the heating zone, quartz sand with radioisotopes collected on its surface is transferred to the starting zone of quartz TXK, in front of which a solid reagent - phosphorus or arsenic is placed. A column ready for the experiment is installed inside the cascade of tubular electric furnaces having various functional purposes. The first furnace (1) is designed to heat the solid reagent to a certain temperature, the second (2) provides hot transport of the reagent vapor, the third (3) heats the original radioactive sample to a high temperature, and the fourth (4) creates a negative temperature gradient along the column. After purging the installation with purified helium, a predetermined temperature distribution is established along the column. In the process of high-temperature chemical treatment of the initial sample with reagent vapors, silver radioisotopes form volatile pnictides transported along the TCA in a helium stream and adsorbed at certain temperatures. Radioisotopes associated with silver elements of volatile compounds do not form and remain in the original sample. The bulk of gaseous reactants that have not entered into chemical reactions are deposited on the walls of TCA at relatively low temperatures. The distribution of ^105.106 Ag along TCA and their chemical yield Y are determined using a γ spectrometer. The value of Y depends on a number of parameters, in particular, on the concentration of reagents in the gas phase, which, in turn, is determined by the heating temperature of the solid reagent t ₁ . When working with red phosphorus heated to 320 ° C, the Y value was 43%, at t ₁ = 330 ° C the value Y = 65%, and at t ₁ = 340 ° C the Y value reaches 76%. Heating phosphorus at higher temperatures leads to a noticeable increase in the concentration of its vapors, which, precipitating, overlap the column. Thus, the temperature range of 330-340 ° C is optimal for the implementation of the method.

When choosing the concentration in the gas phase of arsenic, the data were used (Tables of physical quantities. Handbook edited by I.K. Kikoin, M., Atomizdat, 1976, p.206). It was found that when this reagent was heated to 370 ° C, the Y value was 51%. At t ₁ = 390 ° C, the chemical yield of silver radioisotopes increased to 75%, at t ₁ = 405 ° C - Y = 87%, and at t ₁ = 415 ° C the value Y = 84%. Based on the data obtained, it was concluded that the temperature range of 395-415 ° C is optimal for solving the task. Transfer of the isolated radioisotopes to the aqueous phase is carried out by treating the pnictide adsorption zone with a suitable solvent, for example, nitric acid.

Example 1

The proposed method was used to obtain ultrapure preparations of isotopes ¹⁰⁶ Ag (T _1/2 = 8.3 days) and ¹⁰⁵ Ag (T _1/2 = 41.3 days). 8 g of granular cadmium grade o.s.ch. irradiated with accelerated protons with an energy of 660 MeV and a beam intensity of 5 × 10 ¹² s ^-1 . cm ^-2 for 72 hours. At the end of the irradiation, the target is “cooled” for 2-3 days, transferred to the surface of quartz sand (d = 100-200 μm), previously placed in a quartz tube (d = 10 mm), and the target substance is distilled off in a stream of hydrogen at a temperature 600 ° C. At the end of the sublimation and cooling of the device, the obtained initial radioactive sample is transferred to the starting zone of quartz TXC (d = 3 mm), and at the beginning of the column, a solid reagent - red phosphorus of the o.s.ch grade is placed The prepared column is placed inside the cascade of tubular electric furnaces. After purging the column in a stream of purified helium (residual water vapor content of less than 10 ^-4 % and oxygen less than 10 ^-6 %), a voltage was applied to the furnace (4), which provided a negative temperature gradient with α = -17 ° С / cm, furnace (2) (360-380 ° С), then to the furnace for heating the initial sample (3) at 900 ° С. Upon reaching the specified parameters, voltage was applied to the furnace (1), in which phosphorus was heated at 340 ° C. The concentration of phosphorus vapor was 4 × 10 ⁻⁶ mol cm ^–3 . The volumetric speed of helium was 20 · cm ³ · min ^-1 , and the duration of the process was 1 hour. The resulting silver phosphide precipitated at 680 ° C with a chemical yield of 75%. The radiochemical purity of radioactive silver preparations was 99.99%. The result obtained is illustrated in FIG. 1, which shows the distribution of ^105.106 Ag phosphide along the column. It can be seen that the deposition zones of silver phosphide and phosphorus are separated, which indicates a high chemical purity of the isolated silver radioisotopes.

Example 2

Ultrapure preparations of ¹⁰⁶ Ag radioisotopes (T _1/2 = 8.3 days) were also obtained when using arsenic vapor as a reagent. 6.5 g of granular cadmium brand o.s.ch. irradiated with accelerated protons with an energy of 660 MeV and a beam intensity of 7 × 10 ¹² s ^-1 · cm ^-2 for 48 hours. At the end of the irradiation, the target is “cooled” for 2-3 days, transferred to the surface of quartz sand (d = 100-200 μm), previously placed in a quartz tube (d = 10 mm), and the target substance is distilled off in a stream of hydrogen at a temperature 600 ° C. At the end of the sublimation and cooling of the device, the obtained initial radioactive sample is transferred to the starting zone of quartz TXC (d = 3 mm), and a solid reagent, arsenic grade, is placed at the beginning of the column, which was previously purified by vacuum sublimation. Then the column is placed inside the tubular electric furnaces (1) to (4). After purging the column in a stream of purified helium (residual water vapor content of less than 10 ^-4 % and oxygen less than 10 ^-6 %), a voltage was applied to the furnace (4), which provided a negative temperature gradient with α = -17 ° С / cm, furnace (2) (430-450 ° C), then to the heating furnace of the initial sample (3) (900 ° C). Upon reaching the specified parameters, voltage was applied to the furnace (1), in which arsenic was heated at 405 ° C. The concentration of arsenic vapor was 2 × 10 ^-6 mol cm ^–3 . The volumetric velocity of helium was 20 cm ³ · min ^-1 , and the duration of the process was 1 hour. The resulting silver arsenide precipitated at 640 ° C with a chemical yield of 87%. The radiochemical purity of radioactive silver preparations was also 99.99%. Figure 2 shows the distribution of silver arsenide along the column. Figure 2 shows that the deposition zone of silver arsenide and arsenic are at a considerable distance from each other, which ensures high chemical purity of the obtained silver isotopes.

The proposed method can be used both in traditional applications (electrochemistry, physical chemistry), and for the chemical identification of an superheavy element with Z = 111 - the alleged chemical analogue of silver and gold.

Claims (1)

A method for producing silver radioisotopes without a carrier, namely, that cadmium metal is used as the target substance, which is irradiated with high-energy protons, the target material is separated by sublimation in a hydrogen atmosphere, the products of nuclear reactions and transformations are collected on the surface of silica sand, and the resulting radioactive sample into the starting zone of a quartz thermochromatographic column; its high-temperature chemical processing is carried out in the presence of a reagent with the implementation of trans mouth of the resulting volatile compounds and their subsequent deposition on the walls of the TCA at certain temperatures, characterized in that as a reagent using a pair of phosphorus or arsenic.

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