Natural Thorium Research Articles

An alternative radiochemical separation strategy for isolation of Ac and Ra isotopes from high energy proton irradiated thorium targets for further application in Targeted Alpha Therapy (TAT)

Targeted Alpha Therapy (TAT) has shown very high potential for the treatment of cancers that were not responsive to other therapy options (e.g., β− therapy and chemotherapy). The main constraint to the widespread use of TAT in clinics is the limited availability of alpha-emitting radionuclides. One of the most promising candidates for TAT is 225Ac (t1/2 = 9.92 days), which can be used directly in combination with selective biomolecules (e.g., antibodies, peptides, etc.) or be a generator source of 213Bi (t1/2 = 45.6 min), another shorter-lived TAT radionuclide. Several strategies are currently under investigation to increase the supply of 225Ac. One of the most attractive options is the irradiation of natural thorium-232 targets with high-energy protons (≥100 MeV). However, there are several challenges associated with this production method including the development of an efficient radiochemical purification method.During irradiation of natural thorium with proton energy above 100 MeV, several Ra isotopes (223,224,225Ra) are produced. 223Ra (t1/2 = 11.43 days) is used for the treatment of bone metastases and can also be used as a generator source for 211Pb. Additionally, 225Ra (t1/2 = 14.9 days) can be a valuable source of isotopically pure 225Ac.In the present work, we address the radiochemical separation aspects of isolating Ac and Ra isotopes from irradiated thorium targets.

Estimation of uranium concentration in ore samples with machine learning methods on HPGe gamma-ray spectra

Within the scope of determining the concentration of uranium in ore samples by gamma-ray spectrometry, we tested a series of machine-learning (ML) algorithms with a database including 1288 HPGe gamma spectra measured by Orano Mining. Instead of detecting and identifying peaks, a global interpretation of the spectra is carried out. Two different approaches were used. First, we reduced the size and the dimension of the dataset by selecting 728 spectra acquired with a same experimental setup and by resampling their 8192 channels into 168 energy bands according to the important peaks due to the natural uranium, thorium and potassium activity. Classical ML algorithms have been trained on this reduced dataset and the best uranium concentration predictions show Symmetric Mean Absolute Percentage Error lower than 6%. In a second step, the complete dataset with 1288 gamma spectra including six different measurement setups was used to train deep neural network with a re-sampling of the spectra into 2048 channels. Despite the small dataset, a Convolutional Neural Network (CNN) model provides satisfactory results with mean errors lower than 15% on this broader and more complex dataset in terms of uranium concentrations and experimental setups. These outcomes shows that ML methods can predict uranium concentration with similar uncertainties as classical gamma-ray spectroscopy (10% to 20%), but without requiring an expert knowledge to interpret the spectra.

Isolation of 212Pb from natural thorium for targeted alpha-therapy

Targeted alpha-therapy (TAT) is increasingly attractive due to its extraordinary antitumor efficacy. However, the supply of α-emitters for TAT is insufficient and under control by a limited number of countries. 212Pb is a promising α-emitter with an optimal half-life (10.6 h) and favored decay chain. Of interest, 212Pb can be extracted directly from natural thorium, which may be abundant in the mining waste of rare-earth, uranium, etc. Indeed, radioactive thorium waste has been a longstanding environmental challenge that needs immediate action. Developing an on-demand and facile process to isolate 212Pb from natural thorium would be ideal to meet the above challenges, yet is difficult. In theory, the ratio of 212Pb to natTh is below 10−13 in commercially available thorium salts. As a pilot study, 2.2 MBq of 212Pb was successfully extracted from a 5 L solution of thorium nitrate by using a Pb-selective resin. The radiochemical purity of 212Pb is over 99.9% according to gamma-ray analysis. The purified 212Pb was applied to radiolabel a couple of peptides used in clinics (i.e. PSMA, TATE and FAPI-04), and the radiochemical yields are >85%. Of note, 212Pb can be repeatedly separated from the thorium solution every 2 days. In summary, a practical and scalable method was developed to isolate 212Pb for potentially clinical use, which may be of great importance as it does not require either cyclotron or nuclear reactor.

Feasibility of a novel photoproduction of 225Ac and 227Th with natural thorium target

We propose an innovative way to produce both 225Ac and 227Th, two precious radioisotopes enabling promising targeted alpha therapy, in a natural thorium target bombarded with a 30–90 MeV electron beam. Bremsstrahlung photons in the target are analyzed by MCNP and in-situ photonuclear transmutation of 232Th is evaluated by using the TENDL nuclear data. In the photo-transmutation analysis, 13 nuclides including 229Th and 231Pa are modelled. Special procedures with chemical separations are also proposed to produce pure 225Ac and 227Th in separate streams. In addition, performance of the new approach is compared with conventional methods in terms of the 225Ac and 227Th yields. After a Th target is bombarded with a 500 kW electron beam for a year, yearly 225Ac yield is ~ 8.47 GBq (semi-permanently) and yearly 227Th yield is ~ 48.9 GBq over 50 years, and their yields are at least doubled in a 2-year irradiation. This work will help increase global supply of the two precious isotopes and would invariably help advance TAT-related researches and developments.

Review on monitoring natural and environmental radiation and its potential from mining products

Monitoring of natural radiation in Indonesia has been carried out by various parties, from researchers, academics at universities to special agencies tasked with handling this matter, such as the National Nuclear Energy Agency (Batan) and the Nuclear Energy Supervisory Agency (Bapeten). Batan through the Center for Radiation Safety and Metrology Technology (PTKMR) is in charge of monitoring natural radiation at the national level. The purpose of this paper is to review the monitoring of natural and environmental radiation in Indonesia and the potential of mining products as a source of natural radiation. The mining products that will be reviewed in this paper are natural uranium and thorium which are usually found in several mines, such as tin mines and others.

Review on monitoring natural and environmental radiation and its potential from mining products

Monitoring of natural radiation in Indonesia has been carried out by various parties, from researchers, academics at universities to special agencies tasked with handling this matter, such as the National Nuclear Energy Agency (Batan) and the Nuclear Energy Supervisory Agency (Bapeten). Batan through the Center for Radiation Safety and Metrology Technology (PTKMR) is in charge of monitoring natural radiation at the national level. The purpose of this paper is to review the monitoring of natural and environmental radiation in Indonesia and the potential of mining products as a source of natural radiation. The mining products that will be reviewed in this paper are natural uranium and thorium which are usually found in several mines, such as tin mines and others.

Management of nuclear materials containing natural uranium and thorium salts

This paper highlights an experimental model proposed for the management of nuclear materials containing natural uranium and thorium salts, based on technical and legislative methods. The investigated nuclear materials originate from laboratory chemicals with expired validity, having as manufacturers companies specialized in the manufacture of laboratory substances such as: Merck, Chemapol, Sigma Aldrich, Bucharest Reagent. The experimental program refers to several issues of great importance in the waste and environmental management, such as: a) the processing of radioactive substances containing nuclear materials and radioactive waste represented by solid objects contaminated with radionuclides from the radioactive series of U-238 and Th-232; b) gamma dose rate measurement during handling and processing of open sources of ionized radiation; c) measurement of suspicious contamination of the operating personnel which handles the equipment, including the materials used in the processing of open sources of ionizing radiation; and d) the inventory of nuclear materials according to the chemical formula, the mass of chemical substance, the mass of the nuclear element in each container and type of packaging. For the good development of processing these open sources of ionizing radiation containing nuclear materials, the ALARA principle (As Low As Reasonably Achievable) was applied, which is fundamental to the principles of radiation protection. All the measurements for determining the gamma dose rate and suspicious contamination were performed with the aid of a CoMo 170 radiometric device produced by Nuvia Instruments Gmbh Germany, equipped with a 170x100 mm2 PL detector with zinc sulfide calibrated with the aid of C-14, Co-60, Cs-137, U-238 and Am-241 radioactive isotopes and an external probe containing a scintillating crystal with sodium iodide enriched with thallium calibrated with Cs-137.

Determination of natural thorium isotopes (230Th and 232Th) in calcium and magnesium supplements and the potential effective exposure radiation dose for human

The article presents a study on the content of radiotoxic thorium radionuclides, alpha-emitting 230Th and 232Th, as a possible additional source of these radioisotopes in the human diet in the most popular calcium and magnesium supplements available for adults in Poland. It was also examined whether the supplements impact the value of effective radiation doses to the consumers. The analyzed pharmaceuticals contained different organic or inorganic calcium or magnesium compounds, and some of them were of natural origin, while most of the organic compounds were synthetic. Based on the study, the 230Th concentrations in natural origin calcium and magnesium supplements were significantly higher than in synthetic. The results showed that the highest value of 230Th activity was found in natural origin pills produced from chalk and equalled 6.20 ± 0.17 m Bq/g, while the highest 232Th activity concentration was determined in the dolomite sample and determined at 0.58 ± 0.05 m Bq/g. The evaluation showed that calcium and magnesium supplements could contribute to an annual effective radiation dose of less than 3 μSv, but the amount is much than the annual radiation dose from 230Th and 232Th decay ingested with daily food (0.3 μSv). For this reason, the consumption of these supplements may increase the annual effective radiation dose received by a human. Notwithstanding, the exposure is considered low from the radiological and toxicological points of view.

Effect of natural radionuclide's in the environment along the Jwalamukhi thrust of Himachal Pradesh, North West Himalayas, India.

This research paper is devoted to measure the activity contents of natural radionuclide, like, radium (226Ra), thorium (232Th) and potassium (40K) in the soil gathered along the Jwalamukhi thrust of Himachal Pradesh, North Western Himalayas, India. NaI(Tl) Scintillator detector was utilized for the estimation of activity content. The activity concentration of 226Ra, 232Th and 40K for some of the soil samples have been observed to be above the global normal mean values. The outcomes acquired for indoor and outdoor effective dosage are well below the normal international and national proposed results. The determined values of external hazard (Hex) for studied locations are less than unity, therefore; samples assembled from these regions are safe from a health hazard point of view and can be utilized as a construction purposes without producing any radio-logical hazard to human beings. The average estimations of radium equivalent activity were found to be within the limits suggested by Organization for Economic Cooperation and Development (OECD). Radon (222Rn) and thoron (220Rn) exhalation rates have also been calculated and discussed.

Electricity Generation Options for India-A Critical Evaluation

Objectives : This review is to study the electricity generating energy sources in the world at large and India in particular, considering the impact on the environment and arrive at the energy sources which India needs to focus in the future. Methods : The world data on the various aspects like greenhouse emissions, deaths, health effects, levelized cost of electricity, energy return on investment, water, and land requirements for various energy sources have been studied. Findings : The need for reduction of energy from coal is clear as its emissions affect the health and contribute to climate changes. The alternative large source appears to be nuclear. Wind and solar power with low emissions of Greenhouse gases are also favored. However, wind is seasonal and solar power can be generated only during daytime which leads to low-capacity factor (~20%) compared to 32% for nuclear and 42% for Coal plants. This has also impact on the grid management. The environmental impacts of Nuclear, Coal, Solar, Wind and Hydro have been brought out in detail. More weightage is given to sources that have a higher growth rate based on the energy return on investment and environmental impacts rather than capital cost. The accidents of nuclear reactors in USA, Russia and Japan have shaken the public faith in nuclear power. The real fact that the impacts on the health of the people due to release of radiation in these accidents is negligible has been brought out. Comparison between natural and manmade radiation has been brought out. Finally, the applicability of energy sources in the context of India are discussed and a ranking approach arrived at. Recommendations : Nuclear has been favored based on the availability of natural uranium and thorium in the country and long-term energy security. Solar and wind need to be deployed, wherever possible, in view of the slow introduction of nuclear reactors due to high capital cost. Import of nuclear designs from abroad is also recommended to meet the electricity demands as a stop gap arrangement. Novelty : This study has taken a ranking approach considering most important metrices and has applied to India. Keywords: Pollution, coal, hydro, biomass, nuclear, risk, benefits

An Internet of Thing Architecture Based on Message Queuing Telemetry Transport Protocol and Node-RED: A Case Study for Monitoring Radon Gas

This work aims to monitor air quality in places where humans spend most of their time, such as workplaces and homes. Radon gas is a naturally occurring, colourless, odourless and tasteless gas that accumulates in enclosed spaces. It is a radioactive element produced by the decay of its natural parent elements, uranium and thorium, which is harmful to our respiratory system when inhaled. The Internet of Things (IoT) is the key to the problems of contemporary life; we are witnessing an emerging connected world, and these architectures have the potential by using sensors to take data from the physical world, transfer it over the network and store it for further decision making or action. The proposal of this work is based on a radon sensor connected to an IoT device, the Message Queuing Telemetry Transport protocol (MQTT), the Node-RED for managing data flows and a database management system on a web server. The information collected by the sensor is sent by the IoT device to be processed by Node-RED. The obtained data is stored in a database to be represented on a web server. Therefore, this work includes a case study where the technologies involved in the indoor radon gas monitoring system are presented. It is a way to perform radon gas measurements automatically. The final application would allow: displaying radon concentrations on a map with placemarks and updating the information in real-time. The database could record data from other radon sensors that any user wants to associate with this website.

Internal calibration of the PandaX-II detector with radon gaseous sources

We have developed a low-energy electron recoil (ER) calibration method with 220Rn for the PandaX-II detector. 220Rn, emanated from natural thorium compounds, was fed into the detector through the xenon purification system. From 2017 to 2019, we performed three dedicated calibration campaigns with different radon sources. We studied the detector response to α, β, and γ particles with focus on low energy ER events. During the runs in 2017 and 2018, the amount of radioactivity of 222Rn were on the order of 1% of that of 220Rn and thorium particulate contamination was negligible, especially in 2018. We also measured the background contribution from 214Pb for the first time in PandaX-II with the help from a 222Rn injection. Calibration strategy with 220Rn and 222Rn will be implemented in the upcoming PandaX-4T experiment and can be useful for other xenon-based detectors as well.

Possibility assessment for production of non-traditional nuclear fuel in thorium blanket of hybrid thermonuclear reactor

The paper aims at studying specific peculiarities in isotope composition of thorium blanket under irradiation by fusion neutron source (FNS) in hybrid thermonuclear reactor (HTR). High-energy (14 MeV) component of neutron spectrum in thorium HTR blanket results in production of non-traditional fissile mixture including not only233U, but also231Pa232U and 234U. Extraction of such non-traditional fuel from spent Th-blanket and its utilization in traditional nuclear power reactors could increase fuel burn-up and strengthen regime of nuclear non-proliferation. The detailed investigations of these positive effects require high-precision neutron-physical analyses of thorium HTR blanket. The results obtained in these investigations are presented in the paper. The following results were obtained: the chosen model of HTR allowed us to form high-energy neutron spectrum in Th-blanket with significant fraction of 14 MeV neutrons; it was evaluated that threshold (n,2n) and (n,3n)-reactions are able to produce significant amounts of non-traditional target isotopes231Pa and232U; it was shown that accumulation of non-traditional target isotopes weakened substantially in depth of Th-blanket. So, it seems reasonable to seek for optimal thickness of Th-blanket and, thus, to find optimal loading of natural thorium.

Characterization of vanadium of biological origin for possible applications in physics experiments

For the first time, vanadium of biological origin, extracted from centrifugal fraction of vanadium-storing blood cells of the Ascidia sydneiensis samea species, was characterized as regards its isotopic composition and content of natural radioactive elements potassium (K), thorium (Th) and uranium (U). The natural abundance of vanadium isotopes has been confirmed with high accuracy, thus excluding a possible selectivity within bio-chemical reactions of vanadium concentration in blood cells from seawater. A large potassium concentration (up to 5500 × 10−6 g g−1) was found in the blood cell samples. The concentration of thorium was determined to be about 30 × 10−9 g g−1, while the uranium concentration was about 150 × 10−9 g g−1. Hence, a highly efficient two-stage purification approach with a total vanadium recovery of better than 70% was developed and applied. The final concentrations of K < 100 × 10−6 g g−1 and of U/Th < 0.5 × 10−9 g g−1 in the purified vanadium-containing samples were achieved. Vanadium extracted from centrifugal fraction of vanadium-storing blood cells after two-stage purification approach could be utilized in various applications, where a high chemical purity compound is required. However, to be used as a source of radiopure vanadium in ultra-low-background experiment aimed to search for 50V beta decay, it should be further purified by Electron Beam Melting against residual potassium.

Determination of uranium and thorium isotopes in kaolinitic samples by ICP-MS/MS

The use of natural uranium and thorium long-lived isotopes was applied to study the evolution of kaolinitic materials. To do that, a radiochemical method for separation of Th and U in phyllosilicate samples was developed with the main aim of their analysis by ICP-MS/MS. Given the lack of certified phyllosilicate reference materials with certified isotope abundances, the method was tested using a stepwise approach. First, a preliminary setup was done using a sediment reference sample. Then, the extrapolation of this method to the samples of interest has been tested using a phyllosilicate sample certified for U and Th concentrations. The results showed that an extension of the plateau time of digestion in the used microwave system was peremptory as to get full digestion of the sample. The use of the isotope dilution technique allowed both the quantification of major isotopes (238U and 232Th) simultaneous to the determination of isotope ratios (234U/238U, 235U/238U for quality control and 230Th/232Th). The established method was applied to six kaolinitic samples from the Iberian Range (NE Spain), showing the potential of this isotope approach for the characterization of their time evolution.

Geochemical behavior of uranium and thorium in sand and sandy soil samples from a natural high background radiation area of the Odisha coast, India.

Owing to their natural radioactivity, uranium (U) and thorium (Th) play significant roles in environmental sciences for monitoring radiation dose and in geological sciences for understanding sedimentary processes. The Odisha coastal area, in eastern India, is a well-known high background radiation area that is rich in monazites and rutile. This area was selected to study geochemical characteristics of U and Th in sand and sandy soil samples. The concentrations of U and Th were measured using inductively coupled plasma mass spectrometry (ICP-MS). The median, geometric mean, and standard deviation for U were determined to be 6, 4.5, and 2.5μg/g and for Th were186, 123.3, and 3.1μg/g, respectively. Major element concentrations were evaluated using X-ray fluorescence spectroscopy to get the mineralogical composition and state of chemical weathering. The ratios of Th/U and Th/K varied from 4 to 37 and from 13 to 1058, respectively. These results clearly indicate that the samples from the coastal region were formed in an oxidizing and intense chemical weathering terrestrial environment with an enrichment of radiogenic heavy minerals (monazites and zircon) and clay mineral association. Since the majority of the samples have undergone moderate to intense weathering in the oxidizing environment, U is leached from the soil and sand matrix. Eventually, Th resides in the matrix and becomes a major source for radiation exposure in the environment. The high ratios of Th/U, along with the strong positive correlation between Th and P2O5, evidence the enrichment of the Th-bearing radioactive mineral, monazite, in these samples.

Uranium (234U, 238U) and thorium (230Th, 232Th) in mushrooms of genus Leccinum and Leccinellum and the potential effective ionizing radiation dose assessment for human

Evaluated has been bioconcentration potential by fungi and risk to human consumers from exposure to natural long-lived radioactive uranium (234U, 238U) and thorium (230Th, 232Th) sequestered in stems, caps and the whole fruiting bodies by mushrooms of the genus Leccinum and Leccinellum. Edible species in the study were collected from boreal forests in the northern regions of Poland and investigated: red-capped scaber (Leccinum aurantiacum), orange oak bolete (Leccinum aurantiacum var. quercinum), foxy bolete (Leccinum vulpinum), slate bolete (Leccinum aurantiacum var. duriusculum) and hazel bolete (Leccinellum pseudoscabrum). The study showed the species accumulated uranium (234U, 238U) and thorium (230Th, 232Th) form soil to some degree but the calculated values of the bioconcentration factor were below 1. The evaluation showed that Leccinum and Leccinellum mushrooms can contribute to annual effective radiation dose maximally at about 0.9 μSv. Hence, consumption of these mushrooms might increase the annual effective ionizing radiation dose received by a human, while the exposure is considered low from the toxicological point of view even if eaten at elevated amounts.

THE EFFECTS OF TYPICAL THORIUM IMPURITIES ON THORIUM-BASED NUCLEAR FUELS

Natural thorium contains impurities of numerous isotopes. A study was performed to examine the influence of naturally occurring impurities in thorium-based fuels on a few parameters of interest such as: exit burnup, coolant void reactivity (CVR), fuel temperature coefficients (FTC), and the radiotoxicity of the used fuel. Two different fuel bundle designs were modeled: a 43-element bundle containing 2.25% U-233, and a 35-element bundle containing 1.45% U-233. Naturally occurring thorium fuel impurities were applied to both fuel bundle models at various concentrations, from 0% to 100% of the expected maximum. For burnup-averaged k-infinity (k∞) values of 1.050 and 1.030, exit burnup, burnup-weighted CVR, and burnup-weighted FTC were calculated using the neutron transport code WIMS-AECL, and plotted against fraction of full impurity concentration to determine how the impurity levels affect these reactor physics parameters of interest. For the most-realistic (for CANDU) burnup-averaged k∞ of 1.050, both the inhalation radiotoxicity and the production of U-232 were calculated using the fuel depletion code WOBI. Up to the maximum impurity concentrations considered, no effects on the investigated fuel performance parameters were found to be greater than a few percent.

Neutronic analysis of comparation UN-PuN fuel and ThN fuel for 300MWth Gas Cooled Fast Reactor long life without refueling

Neutronic analysis of comparation UN-PuN fuel and ThN fuel for 300MWth Gas Cooled Fast Reactor long life without refueling has been done. Gas Cooled Fast Reactor is a Generation IV reactor with gas coolant (i.e. helium) and using fast spectrum neutron. The neutronic calculation was carried out using SRAC (Standard Reactor Analysis Code) version 2006 under the Linux Operating System with nuclear data library JENDL4.0. The first calculation is fuel pin cell calculation (PIJ-method) by using a hexagonal cell and then followed by the calculation of the core reactor (CITATION-method). The calculation of the core reactor used homogeneous and heterogeneous core configuration. The UN-PuN fuel use plutonium as a fissile material and natural uranium as a fertile material and the ThN fuel use U233 as a fissile material and natural thorium as a fertile material. The percentages of fissile material are varied in heterogeneous core configuration. It is used to decrease the peaking power in the center of the core. The heterogeneous core configuration contains of Fuel 1 (F1) 8% fissile materials, Fuel 2 (F2) 10% fissile materials, and Fuel 3 (F3) 12% fissile materials. F1 is located in the central core, F2 middle core and F3 outer core. The diameter and height active core are 240 cm and 100 cm. The reflector radial-axial width is 50 cm. All of the calculations can reach burn up time more than 20 years with excess reactivity less than 1 percent (Δk/k <1%) both UN-PuN fuel and ThN fuel. It means that the reactor stable in 20 years. The average of power density both of UN-PuN fuel and ThN fuel are around 66 Watt/cc. The maximum power density of UN-PuN fuel is 94Watt/cc and ThN fule is 129Watt/cc. The UN-PuN fuel has lower maximum power density value than ThN fuel. So, for fast neutron spectrum reactor especially Gas Cooled Fast Reactor type, it is better used UN-PuN fuel than ThN fuel.

Production of 230Pa from Proton-irradiated Thorium and Developing 230Pa/230U/226Th Tandem Generator

Targeted alpha-therapy of various oncology diseases is based on the coupling of alpha-emitting radionuclides to tumour-selective carrier molecules. 230U (t1/2 = 20.8 d) is accumulated via decay of 230Pa and has strong potential for alpha-therapy due to 5 emitting alpha particles with total energy 33.5 MeV. It can be used directly or as a parent of 226Th in a generator system. A prospective way for production of 230Pa/ 230U is irradiation of natural thorium with medium-energy protons. Curie amounts of 230Pa can be generated in one irradiation run together with other useful alpha-emitters 225Ac and 223Ra. After dissolving Th-target in 6M nitric acid with the addition of catalytic amounts of hydrofluoric acid Pa was isolated by liquid extraction with octanol. The water phase may be further used for isolation of 225Ac and 223Ra according the method, proposed in [1, 2]. Namely, the most part of thorium was removed by liquid extraction with di(2-ethylhexyl)phosphoric acid in toluene. Organic phase was kept for accumulation 223Ra from parent 227Th. 225Ac and 223Ra were concentrated from aqueous phase and then separated and purified by extraction chromatography. After re-extraction 230Pa was purified on silica gel using different oxalic acid solutions. Up to 85% of 230Pa with radionuclidic purity >99% was recovered and stored for 230U accumulation. Basing on distribution coefficients 230U was separated from 230Pa in diluted nitric acid solution on DGA resin. Obtained 230U may be used for development of 230U/226Th – generator. Distribution coefficients for U and Th were obtained for a wide range of extraction chromatographic resins. TEVA (mixture of trioctyl and tridecyl methyl ammonium chloride as an extractant) and WBEC (based on a mixture of tertiary octyl and decylamines) resins are most suitable for this purpose. [1]R.A. Aliev, S.V. Ermolaev, A.N. Vasiliev, V.S. Ostapenko, E.V. Lapshina, B.L. Zhuikov, N.V. Zakharov, V.V. Pozdeev, V.M. Kokhanyuk, B.F. Myasoedov, S.N. Kalmykov. Isolation of medicine-applicable actinium-225 from thorium targets irradiated by medium-energy protons. Solvent Extraction and Ion Exchange, 2014, v. 32, p. 468-477.[2]A.N. Vasiliev, V.S. Ostapenko , E.V. Lapshina, S.V. Ermolaev, S.S. Danilov, B.L. Zhuikov and S. N. Kalmykov. Recovery of Ra-223 from natural thorium irradiated by protons. Radiochimica Acta, 2016, v. 104, N.8, p. 539-547.