The determination of radium-226 and radium-228 in soils and plants,using radium-225 as a yield tracer

Recovery of²²⁶Ra in analysis is determined using²²⁵Ra separated by anion exchange from²²⁹Th and²³³U. Radium is coprecipitated with barium, and purified by ion exchange.²²⁶Ra and²¹⁷At (decay product of²²⁵Ra) are measured by α-spectrometry.²²⁸Ra is determined both by β-counting²²⁸Ac and²²⁵Ac separated from²²⁸Ra and²²⁵Ra, and by α-counting its daughters after the decay of²²⁵Ra. Sources for α-spectrometry are prepared by electrodeposition (molecular plating).     

Rapid radiochemical separation of radium from environmental samples using ion-exchanger Zeokarb-225

A rapid radiochemical method has been developed for the separation of radium in the presence of excess calcium from environmental samples such as spring waters and marine sediments. Radium is preconcentrated by co-precipitation as carbonates along with other alkaline earths. Subsequently, most of the alkaline earths are complexed with EDTA at pH 7.5 and the solution is passed through a column of Zeokarb-225 (NH ₄ ⁺ ). Radium, along with traces of calcium, is sorbed on the exchanger. Radium is desorbed with 2N HNO₃ and finally coprecipitated with 400 μg of barium as isulfate. The alphas of²²⁶Ra are counted in a silicon surface barrier detector and²²⁸Ra betas are counted in an end-window GM Counter.     

A generator system for production of medical alpha-radionuclides Ac-225 and Bi-213

A generator system, consisting of two anion- and one cation-exchange columns for production of medical α-radionuclides ²²⁵Ac and ²¹³Bi, has been developed. The first anion-exchange column was used for periodical separation of ²²⁵Ac from Th with 8 M HNO₃, while the second anion-exchange column was employed for purification of ²²⁵Ac from Ra and inactive impurities in mixed HNO₃/CH₃OH media. From anion-exchange column ²²⁵Ac was stripped with 0.1–0.2 M HNO₃ and loaded directly onto cation-exchange column, used as a generator for repeated isolation of ²¹³Bi. The cation exchange behavior of Bi and other radionuclides of the interest were studied in diluted HCl, HBr and DTPA solutions used as eluents. As result, a simple and effective method for the production and purification of ²²⁵Ac and ²¹³Bi suitable for biomedical studies was elaborated.     

Influence of Ba on the electrodeposition of226Ra

A detailed study of the influence of barium on the electrodeposition of²²⁶Ra was made using two different procedures. High yields (80–90%) were attained when the amounts of barium were not very significant. However, the²²⁶Ra yields fell drastically for amounts slightly greater than 0.10–0.15 mg of Ba, according to the electrodeposition procedure. Samples containing trace amounts of barium less than 100–150 g can thus be treated with no barium-radium separation being required.²¹⁰Po was also deposited, although practically no influence of barium on the Po plating was observed. The²²⁵Ra resolution rose uniformly (25 to 55 keV) as the amount of barium rose up to 1 mg. These resolutions allow one to make a direct accurate determination of²²⁶Ra as well as an indirect determination of²²⁴Ra and²²³Ra via measurement of their daughter products.     

On the use of232U and its daughters for the determination of226Ra in water samples

The authors propose a method to determine 226Ra by using a solution of²³²U and its daughters in equilibrium as a tracer.²²⁴Ra of the²³²U solution can be used as yield determinant for²²⁶Ra. The growth of²¹⁴Po from²²⁶Ra and of²¹²Po from²²⁴Ra is measured at different times after the isolation of the radium fraction.     

Contribution to the simultaneous determination of228Ra and226Ra by using 3M's EMPORETM radium rad disks

New method for simultaneous determination of²²⁸Ra and²²⁶Ra by using 3M's EMPORE^TM Radium Rad Disks in water has been developed. Both radionuclides²²⁶Ra and²²⁸Ra were counted through their daughter products,²²⁶Ra by conventional radon emanation techniques and²²⁸Ra through its daughter²²⁸Ac by using a proportional counter. Different molarity of diammonium hydrogen citrate were used for elution of²²⁸Ac and²²⁶Ra from EMPORE^TM Radium Rad Disks. 79% of²²⁸Ac was eluted in 10 ml of 0.0003M diammonium hydrogen citrate. The recovery of²²⁶Ra was 99% by using 40 ml of 0.2M diammonium hydrogen citrate adjusted by ammonium to pH 7.8.     

Sorption and distribution of226Ra in an electrolytic manganese dioxide column in the presence of other ions

Distribution of²²⁶Ra within a segmented electrolytic manganese dioxide (EMD) column was investigated under varying flow rates. Tests show uniform distribution of²²⁶Ra within the EMD column at higher flow rates, as compared to a lower flow rate whereby an apparent two stage sorption process is contributing to the sorption amount. The sorption of²²⁶Ra on EMD decreases from 57% to 14.2% over a short range of Ba²⁺ concentration (5–30 mg Ba²⁺ per 750.0 g solution) using flow rates of 200–300 ml min^–1. The sorption of²²⁶Ra on EMD decreases (58–15%) a consistent higher sorption of²²⁶Ra compared to¹³³Ba under all Ra:Ba ratios indicating the preference for Ra²⁺ ions.     

Background levels of238U and226Ra in atmospheric aerosols

The²³⁸U and²²⁶Ra contents of small-volume aerosols are determined by a chemical analysis technique. Mean activity concentrations of²³⁸U and²²⁶Ra in aerosols over approximately ten years are 0.29·10^–5 and 0.93·10^–5 Bq/m³, respectively. The yearly variation of²³⁸U and²²⁶Ra in aerosols is small. The concentrations of²²⁶Ra are always larger than those of²³⁸U in the same sampling time. The correlation of²³⁸U and²²⁶Ra cannot be recogonized (r=0.18). The concentrations of summer samples are greater than those of winter samples for²³⁸U. One of the causes of seasonal difference may be due to the fact that the components of aerosols are different according to soil size, soil components, weathering states, etc.     

Studies on226Ra and210Pb activities and the concentration factors of226Ra in the surface organic layers of the estuarine sediments of Mindola and Purna rivers in India

The sediment samples have been collected from estuarine regions of Mindola and Purna of Gujarat State. These samples are found to contain less than 3% of organic matter which scavange and carry most of the activity of²²⁶Ra, etc., to the sediment floor. The activities of²²⁶Ra are found to vary from 0.1 to 0.5 pCi/g, while²¹⁰Pb activities lie in the range of 3 to 8 pCi/g. These activities find their way into the organisms present in sea water and then into fish which is finally consumed by humans. This paper gives in detail the sampling techniques, experimental procedures and the distribution of the isotopes of²²⁶Ra and²¹⁰Pb in the estuarine regions and the concentration factors of²²⁶Ra in the region.     

Radium-226 in uranium mill tailings

A study of the physical state of²²⁶Ra in uranium mill tailings was undertaken by Chemex Laboratories Ltd. under contract to NUTP. A test portion of a leached uranium ore was collected just prior to neutralization with lime and subjected to repetitive batch water leaching. The leachates were analyzed for barium, lead,²²⁶Ra, iron and sulphate. The experimental results suggest that²²⁶Ra is co-precipitated with lead sulphate during uranium leaching of the ore with sulphuric acid. The attainment of equilibrium conditions in the pore water of the leached ore then allows a re-proportioning of²²⁶Ra between solid lead and barium sulphates resulting in a depletion of²²⁶Ra in the outer layers of the crystals of solid lead sulphate and an enrichment in²²⁶Ra in the outer layers of solid barium sulphate.     

A sequential radiochemical procedure for isotopic analysis of uranium and thorium in soil

A sequential radiochemical procedure for isotopic analysis of uranium and thorium in soil has been developed. Analysis involves total dissolution of the samples to allow equilibration of the natural isotopes with added tracers, followed by radiochemical separation using anion exchange chromatography (BioRad AG 1–X8). Further separation and purification is performed employing solvent extraction techniques. Finally, the U and Th fractions are co-precipitated with lanthanum and cerium fluoride, respectively, and quantified by alpha-particle spectrometry. Overall chemical yields range from 60 to 90%. Under normal operating conditions and present counting set up, the minimum detectable concentration (MDC) is approximately 2 Bq/kg for soil samples. This is based on one gram aliquot of sample, 80% chemical yield, and 1000 minute counting with a detector having about 15% counting efficiency. The procedure has been successfully tested with Standard Reference Materials. Various soil samples were analyzed with high chemical yields and fine quality of alpha-spectra. Decontamination factor studies were performed to determine the extent of the carry over of²¹⁰Po,²²⁵Ac,²²⁶Ra, and²²⁹Th into U fraction and²¹⁰Po,²²⁵Ac,²²⁶Ra, and²³²U into Th fraction.     

Activity concentrations of238U and226Ra in agricultural samples

Distributions of²³⁸U and²²⁶Ra in agricultural samples and cultivated soils have been studied over ten years. The crops are rice, spinach and Chinese cabbage. Two investigated areas have been selected (35° 18 N, 113° 35 E). The agricultural samples and soils were collected annually from May 1982 through October 1991. The activity concentrations of²²⁶Ra in agricultural samples are greater than those of²³⁸U. The transfer factors of²³⁸U,²²⁶Ra are from 0.06·10^–3 to 1.2·10^–3. The²²⁶Ra/²³⁸U ratios for three agricultural samples have their characteristic values.     

Synthesis and Evaluation of a Macrocyclic Actinium-225 Chelator,Quality Control and In Vivo Evaluation of 225Ac-crown-αMSH Peptide

Targeted alpha-therapy (TAT) has great potential for treating a broad range of late-stage cancers by delivering a focused and lethal radiation dose to tumors. Actinium-225 (²²⁵Ac) is an emerging alpha emitter suitable for TAT; however, the availability of chelators for Ac remains limited to a small number of examples (DOTA and macropa). Herein, we report a new Ac macrocyclic chelator named ‘ crown’ , which binds quantitatively and rapidly (<10 min) to Ac at ambient temperature. We synthesized ²²⁵Ac- crown -αMSH, a peptide targeting the melanocortin 1 receptor (MC1R), specifically expressed in primary and metastatic melanoma. Biodistribution of ²²⁵Ac- crown -αMSH showed favorable tumor-to-background ratios at 2 h post injection in a preclinical model. In addition, we demonstrated dramatically different biodistrubution patterns of ²²⁵Ac- crown -αMSH when subjected to different latency times before injection. A combined quality control methodology involving HPLC, gamma spectroscopy and radioTLC is recommended.     

Activity concentration of226Ra and238U in various soils

The distribution of²²⁶Ra and²³⁸U in various soils has been studied. Supposing that radioactive equilibrium were in existence, the average activities of²²⁶Ra and²³⁸U would show a nearly 11 correlation. As weathering affects radioactive equilibrium in surface soil, radioactive equilibrium was not in existence. Therefore, four kinds of soil were selected from different weathering conditions, viz. river bed soil, paddy field soil, field soil and uncropped soil. The²²⁶Ra/²³⁸U ratio of various soils lies in the range of 1.63 to 2.41. The activity concentrations of²²⁶Ra were greater than²³⁸U in various soils. The ratio²²⁶Ra/²³⁸U can be shown to be a quantitative index of weathering. Phosphatic manure contains²³⁸U and its daughter isotopes in concentrations far exceeding the average abundance in the earth's crust. But the cultivated soils (paddy field soil, field soil) are not affected by fertilizers in Kamisaibara.     

Rapid determination of radium isotopes by alpha spectrometry

An efficient analytical method for the determination of low-levels of²²⁶Ra and²²⁴Ra by alpha spectrometry is described. A cation exchange column was used to separate the analyte from other constituents in the sample (1–50 mL). After preconcentration and separation, the radium was electrodeposited onto a stainless steel disc from a solution of ammonium oxalate and hydrochloric acid. The electrodeposition was accomplished by the addition of platinum in microgram amounts. Linear responses were greater than two orders of magnitude. Detection limits of the procedure, taken as three times the standard deviation of several reagent blank analyses, were (1.8±0.3)×10^–4 Bq and (2.9±0.3)×10^–4 Bq for²²⁶Ra and²²⁴Ra, respectively. Recoveries of²²⁶Ra and²²⁴Ra ranged from 90% to 100% when samples of drinking water, well water, and dissolved bones were analyzed. Precision was calculated to be less than 5% for the determination of²²⁶Ra. Matrix effects were studied for salts of barium, magnesium, iron, and calcium.     

<Superscript>226</Superscript>Ra and <Superscript>228</Superscript>Ra determination in environmental samples by alpha-particle spectrometry

A complete methodology for ²²⁶Ra and ²²⁸Ra determination by alpha-particle spectrometry in environmental samples is being applied in our laboratory using ²²⁵Ra as an isotopic tracer. This methodology can be considered highly suitable for the determination of these nuclides when very low absolute limits of detection need to be achieved. The ²²⁶Ra determination can be performed at any time after the isolation of the radium isotopes from the analyzed samples while the ²²⁸Ra determination needs to be carried out at least six months later through the measurement of one of its grand-daughters. The method has been validated by its application to samples with known concentrations of these Ra nuclides, and by comparison with other radiometric methods.     

Dose rate associated with activity of radium-226 in Canadian soils

Background levels of²²⁶Ra on non-cultivated soils in Canada (in southern and northern Quebec and in the North-West Territories) are presented. The activity of²²⁶Ra was measured at 34 sites. The specific activity levels ranged from 4.4 to 56.4 Bq/kg with an overall mean of 19.1±12.8 Bq/kg. This activity generates an annual absorbed dose in air of 0.07 mGy. The activities were found to be approximately lognormally distributed with the median activity equal to 15.4 Bq/kg. The activity of²²⁶Ra in the soil does not change with the depth. There is a significant difference between Ra concentrations in soils in all three regions studied.     

An Eighteen‐Membered Macrocyclic Ligand for Actinium‐225 Targeted Alpha Therapy

The 18‐membered macrocycle H₂macropa was investigated for ²²⁵Ac chelation in targeted alpha therapy (TAT). Radiolabeling studies showed that macropa, at submicromolar concentration, complexed all ²²⁵Ac (26 kBq) in 5 min at RT. [²²⁵Ac(macropa)]⁺ remained intact over 7 to 8 days when challenged with either excess La³⁺ ions or human serum, and did not accumulate in any organ after 5 h in healthy mice. A bifunctional analogue, macropa‐NCS, was conjugated to trastuzumab as well as to the prostate‐specific membrane antigen‐targeting compound RPS‐070. Both constructs rapidly radiolabeled ²²⁵Ac in just minutes at RT, and macropa‐Tmab retained >99 % of its ²²⁵Ac in human serum after 7 days. In LNCaP xenograft mice, ²²⁵Ac‐macropa‐RPS‐070 was selectively targeted to tumors and did not release free ²²⁵Ac over 96 h. These findings establish macropa to be a highly promising ligand for ²²⁵Ac chelation that will facilitate the clinical development of ²²⁵Ac TAT for the treatment of soft‐tissue metastases.     

Intercalibrated radionuclide activities in spiked water samples of the IAEA worldwide open proficiency test

Proficiency testing is one of methods for regularly assessing the accuracy of the analytical data produced by laboratories for particular measurements. In 2008 and 2010, we participated in the IAEA 2008 and 2010 worldwide open proficiency tests on the determination of natural radionuclides in water spiked with ²²⁶Ra, ²³⁴U and ²³⁸U for activity analysis and with ⁹⁰Sr and ²³⁰Th for gross alpha/beta analysis. Feedback statistics from the IAEA final report showed that the radioactivities of all of the samples fell within an acceptable range according to the IAEA. For ²²⁶Ra analysis, our result showed that ²²⁹Th–²²⁵Ra is suitable as a chemical tracer, although there are doubts that different co-precipitation efficient between parent ²²⁹Th and its daughter nuclide ²²⁵Ra in published literature. The impact factors of the analysis results, such as the lower limit of detection, standard substances, the background and efficiency for daily determination, are discussed in detail.     

The determination of134Cs,137Cs,210Pb,226Ra and228Ra concentrations in nearshore marine sediments and seawater

Multi-radionuclide analyses of coastal marine sediments and seawater can be of considerable value in defining rates and mechanisms of nearshore processes. A preliminary study of¹³⁴Cs,¹³⁷Cs,²¹⁰Pb,²²⁶Ra and²²⁸Ra in the Clyde Sea Area has been performed. A summary of the marine geochemistries of these species and a detailed account of methods involved in their routine analysis are described.