Photoactivation analysis of ores using short-lived radionuclides

The results of applying photoactivation for express nondestructive multicomponent analysis of apatite-nepheline, gold-bearing, polymetal and lapparite ores are presented. The experiments were carried out at the IPP microtron with bremsstrahlung of 10 to 15 MeV electrons. A setup with mixed gamma-neutron field was built and used for elemental analysis. Experiments show that such elements as P, Al, Ti, Ba, and Ce can be determined with a sensitivity of approximately 0.1 mass% and a statistical error of a few percents. These values are wholly satisfactory to modern demands of industry. Gold and silver can be successfully determined in gold-bearing ores on the level of grams per ton.     

Fast neutron activation analysis using short-lived radionuclides

Fast neutron activation analysis experiments were performed to investigate the analytical possibilities and prospective utilization of short-lived activation products. A rapid pneumatic transfer system for use with neutron generators has been installed and applied for detecting radionuclides with a half-life from 300 ms to 20 s. The transport time for samples of total mass of 1–4 g is between 130 and 160 ms for pressurized air of 0.1–0.4 MPa. The reproducibility of transport times is less than 2%. The employed method of correcting time-dependent counting losses is based on the virtual pulse generator principle. The measuring equipment consists of CAMAC modules and a special gating circuit. Typical time distributions of counting losses are presented. The same 14 elements were studied by the conventional activation method (single irradiation and single counting) by both a typical pneumatic transport system (run time 3 s) and the fast pneumatic transport facility. Furthermore, the influence of the cyclic activation technique on the elemental sensitivities was investigated.     

Extraction of radionuclides from natural waters using alginates

Fourteen samples of wastes from algal plants were tested for possible analytical and/or technological use for⁹⁰Sr and¹³⁷Cs extraction from natural waters. Sorption experiments were carried out in static and dynanic conditions. It was noted that the examined sorbents posses high affinity for Sr²⁺. The sorption capacity reached the value of 4.72·10⁻³ mole/g. Simple and express analytical procedures for⁹⁰Sr determination were developed and tested in the Dnieper estuary region.     

Kinetic aspects of the syntheses using short-lived radionuclides

“ACTIVA” is an activation analysis programme written for small computers (16 to 32 k-words) in FORTRAN-IV. Input-mode for operating commands is interactive, guided with self-explenatory questions. This enables the evaluation of gamma-spectra which could be registered under 4 different conditons (flux, geometry, etc.) with two different counting systems existing in Atominstitute. In each case another data-library with different calibration factors will be chosen and used automaticly. Programme “ACTIVA” is originally designed for gamma-spectra registered with “Loss-Free-Counting” (LFC) electronic with 2×2048 channels, but can be modified for 1024 or 4096 channels easily. Two different multichannel analysers (MCA) can be chosen for data-input: ORTEC-6240 MCA, or NOVALFC (Loss-Free-Counting). The correct energy calibration constants will also be chosen automaticly. The programme has a modular constraction and combined (linked) with overlay technique.     

Beta spectroscopy of short-lived radionuclides using in-cocktail neutron activation

Low-flux, in-cocktail neutron activation analysis was used to quantify atmospheric tracer aerosols. Liquid scintillation was necessary to reduce the experimental uncertainty due to low sample activity. Activation of the tracers was performed in-cocktail since the short half lives of the nuclides did not allow time for sample preparation. Most of the tested cocktails proved inadequate for such analysis because of activation of their components. Neutron and gamma induced luminescence, and neutron generated bubbles in suspensions introduced further difficulties. Only a few cocktails showed activity levels after irradiation comparable to background. This method allowed substantial cost reduction by eliminating the need for irradiation in a research reactor.     

Routine multielement instrumental neutron activation analysis of silicate rocks using short-lived radionuclides

By means of thermal neutron activation and countings on the small planar and large coaxial Ge(Li) detector, 13 elements are determined in various silicate rocks, using short-lived radionuclides with half-lives from 2 min to 15 h. A method of routine analysis with simple dead-time and pile-up correction is described and tested with the standard rocks AGV-1 and G-2.     

Monostandard instrumental neutron activation analysis of Chinese Biological Standard Reference Material using short-lived radionuclides

A routine procedure for monostandard INAA using short-lived radionuclides with half-lives from 2 min to 15 hrs is described. Ten elements (Al, Mg, Ti, V, Mn, Cl, Na, K. Br and Cu) are determined in Chinese Biological Standard Reference Material (peach leaves). The quality of analysis was checked by analyzing the U. S. NBS Standard Reference Materials SRM-1571 and SRM-1648.     

Corrections of counting losses in gamma-spectrometry of short-lived radionuclides

A short-lived radionuclide is characterized essentially by the decrease of its activity even while it is counted. The relations used between the number of counts recorded in a given time and the half-life in order to obtain the true counting rate are reviewed. Moreover, in gamma-spectrometry with multichannel analysers having variable dead-time, counting losses are observed. Exact corrections are calculated for pure short-lived radionuclides and for mixtures of one short-lived and one or more long-lived radionuclides. Based on these calculations, the approximations given by the built-in “live-timer” device of the analysers and by a new “actual-time” concept (with external live-time measurement) are evaluated. Curves are drawn as functions of the ratio counting time vs. half-life, to ensure minimal errors of less then 1%.     

Determination of short-lived radionuclides in neutron-activated human head-hair samples

The Al, Na, Mn, Cl and Mg contents of human head-hair samples were determined by irradiating the samples in a thermal reactor and measuring their γ-activity by scintillation techniques. The concentration variations of these elements in hair samples originating from the same and different persons were studied.     

Analysis of the interaction of radionuclides with solid phase in surface waters using laboratory model experiments: Methodical problems

Use of laboratory model experiments for analysis of interaction of radionuclides with surface water solids is connected with methodical problems concerning selection of solid phase, sampling, storage and pretreatment of solid phase, concentration of radionuclide, selection of liquid to solid ratio, adsorption of radionuclide on vessel walls, choice of experimental procedures and change in radionuclide speciation in the solid phase. These problems are discussed on the basis of literature data and of experiments with radiocobalt or radiocesium in a system river water-suspended solids or bottom sediments. Possible ways of solution of the problems are shown. Two modifications of batch method are described in detail and their merits or drawbacks evaluated. Comparison of the modifications shows their possible use as complementary methods for the study of radionuclide behaviour in surface waters.     

Separation of species of radionuclides from precipitation and fallout samples

The experience with determination of species of radionuclides using the method based on in-line separation of these species by filtration and retention on columns of cation and anion exchange resins and activated charcoal, respectively, is presented. For the combined precipitation and fallout samples from the point of view of their sampling passive and indicatively active arrangements of the method have been proved. During 1984–1986 some real samples from the locality of the Institute have been analyzed, obtained results are briefly discussed and evaluated.     

Leaching of manganese dioxide from porous bodies

Results of a study of the kinetics of manganese dioxide leaching from pores in anodes of solid-electrolyte capacitors are presented. It is shown that manganese dioxide present in pores is the most effectively dissolved at room temperature under treatment with dilute solutions of sulfuric and hydrochloric acids to which hydrogen peroxide is added in not-less-than-stoichiometric amounts according to the reactions MnO₂ + H₂SO₄ + H₂O₂ = MnSO₄ + 2H₂O + O₂?? and MnO₂ + 2HCl + H₂O₂ = MnCl₂ + 2H₂O + O₂??. The initial acid concentration does not exceed 36% for H₂SO₄ and 18% for HCl.     

Removal of radionuclides from low level radioactive liquid waste by precipitation

Six elements in several organs of mice fed with Zn deficient diet (Zn-def. mice) and those fed with control diet (control mice) were analyzed by INAA. Zinc concentrations in the organs of Zn-def. mice were not distinctly lower than those of control mice except for bone and pancreas. However, Ce content increased significantly in all organs of Zn-def. mice compared with control mice, indicating the partial substitution of Co with Zn in metal proteins or other materials for the Zn-def. mice.     

Extraction of thorium,uranium and cerium from fresh water using manganese dioxide coprecipitation

A manganese dioxide coprecipitation procedure is utilized to replace a time-consuming evaporation step for the extraction of thorium, uranium and cerium from freshwater samples. The average recovery for 20-liter samples is greater than 95% for²³⁴Th and¹⁴⁴Ce. The data indicate that the manganese dioxide coprecipitation process does not affect the recovery of thorium and uranium during our routine analytical procedure.     

Experimental comparison of multi-channel analyzer. Dead-time corrections for short-lived radionuclides

The accuracy of the live-time circuit of a 400-channel analyzer was studied in detail, and was found to be unsatisfactory even for long-lived radionuclides. It was found that automatic live-time correction with the multi-channel analyzer gave rise to increasing positive errors with increasing count rate; this overall positive error was composed of a positive error due to the slowness of the electronic circuitry, and a smaller negative error due to the finite pulse-width. Adequate correction could be performed by feeding the information from the dead-time output of the multi-channel analyzer to an external live-time circuit with variable oscillator frequency and pulse-width. Four methods for dead-time correction were compared experimentally in the case of short-lived radionuclides (T as low as 7 sec): the method of Bartošek et al., the method of Schonfeld, the use of a sufficiently short counting time as compared to the half-life, and the live-time mode of counting without additional correction. These four methods were applied to the determination of oxygen and silicon in rocks by 14 MeV neutron activation analysis. Results are given for USGS standard rock G-2. Research associate of the I. I. K. W.     

Purification of arsenic contaminated ground water using hydrated manganese dioxide

An analytical methodology has been developed for the separation of arsenic from ground water using inorganic material in neutral medium. The separation procedure involves the quantitative retention of arsenic on hydrated manganese dioxide, in neutral medium. The validity of the separation procedure has been checked by a standard addition method and radiotracer studies. Neutron activation analysis (NAA), a powerful measurement technique, has been used for the quantitative determination of arsenic.     

Removal of radionuclides from acid mine waters by retention on adsorbing materials

Summary This study proposes a method for decontamination of acid drainage water from a uranium mine, as an alternative process to lime treatment. The research embodied the recovery of uranium with an ion-exchange resin, treatment of effluent resin with lime, or with inorganic adsorbents and biosorbents. The uranium decontamination level using the resin process was 94% and allowed the recovery of this element as a commercial product. Among the inorganic adsorbents studied, phosphogypsum was effective for ²²⁶Ra, ²²⁸Ra, and ²¹⁰Pb removal. Among the biosorbents, Sargassum sp.was superior in relation to its specific capacity to accumulate and remove ²²⁶Ra.     

Enhanced recovery of chlorophenols from surface waters using polymer based extraction cartridges

 The effectiveness of a new polymer based solid phase extraction cartridge (SDB 1) to recover phenolic compounds from aqueous samples has been evaluated by comparison of performance against conventional silica based cartridges. The polymer based material is found to be much more retentive, requiring a larger volume of solvent to achieve maximum recovery. Recovery efficiency is enhanced if the recovery solvent (methanol) is acidified to 0.1% with trifluoroacetic acid. The optimised extraction procedure has been applied to surface water samples and yields quantitative recovery at the 10 ng ml^-1 level of all nine phenols studied. Received: 26 November 1996/Revised: 21 March 1997/Accepted: 30 March 1997