The sub- and super-equivalence method of isotope dilution XIII. Theoretical error of the CVC and VCC variants

The theoretical error of both the CVC and VCC variants at non-quantitative complex forming reaction M+LML has been studied. The erros of analysis for the following analytical curve determinations are considered: (1) measurement with constant error of the analytical function, (2) measurement with registration of a constant number of disintegrations, (3) measurement at constant time of radioactivity measurement of isolated products. Conditions of isoconcentration point existence are determined. Intervals of parameters at which the relative error of the analysis result is comparable with that of the analytical curve are found out. The optimal conditions of analysis are discussed. Errors of both the CVC and VCC variants are compared with that of the CCV variant. Graphs of the theoretical error of analysis are given. The sub-super equivalent isotope dilution method (SSE IDA) has seven basic variants which can be classified by the CCV, CVC, VCC, VVC, VCV, CVV and VVV codes. The theroretical error of the CCV variant was studied earlier. In the present work, a study of errors of both the CVC and VCC variants is performed and extended to radioactivity measurement regimes that can be easily automated. The radioactive background of measurements is taken into account. Previous results and conclusions are corrected. Erros of both the CVC and VCC variants are compared with that of the CCV variant.     

Study of quantitative evaluation of liver volume and accumulation rate of radioactive agent with single photon emission computed tomography

The quantitative evaluation on measurement of liver volume and the hepatic accumulation rate of the radioactive agent were studied with respect to body constitution, background activity and splenic consumption rate, using single photon emission computed tomography (SPECT). The optical cut-off level for liver volume determination was proved to be reasonable as 35%. The background less than 5% had no influence to their clinical estimation with the error of less than 1.6%. The estimation of liver volume was mostly influenced by the splenic activity. When the splenic activity was increased two times of the hepatic activity, the liver volume was determined as 4.2% larger. Calculated counts by SPECT was well correlated with the hepatic activity. This study proved that SPECT was useful for the quantitative evaluation of the liver volume and the hepatic accumulation rate.     

Sensitivity of radioisotope XRF technique with particular reference to portable units

The minimum detection limit of chemical elements attainable with X-ray fluorescence analysis induced by X or γ radioactive sources are evaluated. To this purpose, after a short review of the characteristics peculiar of XRF analysis systems, the contribution of the various physical processes which determine the background for thick or thin samples, under typical operational conditions, are discussed and theoretically evaluated. Furthermore the behaviour of minimum detection limits versus the atomic number of element to be detected is theoretically evaluated for typical matrices. Such results are compared with the experimental data obtained by means of simple portable units. Useful criteria are given in order to reach the best sensitivity.     

Line absorption of matrix elements as a background correction error in atomic absorption spectrometry

Accurate measurement of weak atomic absorption signals is only possible after exact background correction. If the accompanying elements in excess have their own resonance lines in the immediate vicinity of the resonance line of the element to be determined,and these fall within the spectral band transmitted by the monochromator, then the value the measured apparent background absorbance is higher than the true one. The error may usually be diminished by choosing an appropriate spectral bandwidth. Tables of such bandwidths for a large number of pairs of elements are given.     

Industrial applications of activable tracers

The use of activable tracers for industrial applications proved to be a favorable alternative to the use of radiotracers in a number of cases. Difficulties belonging to the procedure to obtain the permit for handling radioactive materials by public health authorities are avoided: delay in time and details of the processes involved open to the public. Economic advantages of activable tracers are low cost of activable tracers and absence of labor costs for radiological control. Three examples are given: a mixing process, material losses by a stack and wear measurements.     

The controlled potential coulometric and controlled potential polarographic determinations of substituted nitrobenzene compounds in dimethylsulfoxide

The n-values for the reduction of the isomers of nitrophenol and nitrobenzoic acid and for several other nitro compounds were determined in dimethylsulfoxide by controlled potential coulometry. A procedure is given in which one μmole of nitro compound may be determined in less than 8 min with an error of approximately ±l%. The associated background currents were quantitatively evaluated, and electrolysis conditions for their minimization were discussed. A procedure and results are given for the controlled potential polarography of these nitro compounds in dimethylsulfoxide.     

Determination of selenium in animal tissue samples using radioisotope induced X-ray fluorescence

A summary of sources of background affecting gamma-ray spectrometers and methods for eliminating each are discussed, along with practical cost/benefit ratios. Background contributed by samples generally defines practical levels for system background. The practical bottom line can be obtained for relatively modest costs. A realistic bottom line is attained in underground systems when the major contributions to the background come from cosmogenically produced⁶⁸Ge and double-beta decay of⁷⁶Ge in the detector. The true bottom line is reached with isotopically enriched detectors that eliminate these two chemically inseparable radioactive impurities. Data from isotopically enriched detectors are presented.     

Adaptive finite element simulation of currents at microelectrodes to a guaranteed accuracy. Theory

In our accompanying paper (K. Harriman et al., Electrochem. Commun. 2 (2000) 150) we demonstrated how, for the finite element method, an automatic mesh-adaptation algorithm can be derived, given an a posteriori error bound on the simulated current. In this paper we give the technical details of the background theory of the finite element method, and the derivation of the a posteriori error bound.     

Implementation of radionuclide measurements for the Comprehensive Nuclear-Test-Ban Treaty and associated on-site inspections

The Comprehensive Nuclear-Test-Ban Treaty (CTBT) plans the installation of an International Monitoring System (IMS) based upon four global networks. Seismic, hydroacoustic and infrasound waves will help detect underground, underwater and atmospheric nuclear tests and will permit their discrimination from natural events. 80 particulate stations will detect radioactive aerosols, this network being completed with a sub-set of 40 stations which will measure rare gases, typically xenon isotopes. 16 IMS laboratories will perform additional analysis mainly by gamma-spectrometry, using the most sensitive methods such as particulate analysis. In order to have the most effective network, modeling was performed by using an inverse method in which the radioactive tracer is transported back from detectors. Examples will be given, regarding the maps of detection probability, background effects of existing xenon or radon, or the decoupling effects. All these tools and means are anticipated to have a complete process of certification, authentication of the data and discrimination capabilities between nuclear test and releases from civilian nuclear industry (reactors, reprocessing plants,). If a State Party identifies events that it feels could be a nuclear explosion, it can ask for clarification and finally it may send a request for an On-Site Inspection. The rights of the State Party and the constraints for the Inspection Team are defined in the Treaty. That leads to limited time, to limited number of inspectors on the site and to precise methods to be authorized. The means and resulting data have to be blinded in order to make sure the confidentiality is observed. Examples of restricting measurements will be given regarding airborne or vehicle mounted spectrometry as well as laboratory analysis. Cooperation with international organizations (WMO, WHO) will be discussed, depending on confidentiality issues.     

The Formation of Analytical and Background Signals in Radioisotope X-ray Fluorescence Analysis Using a 241Am Radioactive Source and a Si(Li) Detector

Reasons for the appearance of a background signal in the relatively soft x-ray range (2–15 keV) upon fluorescence excitation with the ²⁴¹Am radioisotope are discussed. Mathematical models are proposed for the interaction of the radiation of the radioactive source with the sample and the Si(Li) detector, capable of describing the appearance of the analytical and background signals. It was shown that processes occurring in the Si(Li) detector should be taken into account to explain and calculate the background signal in this range. The results of calculations agree well with the experimental data obtained using an ²⁴¹Am radiation source for fluorescence excitation.     

Principle of single and multiple time interval analysis applicable to radioactive nuclides with half-lives of millisecond order

A delayed coincidence method has been developed for the selective extraction of radionuclides with half-lives of millisecond order using a personal computer. The time interval analysis is fundamentally based on the distinction of the time interval distribution between the correlated and random events, which arise from radioactive disintegration and/or background events within a certain fixed time. Theoretical functions of a time spectrum or a time distribution curve were dealt with from aspects of statistical treatments consisting of a single time interval analysis and a multiple one (STA and MTA). The theoretical equations obtained were used to simulate time spectra on the assumption of some ideal data and compared with the experimental results. Conclusively, the MTA method has been verified to be more suitable for the selective extraction of the objective correlated events from random or background events for the search of radioactive nuclides with millisecond life-times.     

Single crystal HPGe (80%) versus BGO shielded CLOVER detector for high precision decay rate measurements: a comparative study

In this study, various detector configurations have been investigated in order to explore the optimal condition for decay rate measurements of radioactive samples using gamma spectroscopy technique. A limitation of detecting low energy gamma rays from decaying radioactive nuclei, is the Compton background which can be significantly reduced by rejecting Compton scattered events through active Bismuth germanate (BGO) shielding. On the other hand, for a CLOVER detector without BGO shielding, one can place the radioactive samples very close to the detector for enhancing geometrical efficiency. A single crystal High Purity Germanium (HPGe) detector can also be used for decay rate measurements. In order to measure the decay rate of nuclei decaying via gamma emission with reasonable intensity, optimal close geometry options have been investigated for various HPGe detector configurations.

     

On the theory of the radioactive reagents method

The possibilities of the radioactive reagent method are surveyed. Equations are derived which allow to calculate, the error of analysis in different variants of the method, as well as equations for the calculation of pH_min and the minimum determinable concentration of a test element.     

New mathematical models with associated equations for isotope dilution mass spectrometry (IDMS)

Vector models which progressively lead to a general model for isotope dilution mass spectrometry (IDMS) are presented for the case of two 'monitor isotopes' and one blend involved. They enable one to find the boundary conditions for performing IDMS, and cover the cases of highly enriched isotopes, radioactive isotopes and ratios that are given with different denominator. The models identify the key measurements in their simplest form as well as the conditions which minimise the measurement effort and in some cases the propagated measurement uncertainties. The equations are discussed and compared with other published IDMS equations. Combined with discussion on fundamental aspects of IDMS, this results in an even more 'general' but also more complex IDMS equation.     

Optimizing the use of the Kezdy–Mangelsdorf–Swinbourne method for analysis of data following a exp(–kt) + Z

The use of the KMS method for the evaluation of the exponent by the experimentalist requires that a lag or retardation be chosen. The best choice of lag is discussed quantitatively. Its dependence upon the decade range of the data, the relative magnitude of the background, the level and character of the noise, the number and distribution of the data, and the weighted least-squares method of analysis are all detailed. A table of lags and error factors is given, for various ranges, backgrounds, and kinds of noise. Bias in the extracted rate (k), due to noise and treatment of the data, is also discussed.     

Effects of uranium mining on radioactive contamination in the Kletno Region in Poland

In the Lower Silesia region, in the vicinity of Kletno town (near Kodzko), there are remainders of uranium ores being mined there, such as dump sites, abandoned pits and the like. Extensive research has indicated an increase in radioactivity there. The present research was aimed at defining the radioactive contamination in the neighborhood of Kletno. The research involved gauging the radiation background, especially at the mine dumps and measuring the concentration of natural radioactive isotopes and Cs in the rocks and soil. Besides, the concentration of radium isotopes in waters was determined. Two spots only were found with higher radiation levels. A method for dealing with radiation hazards is proposed. Water analyses have indicated that flushing of radium isotopes from the rock-mass and the dumps is not significant. Therefore, it can be concluded that uranium ore mining in the region of Kletno has not caused any significant radioactive contamination.     

A review and tutorial discussion of noise and signal-to-noise ratios in analytical spectrometry—I. Fundamental principles of signal-to-noise ratios

This review consists of two parts which discuss signal-to-noise in a tutorial manner. The sources of noise, the mathematical representation of noise, and the major types of noises in emission and luminescence spectrometry are discussed. An extensive treatment of noise and signal-to-noise ratios of paired readings is given using the relation between the auto-correlation function and the spectral noise power. These signal-to-noise expressions under optimized measurement conditions are given in terms of currents and count rates as well as in terms of charge and counts for the cases of d.c. and a.c. measurements; the present treatment is limited to the cases when the background shows only either shot noise or flicker noise. Finally, the consequences of the combination of these noise sources is considered. Signal expressions for optical spectrometry are also given. Tables give the expressions for signal-to-noise ratios in the various cases.     

Spectral interferences and background overcompensation in inverse zeeman-corrected atomic absorption spectrometry : Part 2. The effects of cobalt,manganese and nickel on 30 elements and 53 elements lines

The background compensation performance of a transversal alternating-current Zeeman corrector system with the magnet acting on the graphite atomization cell was assessed for 30 elements and 53 element lines in the presence of relatively large amounts of cobalt, manganese or nicke. The study reveaaled three cases of background overcompensation, all being caused by a cobalt line adjacent to the analytical line. When the magnetic field is on (and the background is measured), a σ-component of the cobalt lines overlaps the emission lines of boron (249.7 nm), mercury (253.7nm) and gold (267.6 nm). The interfering effect on boron is small, but mercury and gold are more seriously affected; for both elements a serious negative systematic error is introduced. Manganese and nickel did not give any overcompensation effects on the elements and lines studied. When gold and mercury were measured with the use of the same experimental parameters and a conventional deuterium-arc background corrector, only mercury suffered from spectral interference. The spectral interference of cobalt on mercury, with either type of background correction, can be avoided by selecting a proper furnace program. When gold is tobe measured in the presence of cobalt and with the present Zeeman background-correction system, the 267.6.-nm line should not be used; the more sensitive 242.8 nm line is recommended.     

Accurate technetium-99 determination using the combination of TEVA resin pretreatment and ICP-MS measurement and its influence on the Tc-99/Cs-137 scaling factor calculation

Accurate determination of technetium-99 (Tc-99) is very important because any overestimation will cause the examined radioactive wastes to be categorized into super C class, which dramatically increases the cost of waste management. Herein, we demonstrated that by adopting the analytical method comprising TEVA resin pretreatment and ICP-MS measurement, the determined Tc-99 concentrations in representative waste stream samples from the Lan-Yu low-level radioactive waste temporary storage site in Taiwan were approximately two orders of magnitude lower than those determined from the beta radiation measurement using a low background liquid scintillation counter. Two important concerns emerged from our results. First, severe interferences from other nuclides residing in the matrix considerably affect the determination of Tc-99, even when a low background liquid scintillation counter was used. Second, the currently used Tc-99/Cs-137 scaling factor should be carefully revised, or it might lead to a considerable overestimation of the Tc-99 concentration.     

Practical considerations regarding high resolution gamma-spectrometry measurements of naturally occurring radioactive samples

High-resolution gamma-spectrometry provides fast, accurate, non-destructive isotopic analysis of natural radionuclides in environmental samples. Low energy HPGe detectors (30%) with resolution less than 2.0 keV at 1332 keV of ⁶⁰Co and with linked analytical software, provide good peakto-background performance and accurate unfolding of multiplet regions. A procedure regarding high-resolution gamma-spectrometry measurements of naturally occurring radioactive samples is presented here including calibration, background interference, self-absorption, practical considerations and validation with respect to IAEA reference materials. Recommended peaks for quantitative measurements, deriving from the analysis of observed spectral interferences as well as from radioactive equilibrium considerations, are reported.