Low-level Radioactivity Measurements Research Articles

Precise detection of coal and gangue based on natural γ-ray

To address the technical limitations of automatic coal and gangue detection technology in fully mechanized top coal caving mining operations, the low radiation level radioactivity measurement method is utilized to assess the degree of coal-gangue mixture in top coal caving process. This approach is based on the distinguishing radiation characteristics of natural γ-rays between coal and gangue. This study analyzed the distribution characteristics of natural γ-rays in coal and rock layers of thick coal seams and the applicability of this method, introduced the basic principle of coal-gangue detection technology based on natural γ-ray, developed the test system about automatic coal-gangue detection, studied the radiation characteristics of coal and gangue, proposed determination model of the coal-gangue mixed degree, combined with the time sequence characteristics of the top coal’s releasing flow and the energy spectrum characteristics of different layers of rock, realized the precise coal-gangue detection technology in complex structure thick coal seam with multiple gangue. Field tests were conducted in Lilou, Xiaoyu and Tashan Coal Mine. The test results were well corroborated with the research results and achieved the expected results, which laid the foundation for the field application of intelligent coal mining.

A Monte Carlo method for calculation of the characteristic limits decision threshold and detection limit in low-level radioactivity measurements

In this study, calculation of decision threshold and detection limit expressed in counts for low-level radioactivity measurements were evaluated and compared to a Monte Carlo method for the case of paired Poisson-distributed observations, i.e. for discrete variables. The calculated characteristic limits obtained from Monte Carlo calculations were compared with analytical expressions given in literature. The results in this study show that the equations given by Currie are in good agreement with the results from the Monte Carlo calculations simulating nuclear counting applications with a low number of observed counts. An exception is observed for a background corresponding to zero counts. This study also shows that at a low number of counts, the specific boundary conditions of the interval that represents counts corresponding to the presence of the analyte (>or ≥), have an impact on the false positives and negatives rates as defined by the parameters α and β.

A well typed phoswich detector consisting of CsI and plastic scintillators for low level radioactivity measurements

In this paper, a well typed phoswich detector consisting of CsI and plastic scintillators has been designed. This detector can measure Beta and Gamma rays simultaneously. Beta signals, Gamma signals and combination signals can be distinguished using Pulse Shape Analysis. 137Cs, 241Am and 133Ba radioactive sources have been used to test this detector. It clearly shows that this phosiwch detector can be used for low level radioactivity measurement with Beta-Gamma coincidence method.

A method of lowering the background in low-level radio-activity measurements

This paper discusses the main source of background in detecting radioactivity of low-level radiation and the methods to reduce the background in practical application.

Photopeak Efficiency and Coincidence Summing Factors for HPGe Detectors Using Bulk Sources.

In the field of gamma-ray spectroscopy with high-purity germanium detectors, used to measure the activity when the sample to be measured has low radioactivity, volumetric sources are widely used. To determine the sample activity, the full-energy peak efficiency is needed. Bulk sources are very common for low-level radioactivity measurements in activation analysis and environmental samples. The main problem with these measurements is that coincidence effects are large for close source-detector geometries. Ignoring these effects can lead to an error typically of a factor of 2 in the determination of Co and Y activity, which was used in this work in the calibration process. Extensive experimental readings have been carried out, and bulk gamma aqueous sources containing several radionuclides covering the energy range from 60 to 1,840 keV were used. By comparison, the experimental (present work) and theoretical (published) full-energy peak efficiency values are in good agreement; the overall percentage error is less than 6%.

Measurement of absolute activation cross sections from carbon and aluminum for proton therapy

This experimental study aims to measure nuclear cross sections from natC and 27Al which serve as reference targets regarding radioactivation in proton therapy. Graphite and aluminum foils were activated in broad, quasi-monochromatic proton fields generated with the pencil-beam scanning technique. The γ-emissions were analyzed subsequently in a nearby γ-ray spectrometry facility designed for low-level radioactivity measurements. The number of incident protons was measured with a Faraday Cup. A detailed evaluation of the uncertainties was performed.The cross section for the natC(p,x)11C reaction at 100 MeV is (70.2 ± 1.6 (sys.) ± 0.2 (stat.)) mb. The production cross sections from 27Al at 100 MeV are (19.9 ± 0.4 ± 0.3) mb for 22Na and (11.5±0.3±0.1) mb for 24Na. The systematic uncertainties contribute 2.0%–2.4% of the quoted uncertainties (k=1) of cross sections. Concluding, radioactivation cross sections were measured with proton fields in a clinically commissioned environment. The measured activation cross sections from aluminum used for monitoring of the proton fluence agree with the averaged values compiled in nuclear reaction data bases. For proton-induced radioactivation from carbon the chemical purity of the target strongly affects the experimental results. The cross section for the production of 11C derived from a measurement with a high-purity graphite target is in line with the largest cross section obtained in prior studies.

Method validation and verification in liquid scintillation counting using the long-term uncertainty method (LTUM) on two decades of proficiency test data

Results from proficiency tests gathered over the past two decades by the laboratory for low level radioactivity measurements for liquid scintillation counting of 3H (184 results) and 14C (74 results) are used to verify the validated measurement methods used by the laboratory, in particular the estimated uncertainty budget of the method and its reproducibility and stability. A linear regression approach is used for the analysis of the results, described in the literature as the long term uncertainty in measurement method. The present study clearly indicates the advantages of using proficiency test results in identifying possible constant or proportional bias effects as well as the possibility to compare the laboratory performance with the performance of peer laboratories.

第7回低レベル放射能測定技術に関する国際会議 (ICRM-LLRMT2016) への参加報告

第7回低レベル放射能測定技術に関する国際会議 (ICRM-LLRMT2016) への参加報告

Low-level atmospheric radioactivity measurement using a NaI(Tl) spectrometer during aerosol sampling

In order to increase the early warning ability of the radiation monitoring network of the Czech republic, a high-volume aerosol sampler was upgraded with a NaI(Tl) probe placed directly above the aerosol filter. The paper demonstrates the possibility of using a method based on principal component regression to accurately subtract the complicated natural background caused by radon decay products. This approach yielded minimum detectable activities of 8mBq/m3, 3mBq/m3 and 7mBq/m3 for 131I, 134Cs and 137Cs, respectively, after 24h of sampling.

A practical method for determining γ-ray full-energy peak efficiency considering coincidence-summing and self-absorption corrections for the measurement of environmental samples after the Fukushima reactor accident

A method for determining the γ-ray full-energy peak efficiency at positions close to three Ge detectors and at the well port of a well-type detector was developed for measuring environmental volume samples containing 137Cs, 134Cs and 40K. The efficiency was estimated by considering two correction factors: coincidence-summing and self-absorption corrections. The coincidence-summing correction for a cascade transition nuclide was estimated by an experimental method involving measuring a sample at the far and close positions of a detector. The derived coincidence-summing correction factors were compared with those of analytical and Monte Carlo simulation methods and good agreements were obtained. Differences in the matrix of the calibration source and the environmental sample resulted in an increase or decrease of the full-energy peak counts due to the self-absorption of γ-rays in the sample. The correction factor was derived as a function of the densities of several matrix materials. The present method was applied to the measurement of environmental samples and also low-level radioactivity measurements of water samples using the well-type detector.

Clarification of the calculation of minimum detectable activity in low-level radioactivity measurements

We discuss a new method to determine the value of minimum detectable activity (MDA) in low-level measurements. The method is based on the Feldman–Cousins unified approach which effectively combines the construction of confidence intervals with the determination of the decision threshold and MDA. The new method requires a single probability to be pre-specified for the determination of MDA as well as decision threshold and confidence interval, in contrast with the ISO 11929 method requiring three probabilities.

Comparisons organized by Ionizing Radiation Metrology Laboratory of FTMC, Lithuania

The newly established Ionizing Radiation Metrology Laboratory of the National Metrology Institute (FTMC) in Lithuania organized four comparisons in the field of low-level radioactivity measurements in water. For gamma-ray emitters, the activity concentration in the samples was in the range 1–25Bq/kg, while for tritium it was around 2Bq/g. The assigned values of all comparisons were traceable to the primary standards of the Czech Metrology Institute (CMI).

Radionuclide, scintillation cocktail and chemical/color quench influence on discriminator setting in gross alpha/beta measurements by LSC

Gross alpha/beta measurements in drinking waters enable radiochemical composition analysis in environmental studies providing efficient screening method that can indicate whether water contains elevated levels of any radionuclide. Routine gross alpha/beta activity monitoring in drinking waters has been carried out for a few years in laboratory for low-level radioactivity measurements in Novi Sad according to ASTM method, performing measurements on liquid scintillation counter Quantulus 1220 which can simultaneously generate alpha/beta spectra of samples by Pulse Shape Analysis (PSA circuit). In this paper, PSA discriminator impact was investigated to ensure obtaining of accurate and reliable alpha/beta activities. One novelty of presented work is PSA parameter setup with two combinations of radionuclides (241Am, 226Ra and 90Sr/90Y) with varying activity concentrations. Performed experiments also make contribution to investigations on the manner in which chemical and color quench affect optimal PSA parameter setting and further on, their altogether influence on gross alpha/beta activity measurements. Nitromethane, 15.8 M nitric acid and water, as well as yellow and yellow-orange dye, were used as quenching agents in order to test PSA/interference factor behavior in the presence of quenchers with different quenching strengths. Variation of PSA setting in quenched samples with two different commercially available cocktails (Ultima Gold LLT and OptiPhase HiSafe 3) was also tested. Lastly, application i.e. assessment of obtained PSA-SQP(E) correlation on the obtained results of activity concentrations of few artesian well water samples and colored spiked samples, based on the measured SQP(E) value of samples, has been demonstrated.

Measurement uncertainties in whole body counting and radon progeny.

Measurement uncertainty is an important quality index in gamma spectrometry related to the level of bias and precision involved in the measuring procedure. Quality control measurements during the commissioning of a 16-input whole body counter showed substantial deviations between the experimentally determined precision and the theoretical estimation, indicating either equipment malfunction or lack of reproducibility of the experimental setup. In this study, the role of the magnitude and variability of airborne background radiation present in the counting room and the human body in the deterioration of the precision of counters employing NaI(Tl) detectors was investigated. Correction methods and actions based on case-specific background features were developed and applied. The experimental observations were benchmarked using a mathematical model of the counter. The efficacy of the developed methods was tested by measurements, and updated precision values were obtained. Quasi-equilibrium between the gamma-emitters Bi and Pb in the counting room and the human body is a prerequisite for accurate direct low-level radioactivity measurements in the human body.

DÖME: revitalizing a low-background counting chamber and developing a radon-tight sample holder for gamma-ray spectroscopy measurements

There was an emerging need at the Nuclear Analysis and Radiography Department of the Centre for Energy Research, Hungarian Academy of Sciences, Budapest to be able to perform low level radioactivity measurements of various samples from in-beam activation and from environmental studies. Important aspects of reusing the low-background chamber called DOME, which had been unused for some years, were the development of an easily reusable radon-tight sample container and the setup of a measurement system capable of counting extended samples in close-in geometry. As a result of our efforts a special sample container made of HDPE (High-density Polyethylene) was developed, and it is proved that the probability of a radon loss larger than the 2 % of its radioactive decay constant is <95 %. Due to the lack of reference samples, containing the same radionuclides as the unknown sample, the absolute method of measuring the activity concentration of nuclides in the sample had to be applied, which implied the reliable determination of the full-energy peak efficiency. A method called efficiency transfer combined with the correction for true coincidence summing effects is proven to be providing appropriate results and applied.

New method to determine the decision threshold for low-level radioactivity measurements

We discuss a new method to determine the value of a decision threshold that can be used to decide whether to choose a one-sided confidence interval or a two-sided confidence interval. The method is based on the Feldman–Cousins unified approach providing a unique confidence region for estimated parameters. We apply this method to a net count rate measurand in low-level radioactivity measurements which is physically restricted to nonnegative values. We tabulate the values of the decision threshold and detection limit of the measurand for some typical coverage probabilities. The decision threshold in this method does indeed enable a decision on whether or not the physical effect quantified by the measurand is present.

Thirteenth international symposium on biological and environmental reference materials (BERM-13)

The 13th international symposium on biological and environmental reference materials (BERM-13) was held at the International Atomic Energy Agency (IAEA) Headquarters in Vienna, Austria, from 25 to 29 June 2012. The BERM-13 carried on a series of BERM Symposia, which was launched in 1983 and has been held on a regular basis since then [1–3]. As one of the main producers of reference materials (RMs) characterized for radionuclides and stable isotope amount ratios, the IAEA has a specific interest in biological and environmental reference materials and has been actively involved in BERM symposia since their inception. However, this was the first time that the symposium was organized by the IAEA. The main symposium topics were: recent developments, current trends and future needs for RMs; selection and proper use of RMs; the role of RMs in assuring harmonization and comparability of measurement results; availability and distribution of RMs; and education and training related to RMs production and their use. The symposium was organized in several sessions, namely food and reference materials; standardization, metrology and international cooperation; health, medicine and forensic; reference materials production, trends and techniques; environmental reference materials; including plenary sessions each day and two poster sessions. Taking the advantage of the fact that BERM-13 was organized as an IAEA conference, three special sessions were also organized on topics of high importance to the IAEA and in general, namely special sessions on environmental nuclear fingerprints, stable isotope reference materials and reference materials for emergency situations. Altogether there were 92 oral presentations (4 opening remarks, 23 invited, and 65 oral lectures), 77 posters, and 3 round table discussions. The symposium was attended by 197 participants from 49 countries and five international organizations (the International Bureau of Weights and Measures—BIPM, the European Commission/Joint Research Centre—EC/JRC, the European Directorate for the Quality of Medicines & Health Care—EDQM, the IAEA and the International Organization for Standardization—ISO). The highlights of the BERM-13 symposium were invited presentations, covering RMs related to food and human nutritional status and biomarkers (S. Wise, C. M. Pfeifer, USA), metabolomics (K. W. Phinney, USA), RMs required to support harmonized human biomonitoring programs (M. Horvat, Slovenia), RMs needed for key enabling technologies (H. Emons, EC/JRC/IRMM), RMs for pharmaceuticals (A. Lodi, CE/EDQM), elemental speciation (O. Donard, France) and nanoscale RMs (D. L. Keiser, USA), new organic stable isotope RMs (A. Schimmelmann, USA), as well as lectures related to large RM programs (T. Saito, Japan; Z. Mester, Canada; M. Betti, IAEA), legislation (A. Held, EC/JRC/IRMM), top metrology (M. Kuehne, BIPM), and certain technical requirements, for example, stability testing and monitoring strategies (S. L. R. Ellison, UK). The special sessions have, among others, revealed a strong need for new environmental RMs suitable for low-level radioactivity measurements. This is an area where new very sensitive measurement techniques have been developed for characterization of ‘hot particles’ but face a lack of appropriate quality assurance tools. A similar situation was presented in the case of RMs for emergency preparedness, where the Gulf oil spill (M. M. Schantz, USA; A. R. Wagener, Brazil) A. Fajgelj (&) International Atomic Energy Agency, Department of Nuclear Sciences and Applications, Vienna International Centre, PO Box 100, 1400 Vienna, Austria e-mail: A.Fajgelj@iaea.org

Performance of HPGe gamma spectrometry system for the measurement of low level radioactivity

Comprehensive quality assurance/quality control procedure is very much necessary to obtain accurate and precise analytical measurement result. This paper discusses the quality control aspects of the High-Purity Germanium (HPGe) based gamma spectrometry system, which has been used for the measurement of low-level radioactivity in environmental samples. The gamma spectrometry system consisting of coaxial n-type HPGe detector having 50% relative efficiency with respect to 7.62 cm x 7.62 cm NaI (Tl), Nuclear Instrumentation Module (NIM) based pulse processing electronic accessories and 8 k MCA. To reduce the background contribution, 7.5 cm thick lead has been placed surrounding the detector. The minimum detectable activities (MDA) with 95% confidence level (for 300 g soil sample and 100,000 s counting time) for important radionuclides such as 238U, 226Ra, 232Th, 40K, and 137Cs are 10.4, 4.3, 4.1, 16.9 and 0.1 Bq kg−1, respectively. The Quality control (X bar R) charts were plotted using 137Cs and 40K background counts observed periodically, which showed that the fluctuation is well within the confidence limit and confirms the stability of the system. The laboratory has been participating in the proficiency tests (PTs) of the International Atomic Energy Agency (IAEA). In recently concluded PTs, the samples include soil, spiked standard solution, spinach, phosphogypsum and spiked air filter were analysed for the natural, fission and activation products radionuclides. The performance evaluation of the IAEA PTs showed that the laboratory results were in good agreement with the target value, which confirms the reliability and traceability of the gamma spectrometric measurement result of the laboratory.

Disaggregating measurement uncertainty from population variability and Bayesian treatment of uncensored results

In making low-level radioactivity measurements of populations, it is commonly observed that a substantial portion of net results is negative. Furthermore, the observed variance of the measurement results arises from a combination of measurement uncertainty and population variability. This paper presents a method for disaggregating measurement uncertainty from population variability to produce a probability density function (PDF) of possibly true results. To do this, simple, justifiable and reasonable assumptions are made about the relationship of the measurements to the measurands (the 'true values'). The measurements are assumed to be unbiased, that is, that their average value is the average of the measurands. Using traditional estimates of each measurement's uncertainty, a likelihood PDF for each individual's measurand is produced. Then using the same assumptions and all the data from the population of individuals, a prior PDF of measurands for the population is produced. The prior PDF is non-negative, and the average is equal to the average of the measurement results for the population. Using Bayes's theorem, posterior PDFs of each individual measurand are calculated. The uncertainty in these bayesian posterior PDFs appears to be all Berkson with no remaining classical component. The method is applied to baseline bioassay data from the Hanford site. The data include (90)Sr urinalysis measurements of 128 people, (137)Cs in vivo measurements of 5337 people and (239)Pu urinalysis measurements of 3270 people. The method produces excellent results for the (90)Sr and (137)Cs measurements, since there are non-zero concentrations of these global fallout radionuclides in people who have not been occupationally exposed. The method does not work for the (239)Pu measurements in non-occupationally exposed people because the population average is essentially zero relative to the sensitivity of the measurement technique. The method is shown to give results similar to classical statistical inference when the measurements have relatively small uncertainty.

Analytical approach to calculate the efficiency of 4π NaI(Tl) gamma-ray detectors for extended sources

The 4π NaI(Tl) detectors are usually utilized for low-level radioactivity measurements of environmental samples in gamma-ray spectroscopy due to the near 4π solid angle and high full-energy peak and total efficiencies. An analytical theoretical approach is presented here and used to calibrate a 4 π NaI(Tl) (2 a×2 b× 2c) detector, with a central rectangle hole (2 l×2 m×2 c) was left empty for sample access, for isotropic radiating (point, plane and volumetric) sources. The approach depends on the accurate calculation of two important factors; the path length d, the photon traverses within the active volume of a gamma detector, and the geometrical solid angle Ω, subtended by the source to the detector at the point of entrance. The comparisons with the experimental and Monte Carlo method works reported in the literature indicate that the present approach is useful in the efficiency calibration of such complicated gamma-ray spectrometer.