Minimum Detectable Activity Concentration Research Articles

High sensitive airborne radioiodine monitor

Airborne radioiodine monitoring includes a problem in that commercial radioactive gas monitors have inadequate sensitivity. To solve this problem, we designed a highly sensitive monitoring system. The higher counting efficiency and lower background made it possible to perform the low-level monitoring. The characteristics of the system were investigated using gaseous 125I. The minimum detectable activity concentration was 1×10−4Bqcm−3 for 1min counting, which is one tenth of the legal limit for the radiation controlled areas in Japan.

The determination of trace amounts of natural 133Xe in gas under high radon activity concentration levels

Radioxenon monitoring has become one of the major concerns in both international monitoring systems and on-site inspection. The most important technical specifications for radioxenon system are the radon removal coefficient and the minimum detectable activity concentration. We have developed one kind of on-site radioxenon sampling, separation and measurement system, and have tested it under high radon activity concentration levels. The result shows the natural 133Xe background activity concentration, the 133Xe/222Rn ratio and the radon removal coefficient to be in the ranges 0.73–1.6 mBq/m3, (1.5–3.5) × 10−8 and (2.3–57) × 10−8, respectively.

Monte Carlo simulation of in situ LaBr gamma-ray spectrometer for marine environmental monitoring

Monte Carlo simulation of energy-response functions of gamma rays from natural/artificial radionuclides in seawater and simulation of energy spectrum due to self-activity in LaBr crystal were carried out using MCNPX codes and MATLAB programs for the in situ LaBr gamma-ray spectrometer immersed in homogeneous seawater. The effective detection distance, the detection efficiency and the minimum detectable activity concentration (MDAC) for artificial radionuclides (137)Cs were worked out as an instance. Similar researches for NaI detector was also implemented for comparison. The results indicate that the self-activity in LaBr deteriorates the MDAC to merely several times of that of NaI detector. The LaBr detector is possible to be used as in situ gamma-ray spectrometer for monitoring of artificial radionuclides in seawater.

Isotopic uranium analysis in urine samples by alpha spectrometry

Urine assay is the preferred method for monitoring accidental or chronic internal intake of uranium into the human body. A new radiochemical separation procedure has been developed to provide isotopic uranium analysis in urine samples. In the procedure, uranium is co-precipitated with hydrous titanium oxide (HTiO) from urine matrix, and is then purified by anion exchange chromatographic column. Alpha spectrometry is used for isotopic uranium analysis after preparation of a thin-layer counting source by cerium fluoride micro-precipitation. Replicate spike and procedural blank samples were prepared and measured to validate the procedure. The 232U tracer was utilized for chemical recovery correction, and an average recovery of 76.2 ± 8.1% was found for 1400 mL urine samples. With 48 h of counting, the minimum detectable activity concentrations were determined to be 0.43, 0.21 and 0.42 mBq/L for 238U, 235U and 234U, respectively.

The revised program for measurements in intense operation mode according to AVV-IMIS

Abstract The monitoring program for measurements in intense operation mode has been revised recently by a working group at the Federal Ministry for Environment, Nature Conservation and Reactor Safety (BMU). The major issues of the revision are reported in this contribution. Measurements in intense operation must be appropriate for fast assessment of the radiological situation, for estimating the dose to the population and for decisions on countermeasures to minimize the dose. In order to meet these requirements the structure of the measurement program in intense operation mode was divided into three phases when different exposition paths are relevant: before and during dispersion of radioactive material, immediately after dispersion of radioactive material has ended and a late phase when contamination values have decreased in different environmental media. For each of these phases a special measurement program was defined that is tailored to achieve the above mentioned objectives. Minimum detectable activity concentrations were introduced similar to the measurement program in routine operation mode. They follow the intervention levels in the catalogue of countermeasures and maximum permitted values given by the European Union (EU) for food and animal feed. The minimum detectable activity concentrations were defined such that the detection of 1/10 of the intervention levels for countermeasures is ensured.

Feasibility of using proportional gas counters as a primary standard for positron emitters in gas

The increasing usage of Positron Emission Tomography (PET) has resulted in the commissioning of new cyclotron facilities. Emissions from exhaust ducts at these facilities are continuously monitored for radioactivity in order to ensure compliance with regulations. A primary standard for positron emitters in gas is essential to ensure the accuracy and traceability of these measurements. Up to now, all the primary standardisations for positron emitters have been carried out on liquid or solid sources; there is no primary calibration facility for the instrumentation used to monitor the radioactive effluent from the PET/cyclotron sites. A system of gas flow proportional counters, already established at NPL for calibration of β − emitters, will be the basis of the primary standard. This paper focuses on the calculation of positron energy deposition in proportional counters, and how this differs from electron energy deposition in order to predict the counters response. The PENELOPE Monte Carlo code has been used to study the energy deposition of positrons arising from the radionuclides 11C, 13N, 15O and 18F in a P10 gas for each of the three counters, and how these differ from energy depositions of electrons of the same energy at a pressure of 725 mmHg and temperature of 20.2 °C. The positrons were found to deposit from around 1.5 to 2.5 times more energy than electrons to the gas per primary shower depending on the maximum energy of the positron, affecting the minimum detectable activity concentration limit of the counters to positrons.

Low-level activity measurement of 131Xe m, 133Xe m, 135Xe and 133Xe in atmospheric air samples using high-resolution dual X–γ spectrometry

High-resolution dual X and γ spectrometry has been optimized to improve the sensitivity in analyzing radioxenon from environmental samples, especially for the metastable isotopes ( 131Xe m and 133Xe m). The full-energy peak (FEP) efficiency curve in the 20–700 keV range has been established with a global uncertainty better than ±3% using a Monte Carlo simulation. The minimum detectable activity concentrations (MDC) achievable at the laboratory for 131Xe m, 133Xe m, 133Xe and 135Xe are presented and the influence of 133Xe activity on the metastable radioxenon MDCs is evaluated.

Optimization of 210Pb determination via spontaneous deposition of 210Po on a silver disk

The accuracy of 210Pb determination via spontaneous deposition of 210Po on a silver disk and alpha spectrometric measurement was examined. The study focused on the storage conditions of the polonium-containing solutions, the tracer used in polonium analysis and the effect of storage time and acid concentration on 210Po deposition. The intermediate precision and repeatability associated with the improved 210Pb analysis of fresh groundwater samples was 5 and 14%, respectively. These improved values were achieved by using glass bottles as storage containers for the solution remaining from the first 210Po deposition, by rinsing the sample container with concentrated hydrochloric acid after storage and by using different isotopes of polonium as the yield determinant tracer in the first and the second deposition. Less polonium adsorption onto the storage container walls occurred with HCl than with HNO 3. The overall uncertainty in 210Pb analysis was (11 ± 7)% at the 95% confidence level. The minimum detectable activity concentration was 0.1 mBq l −1 calculated from blank samples and 0.05 mBq l −1 using the background counts of the alpha spectrometer.

Highly sensitive measurements of radioactive noble gas nuclides in the B orexino solar neutrino experiment

Low background miniaturized proportional counters as developed for the G allex solar neutrino experiment can be applied to the detection of radioactive noble gas nuclides at very low activities. We have developed an apparatus that allows the activity of trace amounts of isotopes of the four noble gases Ar, Kr, Xe and Rn to be measured. The technique includes contamination-free chromatographic purification of raw gas samples and subsequent low-level counting. Minimum detectable activities of 100 μBq and below have been attained. The developed techniques can be used to determine the 222Rn and 85Kr concentration in nitrogen for the solar neutrino experiment B orexino. By applying efficient techniques to concentrate noble gases from nitrogen, minimum detectable activity concentrations below 1 μBq/m 3 of nitrogen (STP) have been reached for both nuclides.

Low-level measurements of tritium in water

Using a liquid scintillation counter, an experimental procedure for measuring low-level activity concentrations of tritium in environmental water has been developed by our laboratory, using the electrolytic tritium enrichment. Additionally, some quality tests were applied in order to assure the goodness of the method. Well-known water samples collected in the Tagus River (West of Spain) and the Danube River (Bulgaria), both affected by nuclear plant releases, were analysed and results were compared to previous data. The analytical procedure was applied to drinking water samples from the public water supply of Seville and mineral waters from different springs in Spain in order to characterize its origin. Due to the very low levels of tritium in the analysed samples, some results were reported as lower than the minimum detectable activity concentration (MDA). However, the count rate of these measurements was over the background count rate of LS counter in all the cases. For that reason, an exhaustive discussion about the meaning of the MDA, using an experimental essay, was made in order to establish a rigorous criterion that leads to a reliable value in the case of low-level measurements.

Determining detection limits and minimum detectable concentrations for noble gas detectors utilizing beta-gamma coincidence systems

Beta-gamma coincidence counting is one of two acceptable noble gas monitoring measurement modes for Comprehensive Nuclear-Test-Ban-Treaty (CTBT) verification purposes defined in CTBT/PC/II/WG.B/1. Rigorous derivations of detection limits and minimum detectable activity concentrations for β-γ coincidence data are derived in this paper. Different sampling methodologies are modeled to show how the MDC is affected by different sample collection times, spectral collection times, background radon levels, and other factors.

Rapid determination of radon daughters and of artificial radionuclides in air by online gamma-ray spectrometry.

For the determination of airborne radionuclide concentrations in real time, a fixed filter device was constructed which fits directly onto a germanium detector with standard nuclear electronics and a multichannel analyzer buffer connected via a data line to a personal computer for remote control and on-line spectrum evaluation. The on-line gamma-ray spectrometer was applied to the study of radon decay product concentrations in ground-level air and to the rapid detection of any contamination of the environmental air by artificial radionuclides. At Munich-Neuherberg, depending on the meterological conditions, the measured air concentrations of 214Pb, the first gamma-ray-emitting member of the 222Rn decay series, varied from about 1 to 50 Bq m-3. For the artificial radionuclides 60Co, 131I and 137Cs the detection limits were determined as a function of the varying natural radon daughter concentrations at sampling and counting times of 1 h or 1 day. For these radionuclides minimum detectable air activity concentrations of 0.3 or 0.001 Bq m-3, respectively, were obtained at low radon daughter levels. At high radon daughter levels the respective detection limits were found to be higher by a factor of only about 2.

A nuclide-separation wire precipitator for measurement of noble-gas fission products

A wire precipitator, which has a capability of determining separately the activity concentrations of three radioactive noble-gas fission products, 88Kr, 89Kr and 138Xe, was developed. The precipitator utilizes the characteristics that the respective daughter nuclides of the fission products emit beta particles of different energy spectra. The activity concentrations of the noble gas fission products were separately quantified even when a large difference of 50 times exists among the activity concentrations of the three noble-gas fission products. The maximum deviation of the measured activity concentrations was 21%. The minimum detectable activity concentration was 2 Bq/cm 3 at a precipitation time of 90 s.