Minimum Detectable Activity Concentration Research Articles

Design and application of a shipborne underwater radiation detector array for the monitoring of seawater radioactivity

A navigable online monitoring system for marine radioactivity was developed to cope with possible large-scale marine nuclear pollution incidents. This system used a NaI(Tl) detector array mounted on a ship to collect radioactive data across wide marine areas rapidly. High volume-efficiency aids the system in rapidly identifying radionuclides exceeding standard levels. This feature enables the system to monitor the seawater in a wide area within a shorter time and promptly detect marine nuclear pollution incidents. Monte Carlo simulations were used to optimize the number of NaI(Tl) crystals and the detector spacing for enhancing the volume-efficiency of the system. Three Φ3" × 6″ NaI(Tl) detectors and the mounting bracket with a fixed detector spacing of 30 cm were fabricated based on the simulation outcomes. The volume-efficiency for 137Cs of the system was around six times higher than that for the buoy-based monitoring system with a 3-inch NaI(Tl) detector. The theoretical volume-efficiency curve, which was calculated through Monte Carlo simulation, was verified in a standard liquid source. The minimum detectable activity concentration (MDC) for radioisotopes of the system under various radioactive measurement durations was discussed, such as the MDC for 137Cs for 5 min measurement was 0.152 Bq/L. Marine radioactivity measurement experiments were conducted in the sea near the Tianwan nuclear power plant in Lianyungang, China. The test results showed that the activity concentration of 40K was 11.4 Bq/L. The results of navigation monitoring were consistent with those of sampling and laboratory measurement, which verified the stability and accuracy of the system.

Feasibility Analysis of Tritium Measurement in the Aqueous Medium Based on a Plastic Scintillating Fiber Array

Tritium causes internal dose hazards to humans. Currently, tritium in the environment mainly comes from nuclear power plants, and tritiated water (HTO) is the main form of liquid emission. Therefore, online monitoring activity of tritium in the aqueous medium is vital for protecting human health, and it can warn of the operation status of nuclear power plants. In this paper, we present an improved structure of plastic scintillating fiber (PSF) and a PSF array design, and the detection parameters of PSF arrays with different radii and lengths under different radius detection chambers are simulated using Geant4. Based on the simulation results, the detector is designed, and the minimum detectable activity concentration (MDAC) of the detector is calculated. With calculated MDACs down to 3.09 Bq/L, the proposed design can meet the Chinese requirements for HTO release of inland nuclear power plants of <100 Bq∙L−1. Therefore, the detector designed with a PSF array can be applied to online monitoring of tritium in the aqueous medium.

Low-level tritium measurements in freshwater and seawater samples

The aim of this study was to test two potential tritium determination methods (with and without electrolysis enrichment) suitable for low-level measurements. Both methodologies were applied to water samples from the Baltic Sea and ten Polish rivers providing new data on tritium activity concentration. Optimization steps carried out to the standard method lowered minimum detectable activity concentration (MDC) from 3.1 to 1.8 Bq L–1 (at 95% confidence level) enabling to apply it to environmental water samples. However, electrolytic enrichment method of MDC of 0.20 Bq L–1 provided more accurate results for tritium activity concentration in surface waters.

Measurement of 90Sr and 87Sr/86Sr isotope ratio in Japanese cow milk sample using thermal ionization mass spectrometry

The pure beta emitter 90Sr (T1/2 = 28.8y) is a typical contaminant released by nuclear accidents and nuclear explosions. In the event of a nuclear disaster, it is crucial to identify radioactive pollutants quickly, to expedite the public's awareness of radiation exposure. In this work, a rapid 90Sr analysis protocol using thermal ionization mass spectrometry (TIMS) was developed for milk samples. With the improved sample preparation, Sr separation, and a newly developed TIMS method, 18 milk samples can be analyzed in less than 30 h and only 1 mL of cow milk is required for the complete analysis. The minimum detectable activity concentration of 90Sr is affected by the stable Sr concentration therefore, it is around 500 mBq·kg−1 (∼100ag·g−1). Additionally, 87Sr/86Sr isotope ratios (0.71518(9)–0.74132(4)) were determined for the first time in Japanese cow milk samples.

Levels of caesium-137 in food of animal origin in Poland.

Radioactive contamination of the environment is one of the greatest threats after a nuclear accident due to released radionuclides. From a radiotoxicological point of view, the most important radionuclide is caesium-137. Formed mainly during nuclear explosions, caesium-137 can persist in the soil for many years, from where it constantly enters the food chain. One of the elements of ensuring food safety is the monitoring of its radioactive contamination, mainly with radioactive caesium isotopes. The aim of the study was to determine the content of caesium-137 in food of animal origin. A total of 1,416 muscle samples from cattle, sheep, pigs, game and fish, as well as chicken eggs and dairy products were examined using gamma-ray spectrometry. Caesium-137 activities ranged from below the minimum detectable activity concentration (MDC) to over 4,000 Bq/kg wet weight (w.w.). Most often, the values did not exceed the MDC or were in a range below 100 Bq/kg. The exception was the muscle tissue of game animals, especially wild boar, where a significant activity of caesium-137 was recorded, the highest of which was 4,136.8 ± 238 Bq/kg w.w. Committed effective doses determined for each matrix ranged from 0.01 to 0.83 µSv/kg, with the highest value determined for wild boar. The calculated exposure doses with values well below the accepted low radiation dose (100 mSv) did not indicate any significant amounts of ionising radiation from the food consumed.

A fast algorithm for real-time monitoring of artificial radioisotopes in presence of variable natural radioactivity

We present an agile, hardware independent analysis methodology based on the spectral windows technique to detect and quantify the environmental activity concentration of artificial isotopes of interest. The method removes counts from Compton scattering, peak overlapping, intrinsic background and other unconsidered contributions to the spectral region where photopeaks from artificial elements are expected. Taking into account the varying concentration of 214Bi, 214Pb, and 212Pb, we compute the activity concentration of the artificial isotopes (when detectable), or a variable Minimum Detectable Activity Concentration (MDAC). This allows to set statistically robust early-warning levels. In the scenario with the lowest concentration of natural occurring isotopes, and for 10-min integration time, we achieve a MDAC of 5.4/4.1/3.9 (Bq/m³) for 131I/137Cs/60Co using a LaBr3(Ce) detector; and 4.2/2.8/2.7 (Bq/m³) for 131I/137Cs/60Co with a SrI2(Eu) detector.

A rapid method for determining low concentrations of 210Pb in drinking water using MnO2 fibers

A rapid method for determining low activity concentrations of 210Pb in drinking water was developed and tested. The method consists of a few stages for sample preparation that involve passing 12 L of water through a column with acrylic fibers implanted with MnO2 (used to adsorb 210Pb). The MnO2 fibers are oven-dried, compressed and measured by a broad-energy germanium detector used to quantify 210Pb via its characteristic 46.5 keV γ-ray. The time taken for sample preparation is approximately 4 h and recovery factors for lead in tap water of 87 ± 3% were achieved. After a measurement duration of 4 h, the minimum detectable activity concentration reaches 0.02 Bq/L for 210Pb, being well below the respective limit for drinking water in Israel (0.2 Bq/L) as well as the value recommended by the World Health Organization (0.1 Bq/L). Furthermore, a measurement duration of 48 h provides a minimum detectable activity concentration of ∼0.006 Bq/L, which is similar in magnitude to other, well-established methods that rely on lengthy and rather complex procedures. Thus, the combination of MnO2 fibers and gamma-ray spectrometry may be attractive for routine use by analytical laboratories that monitor radioactivity in drinking water.

Lesion Quantification Accuracy of Digital 90Y PET Imaging in the Context of Dosimetry in Systemic Fibroblast Activation Protein Inhibitor Radionuclide Therapy.

Therapy with 90Y-labeled fibroblast activation protein inhibitors (90Y-FAPIs) was recently introduced as a novel treatment concept for patients with solid tumors. Lesion and organ-at-risk dosimetry is part of assessing treatment efficacy and safety and requires reliable quantification of tissue uptake. As 90Y quantification is limited by the low internal positron-electron pair conversion rate, the increased effective sensitivity of digital silicon photomultiplier-based PET/CT systems might increase quantification accuracy and, consequently, allow for dosimetry in 90Y-FAPI therapy. The aim of this study was to explore the conditions for reliable lesion image quantification in 90Y-FAPI radionuclide therapy using a digital PET/CT system. Methods: Two tumor phantoms were filled with 90Y solution using different sphere activity concentrations and a constant signal-to-background ratio of 40. The minimum detectable activity concentration was determined, and its dependence on acquisition time (15 vs. 30 min per bed position) and smoothing levels (all-pass vs. 5-mm gaussian filter) was investigated. Quantification accuracy was evaluated at various activity concentrations to estimate the minimum quantifiable activity concentration using contour-based and oversized volume-of-interest-based quantification approaches. A ±20% deviation range between image-derived and true activity concentrations was regarded as acceptable. Tumor dosimetry for 3 patients treated with 90Y-FAPI is presented to project the phantom results to clinical scenarios. Results: For a lesion size of 40 mm and a clinical acquisition time of 15 min, both minimum detectable and minimum quantifiable activity concentrations were 0.12 MBq/mL. For lesion sizes of greater than or equal to 30 mm, accurate quantification was feasible for detectable lesions. Only for the smallest 10-mm sphere, the minimum detectable and minimum quantifiable activity concentrations differ substantially (0.43 vs. 1.97 MBq/mL). No notable differences between the 2 quantification approaches were observed. For the investigated tumors, absorbed dose estimates with reliable accuracy were achievable. Conclusion: For lesion sizes and activity concentrations that are expected to be observed in patients treated with 90Y-FAPI, quantification with reasonable accuracy is possible. Further dosimetry studies are needed to thoroughly investigate the efficacy and safety of 90Y-FAPI therapy.

Rapid determination of 99Tc in water samples using Ti(OH)3-TcO2 co-precipitation and TK200 resin by liquid scintillation counting

A novel method for the determination of 99Tc in water samples was developed using stable Re as a chemical yield tracer and TiCl3 as a reducing agent. The influences of several experimental parameters, including TiCl3 concentration, HCl concentration and reaction time, on the reduction of TcO4− and ReO4− as well as Ti(OH)3-TcO2-ReO2 co-precipitation were investigated. Tc(VII) and Re(VII) retained on TK200 resin were effectively eluted by 5 mL of 1 mol/L NH4SCN, which can be directly mixed with the scintillation cocktail for liquid scintillation counting. The results show that the chemical behaviors of Tc and Re are very consistent in the whole procedure. The decontamination factors of potential interferences from β-emitting nuclides mainly released from nuclear fuel reprocessing plants were also evaluated, and the minimum detectable activity concentration was calculated to be 0.08 Bq/L for 99Tc in water samples with a counting time of 2 h.

Minimum detectable activity concentration of radio-cesium by a LaBr3(Ce) detector for in situ measurements on the ground-surface and in boreholes

A 3.81 × 3.81 cm LaBr3(Ce) detector based portable measurement setup has been developed for in situ gamma spectrometric survey of a contaminated site. This system is suitable for above- and below ground surface gamma spectrometric measurements of 137Cs. However, the minimum detectable activity concentration (MDAC), an important parameter of a measurement system, should be estimated for planning purposes of the gamma spectrometric survey. In this study, the MDAC of 137Cs for the measurement setup was investigated. The efficiency of the measurement setups was calculated from Monte Carlo simulations using MCNP code. The numerical model of the different studied set-ups, used in MCNP, performed well for the known cases. The results show that the MDAC varies with the position of the detector with respect to ground surface. A 5–20 min acquisition time, depending on the detector position, can be sufficient to get a MDAC of about 10% of the exemption limit of 137Cs (100 Bq/kg).

Investigating the minimum detectable activity concentration and contributing factors in airborne gamma-ray spectrometry

Investigating the minimum detectable activity concentration and contributing factors in airborne gamma-ray spectrometry

Absence of Detectable Radionuclides in Breast Milk in Sendai, Japan in 2012 Even by High-Sensitivity Determination: Estimated Dose among Infants after the Fukushima Nuclear Disaster.

The aim of this study was to estimate radionuclide levels in breast milk and the transferred dose to their infants in Sendai (100 km from Fukushima), Japan after the 2011 Fukushima nuclear disaster. Radionuclide concentrations were analyzed in 101 specimens of breast milk collected in 2012. Median values for minimum detectable activities were 0.39, 0.34, 1.1, 1.89, and 17.1 Bq/kg for 137Cs, 134Cs, 131I, 110mAg, and 40K, respectively. Only radionuclides from 40K were detected. To estimate potential exposure and radiocesium dose, we assumed that the samples contained each minimum detectable activity level. The mean minimum detectable activity concentrations (standard deviation) of 137Cs and 134Cs were 0.42 (0.15) and 0.37 (0.14) Bq/kg, respectively. Means of estimated dietary intakes of 137Cs and 134Cs among infants were 0.35 (0.12) and 0.31 (0.11) Bq/day, respectively. The committed effective doses of radiocesium in infants aged 3 and 12 months via breastmilk were estimated at 5.6 (2.1) and 3.3 (1.2) μSv/year, respectively. Dietary intakes of 137Cs and 134Cs in breastfeeding mothers were back-calculated at 1.9 (0.71) and 1.7 (0.65) Bq/day, respectively. The study verified no discernible exposure to radionuclides among infants. The most conservative estimates were below the Japanese internal exposure limit of 1 mSv/year.

Analysis of Minimum Detectable Activity Concentration of Water Samples and Evaluation of Effective Dose

Analysis of Minimum Detectable Activity Concentration of Water Samples and Evaluation of Effective Dose

Assessment of radionuclide impurities in [18F]fluoromethylcholine ([18F]FMCH).

[18F]Fluoromethylcholine ([18F]FMCH) is a radiopharmaceutical used in positron emission tomography (PET) imaging for the study of prostate, breast, and brain tumors. It is usually synthesized in cyclotron facilities where 18F is produced by proton irradiation of [18O]H2O through 18O(p,n)18F reaction. Due to the activation of target materials, the bombardment causes unwanted radionuclidic impurities in [18O]H2O, that need to be removed during the radiopharmaceutical synthesis. Thus, the aim of this study is to quantify the radionuclide impurities in the 18F production process and in the synthesized [18F]FMCH, demonstrating the radionuclidic purity of this radiopharmaceutical. Long-lived radionuclide impurities were experimentally assessed using high-resolution gamma and liquid scintillation spectrometries, while short-lived impurities were monitored analyzing the decay curve of the irradiated [18O]H2O with an activity calibrator. As spectrometric radionuclide library, a Geant4 Monte Carlo simulation of the 18F-target assembly was previously performed. 3H, 52,54Mn, 56,57,58Co, 95m,96Tc, 109Cd, and 184Re were found in the irradiated [18O]H2O, but no radionuclide was found in the non-irradiated [18O]H2O neither in the final [18F]FMCH solution with an activity concentration greater than the minimum detectable activity concentration. A total impurity activity<6.2kBq was measured in the irradiated [18O]H2O, whereas a [18F]FMCH radionuclide purity>99.9999998% was estimated. Finally, the decay curve of the irradiated [18O]H2O revealed a very low maximum of 13N activity (<0.03% of 18F) even immediately after the end of bombardment. This study demonstrated the radionuclidic purity of [18F]FMCH according to the EU Pharmacopeia.

Experimental study of tritium activity concentration in cooling water of heavy ion research facility in Lanzhou

Cooling water of Heavy Ion Research Facility in Lanzhou is the media of choice for absorbing heat generated by a multitude of accelerator components. During the operation, tritium is produced by the secondary neutrons in the accelerator loop of accelerator cooling water, which is uniformly distributed in the water system in the form of hydrogen tritium oxide. The purpose of this study is to establish a rigorous method to measure the low levels of tritium in the accelerator cooling water system. The cooling water samples of Sector Focusing Cyclotron and Separated Sector Cyclotron of Heavy Ion Research Facility in Lanzhou, as well as the natural levels of tritium, were measured successfully, using Quantulus1220 ultra-low-level background liquid scintillation spectrometer. The electrolytic enrichment method was employed to measure the tritium activity concentrations of the cooling water samples. Moreover, the minimum detectable activity concentration and the counting rate efficiency curve of the liquid scintillation spectrometer were obtained to ensure reliability. In this work, we provide a reference to establish the related standards and specifications for monitoring the tritium levels in heavy-ion accelerator cooling water system.

OPTIMIZATION OF THE RADIOACTIVE AEROSOL SAMPLING AND MEASURING PROCEDURE WITH RESPECT TO RADON CONCENTRATION IN THE AIR.

High-volume aerosol samplers combined with laboratory analysis using high-resolution gamma ray spectrometry allow determining artificial radionuclides in the atmosphere at sub μBq/m3 levels. A major drawback of this procedure is a significant delay of the analysis result after any potential radioactive contamination deposition on the aerosol filter. Within the scope of the HAMRAD project, an autonomous device was developed in order to increase the sampling and measuring frequency. This approach yields higher detection limits (minimum detectable activity concentration [MDAC]) due to the deposited activity of radon decay products on the filter. In order to quantify the radon effect, a simple mathematical model was developed to predict MDAC for the particular radionuclide of interest for the given background conditions. It was found that MDAC can vary by a factor of ~2 for typical 'radon' conditions (~10Bq/m3) at SÚRO Prague and by a factor up to 5 for high radon concentration (100Bq/m3).

Set up of a gamma spectrometry mobile unit equipped with LaBr3(Ce) detectors for radioactivity monitoring

This paper presents the development, calibration and testing of a mobile unit for radioactivity monitoring. A 4 × 4 vehicle was equipped with a GPS and two 2″×2″ LaBr3(Ce) scintillation detectors. It was modelled using MC simulations with the EGS5 code to obtain efficiency curves for different source term scenarios. The attenuation produced by the car structure was determined using MC and experimental measurements. A self-developed software was used to acquire and analyse the gamma spectra. In addition, Minimum Detectable Activity Concentrations were calculated for 137Cs and 131I.During standard operation, the mobile unit will create a radiological map of Catalonia (Spain), calculating in real time the ambient dose equivalent H*(10) and the activity concentration of natural and anthropogenic radionuclides. After its set up and calibration, the system was tested on the field and provided adequate results. Therefore, the mobile unit is available to assist in the event of a nuclear emergency tracking radioactive plumes and participating in radioisotope mapping surveys. It is also ready to obtain the required data to build the radiological map of Catalonia.

Direct analysis of 210Pb in drinking water by liquid scintillation counting after sulfate precipitation

Lead-210 in drinking water can be rapidly determined by liquid scintillation counting (LSC) using a new sulfate precipitation method. In this method, 210Pb was first preconcentrated from water using iron hydroxide co-precipitation followed by sulfate precipitation to decontaminate most of non-alkaline earth elements. The Pb in the sulfate precipitate was then dissolved in strong alkaline solution, while alkaline earth elements (Sr, Ba, Ra) were separated as the sulfate/carbonate precipitate. To optimize the method, the influences of different acids and sulfate concentration on sulfate precipitation as well as the effects of pH, the added SO42−/CO32− concentrations and the Sr/Ba contents in the sulfate precipitate on the dissolution of PbSO4 were studied. In addition, X-ray fluorescence (XRF) analysis was applied for rapid determination of the chemical recovery and triple-to-double coincidence ratio (TDCR) quench correction curve for counting of 210Pb by LSC was established. The method was validated using 5 L of tap water samples and minimum detectable activity concentration (MDC) of ∼0.016 Bq·L−1 was achieved, which is sufficiently sensitive to meet the guidance level of 0.1 Bq·L−1 for 210Pb in drinking water as recommended by the World Health Organization (WHO).

Method for sequential determination of 55Fe and 63Ni in leaching solution from cement solidification

A method for sequential determination of 55Fe and 63Ni in leaching solution of cement solidification using liquid scintillation counting (LSC) was developed. In this method, 55Fe and 63Ni were first precipitated in the form of hydroxide and subsequently purified by anion exchange chromatography and dimethylglyoxime precipitation. After the purification, 55Fe and 63Ni were determined by LSC. The performance of the method was examined, and minimum detectable activity concentration was determined to be 0.82 Bq L−1 for 55Fe and 0.42 Bq L−1 for 63Ni in leaching solution samples with a counting time of 1 h. High decontamination factors for 55Fe and 63Ni were also obtained.

Passive radon monitors with part-time sensitivity to radon

The recent European directive 59/2013 set reference levels for radon at working places. Since usually the personnel spend only part of the day (e. g. 8 h) at work, it is useful to have passive radon monitors that are sensitive only within a certain time window (e. g. the working hours). This work proposes a conceptual design of such a monitor and tests the feasibility of the approach. The design is based on a solid state nuclear track detector (SSNTD) that rotates over a radon absorber during the monitored period of the day. The SSNTD (Kodak Pathe LR-115 type II) has an energy window that makes it insensitive to 222Rn and 220Rn progeny plated-out on the surfaces. It only registers alpha particles of the absorbed 222Rn and its short-lived progeny 218Po, which is achieved by optimization of the absorber thickness. The absorber construction is further optimized to decrease the inertia of the signal. The modeling and the pilot experimental results show that with a composite absorber consisting of a stack of Makrofol N foils with thickness of less than 7 μm each, the inertia of the signal is less than 20 min. The estimated minimum detectable activity concentration (MDAC) for the proposed 222Rn monitor is about 15 Bq m−3 for year-long working time exposure (2000 h/year) or 60 Bq m−3 for 3- month exposure period (500 h).