Search

The concept of minimal detectable bias (MDB) as initiated by Baarda (Publ Geod New Ser 2(5), ) and later developed by Wang and Chen (Acta Geodaet et Cartograph Sin Engl Edn 42-51, ), Schaffrin (J Eng Surv 123:126-137, ), Teunissen (IEEE Aerosp Electron Syst Mag 5(7):35-41, , J Geod 72:236-244 , Testing theory: an introduction. Delft University Press, Delft, ) and others, refers to the issue of outlier detectability. A supplementation of the concept is proposed for the case of correlated observations contaminated with a single gross error. The supplementation consists mainly of an outlier identifiability index assigned to each individual observation in a network and a mis-identifiability index being the maximum probability of identifying a wrong observation. To those indices there can also be added the MDB multiplying factor to increase the identifiability index to a satisfactory level. As auxiliary measures there are indices of partial identifiability concerning pairs of observations. The indices were derived assuming the generalized outlier identification procedure as in Knight et al. (J Geod. doi:, ), which with one outlier case being assumed is similar to Baarda's w-test (Baarda in Publ Geod New Ser 2(5), ). The following two options of identifiability indices and partial identifiability indices are distinguished: I. the indices related to identification of a contaminated observation within a set of observations suspected of containing a gross error (identifiability), II. the indices related to identification of a contaminated observation within a whole set of observations (pseudo-identifiability). To characterize the proposed approach in the context of the existing solutions of similar topic being the separability testing, the properties of both types of identifiability indices are discussed with reference to the concept of Minimal Separable Bias (Wang and Knight in J Glob Position Syst 11(1):46-57, ) and a general approach in Yang et al. (J Geod 87(6):591-604, ). Numerical examples are provided to verify the proposed approach. [ABSTRACT FROM AUTHOR]

This paper reports on the performance of a recently developed Small Anode Germanium (SAGe) well detector from Canberra Industries. This has been specifically designed to improve the energy resolution of the detector, such that it is comparable to the performance of broad-energy designs while achieving far higher efficiencies. Accurate efficiency characterisations and cascade summing correction factors are crucial for quantifying the radionuclides present in environmental samples, and these were calculated for the complex geometry posed by the well detector using two different methodologies. The first relied on Monte-Carlo simulations based upon the GEANT4 toolkit, and the second utilised Canberra Industries GENIE™ 2000 Gamma Analysis software in conjunction with a LabSOCS™ characterisation. Both were found to be in excellent agreement for all nuclides except for 152 Eu, which presents a known issue in the Canberra software (all nuclides affected by this issue were well documented, and fixes are being developed). The correction factors were used to analyse two fully characterised reference samples, yielding results in good agreement with the accepted activity concentrations. Given the sensitivity of well type geometries to cascade summing, this represents a considerable achievement, and paves the way for the use of the SAGe well detector in analysis of ‘real-world’ environmental samples. With the efficiency increase when using the SAGe well in place of a BEGe, substantial reductions in the Minimum Detectable Activity (MDA) should be achievable for a range of nuclides. [ABSTRACT FROM AUTHOR]

The detection limit ( L D ) or Minimum Detectable Activity (MDA) is an a priori evaluation of assay sensitivity intended to quantify the suitability of an instrument or measurement arrangement for the needs of a given application. Traditional approaches as pioneered by Currie rely on Gaussian approximations to yield simple, closed-form solutions, and neglect the effects of systematic uncertainties in the instrument calibration. These approximations are applicable over a wide range of applications, but are of limited use in low-count applications, when high confidence values are required, or when systematic uncertainties are significant. One proposed modification to the Currie formulation attempts account for systematic uncertainties within a Gaussian framework. We have previously shown that this approach results in an approximation formula that works best only for small values of the relative systematic uncertainty, for which the modification of Currie׳s method is the least necessary, and that it significantly overestimates the detection limit or gives infinite or otherwise non-physical results for larger systematic uncertainties where such a correction would be the most useful. We have developed an alternative approach for calculating detection limits based on realistic statistical modeling of the counting distributions which accurately represents statistical and systematic uncertainties. Instead of a closed form solution, numerical and iterative methods are used to evaluate the result. Accurate detection limits can be obtained by this method for the general case. [ABSTRACT FROM AUTHOR]

Performance characteristics of the megavoltage photon dose measurements with EPR and table sugar were analyzed. An advantage of sugar as a dosimetric material is its tissue equivalency. The minimal detectable dose was found to be 1.5 Gy for both the 6 and 18 MV photons. The dose response curves are linear up to at least 20 Gy. The energy dependence of the dose response in the megavoltage energy range is very weak and probably statistically insignificant. Reproducibility of measurements of various doses in this range performed with the peak-to-peak and double-integral methods is reported. The method can be used in real-time dosimetry in radiation therapy. [ABSTRACT FROM AUTHOR]

To develop in situ NaI(Tl) detector for radioactivity measurement in the marine environment, the Monte Carlo N-Particle (MCNP) Transport Code was utilized to simulate the measurement of NaI(Tl) detector immersed in seawater, taking into account the material and geometry of the detector, and the interactions between the photons with the atoms of the seawater and the detector. The simulation results of the marine detection efficiency and distance were deduced and analyzed. In order to test their reliability, the field measurement was made at open sea and the experimental value of the marine detection efficiency was deduced and seems to be in good agreement with the simulated one. The minimum detectable activity for 137 Cs in the seawater of NaI(Tl) detector developed was determined mathematically at last. The simulation method and results in the paper can be used for the better design and quantitative calculation of in situ NaI(Tl) detector for radioactivity measurement in the marine environment, and also for some applications such as the installation on the marine monitoring platform and the quantitative analysis of radionuclides. [ABSTRACT FROM AUTHOR]

In case of a nuclear emergency, many samples need to be measured in a short time period. Therefore, it is of vital importance to have a quick and reliable (screening)method. Most methods to determine total beta activity are time-consuming because of extensive sample preparation, such as ashing. In this article three different rapid screening methods for beta emitting nuclides in agriculture, livestock and fishery products were tested and compared to each other, and to an accurate but more time consuming reference method. The goal was to find the method with the optimal trade-off between accuracy, speed and minimal detectable activity (MDA). All of the methods rely on liquid scintillation counting (LSC) or Cerenkov counting, and differ mainly in sample preparation. For matrices with little or no colour, the direct LSC-method is the most accurate and fastest option, while for darker coloured samples this method is not suitable because of high colour quenching. For such samples, two additional methods using a microwave digestion during sample preparation, produced good results. [ABSTRACT FROM AUTHOR]

A new method of directly measuring 222Rn progeny in a worker′s lung using a lung counting system is introduced. To determine the efficiency of the lung counting system, a torso phantom manufactured by the China Institute for Radiation Protection was used, where activated carbon that had been loaded in a radon chamber with a defined quantity of radon represented the lungs, which were usually made of urethane foam. The minimum detectable activity (MDA) of 214Bi, one of the 222Rn progenies, was estimated to be 7.3 Bq for a measurement time of 4000 s. Based on the time 222Rn progenies stay in the lung, it may be concluded that the lung counting system described can be well used for directly measuring the activity of 214Bi in the lung short time after a worker inhaled 222Rn at his/her workplace. [ABSTRACT FROM AUTHOR]

In the European registration procedure for pesticides, microcosm and mesocosm studies are the highest aquatic experimental tier to assess their environmental effects. Evaluations of microcosm/mesocosm studies rely heavily on no observed effect concentrations (NOECs) calculated for different population-level endpoints. Ideally, a power analysis should be reported for the concentration-response relationships underlying these NOECs, as well as for measurement endpoints for which significant effects cannot be demonstrated. An indication of this statistical power can be provided a posteriori by calculated minimum detectable differences (MDDs). The MDD defines the difference between the means of a treatment and the control that must exist to detect a statistically significant effect. The aim of this paper is to expand on the Aquatic Guidance Document recently published by the European Food Safety Authority (EFSA) and to propose a procedure to report and evaluate NOECs and related MDDs in a harmonised way. In addition, decision schemes are provided on how MDDs can be used to assess the reliability of microcosm/mesocosm studies and for the derivation of effect classes used to derive regulatory acceptable concentrations. Furthermore, examples are presented to show how MDDs can be reduced by optimising experimental design and sampling techniques. [ABSTRACT FROM AUTHOR]

The determination of the effective minimum detectable activity (MDA) of radionuclides by a detection system plays an important role in environmental radiation monitoring. In this study, the responses of an NaI(Tl) airborne γ ray spectrometry (AGRS) system to different radionuclides (Cs and I) were investigated using the Monte Carlo technique. The MDA values were determined under different conditions according to the counting spectra obtained from the Monte Carlo simulation. The equivalent mass thickness method was applied to the Monte Carlo modeling for monitoring ground radiation to reduce statistical uncertainty. The secondary source method was used to monitor both air and ground radiation. A quadratic relationship was found between the MDA and activity concentration. An exponential relationship was found between the MDA and altitude. The MDA of a specific radionuclide from external detectors was found to be superior to that obtained from internal detectors under the same conditions. The MDA values in an NaI(Tl) AGRS system under different conditions can be estimated based on the results of this study. [ABSTRACT FROM AUTHOR]

Abstract: The ability to quantify isotopic ratios of 135, 133m, 133 and 131m radioxenon is essential for the verification of the Comprehensive Nuclear-Test Ban Treaty (CTBT). In order to improve detection limits, CEA has developed a new on-site setup using photon/electron coincidence (Le Petit et al., 2013. J. Radioanal. Nucl. Chem., DOI : 10.1007/s 10697-013-2525-8.). Alternatively, the electron detection cell equipped with large silicon chips (PIPS) can be used with HPGe detector for laboratory analysis purpose. This setup allows the measurement of β/γ coincidences for the detection of 133Xe and 135Xe; and K-shell Conversion Electrons (K-CE)/X-ray coincidences for the detection of 131mXe, 133mXe and 133Xe as well. Good energy resolution of 11keV at 130keV and low energy threshold of 29keV for the electron detection were obtained. This provides direct discrimination between K-CE from 133Xe, 133mXe and 131mXe. Estimation of Minimum Detectable Activity (MDA) for 131mXe is in the order of 1mBq over a 4 day measurement. An analysis of an environmental radioxenon sample using this method is shown. [Copyright &y& Elsevier]

Abstract: Liquid scintillation counting (LSC) is the most commonly used technique for measuring tritium. To optimize tritium analysis in waters by ultra-low background liquid scintillation spectrometer Quantulus 1220 the optimization of sample/scintillant ratio, choice of appropriate scintillation cocktail and comparison of their efficiency, background and minimal detectable activity (MDA), the effect of chemi- and photoluminescence and combination of scintillant/vial were performed. ASTM D4107-08 (2006) method had been successfully applied in our laboratory for two years. During our last preparation of samples a serious quench effect in count rates of samples that could be consequence of possible contamination by DMSO was noticed. The goal of this paper is to demonstrate development of new direct method in our laboratory proposed by Pujol and Sanchez-Cabeza (1999), which turned out to be faster and simpler than ASTM method while we are dealing with problem of neutralization of DMSO in apparatus. The minimum detectable activity achieved was 2.0Bql−1 for a total counting time of 300min. In order to test the optimization of system for this method tritium level was determined in Danube river samples and also for several samples within intercomparison with Ruđer Bošković Institute (IRB). [Copyright &y& Elsevier]

Abstract: An HPGe gamma-ray spectrometry system for radioxenon isotopes detection has been developed. The system was comprised of two low-energy planar HPGe detectors that were horizontally and oppositely placed, and a gas source cell made of carbon fiber in both sides was used. The spectra obtained simultaneously by the two HPGe detectors were analyzed by summing spectrum method. After the radioactive concentration of 133Xe was determined with three internal gas proportional counters, the efficiency of 81keV gamma-ray for 133Xe was calibrated to be 0.50 (1), and the Minimum Detectable Activity (MDA) for 133Xe detection was determined to be 10mBq during 1 day measurement time. Finally, the system was applied in atmospheric 133Xe monitoring at Xi'an of China after the Fukushima nuclear accident. [Copyright &y& Elsevier]

Background The Child Health Questionnaire (CHQ) is a widely used instrument for measuring health-related quality of life covering both the physical and psychosocial domain. This study examined the responsiveness of the Dutch CHQ 50-item Parent Form ( PF50) in a sample of adolescents with chronic non-specific pain and/or fatigue. Method Five different methods were used to calculate the responsiveness for the physical ( PhS) and psychosocial ( PsS) subscale of the CHQ-50: standardized response mean ( SRM), pooled effect sizes ( ESs), standard error of measurement of agreement ( SEMagreement), minimal detectable change ( MDC) and the area under the receiver operating characteristics ( ROC) curve. For data analysis, the population was divided into two groups based on the parent's global perceived effect of treatment: a changed group (A) and an unchanged group (B). Results The responsiveness analyses were performed including 92 adolescents (88.0% girls; mean age 16.4 years). The SRMs are 2.89 and 1.01 for the PhS and PsS, respectively. Large ESs are found for group A ( PhS = 3.30; PsS = 1.16). The method used for calculating SEMagreement results in a score of PhS = 18.92 and PsS = 11.39. The MDCs of PhS and PsS are 52.45 and 31.57, respectively. The area under the ROC curve ( AUC) for PhS = 0.79 and for PsS = 0.64, and the corresponding optimal cut-off points are 21.1 and 7.0. Conclusion Using the methods SRM, ES and AUC, the responsiveness of the CHQ- PF50 in adolescents with non-specific chronic pain or fatigue treated in a rehabilitation clinic is adequate for the physical scale and moderate for the psychosocial scale. [ABSTRACT FROM AUTHOR]

The analysis of 226Ra, 232Th and 40K radionuclides has been carried out in geothermal water and residue samples collected from six wells of geothermal power plant and disposal site, using gamma-spectrometry system equipped with a high-purity germanium detector. The activity concentrations of nine geothermal water samples were found to be lower than minimum detectable activity (MDA) values. The activity concentration of the residue samples ranged from 40±4 to 2694±85 Bq kg−1 for 226Ra, 33±4 to 2388±85 Bq kg−1 for 232Th, and MDA value to 967±30 Bq kg−1 for 40K. In the study, some radiological indexes were examined and found to be higher than the reference values for majority of the residue samples. The annual effective doses arising from some residue samples were calculated to be higher than the permitted dose rate for the public, i.e. 1 mSv y−1. [ABSTRACT FROM PUBLISHER]

Abstract: The purpose of the present study was to examine test-retest reliability and minimal detectable change (MDC) values for Achilles tendon (AT) length determined using panoramic ultrasound (US) imaging. Seventeen men (age = 21.0 ± 2.3 y) visited the laboratory on two separate days, where AT length was examined along the mid-longitudinal axis of the right lower leg with a portable B-mode panoramic US device. These measures were found to have acceptable reliability with intra-class correlation coefficient (ICC) and standard error of measurement (SEM) values of 0.954 and 4.43 mm (SEM% of the mean = 2.37%), respectively. In addition, the MDC for the panoramic US assessment of AT length was 12.27 mm (MDC% of the mean = 6.57%). These findings suggest that panoramic US imaging is a reliable technique for detection of clinically relevant changes in AT length and may therefore be a practical and time-efficient clinical tool for future studies examining AT length in vivo. [Copyright &y& Elsevier]

The influence of electron-phonon interaction on the shape of the optically stimulated luminescence decay curve of AlO:C has been studied using thermally assisted optically stimulated luminescence (TA-OSL). The minimum detectable dose (MDD) of a phosphor depends on the standard deviation of the background signal which affects the signal-to-noise ratio. The standard deviation of the background signal reduces at lower stimulation light intensity while the readout time increases. Further, measurement at higher temperature enhances the OSL signal with faster decay due to the temperature dependence of photo-ionization cross-section. To achieve the same decay constant and more signal, the temperature of measurement was raised. As a result of lowering the stimulation in-tensity at higher temperature (85°C) the overall MDD of α-AlO:C was found to improve by 1.8 times. For extension of dose linearity in higher range, deeper traps were studied by simultaneous application of CW-OSL and thermal stimulation up to 400°C, using a linear heating rate of 4K/s. By using this method, two well defined peaks at 121°C and 232°C were observed. These TA-OSL peaks have been correlated with two deeper defects which can be thermally bleached at 650°C and 900°C respectively. These deeper defects are stable up to 500°C, so they can store absorbed dose information even if the sample is inadvertently exposed to light or heat. The dose vs. TA-OSL response from deep traps of α-AlO:C was found to be linear up to 10 kGy, thus extending its application for high dose dosimetry. [ABSTRACT FROM AUTHOR]

The Minimum Detectable Activity (MDA) reduction and Compton continuum suppression were performed using portable High-purity Germanium (HPGe) and annular NaI(TI) detectors. In this research, instead of using timing and coincidence electronic modules, the list mode data acquisition was used. This method was very simple but the results was attractive. In the list mode data acquisition technique, the Multiparameter Analyzer (MPA) recorded the time stamp of each event, and the coincidence spectrum can be replayed for a specific coincidence window. Using this method, there is no need for the further data acquisition and by one-time data acquisition, we can replay data for another coincidence time. The suppression factor (SF) for the high-volume standard air filter sample was estimated to be 2.9 while the amount of MDA reduction for this sample was about 30%. • List mode data acquisition technique was very simple for background reduction. • The internal timing circuit of MPA was used to detect coincident events. • The simple method was proposed for minimum detectable activity (MDA) reduction. • The suppression factor (SF) in the high-volume air filter sample was calculated. • Using this technique to identify the low-radioactivity radionuclides. [ABSTRACT FROM AUTHOR]

Abstract: In this study, to improve the problem of waiting for the growth of 90Y for Cerenkov counting and save the time of 90Sr analysis, an organic cocktail sample was counted by a liquid scintillation counting system immediately after the purification of 90Sr without waiting for the growth of 90Y. The chemical separation and the measurement procedures for 90Sr radioactivity analysis can be completed in 24h. In order to verify the performance of the improved method, the activity of 90Sr in six environmental reference samples was determined after radiochemical purification with a crown-ether resin column, and subsequent measurement by both the Cerenkov and the organic cocktail liquid scintillation counting methods. The results revealed that the organic cocktail liquid scintillation counting was quicker and had higher efficiency and lower minimum detectable activity (MDA) than the Cerenkov counting. [Copyright &y& Elsevier]

Abstract: The determination of low level activities of natural radionuclides from the uranium and thorium series by gamma-spectrometry faces the problem of proper natural background subtraction. Background fluctuation can cause differences in activity determination. Also the minimum detectable activity (MDA) of natural and artificial radionuclides can be influenced by background fluctuation. In this paper, results of the background fluctuation of shielded HPGe detectors with relative efficiency of 50–150% are presented together with the assessment of its influence on the determination of natural and artificial radionuclides. [Copyright &y& Elsevier]

Abstract: 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 1×10−4 Bqcm−3 for 1min counting, which is one tenth of the legal limit for the radiation controlled areas in Japan. [Copyright &y& Elsevier]

Abstract: To realise radioactive environmental reference materials in Taiwan, seven environmental materials of soil, water, vegetation, meat, airborne particles (filter paper), milk and mushroom samples that are frequently encountered were used to establish the preparation of the reference materials. These seven environmental materials were collected, checked for freedom from radioactivity and prepared according to their properties. The preparation was carried out by using activity about 10–100 times that of the minimum detectable activity (MDA) in routine measurements in the radioactive standard used to spike the inactive material and this standard is traceable to national ionising radioactivity standards (TAF, 2004). To demonstrate sample traceability to the added standard, each sample was carefully measured and its uncertainty evaluated. Based on the recommendations of ISO Guide 35 for evaluation of reference materials and with the above assessment and verification procedures, the uncertainties (k=1) of the spike activity used in making reference materials were: 60Co≤4.6%, 134Cs≤4.7%, 137Cs≤5.0%, total β≤0.6% and 3H≤1.3%. [Copyright &y& Elsevier]

Purpose: In this work, the authors aim for the estimation of the effect of 176Lu intrinsic radioactivity on the performance of a dual head PET system dedicated to small animal imaging. Methods: A prototype camera has been used as a reference system in order to validate two GATE simulation models, which were used for the investigation. The first model includes the 176Lu intrinsic radioactivity, while the second does not. The two models have been designed in order to provide similar sensitivities, in terms of count rate performance and scatter fraction, in the linear range of activities. In addition, the model with the 176Lu intrinsic radioactivity, has been validated in terms of background count rate. Different acquisition schemes have been examined in order to determine the optimum conditions to minimize the 176Lu effects, while maintaining a high trues count rate. In addition, the effect on the image quality, in terms of spatial resolution, signal-to-noise ratio, and minimum detectable activity, was investigated. Results: Both models are in good agreement with the measured data. While, the presence of the 176Lu altered the dead time of the model, it also affected the singles, trues, and randoms count rates. The noise equivalent count rate curves of the two models indicate that for low activities, the lack of 176Lu radioactivity leads to better noise properties due to the underestimation of the randoms. Signal-to-noise ratio measurement on coincidence images confirm the aforementioned claim, since the model without the 176Lu provides better less noisy images. Furthermore, the spatial resolution and the minimum detectable activity are overestimated. Conclusions: It has been proven that the lack of the 176Lu intrinsic radioactivity has an impact on the design of the simulation model's dead time. Even if there is an alignment with experimental results still the noise properties, for a wide range of activities, are overestimated. In addition, for low activities, better image quality, is presented, mainly due to the lack of the 176Lu photons which blur the images. Furthermore, it was shown that the use of a high hardware threshold allows the application of a wide energy window, which improves the statistics without a significant compromise on the quality of the detected photons, mainly, due to the early rejection of the low energy photons and the low scatter factor. [ABSTRACT FROM AUTHOR]

A new method for the determination of radiostrontium in seawater samples has been developed at the Savannah River National Laboratory (SRNL) that allows rapid pre-concentration and separation of strontium and yttrium isotopes in seawater samples for measurement. The new SRNL method employs a novel and effective pre-concentration step that utilizes a blend of calcium phosphate with iron hydroxide to collect both strontium and yttrium rapidly from the seawater matrix with enhanced chemical yields. The pre-concentration steps, in combination with rapid Sr Resin and DGA Resin cartridge separation options using vacuum box technology, allow seawater samples up to 10 L to be analyzed. The total Sr + Sr activity may be determined by gas flow proportional counting and recounted after ingrowth of Y to differentiate Sr from Sr. Gas flow proportional counting provides a lower method detection limit than liquid scintillation or Cerenkov counting and allows simultaneous counting of samples. Simultaneous counting allows for longer count times and lower method detection limits without handling very large aliquots of seawater. Seawater samples up to 6 L may be analyzed using Sr Resin for Sr and Sr with a minimum detectable activity (MDA) of 1-10 mBq/L, depending on count times. Seawater samples up to 10 L may be analyzed for Sr using a DGA Resin method via collection and purification of Y only. If Sr and other fission products are present, then Y (beta energy 1.55 MeV, 58.5 day half-life) is also likely to be present. Y interferes with attempts to collect Y directly from the seawater sample without initial purification of Sr isotopes first and Y ingrowth. The DGA Resin option can be used to determine Sr, and if Y is also present, an ingrowth option with using DGA Resin again to collect Y can be performed. An MDA for Sr of <1 mBq/L for an 8 h count may be obtained using 10 L seawater sample aliquots. [ABSTRACT FROM AUTHOR]

Abstract: We describe a new approach for the detection and identification of actinides at low activity levels directly in aqueous solution. The measurement consists initially, in immobilizing alpha emitters in the form of insoluble hydroxides onto the entrance window of an immersed alpha particles detector. For this, a boron doped diamond detector window is negatively polarized to produce a basic layer on its surface by water decomposition. Actinides elements that are known to be very sensitive to hydrolysis are precipitated as solid hydroxides onto the entrance window of the sensor. Due to the absence of an air layer between the radioactive source and the detector, there is no need for vacuum during the alpha spectrometry measurement. After analysis, the detector can be easily cleaned by anodization in the aqueous medium to be reused at once. The minimum detectable activity concentration (MDA) of the system has been evaluated with 241Am at 0.5Bq/L for a 0.33cm2 area Si PIN diode. [Copyright &y& Elsevier]

Highlights: [•] A two-groups reliability study of fall-related gait variables in older fallers. [•] Reliability estimates were reported for single- and dual-task gait conditions. [•] Gait variability measures were consistently associated with higher measurement error. [•] Larger minimal detectable change values were found for all variables under dual-task. [•] Consider gait variability measures cautiously as evaluative outcomes at patient level. [Copyright &y& Elsevier]

This section presents charts and graphical representations of micromachine activities, including the schematic of a microreactor in the microfluidic scMDA chip, amplification factors from microscale and macroscale MDA reactions, and lysis protocols for Synechocystis sp. PCC 6803 and their effects.

In many polarimetry applications, including observations in the X-ray band, the measurement of a polarization signal can be reduced to the detection and quantification of a deviation from uniformity of a distribution ofmeasured angles of the form A + B cos2(ϕ − ϕ0) (0 < ϕ < π). We explore the statistics of such polarization measurements usingMonte Carlo simulations and χ2 fitting methods.We compare our results to those derived using the traditional probability density used to characterize polarization measurements and quantify how they deviate as the intrinsic modulation amplitude grows.We derive relations for the number of counts required to reach a given detection level (parameterized by β the "number of σ' s" of the measurement) appropriate for measuring the modulation amplitude a by itself (single interesting parameter case) or jointly with the position angle ϕ (two interesting parameters case). We show that for the former case, when the intrinsic amplitude is equal to the well-known minimum detectable polarization, (MDP) it is, on average, detected at the 3σ level. For the latter case, when one requires a joint measurement at the same confidence level, then more counts are needed than what was required to achieve the MDP level. This additional factor is amplitude-dependent, but is ≈2.2 for intrinsic amplitudes less than about 20%. It decreases slowly with amplitude and is ≈1.8 when the amplitude is 50%.We find that the position angle uncertainty at 1σ confidence is well described by the relation σϕ = 28◦.5/β. [ABSTRACT FROM AUTHOR]

Gross alpha and beta activities were determined in seawater and plankton samples collected during the wet and dry seasons from 10 different sampling stations in Chonburi, the Upper Gulf of Thailand. Seawater samples were sampling, 1 km from the coastal and 2 m below the water surface, during July 2008 to July 2009. Seawater samples were prepared by coprecipitation technique. Plankton samples were prepared by filtration and dryness on filter paper. Both types of samples were counted using a low background alpha/beta proportional counter with multiple detector type (Berthold LB770). The results showed that gross alpha activities in seawater and plankton sample are in the range of 0.0591 ± 0.0209-0.3914 ± 0.0606 Bq/l and 0.0029 ± 0.0020-0.0294 ± 0.0043 Bq/l, respectively and also showed the lowest and highest activity level in the same sampling time. The activities of gross beta in seawater and plankton sample are in the range of 0.2803 ± 0.0177-1.3064 ± 0.0319 Bq/l and 0.0208 ± 0.0123-0.9151 ± 0.0262 Bq/l, respectively. Minimum detectable activity (MDA) had been observed in the measurements. The MDA of seawater sample were estimated to be 0.0832 Bq/l for alpha and 0.0577 Bq/l for beta at counting time of 100 and 200 min, respectively. In plankton samples, the MDA were estimated to be 0.0053 Bq/l for alpha and 0.0409 Bq/l for beta at the same counting time of 250 min. [ABSTRACT FROM AUTHOR]

Abstract: This article describes a conglomerate measure of gait variability based on nine spatiotemporal parameters: the Gait Variability Index (GVI). Concurrent validity, inter-session reliability and minimum detectable change (MDC) were evaluated in 31 patients with Friedreich's Ataxia (FRDA), through comparisons with classically used evaluation tools such as the International Cooperative Ataxia Rating Scale (ICARS). GVI scores for the healthy population were 100.3±8.6 and were significantly reduced in FRDA patients (70.4±7.9). The GVI was correlated with the global ICARS score and was sensitive enough to differentiate between groups of FRDA patients categorized by the Posture and Gait Disturbances sub-score. The GVI was found to have a high inter-session reliability with an intraclass correlation coefficient of 0.91. A MDC of 8.6 points was found necessary to ensure that a change in GVI reflects a true change rather than measurement error. The GVI provides a quantitative measure of variability which behaves well statistically in both HP and patients with FRDA. It can be easily implemented using the supplemental data provided with this article. Complementary work is necessary to strengthen the GVI validation. [Copyright &y& Elsevier]

Abstract: A detailed analysis is presented of background radiation spectra for a high-resolution gamma-ray spectrometer used to measure environmental radioactivity, for various shielding configurations. The main goal is to improve the detection limits of low-level activity measurements by reducing the background as much as possible. Passive shielding configurations are used to decrease the total background counting rate by adding new layers. Subsequently, for the maximum shielding configuration, the Minimum Detectable Activity (MDA) is improved by at least 13-fold for 137Cs, 8-fold for 214Bi (609.31keV), 7-fold for 40K and 5.5-fold for 208Tl (2614.53keV). A reduction factor of 240 for the 137Cs peak (counting rate) at maximum shielding and an insignificant peak for this radionuclide was determined. For other radionuclides, peaks below the detection limit of the detector system were also found. These results show that the shielding was successful in reducing and removing peaks from the background spectrum. [Copyright &y& Elsevier]

The Currie formulation for minimum detectable activity (MDA) has served for decades as the standard method for estimating radiological detection limits-it is simple and statistically defendable. It does, however, lack a means to account for the effects of systematic uncertainties. In recent years we have seen various efforts to incorporate systematic uncertainties into an MDA framework. Perhaps most notable of these is the recent ISO standard 11929 for the determination of characteristic limits in ionizing radiation measurements. This standard brings a Bayesian perspective to the problem of characteristic limits in radiation measurements that are in many ways both welcome and long overdue. In this paper, however, we note some apparent drawbacks to the ISO 11929 approach. Namely, for small values of the systematic uncertainty the correction it makes to the Currie MDA is negligible, while for large systematic uncertainties the calculated MDA values can become infinite. In between these two extremes, the user has little basis for evaluating the reliability of the result. To address these issues, we consider the problem from a new approach, developing a straightforward phenomenological statistical model of the MDA that treats systematic uncertainties explicitly. We compare predictions from our model with results of the ISO 11929 formulation as well as the traditional Currie approach. Finally, some recommendations for alternative handling of the MDA in the face of significant systematic uncertainties are presented. [ABSTRACT FROM AUTHOR]

We developed a new method for the determination of Ac in geological samples. The method uses extraction chromatographic techniques and alpha-spectrometry and is applicable for a range of natural matrices. Here we report on the procedure and results of the analysis of water (fresh and seawater) and rock samples. Water samples were acidified and rock samples underwent total dissolution via acid leaching. A DGA ( N, N, N′, N′-tetra- n-octyldiglycolamide) extraction chromatographic column was used for the separation of actinium. The actinium fraction was prepared for alpha spectrometric measurement via cerium fluoride micro-precipitation. Recoveries of actinium in water samples were 80 ± 8 % (number of analyses n = 14) and in rock samples 70 ± 12 % ( n = 30). The minimum detectable activities (MDA) were 0.017-0.5 Bq kg for both matrices. Rock sample Ac activities ranged from 0.17 to 8.3 Bq kg and water sample activities ranged from below MDA values to 14 Bq kgof Ac. From the analysis of several standard rock and water samples with the method we found very good agreement between our results and certified values. [ABSTRACT FROM AUTHOR]

This work analyzes the optimal combination between HPGe detectors and sample geometries that result in the lowest Minimum Detectable Activities (MDA) for a given type of shielding. The minimum MDA for a set of nuclides is the criteria to optimize the HPGe detector and the sample geometry. The analysis is made on a large set of detectors of different sizes, p-n junction configuration and aspect ratio available from Canberra Industries Inc., whose response has been characterized with the In-Situ Object Counting System (ISOCS) software. Background spectra in two standard shielding configurations have been acquired and a spectra library has been assembled. This offers the extended capability to establishing the optimal detector for a given application, before purchasing the detector. For each detector, the absolute efficiency is calculated for various sample geometries using ISOCS and an interface that uses the standard Genie2000 spectroscopy software engine. We present two comparisons, one of a coaxial detector and a Broad Energy Ge detector (BEGe) a.k.a planar point contact detector of the same relative efficiency, and comparison of two coaxial detectors of different relative efficiency. The preliminary conclusion is that a larger detector with more efficiency is not always the best choice for the given measurement geometry. Instead, the optimal matching of the detector size with measurement geometry provides the best experimental and economical solution. [ABSTRACT FROM PUBLISHER]

This paper and the accompanying tool are intended to complement existing supports for conducting power analysis tools by offering a tool based on the framework of Minimum Detectable Effect Sizes (MDES) formulae that can be used in determining sample size requirements and in estimating minimum detectable effect sizes for a range of individual- and group-random assignment design studies and for common quasi-experimental design studies. The paper and accompanying tool cover computation of minimum detectable effect sizes under the following study designs: individual random assignment designs, hierarchical random assignment designs (2-4 levels), block random assignment designs (2-4 levels), regression discontinuity designs (6 types), and short interrupted time-series designs. In each case, the discussion and accompanying tool consider the key factors associated with statistical power and minimum detectable effect sizes, including the level at which treatment occurs and the statistical models (e.g., fixed effect and random effect) used in the analysis. The tool also includes a module that estimates for one and two level random assignment design studies the minimum sample sizes required in order for studies to attain user-defined minimum detectable effect sizes. [ABSTRACT FROM PUBLISHER]

In a food-rewarded two-alternative forced-choice procedure, it was determined how well the weakly electric elephantnose fish Gnathonemus petersii can sense gaps between two objects, some of which were placed in front of complex backgrounds. The results show that at close distances, G. petersii is able to detect gaps between two small metal cubes (2 cm × 2 cm × 2 cm) down to a width of c. 1·5 mm. When larger objects (3 cm × 3 cm × 3 cm) were used, gaps with a width of 2-3 mm could still be detected. Discrimination performance was better ( c. 1 mm gap size) when the objects were placed in front of a moving background consisting of plastic stripes or plant leaves, indicating that movement in the environment plays an important role for object identification. In addition, the smallest gap size that could be detected at increasing distances was determined. A linear relationship between object distance and gap size existed. Minimal detectable gap sizes increased from c. 1·5 mm at a distance of 1 cm, to 20 mm at a distance of 7 cm. Measurements and simulations of the electric stimuli occurring during gap detection revealed that the electric images of two close objects influence each other and superimpose. A large gap of 20 mm between two objects induced two clearly separated peaks in the electric image, while a 2 mm gap caused just a slight indentation in the image. Therefore, the fusion of electric images limits spatial resolution during active electrolocation. Relative movements either between the fish and the objects or between object and background might improve spatial resolution by accentuating the fine details of the electric images. [ABSTRACT FROM AUTHOR]

New analytical methods developed at the facilities here, based on two ultra-sensitive mass spectrometry (MS) techniques, inductively coupled plasma sector field mass spectrometer with a desolvator system (Aridus-ICP-SFMS) and accelerator MS (AMS), have been applied in this work for the reassessment of 239Pu in alpha spectrometry (AS) planchets corresponding to spiked human urine samples. The obtained 239Pu minimum detectable activities (MDAs) values by Aridus-ICP-SFMS and AMS were 3 fg (∼6.92 µBq) and 0.4 fg (∼0.92 µBq), respectively, per sample, which are much better than those attainable by AS [50 fg (∼115.3 µBq) of 239Pu per sample, approximately]. Therefore, it is demonstrated that the MS techniques employed in this work are very powerful tools for internal dosimetry studies in human urine samples, giving excellent results when the reassessment of AS planchets is needed (samples with a Pu concentration below or at the MDA levels measurable by AS). This work is the continuation of an article published in J. Anal. At. Spectrom. 25 (1410–1415) 2010. [ABSTRACT FROM AUTHOR]

This study explores the possibility of developing a field-deployable 90Sr detector for rapid lung counting in emergency situations. The detection of beta-emitters 90Sr and its daughter 90Y inside the human lung via bremsstrahlung radiation was performed using a 3″ × 3″ NaI(Tl) crystal detector and a polyethylene-encapsulated source to emulate human lung tissue. The simulation results show that this method is a viable technique for detecting 90Sr with a minimum detectable activity (MDA) of 1.07 × 104 Bq, using a realistic dual-shielded detector system in a 0.25-µGy h−1 background field for a 100-s scan. The MDA is sufficiently sensitive to meet the requirement for emergency lung counting of Type S 90Sr intake. The experimental data were verified using Monte Carlo calculations, including an estimate for internal bremsstrahlung, and an optimisation of the detector geometry was performed. Optimisations in background reduction techniques and in the electronic acquisition systems are suggested. [ABSTRACT FROM AUTHOR]

This study described the performance of an array of high-purity Germanium detectors, designed with two different end cap materials—steel and carbon fibre. The advantages and disadvantages of using this detector type in the estimation of the minimum detectable activity (MDA) for different energy peaks of isotope 152Eu were illustrated. A Monte Carlo model was developed to study the detection efficiency for the detector array. A voxelised Lawrence Livermore torso phantom, equipped with lung, chest plates and overlay plates, was used to mimic a typical lung counting protocol with the array of detectors. The lung of the phantom simulated the volumetric source organ. A significantly low MDA was estimated for energy peaks at 40 keV and at a chest wall thickness of 6.64 cm. [ABSTRACT FROM AUTHOR]

A new radio spectropolarimeter for solar radio observation has been developed at Tohoku University and installed on the Iitate Planetary Radio Telescope (IPRT) at the Iitate observatory in Fukushima prefecture, Japan. This system, named AMATERAS ( the Assembly of Metric-band Aperture TElescope and Real-time Analysis System), enables us to observe solar radio bursts in the frequency range between 150 and 500 MHz. The minimum detectable flux in the observation frequency range is less than 0.7 SFU with an integration time of 10 ms and a bandwidth of 61 kHz. Both left and right polarization components are simultaneously observed in this system. These specifications are accomplished by combining the large aperture of IPRT with a high-speed digital receiver. Observational data are calibrated and archived soon after the daily observation. The database is available online. The high-sensitivity observational data with the high time and frequency resolutions from AMATERAS will be used to analyze spectral fine structures of solar radio bursts. [ABSTRACT FROM AUTHOR]

Tritium activity concentration were monitored in monthly precipitation at five locations in Serbia (Meteorological Station of Belgrade at Zeleno Brdo, Vinča Institute of Nuclear Sciences, Smederevska Palanka, Kraljevo and Niš) over 2005, using electrolytic enrichment and liquid scintillation counting. The obtained concentrations ranged from 3.36 to 127.02 TU. The activity values obtained in samples collected at Zeleno Brdo were lower or close to the minimum detectable activity (MDA), which has a value of 3.36 TU. Significantly higher tritium levels were obtained in samples collected in Vinča Institute of Nuclear Sciences compared with samples from the other investigated locations. Amount of precipitation were also recorded. A good linear correlation (r = 0.75) for Zeleno Brdo and VINS between their tritium activity was obtained. It was found that the value of the symmetrical index n (which indicates the magnitude of tritium content changes with time (months) through its second derivative) is the highest for Vinča Institute of Nuclear Sciences compared to other locations, which is in accordance with the fact that the highest concentrations of tritium were obtained in the samples from the cited place. [ABSTRACT FROM AUTHOR]

A newly designed Pb(II) potentiometric sensor based on intrinsically conducting nanoparticles of solid poly(aniline-co-2-hydroxy-5-sulfonic aniline) possessing many ligating functional groups like -NH-, -N=, -OH, -SO3H, -NH3 as ionophores in plasticizer-free vinyl resin solid membranes has been fabricated. A linear Nernstian response is obtained within a wide Pb(II) activity range from 1.0 x 10-3 to 1.0 x 10-10 M with a detection limit as low as 2.2 x 10-11 M. The pH independent plateau ranges between 3.5 and 7.0. After 15 months' usage, the sensor maintains 95% performance parameters. Its anti-interference ability to Cu(II), Cd(II), Ag(I), and Hg(II) is much stronger than other sensors with a detection limit at (sub)nanomolar level. Electrochemical impedance spectroscopy reveals that the solid sensing membrane has a diffusion coefficient of around 5 x 10-14 to 1 x 10-13 cm² s-1. The much lower diffusion coefficient for Pb(II) is highly beneficial for the elimination of Pb(II) flux across the membrane. The wide detection concentration range, low detection limit, high selectivity, extensive pH window, and long lifetime make for a robust sensor giving reliable measurement of Pb(II) content with potential application in real-world samples at trace levels. [ABSTRACT FROM AUTHOR]

The performance of the ORTEC® Detective™ as a field deployable tool for emergency urine bioassay of 137Cs, 60Co, 192Ir, 169Yb and 75Se was evaluated against ANSI N13.30. The tested activity levels represent 10 % RL (reference level) and 1 % RL defined by [Li C., Vlahovich S., Dai X., Richardson R. B., Daka J. N. and Kramer G. H. Requirements for radiation emergency urine bioassay techniques for the public and first responders. Health Phys (in press, 99(5), 702–707 (2010)]. The tests were conducted for both single radionuclide and mixed radionuclides at two geometries, one conventional geometry (CG) and one improved geometry (IG) which improved the MDAs (minimum detectable amounts) by a factor of 1.6–2.7. The most challenging radionuclide was 169Yb. The measurement of the mixture radionuclides for 169Yb at the CG did not satisfy the ANSI N13.30 requirements even at 10 % RL. At 1 % RL, 169Yb and 192Ir were not detectable at either geometry, while the measurement of 60Co in the mixed radionuclides satisfied the ANSI N13.30 requirements only at the IG. [ABSTRACT FROM PUBLISHER]

Abstract: We investigate the caesium concentrations in soils in mountain areas near Gori nuclear power plant in Korea, focusing on the measurement limits to the 134Cs. In order to lower the minimum detectable amount (MDA) of activity for the 134Cs, we have used the ammonium molybdophosphate (AMP) precipitation method to get rid of the 40K existing in natural radioactivity, which reduces the MDA activity about 10 times smaller than those without the AMP precipitation method. The MDA results for the 134Cs were found to be in the range between 0.015 and 0.044Bq/kg-dry weight. In order to diminish the background, we also have measured a part of the soil samples in Yangyang, a small town in the east coast of Korea. However, it turns out that in order to detect the 134Cs in the samples the MDA should be reduced to the level of mBq/kg-dry weight. [Copyright &y& Elsevier]

Abstract: In the field of space–time adaptive processing (STAP), direct data domain (D3) methods avoid non-stationary training data and can effectively suppress the clutter within the test cell. However, this benefit comes at the cost of a reduced system degree of freedom (DOF), which results in performance loss. In this paper, by exploiting the intrinsic sparsity of the spectral distribution, a new direct data domain approach using sparse representation (D3SR) is proposed, which seeks to estimate the high-resolution space–time spectrum only with the test cell. The simulation of both side-looking and non-side-looking cases has illustrated the effectiveness of the D3SR spectrum estimation using focal underdetermined system solution (FOCUSS) and L1 norm minimization. Then the clutter covariance matrix (CCM) and the corresponding adaptive filter can be effectively obtained. D3SR maintains the full system DOF so that it can achieve better performance of output signal-clutter-ratio (SCR) and minimum detectable velocity (MDV) than current D3 methods, e.g., direct data domain least squares (D3LS). Therefore D3SR can deal with the non-stationary clutter scenario more effectively, where both the discrete interference and range-dependent clutter exists. [Copyright &y& Elsevier]

A simple and economical passive graded shielding which is combination of low and high Z materials for HPGe detector for background radiation minimisation is developed for better identification of the peaks in acquired spectrum by reducing Compton continuum. The present paper discusses the design and advantages of the passive graded shielding (lead + copper + aluminium) which encloses the HPGe detector. The passive graded shielding improved sensitivity of the detector and reduced Minimum Detectable Activity (MDA) for planchet source from 19.6% to 11.7% for gamma photon energies in the range of 81-1408 keV and brought down the MDA, 35.25 GBq d

The effects of the intrinsic activity of lutetium-based scintillators used in PET imaging such as LSO have been well documented and are not usually a concern in most in vivo situations. This activity can, however, become an issue when using a wide energy window or in low count rate scenarios as seen in cell trafficking studies in small animal imaging. To date there has been no systematic validation of Monte Carlo simulations that compare a model of intrinsic ^176Lu activity to measured data, making it difficult to include these effects in simulations of proposed scanners. This work seeks to validate a GATE model of intrinsic ^176Lu activity against results from a bench-top system of two detector modules from a Siemens Inveon preclinical PET system and also against results from a complete Inveon system. The bench-top measurements and simulations agree well in terms of both count rates and energy spectra, with small differences in the photopeak positions at 202 and 307 keV attributed to LSO non-proportionality, which is not modeled. Measurements and simulations for the full Inveon system exhibited similar discrepancies at low energies attributed to LSO non-proportionality as well as non-uniform detector triggering. For energy thresholds above 200 keV the simulation and measurements exhibited good agreement in count rates and energy spectra. Simulations are performed demonstrating the effect of the intrinsic activity on the minimum detectable activity for the Inveon system, demonstrating agreement with previously published measured results. The results demonstrate that this GATE model of ^176Lu activity can be used to accurately simulate the effects of this intrinsic activity in PET systems. [ABSTRACT FROM AUTHOR]

The article offers information on a study which examine the test-retest reliability and minimal detectable change (MDC) applied in the submaximal graded exercise test to measure graded exercise test duration. It says that the study constantly measures the heart rate and duration of the test of the 15 people that participated in the study. It argues that clinicians could use submaximal graded exercise test as an alternative for maximal graded exercise testing.

Purpose: The traditional figures of merit used in the evaluation of positron emission tomography (PET) systems, including system sensitivity and spatial resolution, do not directly reflect the minimum detectable activity (MDA) performance, despite the fact that it is one of the most important tasks for a PET system. MDA, as a combination of the more traditional PET system parameters, is directly related to lesion detection. However, MDA evaluation is task specific and cannot be done by a single measurement. Therefore, a simple method to evaluate system detectability needs to be developed. Methods: In this work, an analytical method of MDA estimation was developed, taking into account system sensitivity, spatial resolution, source properties, and noise propagation in image reconstruction by using the Rose criterion and/or the Curie equation as the detection standard. In the implementation, the source background, as well as the intrinsic activity background from the scintillation material of the system, was also taken into consideration. The accuracy of this method was evaluated in two commercially available preclinical PET systems, with phantom experiments that were designed to closely mimic in vivo tumor uptake without introducing finite boundaries between the source and the background. Results: The lesion contrast-to-noise ratio calculated by the analytical evaluation showed good agreement with that obtained from the experiments. Visual assessment of the reconstructed images at the detection limit (based on analytical evaluation) also was in agreement with the Rose criterion. The MDA performance was quantitatively compared between the two preclinical PET systems and showed different detection limits under different imaging conditions, suggesting that the detection limit of a PET system strongly depends on the lesion properties and acquisition settings. Conclusions: An analytical method of evaluating the PET system detectability was developed and validated by experiments. Overall, the analytical MDA calculation provides a simple way to evaluate the signal detectability of a PET system and can be used for comparing different systems. It also provides guidelines for designing new PET tomographs as well as optimizing data acquisition protocols. [ABSTRACT FROM AUTHOR]

A model of adaptation and visual coding was used to simulate how color appearance might vary among individuals that differ only in their sensitivity to wavelength. Color responses to images were calculated for cone receptors with spectral sensitivities specific to the individual, and in postreceptoral mechanisms tuned to different combinations of the cones. Adaptation was assumed to normalize sensitivity within each cone and postreceptoral channel so that the average response to an ensemble of scenes equaled the mean response in channels defined for the reference observer. Image colors were then rendered from the adapted channels’ outputs. The transformed images provide an illustration of the variations in color appearance that could be attributed to differences in spectral sensitivity in otherwise identical observers adapted to identical worlds, and examples of these predictions are shown for both normal variation (e.g. in lens and macular pigment) and color deficiencies (anomalous trichromacy). The simulations highlight the role that known processes of adaptation may play in compensating color appearance for variations in sensitivity both within and across observers, and provide a novel tool for visualizing the perceptual consequences of any variation in visual sensitivity including changes associated with development or disease. [ABSTRACT FROM AUTHOR]