Search

In radioactivity analysis, counting efficiency(E) and background(to be precise, it should be deterministic background) are usually discussed, but apparent counting efficiency(E') and random background are rarely mentioned. However, the influence of background(including both deterministic background and random background) on apparent counting efficiency must be considered, especially for samples with low radioactivity. The relation between E and E' can be described as the equation E' = E + ΔB/A, where A is the sample radioactivity, and ΔB is the residue background, including two parts: the counting rate of residual deterministic background caused by inaccurate deduction of background and the counting rate of random background that cannot be deducted. In this paper, E' was studied on the following assumptions: E was fixed at 90%; A was changing from 0.1 to 100, with a step of 0.1(relative unit, similarly hereinafter); and ΔB was set to be fixed, or to follow a specific distribution. The simplest continuous distribution(uniform distribution) and the most commonly used continuous distribution(normal distribution) were chosen for this research, and the function “random number generator ” of the software Excel was used to simulate the random variable ΔB. Specifically speaking, the random variable ΔB was assumed to follow ±0.1·U(0,1), ±0.1·U(−0.5,0.5), ±0.1·N(0.5,1), or ±0.1·N(0,1), where U stands for uniform distribution and N for normal distribution. The influence of background on apparent counting efficiencies is divided into two aspects: one is the systematic error introduced by inaccurate background deduction, which makes all apparent counting efficiencies deviate from the counting efficiency in the same direction; the other is the accidental error caused by background fluctuations, which makes apparent counting efficiency fluctuate within a certain range. Regardless of the error type, the influence of background on apparent counting efficiency will increase as the radioactivity of the sample decreases. For samples with high radioactivity, the difference between apparent counting efficiency and counting efficiency is so small that it can be ignored, therefore it is not necessary to distinguish between the two concepts of apparent counting efficiency and counting efficiency; but for samples with low radioactivity, they must be used differently. Unless there is no standard sample with high radioactivity, it is not recommended to use the inefficient method, which is reported in Lin’s paper(ACS Earth Space Chem, 2022, 6(7): 1868-1875), to obtain counting efficiency by measuring a large number of samples with low radioactivity. It is advisable to obtain counting efficiency by measuring standard samples with sufficiently high radioactivity, in which the influence of background can be negligible.

The results of the study of the contributions of the interaction reactions of fast neutron sources of 239Pu-Be and 252Cf to the counting efficiency of registration by oxide scintillators CdWO4, ZnWO4, Bi4Ge3O12 and Gd2SiO5, presented. The amount of gamma quanta per input neutron emitted from final nuclei excited in the reactions of inelastic scattering (n, nʹγ)in, resonant scattering (n, n)res and capture (n, γ)res and radiation capture (n, γ)cap was measured. PMT R1307 operating in single-electron mode was used as a photodetector, the background rate was ~ 5*103 s-1. The measured efficiency ε for scintillators ø40x40 mm was 752 for ZWO, 532 for CWO, 37 for GSO, and 23 for BGO in "counts/neutron" units, measurement error rate ~ 3-5%. The formation of the detector response is influenced by the parameters of the scintillator nuclei, such as the values of the interaction cross sections in the resonance region, the density of nuclear levels of the final nuclei, the lifetime of excited nuclear states, the upper limit of the resonance region of the cross section, as well as the scintillation time and geometric parameters of the scintillators. A phenomenological model of the response of an oxide scintillator to fast neutrons is proposed.

In recent times, ion implantation has received increasing interest for novel applications related to deterministic material doping on the nanoscale, primarily for the fabrication of solid-state quantum devices. For such applications, precise information concerning the number of implanted ions and their final position within the implanted sample is crucial. In this work, we present an innovative method for the detection of single ions of MeV energy by using a sub-micrometer ultra-thin silicon carbide sensor operated as an in-beam counter of transmitted ions. The SiC sensor signals, when compared to a Passivated Implanted Planar Silicon detector signal, exhibited a 96.5% ion-detection confidence, demonstrating that the membrane sensors can be utilized for high-fidelity ion counting. Furthermore, we assessed the angular straggling of transmitted ions due to the interaction with the SiC sensor, employing the scanning knife-edge method of a focused ion microbeam. The lateral dimension of the ion beam with and without the membrane sensor was compared to the SRIM calculations. The results were used to discuss the potential of such experimental geometry in deterministic ion-implantation schemes as well as other applications. [ABSTRACT FROM AUTHOR]

Whole-body counters are widely used to assess internal contamination after a nuclear accident. However, it is difficult to determine radioiodine activity due to limitations in conventional calibration phantoms. Inhaled or ingested radioiodine is heterogeneously distributed in the human body, necessitating time-dependent biodistribution for the assessment of the internal contamination caused by the radioiodine intake. This study aims at calculating counting efficiencies considering the biodistribution of 131I in whole-body counting measurement. Monte Carlo simulations with computational human phantoms were performed to calculate the whole-body counting efficiency for a realistic radioiodine distribution after its intake. The biodistributions of 131I for different age groups were computed based on biokinetic models and applied to age- and gender-specific computational phantoms to estimate counting efficiency. After calculating the whole-body counting efficiencies, the efficiency correction factors were derived as the ratio of the counting efficiencies obtained by considering a heterogeneous biodistribution of 131I over time to those obtained using the BOMAB phantom assuming a homogeneous distribution. Based on the correction factors, the internal contamination caused by 131I can be assessed using whole-body counters. These correction factors can minimize the influence of the biodistribution of 131I in whole-body counting measurement and improve the accuracy of internal dose assessment.

In recent times, ion implantation has received increasing interest for novel applications related to deterministic material doping on the nanoscale, primarily for the fabrication of solid-state quantum devices. For such applications, precise information concerning the number of implanted ions and their final position within the implanted sample is crucial. In this work, we present an innovative method for the detection of single ions of MeV energy by using a sub-micrometer ultra-thin silicon carbide sensor operated as an in-beam counter of transmitted ions. The SiC sensor signals, when compared to a Passivated Implanted Planar Silicon detector signal, exhibited a 96.5% ion-detection confidence, demonstrating that the membrane sensors can be utilized for high-fidelity ion counting. Furthermore, we assessed the angular straggling of transmitted ions due to the interaction with the SiC sensor, employing the scanning knife-edge method of a focused ion microbeam. The lateral dimension of the ion beam with and without the membrane sensor was compared to the SRIM calculations. The results were used to discuss the potential of such experimental geometry in deterministic ion-implantation schemes as well as other applications.

The counting efficiencies obtained using anthropomorphic physical phantoms are generally used in whole-body counting measurements to determine the level of internal contamination in the body. Geometrical discrepancies between phantoms and measured individuals affect the counting efficiency, and thus, considering individual physical characteristics is crucial to improve the accuracy of activity estimates. In the present study, the counting efficiencies of whole-body counting measurements were calculated considering individual physical characteristics by employing Monte Carlo simulation for calibration. The NaI(Tl)-based stand-up and HPGe-based bed type commercial whole-body counters were used for calculating the counting efficiencies. The counting efficiencies were obtained from 19 computational phantoms representing various shapes and sizes of the measured individuals. The discrepancies in the counting efficiencies obtained using the computational and physical phantoms range from 2% to 33%, and the results indicate that the counting efficiency depends on the size of the measured individual. Taking into account the body size, the equations for estimating the counting efficiencies were derived from the relationship between the counting efficiencies and the body-build index of the subject. These equations can aid in minimizing the size dependency of the counting efficiency and provide more accurate measurements of internal contamination in whole-body counting measurements.

The aim of this study is to determine an easy and fast method to calculate efficiencies in different volumes, in the same counting geometry, for gamma-ray spectrometry technique. Reference Material Soil IAEA 326 was packed in a 100 mL capacity polyethylene bottle with different masses and volumes, and sealed for about four weeks, prior measurement, in order to ensure that radioactive equilibrium had been reached between 226Ra and its progeny. After this time, they were measured by gamma-ray spectrometry with a hyper-pure germanium detector. The masses of the reference material used were 25, 60, 80, 95 and 128g. The energies of gamma-rays used in this paper are recommended due to the considerations: gamma intensity value, peak quality, spectral region without interference and the gamma- ray energies of the 238U and 232Th series very important for determining the natural radioactivity. The efficiency values obtained compared to the adjusted efficiency values were similar and presented a good correlation coefficient. The performance was acceptable for all different masses studied, indicating results consistent for the method. The proposed method could be useful as a tool for laboratories, dealing with of samples on a routine basis, by reducing the cost on the purchase of another counting geometry and optimizing the use of the detection system, thus improving their performance.

Qualitative analysis of radionuclides requires the use of reliable gamma-ray detection system. The NaI(Tl) detector has been widely used and still one of the most used detectors today. It is therefore imperative to validate the reliability of the 5 × 5 cm2 NaI(Tl) gamma spectrometry system used in carrying out gamma-ray analysis of soil samples in the Radiation and Health Laboratory, Federal University of Agriculture Abeokuta, Nigeria. The gamma ray spectrometer is housed in a 5 cm thick cylindrical lead shield. Calibration was executed using standard materials produced under the auspices of the International Atomic Energy Agency (IAEA). Resolution and detection limit (LD) of the detector were determined using full width at half the maximum of the energy peak of 137Cs and background signal level of the reference materials respectively. Counting efficiencies of the detector was calculated using energies of 1460 keV, 1764 keV and 2615 keV for 40K, 226Ra and 232Th respectively. Secondary samples, RGMIX1 and RGMIX2 were formulated and counted to calculate activity concentrations using the NaI(Tl) detector. Resolution of the detector was calculated to be 7.8% of 137Cs, which is good for a NaI(Tl) detector. The counting efficiency of the detector is seen to depend on the gamma ray energy. The results from this work shows that the detector system is suitable gamma spectrometry and will give quality measurements when used for quantitative determination of radionuclides in environmental samples. The efficiency and resolution of the NaI(Tl) detector should also be determined using photon energies obtained from other radioactive sources.

The aim of this work is to investigate, in a wide range of gamma-ray energies, the validity of the "Virtual Point Detector" (VPD) approach to evaluate Full-Energy-Peak Efficiency (FEPE) values for a Cerium-doped Lanthanum Bromide scintillator (LaBr 3 :Ce). With VPD approximation, the detector is assumed equivalent to a virtual point inside the crystal where all the interactions can be considered to occur. The distance of VPD from detector cap is evaluated through experimental point source measurements. The knowledge of the trend of VPD depth as a function of gamma radiation energy allows the evaluation of FEPE values starting from an experimental reference value. The validation of the procedure has been performed by applying the VPD approach to measurement geometries already characterized such as a disk source, an Havar foil irradiated inside a target of a medical cyclotron, and a parallelepided sample geometry, an atmospheric particulate paper filter reduced to 6 cm × 6 cm × 0.7 cm dimensions. FEPE values determined by VPD approach lead to radionuclide activities very close to the ones already obtained with measurements carried out with other detectors. • Validity of Virtual Point Detector approach for a LaBr 3 :Ce scintillator. • Efficiency evaluation for a LaBr 3 :Ce scintillator through a VPD approximation. • Experimental validation of VPD approach also for disk and volume sources. • Knowledge of the detector size and composition is not necessary. [ABSTRACT FROM AUTHOR]

A method for absolute measurements of the 225Ac activity in equilibrium with its progeny was developed. Measurements were performed using the triple-to-double coincidence ratio (TDCR) method in two different TDCR counters. The activity concentration of an 225Ac solution was determined and the solution was sent to the SIR system for a comparison. The half-life of 225Ac was determined by one of the TDCR counters and found to be 9.9150(63) days. • Detailed determination of the counting efficiency of the 225Ac in radioactive equilibrium with its progeny. • Description of the measurements of the activity of 225Ac sources using the TDCR method. • Result of activity comparison in the International Reference System (SIR) at BIPM. • Results of half-life determination of 225Ac at POLATOM compared to other published values. [ABSTRACT FROM AUTHOR]

In this article the properties of four new luminophores, from the group of bifluorenes and other substances with multiple aromatic rings, were measured and studied for possible use in liquid scintillation, namely 1-phenyl-3-(2,4,6-trimethyl-phenyl)-2-pyrazoline, 2,2′,7,7′-tetrakis(N,N-diphenyl-amino)-9,9′-spirobifluorene, 2-(4-biphenylyl)-6-phenylbenzoxazole and 9,9′-bifluorenyl. The measurement was also done for the most commonly used luminophore (2,5-diphenyloxazole (PPO)). To improve counting efficiency the wavelength shifters were added to scintillation cocktail in particular POPOP and bis-MSB. The main effort was focused on the determination of sample counting efficiency of experimental cocktails using radionuclides Am-241, Sr-90 and H-3, especially for acidic, alkaline and neutral water solutions. The results were compared with the commercially used Aqualight scintillation cocktail. [ABSTRACT FROM AUTHOR]

Abstract The experimental characterization of an aged PIPS detector used in an alpha-particle spectrometry is performed using a standard mixed source of 238U, 234U, 239Pu, and 241Am. The variations in the detector efficiency and resolution (FWHM) at the main energy lines of the 238U, 234U, 239Pu and 241Am source were investigated at all possible source–detector distances under chamber air pressure of ∼ 1.33 Pa. Finding shows that on average, the counting efficiency data obtained from measurements are lower than those obtained by theoretical data and Monte Carlo simulation (SOLANG and AASI) methods. A combination of polymeric strippable coating and both traditional wiping and cleaning method for the detector decontamination works only show a significant reduction in the background activity. The counting efficiency improvement process by an increase of the higher voltages within the recommended range results in a good agreement in the counting efficiency comparison and a slight decrease of the detector dead layer thickness. Novel method to evaluate the dead layer thickness for PIPS detector via the variations in experimental energy loss with respect source to detector distance using alpha standard sources of 242Pu has been proposed. This method can help to predict a default dead layer thickness value which will be as close as it was originally, is less than 50 nm from the manufacturer. Highlights • Efficiency response of an aged PIPS detector was conducted. • Theoretical data and Monte Carlo simulation methods were involved for comparison. • Decontamination work shows an insignificant increase in the counting efficiency. • Novel method to evaluate the dead layer thickness for PIPS detector was developed. • An increase of the higher voltages can improve the counting efficiency and dead layer thickness. [ABSTRACT FROM AUTHOR]

Based on the principle of Mie scattering, we design a small flow optical sensor of particle counter. Firstly, laser illumination system was simulated and designed by ZEMAX optical design software, and the uniform light intensity of photosensitive area was obtained. The gas circuit structure was also designed according to the related theory of fluid mechanics. Then, the method of combining with MIST scattering calculation software and geometric modeling was firstly used to design spherical reflection system, on the basis of the formula of object-image distance. Finally, the test was conducted after the optical sensor placed in self-designed pre-amplification and high-speed processing circuit. The test results show that the counting efficiency of 0.3 μ m gear is above 70%, 0.5 μ m gear and 1.0 μ m gear are both reached more than 90%, and the dispersion coefficient of each gear is very nearly the same, compared with the standard machine of Kanomax 3886 under the particle spraying flow of 2.5SCFH, 3.0SCFH, 3.5SCFH. [ABSTRACT FROM AUTHOR]

In this work, the extrinsic counting efficiency and extrinsic sensitivity of a cylindrical source and a gamma camera with a rectangular detector were determined using homogeneous Tc-99 m . Scattered radiation effects were evaluated by both analyzing the energy spectrum of 99m Tc for the scatter fraction and plotting the extrinsic counting efficiency and sensitivity. It is found that the scattered fraction values increased with increasing source thickness. Calculated extrinsic sensitivity shows a gradually decreasing trend with increasing source thickness. The extrinsic efficiency decreases with increasing source thickness. It is concluded that increasing source to detector distances results with increasing extrinsic counting efficiency but decreasing extrinsic sensitivity. [ABSTRACT FROM AUTHOR]

In this study, a water-based compact handheld condensation particle counter (Hy-WCPC) is developed and its performance is evaluated. The Hy-WCPC is a small and light water-based CPC and the operating principle is the same as the conventional continuous flow conductive cooling alcohol-based condensation particle counters (CPC). This study presents the particle material dependent Hy-WCPC cut-off sizes and the particle concentration counting linearity between the Hy-WCPC and electrometer by generating silver, sodium chloride, zinc and paraffin particles. Moreover, the comparison between the Hy-WCPC and commercially available ultrafine CPC (TSI 3776) for ambient airborne particles is presented. The cut-off sizes of the Hy-WCPC for silver and paraffin particles are 3.61 nm and 5.30 nm, respectively. For sodium chloride and zinc particles, the Hy-WCPC lower detection limit is achieved less than 4 nm. Moreover, the particle concentration counting linearity between the Hy-WCPC and electrometer is presented. The excellent particle number concentration counting linearity agreement between the Hy-WCPC and electrometer is shown for the laboratory generated particles. Also, the particle concentration counting linearity between the Hy-WCPC and the TSI 3776 for outdoor ambient airborne particles is shown. The reasonable agreement between the Hy-WCPC and the TSI 3776 was obtained. In the long-term measurement of outdoor ambient airborne particles for 7 days, this agreement had been maintained, however, after 7 days, the TSI 3776 did not operate properly due to the high humidity, while the Hy-WCPC was operating without the problem. [ABSTRACT FROM AUTHOR]

A point source is used to investigate the effect of water phantom thickness and source-to-detector distance (SDD) on the sensitivity and counting efficiency of a rectangular detector gamma camera. The increase in water thickness resulted in an increase in scatter fraction, a decrease in sensitivity, and counting efficiency. The increase in SDD resulted in a decrease in sensitivity and an increase in counting efficiency. An SDD of 0.79±0.02 m is found to provide a good compromise for acceptable sensitivity and reasonable counting efficiency. [ABSTRACT FROM AUTHOR]

The Laboratory of Internal Dosimetry of the Center for Development of Nuclear Technology (LDI/CDTN) is responsible for routine internal monitoring of occupationally exposed individuals. The determination of photon emitting radionuclides in the human body requires calibration of the detector in specific counting geometries. The calibration process uses physical phantoms containing certified activities of the radionuclides of interest. The objective of this work was to obtain calibration efficiency curves of the Whole Body Counter in operation at the LDI/CDTN using a BOMAB physical phantom and Monte Carlo simulations. [ABSTRACT FROM AUTHOR]

The effect of the density of environmental samples on the counting efficiency of Ge detectors used in gamma-spectrometry was studied. The dependence εff(ρ) was determined for two HPGe detectors (relative efficiencies 18% and 20%) using five radioactive standard reference materials (silicone resins, epoxy resin, milk powder, soil) with different matrix densities (0.45-1.22 g/cm3) in Marinelli beakers (V = 500 cm3). The dependence of efficiency vs. density was found to be linear and the regression parameters for energies in the range of 60-2000 keV were determined, too. The effect of variation in density on the counting efficiency of Ge detectors is dominant in the range of lower energies (60-600 keV) and de creases with energies in the higher energy range.