Calibration Chamber Research Articles

A Study on Measurement of Small Strain Shear Moduli with a Calibration Chamber

A Study on Measurement of Small Strain Shear Moduli with a Calibration Chamber

Calibration of a Farmer Type Ionization Chamber in a Therapeutic Proton Scanning Beam Using a Faraday Cup and the Geant4 Monte Carlo Program

Calibration of a Farmer Type Ionization Chamber in a Therapeutic Proton Scanning Beam Using a Faraday Cup and the Geant4 Monte Carlo Program

МЕТОД СВЧ АКУСТИЧЕСКОГО ИССЛЕДОВАНИЯ МАТЕРИАЛОВ ПОД ВЫСОКИМ ДАВЛЕНИЕМ

The arrangement of a new integrated measuring system (IMS) "HBAR + DAC" and its application to study changes in the acoustic properties of a paper and polycrystalline molybdenum samples under the influence of high pressure are discussed. When creating an IMS for the synthesis of piezoelectric films of aluminum-scandium nitride, the magnetron deposition method was used. The quality and thickness of the films were controlled by X-ray diffraction analysis and atomic force microscopy. For the first time, it is shown that the HBAR in the IMS content has good operational characteristics in the microwave band up to 8.8 GHz under the high-pressure impact on the samples. A decrease in the Q-factor of an HBAR as a sensitive element occurred to values of ~2500 – 3000 at the upper pressure limit, which is quite sufficient for accurate measurements of the resonant frequencies of acoustic overtones. The possibilities of IMS for studying the features in the behavior of solids under the high-pressure impact and the registration of plastic deformations in metals are demonstrated. It is found that the pressure dependence of the relative frequency shift of overtones during compression of a paper sample has a linear character. Thanks to this, the calibration of the high-pressure chamber on diamond anvils was performed using the RAMAN method. It is found that the frequency shift of overtones allows more accurately determining the stresses in the diamond anvil up to 5 GPa. When compressing a sample of polycrystalline molybdenum, the phenomena of plastic deformation and creep, as well as the transit flight of an acoustic wave through the sample, starting from a pressure of 3 GPa, were detected. The results obtained will be useful for researchers, students and postgraduates in the fields of high pressure physics and physical acoustics.

Feasibility of Implementing a Megavoltage Ionization Chamber Calibration Service at the Secondary Standards Level

Feasibility of Implementing a Megavoltage Ionization Chamber Calibration Service at the Secondary Standards Level

Development of a Thoron Calibration Chamber Based on a Computational Fluid Dynamics Simulation and its Validation with Measurement Results

Development of a Thoron Calibration Chamber Based on a Computational Fluid Dynamics Simulation and its Validation with Measurement Results

Nucleation efficiency of nuclear recoils in bubble chambers

Bubble chambers using liquid xenon (and liquid argon) have been operated (resp. planned) by the Scintillating Bubble Chamber (SBC) collaboration for GeV-scale dark matter searches and CEνNS from reactors. This will require a robust calibration program of the nucleation efficiency of low-energy nuclear recoils in these target media. Such a program has been carried out by the PICO collaboration, which aims to directly detect dark matter using C3F8 bubble chambers. Neutron calibration data from mono-energetic neutron beam and Am-Be source has been collected and analyzed, leading to a global fit of a generic nucleation efficiency model for carbon and fluorine recoils, at thermodynamic thresholds of 2.45 and 3.29 keV. Fitting the many-dimensional model to the data (34 free parameters) is a non-trivial computational challenge, addressed with a custom Markov Chain Monte Carlo approach, which will be presented. Parametric MC studies undertaken to validate this methodology are also discussed. This fit paradigm demonstrated for the PICO calibration will be applied to existing and future scintillating bubble chamber calibration data.

Performance of a cyclic miniature cone penetration test in dry granular soil: experimental approaches

Shaft friction degradation in geotechnical problems occurs alongside large uncertainties. Under cyclic loadings, offshore foundations can episodically suffer the loss of stiffness and strength. In such cases, initial in situ soil state is lost as soil is disturbed during cyclic loading. In this sense, it is important to develop a testing procedure to assess the lateral friction degradation. Considering that a cone is a miniature driven pile, the use of this testing technique allows monitoring the degradation of sleeve friction during cyclic loading. This paper aims to improve the knowledge on the feasibility of using cone testing for the recognition of lateral friction degradation of a dry granular soil. Cyclic miniature cone penetration tests were performed in a calibration chamber considering a range of loading conditions. The effect of cyclic displacement amplitude and the confining pressure were investigated. Lateral friction, fs, degrades while repeating the load cycling, resulting in loss of lateral strength due to soil–cone interface friction degradation. After about ten load cycles, degradation tended to stabilise for all tests.

Alpha track distribution on lateral wall of cylindrical radon diffusion chamber

Cylindrical diffusion chamber with solid state nuclear track detector placed at the bottom of the chamber is frequently used device for measuring radon concentration in dwellings. In this work, the diffusion chamber with CR-39 detector was modeled to determine track distribution on the lateral (cylinder) wall of the chamber and compare track density between cylinder wall and bottom. Model is based on the diffusion, deposition and decay of radon and its progeny in diffusion chamber. Equations for criteria of track visibility and track density were derived. Along with theoretical model, measurements were performed to verify the theoretical results. Three different chambers with CR-39 detectors slabs attached along the cylinder wall were investigated. It was found that alpha track density on cylinder wall is not uniform and depends on the shape and size of the chamber. Deviation of track density along cylinder wall was up to 30% for chambers used in this work. Sensitivity of the cylinder wall was found to be almost the same as the sensitivity of the bottom. In comparison with the experiment, theoretical results give good predictions. Along with previous results of the authors where bottom track density was modeled, presented model can be used for calibration and optimization of the diffusion chambers used for radon measurements.

Displacements, Strains, and Shear Bands in Deep and Shallow Penetration Processes

When penetrometers or probes are pushed into sand, complex displacement fields, strain fields, and shear band patterns develop. Deep and shallow penetration processes in sands generate substantially different patterns. This paper reports the results of penetration experiments performed in dense air-pluviated sand samples prepared in a half-cylindrical calibration chamber equipped with observation windows that allow the collection of images of the sand during penetration. Both a cone penetrometer (diameter d=38 mm) and a model footing (width B=90 mm) are used in the penetration experiments. Incremental displacement and strain fields in the soil domain are obtained by analysis of the collected images using digital image correlation (DIC) and continuum mechanics. The zero-extension line concept is used to study shear strain localization, and a method is proposed to automatically obtain the orientation of shear band patterns from the incremental strain fields. For the model footing, the strain fields are found to localize not only near the footing but also away from it, depending on the level of penetration. The shear bands develop in a traditional wedge shape below the model footing and in a fan shape on either side of it. In contrast, for the cone penetrometer, the strain fields localize more intensely near the penetrometer tip. The shear bands develop along the inclined face and near the shoulder of the penetrometer.

Interpretation of CPT in unsaturated sands under drained conditions: A numerical study

AbstractA finite difference‐based numerical model simulating the cone penetration process in unsaturated sands is presented. Mohr–Coulomb model (MCM) with simple modifications and Sun model (SM) were implemented to capture the unsaturated sand behaviour. It was shown that the cone tip resistance values resulting from the two models were fairly comparable. Predicted cone tip resistance values in dry, saturated and unsaturated sands using MCM were validated by the results of field and calibration chamber tests. Sensitivity analyses were performed, and the influence of parameters including relative density, mean effective stress and apparent cohesion due to suction on the tip resistance was investigated. Based on a large number of numerical analyses, a simple relationship was suggested to predict the cone tip resistance in dry, saturated and unsaturated sands. The accuracy of the proposed relationship was evaluated by a large database of Cone penetration test (CPT) results performed in various calibration chambers containing different sands. Finally, the applicability of the suggested equation in the estimation of the soil relative density and friction angle from CPT results was shown through useful and practical charts and illustrative examples.

Robust identification and characterization of thin soil layers in cone penetration data by piecewise layer optimization

Cone penetration testing (CPT) is a preferred method for characterizing soil profiles for evaluating seismic liquefaction triggering potential. However, CPT has limitations in characterizing highly stratified profiles because the measured tip resistance (qc) of the cone penetrometer is influenced by the properties of the soils above and below the tip. This results in measured qc values that appear “blurred” at sediment layer boundaries, inhibiting our ability to characterize thinly layered strata that are potentially liquefiable. Removing this “blur” has been previously posed as a continuous optimization problem, but in some cases this methodology has been less efficacious than desired. Thus, we propose a new approach to determine the corrected qc values (i.e. values that would be measured in a stratum absent of thin-layer effects) from measured values. This new numerical optimization algorithm searches for soil profiles with a finite number of layers which can automatically be added or removed as needed. This algorithm is provided as open-source MATLAB software. It yields corrected qc values when applied to computer-simulated and calibration chamber CPT data. We compare two versions of the new algorithm that numerically optimize different functions, one of which uses a logarithm to refine fine-scale details, but which requires longer calculation times to yield improved corrected qc profiles.

Validation of 3D printing materials for high dose-rate brachytherapy using ionisation chamber and custom phantom

Methods. Measurements were taken with the Exradin A20 (Standard Imaging) ionisation chamber, and the ‘homemade’ MARM phantom was made with the 3D Ultimaker 2+ printer using PLA material. The material used for validation was ABS Medical from Smart Materials 3D. The irradiation was undertaken with a 192Ir source by means of Varian’s GammaMed Plus iX HDR equipment. EBT3 films were used to run additional tests. We compared different measurements for PLA, ABS Medical, and water. Additional validation methods, described in the bibliography, were also compared. Results. The measurements with the ionisation chamber that we obtained using the MARM phantom with PLA and ABS within the clinically relevant range (0.5–1.5 cm) differ with respect to the measures in the water reference, by 2.3% and 0.94%, respectively. Discussion. The literature describes highly heterogeneous validation methods, complicating the performance of systematic reviews and comparisons between materials. Thus, creating a phantom represents a single effort that will quickly pay off. This system enables comparisons, ensuring that geometric conditions remain stable—something that is not always possible with radiochromic films. The use of a calibrated ionisation chamber in the corresponding energy range, combined with the ‘homemade’ MARM phantom applied according to the proposed methodology, allows a differentiation between the attenuation of the material itself and the drop in the dose due to distance. Conclusion. The validation method for 3D printing materials, using an ionisation chamber and the MARM PLA phantom, represents an accessible, standardisable solution for manufacturing brachytherapy applicators.

Accurate Dosimetry for Radiobiology

Accurate radiation dose is required to ensure reproducibility in establishing the radiobiological effect in biological systems among institutions. The dose should be the most precise and accurate parameter of the entire process. The goal is a system to provide uniform radiation dose verification among institutions that is traceable to the National Institute of Standards and Technology (NIST) through an Accredited Dosimetry Calibration Laboratory.Radiobiological beams are not NIST traceable but can be approximated based on the radiograph's half value layer. Phantoms have been developed containing detectors to measure the dose from total body irradiation of mice and others. Ionization chambers calibrated to NIST-traceable beams are the best detectors for precise and accurate dose determinations. However, thermoluminescent dosimeters have been mostly used for this application for comparison between institutions.A comparison of thermoluminescent dosimeters results among surveyed institutions showed a large variation in delivered dose. The range of radiograph doses that were measured deviated from the standard dose by 12% to 42%. The results have an uncertainty of 2.5% at 1 standard deviation. The surveyed radionuclide irradiators demonstrated a dose range variation of 1.6% to 13.5% from target dose. There is less variation among high energy (linacs) because a calibrated ionization chamber is generally used by personnel (eg, medical physicist) and the output is determined for radiation therapy applications as well.Radiobiological dosimetry is lacking with respect to its precision and accuracy. The accuracy of radiograph calibrations for radiobiology can be estimated to be approximately 5%, because there are no NIST-traceable beams. However, among institutions, the variations can be up to 42%. Intercomparisons between institutions is important to have a clear understanding of the transference of dose between given studies.

A low-cost portable chamber based on Arduino micro-controller for measuring cover crops water use

Cover crop adoption is growing in sustainable vineyard management to replace tillage and limit its ecosystem disservices. However, water use of such crops must be known and low-cost, yet fast reading, portable and accurate equipment is therefore needed for multipoint measurements in the field. Using an Internet of Things (IoT) approach, in this study we provide details for setup, calibration and operational data of a very low cost (~210 $), small closed type chamber. Chamber calibration was performed either as instantaneous evaporation (E) rates under laboratory condition (25 runs, 2 min each) and daytime cumulative evapotranspiration (ET) rates performed outside in small pots sown with different cover crops or managed with light tillage. In both cases chamber’s derived water loss rates were validated against a gravimetric method. A very close linear relationship between gravimetric vs chamber values was found for lab and outdoor calibration runs (R2 = 0.96 and 0.99, respectively) within ranges of 0–0.8 mm h−1 (lab) and 0–23 mm d-1 (outdoor). Ideal measurement time window was estimated at 60 s after “time zero” set at 15 s upon chamber positioning. Under any condition, chamber heating never exceeded 2 °C above air temperature. In the warmest hours of the day (i.e. from 11:00 to 16:00) Festuca arundinacea hourly ET was 0.56 mm while Lotus corniculatus and wet soil tillage registered 0.71 and 0.69 mm h−1, respectively. Dry soil tillage showed ET values between 0.2 and 0.3 mm h−1. The proposed device represents an effective IoT application as total cost of the needed components does not reach a total amount of 200 euros and its size as well as flexibility of use makes it an ideal tool for fast multipoint readings of soil and grass water losses in the field.

Mathematical estimation of half-value layer thicknesses.

ObjectiveThe objective of this article is to introduce a simplified and swift method to satisfactorily estimate the half‐value layers (HVL), quarter‐value layer (QVL), and tenth‐value layer (TVL) from the x‐ray spectra emitted by any diagnostic radiology or kV radiotherapy x‐ray tubes.MethodsA CdTe x‐ray and Gamma detector (X‐123 CdTe, AmpTek Inc.) is used to measure the x‐ray spectra at four different x‐ray energies (low, mid, high energy x‐rays) with different external filtering. The software “SpekCalc GUI” (Developed in McGill University, Montreal, Canada) is also used to obtain the simulated x‐ray spectra. Both measured and simulated spectra are used to compute the HVL thicknesses of Aluminum by a mathematical method presented in this article. Next, the HVL thicknesses for corresponding tube potentials are also measured by calibrated ionization chamber and varying thicknesses of aluminum plates. Finally, the computed and measured HVL, QVL, and TVL thicknesses are compared to evaluate the efficacy of the presented method.ResultsThe results show acceptable concordance between computed and measured quantities. The disagreement rates between measured HVL and the values derived mathematically from the x‐ray spectra are 10 to 90 micrometers of Aluminum at tube potentials of 31 kV to 120 kV. As it is shown, a negligible discrepancy is observed between the analytical estimation and the experimental assessments.ConclusionThe HVL is an essential component in the evaluation of the quality of an x‐ray beam. However, its measurement could occasionally be challenging, time‐consuming, or uncertain due to some technical difficulties. Although the scope of this study is not to undermine the value of conventional and widely accepted practice to determine the HVL thickness, the introduced method provides the fast, more convenient, and comparably reliable technique to estimate the HVL, QVL, and TVL by employing the given x‐ray spectrum.

Revisiting interpretation of relative density from shallow depth CPTs in sand

The relative density is an important state parameter in the determination of engineering properties of marine sands. Existing industry-acknowledged cone penetration test (CPT) correlations to relative density have been developed almost exclusively from the results of calibration chamber testing performed at stress levels higher than 50 kPa. A few studies suggest correlations for low stress levels as well, however, mainly for unaged normally consolidated soils. Existing formulations are often found to be challenged in the application for dense to very dense aged overconsolidated marine sands. This paper investigates the conditions and response of overconsolidated medium dense to very dense sand (as typically found in the North Sea) at shallow depths (less than 50 kPa) for a penetrating cone. It provides recommendations for a consistent set of parameters linking CPT parameters to the stress conditions, expressed by the apparent overconsolidation ratio and coefficient of earth pressure at rest, and the relative density. The recommendations are based on a comprehensive field-testing campaign at a sand site in Cuxhaven, Germany, supported by a suite of laboratory testing and numerical analyses.

Evaluation of small-strain shear modulus of Fontainebleau sand based on innovative pressuremeter probe testing in a calibration chamber

This paper presents an experimental study aimed at evaluating the measuring capabilities of an innovative monocellular pressuremeter probe, the Monocell Francis Cour probe, based on calibration testing in the laboratory. The originality of the tested equipment is to allow evaluation of soil properties in both small- and large-strain domains, without the need of sophisticated point displacement measuring arms. This paper focuses on the evaluation of small-strain shear modulus G of Fontainebleau sand, NE34, based on tests carried out with this specific pressuremeter probe. Shear modulus values obtained with this probe are then compared with values resulting from more classical elementary tests, showing a fairly good consistency. It is shown, with satisfactory agreement, that it is possible to quantify the influence of the density index of the sand as well as the influence of the mean effective stress around the probe on the shear modulus, based on the analysis of specific unload−reload loops performed during the test. The experimental programme carried out under well-controlled laboratory conditions allows a validation to be proposed for a method of derivation of the shear modulus of sand at small strain levels using this prototype pressuremeter.

Model pile behavior in calibration chamber under very large number of cycles of axial loading in saturated clay

ABSTRACT The results of a series of displacement-controlled cyclic axial loading tests of model pile in saturated kaolinite clay, carried out in a calibration chamber, are presented. An instrumented pile-probe was used to investigate the evolution of local skin friction and excess pore water pressure during cyclic loading. After a brief description of the experimental setup and the testing procedure, the tests results are presented concerning the response of the probe during installation, initial monotonic axial loading, cyclic loading up to large numbers of cycles (105 cycles) and post-cyclic monotonic axial loading. During cyclic loading, an initial degradation phase of local skin friction followed by a stabilization phase is observed. Generation of excess pore water pressure occurs during the 60 first cycles followed by a dissipation phase. Parametric study showed that, for initial monotonic loadings, maximum tip resistance and local skin friction are proportional to stress level. Furthermore, excess pore water pressure generated during cyclic loading depends both on initial stress level applied to the clay specimen and cyclic displacement amplitude. A peak value of local skin friction resistance has been observed during post-cyclic monotonic loadings.

Implementation of Fuzzy Logic Controller for Pressure Sensor Calibration Chamber

Atmospheric pressure is a weather element that must be observed in the field of meteorology. Electronic barometers, aneroid barometers, mercury barometers are generally instruments for atmospheric pressure measurement. The barometer must be calibrated periodically to ensure the performance of the instrument. To achieve the best target uncertainty during calibration, besides using an accurate primary standard barometer, a stable pressure controller is also needed. Pressure calibration media using a pressurised test chamber is more beneficial due to its capability to accommodate all types of pressure sensors. However, pressurise test chamber still requires an operator to control and stabilise pressure inside the test chamber. In this study, fuzzy logic has been programmed into a microcontroller to control the solenoid valve and vacuum pump for regulating air pressure inside a pressurised test chamber automatically. Fuzzy logic changes the solenoid valve states periodically by varying the opening and closing times. The final result of this study is a comparison between the calibration results using pressure controller with fuzzy logic and without fuzzy logic with the same primary standard and unit under test. The result of expanded uncertainty without a fuzzy logic controller is 13.06 hectopascal. Meanwhile, the pressure calibration process using fuzzy logic to control pressure in pressurised test chamber achieve 0.09 hectopascal of expanded uncertainty in 1000 hectopascal pressure value with coverage factor, k=2, and confidence level of no less than 95 %.

Water calorimetry-based k Q factors for Farmer-type ionization chambers in the SOBP of a carbon-ion beam

The dosimetry of carbon-ion beams based on calibrated ionization chambers (ICs) still shows a significantly higher uncertainty compared to high-energy photon beams, a fact influenced mainly by the uncertainty of the correction factor for the beam quality k Q . Due to a lack of experimental data, k Q factors in carbon-ion beams used today are based on theoretical calculations whose standard uncertainty is three times higher than that of photon beams. To reduce their uncertainty, in this work, k Q factors for two ICs were determined experimentally by means of water calorimetry for the spread-out Bragg peak of a carbon-ion beam, these factors are presented here for the first time. To this end, the absorbed dose to water in the 12C-SOBP is measured using the water calorimeter developed at Physikalisch-Technische Bundesanstalt, allowing a direct calibration of the ICs used (PTW 30013 and IBA FC65G) and thereby an experimental determination of the chamber-specific k Q factors. Based on a detailed characterization of the irradiation field, correction factors for several effects that influence calorimetric and ionometric measurements were determined. Their contribution to an overall uncertainty budget of the final k Q factors was determined, leading to a standard uncertainty for k Q of 0.69%, which means a reduction by a factor of three compared to the theoretically calculated values. The experimentally determined values were expressed in accordance with TRS-398 and DIN 6801-1 and compared to the values given there. A maximum deviation of 2.3% was found between the experiment and the literature.