Calibration Chamber Research Articles

Characterization of a high-resolution 2D transmission ion chamber for independent validation of proton pencil beam scanning of conventional and FLASH dose delivery.

Ultra-high dose rate (FLASH) radiotherapy has become a popular research topic with the potential to reduce normal tissue toxicities without losing the benefit of tumor control. The development of FLASH proton pencil beam scanning (PBS) delivery requires accurate dosimetry despite high beam currents with correspondingly high ionization densities in the monitoring chamber. In this study, we characterized a newly designed high-resolution position sensing transmission ionization chamber with a purpose-built multichannel electrometer for both conventional and FLASH dose rate proton radiotherapy. The dosimetry and positioning accuracies of the ion chamber were fully characterized with a clinical scanning beam. On the FLASH proton beamline, the cyclotron output current reached up to 350 nA with a maximum energy of 226.2MeV, with 210±3nA nozzle pencil beam current. The ion recombination effect was characterized under various bias voltages up to 1000V and different beam intensities. The charge collected by the transmission ion chamber was compared with the measurements from a Faraday cup. Cross-calibrated with an Advanced Markus chamber (PTW, Freiburg, Germany) in a uniform PBS proton beam field at clinical beam setting, the ion chamber calibration was 38.0 and 36.7 GyE·mm2 /nC at 100 and 226.2MeV, respectively. The ion recombination effect increased with larger cyclotron current at lower bias voltage while remaining ≤0.5±0.5% with ≥200V of bias voltage. Above 200V, the normalized ion chamber readings demonstrated good linearity with the mass stopping power in air for both clinical and FLASH beam intensities. The spot positioning accuracy was measured to be 0.10±0.08mm in two orthogonal directions. We characterized a transmission ion chamber system under both conventional and FLASH beam current densities and demonstrated its suitability for use as a proton pencil beam dose and spot position delivery monitor under FLASH dose rate conditions.

Wire mesh capped DRPS based bronchial dosimeter for personal inhalation dosimetry due to radon progeny

A study has been carried out to experimentally determine the calibration factor (CF) of the passive bronchial dosimeter, which consists of a direct radon progeny sensor capped with a 100-wire mesh. First, the CF was determined in controlled environmental conditions simulated in a calibration chamber. With aerosol concentrations varying from 104 p cm−3 to 105 p cm−3 and relative humidity varying from 60% to 80% in the chamber, CF was observed to be nearly constant with an average value of (3.8 ± 0.5) × 10−3 mSv tracks−1 cm2. Then, the CF was determined in real indoor environments in which it was again observed to be almost constant and the mean value was found to be (5.6 ± 0.1) × 10−3 mSv tracks−1 cm2. Pooling all the data on CFs obtained under controlled conditions and in real indoor environments, a lognormal distribution of the CF was observed with a geometric mean and geometric standard deviation of 0.0052 mSv tracks−1 cm2 and 1.28 respectively. The experimentally determined value of CF was found to be in close agreement with the theoretically estimated value, taking into consideration the unattached fraction of radon progeny. This dosimeter is passive, cheap, lightweight and, moreover, the CF being stable against environmental variations, will be useful in monitoring inhalation doses due to radon progeny for occupational workers.

Laboratory Evaluation of the Measuring Capabilities of an Innovative Pressuremeter Probe in Dry Sand

Abstract This article presents the experimental procedures performed in a laboratory to evaluate the measuring capabilities of an innovative monocellular pressuremeter probe. This probe takes advantage of recent technological developments in the domain of inflatable membranes currently applied in the so-called Francis Cour standard tricellular probes, which allow covering an expansion range up to large cavity strains. Those improvements were found to enable increasing the accuracy in the assessment of radial expansion through volume injection in the probe measuring cell at relatively small strain levels without the need of sophisticated punctual measuring arms. Assessing this domain via in situ tests makes up a major contribution to the design of geotechnical structures under cyclic loads, for which the current design practice is mainly developed through laboratory soil tests. To reach this final objective, the probe’s validation program was launched based on pressuremeter tests with unload-reload loops performed in a laboratory calibration chamber and in situ on reference testing sites. This paper focuses on the laboratory testing protocols performed in dry Fontainebleau sand specimens. Shear moduli obtained with the pressuremeter are compared with the expected elementary values for this sand, and it is shown that it was possible to assess sand stiffness at a small strain level using this probe under controlled conditions in a laboratory.

Standardisation of 133Ba by efficiency extrapolation method and calibration of ionisation chamber

133Ba has been standardised by direct measurements for the first time in the laboratory using two counting systems: (i) the 4πβ (plastic scintillator) -γ coincidence, (ii) the 4πβ (proportional counter) -γ coincidence. Furthermore, this standardisation experiment demonstrates the performance and applicability of the recently developed 4πβ (plastic scintillator)-γ coincidence system for radionuclides decaying with complex decay schemes as well as for e, X-γ emitters. Additionally, 133Ba solution standards were prepared to calibrate the pressurized 4π γ ionisation chamber and determination of the calibration coefficient. The En score is a statistical indicator of the agreement between two independent estimations. Thus, the performance of the PS system was compared to the result obtained with the PC system using the En score as specified in the ISO13528:2015. The results of measurements are acceptable if En ≦ 1.0. An En score of 0.2 was obtained which indicates that, the 133Ba activity concentration obtained by the 4πβ (plastic scintillator) -γ coincidence and 4πβ (proportional counter) -γ coincidence systems are in agreement. This paper presents the standardisation procedure, the results obtained by the measurements and their comparison.

MODELING IN THE INFORMATION AND MEASURING SYSTEM OF CUSTOMS CONTROL

The possibility of application in the practice of customs control of the anechoic regime created by means of non-standardized measuring instruments in the form of an anechoic chamber is analyzed. From the standpoint of the principle of reliability of confirmation of conformity, the calibration of a hole-like anechoic chamber was performed as a basis for additional tools in the information system of customs control of an anechoic chamber. The task is to create a data bank of images of typical objects for the introduction into customs practice of methods and means of radar detection and recognition. The functional scheme of the laboratory installation from the anechoic chamber is given and the results of experimental researches are presented. Comprehensive mathematical modeling in the information-measuring system of customs control was carried out, which allowed to choose a more reliable required mode of certification of the involved control-measuring equipment not only from the point of view of their information security due to detection of own accompanying parasitic electromagnetic radiation objects. Note that, for the purity of the experiment when creating a catalog of images of hidden objects of artificial origin, it is advisable to use the anechoic mode, created by special methods and techniques that implement them, for example, anechoic cameras. Thus, without a priori information about hidden objects of artificial origin, it is advisable to create banks of images of hidden objects, taking into account their interaction in the process of detection, measurement and recognition.

Comparison of performance of single- and double-core prefabricated vertical drains for thick reclaimed ground improvement

The performance of a double-core prefabricated vertical drain (PVD), which could reduce the well resistance via its large cross-sectional area and structural stability, was investigated experimentally and numerically. The double-core and the conventional single-core PVD, which has been widely adopted in reclaimed ground improvement, were compared in this study. In the experimental investigation, modified Delft tests and a calibration chamber test were carried out in a laboratory to determine the discharge capacities of the PVDs. Thereafter, single- and double-core PVDs were installed in the Busan New Port site, which had a 40 m thickness of clay deposit, and the performances of the PVDs estimated through surface settlements were compared. In addition, a numerical program named ILLICON was applied with field measurements, and a parametric study was conducted for different discharge capacities of the PVDs. The result of the laboratory tests and field measurements indicated that there was no difference in the performance between the two types of PVDs for improving the soft ground, considering actual ground conditions. Similarly, the parametric study results also implied that both PVDs could be satisfactorily applied in thick reclaimed ground, and there is no significant difference in the performance of single- and double-core PVDs.

Cone penetration tests in dry and saturated Ticino sand

It is commonly assumed that dry and saturated sands exhibit similar cone resistance–relative density relationships. Some studies pointed out that partial saturation and calcareous sands with considerable fines content are potential factors affecting these relationships. However, there is experimental evidence in Shaqour Bull Eng Geol Environ 66:59-70, (2006) that clean uncemented quartz sand may exhibit lower cone resistance in saturated conditions. The present study aims on contributing towards better understanding the effect of water saturation on cone resistance in sand. For this purpose, Ticino sand samples were prepared dry and saturated in a calibration chamber and cone penetration tests were performed over a wide range of relative densities and at two consolidation stresses. Overall, it was observed that dry and saturated samples exhibited similar cone resistances. Only slightly higher cone resistances were observed for dry samples at the lower consolidation stress. Two anomalous samples, which were tested dry at medium relative density, were found to exhibit way higher cone resistances than expected from published cone resistance–relative density relationships. The Young's modulus was observed to be proportional to cone resistance and independent of whether a sample was tested dry or saturated, being therefore considered as more robust soil property for cone resistance relationships.

Assessment of the efficacies of correction procedures for multiple thin layer effects on Cone Penetration Tests

Multiple interbedded fine-grained layers in a sand deposit have a “smoothing” effect on the measured Cone Penetration Test (CPT) tip resistance (qc), resulting in a significant underestimation of the predicted liquefaction resistance of the sand layers. Trends identified by De Lange [14] through calibration chamber tests on stratified sand-clay profiles are used herein to develop a new thin-layer correction procedure for qc (the “Deltares” procedure). The efficacies of the Deltares and the independently-developed Boulanger and DeJong [6] procedures are both directly assessed using CPT data from calibration chamber tests and indirectly inferred from CPT-based liquefaction case histories in Christchurch, New Zealand. The results highlight limitations of the assessed thin-layer CPT qc correction procedures for layers less than 40 mm thick. Multiple, interbedded thin layers also influence the measured CPT sleeve friction (fs), but in a more complex way than they influence qc. To-date, no procedures have been proposed to address all the thin-layer-effects phenomena on the measured fs, with errors in properly characterizing the fs of a layer inherently influencing the accuracy of predicting the liquefaction susceptibility and potential of the layer. In totality, the thin-layer-effects correction procedures proposed to-date generally result in slightly less accurate predictions of the observed liquefaction severity for cases having highly stratified profiles, opposite of what would be expected and desired.

Energy balance analyses during Standard Penetration Tests in a virtual calibration chamber

The Standard Penetration Test (SPT) is the most popular example of dynamic probing, a large category of soil testing techniques. Understanding and interpretation of these tests is hampered by the difficulties of reproducing them under controlled laboratory conditions. The virtual calibration chamber technique, based on the Discrete Element Method (DEM), may supplement or substitute this complex experimentation. In this paper SPT in sand are analyzed considering the energy transfer involved. Energy balances are written for the penetrating rod and for the material in the chamber. All the terms are computed for a number of cases in which the main variables controlling test response in the field -initial density and stress level- are systematically varied. The analysis confirms previous field observations indicating that, when an energy-based interpretation is used, SPT provides a value of equivalent penetration resistance that is the same that would be obtained with a static cone penetration test. The analyses also provide an unequivocal explanation for this observation: although the impacting rod shows complicated dynamics the response of the sand is quasi-static.

Effect of Oxygen Mole Fraction on Static Properties of Pressure-Sensitive Paint.

The effects of the oxygen mole fraction on the static properties of pressure-sensitive paint (PSP) were investigated. Sample coupon tests using a calibration chamber were conducted for poly(hexafluoroisopropyl methacrylate)-based PSP (PHFIPM-PSP), polymer/ceramic PSP (PC-PSP), and anodized aluminum PSP (AA-PSP). The oxygen mole fraction was set to 0.1–100%, and the ambient pressure () was set to 0.5–140 kPa. Localized Stern–Volmer coefficient increased and then decreased with increasing oxygen mole fraction. Although depends on both ambient pressure and the oxygen mole fraction, its effect can be characterized as a function of the partial pressure of oxygen. For AA-PSP and PHFIPM-PSP, which are low-pressure- and relatively low-pressure-type PSPs, respectively, peaks at kPa. In contrast, for PC-PSP, which is an atmospheric-pressure-type PSP in the investigated range, does not have a peak. has a peak at a relatively high partial pressure of oxygen due to the oxygen permeability of the polymer used in the binder. The peak of , which is the emission intensity change with respect to normalized pressure fluctuation, appears at a lower partial pressure of oxygen than that of . This is because the intensity of PSP becomes quite low at a high partial pressure of oxygen even if is high. Hence, the optimal oxygen mole fraction depends on the type of PSP and the ambient pressure range of the experiment. This optimal value can be found on the basis of the partial pressure of oxygen.

Standardization of 223Ra by live-time anticoincidence counting and gamma-ray emission determination

From a commercial supplier, three independent lots of an aqueous solution containing 223Ra in equilibrium with its deteriorating progeny were considered for standardization, by using live-time anticoincidence counting (LTAC) in the Laboratório Nacional de Metrologia das Radiações Ionizantes (LNMRI) Brazil. The ionization chamber calibration factors were obtained using measurements of independent lots of 223Ra in LTAC considering the absolute method in order to evaluate the constancy and reproducibility of the standardization. The calibration factors of three high-performance well-type ionization chamber systems and four commercial well-type ionization chambers were determined. The LTAC results showed that lots 2 and 3 were 1069.88 and 1097.44 kBq/kg, with corresponding relative standard uncertainties 0.12% and 0.20%, respectively. The spectrometry method results of each lot value were classified as positive by ANOVA hypothesis testing. The emission probabilities relating to the X- and γ-rays in region from 81 to 830 keV ware determined.Hence, LNMRI can provide calibration services for 223Ra.

Calibration of CFUL01 fission chambers in the standard neutron fields of the BR1 reactor at SCK CEN

Recent subcritical VENUS-F experiments showed that fission chambers with a threshold deposit like U-238 can essentially improve the on-line sub-criticality measurments with the beam interruption method, which is currently supposed to be the main method for the ADS MYRRHA. To suppress the uncertainty caused by fissions in the U-235 impurities, the fraction of U-235 in the U deposit should be accurately known. Three PHOTONIS CFUL01 type fission chambers with U-238 deposit were purchased for sub-critical experiments in the VENUS-F reactor. To verify the purity of their deposits, the effective U-235 masses were measured in the empty cavity of the BR1 reactor with a well-known thermal neutron spectrum. It turned out that the measured effective U-235 mass in two fission chambers is lower than the declared mass (as it should be), but this is not the case for the third fission chamber. Then, the effective U-238 mass in these FCs was measured in the well-known fast spectrum of the MARK-III convertor in the BR1 reactor. Finally, the isotopic composition was obtained and it was found that the purity of two CFUL01 FCs is in agreement with the values declared in the certificates but it is not the case for the third fission chamber. As the length of the deposit is bigger than the length of the MARK-III convertor, necessary corrections were calculated with MCNP. The developed procedure using the BR1 standard irradiation fields can be applied for calibration and impurity determination of large fission chambers.

Dosimetry audits in Taiwan radiotherapy departments

Objectives:This study examines the practice of the regulation of Standards for Medical Exposure Quality Assurance (SMEQA) in Taiwan based on on-site quality audit for radiation therapy systems from 2016 to 2019.Methods:81 radiation therapy departments, 141 linacs, 9 γ knife systems, 34 high dose rate brachytherapy systems, 20 Tomotherapys, and 6 Cyberknives were audited yearly. Data collection and analysis for each institute’s documents including QA procedure, ion chamber and electrometer calibration reports, and a questionnaire relating to machine type and staffing, were requested first and reviewed by auditors. On-site SMEQA core item measurements, including beam output, beam profile and energy constancy for external beam therapy systems, and the source strength, positioning, and timer accuracy for brachytherapy systems were audited second. More than 300 photon beams and more than 400 electron beams were measured each year.Results:There were approximately 8.9 radiotherapy units per million population, and 1.2 medical physicists per unit in Taiwan. For the output measurements, more than 78 and 75% of the photon beams and electron beams, respectively, from linacs were with deviations within ±1.0%. Photon beams have lower beam quality measurement deviations than electron beams. Including in-plane and cross-plane measurements, more than 90 and 85% photon and electron beams, respectively, were with flatness consistency within 1.0%. All audit measurements were within the SMEQA acceptance criteria.Conclusions:According to SMEQA regulations on-site QA audits were successfully carried out from 2016 to 2019 for all Taiwan radiotherapy units. The measurement results showed high quality machine performance in Taiwan.Advances in knowledge:Dosimetry audits with directly acquired measurement readings have lower uncertainties; allow immediate feedback, discussion, and adjustment in a timely manner. In addition to regulation system establishment and education and training implementation, the machine quality is closely related to machine maintenance implementation.

Measurement of absorbed dose rate in water phantom maintained at body temperature by 60Co irradiator – comparison of experimental results and Monte Carlo simulation

To analyze the biological effects of radiation, it is important that the conditions of in vitro experiments match closely with those of in vivo experiments. In this study, we constructed an irradiation system to conduct irradiation experiments under conditions similar to those of in vivo experiments. The Dongnam Institute of Radiological and Medial Sciences has a gamma irradiator including 60Co radioisotope for research purposes and accreditation for standard calibration of the ion chamber. The temperature of the water phantom was maintained the same as that of the normal human body, and the physical dosimetry was carried out accurately using the ion chamber with traceability. We report the measurement of lateral profiles, depth profiles, and absorbed dose rate in water, Dw, at the irradiation location of the blood samples using a farmer-type ion chamber. We simulated the source, collimator, irradiator, phantom, and extra structure of the gamma irradiation system using the Monte Carlo code and compared the simulated and the experimental results. The experimentally and theoretically evaluated dose rates were 0.2975 ? 0.0055 Gymin?1 (at coverage factor k = 2) and 0.2978 ? 0.0052 Gymin?1 (at coverage factor k = 2) at source-to-surface distance of 100 cm and 5 gcm?2 depth in the water phantom, respectively. Blood irradiation will be conducted in vitro, under conditions similar to in vivo conditions, to provide the dose-response curve based on dosimetry with traceability.

Grain-scale DEM study of open-ended pipe pile penetration in granular soils

Open-Ended Pipe Piles (OEPP) are particularly popular in offshore engineering. An important feature of the installation of these piles is the rate with which soil enters the pile from the bottom, and its interaction with the internal pile shaft. The response of OEPP crucially depends on the occurrence of soil plugging, which can make the behavior of an OEPP similar to a pile of solid cross section. Plugging is generally attributed to arching effects in the soil; therefore, understanding this phenomenon requires an investigation at the grain scale. This is precisely the objective of this study, where the Distinct Element Method (DEM) is used to study the installation of an Open-Ended Pipe Pile in a Virtual Calibration Chamber comprising 128000 grains, under constant horizontal stress. Despite the relatively small number of particles, this numerical model is found to be able to reproduce several aspects of the mechanisms actually observed in thefield. The results are compared to those obtained from actual experiments of miniature pile penetration tests. Stress and strainfields that develop in the soil inside and outside the pile provide interesting data and shed light on the mechanisms at play during OEPP installation, especially as for the influence of grains interlocking.

Ra-224 activity, half-life, and 241 keV gamma ray absolute emission intensity: A NIST-NPL bilateral comparison

The national metrology institutes for the United Kingdom (UK) and the United States of America (USA) have compared activity standards for 224Ra, an α-particle emitter of interest as the basis for therapeutic radiopharmaceuticals. Solutions of 224RaCl2 were assayed by absolute methods, including digital coincidence counting and triple-to-double coincidence ratio liquid scintillation counting. Ionization chamber and high-purity germanium (HPGe) γ-ray spectrometry calibrations were compared; further, a solution was shipped between laboratories for a direct comparison by HPGe spectrometry. New determinations of the absolute emission intensity for the 241 keV γ ray (Iγ = 4.011(16) per 100 disintegrations of 224Ra) and of the 224Ra half-life (T1/2 = 3.6313(14) d) are presented and discussed in the context of previous measurements and evaluations.

Technical Note: Vendor miscalibration of preclinical orthovoltage irradiator identified through independent output check.

Accurate radiation dosimetry in radiobiological experiments is crucial for preclinical research in advancement of cancer treatment. Vendors of cell irradiators often perform calibration for end-users. However, calibration accuracy remains unclear due to missing detailed information on calibration equipment and procedures. In this study, we report our findings of a vender miscalibration of the radiation output and our investigation on the root cause of the discrepancy. Independent calibration verification for a commercial preclinical orthovoltage irradiator was conducted. Initially, in the absence of ionization chambers calibrated at kV energy, radiochromic films (EBT3) was first calibrated at MV energy. Energy correction factors from literature were used to create an in-house kV dosimetry system. The miscalibration identified with the in-house kV EBT3 dosimetry was later confirmed by ADCL calibrated ionization chambers (Exradin A1SL and PTW 30013) at kV energy. Ionization chambers were suspended in-air following TG-61 recommendation for output calibration. To investigate the root cause of the miscalibration, additional measurements were performed with ionization chambers placed on the shelf. A validated Monte Carlo simulation code was also used to investigate the impact of placing the ionization chamber on the shelf instead of suspending it in air during the vendor-performed calibration process. Up to a 6% dosimetry error was observed when comparing the vendor calibrated output of the preclinical irradiator with our independent calibration check. Further investigation showed incorrect setups in the vendor's calibration procedure which may result in dose errors up to 11% from the backscatter of the shelf board during calibration, and up to 5% from omitting temperature and pressure corrections to ionization chamber readings. Our study revealed large dose calibration errors caused by incorrect setup and the omission of temperature/pressure correction in the vendor's calibration procedure. The findings also highlighted the importance of performing an independent check of the dose calibration for preclinical kV irradiators. More absolute dosimetry training is needed for both vendors and end users for establishing accurate absolute dosimetry.

Cone penetration testing on silty tailings using a new small calibration chamber

This study presents the results of the first cone penetration testing on predominately silty gold tailings in a calibration chamber, with results interpreted within the critical state soil mechanics framework. Samples were prepared in a wide range of void ratios, prioritising loose contractive states. The results are presented in terms of the state parameter against the normalised tip resistance and are compared with some common state parameter interpretation screening tools. The modified laboratory equipment, sample preparation methods and characterisation of the tested silty tailings are described along with the adapted void ratio tracking method.

Direct determination of for cylindrical ionization chambers in a 6 MV 0.35 T MR-linac

To ensure accurate reference dosimetry with ionization chambers in magnetic resonance linear accelerators (MR-linacs), the influence of the magnetic field on the response of the ionization chambers must be considered. The most direct method considering the influence of magnetic fields in dosimetry is to apply an appropriate absorbed-dose-to-water primary standard. At PTB, a new water calorimeter has been designed which is capable to determine Dw,Q in an MR-linac. The new device allows the direct calibration of ionization chambers in terms of absorbed dose to water for MR-linac irradiation conditions. Hence, the correction factors can be determined which replace the current radiation-quality dependent correction factors for dosimetry in the presence of magnetic fields. In cooperation with Heidelberg University Hospital, factors were measured at the 6 MV 0.35 T Viewray MR-linac for different cylindrical ionization chambers with sensitive volumes ranging from 0.015 cm3 to 0.65 cm3. The chambers were placed both perpendicular and parallel in respect to the magnetic field. Standard uncertainties of about 0.5% were achieved.

Desarrollo de correlaciones para determinar el potencial a licuefacción mediante la aplicación del ensayo de penetración estática de piezocono (CPTu) en una cámara de calibración (CC).

El objetivo principal de este proyecto fue desarrollar correlaciones para determinar el potenciala licuefacción de depósitos de arenas sueltas empleando el ensayo de penetración estáticade piezocono CPTu; para ello fue necesario determinar el comportamiento de ensayos (CPTu)en la cámara de calibración (CC) del Laboratorio de Mecánica de Suelos y Rocas (IBF) en elInstituto Tecnológico de Karlruhe, además determinar la resistencia a licuefacción por mediode ensayos triaxiales cíclicos no drenados para muestras de arena, plantear una correlaciónentre la densidad relativa de almacenamiento (ID) de la muestra, la resistencia de punta(qc) del CPTu y la resistencia al flujo (CRR) de los ensayos triaxiales y por último compararla correlación experimental obtenida con correlaciones existentes de la literatura. Con esteproyecto se concluyó que en la región de bajas densidades de almacenamiento y bajasresistencias en punta una buena similitud, esto al comparar las correlaciones para los materialesexperimentales estudiados por el IBF con correlaciones provenientes de la literatura. Ahora bien,para densidades altas y, por lo tanto, mayores resistencias en punta, las curvas de correlaciónpara los materiales experimentales fueron más planas que en referencias bibliográficas; enotras palabras, la resistencia a licuefacción de los materiales experimentales en esta área esmenor de lo que habrían predicho las curvas de la literatura. Así pues, no es posible aplicardirectamente los resultados de este proyecto a otros sitios de estudio; ya que los materialesde las correlaciones realizadas (Kali4) y otros suelos difieren en aspectos como la mineralogía(criterios geológicos), la granulometría y la forma de partícula (criterios de composición); loscuales influyen sobre la susceptibilidad a la licuación.