Standard Ionization Chamber Research Articles

Portable Gamma Irradiation System with 57Co, 133Ba, 137Cs, and 60Co for On-site Calibration of Environmental Radiation Monitoring Devices

Background: A portable gamma irradiation system was developed for on-site calibration of environmental radiation monitoring devices. This system uses a portable collimator and gammaray sources such as 57Co, 133Ba, 137Cs, and 60Co, each with a nominal radioactivity of 10 MBq or less.Materials and Methods: The air kerma rate produced by the system was measured using a spherical ionization chamber with a 10 L sensitive volume. This chamber was calibrated against the air kerma rate measured with primary standard ionization chambers. The system’s performance was evaluated by comparing the calibration results of the monitoring device with those obtained using a conventional method involving a standard ionization chamber for outdoor use.Results and Discussion: The calibration coefficient of the spherical ionization chamber was within ±2% of the value of 3.029×103 Gy/C for photon energies ranging from 50 keV to 1,250 keV. The air kerma rate of the irradiation field produced by the portable system ranged from 0.17 μGy/hr to 4.7 μGy/hr, with an uncertainty between 2.4% and 10%. The calibration coefficients obtained using the portable system were consistent with those from the conventional method.Conclusion: The portable gamma irradiation system offers significant advantages, including preventing damage to standard ionization chambers used outdoors and reducing measurement time compared to conventional methods. Due to its ease of construction and implementation, the system is expected to be useful not only for on-site calibration of monitoring devices but also in various radiation safety management scenarios.

Calibration coefficients of epitaxial diodes used in diagnostic radiology and computed tomography beams

The assessment of the calibration coefficients of an epitaxial diode, previously characterized for diagnostic radiology (RQR qualities) and computed tomography (RQT qualities) dosimetry, is reported in this work. The diode, with an n-type epitaxial layer (50 µm) grown on a thick (300 µm) Czochralski silicon substrate, is directly connected to an electrometer Keithley 6517B in the photovoltaic mode and exposed to X-ray beams from a Pantak/Seifert generator, model Isovolt 160 HS. Under this operational condition, the dosimetric quantity is the dose rate correlated with the output current signal from the diode when exposed to radiation. The corresponding collected charge (the integral of the current signal) is proportional to the dose. The repeatability of the current signals and the dose response of the diode are investigated in several RQR and RQT beam qualities spanning from 50 kV to 150 kV. The calibration coefficients (Nk) are assessed by linking the diode readings to those from the standard ionization chambers for reference beam qualities (RQR-5 and RQT-9) following the formalism recommended by Technical Reports Series No. 457. To take into account the variations of the X-ray beams related to the correspondent reference beam qualities, the correction factors are also calculated. Despite being close to 1, they evidence the energy dependence of the EPI diode for voltages above 100 kV.

Experimental and Monte Carlo Evaluation of Spherical Ionization Chambers’ Response to 137Cs Radioactive Source

Measurements were performed for the calibration of an ionization chamber in the secondary standard dosimetry laboratory of IFIN-HH. A 10-liter spherical ionization chamber was calibrated using a 1-literspherical reference standard ionization chamber. The ionization chamber’s response to 137Cs was also evaluated computationally by MCNP and FLUKA Monte Carlo codes. The models of the experimental setup are validated and can be used for further studies, especially in cases where the real experiment is hard or impossible to perform

Characterization of Inorganic Scintillator Detectors for Dosimetry in Image-Guided Small Animal Radiotherapy Platforms.

The purpose of the study was to characterize a detection system based on inorganic scintillators and determine its suitability for dosimetry in preclinical radiation research. Dose rate, linearity, and repeatability of the response (among others) were assessed for medium-energy X-ray beam qualities. The response's variation with temperature and beam angle incidence was also evaluated. Absorbed dose quality-dependent calibration coefficients, based on a cross-calibration against air kerma secondary standard ionization chambers, were determined. Relative output factors (ROF) for small, collimated fields (≤10 mm × 10 mm) were measured and compared with Gafchromic film and to a CMOS imaging sensor. Independently of the beam quality, the scintillator signal repeatability was adequate and linear with dose. Compared with EBT3 films and CMOS, ROF was within 5% (except for smaller circular fields). We demonstrated that when the detector is cross-calibrated in the user's beam, it is a useful tool for dosimetry in medium-energy X-rays with small fields delivered by Image-Guided Small Animal Radiotherapy Platforms. It supports the development of procedures for independent "live" dose verification of complex preclinical radiotherapy plans with the possibility to insert the detectors in phantoms.

EURAMET DOSEtrace supplementary comparison in terms of the ambient dose equivalent/rate for photon radiation (EURAMET.RI(I)-S18)

Main textA supplementary comparison in terms of the ambient dose equivalent/rate was organized within EURAMET as a part of the DOSEtrace project, between 13 national metrology institutes and designated institutes. Calibration coefficients were compared for a secondary standard ionisation chamber for 3 X-ray and 2 γ-ray radiation qualities used in the field of radiation protection. Radiation qualities were established according to ISO 4037-1. Measurements were performed between 2019 and 2021.For the purpose of this comparison, it was considered that the reported uncertainty was confirmed if the relative deviation from the comparison reference value was smaller than or equal to the associated uncertainty. All the reported results by all the partners satisfied this criterium. Three participants were not able to perform calibrations in all mandatory radiation qualities, due to technical problems. The results are published in the Key Comparison Data Base (KCDB) of the BIPM as supplementary comparison EURAMET.RI(I)-S18.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

A new solution for UHDP and UHDR (Flash) measurements: Theory and conceptual design of ALLS chamber

Ultra-High dose-per-pulse regimens (UHDP), necessary to trigger the “FLASH” effect, still pose serious challenges to dosimetry. Dosimetry plays a crucial role, both to significantly improve the accuracy of the radiobiological experiments necessary to fully understand the mechanisms underlying the effect and its dependencies on the beam parameters, and to be able to translate such effect into clinical practice. The standard ionization chamber in UHDP region is significantly affected by the effects of the electric field generated by the enormous density of charges produced by the dose pulse.This work describes the theory and the conceptual design of a gas chamber (the ALLS chamber) which overcomes the above-mentioned problems.

Determination of beam quality correction factors for the Roos plane-parallel ionisation chamber exposed to very high energy electron (VHEE) beams using Geant4

Detailed characterisation of the Roos secondary standard plane-parallel ionisation chamber has been conducted in a novel 200 MeV Very High Energy Electron (VHEE) beam with reference to the standard 12 MeV electron calibration beam used in our experimental work. Stopping-power-ratios and perturbation factors have been determined for both beams and used to calculated the beam quality correction factor using the Geant4 general purpose MC code. These factors have been calculated for a variety of charged particle transport parameters available in Geant4 which were found to pass the Fano cavity test. Stopping-power-ratios for the 12 MeV electron calibration beam quality were found to agree within uncertainties to that quoted by current dosimetry protocols. Perturbation factors were found to vary by up-to 4% for the calibration beam depending on the parameter configuration, compared with only 0.8% for the VHEE beam. Beam quality correction factors were found to describe an approximately 10% lower dose than would be originally calculated if a beam quality correction were not accounted for. Moreover, results presented here largely resolve unphysical chamber measurements, such as collection efficiencies greater than 100%, and assist in the accurate determination of absorbed dose and ion recombination in secondary standard ionisation chambers.

Evaluation of a micro ionization chamber for dosimetric measurements in image-guided preclinical irradiation platforms

Image-guided small animal irradiation platforms deliver small radiation fields in the medium energy x-ray range. Commissioning of such platforms, followed by dosimetric verification of treatment planning, are mostly performed with radiochromic film. There is a need for independent measurement methods, traceable to primary standards, with the added advantage of immediacy in obtaining results. This investigation characterizes a small volume ionization chamber in medium energy x-rays for reference dosimetry in preclinical irradiation research platforms. The detector was exposed to a set of reference x-ray beams (0.5–4 mm Cu HVL). Leakage, reproducibility, linearity, response to detector’s orientation, dose rate, and energy dependence were determined for a 3D PinPoint ionization chamber (PTW 31022). Polarity and ion recombination were also studied. Absorbed doses at 2 cm depth were compared, derived either by applying the experimentally determined cross-calibration coefficient at a typical small animal radiation platform ‘user’s’ quality (0.84 mm Cu HVL) or by interpolation from air kerma calibration coefficients in a set of reference beam qualities. In the range of reference x-ray beams, correction for ion recombination was less than 0.1%. The largest polarity correction was 1.4% (for 4 mm Cu HVL). Calibration and correction factors were experimentally determined. Measurements of absorbed dose with the PTW 31022, in conditions different from reference were successfully compared to measurements with a secondary standard ionization chamber. The implementation of an End-to-End test for delivery of image-targeted small field plans resulted in differences smaller than 3% between measured and treatment planning calculated doses. The investigation of the properties and response of a PTW 31022 small volume ionization chamber in medium energy x-rays and small fields can contribute to improve measurement uncertainties evaluation for reference and relative dosimetry of small fields delivered by preclinical irradiators while maintaining the traceability chain to primary standards.

THE IN-SITU CALIBRATION METHOD FOR AMBIENT DOSE EQUIVALENT DOSEMETERS.

Ambient dose equivalent dosemeters are widely distributed in nuclear facilities for routine continuous monitoring or nuclear accident emergency monitoring, they are inconvenient to be disassembled and sent to the metrology laboratory for calibration. To ensure the accuracy of such dosemeters, the research of in-situ calibration method has been carried out. Ambient dose equivalent secondary standard ionization chamber and portable gamma ray irradiation facility have been designed for in-situ calibration. The experiments of in-situ calibration were carried out in five typical sites located in China Institute of Atomic Energy, results showed that the relative deviation between in-situ calibration factors and metrology laboratory calibration factors are within 5%.The combined standard uncertainty of the in-situ calibration factor is 2.8%, and the expanded uncertainty is 5.6% (k=2).The in-situ calibration method can meet the calibration requirements of the fixed ambient dose equivalent dosemeters.

The operation of an ionization chamber with depleted gas for radioactivity measurement: Calibration procedure and utilising normalized manufacturer's radionuclide factors

At the National Metrology Institute of South Africa (NMISA) absolute activity measurements of γ-emitting radionuclides are maintained for longevity on a secondary standard ionization chamber. Because the ionization chamber has lower gas pressure than that normally produced by the manufacturer, this paper focuses attention on explaining a normalization scheme devised to allow NMISA to make use of the manufacturer's supplied radionuclide calibration factors when necessary. The applicability of the procedure is justified through analysis of some results from a comprehensive simulation of the chamber undertaken in an independent study. Comparisons of the derived normalized calibration factors against those obtained through measurement at NMISA are made for a variety of radionuclides.

Calibration and measurement of X-ray personal dose equivalent with a Hp(10) ionization chamber

The value of the personal dose equivalent at a 10 mm depth is to characterize the energy deposition of strong penetrating radiation in the human body and is derived by measurement of air kerma and application of conversion coefficients from the ISO report. However, the conversion coefficients depend strongly on the photon energy and angles of incidence for low-energy photons. In order to overcome the problem that the conversion coefficient of low energy rays changes greatly due to the small change of energy, a secondary standard ionization chamber was used to measure the personal dose equivalent directly. A matched reference field was established with 20-250 kV X-rays and correction factors with the Hp (10) chamber were calculated under these radiation qualities with different angles of incidence. The results showed that the differences were almost 22.7 % of correction factors for the low energy photons at angles of incidence 0?. With the conversion coefficient recommended in ISO 4037-3-2019, the performance of the chamber response with respect to Hp (10) in the energy range from 33 keV to 208 keV was within about 10 %, and in the energy range from 12 keV to 208 keV and for angles of incidence between 0? and 75? was within about ?19 %.

An international multi-center investigation on the accuracy of radionuclide calibrators in nuclear medicine theragnostics

BackgroundPersonalized molecular radiotherapy based on theragnostics requires accurate quantification of the amount of radiopharmaceutical activity administered to patients both in diagnostic and therapeutic applications. This international multi-center study aims to investigate the clinical measurement accuracy of radionuclide calibrators for 7 radionuclides used in theragnostics: 99mTc, 111In, 123I, 124I, 131I, 177Lu, and 90Y.MethodsIn total, 32 radionuclide calibrators from 8 hospitals located in the Netherlands, Belgium, and Germany were tested. For each radionuclide, a set of four samples comprising two clinical containers (10-mL glass vial and 3-mL syringe) with two filling volumes were measured. The reference value of each sample was determined by two certified radioactivity calibration centers (SCK CEN and JRC) using two secondary standard ionization chambers. The deviation in measured activity with respect to the reference value was determined for each radionuclide and each measurement geometry. In addition, the combined systematic deviation of activity measurements in a theragnostic setting was evaluated for 5 clinically relevant theragnostic pairs: 131I/123I, 131I/124I, 177Lu/111In, 90Y/99mTc, and 90Y/111In.ResultsFor 99mTc, 131I, and 177Lu, a small minority of measurements were not within ± 5% range from the reference activity (percentage of measurements not within range: 99mTc, 6%; 131I, 14%; 177Lu, 24%) and almost none were outside ± 10% range. However, for 111In, 123I, 124I, and 90Y, more than half of all measurements were not accurate within ± 5% range (111In, 51%; 123I, 83%; 124I, 63%; 90Y, 61%) and not all were within ± 10% margin (111In, 22%; 123I, 35%; 124I, 15%; 90Y, 25%). A large variability in measurement accuracy was observed between radionuclide calibrator systems, type of sample container (vial vs syringe), and source-geometry calibration/correction settings used. Consequently, we observed large combined deviations (percentage deviation > ± 10%) for the investigated theragnostic pairs, in particular for 90Y/111In, 131I/123I, and 90Y/99mTc.ConclusionsOur study shows that substantial over- or underestimation of therapeutic patient doses is likely to occur in a theragnostic setting due to errors in the assessment of radioactivity with radionuclide calibrators. These findings underline the importance of thorough validation of radionuclide calibrator systems for each clinically relevant radionuclide and sample geometry.

Assessment of calibration coefficient ND, W in terms of absorbed dose-to-water of some ionization chambers

The absorbed dose-to-water calibration coefficients ND,W of some ionization chambers were determined in terms of the secondary standard chambers in 60Co gamma-ray beam based on the TRS-398 protocol. The reference absorbed dose-to-water Dw were measured using secondary standard ionization chambers of model NE 2781#0537 (0.60 cm3 volume) and NE 2771#1205 (0.69 cm3 volume) which are traceable to the dosimetry laboratory of the International Atomic Energy Agency (IAEA). This study mainly focuses on the comparative assessment of the determined ND,W coefficients of twenty cylindrical ionization chambers from various user groups. The determined ND,W coefficients were compared with the manufacturer provided ND,W coefficients. The observed percentage of deviation between the measured and the manufacturer’s ND,W coefficients among all the chambers were found to be in the range of 0.019% and -2.263% as the least and highest, respectively. The observed percentage of deviations for studied chambers were found within the IAEA’s acceptance limit of 1.5% with an exception for three chambers. This observed discrepancy with the IAEA’s acceptance limit for the three chambers out of the twenty chambers, indicates the calibration necessity before using chambers in routine reference dosimetry. In ND,W measurement, the uncertainty Uc is reported with the coverage factor k=1 that providing a level of confidence of approximately 68%.

Performance of a twin position-sensitive Frisch-grid ionization chamber for photofission experiments

A position-sensitive twin Frisch-grid ionization chamber has been constructed for future photofission experiments using nearly monochromatic, linearly polarized gamma-ray beams. By exchanging the anode plates in the standard ionization chamber on both sides by an array of grid- and strip-anodes, which are rotated by 90° relative to each other and read out by means of resistive charge division, a position sensitivity is achieved that allows the azimuthal fragment emission angle and hence the fission axis orientation to be determined. The performance of this gaseous detector has been studied using the well-known 252Cf spontaneous fission process. The fission axis orientation could be determined relative to an arbitrary axis in space with a resolution better than 7° FWHM. Measured pre-neutron mass and total kinetic energy distributions are consistent with literature, which ensures that the mass and energy resolution for fission fragments is not affected by the position-sensitive structure.

Primary standardization of 224Ra activity by liquid scintillation counting

A standard for activity of 224Ra in secular equilibrium with its progeny has been developed, based on triple-to-double coincidence ratio (TDCR) liquid scintillation (LS) counting. The standard was confirmed by efficiency tracing and 4παβ(LS)-γ(NaI(Tl)) anticoincidence counting, as well as by 4πγ ionization chamber and NaI(Tl) measurements. Secondary standard ionization chambers were calibrated with an expanded uncertainty of 0.62% (k = 2). Calibration settings were also determined for a 5 mL flame-sealed ampoule on several commercial reentrant ionization chambers (dose calibrators).

Techniques for Irradiating Primate Brains with a 78Kr Beam from the JINR-LHEP Nuclotron

Experimental techniques for irradiating primate and rat brains by a narrow 78Kr beam with an energy of 2.58 GeV/n extracted from the JINR Nuclotron is described. The brain is irradiated near the F3 focal point located in the experimental hall of Building 1 of the JINR Laboratory of High-Energy Physics (LHEP). The beam profile is measured with multiwire ionization chambers and radiochromic films, and its quality is monitored using time-of-flight scintillation counters. The radiation dose absorbed by the irradiated object is measured using a dosimetric ionization chamber with tilted electrodes. This air-filled chamber has been designed so as to suppress the effect of ion column recombination in the tracks of high-Z nuclei. The extracted beam of 78Kr ions is calibrated and monitored using nuclear photoemulsions and by comparing the readings from the standard ionization chamber at the beam extraction point with the ion counting rate in scintillation counters. The experiment benefits from Nuclotron’s stable operation and from the high intensity of the 78Kr beam reached in the 55th run (~2 × 106 ions per beam impulse at the F3 focal point). In this unique radiobiological experiment, the effects of the heavy ions of galactic cosmic rays on cerebral cognitive functions of astronauts are emulated and investigated.

Standardisation of Rhenium-188 and determination of calibration factors for secondary standard and radionuclide calibrator

The use of Rhenium-188 for various therapeutic applications in the field of nuclear medicine has increased in recent years due to its favourable properties like decay scheme, cost effective availability and easy chemistry. Two independent measuring setups were used to standardise 188Re radioactive solution. The modus operandi of standardisation was 4πβ-γ coincidence technique where the beta detection was done by proportional counting and liquid scintillation counting and the gamma detection was done by using NaI(Tl) detectors. The secondary standard, high pressure ionisation chamber type Centronic IG12, 20A was calibrated with the standardised 188Re solution and the sensitivity coefficient (pA MBq−1) was determined. To enhance the accuracy of the commercial radionuclide calibrator and to ensure that patients receive optimum dose of these radiopharmaceuticals, calibration number of the Capintec CRC-15β radionuclide calibrator was also verified. This paper presents the standardisation of 188Re radioactive solution by primary methods and calibration of BARC secondary standard ionisation chamber system and a Capintec CRC-15β radionuclide calibrator.

Experimental Measurement and Monte Carlo Simulation the Correction Factor for the Medium-Energy X-ray Free-air Ionization Chamber

A key comparison has been made between the air-kerma standards of the National Institute of Metrology (NIM), China, and other Asia Pacific Metrology Programme (APMP) members in the medium-energy X-ray. This paper reviews the primary standard Free-air ionization chamber correction factor experimental method and Monte Carlo simulation method in the NIM. The experimental method and the Monte Carlo simulation method are adopted to obtain the correction factor for the medium-energy X-ray primary standard free-air ionization chamber at 100 kV, 135 kV, 180 kV, 250 kV four CCRI reference qualities. The correction factor has already been submitted to the APMP as key comparison data and the results are in good agreement with those obtained in previous studies. This study shows that the experimental method and the EGSnrc simulation method are usually used in the measurement of the correction factor. In particular, the application of the simulation methods is more common.

A reference material for evaluation of 137 Cs radiochronometric measurements.

A new nuclear forensic reference material has been characterized as a standard for radiochronometric determination of the model purification date for 137Cs sources. The purification date of a radioactive source is a potentially diagnostic nuclear forensic signature for determining the provenance of a radioactive material. Reference values have been measured for the attributes needed to use the 137Cs/137Ba chronometer: the molality (reported here as nmol g-1) of 137Cs and of the radiogenic portion of 137Ba in the material (hereafter referred to as 137Ba*). All measurement results were decay-corrected to represent the composition of the material on the reference date of July 7, 2011. The molality of 137Cs is (0.7915 ± 0.0073) nmol g-1; this value was calculated from the massic activity of 137Cs, (348.4 ± 3.0) kBq g-1, as measured in the NIST 4π-γ secondary standard ionization chamber (previously calibrated by 4π-(e+x)-γ-coincidence efficiency extrapolation counting) and the evaluated half-life of 137Cs, (30.05 ± 0.08) years. The molality of 137Ba*, (1.546 ± 0.024) nmol g-1, was measured by isotope dilution mass spectrometry using the measured relative proportion of 138Ba in the material to apply a correction for the 137Ba contribution from natural Ba. A model age of (47.04 ± 0.56) years, corresponding to a model purification date of June 22, 1964 with an expanded uncertainty of 200 days is calculated from the reference material values. This age is consistent with the date engraved on the capsule that contained the 137Cs starting material and with a prior independent determination of the model purification date. A full discussion of the uncertainties of the reference material values is included.

Production and standardization of an on-demand protactinium-233 tracer

Protactinium-233 (233Pa) was generated by neutron activation of thorium and isolated by column chromatography using an octanol-impregnated resin. Absolute activity standardization was performed on 233Pa using three independent methods, the results of which agreed within their associated uncertainties. The standardized 233Pa was used to calibrate a secondary standard ionization chamber and high purity germanium detectors to enable a rapid and traceable method for the production and quantification of this radiotracer.