Pressure Ionization Chamber Research Articles

Activity standard and calibrations for 227Th with ingrowing progeny

Thorium-227 was separated from its progeny and standardized for activity by the triple-to-double coincidence ratio (TDCR) method of liquid scintillation counting. Confirmatory liquid scintillation-based measurements were made using efficiency tracing with 3H and live-timed anticoincidence counting (LTAC). The separation time and the efficiency of the separation were confirmed by gamma-ray spectrometry. Calibrations for reentrant pressurized ionization chambers, including commercial radionuclide calibrators, and a well-type NaI(Tl) detector are discussed.

Quality control measures of thermoluminescent dosimetry system used in environmental radiation monitoring

Objective To discuss the quality control measures of the thermoluminescent dosimetry system and to verify its propriety of when used in environmental radiation monitoring. Methods The quality control measures included the stability test, the dispersibility screening and the uncertainty evaluation of measurement results of the TLD reader and TLD detector, in addition, the environmental radiation accumulated dose monitoring results obtained by the high pressure ionization chamber were compared with those by the thermoluminescent dosimetry system. Results The variation range of TLD reader’s light source coefficient is within 0.070~0.073 during the preheating and measuring process, which meets the requirements of stability; The χ 2 value of the TLD detector is 2.088, which obeys the normal distribution; The thermoluminescent dosimetry system’s nonlinear response, coefficient of variation and energy response meet the measurement requirements; There is a deviation of −6.58% the largest between the cumulative dose obtained by TLD and the high pressure ionization chamber. Conclusion The quality control measures discussed in this paper can be used as a reference for similar thermoluminescent dosimetry system. Our system has passed all the tests and can meet the environmental radiation cumulative dose monitoring requirements. 摘要： 目的 探讨热释光测量系统的质量控制方法, 验证热释光测量系统能否准确有效的用于环境辐射水平监测。 方法 采取的环境辐射监测用热释光测量系统质量控制方法包括热释光测量系统的稳定性检验、热释光探测器的分 散性筛选、测量结果不确定度评定, 并与高气压电离室测量方法进行对比。 结果 读出器预热及测读过程中光源系数 变化范围在 0.070~0.073, 稳定性符合使用要求; 热释光探测器的 χ 2 值为 2.088, 服从正态分布;热释光测量系统满足 非线性响应、变异系数和能量响应的计量要求; 热释光累积剂量测量结果与高气压电离室相比偏差最大 −6.58%。 结论 本实验室采取的质控措施可作为同类热释光测量系统的质控措施的参考;本实验室的热释光测量系统通过了 各项检验, 满足环境辐射累积剂量监测的使用要求。

On the stability of well-type ionization chamber source strength calibration coefficients.

To investigate the variability and stability of brachytherapy source strength calibration coefficients for air-communicating and pressurized well-type ionization chambers among high-dose rate (HDR), low-dose rate (LDR), and electronic brachytherapy (EBT) source qualities. These qualities of an ionization chamber are important features to assess given their role in maintaining traceability to a primary national standards laboratory and facilitating efficacious patient care in brachytherapy. The calibration records from the University of Wisconsin Accredited Dosimetry Calibration Laboratory (UWADCL) customer well-type ionization chamber database were retrospectively analyzed for calibrations performed between 1996 and 2019. A statistical analysis was performed and differentiated among calibration type to quantify the distribution of chamber calibration coefficients among several chamber models. Distributions were quantified based on their moments and by quantile analysis. For LDR calibrations, chamber response was further differentiated by seed type to study the variability in seed dependence within and across chamber models. In addition to these metrics, the calibration lineage at the UWADCL was used to assess the stability of these calibration coefficients among chamber model and source type based on the ratio of subsequent calibration coefficients. The distribution of brachytherapy source strength calibration coefficients for a particular chamber model is not necessarily normally distributed and is sensitive to changes in the machining tolerances or design of the chamber model. Calibration source quality also influenced the distributions of calibration coefficients for a chamber model; the air-kerma rate calibration coefficients for EBT sources were the most variable followed by LDR and then HDR source types. The stability of a chamber's source strength calibration coefficient exhibited a similar dependence on the source quality. Air-communicating and pressurized chambers exhibited an average stability between subsequent calibrations of 0.2% and 3.0%, respectively, for HDR calibrations, but could exhibit more than double this variability characteristic of their leptokurtic distributions. For LDR calibrations, the spread and stability in a model's calibration ratio toward another seed type is extensive and notable. For some seed types and chamber models exhibit variations of <0.5% while others exceeded 2.0%. Furthermore, the magnitude of this dependence is outside the variability of the source's source strength due to manufacturing, which was determined from the manufacturer and NIST source strength intercomparison records at the UWADCL. As a result, establishing and disseminating calibration conversion factors among different source and chamber models is not advised as it would substantially increase the uncertainty in a clinical user's determination of source strength. The calibration of a well-type ionization chamber is unique to the chamber, source, and source holder. Attempting to generalize source strength calibration coefficients among chambers of the same model or source type is impractical given the variation in response observed across the calibration history of the UWADCL. Attempting to quantitate and transfer calibration coefficients in such a relative sense may significantly degrade the uncertainty relative to specifically calibrating a chamber for an individual source.

Development of a silicon microstrip detector prototype for ultra-fast imaging at a synchrotron radiation beam

A method of imaging of ultra-fast processes, like explosion or fast combustion, at a synchrotron radiation beam is being developed at the Siberian Synchrotron and Teraherz Radiation Center (SSTRC) . Two stations are operating at beam line 0 at the VEPP-3 storage ring and at beam line 8 at the VEPP-4M storage ring. Both stations are equipped with the detector for imaging of explosions DIMEX, based on high pressure ionization chamber, and allowing to record up to 100 one dimensional images with the frame rate of 8 MHz. However the maximum flux that DIMEX can detect is limited as well as spatial resolution and frame rate because of gas technology used. In view of significant increase of SR flux at the VEPP-4M beam line due to the new 9-pole 2 T wiggler, a new detector is being developed for this beam line, based on Si microstrip sensor. The first Si microstrip detector prototype has been mounted with new specially developed front-end ASIC that allows to record data with the rate of 50 MFrames/s. The first measurements with this prototype demonstrated significant improvement of all critical parameters of the detector compared to the gaseous version.

Operation of a silicon microstrip detector prototype for ultra-fast imaging at a synchrotron radiation beam

A method of imaging of ultra-fast processes, like explosions or fast combustion, at a synchrotron radiation beam is being developed at the Siberian Synchrotron and Terahertz Radiation Center (SSTRC). Two stations are equipped with the detector for imaging of explosions, DIMEX, based on high pressure ionization chamber, and allowing to record up to 100 one dimensional images with a frame rate of 8 MHz. However the maximum flux that DIMEX can detect is limited as well as the spatial resolution and the frame rate because of the gas technology used. In view of the significant increase of SR flux at the VEPP-4M beam line due to the new 9-pole 2 T wiggler, a new detector is being developed for this beam line, based on Si microstrip sensor. The first Si microstrip detector prototype has been mounted with a new specially developed front-end ASIC that allows to record data with a rate up to 40 MFrames/s. The first measurements with this prototype demonstrated significant improvement of all critical parameters of the detector compared to the gaseous version. The maximum detected photon rate before saturation is increased to 20000 photons/(channel x bunch) compared to 1500 photons/(channel x bunch). The spatial resolution is improved from 240μm to 130μm (FWHM) and the frame rate is increased by a factor 5.

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.

Application of a SrI2(Eu) scintillation detector to in situ gamma-ray spectrometry in the environment

Using scintillation detectors to spectrometrically determine dose rate is useful in response to a nuclear accident, because the nuclide contribution in the measured dose rate can be determined. However, to select an appropriate scintillator for in situ gamma-ray spectrometry in the environment, energy resolution and counting efficiency should be evaluated. A SrI2(Eu) crystal is one of the promising scintillators, with good energy resolution and light output performance. But its long scintillation decay time of about 1 μs needs to be well matched with the signal processing unit of the gamma-ray spectrometer to avoid degrading its good performance. In this study a performance test was first conducted to determine the optimized pulse shaping time in the gamma-ray detection process. In addition, a Monte Carlo simulation of the SrI2(Eu) detector was performed to establish the algorithm for the spectrometric determination of dose rate. Finally, in situ gamma-ray spectrometry was performed with the SrI2(Eu) detector to determine the ambient dose rate, as well as the dose rate of nuclides in the environment. The results were successfully compared with those of HPIC (high pressure ion chamber), portable HPGe (high purity Ge), and NaI(Tl) detectors at the same site.

Comparative analysis of gamma dose rates measured by ion chamber in and around the historical sacral objects in Bosnia and Herzegovina

The main objective of this study was to investigate the correlation between the indoor and outdoor ambient dose equivalent rates measured by the ion chamber inside and around the historical sacral objects at a few locations in Bosnia and Herzegovina. The investigated objects made of the traditional building materials were built in the Late Medieval, Post Medieval, and Ottoman Period of Bosnia and Herzegovina history. The LUDLUM Model 9DP instrument based on a pressurized ion chamber was selected for natural low level radiation measurements since the ionisation chambers have higher sensitivities than the other types of detectors. The detection capability of the LUDLUM Model 9DP pressurized ion chamber was examined in the laboratory conditions with a source of low activity and under natural environmental radiation conditions by measuring the indoor and outdoor dose rates. A weak positive correlation was found between the ambient dose equivalent rates inside the historical sacral objects and the dose rates outside the objects. The average evaluated value of the indoor to outdoor dose rate ratio of 1.07 for the studied historic objects is less than that obtained for the contemporary building materials such as concrete. No study on the indoor to outdoor dose rate ratio in Bosnia and Herzegovina measured by the LUDLUM 9DP dose rate meter based on an ion chamber has been conducted yet. In addition to direct measurements, the first gamma spectrometric analysis of a few samples of building materials from the Late Medieval period in Bosna and Herzegovina was performed. The results of the gamma analysis revealed almost uniform distribution of primordial radionuclides in the investigated samples. It was demonstrated that such materials had the reduced content of radioactive isotopes compared to the contemporary building materials and therefore they could have potential advantages in specific applications related to the environmentally sustainable architecture.

Not all lightweight lead aprons and thyroid shields are alike

ObjectiveWith the explosion of minimally invasive surgery, the use of fluoroscopy has significantly increased. Concurrently, there has been a demand for lighter weight aprons. The industry answered this call with the development of lightweight aprons. Our goal was to see whether lighter weight garments provide reduced protection. MethodsDry laboratory testing was performed in a standard X-ray room, using a standard fluoroscopy table and standard acrylic blocks. A commercial-grade pressurized ion chamber survey meter (Ludlum Model 9DP; Ludlum Measurements, Inc, Sweetwater, Tex) was used to detect gamma rays and X-rays above 25 keV. Nonlead aprons from several manufacturers were tested for scatter radiation penetration above the table at a fixed distance (3 feet) and compared with two standard 0.5-mm lead aprons of different manufacturers. ResultsScatter measurements were made at 60 kVp and 70 kVp for pure lead (0.5 mm), mixed, and nonlead protective garments. Scatter penetration for the nonlead blends and barium aprons was 292% and 258%, respectively, at 60 kVp compared with the pure lead apron. At the higher beam quality of 70 kVp, the scatter penetration was 214% and 233% for the blend and barium aprons, respectively, compared with the pure lead apron. Our measurements demonstrate a noticeable difference in scatter reduction between pure lead and nonlead garments. Pure barium aprons and nonlead aprons from certain companies demonstrated scatter penetration that is inconsistent with the 0.5 mm of lead equivalence as claimed on the label. In addition, there was an incidental finding of a handful of lightweight aprons with significant tears along the seams, leaving large gaps in protection. Our study also demonstrates that several companies rate their lightweight garments as 0.5 mm lead equivalent, when actually only a small area on the chest and abdomen where the garment overlapped was 0.5 mm, leaving the rest of the garment with half the protection at 0.25 mm. ConclusionsOur reliance on protective lead garments to shield us from the biologic effects of radiation exposure and the inferiority of some lightweight garments necessitate a streamlining of the testing methods and transparency in data reporting by manufacturers.

Comparative study of precise measurements of natural radionuclides and radiation dose using in-situ and laboratory \u03b3-ray spectroscopy techniques

In this study, in-situ and laboratory γ-ray spectroscopy techniques were compared to evaluate the activity concentration of natural radionuclides in soil. The activity concentrations of 238U (226Ra), 232Th, and 40K in the soil in 11 sites were simultaneously measured with in-situ portable HPGe and the NaI(Tl) detectors. In parallel, 55 soil samples collected from these sites were analyzed with a laboratory γ-ray spectroscopy technique (HPGe). A strong correlation was observed between the in-situ and laboratory HPGe techniques with a linear correlation coefficient (R2) of 0.99 for 226Ra and 232Th and 0.975 for 40K, respectively. The in-situ HPGe technique shows a strong correlation with the NaI(Tl) detector. γ-Rays cps of 226Ra, 232Th, and 40K of the NaI (Tl) detector were then converted to specific activities (Bq kg−1 unit) in soil using the empirical formulas obtained in this study. The absorbed dose rate in air at 1 m height above ground due to these radionuclides was calculated using the Beck’s formula and the results were compared with measured values obtained with an high pressure ionization chamber. The results of the calculated and measured dose rate show a strong correlation of R2 = 0.96. The reliability and precision of analytical spectroscopy techniques of radioactivity and radiation dose were confirmed in this work.

Standardization of 64Cu activity

The complex decay scheme that makes 64Cu promising as both an imaging and therapeutic agent in medicine also makes the absolute measurement of its activity challenging. The National Institute of Standards and Technology (NIST) has completed a primary activity standardization of a 64CuCl2 solution using the 4πβ(LS)-γ(NaI) live-timed anticoincidence (LTAC) counting method with a combined standard uncertainty of 0.51 %. Two liquid scintillation (LS) counting methods were employed for confirmatory measurements. Secondary measurements were made by high-purity germanium detectors, pressurized ionization chambers (IC), and a well-type NaI(Tl) counter. Agreement between the LTAC-based standard and standards from other laboratories was established via IC calibration factors. Poor agreement between methods and with theoretical IC responses may indicate a need for improved β+/- branching probabilities and a better treatment of β+/- spectra.

Two determinations of the Ge-68 half-life

In nuclear medicine, 68Ge is used to generate 68Ga for imaging by positron emission tomography (PET) and sealed sources containing 68Ge/68Ga in equilibrium have been adopted as long-lived calibration surrogates for the more common PET nuclide, 18F. We prepared several 68Ge sources for measurement on a NaI(Tl) well counter and a pressurized ionization chamber, following their decay for 110 weeks (≈ 2.8 half-lives). We determined values for the 68Ge half-life of T1/2 = 271.14(15) d and T1/2 = 271.07(12) d from the NaI(Tl) well counter and ionization chamber measurements, respectively. These are in accord with the current Decay Data Evaluation Project (DDEP) recommended value of T1/2 = 270.95(26) d and we discuss the expected impact of our measurements on this value.

Determination of photon emission probabilities for the main gamma-rays and half-life measurements of 64Cu

The National Institute of Standards and Technology (NIST) performed new standardization measurements for 64Cu. As part of this work the photon emission probabilities for the main gamma-rays and the half-life were determined using several high purity germanium (HPGe) detectors. Half-life determinations were also carried out with a NaI(Tl) well counter and two pressurized ionization chambers.

Determination of photon emission probability for the main gamma ray and half-life measurements of 64Cu

The National Institute of Standards and Technology (NIST) performed new standardization measurements for 64Cu. As part of this work the photon emission probability for the main gamma-ray line and the half-life were determined using several high-purity germanium (HPGe) detectors. Half-life determinations were also carried out with a NaI(Tl) well counter and two pressurized ionization chambers.

A method for confirming a third-party assay of I-125 seeds used for prostate implants.

The purpose of this work is to describe a method and apparatus that can be used to confirm the source strength of a large number of I‐125 seeds while maintaining sterility, accuracy, reproducibility, and time efficiency. Source strengths ranging from 0.395 to 0.504 U/seed were available for this study. Three different seed configurations were measured: loose, linked, and loaded needles. A third‐party 10% assay (NIST traceable) was provided. A custom stand was built out of aluminum to hold an exposure meter [Inovision (Fluke) 451P pressurized ion chamber] at 25 cm above the I‐125 sources to measure the exposure rate. The measurements were made in an operating room, and a sterile sheet was placed under the nonsterile aluminum stand on a sterile loading table. Seeds and needles were placed in a sterile tray for these measurements. Two hundred and six loose seeds in six batches (0.395, 0.395, 0.409, 0.444, 0.444, and 0.444 U/seed) and 1434 seeds in 10 batches containing various strands (0.444, 0.444, 0.444, 0.444, .0444, 0.466, 0.466, 0.504, and 0.504 U/seed) were measured. For the loose and stranded seeds, the average exposure rate per unit activity was measured to be 0.589 mR/h·U with a standard deviation of 0.017. Loaded needles were measured with an average exposure rate per unit activity to be 0.269 mR/h·U with a standard deviation of 0.014. We conclude that the method described here is capable of confirming a third‐party assay when performed on a large number of loose or stranded seeds in bulk. It is less reliable for preloaded needles.

A radionuclide calibrator based on Cherenkov counting for activity measurements of high-energy pure β¯-emitters

Due to their stability and reproducibility, re-entrant pressurized ionization chambers (also called radionuclide calibrators) are widely used for activity measurements in nuclear medicine services as well as in national metrology institutes to maintain reference standards. Generally, these secondary instruments yield accurate activity measurements for γ-emitting radionuclides. Ionization chambers are easy to use and thus well-adapted to guarantee the metrological traceability between national metrology institutes and end-users. However, the reproducibility of calibration factors can be significantly impaired when measuring high-energy pure β¯-emitters such as radiopharmaceuticals based on 90Y. This is because the bremsstrahlung emission contributing to the instrument response is strongly dependent on the geometry of the components surrounding the radioactive solution. The present article describes a new design based on pulse counting to address this problem. It takes advantage of Cherenkov emission resulting from Compton scattering in transparent materials. The interest of Cherenkov counting is to obtain a low-sensitivity detector that enables direct measurements of high-activity solutions (at least up to 10 GBq for 90Y-microspheres in aqueous suspensions used in nuclear medicine). A simple design based on a geometry close to an ionization chamber used at LNHB (Vinten 671 type) is described. The feasibility in terms of detection efficiencies (lower than 10−4 for 90Y solutions) of the new radionuclide calibrator is investigated by Monte Carlo calculations using the Geant4 code.

SU‐D‐201‐01: Attenuation of PET/CT Gantries with 511 KeV Photons

Purpose:PET shielding requires the use of large amounts of lead because of the penetrating nature of 511 keV photons. While the uptake rooms generally require the thickest lead, the scan room often requires substantial shielding. Attenuation by the PET/CT gantry is normally assumed to be zero, but may be significant in directions perpendicular to the scanner axis.Methods:A 5 mL tube was filled with between 14.7 and 20.5 mCi of F‐18 and inserted into a phantom (70 cm NEMA PET Scatter Phantom). Exposure rates were recorded at several distances and 15° intervals with a pressurized ionization chamber (Ludlum 9DP) both with the phantom outside the gantry and centered in the CT and PET acquisition positions. These measurements were repeated with three scanners: Siemens Biograph TruePoint 6, GE Optima 560, and Philips Gemini 64. Measurements were decay corrected and normalized to exposure rates outside the gantry to calculate percent transmission.Results:Between 45° to 135° (measured from the patient bed at 0°), average transmission was about 20% for GE, 35% for Philips, and 30% for Siemens. The CT gantry was roughly twice as attenuating as the PET gantry at 90° for all three manufacturers, with about 10% transmission through the CT gantry and 20% through the PET gantry.Conclusion:The Philips system is a split‐gantry and therefore has a narrower angle of substantial attenuation. For the GE and Siemens systems, which are single‐gantry design, transmission was relatively constant once the angle was sufficient to block line‐of‐sight from the phantom. While the patient may spend a greater fraction of time at the PET position of the scanner, transmission characteristics of the two components are similar enough to be treated collectively. For shielding angles between 45° and 135°, a reasonably conservative assumption would be to assume gantry transmission of 50%.

Uncertainty evaluation in activity measurements using ionization chambers

SummaryPressurized re-entrant (or 4π) ionization chambers (ICs) connected to current-measuring electronics are used for activity measurements of photon emitting radionuclides and some beta emitters in the fields of metrology and nuclear medicine. As a secondary method, these instruments need to be calibrated with appropriate activity standards from primary or direct standardization. The use of these instruments over 50 years has been well described in numerous publications, such as the Monographie BIPM-4 and the special issue of Metrologia on radionuclide metrology (Ratel 2007 Metrologia 44 S7–16, Schrader1997 Activity Measurements With Ionization Chambers (Monographie BIPM-4) Schrader 2007 Metrologia 44 S53–66, Cox et al 2007 Measurement Modelling of the International Reference System (SIR) for Gamma-Emitting Radionuclides (Monographie BIPM-7)). The present work describes the principles of activity measurements, calibrations, and impurity corrections using pressurized ionization chambers in the first part and the uncertainty analysis illustrated with example uncertainty budgets from routine source-calibration as well as from an international reference system (SIR) measurement in the second part.

A real-time multichannel detector system for large-scale environmental radiation survey

In this work, we established a real-time multichannel detector system for large-scale environmental radiation survey. The system consists of a Berkeley Lab cosmic-ray detector for the measurement of muons, a moderated He detector for neutrons, a NaI(Tl) as well as a HPGe spectrometer for terrestrial gamma rays, and a high pressure ionization chamber, which responses to both cosmic rays and terrestrial gamma rays. The measured data of these five detector channels as well as signals from a global position system are acquired and displayed by a LabVIEW program on a notebook computer every one minute (10 min for HPGe and 20 min for NaI(Tl) gamma-ray spectrometers). The advantage and merit of this multichannel detector system have been demonstrated by test runs with the equipment set up both on a train and on a bus to show in real time the variation of cosmic-ray intensity as a function of altitude and the gamma-ray dose rates as well as the relative concentrations of the natural radioactive elements over a large survey area. This real-time multichannel detector system was originally developed for natural background radiation measurements for popular science education to general public, however, due to the specific features of each detector of the system it appears to be an ideal system for radiation survey over a large radiation polluted or contaminated area resulted from a severe nuclear accident, such as Fukushima Dai-Ichi Nuclear Power Plant accident.

Gamma dose rate due to natural and manmade radiation sources from a nuclear facility in Mexico

The environmental external gamma dose rate has been determined at the Mexican Nuclear Research Centre and surrounding communities, located in a forest area. Outdoor direct measurements of external gamma exposure and absorbed dose rates in air were performed using passive integrating thermoluminescent dosimeters. Radiological measurements were also carried out with a portable high pressure ionization chamber. The gamma dose rate was evaluated from data obtained along 10 years measurements. The activity concentrations of 40K, 226Ra, 232Th, 137Cs, and 235U in surface soil samples at sampling sites are also presented. The radionuclide activity concentrations were determined by low background gamma spectrometry with hyper-pure germanium detectors. A site specific lineal model to describe the relationship between the external gamma dose rate and the 226Ra concentration values in the soil is proposed.