Measuring^(222)Rn in aquatic environment via Pulsed Ionization Chamber Radon Detector

Radon(Rn)is a naturally occurring radioactive inert gas in nature,and^(222)Rn has been routinely used as a powerful tracer in various aquatic environmental research on timescales of hours to days,such as submarine groundwater discharge.Here we developed a new approach to measure^(222)Rn in discrete water samples with a wide range of^(222)Rn concentrations using a Pulsed Ionization Chamber(PIC)Radon Detector.The sensitivity of the new PIC system is evaluated at 6.06 counts per minute for 1 Bq/L when a 500 mL water sample volume is used.A robust logarithmic correlation between sample volumes,ranging from 250 mL to 5000 mL,and system sensitivity obtained in this study strongly suggests that this approach is suitable for measuring radon concentration levels in various natural waters.Compared to the currently available methods for measuring radon in grab samples,the PIC system is cheaper,easier to operate and does not require extra accessories(e.g.,drying tubes etc.)to maintain stable measurements throughout the counting procedure.

Collection efficiency of a monitor parallel plate ionization chamber for pencil beam scanning proton therapy

The collection efficiency of monitor parallel plate ionization chambers is the main uncertainty in the beam control of pencil beam scanning systems.Existing calculation methods for collection efficiency in photon or passive scattering proton systems have not considered the characteristics of non-uniform charge density in pencil beam scanning systems.In this study,Boag’s theory was applied to a proton pencil beam scanning system.The transverse distribution of charge density in the ionization chamber was considered to be a Gaussian function and an analytical solution was derived to calculate collection efficiency in the beam spot area.This calculation method is called the integral method and it was used to investigate the effects of beam parameters on collection efficiency.It was determined that collection efficiency is positively correlated with applied voltage,beam size,and beam energy,but negatively correlated with beam current intensity.Additionally,it was confirmed that collection efficiency is improved when the air filling the monitor parallel plate ionization chamber is replaced with nitrogen.

Simulation method for measurement of the cross-section of the^(14)N(n,a)^(11)B reaction using a gridded ionization chamber

A simulation method for measurement of the cross-section of the^(14)N(n,a)^(11)B reaction with gas and solid samples using a gridded ionization chamber(GIC)has been established.Using the simulation,the experimental spectra of both^(14)N(n,a)^(11)B events and background from other reactions can be predicted,and the experimental scheme can be optimized.According to the simulation results,the optimal experimental parameters,including the pressure of the working gas and the compositions of the working gas and the sample,can be determined.In addition,the simulation results can be used to determine the valid event area and calculate the detection efficiency for valid events.A measurement of the cross-sections of the^(14)N(n,a)^(11)B reaction at E_(n)=4.25,4.50,4.75,5.00,5.25,and 5.50 MeV,based on the 4.5-MV Van de Graff accelerator at Peking University(PKU)using a GIC as the detector for the outgoing a particles,has been performed.The good agreement of the spectra from the simulation and experiment demonstrated the universality of this simulation method,which can be used to accurately measure neutroninduced light-charged particle emission reactions.

Saturation characteristics of low voltage ionization chamber filled with argon or xenon

Argon and xenon are both attractive working gas for low voltage ionization chamber(LVIC),which is a promising candidate for ITER X-ray detectors.In this work,the performances of Arfilling LVIC(Ar-LVIC)and Xe-filling LVIC(Xe-LVIC)as well as the impacts of operation parameters were investigated.Saturation curves of Ar-LVIC and Xe-LVIC with pressure from 0.4 to 1.2 bar were measured with a tungsten X-ray source.The minimum voltage of saturation region(V_(min))of Ar-LVIC and Xe-LVIC,the relationship between V_(min)and saturation current,the ideal operating voltage in ITER and impacts of pressure on saturation current were studied.It was found that Ar-LVIC had smaller V_(min)and saturation currents which decreased with the drop of pressure from 1.2 to 0.4 bar;Xe-LVIC had larger V_(min)and saturation currents which did not obviously decrease with the same pressure drop.It is envisaged that ITER can take advantage of the larger saturation current and lower pressure of Xe-LVIC in the non-nuclear operation phase,and flexibility of pressure and low sensitivity to neutron/gamma radiation of Ar-LVIC in the nuclear operation phase.

Use of a 2-Dimensional Ionization Chamber Array to Measure Head Leakage of a Varian Truebeam^®Linear Accelerator

The purpose of this work is to evaluate the use of a two-dimensional (2D) planar ion chamber array to characterize leakage radiation from the head of the linear accelerator. Ion chamber arrays provide a benefit over a singular ion chamber measurement as they allow for the measurement of a larger area in order to isolate the point of maximum leakage dose and the small size of each individual ion chamber minimizes volume-averaging effects. A Varian Truebeam® undergoing acceptance testing was used for all measurements. The gantry was wrapped in Portal Pack for Localization (PPL) radiographic film in order to isolate the location of maximum leakage. A calibration curve was developed and used to determine dose-to-film. An Ion Chamber Profiler (IC Profiler™) manufactured by Sun Nuclear Corporation was used to confirm measurements by the PPL film. All measurements were normalized to leakage at 100 cm from the target relative to the central axis. Three points were investigated with the IC Profiler, including the top of the gantry, the Varian logo, and the side of the gantry. For the three locations, respectively, the PPL film and the IC profiler were measured 0.142% and 0.131%, 0.036% and 0.030%, and 0.014% and 0.019%. The good agreement between the PPL film and the IC Profiler provides confidence in the use of a more efficient and accurate ion chamber array for head leakage measurements.

Study of the energy response of high pressure ionization chamber for high energy gamma-ray

The energy response calibration of the commonly used high pressure ionization chamber is very difficult to obtain when the gamma-ray energy is more than 3 MeV. In order to get the calibration of the higher part of the high pressure ionization chamber, we use the Fluka Monte Carlo program to perform the energy response in both the spherical and the cylindrical high pressure ionization chamber which are full of argon gas. The results compared with prior study when the gamma-ray energy is less than 1.25 MeV. Our result of Monte Carlo calculation shows agreement with those obtained by measurement within the uncertainty of the respective methods. The calculation of this study is significant for the high pressure ionization chamber to measure the high energy gamma-ray.

Design and construction of the first prototype ionization chamber for CSNS and PA beam loss monitor (BLM) system

Design and construction of the first prototype ionization chamber for CSNS and Proton Accelerator （PA） beam loss monitor （BLM） system is reported. The low leakage current （〈0.1 pA）, good plateau （≈800 V） and linearity range up to 200 Roentgen/h are obtained in the first prototype. All of these give us good experience for further improving the ionization chamber construction.

Improved design and construction of an ionization chamber for the CSNS beam loss monitor (BLM)

Based on the first ionization chamber （IC） prototype, the structure, working gas component and electrode material of the IC are improved. The test of the improved IC shows that the plateau length is about 2000 V, the plateau slope is less than 0.2%/100 V, the sensitivity is 19.6 pA/rad·h 1, the up-limitation of the linearity can be up to 3.6×105 rad/h, and the applied voltage can be operated to 3500 V. The test results show that the performance of the improved IC meets the requirements of the beam loss monitor.

LARGE VOLUME IONIZATION CHAMBER USED AS LABORATORY REFERENCE FOR LOW ENERGY X－RAY MEASUREMENT

A large volume spherical ionization chamber of 195 mm diameter and 0.36 mg/cm2wall thickness made from conducting carbon-fibre epoxy composite material has been developed. The mechanical intensity of the chamber is satisfactory for a good longterm volume stability. Owing to its large volume and thin wall, the chamber is sensitive to low energy photon beams and has excellent energy-response characteristics. This ionization chamber is suitable not only for a laboratory reference but also for measurement of low energy photon beam exposure rates at protection-level.

Design of weak current measurement system and research on temperature impact

A dedicated weak current measurement system was designed to measure the weak currents generated by the neutron ionization chamber.This system incorporates a second-order low-pass filter circuit and the Kalman filtering algorithm to effectively filter out noise and minimize interference in the measurement results.Testing conducted under normal temperature conditions has demonstrated the system's high precision performance.However,it was observed that temperature variations can affect the measurement performance.Data were collected across temperatures ranging from -20 to 70℃,and a temperature correction model was established through linear regression fitting to address this issue.The feasibility of the temperature correction model was confirmed at temperatures of -5 and 40℃,where relative errors remained below 0.1% after applying the temperature correction.The research indicates that the designed measurement system exhibits excellent temperature adaptability and high precision,making it particularly suitable for measuring weak currents.

Evaluation of Dosimetric Impact of Uncertainty of Measurement in Estimating External Radiotherapy Dose

Cancer is a major societal public health and economic problem, responsible for one in every six deaths. Radiotherapy is the main technique of treatment for more than half of cancer patients. To achieve a successful outcome, the radiation dose must be delivered accurately and precisely to the tumor, within ± 5% accuracy. Smaller uncertainties are required for better treatment outcome. The objective of the study is to investigate the uncertainty of measurement of external radiotherapy beam using a standard ionization chamber under reference conditions. Clinical farmers type ionization chamber measurement was compared against the National Reference standard, by exposing it in a beam 60Co gamma source. The measurement set up was carried out according to IAEA TRS 498 protocol and uncertainty of measurement evaluated according to GUM TEDDOC-1585. Evaluation and analysis were done for the identified subjects of uncertainty contributors. The expanded uncertainty associated with 56 mGy/nC ND,W was found to be 0.9% corresponding to a confidence level of approximately 95% with a coverage factor of k = 2. The study established the impact of dosimetry uncertainty of measurement in estimating external radiotherapy dose. The investigation established that the largest contributor of uncertainty is the stability of the ionization chamber at 36%, followed by temperature at 22% and positioning of the chamber in the beam at 8%. The effect of pressure, electrometer, resolution, and reproducibility were found to be minimal to the overall uncertainty. The study indicate that there is no flawless measurement, as there are many prospective sources of variation. Measurement results have component of unreliability and should be regarded as best estimates of the true value. .

Measurement of the ^(232)Th(n,f)cross section in the 1-200 MeV range at the CSNS Back-n

The ^(232)Th(n,f)cross section is very important in basic nuclear physics and applications based on the Th/U fuel cycle.Using the time-of-flight method and a multi-cell fast-fission ionization chamber,a novel measurement of the^(232)Th(n,f)cross sec-tion relative to^(235)U in the 1–200 MeV range was performed at the China Spallation Neutron Source Back-n white neutron source(Back-n).The fission event-neutron energy spectra of^(232)Th and^(235)U fission cells were measured in the single-bunch mode.Corrected 232Th/235U fission cross-sectional ratios were obtained,and the measurement uncertainties were 2.5–3.7%for energies in the 2–20 MeV range and 3.6–6.2%for energies in the 20–200 MeV range.The^(232)Th(n,f)cross section was obtained by introducing the standard cross section of^(235)U(n,f).The results were compared with those of previous theoreti-cal calculations,measurements,and evaluations.The measured 232Th fission cross section agreed with the main evaluation results in terms of the experimental uncertainty,and 232Th fission resonances were observed in the 1–3 MeV range.The present results provide^(232)Th(n,f)cross-sectional data for the evaluation and design of Th/U cycle nuclear systems.

In-situ detection equipment for radon-in-water:unattended operation and monthly investigations

Radon is recognized as a powerful tracer of certain geophysical processes in marine and aquatic environments.In the past few decades,the instruments and methods for measuring radon concentration in water have been developed to some extent but still lack underwater in-situ measurements.Here we present an in-situ detection equipment for radon-in-water(pulsed ionization chamber(PIC)-radon)to measure dissolved radon in ocean and groundwater settings.The equipment has been successfully deployed in the Jiaozhou Bay in July 2022 and has achieved 14 d of unattended underwater in-situ observation.Then it was successfully placed in a groundwater monitoring well in the Laizhou Bay in November 2022 and monitored radon activities for over 30 d.The results showed that this instrument had a good indication of submarine groundwater discharge.The PIC-radon detector takes advantage of smaller size,lower power consumption,and is barely influenced by humidity,making it particularly suitable for long-term in-situ measurement,especially in harsh environments with limited human care or deployment spaces.

Monte Carlo simulation of the exposure factor

In this paper, we simulate the exposure factor by a simple model of a flee-air ionization chamber with the Monte Carlo programme Geant4. Special emphasis is placed on the discussion of the exposure factor related to parameters of the chamber model. The reason for the variation in exposure factor with incident ray energy is also analysed in terms of reaction cross section for different types of reactions. The obtained results indicate that our simulation is accurate in the calculation of the exposure factor and can serve as a reference in designing air ionization chambers.

Dosimetric Characteristics of 6 MV Medical Linac at BAEC

Dosimetric characteristic is one of the essential parameters of a medical linear accelerator (LINAC), which must be obtained before clinical use. The dosimetric characteristics for 6 MV photon beam were measured and compared with the corresponding published data. The study was done using a Varian linear accelerator (Model Clinac-iX) at the Institute of Nuclear Medical Physics (INMP), AERE, Savar, Dhaka, under the Bangladesh Atomic Energy Commission (BAEC). The data is taken for 10 field sizes (2 × 2, 3 × 3, 5 × 5, 7 × 7, 10 × 10, 15 × 15, 20 × 20, 25 × 25, 30 × 30 and 40 × 40 cm2) at same conditions. The measured Percent Depth Dose (PDD) curves were obtained for 6 MV photon beams with the field as mentioned above and compared with the calculated PDD curves. The measured depth dose (Dmax) for reference field size (FS) 10 × 10 cm2 is 15.99 mm, and the PDD at 10 cm depth (D10) is 66.87% for 6 MV photon energies that are found to be compatible with the published report BJR supplement 25. The measured PDD curves for photon energies show a good agreement with the standard PDD curves. The photon beam dosimetry data found in the current study are compatible and all the tolerances are within the clinically acceptable tolerance limit.

On Quality Evaluation and Analysis of Metrological Verification and Detection

With the rapid development of China’s economy and society,under the existing economic system,measurement work is of great significance to promote market development and improve people’s living standards.The quality evaluation of testing work is an important means to ensure the accuracy of measurement.Based on the analysis of several factors affecting the quality of measurement work,this paper takes the ionizing radiation monitoring quality as an example,and makes a concrete exposition on the evaluation and analysis of the quality of metrological verification work.

Design of the front-end electronics for parallel plate ion chamber

Background A set of nozzle systems for proton therapy is now being developed at China Institute of Atomic Energy.To real-ize the measurement of beam dose,a set of charge measurement electronics is designed,which is used to measure the output charge signal of the ionization chamber integration plane.Also,the charge measurement device can be used to measure the position information of ion chamber strips just by changing certain parameters.Methods The device realizes the integration and amplification of charge by IVC102,a precise low-noise integrator,and the DSP controls the ADC to collect and process the data.Modbus communication protocol is used to realize communication with the host computer which makes it possible to read data and set the parameter.Results A fixed charge generator is designed to generate 20 pC to 2 nC charge,which is used to test the measuring accuracy of electronics.The results have shown that the accuracy is within 0.62%in the above charge range.Conclusion After experimental tests,the front-end electronics meet the design goal and play a certain pre-test and verification role in the dose and beam position monitoring in the proton therapy system.

Verification of an independent dose calculation method for portal-specific QA of proton and carbon ion beams

Objective:To verify the accuracy of an independent dose calculation method,as incorporated into an in-house developed treatment planning system(TPS),for performing quality assurance of dose distributions delivered to a water phantom planned by a clinical TPS.Methods:A Monte Carlo based track repeating algorithm was incorporated into an in-house treatment planning system for proton and carbon ion beams.Calculations were performed in a flat water phantom for both a traditional pencil beam algorithm and a new Monte Carlo algorithm,and then compared to measurements made at multiple depths with a 2D ionization array for 44 patient portals.The comparisons utilized a Gamma analysis.Results:A total of 124 measurements were performed for proton and carbon ion patient portals.Using a small Gamma criteria of 2%/2 mm,an average of 93%and 97%of measurement points passed for each portal for pencil beam and Monte Carlo calculations,respectively.The passing rate was substantially higher for Monte Carlo calculations than for pencil beam calculations for portals that used a range shifter.Conclusions:The implemented independent method has been verified against measurements.The high passing rate with small tolerances leads to the possibility of reducing the number of required quality assurance measurements.

Construction of high-resolution energy-time-of-flight spectrometer for determination of fission fragmentmass distributions

Purpose With the aim of determining mass yield distributions of primary fission products,a one-arm spectrometer was developed based on kinetic energy and time-of-flight correlation measurement technique.Methods An axial grid ionization chamber(GIC)was designed for energy detecting.In order to minimize energy losses and straggling,a thin silicon nitride film with a thickness of 100 nm was performed as the entrance window of the GIC.The energy resolution is 0.38%for 80 MeV ^(63)Cu particles.Two-timing detectors based on the detection of secondary emission electrons by microchannel plates(MCPs)constitute the time pick-off system,and the time-of-flight resolution is better than 200 ps(FWHM)measured with a ^(241)Amαsource.With a flight path length of 47.6 cm,the path length resolution is 0.21%.Results and conclusion The first result of mass distribution from ^(252)Cf spontaneous fission was reported.Energy losses of fragments in dead layers of the spectrometer were corrected event-by-event depend on the Monte Carlo calculation.The mass resolution for light fission fragments peak A107 amu is 1.3 aum.

Absolute measurement of radiant power for synchrotron radiation monochromatized X-rays

Purpose Absolute measurement of radiant power in the X-ray region is essential for many applications in astrophysics,spectroscopy,and X-ray diagnostics.This paper presents a dependable method of absolute measurement of radiant power for synchrotron radiation monochromatized X-rays.Methods A free-air ionization chamber was examined closely and employed as the detector in the present work.Its measuring principle was discussed,and the correction factors were determined.Absolute measurement of radiant power for synchro-tron radiation monochromatized X-rays in the region of 6-20 keV was performed using the free-air ionization chamber at Beijing Synchrotron Radiation Facility.As a verification and an important application,photodiodes were calibrated against the free-air ionization chamber.Results Relative standard uncertainties of absolute measurement using free-air ionization chamber are about 1%.Calibration of photodiodes within the photon energy range from 6 to 20 keV has relative standard uncertainties below 1.5%.Conclusion The free-air ionization chamber is qualified to be used in many disciplines to support the measurement of opti-cal radiation.