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.

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.

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.

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.

Ionization Chamber Dosimetry for Conventional and Laser-Driven Clinical Hadron Beams

The practice of using the direct ionization radiation (electrons, protons, antiprotons, pions, ions, etc) or of the indirect ionization radiation (photons, neutrons, etc) in economy and social life has led to the introduction of the absorbed dose magnitude (ICRU 1953) defined as the energy absorbed per mass unit of the irradiated substance. This is a fundamental magnitude valid for any type of ionizing radiation, any irradiated material and any radiation energy. In case of clinical hadron beams generated by conventional accelerators or those controlled by lasers, IAEA TRS 398 recommends the absorbed dose to water. This may be determined employing the calorimeter method with water or graphite, chemical method, fluence based measurements as Faraday cups or activation measurements, and the ionization chamber method. In this paper the selected method was the thimble air filled ionization chamber method for determination of absorbed dose to water.

A SPHERICAL GRAPHITE IONIZATION CHAMBER

This paper describes an exposure ratemeter made of graphite ion chamber. The sensitive volume is 14 cm^3. The wall is 5 mm in thickness. The DC amplifier with a high input impedance consists of several stage differential amplifications, and is used for measurement of the ionization currents. Six ranges are able to cover a wide range of exposure rates. The full scale of the maximum range is 75 C/(kg·h). The lowest measurable limit is 5 mC/(kg·h). The zero drift within 8 h is less than 5% of each full scale. This instrument provides with a relatively convenient method for the measurement. The main advantages of the ionization chamber over other methods lie in rapidity and accuracy, and the change in radiation field with time can be indicated directly. It is particularly successful in acting as a routine dosimeter under high exposure rates.

LET Monitoring Using Liquid Ionization Chambers

Relative biological effectiveness (RBE) is an important quantity in planning particle beam cancer therapy. In general, the RBE describes the biological effectiveness of a given primary beam with respect to a reference photon irradiation. RBE varies not only for different primary beams but also with depth in the target for a given beam modality. It is not a quantity that easily lends itself to measurements or computation as it depends on many biological and physical quantities. Numerous experiments in vitro using various cell lines and irradiation modalities have shown that a general relationship between RBE and the physical quantity Linear Energy Transfer (LET) exists. Several groups have proposed including LET in the radiation therapy treatment planning instead of the more complicated and elusive RBE. It has been shown that LET is an important quantity to consider in treating radio-resistant tumors. The concept of LET painting has been proposed with the goal of improving tumor control probability (TCP) for hypoxic tumors by focusing high LET radiation on the hypoxic region of the tumor while restricting the surrounding normal tissue to low LET radiation. In order to properly incorporate LET in clinical treatment, it is important to be able to experimentally measure and verify LET distribution. We propose a novel method for measuring LET using a dual chamber methodology exploiting the difference in the observed recombination between air filled ionization chambers (IC) and liquid filled ionization chambers (LIC). The resulting difference in the measured signals will be used to directly extract the relative LET of an actual treatment beam in real time. This paper describes our initial studies of this method, presents preliminary results, and discusses further improvements toward a practical real-time LET measuring device.

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.

Absorbed Dose to Water Rate in a Cyberknife VSI System Reference Field Using Ionization Chambers and Gafchromic Films

This work investigated the absorbed dose to water rate under reference conditions in a Cyberknife VSI system using radiochromic films EBT3 and MD-V3 and three ionization chambers: an Exradin A12 and two FC65P Welhöfer Scanditronix with different serial numbers. The correction factor,, was studied using a Varian iX linac and the Cyberknife system. The measurements in the Varian iX were performed in a 10 × 10 cm2 field, 10 cm depth in liquid water at 90 cm and 70 cm SSD and in a 5.4 × 5.4 cm2 field, 10 cm depth at 70 cm SSD to simulate the Cyberknife conditions. In the Cyberknife system, measurements were performed using ionization chambers and both film types at 70 cm SSD and 10 cm depth in its 6 cm diameter reference field. The results indicate that ?is independent of the dosimeters and the evaluation methods. Maximum differences of 0.22% - 0.55% (combined uncertainties of 1.22% - 1.98%, k = 1) are obtained on ?using Varian iX, whereas discrepancies of 2.08% - 2.09% (combined uncertainties of 1.87% - 2.13%, k = 1) are observed using the Cyberknife system. Given the agreement between detectors and the combined standard uncertainties, the data from Varian iX could be considered the most accurate and consequently a weighted average factor of 0.902 ± 0.006 could be used for the Cyberknife VSI system reference field. Within measurement uncertainties, the absorbed dose rate measured in the Cyberknife VSI system reference field was found to be independent of the dosimeters used. These results suggest that the absorbed dose measured at a point within a given field size should be the same, regardless the dosimeter used, if their dosimetric characteristics are well known. This highlighted the importance of performing dosimetry by controlling all parameters that could affect the dosimeter response. One can conclude that radiochromic film dosimetry can be considered as an appropriate alternative for measuring absorbed dose to water rate.

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.

Determination of Bragg Peak Location for Heavy Ion Beam by Ionization Chambers

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Improvement of a New Gas Ionization Chamber

In order to identify heavier elements, we have developed a new longitudinal field gas ionization chamber (IC)with an angle of 30° of plate (as shown in Fig.1). The IC is operated in flowing iso-butane gas at a pressure of 10kPa. After testing by using a 3- component α particle source and comparing with the old longitudinal

An online monitor ionization chamber used in particle therapy

The clinical trials of tumor therapy using heavy ions beam 12C are now in progress at Institute of Modern Physics in Lanzhou. In order to achieve the precise radiotherapy with the high energy 12C beam in active pencil beam scanning mode, we have developed an ionization chamber(IC) as an online monitor for beam intensity and also a dosimeter after calibration. Through the choosing of working gas and voltage, optimizing of the electrics and the read-out system, calibrating the linearity, the detector system provide us one of the simple and highly reliable way to monitoring the beam during the active pencil beam scanning treatments. The measurement results of this detector system show that it could work well under the condition of high energy 12C beam in active pencil beam scanning mode.

C_(4)F_(7)N/CO_(2)混合气体在高压断路器中熄弧特性分析

基于磁流体力学理论,对C_(4)F_(7)N/CO_(2)混合气体和SF_(6)气体的断路器在40 kA短路电流情况下的熄弧特性进行仿真计算,分析两种不同气体的温度特性、灭弧室气体压强。结果表明:相同气压下,9%C_(4)F_(7)N/91%CO_(2)混合气体在燃弧过程中产生的气体压强要比SF_(6)气体产生的压强小,混合气体断路器的燃弧过程中9%C_(4)F_(7)N/91%CO_(2)混合气体熄灭电弧能力相对于SF_(6)气体更弱些;对比电弧等离子体的径向温度,在SF_(6)气体的断路器中,其电弧等离子体的径向温度相较于9%C_(4)F_(7)N/91%CO_(2)混合气体的断路器更高。而在燃弧过程中,相较于SF_(6)气体下的电弧半径,混合气体下的电弧半径更大。当混合气体充气压强提升至0.8 MPa时,温度梯度得到提升,缩减了电弧半径,可有效地扩大径向冷却的作用,使电弧熄灭加速,断路器的熄弧性能能够进一步被提升。

YY/T 1834—2022《X射线血液辐照设备》检测要点分析

YY/T 1834—2022《X射线血液辐照设备》于2023年6月1日正式实施,为该产品的检测提供了标准化的依据。本文针对该标准的检测要点进行了分析和探讨,旨在为生产企业、设备检测人员、使用者对标准的理解提供参考。

Effect of Ionizing Radiation on the Expression of p16, CyclinDI and CDK4 in Mouse Thymocytes and Splenocytes

Objective To investigate the effect of ionizing radiation on the expression of p16, CyclinDl, and CDK4 in mouse thymocytes and splenocytes. Methods Fluorescent staining and flow cytometry analysis were employed for the measurement of protein expression. Results In time course experiments, it was found that the expression of p16 protein was significantly increased at 8, 24, and 48 h for thymocytes (P<0.05, P<0.01, and P<0.05, respectively) and at 24 h for splenocytes (P<0.05) after whole body irradiation (WBI) with 2.0 Gy X-rays. However, the expression of CDK4 protein was significantly decreased from 8 h to 24 h for thymocytes (P<0.05,P<0.01) and from 8 h to 72 h for splenocytes (P<0.05-P<0.01). In dose effect experiments, it was found that the expression of p16 protein in thymocytes and splenocytes was significantly increased at 24 h after WBI with 1.0, 2.0, and 4.0 Gy (P<0.05-P<0.01), whereas the expression of CDK4 protein was significantly decreased with 2.0Gy for thymocytes (P<0.05) and 0.5-6.0 Gy for splenocytes (P<0.05-P<0.01). Results also showed that the expression of CyclinDl protein decreased markedly in both thymocytes and splenocytes after exposure. Conclusion The results indicate that the expression of p 16 protein in thymocytes and splenocytes can be induced by ionizing radiation, and the p16-CyclinD1/CDK4 pathway may play an important role for G1 arrest of thymocytes induced by X-rays.

48 keV~1.25 MeV X/γ射线空腔电离室研制及性能测试

防护水平电离室广泛应用于核设施、放射治疗和辐射环境监测等剂量率的测量,为了提高防护水平电离室的国产化水平,设计了测量防护水平剂量率的空腔电离室。通过理论计算、蒙特卡罗模拟对电离室的室壁厚和保护极进行研究。在不同能量辐射场中对电离室性能进行测试,测试结果表明:电离室漏电流绝对值小于5 fA,工作坪区为200~800 V。在N60~N250的X辐射场和^(137)Cs、^(60)Coγ辐射场中对电离室的能量响应进行测试,当剂量率归一化到^(60)Co时,电离室能量响应相对偏差在±5%之内,电离室在半年内的长期稳定性和角响应都优于0.5%。所述电离室能够实现3 mGy/h~30 Gy/h剂量率的测量,且与约定剂量率相对偏差优于±5%。

基于Geant4的碳离子治疗三维电离室阵列仿真设计

为快速准确地实现碳离子治疗计划的三维剂量验证,采用有机玻璃PMMA(聚甲基丙烯酸甲酯)为电离室室壁和水等效模体,设计了一种三维电离室阵列,并通过Geant4软件对三维电离室阵列的结构设计进行了深入研究与验证。首先通过模拟不同能量碳离子束在水和PMMA模体中沉积的剂量分布,计算了PMMA模体的水等效厚度系数;然后研究了三维电离室阵列中电离腔室间的距离及信号导线对其剂量测量准确度的影响;最后模拟并验证了碳离子束在三维电离室阵列中沉积的剂量分布。结果表明:PMMA模体的水等效厚度系数为1.151;相邻电离腔室间的信号串扰主要来源于前侧的电离腔室,且串扰程度与电离腔室间距呈反比,间距为1 mm时串扰程度占电离腔室内剂量的3%,间距为30 mm时串扰影响可完全消除;信号导线对后侧电离腔室内剂量的干扰影响约为1%。将碳离子束在三维电离室阵列中沉积的剂量分布与PMMA模体中的剂量分布进行对比,碳离子束的射程具有良好的一致性,偏差为0.5 mm。

切向电场主导下C_(4)F_(7)N/CO_(2)混合气体中环氧复合材料表面电荷积聚特性及机理研究

气固界面的电荷积聚问题是诱发沿面闪络的重要原因,而当前C_(4)F_(7)N/CO_(2)混合气体中电荷积聚特性的相关研究还不够充分。为研究C_(4)F_(7)N/CO_(2)混合气体中表面电荷积聚特性及机理,本文通过指型电极构建极不均匀电场,测量了环氧复合材料在C_(4)F_(7)N/CO_(2)混合气体中的表面电荷分布特性;进一步的,为理清表面电荷来源及迁移特性,测量了冲击电压下C_(4)F_(7)N/CO_(2)混合气体中材料表面电位,比较了附加背板电极前后的表面电荷分布。研究表明,C_(4)F_(7)N/CO_(2)混合气体与SF_(6)中表面电位分布形态相似,均表现为高压电极附近积聚大量同极性电荷,地电极附近积聚少量异极性电荷。随着C4F7N含量升高,C_(4)F_(7)N/CO_(2)混合气体抑制电荷积聚能力增强。表面电荷来源于气体电离和高压电极注入并且随着电场强度的改变,电荷来源也发生变化,切向电场促进了电荷沿表面向更大范围的迁移。该工作对于明确C_(4)F_(7)N/CO_(2)混合气体中表面电荷积聚特性及环保型绝缘气体的推广应用具有重要意义。

GEANT4 simulation of gamma ray in a double-gap resistive plate chamber

For more than 20 years nuclear physicists have used the GEANT code to simulate particle-matter interaction. In most recent version, GEANT4 is a toolkit for simulating the passage of particles though matter, which contains a complete range of functionality including tracking, geometry, physics models, and hits. In this article, an attempt to use GEANT4 to model a double-gap resistive plate chamber （RPC） with its improved efficiency is presented. The efficiencies of the double-gap RPC have been evaluated as a function of gamma energy range 0.005-1000MeV. A comparison to available previous simulation package GEANT3 data is also performed.