A 10-TW Pulsed Facility "PIRIT" for Investigation of Short-Wave Radiation Generation

The results of experiments with a plasma x-ray source in the PIRIT-2000 facility are presented in this paper. The facility is designed with module capacitive energy storage energizing vacuum inductive storage. The formation of a rapidly growing current pulse as well as its commutation on a load was carried out by a plasma opening switch. A vacuum diode as well as various types of plasma loads can be used for the generation of a high-power x-ray flux. The storage energy of a 54-module capacitive storage is up to 2 MJ, its inductance is 15 nH, and its output voltage is 500 kV. The peak current in the plasma load constituted 4 MA with a 150-ns rise time. The maximum integral energy output of x radiation measured by an open thermocouple calorimeter was as high as 100 kJ, while the primary storage energy was 1 MJ. The plasma load usage at a current of 4 MA ensured a 100-kJ generation in x-ray radiation and the density of the radiation flux at a distance of 1 m from the source was as much as 0.8 J/cm2, while near the source it was 10 J/cm2.     

Long-Duration Soft X-Ray Pulses by XeCl Laser Driven Plasmas and Applications

We report the characterization of a soft x-ray plasma source generated by a long-pulse XeCl excimer laser system. The output energy is 4 J at a wavelength of 308 nm in a 100-ns pulse. The intensity of radiation on target is estimated to be 4 × 1012 W cm-2. X-ray emission spectra of the plasma have been recorded using a double focusing spatial resolution spectrometer with a spherical mica crystal. From these measurements, the plasma temperature and electron density have been estimated. Various applications of such a plasma source have been investigated. First images of whole intact living cells from our system, imaged using the technique of soft x-ray contact microscopy, utilizing x rays in the "water window" region (280-530 eV), are shown. The suitability of the source for other applications, for example, x-ray lithography and radiation damage studies, to living cells are discussed. Possible improvements to the x-ray source for the various applications are proposed.     

A single-shot rapid-mixing device for radiobiological studies with mammalian cells

A single-shot rapid-mixing device is described for the rapid addition of solutions of radiation-modifying agents, to cell suspensions, at well-defined times relative to a pulse of radiation. The liquid injection system could be used to initiate or quench a wide range of chemical or biochemical reactions. The rapid-mixing device is based on a syringe driven by a stepper motor and can inject up to 2 cm3 liquid in less than 100 ms. The radiation source, a 4 MV Van de Graaff accelerator, provides an electron beam which is deflected from the beam dump on to the sample in two stages, providing a 10 ms radiation pulse. A digital delay circuit defines the interval between mixing and irradiation. The apparatus has been designed to study the kinetics of processes that occur over a time range extending from about 0.1 s to some minutes. It bridges the gap between the ranges available with conventional fast-mixing and those using standard X- or gamma-irradiation methods. The time resolution of the technique has been examined by following the timecourse of radiosensitization by oxygen in mammalian cells. The timecourse of radioprotection of aerobic mammalian cells by dithiothreitol has been measured using the technique.     

用治疗级电离室测量短脉冲高剂量率X射线的实验研究

目的 探索研究治疗级电离室用于短脉冲高剂量率X射线的快速测量。方法 利用内插法测量某电子加速器装置所致脉冲X射线半值层,估算其等效能量;采用治疗级电离室和热释光测量方法,对比设备周围同一方向不同距离处相同数量脉冲辐射的累积剂量;分析电离室剂量仪测量结果与源距离之间的关系,对比不同频率下同一位置相同数量脉冲辐射的累积剂量。结果 工作状态下,距设备外壁1~12 m累计接收100个脉冲辐射,热释光测得空气比释动能范围0.08~9.65 mGy,电离室剂量仪所测范围0.08~9.85 mGy,两者相差在10%以内;距设备正前方2 m处,不同频率（1~10 Hz）下,电离室剂量仪所测100个脉冲所致X射线空气比释动能无明显差异（P>0.05）。结论 在实验所涉加速器装置的剂量率和脉冲频率范围内,治疗级电离室剂量仪可用于短脉冲X射线辐射剂量的快速测量。     

Technical Communication

Summary

A single-shot rapid-mixing device is described for the rapid addition of solutions of radiation-modifying agents, to cell suspensions, at well-defined times relative to a pulse of radiation. The liquid injection system could be used to initiate or quench a wide range of chemical or biochemical reactions. The rapid-mixing device is based on a syringe driven by a stepper motor and can inject up to 2 cm³ liquid in < 100 ms. The radiation source, a 4 MV Van de Graaff accelerator, provides an electron beam which is deflected from the beam dump on to the sample in two stages, providing a 10 ms radiation pulse. A digital delay circuit defines the interval between mixing and irradiation. The apparatus has been designed to study the kinetics of processes that occur over a time range extending from about 0·1 s to some minutes. It bridges the gap between the ranges available with conventional fast-mixing and those using standard X- or γ-irradiation methods. The time resolution of the technique has been examined by following the timecourse of radiosensitization by oxygen in mammalian cells. The timecourse of radioprotection of aerobic mammalian cells by dithiothreitol has been measured using the technique.     

Monte Carlo N-particle simulation of neutron-based sterilisation of anthrax contamination

Objective To simulate the neutron-based sterilisation of anthrax contamination by Monte Carlo N-particle (MCNP) 4C code. Methods Neutrons are elementary particles that have no charge. They are 20 times more effective than electrons or γ-rays in killing anthrax spores on surfaces and inside closed containers. Neutrons emitted from a (252)Cf neutron source are in the 100 keV to 2 MeV energy range. A 2.5 MeV D-D neutron generator can create neutrons at up to 10(13) n s(-1) with current technology. All these enable an effective and low-cost method of killing anthrax spores. Results There is no effect on neutron energy deposition on the anthrax sample when using a reflector that is thicker than its saturation thickness. Among all three reflecting materials tested in the MCNP simulation, paraffin is the best because it has the thinnest saturation thickness and is easy to machine. The MCNP radiation dose and fluence simulation calculation also showed that the MCNP-simulated neutron fluence that is needed to kill the anthrax spores agrees with previous analytical estimations very well. Conclusion The MCNP simulation indicates that a 10 min neutron irradiation from a 0.5 g (252)Cf neutron source or a 1 min neutron irradiation from a 2.5 MeV D-D neutron generator may kill all anthrax spores in a sample. This is a promising result because a 2.5 MeV D-D neutron generator output >10(13) n s(-1) should be attainable in the near future. This indicates that we could use a D-D neutron generator to sterilise anthrax contamination within several seconds.     

诊断X射线辐射质的模拟与测量研究

目的 对医疗诊断X射线（RQR辐射质）主射线束进行模拟和能谱测量,验证模拟方法的可行性和能谱模拟结果的可靠性。方法 使用蒙特卡罗模拟程序BEAMnrc,建立了产生医用诊断X射线RQR系列辐射质的简化模型,实验上采用平面高纯锗谱仪对上述辐射质的能谱进行了测量,并与模拟结果进行比较。结果 谱仪测得的脉冲高度谱在未经卷积处理的情况下,两者平均能量的差异<3%;此外,通过BEAMDP程序还得到了RQR系列辐射质的能谱分布、注量、能注量、平均能量等参数。结论 可通过BEAMnrc模拟计算得到的RQR辐射质能谱,为评估诊断X射线RQR辐射质提供依据。     

Image noise in X-ray imaging caused by radiation scattering and source leakage, a qualitative and quantitative analysis

All irradiated objects in the vicinity of an imaging set-up increase the amount of scattered radiation. It is a well-known fact that if this radiation is allowed to impinge on the image collector it naturally degrades the image quality. It also causes problems with equipment characterisation, such as X-ray energy spectra measurements. However, it may not be a well-known fact that when a small radiation safety enclosure is used - common for industrial applications - this type of scattered radiation is astonishing large. In this work a quantitative and qualitative analysis has been carried out in an attempt to explain the origin of the problem, why it occurs and how it may be treated.The scattered radiation increases rapidly when the fractions of X-ray photons in the primary X-ray spectrum above the K-edges of the enclosure wall material increase. High-energy photons are scattered and/or will generate characteristic radiation in the enclosure wall material instead of being absorbed. For lead, which is commonly used as shielding and wall material, this noise becomes significant when tube potentials over 90-100 kV are used, since the K-edges for lead are 72-74 keV (Kα) and 85-87 keV (Kβ). Below tube potentials of 100 kV, the noise from scattered radiation is insignificant, even if the primary beam is wide enough to hit the enclosure walls. Above 100 kV it increases rapidly and for this application the number of scattered photons was 50% of the primary photons at 170 kV.In this particular case this problem was accentuated above tube potentials of 100 kV since the steel housing of the micro focal X-ray source used was penetrated by high-energy photons in unwanted directions. Collimation of the X-ray beam just in front of the X-ray source output window to narrow the solid angle of the primary X-ray beam to avoid direct radiation of the enclosure walls was not enough to suppress this scattered noise. A wider X-ray shield, covering the entire front of the X-ray source had to be applied. Other solutions to decrease scattered radiation would be the following: Increased internal shielding of the X-ray source is the first choice if the same possibilities for geometrical magnification of the imaged object are to be maintained. Increased distances to the enclosure walls and other objects inside, that is, to use larger enclosures or even separate X-ray chambers would also decrease scattered radiation. To line the enclosure with a series of X-ray shielding materials with K-edges at lower and lower energies is another alternative. The lowest K-edge material should be placed closest to the detector followed by the second lowest K-edge material etc., to effectively absorb backscatter and characteristic radiation from the enclosure walls. This would, however, be a rather expensive and complicated solution.     

Calibration of semiconductor detectors in the 200-8500 keV range at VNIIM

At the ionising radiation department of the D.I. Mendeleyev Institute for Metrology, a semiconductor detector was calibrated in the energy range 200-8500 keV using (n,2γ) and (n,γ) reactions. Separate cylindrical targets (77 mm diameter and 10mm height) were made from mercuric sulphate, sodium chloride and metallic titanium. A (252)Cf spontaneous fission neutron source, placed in 150 mm diameter polyethylene ball, was used to generate thermal neutrons. The optimal target dimensions were determined taking into account the thermal neutron cross-sections and gamma-radiation attenuations in the target materials. The influence of the background radiation induced by neutrons from the walls, floors and ceilings was also taken into account. The shapes of the efficiency curves for point and volume sources in the 200-8500 keV range have been investigated. The experimental results are in good agreement with Monte-Carlo calculations. The emission rate of the 6.13 MeV photons from a (238)Pu-(13)C source was determined with an expanded uncertainty, U(c), of 10% (k=2).     

Soft X-Ray Emission of Laser-Produced Plasmas: Comparison for 30-ps and 20-ns Laser Pulses

Soft x-ray emission spectra (250-875 eV) are presented for plasmas, produced by picosecond and nanosecond frequency-doubled Nd:YAG-glass laser pulses incident on 14 different target materials. The emitted spectra have been corrected for various apparatus functions which enables a direct comparison between plasmas produced by pico- and nanosecond laser pulses. The relative integrated emission intensity as a function of Z number, obtained from the corrected spectra, shows an oscillatory behavior, with distinct maxima for those elements exhibiting a dominant line emission in our photon energy window. We found for our two pulse lengths an approximately equal conversion efficiency from laser light into x-ray photons. General suggestions are given as to what target material should be used for different applications using the laser plasma as x-ray source in the energy range Studied.     

The influence of flood source placement on radiation exposure during quality control testing

OBJECTIVE: This study examined the photon energy distribution and exposure rate from a 250-MBq 57Co flood source during quality control (QC) procedures as a function of source placement and measurement location. The optimum placement of the source to reduce the radiation dose to the nuclear medicine technologist during QC checks was determined. METHODS: Measurements of exposure rate were made inside and outside a camera room with the source positioned either above or below the camera head. The energy distribution of the photon field was examined at the same locations using a high-resolution gamma-ray spectrometer. Additional measures of exposure rate were made with the source at various distances from the camera face. RESULTS: The lowest exposure rates occurred when the source was lying directly on the face of the camera head. The exposure rates at locations inside the camera room increased by a factor of 4.3 +/- 3.0 when the source was placed on an imaging table below the camera head. This increase can be attributed to decreased shielding provided by the camera head. CONCLUSION: A large portion of the radiation dose received by technologists during QC checks is due to scattered radiation and x-rays produced by gamma-ray interactions within the camera. This dose can be reduced significantly if QC checks are performed with the flood source lying directly on the inverted gamma camera head rather than placing the flood source on an imaging table under the gamma camera.     

X-Ray energy dependence of the dose response of SIRAD radiation dosimeters.

SIRADs (self-indicating instant radiation alert dosimeters) are designed to measure accident radiation doses. As the energy of radiation is usually unknown in such situations, a detector with a weak energy dependence of its response to dose would be ideal. We have studied the energy dependence of the dose response of SIRADs in the range from 50kVp to 10MV, which corresponds to photon equivalent energies from 25.5keV to 2.2MeV. The response to the same dose at 25.5keV is (29+/-4)%(+/-1s) lower than the response at 1.4MeV. The response to a dose slowly increases with radiation energy. This energy dependence is relatively weak in comparison with the dependence for radiographic films and similar in magnitude to the dependence for lithium fluoride thermoluminescence dosimeters. This energy dependence of the response diminishes the accuracy of dose assessments in radiation fields of unknown energy, but does not significantly compromise the core ability of the devices to provide visual estimates of radiation doses.     

A Soft X-Ray/EUV Reflectometer Based on a Laser Produced Plasma Source

A soft x-ray reflectometer is described which is based on a laser-produced plasma source and is continuously tunable over the range 40 ? < λ < 400 ?. The source is produced by focusing 0.532-μm light from a Q-switched Nd:YAG laser on a solid target. The x-ray wavelength is defined using a high throughput spherical grating monochromator with moderate resolving power (λ/Δλ ≈ 100 to 500). A time-averaged monochromatized flux of more than 109 photons/s in a 1% bandwidth at 100 eV is obtained. Photon "shot noise" limited measurements are obtained by the use of an I0 detector to normalize out the shot-to-shot variations in source intensity. Measurements with submillimeter spot sizes are readily obtainable. Various detectors have been used and the advantages and disadvantages of each are discussed. The higher order contamination of the monochromator output has been analyzed using a second grating for the purpose of making measurement corrections. The reflectometer thus provides the capability for precision absolute measurements of the reflectance of gratings and multilayer mirrors, the transmittance of thin film filters, or other properties of x-ray optical elements.     

Hard X-ray emission from high intensity short laser pulse produced Al, Mo and Ta plasmas

K-edge and Ross filters techniques were used to measure quantitatively the X-ray emission from laser heated Al, Mo, and Ta plasmas in the range of 10 to 100 keV. The INRS Table Top Terawatt laser system using Chirped Pulse Amplification technique supplied a focused laser pulse of about 300 mJ in 450 fs duration at λ = 0.53 μm, achieving irradiation intensities on the target surface up to 5 × 1017 W/cm2. The experimental results are compared to calculation of the hard X-ray radiation based on bombardment of solid target by electrons. Furthermore, the dependence of X-ray emission on laser energy, irradiation intensity and the target atomic number are discussed.     

Quality assurance measurements of a-Si EPID performance.

The performance stability of a Varian aS500 amorphous silicon (a-Si) electronic portal imaging device (EPID) was monitored over an 18-month period using a variety of standard quality assurance (QA) tests. The tests were selected to provide ongoing information about image quality and dose response from the time of EPID acceptance into clinical service. To evaluate imaging performance, we made spatial resolution and contrast measurements using both PortalVision and QC-3V phantoms for 6- and 15-MV photon beams at repetition rates of 100, 300, and 400 MU/min in standard scanning mode. To assess operational stability for dosimetry applications, we measured central axis radiation response and beam pulse variability for the same image acquisition modes. Using the QC-3V phantom, values for the critical frequency of 0.435 +/- 0.005 lp/mm for 6 MV and 0.382 +/- 0.003 lp/mm for 15 MV were obtained. The contrast-to-noise ratio was found to be approximately 20% higher for the lower photon energy. Beam pulse variability remained within the tolerance of 3% set by the manufacturer. The central axis pixel response of the EPID remained constant within +/-1% over a 5-month period for the 6-MV beam, but fell approximately 4% over the same period for the 15-MV beam. The Varian aS500 EPID studied exhibited consistent image quality and a stable radiation response. These characteristics render it suitable for quantitative applications such as clinical dose measurement.     

蒙特卡罗方法计算外照射所致红骨髓剂量方法的研究

目的 对现有的红骨髓剂量模拟计算方法进行比较和分析.为确定更为合理的计算方法提供依据.方法 借助MCNPX蒙特卡罗模拟软件,模拟了能量20 keV～10 MeV的γ光子源,对Rensselaer理工学院(RPI)体素人体模型进行前后(AP)全身均匀照射,分别采用直接能量沉积法、剂量响应函数法(DRF)、King-Spiers因子法和质能吸收系数法(MEAC),进行红骨髓剂量的模拟计算.结果 在入射γ光子能量低于100 keV时,直接能量沉积法的结果最大,而质能吸收系数法和King-Spiels因子法的结果更为合理;在入射γ光子能量高于150 keV时,King-Spiers因子法给出的结果要略高于其他方法的结果,但其能够反映出红骨髓对γ光子能量更强的吸收能力.结论 综合比较低能区和高能区不同方法给出的结果后,发现King-Spiers因子法是最合理的估算红骨髓剂量的方法.     

Difference in the induction, but not in the repair, of X-ray- and nitrogen ion-induced DNA single-strand breaks as measured using human cell extracts

PURPOSE: To compare the repair efficiency of X-ray (low linear energy transfer [LET]) and nitrogen ion (high LET)-induced single-strand breaks (SSB) in a human cell-free end-joining system. MATERIALS AND METHODS: SSB were introduced into a bacterial plasmid, pBR322, by X-rays (4 MeV photons) and nitrogen ions with an LET=125 keV micro m(-1). Repair efficiency was studied under incubation with the protein extracts from human squamous carcinoma cells, UT-SCC-5. RESULTS: A several fold higher dose of nitrogen ion radiation compared with X-ray radiation was needed to induce a similar loss of supercoiled plasmid DNA. There was no difference in the repair efficiency of SSB induced by these two types of radiation. CONCLUSION: The data indicate that X-rays at 25 Gy and nitroging ions at 100 Gy radiation doses, under condition of low scavenging capacity (10 mM Tris), induce SSB of similar complexity or, alternatively, differences in SSB complexity do not alter the repair rate.     

Measurement of patient skin dose in interventional radiology using passive integrating dosimeter

To avoid radiation injury from interventional radiology (IVR), quality assurance (QA) of IVR equipment based on dosimetry is important. In this study, we investigated the usefulness of measuring patient skin dose with a passive integrating dosimeter and water phantom. The optically stimulated luminescence dosimeter (OSLD) was chosen from among various passive integrating dosimeters. The characteristics of the OSLD were compared with a reference ionization dosimeter. The effective energy obtained from the OSLD was compared with that found by the aluminum attenuation method for using the reference ionization dosimeter. Doses and effective energies measured by OSLD correlated well with those of the reference ionization dosimeter. (dose: y=0.971x, r=0.999, effective energy: y=0.990x, r=0.994). It was suggested that OSLD could simultaneously and correctly measure both patient skin dose and effective energy. Patient skin dose rate and effective energy for 15 IVR units of 10 hospitals were investigated using OSLD and a water phantom for automatic brightness control fluoroscopy. The measurement was performed at the surface of a water phantom that was located on the interventional reference point, and source image intensifier distance was fixed to 100 cm. When the 9-inch field size was selected, the average patient skin dose rate was 16.3+/-8.1 mGy/min (3.6-32.0 mGy/min), the average effective energy was 34.6+/-4.1 keV (30.5-42.5 keV). As a result, it was suggested that QA should be performed not only for patient dose but also for effective energy. QA of equipment is integral to maintaining consistently appropriate doses. Consequently, the dosimetry of each IVR unit should be regularly executed to estimate the outline of patient skin dose. It was useful to investigate patient skin dose/effective energy with the passive integrating dosimeter for IVR equipment.     

Prostate brachytherapy seed migration and dosimetry: analysis of stranded sources and other potential predictive factors

PURPOSE: The purpose of this study was to evaluate the influence of potential contributing factors to the incidence of seed migration and quality of prostate brachytherapy dosimetry. METHODS AND MATERIALS: Sixty patients were evaluated with day one and 3-12 month plain films of the pelvis and chest, and day 1 CT-based dosimetry analysis. The incidence and types of seed migration were quantified. The seed migration outcome was evaluated with respect to source type (free vs. stranded), prostate volume, number of seeds, and needles. The day one prostate V100, V150, D90, and urethra D10 outcomes were evaluated with respect to source type, radiation type ((125)I vs. (103)Pd), prostate volume, prostate swelling, and quantity of migrating seeds. RESULTS: An increased incidence of day one and cumulative seed migration was predicted by free vs. stranded source type, with a relative risk of 6.97 and 3.08, respectively. Pulmonary and distal (toward the perineum) migration patterns were significantly reduced in the stranded group. An increased day one prostate V100, V150, D90, and urethra D10 outcome was predicted by stranded source type. CONCLUSION: Stranded source type was associated with decreased seed migration as well as higher prostate and urethra dosimetry values, resulting in an implant in which more radiation resided within the target volume, and less radiation metastasized to undesirable locations.     

Pinch plasma source for x-ray microscopy with nanosecond exposure time

The strong demand for bright, compact, and inexpensive sources for x-ray microscopy has stimulated the development of flash x-ray sources. In this paper, the requirements for such a source are analyzed under boundary conditions given by the concept of an imaging x-ray microscope using mirror condenser and Fresnel zone plates for high-resolution imaging. It is found that the Lyman-α (1s-2p) line of hydrogen-like nitrogen (N VII) at λ = 2.48 nm emitted from a nonequilibrium plasma of about 200 eV temperature and 1020 cm-3 electron density is best suited. These conditions are achieved in medium-current pinch-plasma devices. Using detailed numerical simulation of the physical processes of such a device, optimization criteria for the integrated spectral brightness (ISB) are found. Measurements of the ISB confirm these optimization criteria. The results show that the spectral emission characteristics of an optimized pinch plasma souce are compatible with the demands of the mentioned x-ray microscopy concept. These emission characteristics are compared with laser-produced plasma sources. Using the optimized source with an ISB exceeding 0.6 μJ/(μm2 sr) in a 10-20 ns pulse, wet biological samples are imaged with about 0.1 μm lateral resolution.