A study of gas electron multiplier

A new kind of gas detector based on gas electron multiplier (GEM) is studied for X-ray imaging of high luminosity. A single-GEM device is designed to test the prnperty of GEM foil ,The effective gain and counting capability of a double-GEM detector are measured by an X-ray tube with Cu target. An initial X-ray imaging experiment is carried out using a triple-GEM detcctor and the position iesolution of less than 0.1mm is achieved. The 3D distribution of electrostatic field of GEM mesh is also presented.     

Amplification process of a gas electron multiplier simulated by PIC-MCC model

The performance of a single gas electron multiplier(GEM) in pure Xe at an atmospheric pressure is investigated by Particle in Cell-Monte Carlo Collision(PIC-MCC) model.The micro development processes with electrons and ions distributions in space have been revealed.Based on the micro development processes,the macroscopic parameters such as GEM gain and the effective efficiency have also been obtained.The simulation results indicate that after tens of nanoseconds,electrons are collected by the readout electrode while the ions still exist in the gas space for several microseconds.The main signal current is formed by the electrons arriving at the readout electrode,but electrons and ions are also collected by the copper electrodes near the GEM hole and the thin Kapton film boundary.The simulated gain of GEM exponentially increases with the applied GEM voltage.With the PIC-MCC simulations,both the physical amplification and charging mechanisms in the GEM device can be well understood,which is beneficial to the device design.     

Soft X-Ray Emission in the Water Window Region with Nitrogen Filling in a Low Energy Plasma Focus

For operation of the plasma focus in nitrogen, a focus pinch compression temperature range of 74–173 eV (0.86 × 10⁶–2 × 10⁶ K) is found to be suitable for good yield of nitrogen soft X-rays in the water window region. Using this temperature window, numerical experiments using five phase Lee model have been investigated on UNU/ICTP PFF and APF plasma focus devices with nitrogen filling gas. The Lee model was applied to characterize and optimize these two plasma focus devices. The optimum nitrogen soft X-ray yield was found to be Y_sxr = 2.73 J, with the corresponding efficiency of 0.13 % for UNU/ICTP PFF device, while for APF device it was Y_sxr = 4.84 J, with the corresponding efficiency of 0.19 % without changing the capacitor bank, merely by changing the electrode configuration and operating pressure. The Lee model code was also used to run numerical experiments for optimizing soft X-ray yield with reducing L₀, varying z₀ and ‘a’. From these numerical experiments we expect to increase the nitrogen soft X-ray yield of low energy plasma focus devices to maximum value of near 8 J, with the corresponding efficiency of 0.4 %, at an achievable L₀ = 10 nH.     

Theoretical Study of the Endogenous Production of N-13 in 115 kJ Plasma Focus Device Using Methane Gas

Mather type plasma focus device with the bank energy of 115 kJ (40 kV, 144μF) was studied for induced activity of N-13; a short-lived radioisotope β⁺ emitter with 511 keV of gamma rays and has a half-life of t_1/2 = 9.93 min through ¹²C (d, n)¹³N nuclear reaction. N-13 radioisotope is used in Positron Emission Tomography (PET) for imaging and treatment. In this paper endogenous production of ¹³N is considered. It is shown by adding 3–4 % CH₄ to the chamber, the induced activity of N-13 has increased about 4 %. Our study is representative of producing 10⁶ ? 10⁹ Bq induced activity of this SLR in IR-MPF-100 device.     

一种新的气体电子倍增模式的研究

介绍了一种新的气体放大器件--GEM,制作了一个有效面积为100mm×100mm的GEM+MWPC的模型.用5.9 keV的X射线源测量它的气体倍增系数,并研究了不同气体比例(Ar/CO2)下GEM的放大的性能.GEM的放大倍数可达到94倍.     

Investigation and application of hollow anode glow discharge ion source

In the present work, a new shape of a glow discharge ion source has been designed, fabricated and constructed at Accelerators and Ion Sources Department, Nuclear Research Center, Egyptian Atomic Energy Authority, Egypt. The discharge and output beam characteristics of the ion source at different operating gas pressures have been measured at the optimum distance between the anode and the cathode (3.5 mm) using hydrogen and nitrogen gases. Furthermore, mixture of different gases was studied, e.g., addition of H₂ gas to N₂ gas with different ratios has been investigated. Finally, as an application of this new ion source, ion beam modification of insulators (glass) which depends on glass structure has been achieved. It has been found that, the transmission of light is decreased by coating the glass surface with Ar ion beam more than coating with plasma of Ar gas at the same pressure and the same exposure time. So we could use this ion source as a coating tool for borate glass surface. The parameters affected the glow discharge ion source efficiency have been examined carefully using a mixture of gases. Using helium gas, the glow discharge is in a turbulent state due to instabilities. An investigated H₂-N₂ mixture has been used in order to obtain an optimum percentage of the mixture of the two gases to increase the electric field necessary for ionization balance.     

Kinetics of chlorination of uranium–antimony composite oxide for uranium removal from waste catalyst used for acrylonitrile synthesis

For uranium removal from waste catalyst used for acrylonitrile synthesis, kinetics of chlorination of uranium–antimony composite oxide was studied. During the chlorination treatment with hydrogen chloride gas at a partial pressure of 0.6–6.7 kPa and 873–1173 K, the uranium–antimony composite oxide, USb₃O_10, which was contained in the waste catalyst converted to another composite oxide, USbO₅, then changed to uranium oxide. Both reaction rates of the conversions, from USb₃O₁₀ to USbO₅ and from USbO₅ to U₃O₈, were described by a first order function of the fraction of USb₃O₁₀ and USbO₅, and their activation energies under the condition at 1.0 kPa hydrogen chloride gas were almost same values at (8.0 ± 0.4) × 10⁴ J mol^?1.     

CO2 corrosion of IG-110 nuclear graphite studied by gas chromatography

The CO₂ corrosion behavior of IG-110 nuclear graphite has been investigated using the gas chromatography method which allows the continuous analysis of the CO₂/CO gas mixture at the outlet of the corrosion chamber. The effects of temperature and initial CO₂ concentration are studied based on the Arrhenius-type reaction model. From 745 to 995 °C, the Arrhenius curve shows a linear behavior. For higher temperatures, a non-linear behavior is observed. The activation energy is calculated as 210 kJ/mole and is independent of the initial CO₂ inlet concentrations of 10%, 14% and 17%. The corrosion behavior at 1145 °C, in the diffusion-controlled regime, has also been investigated. At this temperature, the interior of IG-110 graphite is severely attacked by CO₂, and the material's surface morphology is changed drastically. A measurement of the corrosion rate against corrosion time shows that the corrosion rate initially increases to a maximum value at a weight loss degree of 30%–35%, after which it begins to decline.     

带增益的气体探测器读出ASIC的研制

设计了用于带增益的气体探测器比如GEM、RPC等读出的ASIC,实现对探测器信号的放大、成形和对后续实时采样ADC的驱动电路.电荷增益和成形时间可调,有利于探测器不同增益下性能的研究,也扩展了芯片的应用范围.由于成形电路引入的噪声变得显著,在低电荷增益下,ENC会随增益下降而增加.芯片采用Chartered 0.35μm2P4M CMOS工艺,论文介绍了芯片的详细设计和仿真结果.     

Neutron total cross section measurements of polyethylene using time-of-flight method at KURNS-LINAC

ABSTRACT

The neutron total cross sections of polyethylene have been measured in the energy region from 0.001 eV to 40 keV by the time-of-flight (TOF) method using the Kyoto University Institute for Integrated Radiation and Nuclear Science – Linear Accelerator (KURNS-LINAC). A ⁶Li detector and a gas electron multiplier (GEM) detector have been used as a neutron detector, and the polyethylene plates of 0.31 and 0.20 cm thickness were employed for the neutron transmission measurement.

The present results were compared with the previous results and the evaluated data in JENDL-4.0. In the energy region below 0.01 eV, the present results are in good agreement with the data measured by Herdade et al. (1973) and by Granada et al. (1987). On the other hand, the evaluated data in JENDL-4.0 are larger than all the measured data. In the energy region from 0.035 to 0.15 eV, the data measured by Granada et al. and the evaluated data in JENDL-4.0 are up to about 4 ~ 6% larger than the present results.     

Initial Plasma Formation in the GLAST-II Spherical Tokamak

This paper reports the initial plasma formation in glass spherical tokamak (GLAST-II) with electron cyclotron resonance pre-ionization assisted startup. Initially, a plasma current of 3 kA has been produced for duration of about 0.5 ms after establishing optimum conditions for microwave absorption at 2.45 GHz. Plasma current is then enhanced up to 5 kA by applying a small vertical magnetic field that provides additional plasma heating and shaping. Applied vertical field is optimized experimentally and optimal value is found to be 40 Gauss for this experiment. Plasma current and loop voltage are monitored by using Rogowski coil and toroidal loop of wire. A fast framing camera (5000 fps) is used for temporal investigation of plasma during the discharge scenario. A fast photodiode (BPX-65) and USB4000 spectrometer are used to record the signature of plasma current and the impurity content (O₂, H etc.). Cross-sectional average electron temperature is also estimated from plasma resistivity and found to be 6.1 eV for maximum plasma current of 5 kA.     

Al2O3/Y2O3/ZrO2 Ceramic Composite Properties Investigation by Plasma Focus Device

The Al₂O₃–Y₂O₃–ZrO₂ eutectic composition samples were prepared using the Al₂O₃, Y₂O₃, ZrO₂ powder treated at 900 °C for 30 min, pressed at 5 ton for 15 s and sintered at 1500 °C for 2 h. The locally made dense plasma focus (DPF) system with energy 2.8 kJ was used to surface modification of these samples. The samples, mounted at distance about 2 cm from the anode, were exposed to three shots of the DPF in Ar gas at a pressure of 0.8 mbar. The phase and elemental analysis of the untreated and plasma treated samples were conducted by the Raman and EDX spectroscopy. The Raman spectroscopy showed the formation of new phases (α-Al₂O₃ and c-ZrO₂) in the treated samples. The micro-hardness of the plasma treated samples was increased by about 280 % in comparison with the untreated sample.     

A sensitive method for Sr-90 analysis by accelerator mass spectrometry

ABSTRACT

Strontium-90 is one of the most important fission products due to the potential health risks of its uptake and retention in the human body. Conventional analysis techniques involve β counting, which requires ingrowth of ⁹⁰Y over a period of two weeks. Accelerator mass spectrometry (AMS) has the potential to shorten the analysis time while offering a lower limit of detection than β counting. Here, Sr in samples was recovered as SrF₂ to provide sufficient negative ions in the caesium-sputtering ion source. In the sample preparation step, 95–98% of Sr was recovered and 99–100% of Zr removed by ion-exchange separation. Sr recovery was ~30% in the precipitation process, and this can be improved. A maximum 500 nA beam current of SrF₃ ^– ions was obtained from SrF₂ samples mixed with PbF₂. A five-anode gas ionization detector was used to avoid isobaric interference from ⁹⁰Zr. The ⁹⁰Sr/Sr atomic ratio background of ~6 × 10^–13 (~3 mBq ⁹⁰Sr) was comparable with that achieved at other AMS facilities. Good linearity in ⁹⁰Sr/Sr atomic ratios was obtained from 1.75 × 10^–10 to 3.38 × 10^–9. Suitable techniques for sample preparation and measurement were thus achieved for ⁹⁰Sr analysis by AMS.     

Study on the phosphate reaction characteristics of lanthanide chlorides in molten salt with operating conditions

A minimization of waste salt is one of the most important issues for the optimization of pyroprocessing. The separation of fission products in waste salts and the reuse of purified waste salt are promising strategies for minimizing the waste salt amounts. The phosphate precipitation of lanthanide is currently being considered for eutectic (LiCl–KCl) waste salt purification. In this research, the effects of molten salt temperature (400–550 °C) and reaction time (max. 180 min) upon conversion into the phosphate of lanthanides was investigated using 1 and 3 kg of eutectic salt. The conversion efficiency of lanthanides to molten salt-insoluble precipitates and phosphates was increased with an increase in molten salt temperature and operating time until it attained a specific temperature and time. K₃PO₄ as a precipitant was more favorable than Li₃PO₄ in terms of reactivity. To obtain over a 99% overall conversion efficiency, about 30 min was required in the case of using K₃PO₄ at 450 °C, but about 120 min in the case of using Li₃PO₄ at 550 °C. The lanthanide precipitates formed by a reaction with phosphate were a mixture of monoclinic structures, usually representing a polyhedron structure, and a tetragonal structure, representing a platelet structure.     

Simulation of a new hybrid MPGD with improved time resolution and decreased discharge probabilities using Garfield++

In this work,a new hybrid MPGD consisting of two GEM foils and a metallic mesh was proposed.Based on the simulation studies,this design can significantly reduce the rise time of signal and has a better performance in respect of particle identification compared with the triple GEM design.The gain with various voltages setting was computed in order to provide us references for future experiment.The simulation results also show that the time and space resolution compared to the triple GEM detector are also improved.The time and space resolution of hybrid detector with Ar/CO2(70/30) and Ar/isobutane(95/5) were investigated for various drift electric field intensities.This new hybrid detector shows excellent potential for both fundamental research and imaging applications.     

Deposition of Alumina Films on Si (1 0 0) Substrate Using a Low Energy Dense Plasma Focus Device

A 1.5 kJ pulsed low energy Mather type plasma focus (PF) is used to deposit thin films of alumina (α-Al₂O₃) on Si (1 0 0) substrates. The PF device with its anode made of aluminum was operated with argon-oxygen mixture as the filling gas. The Al₂O₃ thin film samples were prepared using 10, 20 and 30 successive shots with substrates placed at 60 mm from the top of the anode at approximately zero angular position with respect to the anode axis. The crystallography of the as-deposited and annealed samples was studied by X-ray diffractometry (XRD). Raman Spectroscopy studies verified the formation of α-Al₂O₃ phase in the annealed films. Scanning electron micrographs (SEM) of the annealed films present many different sized particulates (50–300 nm) distributed upon the film surface. The cross-sectional SEM micrographs show that the thickness of deposited alumina film is linear with a typical rate of 45 nm/shot at focus storage energy of 850 J.     

Effects of Power Terms and Thermodynamics on the Contraction of Pinch Radius in Plasma Focus Devices Using the Lee Model

The influence of the power terms Joule heating and radiative losses on the pinch radius in plasma focus devices is studied. Numerical experiments were carried out using the Lee model on three plasma focus devices spanning a large range of storage energy (PF400, INTI PF, PF1000) with different filling gases (N, O, Ne, Ar, Kr, Xe). Six possible regimes each characterized by a combination of significant power terms affecting plasma focus dynamics are found and discussed. These six possible regimes are further moderated by thermodynamic effects related to the specific heat ratio SHR of the plasma. In PF1000, the thermodynamic compression effects are clearly apparent in the radius ratio versus pressure curve for nitrogen which with atomic number Z_n = 7 is less radiative than neon with Z_n = 10, the dominant line radiation being proportional to Z _n ⁴ . In neon radiative compression at optimum pressure is so dominant that it masks thermodynamic compression in the compression versus pressure graph. Results show that plasma radiation losses enhance the contraction of the plasma focus pinch radius within suitable pressure ranges characteristic of each machine for each gas discussed in this paper. The radiation enhancement of compression increases with the atomic number of the gas.     

Investigation of oxidation behaviors of nuclear graphite being developed and IG-110 based on gas analysis

The oxidation behaviors of the nuclear graphite being developed were investigated using gas chromatograph at 873–1373 K. The oxidation experiments were carried out with the gas flow rate of 0.2 L/min and the oxygen concentrations of 7, 10 and 20 mol%. The oxidation reaction began at 973 K and was accelerated with the increase of temperature. At 1173–1273 K, the oxidation was limited by oxygen supplied to graphite and the reaction rate held steady. From 1273 to 1373 K, the oxidation rate increased obviously due to the significant reaction between CO₂ and graphite. At the low temperature regime (973–1073 K), the apparent activation energies with the oxygen mole fractions of 7%, 10% and 20% were 298, 324 and 321 kJ/mol, respectively. Scanning electron microscope was applied to reveal the pore development of the graphite oxidized at different temperatures. The effect of CO combustion at temperature below 1173 K was discussed based on the oxidation behaviors of the graphite being developed and IG-110. It was suggested that the ASTM D7542-15 standard should be adjusted to fit some popular graphite, such as graphite IG-110.     

Numerical Experiments on Oxygen Plasma Focus: Scaling Laws of Soft X-Ray Yields

Numerical experiments have been investigated on UNU/ICTP PFF low energy plasma focus device with oxygen filling gas. In these numerical experiments, the temperature window of 119–260 eV has been used as a suitable temperature range for generating oxygen soft X-rays. The Lee model was applied to characterize the UNU/ICTP PFF plasma focus. The optimum soft X-ray yield (Y_sxr) was found to be 0.75 J, with the corresponding efficiency of about 0.03 % at pressure of 2.36 Torr and the end axial speed was v_a = 5 cm/μs. The practical optimum combination of p₀, z₀ and ‘a’ for oxygen Y_sxr was found to be 0.69 Torr, 4.8 cm and 2.366 cm respectively, with the outer radius b = 3.2 cm. This combination gives Y_sxr ~ 5 J, with the corresponding efficiency of about 0.16 %. Thus we expect to increase the oxygen Y_sxr of UNU/ICTP PFF, without changing the capacitor bank, merely by changing the electrode configuration and operating pressure. Scaling laws on oxygen soft X-ray yield, in terms of storage energies E₀, peak discharge current I_peak and focus pinch current I_pinch were found over the range from 1 kJ to 1 MJ. It was found that the oxygen soft X-ray yields scale well with $ {\text{Y}}_{\text{sxr}} = 2 \times 10^{ - 7} {\text{I}}_{\text{pinch}}^{3.45} $ and $ {\text{Y}}_{\text{sxr}} = 6 \times 10^{ - 7} {\text{I}}_{\text{peak}}^{ 2. 9 2} $ for the low inductance (L₀ = 30 nH) (where yields are in J and currents in kA). While the soft X-ray yield scaling laws in terms of storage energies were found to be as $ {\text{Y}}_{\text{sxr,O}} = 5.354 \times {\text{E}}_{0}^{1.12} $ (E₀ in kJ and Y_sxr in J) with the scaling showing gradual deterioration as E₀ rises over the range. The oxygen soft X-ray yield emitted from plasma focus is found to be about 8.7 kJ for storage energy of 1 MJ. The optimum efficiency for soft X-ray yield (1.1 %) is with capacitor bank energy of 120 kJ. This indicates that oxygen plasma focus is a good soft X-ray source when properly designed.