Test of a high resolution drift chamber prototype

The performance of a drift chamber prototype for a colliding beam vertex detector in a test beam at DESY is described. At one (two) atmosphere gas pressure a spatial resolution of 40 μm (30 μm) per wire for one cm drift length was achieved with a 100 MHz Flash-ADC system. An excellent double track resolution of better than 300 μm over the full drift length of 5 cm can be estimated.     

Drift chamber readout with flash ADCs: I. Time and spatial resolution

A systematic study of the time, space, and double track resolution for drift chambers with a 100 MHz flash ADC readout is reported. The dependence of the spatial resolution on gas pressure, electric field, drift distance, and the algorithms used for pulse shape analysis has been investigated. At 4 bar gas pressure a spatial resolution of better than 125 μm was obtained for drift distances up to 20 cm. The double track resolution is ≲ 3 mm.     

Design and performance of a diffusion-suppressed streamer chamber

We have designed, built, and tested a high-resolution streamer chamber that employs a novel diffusion suppression scheme. The chamber operates at 60 atm, uses a few-nanoseconds-wide 250 kV high-voltage pulse, has a maximum repetition rate of 10 Hz, and has an active volume of 13.5 × 4.5 × 0.7 cm³. Under these conditions we measure the rms deviation of streamer centers from fitted track trajectories to be about 12 ωm in space, and a two-track resolution of approximately 50 ωm.     

Test results from a precision drift chamber vertex detector prototype using dimethylether

Results of beam tests of a prototype drift chamber vertex detector developed for the D-Zero experiment at the Fermilab collider are reported. The chamber design emphasizes dual goals of high accuracy position measurement and excellent two track resolution. These requirements are met by using a slow gas, dimethyl ether, in a jet chamber geometry with a double plane of field-shaping wires near the anodes. Resolution of nearby hits is facilitated by 100 MHz flash digitization of the signal pulses. The prototype tested consisted of a full-length (97 cm) model of one azimuthal sector of the innermost layer of the detector, with 8 anode wires. Position measurement accuracy of 30–80 μm for drift distances of 2–11 mm and pulse pair resolution of 0.7 mm (for 90% of all pulses) is achieved.     

Pulse shape simulation for drift chambers with long drift paths

A detailed Monte Carlo program for the simulation of drift chamber pulse shapes is described. It has been applied to the case of a jet chamber with drift paths up to 24 cm. Results on pulse shapes and corresponding spatial and double hit resolution are discussed and compared to recent measurements of the OPAL central detector jet chamber full size prototype and to measurements of a small 20-wire prototype, which was designed to study the pulse shapes generated by tracks in a magnetic field. Simulated pulse shapes and spatial resolutions agree well with the experimental data. Clustering, saturation and wire crosstalk are shown to be necessary ingredients in the simulation. A deterioration in resolution due to the influence of crosstalk signals is correctly reproduced, as well as the cancellation of this effect by a hardwired first and second neighbour crosstalk compensation. The simulation correctly describes the asymmetry in spatial resolution observed for tracks with positive or negative inclination against the wire plane when a magnetic field is present. The effect of saturation on double hit resolution is found to be small. The magnetic field is predicted to improve the double hit resolution.     

The HHIRF supersonic gas jet target facility

We describe a supersonic gas jet target built for studying reactions induced by heavy ions with high energy resolution. The device produces very localized high density gas jets in a near vacuum environment and is presently installed in the scattering chamber of a magnetic spectrograph at the ORNL HHIRF. With a 100 MeV ¹⁶O beam collimated to a size of approximately 1 mm² at the target, image sizes of 0.42 mm have been obtained at the focal plane of the spectrograph with a solid angle of 2.4 msr and target densities of 15–30 μg/cm².     

Hot-wire deposition of amorphous and microcrystalline silicon using different gas excitations by a coiled filament

Microcrystalline silicon (μc-Si:H) and amorphous silicon (a-Si:H) films were deposited using a hot-wire CVD (HWCVD) system that employs a coiled filament. Process gasses, H₂ and Si₂H₆, could be directed into the deposition chamber via different gas inlets, either through a coiled filament for efficient dissociation or into the chamber away from the filament, but near the substrates. We found that at low deposition pressure (e.g. 20 mTorr) the structure of the films depends on the way gases are introduced into the hot-wire chamber. However, at higher pressure (e.g. 50 mTorr), Raman measurement shows similar results for films deposited with different gas inlets.     

Monte Carlo simulations of effects due to delta rays in aluminum drift-tube counters

The spatial resolution of drift-tube counters of the VENUS muon detector in the test arrangement for cosmic muons was shown to have two distinct components. The first component, which corresponds to about 96% of the detection efficiency, has a normal distribution with an rms spatial sesolution of about 1 mm. It is evident that the second component with about 3.6% of the total incident muons corresponds to events for which delta-rays generated inside the chamber wall are scattered closer to the sense wire or between the sense wire and the true tracks. Such confused track events are unavoidable in drift-tube counters with a single TDC scaler per cell. The general characteristics of phenomena caused by delta rays in drift-tube counters are studied by Monte Carlo simulations for various detector arrangements. The upper limits of the knockon electron yield and confused track rate are found to be respectively 14% and 6% of the total incident muons with medium energies of the order of 10 GeV or less in typical muon detector systems consisting of aluminum drift-tube counters and iron absorbers. For drift-tube counters with very thin aluminum walls these limits are reduced to about 11% and 5%, respectively.     

Uncertainty in radon measurements with CR39 detector due to unknown deposition of Po

Uncertainty in radon measurements using the CR39 solid-state nuclear track detector in chambers is introduced by the unknown fraction f₁ of ²¹⁸Po that deposited onto the inner chamber walls. This uncertainty was estimated for cylindrical chambers with different size in the present study. It was found that the uncertainty increased with the chamber height and radius. For short chambers with a height H=2 cm the uncertainty was less than 5%, while in tall chambers with H=7 cm it could be up to 17%. The radial track density on the CR39 detector inside the diffusion chamber was also found to be dependent on the fraction f₁. In this work, some examples of this dependence are shown.     

Detection of γ-rays with a 3.5 l liquid xenon ionization chamber triggered by the primary scintillation light

A gridded ionization chamber with a drift length of 4.5 cm and a total volume of 3.5 l, was operated with high-purity liquid xenon and extensively tested with γ-rays from ¹³⁷Cs, ²²Na and ⁶⁰Co radioactive sources. An electron lifetime in excess of 1 ms was inferred from two independent measurements. The electric field dependence of the collected charge and energy resolution was studied in the range 0.1–4 kV/cm, for different γ-ray energies. With an electric field of 4 kV/cm, the spectral performance of the detector is consistent with an energy resolution of 5.9% at 1 MeV, scaling with energy as E^−0.5. The chamber was also used to detect the primary scintillation light produced by γ-ray interactions in liquid xenon. The light signal was successfully used to trigger the acquisition of the charge signal with a FADC readout. A trigger efficiency of 85% was measured at 662 keV.     

高温N2气氛下树脂结合刚玉材料中阿隆相的形成机制

以酚醛树脂为结合剂,分别以100wt%烧结刚玉细粉、100wt%电熔刚玉细粉和50wt%烧结刚玉加50wt%电熔刚玉混合细粉为原料制备试样,试样在N₂气氛下经1 500℃和1 600℃烧成,对烧后试样进行XRD、SEM和EDAS表征分析。结果表明：1 500℃烧后试样中生成了γ-AlON（Al₅O₆N）和12H多型体（Al₆O₃N₄）,1 600℃烧后试样中生成了γ-AlON（Al₅O₆N）、21R多型体（Al₇O₃N₅）和16H多型体（Al₈O₃N₆）。1 600℃烧成试样中生成的阿隆（AlON）含量较1 500℃烧成试样显著增多。在相同温度下,50wt%烧结刚玉加50wt%电熔刚玉混合细粉试样中生成的AlON含量最多,100wt%电熔刚玉细粉试样次之,100%烧结刚玉细粉试样中生成的AlON含量最少。分析了AlON的形成机制并建立了刚玉细粉与碳的反应模型。     

Advanced HfC-TaC Oxidation Resistant Composite Rocket Thruster

Several compositions of HfC-TaC codeposited by chemical vapor deposition were evaluated for oxidation protection of graphite substrates. Oxyacetylene torch ablation tests with an O₂, C₂, H₂, ratio of 4:1 were used to test the adherence and composition of the coating and resulting oxides, which were subsequently characterized by x-ray diffraction and scanning electron microscopy. The preferred HfC-TaC composition of 70:30 was used to fabricate a 25 lbf graphite fiber reinforced rocket thruster with a unique structural design. Thruster testing at NASA Lewis was performed at 0.520 MPa chamber pressure and 1650°C (3000°F) using a 6 to 7:1,0₂,:H₂ fuel mixture; a uniform, adherent oxide layer was observed on the internal surface of the combustion chamber following the test.     

X-ray imaging with “edge-on” microchannel plate detector: first experimental results

A novel scanning slit X-ray imaging system based on an “edge-on” microchannel plate detector was developed and tested. Images were acquired at 50 kV(p) X-ray tube voltage with a limiting spatial resolution of 7 lp/mm. The pixel noise was measured to be 0.3 count/pixel/s for a 50×70 μm² pixel size. This photon counting detector can be considered to be virtually noise free.     

Double core---shell nanostructured Sn---Cu alloy as enhanced anode materials for lithium and sodium storage

Sn-based alloy materials are considered as a promising anode candidate for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs), whereas they suffer from severe volume change during the discharge/charge process. To address the issue, double core–shell structured Sn–Cu@SnO₂@C nanocomposites have been prepared by a simple co-precipitation method combined with carbon coating approach. The double core–shell structure consists of Sn–Cu multiphase alloy nanoparticles as the inner core, intermediate SnO₂ layer anchored on the surface of Sn–Cu nanoparticle and outer carbon layer. The Sn–Cu@SnO₂@C electrode exhibits outstanding electrochemical performances, delivering a reversible capacity of 396 mA·h·g⁻¹ at 100 mA·g⁻¹ after 100 cycles for LIBs and a high initial reversible capacity of 463 mA·h·g⁻¹ at 50 mA·g⁻¹ and a capacity retention of 86% after 100 cycles, along with a remarkable rate capability (193 mA·h·g⁻¹ at 5000 mA·g⁻¹) for SIBs. This work provides a viable strategy to fabricate double core–shell structured Sn-based alloy anodes for high energy density LIBs and SIBs.     

X-ray position resolution in proportional chambers in the region of 100 μm (FWHM) above the xenon K-edge

A brief discussion is presented of the X-ray absorption process in xenon above its K-edge of 34.6 keV. Experimental measurements from a one-dimensional proportional chamber, operating with a gas mixture of Xe/10%CO₂, show that position resolution in the region of 100 μm FWHM can be achieved for X-rays with energy just above the K-edge.     

High-resolution liquid-crystal-based spatial light modulator with a thin crystalline silicon photosubstrate structure

We report an optically addressed, liquid-crystal-based spatial light modulator demonstrating a resolution of 25 line pairs/mm at 50% modulation transfer function and more than 40-line-pair/mm limiting resolution by using a 25-μm-thick silicon Schottky diode-array photosubstrate. This resolution is obtained concurrent with a high photosensitivity of approximately 20 μW/cm(2) and a contrast ratio of over 200:1. The high resolution and photosensitivity obtained with the thin photosubstrate are explained by a fringing field and an equivalent-circuit model, respectively.     

基于常压氦质谱累积检漏的定/变容漏率标定技术研究

漏率标定技术是航天器密封性能检测的重要组成部分,直接决定计算漏率的大小。为减小漏率标定测试数据误差,提高检测精度,本文基于常压氦质谱累积检漏法,通过理论分析与实验,研究了注入氦气量、收集室体积、航天器漏率等参数对漏率标定数据的影响。结果表明,测试数据与注入的氦气量呈线性关系,并随着收集室体积的增加而减小;收集室累积空间体积在30~100 m³之间时,漏率标定测试数据变化率在10^-9量级且相对稳定,有助于完善漏率标定数学模型;通过标准漏孔模拟航天器的漏率,当漏率小于1×10^-4Pa·m³/s时,标定测试数据(1 h内)相对偏差小于30%,同时可采取缩短漏率标定时间、风机循环使氦气分布均匀等方式提高航天器的漏率检测精度。     

The wide gap resistive plate chamber

The resistive plate chamber (RPC) has good time and position resolution; these factors (coupled to its simple construction) make it an attractive candidate for muon trigger systems at future colliders. However, operated in spark mode, the RPC has severe rate problems that make it unusable above 10 Hz/cm². We have previously published our results concerning the operation of the RPC in spark and in avalanche mode; we have shown that the rate limit can be increased to 150 Hz/cm² if the RPC is operated in avalanche mode. Here, we discuss the performance of chambers with 6 and 8 mm gas gaps (compared to the more usual 2 mm gap). We outline the reasons for this choice, and also discuss anode versus cathode strip readout. We have measured the efficiency versus flux, and also show that an enhanced rate limit can be obtained if only a small region of the chamber is exposed to the beam (spot illumination). Finally we have tested the performance of chambers constructed with other materials for the resistive plate and compare it to chambers constructed with our preferred plastic, melamine laminate.     

UV-SLPT for Gas Sensor Research on MISiC Devices

A modified Scanning Light Pulse Technique (SLPT) setup that can be used to evaluate SiC-based gas-sensitive field-effect devices is introduced. This is exemplified with measurements on a Pt-MISiC capacitor that has a metal thickness gradient. The device shows large responses to hydrogen and ammonia in air. The H₂ and NH₃ responses show a complementary dependence on the Pt film thickness at 140degC. The temperature dependence differs however for the two gases. The measurement setup uses UV transparent optics together with mechanical chopping of light from a short wavelength light source. The spatial resolution of the system is found to be approximately 50 mum     

Further study on different dopings into PbWO4 single crystals to increase the scintillation light yield

Since we presented our preliminary result (Nucl. Instr. and Meth. A 486 (2002) 170) at SCINT2001, we have continued our efforts to increase the light yield (LY) of PbWO₄ scintillators by extending different dopings with an aim to find a possibility of using PbWO₄ successfully in Positron Emission Tomography (PET). Overall result obtained for single doping as well as double and tripple co-dopings are summarized, including decay characteristics and radiation hardness. The LY in non-doped PbWO₄ crystals with a size of 10×10×(20–30) mm³ is 25–35 photolectrons/MeV (phe/MeV) corresponding to 3–4% of the LY in BGO, when measured with a bialkali photomultiplier during a gate of 1 μs. The maximum LY increased to 49 phe/MeV for single doping with Mo⁶⁺, 80 phe/MeV for double co-doping of Mo⁶⁺+Sb⁵⁺, and 85 phe/MeV for tripple co-doping of Mo⁶⁺+Cd²⁺+Sb⁵⁺. The radiation hardness is larger than 10⁵ Gy for each of the samples co-doped with Mo⁶⁺+Sb⁵⁺ and Mo⁶⁺+Cd²⁺+Sb⁵⁺, while it is much poorer in PWO:Mo⁶⁺. In each of these co-doped samples, a medium-speed green emission in the microsecond range is created besides the fundamental fast (a few nanoseconds range) blue one, giving a peak at 500 nm in the radioluminescence spectrum similarly as in PWO:Mo⁶⁺.