基于GEM读出的TPC工作气体的研究

针对TPC中对于电子漂移的要求, 结合Garfield软件, 研究了我们所研制的TPC原型所用的工作气体. 分析了不同气体对于电子漂移的寿命、漂移速度、横向和纵向扩散, 以及电离特性等参数的影响; 结合分析论证, 得到了以Ar, CH₄和CF₄为主要成分的气体作为工作气体时TPC的性能指标. 并且测试了该气体中的读出GEM探测器的能量分辨率、气体增益等性能参数, 获得了很好的结果.     

Studies on the drift properties and spatial resolution using a microMEGAS-equipped time projection chamber

R&D studies on the performance as well as on the gas properties of the microMEGAS-based time projection chamber with standard readout were carried out in June 2005 using 4 GeV/c pion beam in a magnetic field from 0 to 1 T at the proton synchrotron beam line at KEK, Japan. Analysis of the electron drift velocity, diffusion constant and point resolution of padrow measurement for MicroMEGAS TPC filled with 95% argon and 5% isobutane gas are presented. The underlying physical mechanism which determines the optimal TPC performance are briefly discussed. Preliminary measurements of gas properties and spatial resolution in close agreement with the analytical calculation and MAGBOLTZ simulation are summarized and presented in this paper.      

Measurement of the production of charged pions by protons on a tantalum target

A measurement of the double-differential cross-section for the production of charged pions in proton–tantalum collisions emitted at large angles from the incoming beam direction is presented. The data were taken in 2002 with the HARP detector in the T9 beam line of the CERN PS. The pions were produced by proton beams in a momentum range from 3 GeV/c to 12 GeV/c hitting a tantalum target with a thickness of 5% of a nuclear interaction length. The angular and momentum range covered by the experiment (100 MeV/c ≤p< 800 MeV/c and 0.35 rad ≤θ< 2.15 rad) is of particular importance for the design of a neutrino factory. The produced particles were detected using a small-radius cylindrical time projection chamber (TPC) placed in a solenoidal magnet. Track recognition, momentum determination and particle identification were all performed based on the measurements made with the TPC. An elaborate system of detectors in the beam line ensured the identification of the incident particles. Results are shown for the double-differential cross-sections d²σ/dpdθ at four incident proton beam momenta (3 GeV/c, 5 GeV/c, 8 GeV/c and 12 GeV/c). In addition, the pion yields within the acceptance of typical neutrino factory designs are shown as a function of beam momentum. The measurement of these yields within a single experiment eliminates most systematic errors in the comparison between rates at different beam momenta and between positive and negative pion production. PACS 13.75.Cs; 13.85.Ni     

毛细管准直微束过程模拟与微束品质分析

利用GEANT4程序对复旦大学单粒子微束的毛细管准直过程进行了蒙特卡罗模拟。计算结果表明:当前采用的1 m孔径、1 mm长度的毛细玻璃管准直器能够引出峰值能量2.2 MeV、能量分辨130 keV、束径2.4 m的质子微束,可达到装置对微束能量与束径分辨的设计指标,从理论上明确了毛细管准直微束引出的可行性。针对影响入射目标细胞微束品质的主要因素,分析了微束品质与准直系统和入射束流各状态参数的依赖关系,为毛细管准直微束的引出与优化提供了必要的理论依据。     

A muti-channel distributed DAQ for n-TPC

A new fast neutron spectrometer named n-TPC has been designed by LPRI (Key Laboratory of Particle & Radiation Imaging, Ministry of Education) at Tsinghua University. The neutron energy spectrum can be calculated from the recoil angle and energy of the recoil proton detected by a 704-pad GEM-TPC. In beam tests at IHIP (Institute of Heavy Ion Physics, Peking University) in 2014, n-TPC performed better than 6%@6 MeV energy resolution and 5‰ detection efficiency. To find the best working parameters (the component and proportion of the gas, the high voltage between each GEM layer, etc.) of the n-TPC and support its application in various conditions, a multichannel distributed DAQ has been {designed} to read out the signals from the 704 channels. With over 25 Ms/s sampling rate and 12 bit resolution for each channel, it can record the time and amplitude information as well as traditional DAQs in the TPC application domain. The main design objective of this distributed DAQ, however, is more flexible parameter modulation and operation. It can support the n-TPC without the limitation of the chassis and categorize signals arriving from the 704 channels at the same time by different events without event triggers.     

Large-angle production of charged pions by 3?GeV/c–12?GeV/c protons on carbon, copper and tin targets

A measurement of the double-differential π^± production cross-section in proton–carbon, proton–copper and proton–tin collisions in the range of pion momentum 100 MeV/c≤p<800 MeV/c and angle 0.35 rad≤θ<2.15 rad is presented. The data were taken with the HARP detector in the T9 beam line of the CERN PS. The pions were produced by proton beams in a momentum range from 3 GeV/c to 12 GeV/c hitting a target with a thickness of 5% of a nuclear interaction length. The tracking and identification of the produced particles was done using a small-radius cylindrical time projection chamber (TPC) placed in a solenoidal magnet. An elaborate system of detectors in the beam line ensured the identification of the incident particles. Results are shown for the double-differential cross-sections d²σ/dpdθ at four incident proton beam momenta (3 GeV/c, 5 GeV/c, 8 GeV/c and 12 GeV/c). PACS 13.75.Cs; 13.85.Ni     

原子能院的核天体物理研究和串列升级工程进展(英文)

在北京串列实验室建立了次级束流实验装置 ,用于放射性核束物理和核天体物理研究 .先后开展了7Be(d ,n) 8B ,11C(d ,n) 12 N ,8Li(d ,p) 9Li和6 He(p ,n) 6 Li核天体物理重要反应的研究 .介绍了串列加速器升级工程的进展情况 .该工程在现有串列加速器的基础上 ,将建立 10 0MeV/ 2 0 0 μA的质子回旋加速器、在线同位素分离器和超导加速段 .在此装置上 ,将可以产生质量数最高为 12 0 ,强度最高为 10 9particles/s的放射性束流 . A secondary beam line (GIRAFFE) at the Beijing Tandem accelerator lab was constructed for yielding low energy secondary beams. The current progress on the study of nuclear astrophysics and nuclear structure is presented. Up to now, We have carried out measurement of~(7)Be(d, n)~( 8)B,~(11)C(d, n)~(12)N,~(8)Li(d, p)~(9)Li, and~(6)He(p, n)~(6)Li reactions. The proposed Beijing radioactive nuclear beam facility (BRIF ) and its current R&D progress are briefly introduced. This facility is based on...     

High resolution spectroscopy of (lambda)(12)B by electroproduction

An experiment measuring electroproduction of hypernuclei has been performed in hall A at Jefferson Lab on a 12C target. In order to increase counting rates and provide unambiguous kaon identification two superconducting septum magnets and a ring imaging Cherenkov detector were added to the hall A standard equipment. An unprecedented energy resolution of less than 700 keV FWHM has been achieved. Thus, the observed (Lambda)(12)B spectrum shows for the first time identifiable strength in the core-excited region between the ground-state s-wave Lambda peak and the 11 MeV p-wave Lambda peak.     

PET用新型深度编码探测器设计

平行性问题或作用深度问题影响着正电子放射层析系统(PET)的成象分辨率。本文提出和评价了一种二阶深度编码探测器,这个探测器是由两层LSO晶体和位置灵敏型光电倍增管(PS-PMT)组成,上层的晶体相对于下层的晶体的位置在X和Y方向上都有半个晶体阵列单元的错位,因为每个晶体的输出光的重心位置分布在PS-PMT上不同的位置,所以通过计算其重心位置就可在象平面上区别开每个晶体。根据PET系统的应用要求,我们验证了探测器的性能。伽马射线垂直入射时,上层晶体阵列的固有空间分辨率为1.15mmFWHM,下层晶体列阵为1.34mm FWHM.钠伽马辐射源的511keV能量峰处的平均能量分辨率对于下层晶体为19.7%,上层为23.6%.通过类似的技术亦可实现3阶、4阶深度编码探测器。     

A numerical model of a coated capillary-plate thermal neutron collimator

A novel thermal neutron collimator was successfully fabricated by coating the inner surface of the capillary plate (CP) with gadolinium oxide using atomic layer deposition (ALD) technology. This CP-based collimator is efficient and compact. A numerical model is presented in the paper to estimate the main performance characteristics of the collimator and to optimize the design for specific applications. According to the results of the calculation based on currently available CPs, the FWHM of the collimator's rocking curve can be smaller than 0.15° while suppressing more than 99.9% of the incident thermal neutrons on the double wings of the curve. Such a coated CP is as thin as 1.25 mm or even thinner, providing high angular resolution with good transmission in a very limited space.     

Proton-hydrogen reaction in an effectively two-body model

A model of total interaction between a proton incident to a hydrogen atom and the proton that is the nucleus of this atom is proposed. This interaction is assumed to be the sum of the short-range nuclear Reid potential and the long-range Thomas-Fermi potential induced by the Coulomb interaction of the electron with the nucleus of the hydrogen atom. The explicit low-energy asymptotic behavior of the cross section for the proton-hydrogen reaction leading to deuteron production is found. It is shown that this cross section increases in inverse proportion to the collision energy for the proton and hydrogen atom in its zero limit.     

The reaction 26Mg(d, τ)25Na and the structure of 25Na

The nuclear structure of the nucleus ²⁵Na has been studied with the (d, τ) proton pick-up reaction on ²⁶Mg at a bombarding energy of 29 MeV with an energy resolution of 25 to 30 keV FWHM. Excited states in ²⁵Na have been measured up to excitation energies of 8 MeV. The experimental angular distributions show good agreement with the predictions from the standard distorted-wave Born-approximation theory (code DWUCK; non-local and finite range). However, the agreement is improved considerably if the procedure of Kunz, Rost and Johnson is applied which accounts approximately for strong couplings to inelastic channels in the initial and final (strongly deformed) nuclei. The influence of this treatment on the evaluation of spectroscopic factors has been investigated and was found to be particularly pronounced for l = 0 transitions. The measured spectroscopic factors are compared to those from other experimental work and from shell-model and Nilsson-model calculations.     

Near-threshold electron impact excitation of ultraviolet-emitting levels of helium atoms

The excitation by electron impact of levels of helium atoms that decay by emission of ultraviolet light has been studied as a function of incident energy up to approximately the first ionization energy. The width (FWHM) of the energy spread of the incident beam was less than 30 meV. A crossed-beam interaction region was used and UV photons emitted approximately normally to the electron and gas beam directions were detected by a channel electron multiplier. Precautions were taken to avoid detection of scattered electrons and metastable atoms by the photon detector. The onset position of the lowest excited level was used in calibrating the incident energy scale. The energies of resonance structures in the cross-sections could therefore be obtained and are compared with the results of experiments detecting other products of the interaction.     

MICROMEGAS探测器初步测试

介绍了一种利用鱼线做放大区间隔的MICROMEGAS探测器, 灵敏面积为50 mm ×50 mm。 在Ar+CO₂（10%）气体条件下, 利用55Fe源5.9 keV的 X射线对MICROMEGAS探测器进行了初步测试: 计数率大于103 Hz的条件下, 计数率坪长达到280 V; 当栅极电压在800 V时能量分辨为30%; 当增益高于104时打火率低于10-4; PCB板读出条周期为400 μm条件下的位置分辨好于120 μm。 结果表明, 研制的MICROMEGAS探测器达到了初步设计的基本要求。 In this paper,A MICROMEGAS(Micro Mesh Gaseous Structure) detector with the amplification gap defined by stretching nylon fishing lines has been described . And its count plateau, gas gain and energy resolution in the condition of a 55Fe X ray source and Ar CO₂ (10%) mixture gases are measured as functions of mesh voltage. The count plateau approaches 280 V at the count rate of 103 Hz. The discharge rate is less than 10－4 when the gas gain is up to 104. The energy resolution is 30% (FWHM) based on －800 V mesh voltage. The position resolution is less than 120 μm at the condition of the sensitive area (50 mm×50 mm) Printed Circuit Boards (PCB) and its strip pitch of 400 μm. The results can satisfy the basic demand of MICROMEGAS detector preliminary design.     

Energy loss effect in high energy nuclear Drell-Yan process

The energy loss effect in nuclear matter, which is a nuclear effect apart from the nuclear effect on the parton distribution as in deep-inelastic scattering process, can be measured best by the nuclear dependence of the high energy nuclear Drell-Yan process. By means of the nuclear parton distribution studied only with lepton deep-inelastic scattering experimental data, the measured Drell-Yan production cross sections for 800 GeV proton incident on a variety of nuclear targets are analyzed within the Glauber framework which takes into account the energy loss of the beam proton. It is shown that the theoretical results with considering the energy loss effect are in good agreement with the FNAL E866 data.Arrival of the final proofs: 24 June 2003     

质子在碳化硅中不同深度的非电离能量损失

利用蒙特卡罗方法,应用Geant4程序,模拟计算了1—500 MeV质子在碳化硅材料中的非电离能量损失,并研究了不同种类的初级反冲原子对非电离能量损失的贡献.模拟结果表明:在相同质子辐照下,碳化硅材料中的非电离能量损失要比硅、镓等半导体材料更小,说明碳化硅器件的稳定性更好,抗位移损伤能力更强;当靶材料足够厚时,在不同能量质子辐照下,材料损伤最严重的区域会随着质子入射能量的增加从质子射程末端逐渐前移到材料表面;不同种类的初级反冲原子对非电离能量损失的贡献表明,在低能质子辐照下,28Si和~(12)C是位移损伤的主要原因,而随着质子能量的增加,通过核反应等过程产生的次级离子迅速增多,并对材料浅层造成严重的位移损伤.     

Superconducting tunnel junctions as detectors for high‐resolution x‐ray spectroscopy

Superconducting tunnel junctions (STJs) are a type of cryogenic detector with a working temperature of about 100 mK. They allow the combination of low energy threshold, high quantum efficiency and good count rate capability with an excellent energy resolution; at an x‐ray energy of 5.9 keV an energy resolution of 10.8 eV (FWHM) has been achieved. The detector system described is based on STJs which consist of two superconducting Al electrodes separated by a thin dielectric tunnel barrier. The tunneling process of quasi‐particles created by deposition of energy in the electrodes leads to a detectable current signal. The STJ is equipped with a superconducting Pb absorber which is read out via phonons. The Pb absorber increases absorption efficiency (～50% at 6 keV) and suppresses detector artefacts. The degeneration of Pb, most probably due to oxidation, is overcome by the introduction of a protective SiO layer on top of the absorber. This layer leads to a slight reduction of energy resolution. Nevertheless, a resolution of 9.7 eV at 1.7 keV and of ～20 eV at 5.9 keV could be realized with a prototype detector. Currently this STJ‐based detector system is being incorporated into a prototype cryogenic spectrometer for XRF analysis. Copyright © 2004 John Wiley & Sons, Ltd.     

A TOF-PET prototype with position sensitive PMT readout

A prototype of time-of-flight positron emission computed tomography(TOF-PET)has been developed for acquiring the coincident detection of 511 keV γ-rays produced from positron annihilation.It consists of two 80.5 mm×80.5 mm LYSO scintillator arrays(composed of 35 ×35 pixel finger crystals)with the position sensitive photomultiplier tubes R2487 as the readout.Each array is composed of 2 mm ×2 mm× 15 mm finger crystals and the average pixel pitch is 2.30 mm.The measured results indicate that the TOF information has the potential to significantly enhance the image quality by improving the noise variance in the image reconstruction.The best spatial resolution(FWHM)of the prototype for the pairs of 511 keV γ-rays is 1.98 mm and 2.16 mm in the x and y directions,respectively,which are smaller than the average pixel pitch of 2.30 mm.     

Continuous proton spectra emitted in 3He and deuteron induced reactions

A study of the energy and angular distributions of protons emitted in ³He induced reactions was undertaken at an incident energy of 25.6 MeV. An analysis in the framework of the pre-equilibrium hybrid model did not succeed in explaining the overall behaviour of proton spectra; a contribution due to a break-up or a double stripping of the incident particle has to be taken into account. An attempt was made to account for these processes by performing a phase space calculation. This formulation was firstly tried in the case of deuteron induced reactions for which a break-up mechanism has already been confirmed in continuous proton spectra. The calculation extended to the case of ³He induced reactions showed that a double stripping mechanism could explain the observed distribution.     

300 eV—1GeV质子在硅中非电离能损的计算

非电离能损(NIEL)引起的位移损伤是导致空间辐射环境中新型光电器件失效的主要因素.引起质子在硅中NIEL的作用机理有库仑相互作用和核相互作用,质子能量范围从位移损伤阈能到1 GeV.当质子能量位于低能区时,库仑相互作用占主导地位,采用解析方法和TRIM程序计算NIEL;当质子能量位于高能区时,NIEL主要来自质子与靶原子核的弹性和非弹性相互作用,使用MCNPX/HTAPE3X进行模拟仿真计算由核反应引起的NIEL.实现了能量范围为300 eV—1 GeV的质子入射硅时NIEL的计算.计算结果表明,MCNPX/HTAPE3X可用于计算高能质子在材料中产生的反冲核所引起的NIEL,结合解析方法和TRIM程序可计算得到由于库仑相互作用引起的NIEL.