The structure of micromegas (micro-mesh gaseous structure) detectors with different micro-meshes of stainless steel wire woven netting and Ni foil has been presented. The counting rates, energy resolution, gain, discharge probability and time resolution have been measured. Wider counter plateaus and gain for the developed detector were obtained. Excellent energy resolution of the micromegas detector, 17% (FWHM) based on Ni foil micro-mesh and 25% (FWHM) based on stainless steel wire woven netting micro-mesh, has been obtained for the 5.9 keV photon peak of the 55Fe X-ray source in an Ar/CO2(10%) gas mixture. The best time resolution at -620 V micro-mesh voltage and -870 V drift voltage is 14.8 ns for cosmic rays in an Ar/CO2 (10%) gas mixture. These results satisfy the basic demand of the micromegas detector preliminary design.
This paper studies the possibility of using the scattering of cosmic muons to identify threatening high-Z materials.Various scenarios of threat material detection are simulated with the Geant4 toolkit.PoCA(Point of Closest Approach) algorithm reconstructing muon track gives 3D radiography images of the target material.Z-discrimination capability,effects of the placement of high-Z materials,shielding materials inside the cargo,and spatial resolution of position sensitive detector for muon radiography are carefully studied.Our results show that a detector position resolution of 50 μm is good enough for shielded materials detection.
In this paper Micromegas has been designed to detect neutrons. The simulation of the spatial reso-lution of Micromegas as neutron detector is carried out by GEANT4 toolkit. The neutron track reconstruction method based on the time coincidence technology is employed in the present work. The influence of the flux of incident 14 MeV neutron and high gamma background on the spatial resolution is carefully studied. Our results show that the spatial resolution of the detector is sensitive to the neutron flux, but insensitive to the intensity of γ background if the neutron track reconstruction method proposed by our group is used. The γ insensitivity makes it possible for us to use the Micromegas detector under condition which has high γ-rays background.
At Jefferson Laboratory the experiment E02-017 was carried out to investigate the fission associated with kaons in the hypernuclei-producing interaction p(e,K+e)Λ.The newly installed high resolution kaon spectrometer(HKS) in Hall C was used as a key instrument to identify kaons.This paper introduces the HKS hardware and describes the way the kaons are identified.Maintaining most of the kaons(nearly 100%) in the data,HKS identifies kaons with a purity of ～67% in this experiment.The resolution of the kaon target time reconstructed by HKS reaches 0.42 ns.
In this paper a two dimensional readout micromegas detector with a polyethylene foil as converter was simulated on GEANT4 toolkit and GARFIELD for fast neutron detection. A new track reconstruction method based on time coincidence technology was developed in the simulation to obtain the incident neutron position. The results showed that with this reconstruction method higher spatial resolution was achieved.
Two couples of low pressure multi-wire proportional chambers (MWPC) were located in the target chamber to detect fission fragments in a hypernuclei producing experiment at Thomas Jefferson National Laboratory (Jlab).In the experiment,a continuous wave (CW) electron beam was applied to form hypernuclei by electromagnetic interaction.In the target chamber,the high energy (1.853 GeV) and high intensity (500 nA) primary electron beam caused a high particle background,which influenced the detection of the fission fragments.This report described the design of the MWPCs and studied the fission-fragment detecting performance of them under such a high background.The efficiency of the MWPCs was given with the help of a high resolution kaon spectrometer.At the same time,the background particles were discussed with a Monte Carlo code based on GEANT4.
