Performance study of a novel sampling TPC prototype detector based on THGEM

Introduction Time projection chamber(TPC)with micropattern gaseous detectors(MPGDs)as readout has been one of the research hotspots in recent years.MPGD-based TPC has been applying to many experiments due to its high spatial and energy resolutions in 3D track measurement.Purpose A novel sampling TPC detector based on thick gaseous electron multiplier(THGEM)was developed to measure the low-energy electron tracks online from 0.1 to 50 MeV with a 100μm spatial resolution in a vacuum tank.The tracks will be extrapolated to determine the hit positions on a target about 200mm behind the TPC.Methods and materials A new type of self-developed THGEM detector was chosen as the TPC readout unit.The field cage has two 50×50mm2 windows welded by Gold-plated tungsten wires for low-energy electrons passing through.The front-end electronics was designed with a self-developed application specific integrated circuit chip,i.e.,CASA-GEM.Seven columns of readout pads were used to equidistantly sample the electron tracks in a length of 75mm.Each column has 72 pads of 0.56×0.56mm2 and two additional strips along each column for drift time measurement.Both Geant4 and Garfield++were chosen to simulate and optimize the detector,such as the penetration efficiency,electric field in field cage and operating gas pressure.Results The design and the preliminary performances of the TPC detector were verified by beam test andβsource test.A drift velocity of 3.415±0.103 cm/μs was measured at 125 V/cm in Ar+iC4H10(97:3)forπ−.The electron detection efficiency is about 88%forβsource.And the gain of the double THGEM reached more than 1.0×10^(4).

Performance study of trial M-THGEM

Background M-THGEM is a new type of electron multiplier,which is developed with a high gain,good stability and uniformity based on THGEM.With the successful application of small area M-THGEM,the large-area M-THGEM is proposed based on large-volume gas detector.Purpose The production of large-area M-THGEM is difficult compared with the small one with more holes and more stable instruments.To meet the requirements of large-area gas detectors,the performances of the large-area M-THGEM need to be measured and researched,which will provide a guidance on the process and design of the M-THGEM.Methods The M-THGEM membrane was loaded into a chamber to complete the test under the conditions of 55Fe/X-ray source(5.9 keV)and working gas Ar∶iC4H10=97∶3.The performance of gain,energy resolution,uniformity and long-term stability can be tested.Results Based on the small area M-THGEM,the research and design of large-area M-THGEM with 200×200 mm^(2)were finished.The basic performances were measured.The results show that the gain with the working gas of Ar∶iC_(4)H_(10)=97∶3 can reach to 6×10^(3),and the energy resolution of the^(55)Fe/X-ray source(5.9 keV)reaches 29.4%with a good gain uniformity and stability.Conclusion At present,the production and measurement of the large-area M-THGEM has been finished.The M-THGEM of 200×200 mm^(2)shows a good performance,which will provide many references for the future design.

Studies of an X-ray imaging detector based on THGEM and CCD camera

Introduction The photons generated by the electron avalanche in gaseous detectors are known as the secondary scintillation light,of which the spectrum range is from ultraviolet to visible.So it is possible to collect directly the avalanche-induced photons in visible range by light sensors,such as charged-couple device(CCD).The optical readout is a new method for 2-D imaging of high spatial resolution based on the micro-pattern gaseous detectors(MPGDs).Purpose The traditional charge readout method for the MPGDs is complicated,expensive,and strongly depends on the technology of application-specific integrated circuit.In some cases,for example,low-frame-rate 2-D imaging,the optical readout has more advantages,such as simple,cheap and easy to use.Therefore,a gaseous detector was developed based on the thick gaseous electron multiplier(THGEM)and the ordinary scientific CCD camera as readout to realize the X-ray imaging instead of charge readout.Methods and materials The THGEMs with 60×60 mm^(2) sensitive area were developed to reach high gain,and the Ar+CF4 gas mixture was chosen for strong light emission.And so a general scientific CCD can be used for readout and replacing the intensified CCD,which is more expensive than general CCD.Results Some clear X-ray images were obtained by this optical readout THGEM detector,and the spatial resolution achieved is 275µm.It is indicated that this kind of detectors have promising imaging capability and great potential for practical application.

A new neutron detector based on ceramic THGEM and boron-coated meshes

Introduction Boron-coated micro-pattern gaseous detectors,such as gaseous electron multiplier(GEM),are widely studied as the neutron detectors.The existing solution to improve the neutron detection efficiency(NDE)is to coat the boron on the surfaces of the cascade GEM films.So the GEM films themselves will be affected by the complicated coating process and the boron layers,and the 10B material will be wasted once the GEM films are damaged.Since the neutron conversion and the electron multiplication regions are not separated,the final gains of different layer ionized electrons are very difficult to control and keep consistent.Materials and methods A new neutron detector based on the ceramic thick GEM(THGEM)was proposed.The boron-coated cathode and multilayer meshes were used as the neutron conversion region and separated from the electron multiplication region consisting of only one THGEM film.The sawtooth surface treatment and the double-sided readout method were applied to improve neutron conversion efficiency(NCE).The neutron conversion and the electron collection efficiencies were simulated and studied based on the new structure.The prototype detector was test by using a ^(252)Cf neutron source.Results The simulation results show that the cascade boron-coated meshes have good neutron conversion and electron collection efficiencies,and the double-sided readout and sawtooth structure can greatly increase the NCE.The neutron test results show that the detection efficiency of the double-sided readout is 1.6 times higher than that of the common single-sided readout.These indicate that the new detector has high neutron conversion and detection efficiencies and is promising for practical applications.

Development and study of an imaging detector based on high-position resolution THGEM

Introduction THickGaseous Electron Multiplier(THGEM)has many advantages while the moderate position resolution is regarded as the main inferiority comparing with the traditional GEM,so this limits the applications of THGEM,such as X-ray imaging and charge particle tracking.Materials and methods By improving the production techniques,THGEMs with smaller pitch and hole diameter can be made,i.e.,0.4 and 0.15 mm by mechanical drilling,and 0.3 and 0.1 mm by laser etching,respectively.Based on the new THGEMs,a two-dimensional imaging detector with 50×50mm sensitive area was developed for 0.1∼50 MeVlow-energy electrons detection and reaching better than 100μm position resolution(sigma).At the same time,a set of front-end electronics was developed based on homemade ASIC chips,i.e.,Charge Amplifier and Shaping Amplifier for GEM(CASAGEM),and applied successfully to the detector.Conclusion The X-ray and beam tests results indicate that both detector and Front End Electronics(FEE)worked well,and the position resolution achieved 74.9μm by using the charge center-of-gravity method.This indicates that the high-position resolution THGEM is promising for imaging and tracking application.

A scintillator detector for beam tuning of low-energy single electron accelerator

Purpose Nine scintillator detectors were developed for beam tuning of low-energy single electron accelerator instead of the picoammeter and Faraday cup,both of which will be insensitive to the weak-current beam lower than picoampere.Methods The detectors are based on plastic scintillator and photomultiplier tube(PMT)and the beam is 100 Hz pulsed electrons in the energy range of 0.1 to 50MeV.The beam flux was tuned from about 107 to quasi-single electron for each bunch according to the measurement results of these detectors installed along the beam pipe and after slits.In order to determine the number of electrons in a bunch,the gains of each PMT were finely calibrated,and the energy response of each detector was calibrated with 207Bi radioactive source.Moreover,the deposited energy in the plastic scintillator,the electron detection efficiency and light collection efficiency,as a function of electron incident energy,were also simulated in detail by Geant4.Results Nine detectors worked well at a gain of 0.6×10^(6) after installation in the beam pipe,and the number of electrons in a bunch could be measured at each detector position.The single electron peak was seen when the beam reached the final detector.Conclusion The commissioning result shows that the beam was tuned to quasi-single electron level successfully and the scintillator detector is an effective method to measure the weak-current beam lower than picoampere.

Precise measurement of attenuation length of the JUNO liquid scintillator

Introduction The Jiangmen Underground Neutrino Observatory has critical requirements on quality of the liquid scintillator,one of which is long attenuation length.Purpose A system with a height of 3 m is used to precisely measure the attenuation length of the liquid scintillators.Methods The light generated by a LED is transmitted through an optical fiber.After being focused,filtered and collimated,the light enters the test tube with the liquid scintillator and is detected by the PMT.The stepping motor is controlled by the Labview program to adjust the level of the liquid scintillator,and the emitted light intensity of different liquid levels can be obtained to fit the attenuation length.In addition,the systematic errors have been studied,which includes the measurement error of the emitted light intensity and the error caused by the movement of light spot,and the latter is responded to the non-uniformity of the PMT photocathode.Meanwhile,analytical methods were improved.Results The system can measure the attenuation length stably and a small error was obtained,including statistical error and systematic error(0.69-23.70 m).