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.

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).