Research And Development Of Neutron Block Detector

Associated Particle Imaging（API）technology is an active fast neutron probe technique that provides a 3-D image of interrogated material.The fast neutrons used are produced by the reaction of T（D,n）4He.The time and space correlation between the alpha particle and fast neutron in the reaction makes the API system easily reject the induced gamma background and the scattering neutrons,which is beneficial for obtaining a better signal-to-noise ratio for detecting special nuclear materials（SNM）,explosives,drugs,and biological weapons in 3D,making it become one of the effective anti-terrorism methods.The API system developed by our team mainly consists of four main components:an associated particle neutron generator,an associated alpha particle detector,a 4×8 array of neutron block detectors,and a rotating platform for 3D scanning samples to be tested.The current work focuses on the development of 32 neutron block detectors with a sensitive volume of 100×100×50mm³ for the said API system.Each neutron detector sensitive unit is composed of 10×10 EJ200 plastic scintillators with a volume of 10.3×10.3×50mm³,and the ESR total reflection film is used between pixels to prevent scintillation light cross talk and improve the light collection efficiency.Each pixelated neutron block detector is coupled pixel by pixel to a 10×10 array of Sensl 6×6 mm2 silicon photomultipliers（SiPM）that are read out with an Anger logic electronics.The research work includes the design,manufacturing and performance testing of the said neutron block detector above:Ⅰ)for the design of the neutron block detectors,please refer the detailed information decribed above;Ⅱ)Detector manufacturing:1)Cutting a large sheet of EJ200 plastic scintillator into 32 plastic scintillator modules with a volume of 115×115×50mm³ with a bench saw;2)Fine cutting each module into 10 smaller pieces with a volume of 115×10.15×50mm³ with a diamond wire cutting machine;3)Grinding and polishing the 320 smaller pieces of plastic scintillators down to the volume of 115×10×50mm³ each;4)Bonding the ESR total reflection film on the polished surface of 320 plastic scintillators with UV-curing adhesives and consolidating it with UV light,and then further bonding every 10 pieces of smaller plastic scintillators together with epoxy resin to form a module volume of 115×100×50mm³;5)Cutting the combined 32 plastic scintillator modules along the direction perpendicular to the first cutting direction with the same diamond wire cutting machine,then repeating the steps of grinding,polishing and bonding the ESR reflective film,and finally obtaining 32 neutron block detectors;Ⅲ)Designing and manufacturing the mechanical frame the neutron block detectors,in which the aluminum alloy frame is formatted into 4 rows and 8 columns and forms an arc related to the neutron emission position with an radius of 1.2m;Ⅳ)Characterizing the spatial resolution of a neutron block detector experimentally with a ²²Na source and CAEN-5730 digitizer,the best achievable spatial resolution is 10 mm.This experiment uses ²²Na source instead of neutron measurement.The experimental design of time resolution is carried out by using the detector composed of Hamamatsu R9420 photomultiplier with EJ200 plastic scintillator and the neutron block detector.