A Fast-Neutron Imaging(FNI) detector based on the Mini-Micromegas TPC(Time Projection Chamber) was proposed and is being developed by Saclay CEA/Irfu and Lanzhou University. Its layout is shown in Fig.1 and Fig.2. In this design, the bulk Micromegas technique will be used to read out a mini-TPC with a 20mm drift length. In order to detect fast neutrons, a converter is needed. Currently, the drift cathode will be coated with a 40 microns polyethylene foil. Fast neutron will knock protons out of this Hydrogen-rich material through the process of elastic scattering. The recoiling protons will then pass through the TPC and leave tracks in it. By detecting and reconstructing the proton tracks, the incidence point of neutrons in the polyethlene foil can be obtained by extrapolation.
Fig.1. Crossection of FNI Detector.
The routing of the readout PCB is shown in the Fig.3 in details. The dimensions of its sensitive area (green area) and the readout PCB are 57.4mm X 88.6mm and 365.5mm X 306.0mm, respectively. The sensitive part is composed of 1,728 rectangular pads, 36 pads in the x direction and 48 pads in the y direction. The dimention of each pad is 1.50mm X 1.75mm, and the distance between them is 0.1mm in both directions. All pads will be read out by the AFTER based electronics which is first designed for T2K experiment. The electronics can provide 511 samples at a tunable frequency between 1 and 100MHz for the output signal of each channel. Also, the peaking time of the shaper in the chip can be adjusted between 100ns and 2 micro-second. All of these properties make it suitable for reading out the Micromegas TPC.
Fig.2. 3D views of FNI Detector.
Fig.3 Readout PCB of FNI detector. ....Coming soon....