Neutron detector for fusion burn history measurements

We have designed a fast, sensitive neutron detector for recording the fusion history of inertial confinement fusion experiments. With a response time of < 40 ps, it was for burn history measurements for deuterium/tritium-filled targets producing as few as similar 108 neutrons/shot. The detector is based on the fast rise-time (< 20 ps) of BC422 plastic scintillator which, shaped in thin cylinder sheet or curved (in a geometry compensating way) plate, acts as a neutron-to-light converter in a Pb shielding. The Pb shielding shields the scintillator from target x-ray, scattered light and target debris and allows the scintillator to be positioned within 3 cm from the target. The scintillator emits light with wavelengths from 350 to 450 nm. A group of achromatic lens relays the scintillator image along a 1 m optical path to the S20 photocathode of a streak camera outside the chamber. Lens coupling was chosen to give acceptable temporal dispersion. In the design phase, a computer code was programmed to calculate and improve the physical parameters of the optical system, such as light collection efficiency, time dispersion, image position, intensity distribution on the image plane, etc. Some of these parameters were finally measured using a deuterium lamp and a piece of BC422 scintillator activated by x-ray or 0.35 μm laser pulse. The measured results agree well with the prediction of the computer code.