The Design, Construction And Performance Test Of The Barium Fluoride Detector

A 4Ï€total absorption barium fluoride detector is designed and built amply by the CIAE(the Chinese Institute of Atomic Energy) for accurate measurement of neutron capture cross sections in the keV energy range. This detector combines about high efficiency for gamma rays with good energy and time resolution. And for it has a time resolution of about 600ps, the energy of the captured neutrons is to be measured by their TOF(time-of-flight). All the features together make the capture cross section ratio of two isotopes can be determined with high accuracy.The 4Ï€barium fluoride detector consists of 42 crystals composed by 12 pentagonal and 30 hexagonal truncated pyramids forming a spherical shell with 10cm inner radius and 15cm thickness. Each crystal is wrapped with reflector and coupled with photomultiplier through silicone oil, thus representing as independent gamma-ray detectors. All segments cover the same solid angle with respect to a gamma-ray source located in the centre.This thesis describes the detailed course of how to design and construct a signal barium fluoride detector, including the choice of the crystal material, the packing method of reflectors , the assembly and test of signal detector module. We tested all 40 detectors' energy resolution and checked the long-term stability of the energy resolution. We also tested the time resolution and detection efficiency of signal barium fluoride detector.The test shows that the choice of the reflectors method has a great effect to the energy resolution. After determined the reflectors' conditions, the signal detector has a energy resolution of about 14% at 662keV for gamma-ray and time resolution around 670ps. We found that after 4 or 5 months, energy resolution of most detectors went bad. We took out 5 detectors for test, after changing these crystals' handling to burnishing instead of polishing, the energy resolution stability of most detectors improved a lot. Such experiments will be kept on in the future.