Commissioning of thermal neutron detector boxes for the time-of-flight spectrometer TOPAS

• Main Authors: Kemmerling, G., Boucher, M., Bussmann, K., Engels, R., Kammerling, H., Lesmeister, W., Mckinny, K., Pistel, S., Vehres, G., Voigt, J., Voss, J.
• Format: Conference Proceeding
• Language: English
• Subjects: Bars; Detectors; Electron tubes; Germanium; Maintenance engineering; Neutrons; Wires
• ISSN: 2577-0829
• DOI: 10.1109/NSSMIC.2018.8824602

The thermal neutron time-of-flight spectrometer TOPAS will be equipped with a large detector system based on 2 meter long position sensitive 3 He-tubes, each having an internal pressure of 10 bar 3 He. In total there are 288 tubes with an overall active area of 14.7 m 2 . In order to decouple the detector from the vacuum chamber as well as to facilitate assembly and maintenance, the 3 He-tubes are grouped on modular detector boxes. 16 tubes are mounted per detector box, which houses the digitizing readout electronics in a vacuum tight compartment at the back. During commisioning of the detector boxes, special emphasis has been put on the straightness of the tubes, as the planarity and parallelism of the their mounting points must ensure a straightness of below 1.2 mm. Additionally, the homogeneity of the signal amplitudes for neutron events has also been inspected, as the tube manufacturer pointed us to deficiencies of the wire quality at the time of the tube production. Measurements for the 3 He-tube and detector box acceptance have been carried out with a moderated 252 Cf-source. The signal amplitudes and event positions have been simultaneously taken and studied for the selection and adjustment of the tubes, which is reported in this paper.