A Fast Pixelated Thermal-Neutron Detector

This thesis presents the study of a position-sensitive scintillation-based detector called the Solid-State Neutron Detector (SoNDe). SoNDe is being developed for cold- and thermal-neutron detection at the small-angle neutron scattering (SANS) instrument SKADI at the European Spallation Source (ESS), currently under construction in Lund, Sweden. The response of the detector scintillator, multi-anode photomultiplier (MAPMT), and readout electronics has been investigated using particles relevant in the ⁶Li(n,³H)α reaction that is at the heart of the detection principle of SoNDe. Scintillation light was read out by the 8×8 pixel H12700A MAPMT. The pixel signal is strongly dependent on position and in general several pixels will register a signal (a hit) above a given threshold. To optimize planned detector operation at ESS, the number of pixels above set thresholds was investigated, with the maximization of the single-hit efficiency over the largest possible area as the primary goal. Paper I describes introductory tests validating the detector concept using signal generators and neutrons read out using the SoNDe electronics. Paper II is the first of three systematic irradiation studies and is performed with a broad α-particle beam from a radioactive source using a VME-based data-acquisition system. Scans of highly focused beams of protons and deuterons from a Pelletron across the detector are presented in Paper III. Scans of a collimated thermal-neutron beam from a reactor read out using the SoNDe readout electronics is presented in Paper IV. A simulation model developed using Geant4 and tuned with the measurements reported in Papers I-IV is described in detail in Paper V. For all of the beams employed in this thesis, the optimal threshold for single-hit efficiency was found at a value of ~50% of the mean of the full-deposition peak. Of the detected particles, ~80% were registered in a single pixel. Lower thresholds resulted in higher pixel multiplicities. These events could be localized with better than 5 mm position resolution and could potentially facilitate operation of the detector in a higher multiplicity mode while still fulfilling the 6 mm neutron position-reconstruction accuracy requirement set by the SANS program to be performed at the SKADI instrument.