Speaker
Dmitry Ilyin
(St. Petersburg Nucl. Phys. Inst., Gatchina)
Description
Two-dimensional detector of thermal neutrons has been designed and
constructed for neutron diffraction experiments at the St.-Petersburg
Nuclear Physics Institute. Detector is based on MWPC with cathode strip
delay line readout and has sensitive area of 170mm×300mm. In order to
achieve the best physical parameters of detector it was necessary to
optimize an anode signal transmission into cathode strips. For this purpose
some more important geometrical parameters of the MWPC have been
chosen according to the following principal: anode wire spacing, ”anode-
cathode” gap and strip width have to be equal to each other. Anode wire
spacing is 4mm. Detector operates with the gas mixture 1.5Bar 3He + 2Bar
CF 4 and has 1mm space resolution. To improve the gas purity by a few
orders of magnitude a new technology for detector’s electrodes fabrication
successfully developed. The electronic noise limited resolution of
FWHM=0.6mm and differential non-linearity of ±5% are achieved in the
detector. It was shown that detector has space resolution of about 1mm
and efficiency of 60% for 9 ̊A neutrons. Pulse height spectra behavior via
high voltage and electric field tension in the drift regions has been
investigated. It was shown that these spectra are very similar to those
observed from proportional counters that have a gas pressure of 10Bar and
intended for thermal neutron detection. Based on obtained results a new
detector with sensitive area of 300mm×300mm and anode wire spacing of
2mm has already constructed. In order to perform efficiency of 90% and
space resolution about 1mm, the gas pressure is increased up to 5-7Bar.
Author
Dmitry Ilyin
(St. Petersburg Nucl. Phys. Inst., Gatchina)
