Abstract
Recently, the Helium-4 gas fast neutron scintillation detectors is being used in time-sensitive measurements, such time-of-flight and multiplicity counting. In this paper, a set of time aligned signals was acquired in a coincidence measurement using the Helium-4 gas detectors and EJ-309 liquid scintillators. The high-speed digitizer system is implanted with a trigger moving average window (MAW) unit combing with its constant fraction discriminator (CFD) feature. It can calculate a “time offset” to the timestamp value to get a higher resolution timestamp (up to 50 ps), which is better than the digitizer's time resolution (4 ns) [1]. The digitized waveforms were saved to the computer hard drive and post processed with digital analysis code to determine the difference of their arrival times. The full-width at half-maximum (FWHM) of the Gaussian fit was used as to examine the resolution. For the cascade decay of Cobalt-60 (1.17 and 1.33 MeV), the first version of the Helium-4 detector with two Hamamatsu R580 photomultipliers (PMT) installed at either end of the cylindrical gas chamber (20 cm in length and 4.4 cm in diameter) has a time resolution which is about 3.139 ns FWHM. With improved knowledge of the timing performance, the Helium-4 scintillation detectors are excellent for neutron energy spectrometry applications requiring high temporal and energy resolutions.
Highlights
Time-of-Flight (TOF) technique is based on a pulsed neutron beam, spanning over a wide range of energies, travels a given distance before reaching the detector under study [2]
For the Helium-4 detector, its low electron density leads to low gamma interaction probability
Gamma rays have a lower light yield longer scintillation collection time in gaseous helium scintillation when compared to liquid scintillators
Summary
Time-of-Flight (TOF) technique is based on a pulsed neutron beam, spanning over a wide range of energies, travels a given distance before reaching the detector under study [2]. With a known distance between the target and the detector, the TOF was converted to determine the incident neutron energy. The outputs of the TOF measurement can be used in many neutron spectrometry applications such as detector light response calibration and mathematical spectrum unfolding [3]. The moderation time in the target-moderator assembly, and the detector response, contribute to the fact that even for neutrons with a given kinetic energy, the measured TOF could have a distribution. Previous studies [3] were mainly focused on the TOF based detector response characterization and the spectrum unfolding algorithm development. It is crucial to characterize the timing performance of the Helium-4 detectors
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