Oxygen Monitoring in Xylene NTOF Detectors using Cosmic Ray Muons

At the Laboratory for Laser energetics, liquid xylene scintillators are used to perform neutron time of flight measurements. To improve the timing response of the detector, the xylene scintillator is oxygenated to decrease the decay time of the photo flash in the detector. This results in a faster detector which can be used to observe both primary and down scattered neutrons from an ICF burn. Over time, the oxygen concentration in the scintillator decreases through chemical mechanisms which are not yet well understood. As oxygen levels decrease, the detector response changes. Currently there is no method to determine the oxygen concentration in the sealed xylene detector. Thus, the detectors must be dismounted, emptied, refilled and remounted on the chamber every three months to ensure that it is working nominally. To mitigate this problem, cosmic ray muons are being used to produce signals in the detector. Changes in the muon signals can be used to determine the oxygen concentration level in the scintillator. When completed it is hoped that this method can be used to measure the oxygen level in situ reducing the need to dismount the detector, fill it and remount it.

Funded in part by the United States Department of Energy through the Laboratory for Laser Energetics