Development of a Particle Time-of-Flight Detector for the iSNAP Experiment using the MTW Laser at LLE*

The in-Situ counting of instantaneous Nuclear Activation Products (iSNAP) experiment was conducted using the Multi-Terawatt Laser (MTW) at the Laboratory for Laser Energetics (LLE) to determine reaction cross sections. MTW uses Target Normal Sheath Acceleration (TNSA) to generate a short intense pulse of deuterons with energies up to 10 MeV. These deuterons activated a ⁷Li target whose short half-life activation products were counted in situ using the Short-Lived Isotope Counting System, SLICS. A particle Time-of-Flight (pToF) detector is needed to determine the energy spectrum of the deuterons at the time the ⁷Li target is activated. The pToF system consists of an EJ-212 plastic scintillator that was fashioned in a wedge shape to sample deuterons from a 1/16th portion of the surface of the ⁷Li target which was mounted on the face of the SLICS.  The wedge-shaped scintillator sampled the spatial variations of the TNSA produced deuterons. Due to the noisy experimental environment, light produced by the scintillator was guided by a fiber optic out of the MTW chamber to a PMT 40 meters away. To ensure the PMT only detected scintillation produced by deuterons, the scintillator was coated with metal and the fiber optic was shielded with a stainless-steel jacket. This blocked residual laser light while enhancing collection of scintillation.  The fiber terminated at a PMT which produced a pToF voltage sweep on a high-speed oscilloscope. The deconvolution of the pToF sweep generated the deuteron energy spectrum and the total number of deuterons which struck the target.  Using this information, the ⁷Li(d,p)⁸Li reaction cross section can be determined.