Determining spectral response of the National Ignition Facility particle time of flight diagnostic to x rays

Abstract

The Particle Time of Flight (PTOF) diagnostic is a chemical vapor deposition (CVD) diamond detector used for measuring multiple nuclear bang times at the National Ignition Facility (NIF). Due to the non-trivial, polycrystalline structure of these detectors, individual characterization and measurement is required to interrogate the sensitivity and behavior of charge carriers. In this paper, a process is developed for determining the xray sensitivity of PTOF detectors and relating it to intrinsic properties of the detector. We demonstrate that the diamond sample measured has a significant non-homogeneity in its properties, with the sensitivity given by a linear model $ax+b$, where $a=0.60 \pm 0.16 V^{-1}mm^{-1}$ and $b=0.00 \pm 0.04 V^{-1}$. We also use this method to confirm an electron to hole mobility ratio of $1.5 \pm 1.0$ and an effective band gap of $1.8 eV$ rather than the theoretical $5.5eV$, leading to a large sensitivity increase.