Determining Scintillator Nonlinearity using the Wide Angle Compton Coincidence Technique

At some level, scintillator materials have an energy response that can be nonlinear. The Wide Angle Compton Coincidence (WACC) technique provides some advantages to finding the nonlinearity of a detector by using Compton scattering from this detector into another detector known to be linear, in this case a High Purity Germanium (HPGe) detector. The detectors are in a close geometry and so the Compton scattering that happens in the tested detector over many angles gives an energy response over a range of energies. From the known gamma ray energy and the HPGe photon energy detected, the analysis of a 2D histogram of the scattering detector response vs. the HPGe response provides a means of measuring the scattering detector's nonlinearity. I will describe our implementation of the WACC technique to measure the nonlinearity of scintillators used for a precision measurement of the $^{20}$F beta spectrum shape as a search for physics beyond the standard model.