Optimization of CFD Parameters to Minimize Jitter Using Floating-Point Constant Fraction Delay

The precision of neutron time-of-flight measurements is dependent upon the precision of the time of arrival assigned to each detection event. Using an EJ-309 liquid scintillator and a Cs137 source, a time of flight distribution was collected with a high-speed digitizer, and the data were analyzed to evaluate alternative implementations of a digital constant fraction discriminator (CFD) for event time assignment. We searched for the optimum combination of pulse height fraction and delay by evaluating the full width half maxima of the pulses and aligning the pulses. In order to minimize the jitter in the assigned time, we used floating-point arithmetic for the constant fraction delay. The jitter observed using floating-point arithmetic was compared to that of constant fraction timing using whole number time steps versus both pulse height and for all pulse heights.