  The Nab experiment will measure the ratio of the weak axial-vector and vector
coupling constants $\lambda=g_A/g_V$ with precision
$\delta\lambda/\lambda\sim3\times10^{-4}$ and search for a Fierz term $b_F$ at
a level $\Delta b_F<10^{-3}$. The Nab detection system uses thick, large area,
segmented silicon detectors to very precisely determine the decay proton's time
of flight and the decay electron's energy in coincidence and reconstruct the
correlation between the antineutrino and electron momenta. Excellent
understanding of systematic effects affecting timing and energy reconstruction
using this detection system are required. To explore these effects, a series of
ex situ studies have been undertaken, including a search for a Fierz term at a
less sensitive level of $\Delta b_F<10^{-2}$ in the beta decay of $^{45}$Ca
using the UCNA spectrometer.
