  Imaging devices made from an ionization target layer of amorphous selenium
(aSe) coupled to a silicon complementary metal-oxide-semiconductor (CMOS)
active pixel array for charge readout are a promising technology for neutrino
physics. The high spatial resolution in a solid-state target provides
unparalleled rejection of backgrounds from natural radioactivity in the search
for neutrinoless $\beta\beta$ decay and for electron neutrino ($\nu_e$)
spectroscopy with $^{82}$Se. In this white paper, we summarize the broad
scientific program of a large imaging detector with a 10-ton target of
$^{82}$Se. We review the detector technology, and outline the ongoing research
program to realize this experiment.
