  The SiPM-based Compton Telescope for Safety and Security (SCoTSS) has been
developed with inorganic crystalline scintillator material for gamma detection.
The instrument is sensitive enough to be used in a mobile survey mode,
accumulating energy deposited in any crystal second-by-second and tagging these
spectra with GPS position. The SCoTSS imager of course has the additional
advantage of being able to produce an image of the radioactive objects in its
field of view using events that satisfy a coincidence trigger between the
scatter and absorber layers. The Advanced Radiation Detector for UAV Operations
(ARDUO) on the other hand, is a non-imaging directional detector intended for
use aboard a small unmanned aerial vehicle (UAV). The ARDUO detector features
exactly the same volume of CsI(Tl) as is used in the absorber layer of a single
SCoTSS module, giving it similar detection and alarming sensitivity, and
map-making capability. However, in the ARDUO detector, the crystals are
arranged closely together to optimize direction determination from
self-shielding effects. Flown in a grid pattern with a UAV over an area of
extended contamination, the ARDUO detector is also capable of making a map or
image of that area. With its close-packed crystal arrangement, the ARDUO
detector makes a poor Compton imager but does have some ability to produce a
peripheral image in a fly-by. In this presentation we investigate the relative
merits of Compton imaging versus mobile directional detection.
