The 44-99-1 is a 3” diameter cylindrical NaI detector with a 1” thickness.  It is housed in an Aluminum frame and surrounded by 1” of lead.  The aluminum frame and the lead leave a cavity under the crystal that serves as an elongated collimer to allow unscattered radiation to be directionally detected.  It is shielded on the sides by an inch of lead and the aluminum housing.  On the bottom, there is an empty void below the detector and the aluminum housing.  The outer housing closes this off.  This detector can be used “looking” down, or sideways.  See the hand sketch of the detector design and shielding.