The detector in the picture uses a Sodium Iodide crystal for detection, so it doesn’t detect alpha particles and most (lower energy) Betas. Those types compose the majority of radiation emitted by Depleted Uranium. There are also some measurable gamma energies, but the amount emitted is very low.
I would suggest you do a background count for at least 5 minutes well away from the object to establish what the natural occurring radiation levels are before measuring the activity of the object.
Then measure the activity of the object for the same amount of time and finally subtract the background value from that result This will give you a better idea of the “true” activity of the object.
FYI, since DU is 19.1 gm/cm3 a cylinder of such with dimensions of 6.25 in (15.875cm) and a dia of 1.75in (4.445cm) would have a volume of (pii x radius squared x height) or approx 246 cm3.
246 cm3 x 19.1= 4705 gm or 4.7 kg That shape obviously has less mass than a cylinder but it might be in the range for DU.
Just some thoughts.