... radioisotopes3. Short spacing: 200mm, Long spacing: 350mm 4. Glimmers body: Nal(T1), 23×40mm 5. Photomultiplier Tube: GDB23 6. Counting range ... -spaced natural gamma probes are all be used2. Scintillating material: Nal(T1), 23×60m3. Photomultiplier Tube: GDB234. Count range: 0 to ...