Table l. Summary of System Efficiency and MDLS for Field WBC System Nuclide Energy 137 Cs 662 KeV 6060 40x Efficiency MDL Time -3 37 Bq (1 nCi) 900 sec «1173 & 1334 Kev «6.7 x 107° 37 Bq (1 nCi) 900 sec 1460 Kev 7.0 x10 222 Bq (6 nCi) 900 sec 8.7 x 10 12 ,