Experimental Investigation of the Use of Solid State Detectors in Radiation Portal Monitors
R.M. Garcia1; F. Stong2; and R. Graff2 (1Tetra Tech EC, Inc.; 2SCM Consultants, Inc.)
Tetra Tech recently completed a feasibility study to determine the effectiveness of replacing photomultiplier tube (PMT) detectors in scintillator-based radiation portal monitors with solid-state devices. Laboratory scale tests were conducted using exempt test sources and a pulsed light emitting diode (LED) to excite scintillators attached to avalanche photodiodes (APDs), charge-coupled devices (CCDs) and PMTs. A modular test rig was constructed that allowed for the detectors to be interchanged as needed and the light/radiation sources to be introduced in a controlled and regular manner. The baseline detector for the test program is the Hamamatsu R580 PMT currently in use in production model portal monitors. Solid state devices tested included the Hamamatsu S8664-55, Advanced Photonix 10 mm and Advanced Photonix 16mm APDs as well as the Kodak KAI 1020D, Kodak KAF 1402ME and Kodak KAI 0340DM CCDs. The APDs and PMTs were tested with both poly-vinyl toluene (PVT) and NaI(Tl) scintillators, while CCDs were tested only with PVT scintillators. Testing with the LED resulted in high light levels within the scintillators that were detectable by each of the detectors in the various testing configurations, thus validating the experimental setup. On the contrary, when the barium, cesium and cobalt check sources were employed, the majority of the solid-state devices did not receive sufficient light levels to produce a detectable signal. The largest APD tested, did provide meaningful results however it is fragile and has other operating costs and concerns that are not competitive with those of the standard PMT. It is thus concluded that solid-state devices are not a viable replacement for PMT detectors in portal monitor type applications.