Radiation Portal Monitor

Radiation Portal Monitors (RPMs) are passive radiation detection devices used for the screening of individuals, vehicles, cargo or other vectors for detection of illicit sources such as at borders or secure facilities. Fear of terrorist attacks with radiological weapons spurred RPM deployment for cargo scanning since 9/11, particularly in the United States. Radiation Portal Monitors (RPMs) are passive radiation detection devices used for the screening of individuals, vehicles, cargo or other vectors for detection of illicit sources such as at borders or secure facilities. Fear of terrorist attacks with radiological weapons spurred RPM deployment for cargo scanning since 9/11, particularly in the United States. RPMs were originally developed for screening individuals and vehicles at secure facilities such as weapons laboratories. They were deployed at scrap metal facilities to detect radiation sources mixed among scrap that could contaminate a facility and result in a costly clean up. As part of the effort to thwart nuclear smuggling after the breakup of the Soviet Union, RPMs were deployed around that territory, and later around many other European and Asian countries, by the US Department of Energy (DOE) National Nuclear Security Administration (NNSA) Second Line of Defense Program (SLD) starting in the late 1990s. After the attack of 9/11, the US Customs and Border Protection (CBP) started the Radiation Portal Monitor Program (RPMP) to deploy RPMs around all US borders (land, sea and air). Radiation Portal Monitor (RPM) was designed to detect traces of radiation emitted from an object passing through a RPM. Gamma radiation is detected, and in some cases complemented by neutron detection when sensitivity for nuclear material is desired. First generation RPMs often rely on PVT scintillators for gamma counting. They provide limited information on energy of detected photons, and as a result, they were criticized for their inability to distinguish gamma rays originating from nuclear sources from gamma rays originating from a large variety of benign cargo types that naturally emit radioactivity, including cat litter, granite, porcelain, stoneware, banana etc. Those Naturally Occurring Radioactive Materials, called NORMs account for 99% of nuisance alarms.It is worth noting that bananas have erroneously been reported as the source of radiation alarms; they are not. Most produce contains potassium-40, but packing density of fruits and vegetables is too low to produce a significant signal. PVT does have the ability to provide some energy discrimination, which can be exploited to limit nuisance alarms from NORM. In attempt to reduce the high nuisance alarm rates of first generation RPMs, the Advanced Spectroscopic Portal (ASP) program was called into life. Some of the portal monitors evaluated for this purposes are based on NaI(Tl) scintillating crystals. These devices, having better energy resolution than PVT, were supposed to reduce nuisance alarm rates by distinguishing threats from benign sources on the basis of the detected gamma radiation spectra. ASPs based on NaI(Tl) had a cost several times that of first generation RPMs. To date, NaI(Tl) based ASPs have not been able to demonstrate significantly better performance than PVT based RPMs. The ASP program was canceled in 2011 after continued problems, including a high rate of false positives and difficulty maintaining stable operation.