Testing of a portal monitor to detect illicit trafficking of anthropogenic radioactivity in operational field use

Measurements were conducted at a cargo container checkpoint of the German Customs Office at the Hamburg Harbour. At this checkpoint a radiation portal monitor (RTM 910 of MIRION Technologies) has previously been installed. The RTM 910 is capable of neutron and gamma detection with a low energy-resolution. To detect the gamma radiation plastic scintillators are used. In this field experiment 30 to 40 cargo containers were controlled per hour. In this time approximately three alarms per hour were given. To examine what kind of radionuclides caused these alarms, it was necessary to analyse spectra of the radiation when such an alarm occured. For the identification of the radioactive substances two other gamma detectors were used in addition to the RTM 910. One detector was a high purity germanium detector with an energy resolution of better than 2 keV. The other detector is based on sodium iodide and has an energy resolution of about 10 keV. Both were used to take spectra exactly at the time an alarm was given by the RTM 910 and to identify the alarm causing radionuclides by analysing spectra with two different programmes. All the detected radionuclides ar naturally occuring. In addition measurements with the germanium detector were conducted in order to estimate radionuclides which cause the background.