The backpack features:

• High sensitivity plastic detector for locating radioactive sources
• Natural Background Rejection  (NBR) indicates artificial sources
• Automatic adjustment to background variations
• No false alarms on NORM and natural background changes
• High neutron detection sensitivity
• Several similar systems have been in use for years by various security agencies
• Can be tied into the ViewPoint Enterprise platform, allowing for a  customizable remote monitoring solution which will provide real-time command and control data

NBR = Natural Background Rejection

The NBR measurement method has been developed by Thermo for extremely fast discrimination between natural and artificial gamma radiation. Worldwide, more than 1000 devices based on this technology are in use. With NBR’s rapid response time, artificial gamma radiation sources are identified in seconds by operators with basic training levels.

Unlike conventional spectroscopic-based gamma identification systems, the systems using NBR do not require the presence and resolution of gamma spectral lines. Because of this flexibility, NBR can also definitively distinguish artificial high energy beta sources and heavily shielded gamma ray sources from fluctuating natural background sources.

NBR has a rapid response time. Artificial gamma radiation sources are identified in seconds by operators with basic training levels. Presence of artificial gamma radiation is simply indicated by a red flashing light and an audible alarm. In addition to the detection of artificial gamma radiation (percentage alarm) a sigma-based net count rate gamma alarm is active as well. Within a preset count rate range this alarm level is constantly and automatically updated according to the present background level.

The detection of neutron sources is performed with the help of 2 ea. He-3 tubes (2.5 bar, 770 ccm active volume ea.). The sliding evaluation window with 100 ms update cycles allows the setting of a very low net alarm threshold level. A neutron source with an activity of 20,000 n/s can typically be detected in a distance of 3 m (10 ft), i.e. the neutron detection limit corresponds to the requirement for installed gate monitors.

Discrimination between artificial and natural radiation

In case of absence of detectable artificial gamma radiation, the green "nat" LED (E) is flashing slowly. The red "art" LED (D) light is blinking once artificial radiation is present. The presence of artificial radiation always triggers an alarm.

Excess of high energy radiation

If both LED indicator lights are on, the presence of an excess of high energy gamma radiation is indicated. Such an unusual background energy distribution results in a slightly reduced NBR-sensitivity to SNM or shielded industrial sources, and can be caused by large amounts of K-40, an AmBe source or N-16 radiation

Alarm indication

Once an alarm had been triggered, the location of the source can be traced by using the acoustical and/or LED bar indication. For stealth operation or in a noisy environment a standard ear-phone can be used. Optionally, a remote indication via wireless vibrator modules can be achieved.