Packing Skills: Matching Detection Capabilities with National Nuclear Security Priorities
Backpack-type radiation detectors (BRDs) are important tools used to detect nuclear and other radioactive material out of regulatory control. They are portable instruments designed to be worn during use and can be placed as stand-alone radiation monitors.
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The backpack design means that BRDs have comparatively larger detectors than other portable devices. This enables their effective use in a wide range of applications, including to scan people, goods, and vehicles, to conduct background radiation surveys or radiation source searches and to monitor crowds for nuclear security at major public events; and complements various nuclear and radiation safety applications.
There are dozens of different makes and models of BRDs manufactured, each outfitted with specific features and designed for specific objectives.
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To enhance the understanding of BRD detection capabilities and to help countries determine which type of BRD best addresses their needs, the IAEA facilitates exchanges of information. During such exchanges, participants share best practices on the use and development of test methods for evaluating detector performance. The technical exchanges build expert capacity within countries to enable national experts to train others.
Effective testing of radiation detection equipment is key in ensuring that equipment functions well in its desired environment and is suitable for the identified task. Testing is necessary to compare the actual performance of a BRD against requirements, to determine the range of applications that a BRD can be used in, and to develop operational guidelines that are required to optimize the performance of BRD use.
While international standards contain specifications relevant to BRDs, there is a wide range in the capabilities and user-interfaces provided by the many different manufacturers. Testing different detector configurations in a variety of environmental and operational settings provides important information about device performance; and assists in their effective deployment and use.
Depending on the planned use of a BRD and the user organization’s capabilities, the following features should be considered as BRD requirements:
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a. Gamma detection sensitivity
b. Neutron detection capability and sensitivity
c. Radionuclide identification capability
d. Weight and size
e. Tolerance of harsh environmental conditions
f. Integration with existing and future systems, and
g. Cost.
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Testing in different operational settings helps identify the best uses for different BRDs. For example, searches for radiation sources in controlled outdoor settings at IAEA facilities enabled national experts to evaluate usability and performance of BRDs by positioning gamma and neutron sources in various locations.
To determine performance of BRDs in an outdoor source search, testers proceeded systematically by moving BRDs at a consistent speed across the search area to assess and compare each system. Ideally, the same user will test multiple devices to avoid differences in the user's height, stride length, and pace, as these factors can impact how a device performs. Testers then used maps, like this one, to chart where the sources were detected.
BRDs can also prove useful in internal environments, for example, a storage facility or warehouse. By carrying out a systemic search of the facility, the test can evaluate whether a BRD would wrongly categorize fertilizer as Naturally-Occurring Radioactive Materials (NORM) material.
Some BRDs are more effective for detecting stationary sources. Stationary sources may be a lost or misplaced radioactive source or a radiation exposure device, which could be an ordinary-looking object containing radioactive material to intentionally expose people to ionizing radiation without their knowledge. Static sensitivity tests help determine the ability of BRDs to detect radiation sources or hotspots when the source is in a fixed position and enable it to identify what caused the radiation alarm to go off. A BRD’s angular sensitivity could affect the accuracy of gamma radiation dosimetry detection. When BRDs are used for radiological mapping, the results can be impacted by the changing orientation of the BRD in relation to a radiation source. Each turn made by the BRD user can cause a change in sensitivity if the BRD system is directionally dependent. Knowing how to conduct angular testing is important to determine the BRD’s angular sensitivity. This knowledge can play an important role in mapping reference radiation areas used to calibrate or verify other in-situ systems, such as mobile or airborne gamma spectrometers.
Experts take static sensitivity measurements of the BRD response to radiation sources placed at different angles and distances with respect to the BRD. The number and arrangement of detectors in the backpack, volume of the detectors, total size of the backpack, and the wearing position on the body are all factors that may affect the angular sensitivity of the BRD. Experts measure all these factors and use well-planned test protocols to provide statistically sound results.
Some BRDs are designed to detect radiation sources that could be located not only in front of the user but also to the side of the user. To obtain this side-detection capability, some BRDs may use two detectors instead of one. A different design, as well as other components such as electronics, batteries, and switches, all affect the resulting detection geometry and overall angular sensitivity of the BRD.
In contrast to the static sensitivity tests, a dynamic alarm response test evaluates each BRD's ability to alarm when a source is moving by the BRD at various distances and various speeds. In most BRD deployment scenarios, the BRD will be used in a situation where either the radiation source, the BRD, or in some cases both, are moving. BRDs are often used to scan moving individuals, vehicles, and items. Understanding the sensitivity of the BRD at different distances under a dynamic situation is extremely important.
The dynamic alarm response test replicates the scenario when a BRD, a radiation source, or both are moving, to assess the BRD’s sensitivity and time required to produce an alarm. Testing the sensitivity of the BRD under dynamic situations requires setting up the BRD at exact distances from a track, like shown in the previous photo. A radiation source is mounted on a remotely controlled sled on the track and then travels along the track at controlled speeds. Numerous measurements at each distance/speed combination are made to determine the sensitivity of the BRD.
By testing a variety of radiation detection equipment in field conditions, practitioners identify the exact technological specifications they need to achieve their national nuclear security goals and avoid costly spending and trial-error experimentation.
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BRDs complement other nuclear security systems and measures and help countries prevent, detect and respond to the threat of malicious use of nuclear or other radioactive material. Having the 'right' equipment, based on a country’s specific priorities and threat assessment, is crucial for the effectiveness of national nuclear security regimes.
