Radiation detection: the current state of the art

For several decades, much of the emphasis within CBRN detection has been most about chemical warfare detection, with occasional blips in biological detection. Radiation detection often gets treated at best as a settled issue and solved problem. After all, we have been able to detect, measure, and identify radiation rather a lot easier than we can do the same for chemicals and biological materials. At worst, radiation detection is considered a backwater in military affairs, with nuclear threats being relegated to the distant past of the Cold War.

The military radiation detection market has moved slowly in recent decades, and has done so on the back of broader developments in customs, border protection, and general antiterrorism measures. The last great emergence of perceived radiological threats that affected the radiation detection market was the collapse of the Soviet Union and the feared (and in retrospect largely non-existent) flooding of the world’s commercial and transportation channels with Soviet-origin radioactive materials. A general boost to antiterrorism spending after 9/11 floated the radiation detection market a bit as well.

Some militaries have now re-discovered the ‘RN’ in CBRN, though. This phenomenon is not so much the emergence of a new threat environment, but a rediscovery that old threats are not going away. Not to put too fine a point on it, but the war in Ukraine involves a combatant (Russia) that still fields tactical nuclear weapons for battlefield use. Furthermore, this conflict occurs upon terrain that includes both older and newer nuclear power plants as well as significant land areas contaminated by the 1986 Chernobyl nuclear accident.

Various nations have let radiological capabilities atrophy somewhat, while others, such as Poland, kept their eye more firmly on the ball. For example, Poland has wanted neutron detection in main battle tanks (MBTs) at a point when others scratched their heads and wondered why. For the curious, small battlefield nuclear weapons create rather more mayhem with neutrons, as a proportion of their harm, than larger ones. Due to the current threat environment, it is worth dusting off the topic and reviewing where these technologies are and what products are available.

Back to basics

Readers of this magazine can probably be forgiven for not paying close attention to radiation detection technology or how it works. A bit of a primer is probably needed, and this correspondent is happy to oblige, and apologises in advance for a few simplifications. This whole particular area is concerned about ‘ionising radiation’ as opposed to ‘non-ionising radiation’. Both are all around us every day, but non-ionising radiation includes such examples as radio waves that carry audio, video, and data signals, microwaves that cook for us or provide radar imaging, and light such as visible, Ultraviolet (UV), and Infrared (IR). As anyone who has had a sunburn can attest, non-ionising radiation can damage us, however, ionising radiation is what we are referring to in military and security circles.

As its name suggests, ionising radiation imparts an electrical charge and ionises matter. This is biologically damaging in ways that are more serious than non-ionising radiation. Broadly speaking, ionising radiation comes from fission, fusion, the decay of radioactive isotopes of matter, and a few other sources such as x-ray machines. We are bathed in cosmic ionising radiation that largely comes from the fusion of hydrogen that fuels the sun. We also have a fair bit of radiation coming at us from the earth itself, from naturally occurring radioactive materials in trace quantities in various minerals.

Ionising radiation can be in the form of alpha particles, beta particles, gamma rays, and x-rays. As the name implies, the alpha and beta are actually physical particles. An alpha particle contains two protons and two neutrons (essentially a Helium-4 nucleus), and is positively charged. A beta particle is an electron, and so is negatively charged. Gamma rays and x-rays are photons, which means they are pure energy and have no mass or charge. From a detection and measurement standpoint, the latter two are identical, only their origin differs. There’s also the odd subcategory of neutrons. Neutrons, singular particles that are neither positive nor negative are occasionally omitted by some radioactive sources. They can be highly destructive.

The way these different types of radiation interact with matter differs somewhat, so no one single technical approach can give us all of the information we may want or need. Radiation sensors can be made for various purposes. Detection sensors tell you whether radiation is present and may be useful for finding radiation sources. Measurement devices provide some sort of quantitative output, in terms of dose rate, such as ‘counts per minute’ or ‘Rads per hour’ somewhat analogous to a speedometer. There is an esoteric variety of units used to measure and describe radiation, but this is somewhat beyond the scope of this article.

Another category, dosimeters, work like an odometer, an provide an accumulated reading of how much radiation has been absorbed over a period of time. So-called ‘isotopic identifiers’ try to not just detect and measure radioactivity, they try to analyse the exact nature of the radiation in order to make a calculated estimate of what type of source may have emitted it. Each of these tasks are different and often require separate instruments. Indeed, few do all of them in one device. It should be noted that naturally background radiation is always present, so this can complicate all of these tasks.

Military and security roles and missions

Military roles for radiation detection include a variety of missions. First there is the need for monitoring to detect whether there is a radiation hazard present, as opposed to merely natural background radiation. If radiation is present, surveying equipment or terrain to find out where contamination is specifically present may be necessary. Is a road safe to use? Is this tank contaminated? Such instrumentation can also aid decontamination by providing some degree of quality control in decontamination processes. Did we clean up the tank properly? Dosimetry, the measurement of accumulated radiation absorbed by individuals, can protect the health of personnel by ensuring that nobody exceeds an unsafe dose. Has this platoon been over-exposed? All of these use cases amount to commanders making decisions about whether a particular location or situation is safe or unsafe or if a particular bit of equipment or infrastructure is ‘clean’ or ‘dirty’. The environmental demands and rigors of combat often dictate product design for ruggedness, but the actual innards are the same.

In the security sector, there are additional, complex tasks and missions. Detection of hidden radioactive materials in baggage, vehicles, or cargo is a core customs and border protection issue. Security and antiterrorism personnel conducting detection missions in urban areas and near civilian populations will be confronted with a bewildering array of annoying false alerts from medical procedures, building materials, and industrial sources. Isotopic identification is often needed to tell if detected radiation is benign (like Potassium-40 which is a natural radiation source found in bananas) or malicious, such as a stolen Caesium-137 medical device. The previous two decades have seen a proliferation of specialty devices for the homeland security market.

Technology overview

All of these missions can be accomplished with scientific instrumentation. A simple way of describing radiation detection, measurement, and identification instrumentation is that science found ways of making objects that interact with radiation in ways that can be measured by electronics. It is a Hollywood trope that radiation detectors are all ‘Geiger counters’. This is not true, but some really are. The Geiger-Müller tube is a venerable technology in this field. It is a gas-filled tube which reacts to incoming radiation and detects the ionisation caused by particles or rays passing through the tube. The number of such ionising events can be used to estimate the amount of radiation. Other types of gas-filled tubes or chambers are also used, using similar principles. These are often rather inexpensive devices, and they remain very much in use in use, either on their own or bundled with other technologies. If you are looking to wave a device over a floor and look for where some radioactive dust has been tracked, for example, a ‘Geiger Counter’ may be your best bet for economy and speed.

Another class of device are known as scintillators. A variety of materials, principally Polyvinyl Toluene, a plastic, Caesium Iodide (CsI), lanthanum Bromide (LaBr₃) and Sodium Iodide (NaI) are in this category. They give out flashes of visible light when radiation interacts with them. In particular, NaI can also measure other characteristics of the radiation and give some clues as to the identity of the substance emitting the radioactivity. Thus, NaI devices are sometimes useful for identification as well as detection.

A further category is composed of semiconductor devices. These substances react electrically when exposed to radiation. Like scintillators, there are a range of these materials ranging from relatively simple to quite expensive and complex. Cadmium-Zinc-Telluride (CdZnTe or CZT) is a mid-range option and used in some detectors. The high end of this market is chilled Germanium. These instruments are expensive, and the Germanium needs to be cooled to very low temperatures, which used to require liquid nitrogen. However, these are the very best portable isotope identification instruments available.

Dosimetry can use a few other technologies, not all of which work in real time. The simplest dosimeters are film badges and pocket ion chambers, which have not changed in decades. Thermoluminescent dosimetry (TLD) is widely used, but needs a dedicated device to read a dosimeter after the fact. It should be noted that many detection instruments have the capability to work as a de facto dosimeter and do some calculations to approximate an acquired dose over time. Some ‘personal electronic dosimeters’ using Geiger-Müller tubes are now actually quite good. Others are more approximate.

Alpha and neutron detection are somewhat more difficult disciplines, are less necessary in field environments, and require specialist instrumentation. Alpha detection often uses traditional Geiger-Müller tubes, but with a fragile thin membrane. As such, they are easily broken in the field. Neutron detection traditionally used Helium-3, but a worldwide shortage of that material has necessitated new approaches to neutron detection, and Lithium-6 is now being used in this role.

Products and market players

Unlike some types of military technology, the military radiological market is broadly supported by a wider market. The nuclear power industry, border protection, and medical sectors have demands for products that do more or less the same thing as military detectors. In most parts of the world, these markets are significantly larger than the military market. Almost universally, the manufacturers make radiation products for the broader markets as well. Often the key distinguishing feature between a military and a civil product is ‘ruggedisation’.

The radiation detection market has long been a space full of specialist SME manufacturers with a handful of products and technologies. While a number of these firms still exist, recent decades have seen mergers and acquisitions. Often, this means that radiation detection product lines are a small percentage of a corporate giant’s turnover. Teledyne FLIR (USA) and Thermo Fisher Scientific (USA) stand as key examples of such market players. They are world leaders in radiation detection, but these firms are leaders in a lot of areas. Canberra, long a name in the field, is now part of Mirion, yet another global firm in the field. Ortec, leader in Germanium isotope identifiers, is a branch of Ametek (USA), the electronics firm. Ludlum (USA) continues to be a name of note. Bubble Technology (Canada) works in neutron detection. Symetrica (UK), Tracerco (UK), Ultra Energy (UK), H3D Gamma (USA), PHDS (USA), Nuvia Group (UK), Radiation Solutions (Canada) and others have diverse product offerings. Argon (UK) holds a special place as well, not as a manufacturer, but as a training and simulation firm that can adapt others’ products for use in training environments.

New frontiers

There are dozens of new products in this area, but many of them represent incremental improvements over existing systems. Compared to the rather nebulous offerings in biological detection and the growing pains of chemical detection, it might seem that radiation detection is more settled. Is there room for innovation and improvement? A casual glance around the exhibition floors at trade shows demonstrates that there certainly are new developments.

One remarkable development from a procurement perspective is that the US military finally adopted a new radiation detector, replacing the 35-year-old AN/PDR-77 and AN/VDR-2 radiation detectors. D-Tect Systems, a Utah-based division of Ludlum, is producing the “Radiological Detection System” for US DoD requirements. A ‘Milestone C’ decision on this system, was reached in the summer of 2023, finally moving procurement and deployment forward. The system is modular; a user-friendly base unit, with basic beta and gamma capability can be augmented with a number of different external probes, covering numerous specialty detection tasks, such as alpha or neutron detection. This development is big news due to the volume required – it has been reported that at least 50,000 units will be procured over the next decade or so. That counts as a truly large order in this sector. Economies of scale may make this product more affordable in other markets in time.

In terms of broader technical developments, there have been developments what we can loosely term the front end (the bit of the detector that interacts with the radiation) and the back end (the processing of the data) of radiation detection systems. In terms of “front end”, germanium-based instruments that do not need liquid gases to chill them are getting smaller and cheaper. Devices that function as “gamma cameras” are becoming more affordable. A gamma camera combines high-resolution radiation detection with imaging technology so that you actually “look” at the world through the eyes of the detector and see where the radiation source is located. These have been around for some time, but have been large and very expensive. Such systems are getting smaller and cheaper, albeit in relative terms – they still cost as much as a new car.

PHDS, a Tennessee-based company combines both Germanium spectroscopy and imaging. Their GeGI instrument, weighing in at less than 7 kg and is mechanically chilled. It not only accurately identifies gamma-emitting radioactive isotopes within a few seconds, it overlays the radiation detection output onto a 60-degree field of view and works out to about 50 meters. If the source is under the seat of a car, it appears on the screen exactly there. There are numerous operational scenarios, where this capability may come in useful, particularly in situations responding to alerts from cheaper and more widely proliferated sensors. Make no mistake, this is a premium product, but one that gives PHDS’s more firmly established competitors like ORTEC something to worry about.

From the perspective of ‘back end’ improvements, basically every manufacturer has benefited from miniaturisation and computing improvements. A good bit of scintillator material is only as good as the electronic components and algorithms interpreting the information coming out of the detection materials. One example of a manufacturer that seems to be doing this well is Symetrica (US/UK). Their Verifinder product line is gaining a lot of traction among security and defence clients who need isotope identification. Part of their success seems to be excellent software and algorithms embedded in the kit. Identifying multiple radiations sources correctly and quickly amidst not just background radiation but also the complexities of a high-radiation environment during an incident is a perplexing mathematical problem. Symetrica appears to have done well with this task and has excellent algorithms to quickly sort through the issues. This is not to say that Symetrica isn’t doing well with the ‘front end’ as well. They are addressing neutron detection by using Lithium-6 based detection. It is also clear that their systems are useable in a wide variety of operational conditions, with a -20°C to + 50°C operating temperature, which is very impressive in this sector. Tellingly, some vendors’ literature does not give operating temperature ranges, and it seems logical that users may have to do some extra work to get accurate information out of scintillator crystals and semiconductors at low and high temperatures.

Truly different approaches have been rare in recent decades in this field. However, a US-based start-up firm, CODEAC Solutions, has come up with a very new approach to surface contamination detection. Examining surfaces for radiological contamination has long been a core mission for radiation detection instruments. CODEAC approaches the issue from a totally different perspective. The primary surface contaminants of concern in a radiological environment are a fairly narrow number of isotopes. How about detecting them chemically instead of radiologically? CODEAC’s surface wipes change colour in the presence of cobalt, uranium, plutonium, and a few other elements. They use the chemical properties, not the radiological properties, of these elements to detect the presence of hazards. For many applications, this may be far easier than electronic methods. Interestingly, this could also have environmental health implications in detection of (relatively un-radioactive) depleted Uranium.

The way forward

Where is the future in all of this? The equipment can get better, cheaper, easier to use, and more accurate. In recent years, this has had to do with both improvements in materials science (i.e., better ways to make and use materials that are responsive to ionising radiation) and electronics improvements, such as smaller hardware and better software. Both aspects can take advantage of improvements from other sectors of industry.

Equipment that is smaller and cheaper will also be easier to field on a more widespread basis. This should make it easier to have more sensors across military units, and not just segregated to specialist teams. It is possible to find some prospects for convergence. The digital camera in a smartphone contains a semiconductor that is not actually bad at detecting gamma rays. There are even apps that do this now. Will the next generation of radiation detection actually just be an app that resides on a smart device that every soldier has on their belt? This author can think of ways that this could happen inside a decade.

Dan Kaszeta