In the Middle East, intelligence services furiously hunt for fissile material in Iran. In Japan, residents still worry about radiation exposure from Fukushima Daiichi. In other places, stolen or missing radioactive sources have made the news.
One solution: the cell phone.
The average, everyday smartphone could be equipped with radiation detectors and an app that would make them into small, highly mobile, radioactive particle mappers.
A network of such phones would mean that gamma-ray spectroscopy would be truly ubiquitous—in other words, this phone technology would be so widespread that it would essentially be encountered everywhere, all the time—and consequently allow for the successful detection and mapping of radiological sources. It would make for a first line of defense, a sort of 21st-century update of the Distant Early Warning system used in the Cold War to spot an incoming attack.
The idea of putting radiation detectors—or to be more precise, gamma ray spectrometers—into cellphones isn’t new: It began more than 20 years ago, then we reprised it after the Fukushima disaster, and several times since. But as the technology has improved dramatically—and the world situation gotten worse—in the time since then, it is worth revisiting the idea. We wish to restate that in our opinion, the only physics solution to track and interdict radiological sources—be they from theft, rogue states, terrorists, or natural disasters—is gamma-ray spectroscopy and real time data-grams from all cellular telephones.
What’s a gamma-ray spectrometer, you ask? When high-energy light waves (gammas) pass through the device, it captures their frequencies (spectra). A prism is a kind of spectrometer for visible light; the color separation is frequency separation. And each radioactive element – plutonium for example—has its own collection of signature frequencies. While gamma-spectroscopy used to cost big bucks, today a decent quality device could be stuffed into your smartphone.
While readers may be more familiar with the term “Geiger counter” from what they have seen in the movies, a Geiger counter (or more precisely, a Geiger-Mueller tube) just counts photons. It is old tech.
What’s the difference between a gamma-ray spectrometer and a Geiger-counter? A Geiger-Mueller counter is sort of like a bucket that provides one count of all baseballs it catches. In contrast, a gamma-ray spectrometer measures the speed, and counts up fastballs, slowballs, curveballs, sometimes measures its spin, of all the baseballs it catches. And a gamma ray spectrometer measures each photon by its frequency—which means that you can discern radioactive material composition at a distance.
In addition, by having a vast sea of devices equipped with a gamma-ray spectrometer, you may detect in two dimensions—not just stumble upon hot spots. Tens of millions of gamma ray spectrometers mean that you are getting into making a map of radioactive materials present, not just having a threshold box near a bomb that goes “beep.” The capability of this proposed system would not be met by having a few Geiger counters; it would be met by having hundreds of millions of gamma ray spectrometers moving around randomly.
In 2012 my co-authors and I wrote an article for the Bulletin on what would be needed to make everyday cell-phones into small, highly mobile, radioactive particle detectors. The article was part of a surge of research interest at that time into using networked detectors to locate hidden sources of radioactivity, and dealing with the fallout after a radiological event.
When first proposed in the late 1990s, the concept was in the toddler days of smartphone technology. In 2003 Los Alamos National Laboratory created “RadNet,” a fledgling cellular-telephone-based radiation detector network. Los Alamos and NIST teamed up later in 2006 for field tests at Los Alamos. But while technology components have been researched, widespread social adoption—which is the only way to really work—hasn’t gone viral.
Our own crude first prototype attempt began at about that same time, running on a Palm Treo 650 with a LabView application communicating by RS-232 with a Geiger-Müller circuit. Today, billions of people carry in each of their pockets what is in effect a cluster supercomputer with high speed internet radio—and you can purchase blue-tooth connectable scintillator spectroscopy.
In 2006, we started our quest to persuade everyone of the usefulness of such a system. We went to cell phone manufacturers. We went to the Pentagon. We went to venture capitalists. We computed. We went to Radio Shack—back when there still was one. We got some small funding from the Indiana Department of Transportation to do a prototype. And while interest was spawned, we have not been successful so far in persuading the world of what we still think is urgent, necessary, and sufficient: The only physical way to protect the world from nuclear terrorism requires real time gamma-ray spectroscopy in everyone’s cell phone.
If this were standard infrastructure now on every Samsung and Apple smartphone, then the entire world would almost always know where most radioactive material was. Since background radiation would be repeatedly measured, and sources constantly measured, any movement would show up as a statistical excursion from established baseline. This would not be unique to Iran, but would become a property of the planet. And it would have applied a few years ago when a hot radioactive source was stolen in Japan, for example.
It is certainly technically available to essentially make every cell phone into a gamma ray detector. The science, engineering, and technology abundantly exist. But governments and the public and the physics community and the cell phone manufacturers must all say “Yes” in order to make it a standard and ubiquitous feature.
And making them “standard” and “ubiquitous” are essential; a few thousand of these phones is useless. A few million is a poster-session. A few hundred million is useful but inadequate. We have simple needs; just give us your 8.3 billion phones.
A few questions inevitably come up; here are the answers: What about civil liberties? The data would be anonymized and frankly if there were radon in my basement, I’d like to know. Couldn’t you do it with satellites? No, they are too far away, the signal too weak. Can’t you do it with trucks or drones? No, the sampling is too sparse. Aren’t they already doing it? No, it’s not in there. Can’t you do it with cops and firemen using a special device? No. Physics statistics is an unforgiving thing—the hope of effectiveness begins in the tens of millions of measurement nodes. The signals from contraband radioactive materials are dim. Unless you have good probability of getting multiple measurements within a few meters, you don’t have signal to noise hope.
Opposition to the proposed network detector concept has raised good points—that many classes or types of hidden bomb would be missed even if every cell phone in the world had the best gamma-ray spectroscopy we could cram into it. But counting gamma-rays is a statistical pursuit; billions of measurements of the background, in every corner of the world, makes all subsequent measurements there better; measuring nothing is important; something is just differential nothing. Ubiquitous spectroscopy give a better signal-to-noise ratio, and it puts pressure on the terrorist—any screwup and he could be seen. Today the terrorist has a free hand and there is pressure on the good guys—there are very few chances to succeed with today’s infrastructure.
Ubiquitous detection makes being a terrorist hard. He can try to resort to heavy lead shielding. But this can become intractably massive and consequently hard to move. A cloud of millions of detectors, counting for thousands of hours, moving unpredictably, can find leaks. Terrorists make mistakes, and ubiquitous cell phone-enabled gamma detectors would be in a position to capitalize on those leaks.
Detection is deterrence. A terrorist who thinks he may get caught is a terrorist on the losing end of a cost/benefit analysis. Cell phone density is directly proportional to target desirability for the terrorist, consequently making deterrence in proportion to vulnerability. The proposed system provides insurance for a few dollars per cell phone. The cost/benefit analysis for implementing ubiquitous gamma spectroscopy by cell phone hugely favors its use.
Thermodynamics has given us the concept of emergent behavior. There are properties that billions of particles possess which thousands do not. As the saying goes, “Quantity has a quality all its own.” Nowhere is this more true than in cell-phone radiological detection. The ubiquity and density of many millions of phones would give rise to two-dimensional image tracking, instead of simple zero-dimensional thresholding. And once the real-time geographic background has been recorded, innumerable machine learning and astronomy algorithms could compete for detection supremacy in ways we could not have anticipated two decades ago; this democratizes the stopping of nuclear terrorism and converts the problem into a machine learning competition.
Convincing a society is a slow percolation problem. Years ago Japan’s MEXT was interested, Chiyoda Technol Corp was curious. Eventually SoftBank released a phone with a small dosimeter in it and an app for putting push-pins on map locations. While we researchers were grateful for these increments, we failed to persuade our colleagues on central points: large detection aperture, spectroscopy, ubiquity, real time reporting, automatic 2D geo-mapping, without human intervention, with server side algorithmic source detection, are all required components. But so far the systems that have been built have had only unconnected pieces of that puzzle.
Systems of thousands of nodes have been done as demonstrators. The Defense Advanced Research Projects Agency, or DARPA (the folks who funded the internet, and did much of the early research into satellite navigation, among other things) showed the effectiveness of this approach at first the levels of 100 detectors, and then 1,000 detectors around the year 2016. By 2018 there was a roll-out to state, local, federal, authorities, but these likely remain in the thousands of nodes. We applaud every baby step, but we wish to be clear that life begins in the tens of millions. Tens of thousands won’t cut it. We will keep insisting after every future radiological crisis that ubiquitous, real time, internet reporting, gamma-ray spectroscopy, has to be on every smartphone if you want to save the world from nuclear terrorism.
As physicists and nuclear engineers, we look out today over the landscape of the world, and we see the Trump administration going full tilt on missile defense. Fine enough; inbound nuclear missiles are bad and stopping them is good. But a missile gives away that it’s coming, and it tells everyone who launched it. By contrast, a pickup truck delivered by a drug cartel, or a package shipped commercially, is less detectable and doesn’t have a return address. And today we have a new delivery method unrealized in the early 2000s—a robot trotting from the wilderness into a city. Or a fixed wing drone, flying at 10 meters above the ground. So, missile defense, while necessary, addresses a 20th-century problem while robots and drug mules are 21st-century problems: delivery systems that are undetectable under the radar. But all of those are (at least potentially) detectable by ubiquitous cell phone gamma-ray spectroscopy.
The 21st-century problem is urgent. According to reports, Iran had in its possession enough fissile material to construct several nuclear weapons. One of the stated primary aims of the Trump and Netanyahu administrations was to destroy the Iranian capability to build and deploy nuclear weapons. And the problem is bigger than just Iran, the IAEA reports that thousands of radioactive sources have been stolen or went missing—as well as radioactive accidents in recent years in France, Russia, and the United States. The incident at Fukishima also shows the need for such a detection and measurement system, as does the unresolved question of a plant leak amid the Ukraine war. At its heart, these are all intrinsically physics problems. Once the network of detection is designed to conform to the physics constraints, then military planners, politicians, private enterprise, and policymakers will have new opportunities to protect people from this existential threat.
And the usefulness of such a smartphone-based detection system would not be limited to just dealing with existential risk.
A fun corollary comes up, regarding how it could be used to advance physics. If every smartphone was a gamma-ray spectrometer, layers of different physics inputs would have to be separated. There would be the terrestrial background from bananas, granite steps, and antique uranium cookware. There would be the signal of interest, the illicit radioactive material. There would also be the astronomical signal, the cosmic ray, the solar wind. Separating these map layers would be an essential function in making the network detector perform its function. As such, a whole-world X-ray observatory data set with several billion pixels and an aperture on the order of the planet would result; the signal you didn’t want would be . . . basic science. In other words, building a system like this would also hand scientists the world’s largest possible X-ray telescope.
The threat posed by smuggled nuclear materials or clandestine weapons programs isn’t going to fix itself. Rogue actors will continue to procure fissile material and attempt to construct civilization-ending bombs for motives that run opposite the love-thy-neighbor religion of most people. The probability that the entire terrorist enterprise will be bombed or lectured out of existence is low. Civil society has only one physics option for counting the statistical particle events that provide partial location and signature information of illicit radioactive sources.
Stolen radioactive sources, leaking nuclear plants, terrorist threats, plant-war-threats, Fukishimas—these are huge problems that aren’t being treated as huge, in part because
no one believes there is a credible solution.
It is our hope that if societies can grasp that there is a physics plus AI solution, then these problems would no longer be treated as “too-big-to-be-solved.”
As we did at Fukushima Daiichi, and now at the Iran crisis, and as we will do in the future at every new radiological event, we call for gamma-ray spectroscopy, with real-time data reporting, in every smartphone.
