Radiation detection in the palm of your hand

By Eric Becker | August 21, 2014

After the March 2011 meltdowns at the Fukushima Daiichi Nuclear Power Station in Japan, which breached reactor containment systems and resulted in the evacuation of about 150,000 people living within 20 kilometers of the site, many people in Japan and elsewhere were concerned about contamination outside the evacuation zone. The amount of radioactivity in seafood, for example, was of particular interest. Although Japanese authorities instituted monitoring and restricted the distribution of products from certain areas, many people wanted to know whether their food was safe to eat. Also, some people distrusted the Japanese government’s assurances that specific areas were safe for human habitation. These worries sharply increased demand for a device that could provide accurate radiation dosimetry measurements but was also mass-marketable and low-cost. Many radiation detectors appeared on the market in the months after Fukushima—some standalone, some ready to plug-and-play with smartphones, and some even incorporated into smartphones.

With the help of associate nuclear engineering professor Abi Farsoni, I developed one such detector at Oregon State University. Still in the prototype stage, it is a proof of the concept that a small, low-cost radiation spectrometer is possible with off-the-shelf technology. The potential applications for such a detector go far beyond the aftermath of nuclear accidents and include education, medicine, and homeland security.

Living in a radioactive world. Atoms emitting radiation are present all around us, a natural part of our world. They are in the food we eat, the air we breathe, and the ground we stand on. They are literally a part of us. Pioneers like Marie Curie and Henri Becquerel established the existence of, and helped to characterize, the radiation emitted from radioactive atoms. As the field advanced, more sophisticated methods for detecting and measuring radiation were introduced, improving upon Wilhelm Röntgen’s barium platinocyanide salt detector to create a variety of modern radiation detection and measurement devices.

Radiation detection systems have become more sensitive and accurate over time, to keep up with the myriad uses for radiation that have been developed since 1895—including medical procedures, electricity generation, mechanical testing, well logging, and fossil dating, among many others. Humans cannot detect radiation with their senses, so radiation detectors are absolutely essential for all applications and locations where radiation is generated, to make sure that they are safe for people living or working in the vicinity.

Not your grandfather’s Geiger counter. The Oregon State device consists of a scintillator-based detector and a digital pulse processor. When radiation interacts with the scintillator material, the material emits light proportional to the amount of energy absorbed. The amount of light is measured by a photosensor, which generates an electrical charge proportional to the amount of light it has measured. A digital pulse processor then measures the charge and generates a visual representation of the energies it has measured, which can be used to identify specific radioactive isotopes, each of which emits a unique radiation signature.

Because it can measure the energy of each particle of radiation detected, this device is called a spectrometer. The compact detector and electronics afford the OSU spectrometer a footprint of only 1.5 by 2.5 by 1 inch. A production model would be even smaller, literally able to fit in a pocket. The current device is designed to operate for at least 10 hours using a typical cell phone battery and can connect to any WiFi device, operating via a Web browser and eliminating the need for a platform-specific application. Though the mini-spectrometer is currently in the prototype stage, it is estimated that a commercial-production model could be sold for as little as $150.

The ability to identify isotopes is vital. For example, some types of radiation do not travel far, such as alpha particles. If radioactive isotopes emitting large numbers of alpha particles were present in one’s food, a detector could warn of the radiation emitted on the surface of the food but not inside it, thus giving an inaccurate measure of the danger of eating the food. Fortunately, radioisotopes that emit alpha particles—the type of radiation most hazardous to human health once inside the body—also frequently emit gamma rays, which can be used to identify the radionuclides present. This allows the OSU device to warn the user of alpha-particle radiation, even though the alpha particles themselves remain undetected.

Potential uses…and misuses. The OSU detector could also be used to assist officials in situations such as airport security, border security, and emergency response. Because of the detector’s identification capability, officials could quickly assess any radiological threats. This would be especially useful in an emergency situation, because individual users could upload radiation readings to create a map that officials could use to determine which areas should be evacuated and in which direction evacuees should go. The more radiation detectors in the area, the more accurate the map would be.

There is, of course, the potential for this type of detector to be misinterpreted and misused. If a user were standing too close to a natural source of radiation—such as Brazil nuts or cat litter—the detector could give a false alarm and cause undue stress and panic. A malicious user could position the detector very close to a radiation source at several locations and upload the results to a radiation map, causing it to appear as though radiation levels at many locations were higher than expected. The identification capability of the device could be used to minimize the number of false alarms and malicious uses, but it is impossible to guarantee it would catch every one.

On the plus side, a compact, affordable spectrometer could not only help keep people safe, but could also serve as an advanced tool that allows students to learn more about what happens when an atom decays —replacing simpler experiments typically conducted with Geiger counters. It could make users more aware of the naturally occurring radiation around them, such as radon that can seep into houses from the soil. And despite the potential for misinterpretation and misuse, the benefits of a small, affordable radiation detector with isotope identification capability seems to vastly outweigh it.

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