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Particle detectors in action

In this video Dr Jamie Brown describes a new generation of handheld and wearable particle detectors, produced in association with tech company Kromek.
Alpha, beta and gamma radiation interact very differently with matter. Due to their large mass and charge, alpha particles are typically stopped very easily, by as little as a few cm of air, or a sheet of paper. Beta particles, being much lighter and only having a single unit of charge, need a few mm of aluminum before they’re blocked. Gamma rays, on the other hand, have no mass or charge, so can travel large distances and penetrate through significant amounts of material. This is one reason why detecting gamma rays is often the best way to detect the presence of radioactive material.
Gamma rays interact with matter in three main ways: Pair production, when a high-energy gamma ray spontaneously decays to an electron/positron pair; Compton scattering, where the gamma ray bounces off an atomic electron, passing it some of its energy; and photoelectric absorption, where the gamma is fully absorbed by a tightly bound inner electron. Many traditional detectors use scintillators, which convert high-energy gamma rays into large quantities of lower-energy optical photons. A photomultiplier tube converts these photons to electrons, and amplifies them to produce an electrical signal. From the amplitude of this signal, and an understanding of how gamma rays interact in the detector, we can determine which radioactive isotopes are responsible for the radiation.
These photomultiplier tubes are often large, bulky and delicate devices, requiring high-voltage power supplies, making them poorly suited to portable, wearable or handheld detectors. Recently, researchers from York’s Nuclear Physics Group, working with a technology company based in County Durham called Kromtek, have developed an innovative new detector. They replaced the photomultiplier tube with a small semiconductor device, capable of converting the optical photons directly to an electrical signal, in only a few millimeters of silicon, and requiring only a small battery to operate. Kromek have integrated this technology, along with a small neutron detector, into a wearable detector system, not much larger than a mobile phone. The detectors are networked, making it possible to build up a map of radiation within a large area.
By distributing a large number of these portable devices across a group of people, such as a city’s police force or postal service, it is possible to detect and monitor sources of dangerous radiation in real-time. This device is a great example of how the research carried out here in York, in collaboration with local business and industry, is creating technologies that help to keep people safe all over the world.

Particle detectors are vitally important for a wide range of industries, from nuclear power, to security, to medical applications. The University of York works with the company, Kromek, to develop our research into commercially available products.

In this video, Dr Jamie Brown highlights one such example – a wearable detector with a smartphone interface. This detector is designed to look for radioactive materials. Such materials give out alpha, beta, or gamma radiation. Alpha particles are helium nuclei (composed of two protons and two neutrons). They are relatively heavy and are therefore easily stopped. Beta particles are either electrons or positrons. Much lighter than the alpha particles, these are stopped by a thin sheet of metal. Gamma particles are high energy photons. As these are massless, they are the most penetrating type of radiation and therefore the best to look for when trying to locate radioactive materials.

The detector Jamie is talking about doesn’t just tell us whether there is radioactive material present. It can also give us information about dosage (how dangerous the material is) and can identify the isotope emitting the radiation within seconds (based on the gamma ray spectrum). Using the phone’s GPS, this detector can then create a map showing the location of any hazards.


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Frontier Physics, Future Technologies

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