Radiation sensor reveals material composition in fraction of a second

The new device, created by SINTEF nanotechnologists at the Micro and Nano Laboratory in Gaustadbekkdalen in Oslo, is said to be able to reveal the composition of materials in a fraction of a second. The researchers believe it could be used to offer advances in everything from materials science to archaeology. "The sensor consists of a double sided microstructure that is fabricated on silican wafers," explained research scientist Niaz Ahmed. "Such structures are complex and difficult to produce. We are one of only two or three suppliers of such sensors in the whole world." Measuring just 8 x 8mm, the sensor is produced by oxidising the silicon wafer in several stages, creating a physical structure on a nanometre scale. Once this has been done, the scientists dope it with charged atoms at various levels. The result is an incredibly light-sensitive diode which, once it has been connected to the appropriate electronics, can reveal changes in the physical structure of most materials. According to the researchers, the sensor uses spectroscopy, which is based on sending light through a transparent object. When the light beam emerges from the other side of the object, the sensor reads off changes in its characteristics. "To put it simply, the sensor sorts the light into its individual energy levels by counting the photons and calculating their energy," noted Ahmed. "Unlike standard silicon based sensors, the way the silicon drift diodes work requires them to have structures on both surfaces of the sensor chip. This can only be done with the help of advanced equipment and extremely high levels of accuracy." Ahmed explained that one side of the sensor is called the 'window side', and is turned towards the source of radiation. It absorbs the X-ray beam almost without loss. The other side is known as the 'ring side' and has a concentric annular structure. This means that the rings have the same centre but increase in radius. This means that the electrons generated by the radiation source are captured by the central electrode, which in turn enables the X-ray sensor to discard all the irrelevant electronic signals, or noise. "Because it easily distinguishes between different materials by registering differences in the absorption energy of their component elements, the chip can be used to identity forbidden materials such as lead, cadmium and mercury," Ahmed concluded.