discovered_01_2016 - The Telltale Glow of Minerals

WWW.HZDR.DE discovered 01.16 TITLE // Lasers are also finding their way as research tools into resource exploration. Geographer Margret Fuchs wants to develop a quick, hands-off method of detecting metals while maintaining maximum efficiency. She is getting support from the TU Bergakademie Freiberg. Every time Margret Fuchs shuts the heavy metal door to her workplace, she leaves the outside world behind her for several hours. The curly-haired, young HZDR scientist conducts her experiments in almost complete darkness. She enters the darkened lab through a windowless lobby. Once her eyes have accustomed themselves to her surroundings she skillfully circumnavigates the silhouette of an experimental set-up. With the beam of her flashlight she scans the UV laser, drops the switches and sends countless photons off on a laser light mission. A point the size of a grain of sand immediately appears at the end of the course: a miniature crystal the UV laser excites so that it glows. The phenomenon that certain materials have the property to emit short-lived light as soon as they are exposed to a certain light source is something we often encounter in shopping malls. Cashiers hold bank bills under UV lamps to check whether they are genuine. This works because while they are being manufactured, the real bills are mixed with fluorescent filaments that show up in color under black light. Margret Fuchs, who has been working at HZDR’s Helmholtz Institute Freiberg for Resource Technology (HIF) since 2015, wants to apply this physical phenomenon to detecting rare earths. These are a group of 17 metals, such as Cerium, Neodymium and Lanthanum, which are needed to manufacture displays and screens as well as extremely strong magnets. Despite the name, rare earths occur quite frequently in the Earth’s crust. But in contrast to other ores, they are usually distributed sparsely and seldom occur in high concentrations, which is why it is often so difficult to find and exploit high-tech metals. Non-destructive exploration The basis for this new method of exploration is laser-induced fluorescence spectroscopy (LIF). Margret Fuchs excites minerals with lasers of different wavelengths, from ultraviolet through to the infrared range. Not all minerals are naturally fluorescent. The luminescent effect is usually a result of impurities in the crystal lattice caused by foreign atoms – such as those of rare earths. This is why the fluorescence method is particularly suited to determining the presence of such metals. The moment the laser excites a foreign atom, the electrons it contains start leaping to a higher energy level and back again. This releases light with a characteristic emission spectrum that is measured by a special camera. "It is just as unique as a person’s fingerprint," Margret Fuchs explains. In future, a scanner is supposed to be developed that will visualize this fingerprint from the rock surface of drill cores and deposits. In contrast to standard methods of investigation, which usually depend on comprehensive chemical and physical analyses, this should make it possible to detect natural deposits of rare earths non-destructively and thus also more quickly. LIF research is part of a whole series of "gentle" exploration methods which the Helmholtz institute is involved in developing and implementing. For example, a flying probe that is affixed to the underside of a helicopter sends signals at certain frequencies to the subsoil. There the signals generate electrical fields which the probe subsequently receives. This allows researchers to identify electrical conductivity, which can indicate whether there are ore minerals in the rock. Furthermore, geoscientists are testing how drones can be combined with different aerial survey exploration methods or spectroscopy to produce high-resolution models of the Earth’s surface. _TEXT . Tina Schulz THE TELLTALE GLOW OF MINERALS Photo: Detlev Müller

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