Hand held x-rays find most metals

Written by: Tom Shelley | Published:

Tom Shelley reports on a Star Trek style tricorder capable of instantly analysing almost anything containing inorganic substances

X-ray detectors originally developed for use on satellites have enabled the development of a safe, hand held chemical analyser that can detect and measure most minerals and inorganic polluting contaminants.

Like the tricorder with which scriptwriters imagined Spock would be equipped in the 23rd century, it can detect and determine the amount of different elements in the range from phosphorous up to uranium, to a level of 5ppm. And lighter elements down to magnesium can be detected with the aid of a vacuum attachment.

We recently took the opportunity to test one of these instruments, made by the US company Innov-Xsystems, at an Institute of Materials, Minerals and Mining's "Mining Sundowner" event in London.

Various people brought what they considered to be difficult samples of things to analyse. We took a sample of a mineral called tetrahedrite that happens to have 0.6% of silver in it; the reason it is mined. For each sample, Todd Houlahan, director, global mining accounts for Innov-X reset the instrument, placed the sample on a table, pointed the instrument at it and pressed the trigger.

In a few seconds it produced a detailed analysis, including the correct assessment of the amount of silver in our sample. Houlahan explained that it depended on its use of a Silicon Positive Intrinsic Negative (PIN) diode detector, a type of device originally developed for use in satellite instruments.

The detector is cooled to –35°C and the tube energy is 40keV. Safety is ensured by a red light to indicate when the window is open, and an additional feature that shuts the tube off if nothing is detected in front of it. Furthermore, the source and detector are arranged in geometry that minimise x-ray dosage at a distance. The tube is of such low power that, according to Houlihan, if you were to aim the device at somebody with the power on they would take months to accumulate a hazardous dose.

There was some discussion about its efficacy in identifying gold. Houlihan said: "A lot of people use the presence of arsenic to imply the likelihood of gold." But mineable gold ores are less than 1g/tonne (1 ppm) making the device impractical for gold prospecting.

However, growth markets for the instruments are currently in checking for environmental pollution in soils or ponds; identifying contaminants in oils and fuels; wear metal in lubricating oils; lead content in the solder of electronics; cadmium, chromium and lead in paints and plastics; checking stock bars of metals and alloys; and also police forensics.

The main competitor of the Innov-X range of products is the Niton range, now part of Thermo Scientific. Both companies are based in Massachusetts: Innov-X in Woburn, a suburb of Boston and Niton in Boston itself. The instruments typically cost around $40,000 each depending on model.

The detectors continue to be used in space exploration, including NASA's Mars Rovers.

Pointers

* Modern x-ray fluorescence analysers are used to detect and analyse elemental content from uranium to phosphorous, and even down to magnesium with the help of a vacuum attachment.

* Can measure to a level of 5ppm.

* The device can be used in one hand, is quick and easy to operate, and totally safe.

* The solid state detectors were originally developed for satellite instrumentation.


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