Chrysos PhotonAssay® uses high-energy X-rays to measure elements in bulk samples. An intense X-ray beam excites atomic nuclei of target elements, and a sensitive detector system measures the gamma-rays subsequently emitted by the excited nuclei. We refer to this as ‘atom-counting’, as we measure a signal that is directly proportional to the number of atoms of the chosen element contained in the sample. The more target atoms present, the more nuclei excited, the stronger the gamma ray signal detected. See [technology page] for more information.
X-ray fluorescence, or XRF for short, is another widely used X-ray technology for measuring elemental composition. However, XRF uses a much lower energy X-ray source, typically about 200 times lower than the one used for Chrysos PhotonAssay®, and relies on measuring a signal from atomic electrons rather than the atomic nucleus itself. XRF is much less penetrating, making it impossible to measure bulk samples directly, and commercial units do not have the sensitivity to measure elements at gram-per-tonne concentrations.
The physics of the Chrysos PhotonAssay® process mean that it is completely agnostic to the physical or chemical form of the sample being analysed. Single rocks or pulverised ore; feed, concentrate or tailings materials; slurries or solutions: all can be measured with equal felicity. Indeed, we have conducted tests showing that the technology can even be used to measure the gold content in electronic waste without any special sample preparation.
Yes! Each element gives rise to a gamma-ray signature with a unique energy. For example, the gamma-ray energy for gold is 279 kiloelectron volts (keV), and for lead it is 570 keV. The high resolution detector system that we use and our proprietary analytical software is easily capable of distinguishing between these signals, allowing grades in polymetallic materials to be separately reported.
Chrysos PhotonAssay® can be tuned to measure different sets of elements in samples. The technique is particularly sensitive for gold, and this is our first target. Elements that can be reported simultaneously with gold include silver, barium, hafnium, yttrium and selenium. By adjusting the operating conditions, different ranges of elements can be measured. For example, we have demonstrated the simultaneous detection of copper, silver, lead and zinc in complex polymetallic ores. See [technology page] for an illustration of the full range of elements sensitive to Chrysos PhotonAssay®.
No! A Chrysos PhotonAssay® unit includes no radioactive source. Instead, the X-rays are generated electronically using an electron linear accelerator. Similar accelerators are widely used in industry for medical product sterilisation and other applications; they are also found in the radiotherapy units of most hospitals. When the source is powered off, it produces no radiation.
The use of all X-ray sources is governed by stringent Federal and State guidelines. Our Chrysos PhotonAssay® units include comprehensive safety measures, including custom-designed shielding, safety interlocks and control systems. All operations are fully automated, and no operators need enter the unit during the analysis process. X-ray levels outside of the units comply with Australian and international guidelines and are completely safe for operating personnel and members of the public.
No. The excitation that we produce in the samples is very short lived. Even immediately after exposure to the X-ray beam, excitation levels are extremely low and samples can be safely handled. A few minutes after exposure, the activity falls to unmeasurably low levels. As an additional precaution, samples are retained in the analysis unit for 2 hours after measurement before being returned to operators. At this time, they can be handled or disposed of as regular waste.