Mineralogy

Detecting traces of paramagnetic impurities | Mineral structure |

Classifying on the geological time scal

Background

Minerals are naturally grown crystals. Their chemical composition can be very complicated compared to synthetic crystals. “Pure” minerals are mostly ESR-inactive. However, impurities, such as Manganese or Vanadium, as well as ionizing radiation, can cause a hole or a vacancy in the structure, thus “activating” the mineral for ESR.

Transition metal impurities can be detected down to smallest concentrations. Irradiated minerals can be analyzed for their physical-chemical behavior. Natural radiation enables dating application by ESR and TL-OSL.


Application Example: hydrogen/double-lithium centre in α-quartz

Quartz is a silicon oxide of the chemical structure SiO2. A pure quartz is ESR-silent. However, it shows distinct ESR signals upon irradiation.

A research group from New Zealand investigated the radiation-induced defects using ESR. α-quartz crystals were irradiated with gamma-rays and measured with an X-Band ESR spectrometer. The results indicated an oxygenic electron hole. Further analysis of the data (hyperfine splitting, spin-Hamiltonian) revealed more details about the interactions in the structure and the preferable location of the defect.

References

  • N. S. Lees, C. J. Walsby, J. A. S. Williams, J. A. Weil, R. F. C. Claridge (2003): EPR of a hydrogen/double-lithium centre in a-quartz. Physics and Chemistry of Minerals 30, 131 - 141