When rocks that have been mechanically strained or exposed to ionizing radiation are heated, they emit from their surfaces electrons which can be measured with a beta-counter. This emission of exoelectrons can be interpreted in terms of trapping energies associated with the defects produced by mechanical strain, trace element impurities, or lattice imperfections. The exoelectrons are emitted over discrete temperature intervals determined by the nature of the rock surface and the defect population in the surface.
The graph of the amount of exoelectron emission versus temperature is known as an exoelectron glow curve. These curves can be compared with thermo-luminescence glow curves and other measurements which characterize the number and energies of defects in the surface and the bulk rock. The defect population may therefore be related to such important properties as the mechanical strength and the influence of the tectonic and thermal history of the rock.
The production of exoelectron glow curves with the accuracy, speed, and convenience needed for geological samples can be accomplished with a gas-counting apparatus which we have developed and constructed for this purpose.