Neutron Emissions and Compositional Changes at the Compression Failure of Iron-Rich Natural Rocks

Abstract

Neutron emissions (NE) were measured during laboratory experiments conducted on iron-bearing and iron-rich rocks. In particular, magnetite specimens were loaded up to the final failure under monotonic displacement control. Also basalt rocks were tested under cyclic loading conditions (2 Hz) up to the final failure. In order to detect neutron emissions, the tests were monitored by two different neutron measurement devices: He3 proportional counter and thermodynamic (bubble) detectors. After the experiments, Energy Dispersive X-Ray Spectroscopy (EDS) analyses were carried out to detect possible direct evidences of low energy nuclear reactions (piezonuclear fission reactions) on the fracture surfaces. In particular, quantitative evidences of nuclear reactions, involving iron decrease and the corresponding increase in lighter elements, were observed in the olivine, crystalline mineral phase widely diffused in the basalt matrix, and in the magnetite. These results reinforce the evidences previously observed for Luserna stone (granitic orthogneiss) and confirm that piezonuclear fission reactions take place in natural iron-bearing materials subjected to damage accumulation and cracking.