Frequency-dependent neutron emissions during fatigue tests on iron-rich natural rocks

The results coming from neutron emission measurements during fatigue experiments performed at low (2 Hz), intermediate (200 Hz), and high (20 kHz) frequency are reported. These results confirm that appreciable neutron emissions, greater than the background level, may be observed during damage accumulation in iron-bearing rocks: granite (Fe oxides ~1.5 %), basalt (Fe oxides ~15 %), and magnetite (Fe oxides ~75 %). The neutron detection, together with temperature measurements obtained by infrared revelation, lead to the conclusion that fatigue tests performed at 200 Hz represent the condition for which the neutron emission is the highest. This evidence seems to be particularly important considering recent results from seismological observation of the Jacinto fault in the Southern California and the neutron emissions detected during seismic activity.