neutron emissions from brittle rocks failure

Electromagnetic and neutron emissions from brittle rocks failure: Experimental evidence and geological implications

A CARPINTERI, G LACIDOGNA, O BORLA, A MANUELLO and G NICCOLINI

Politecnico di Torino, Department of Structural Engineering and Geotechnics, Corso Duca degli Abruzzi 24 – 10129 Torino, Italy
National Institute of Nuclear Physics, INFN Via Pietro Giuria 1 – 10125 Torino, Italy

National Research Institute of Metrology, INRIM Strada delle Cacce 91 – 10135 Torino, Italy

e-mail: alberto.carpinteri@polito.it

Abstract.
It has been observed energy emission in the form of electromagnetic radiation, clearly indicating charge redistribution, and neutron bursts, necessarily involving nuclear reactions, during the failure process of quasi-brittle materials such as rocks, when subjected to compression tests. The material used is Luserna stone, which presents a very brittle behaviour during compression failure.

The observed phenomenon of high-energy particle emission, i.e., electrons and neutrons, can be explained in the framework of the superradiance applied to the solid state, where individual atoms lose their identity and become part of different plasmas, electronic and nuclear.

Since the analysed material contains iron, it can be  conjectured that piezonuclear reactions involving fission of iron into aluminum, or into magnesium and silicon, should have occurred during compression damage and failure.

These complex phenomenologies are confirmed by Energy Dispersive X-ray Spectroscopy (EDS) tests conducted on Luserna stone specimens, and found additional evidences at the Earth’s Crust scale, where electromagnetic and neutron emissions are observed just in correspondence with major earthquakes. In this context, the effects of piezonuclear reactions can be also considered from a geophysical and geological point of view.

[] It is possible to demonstrate experimentally that the failure phenomena, in particular when they occur in a brittle way, i.e., with a mechanical energy release, emit additional forms of energy related to the fundamental natural forces.

The authors have found increasing experimental evidence that energy emission of different forms occurs from solid-state fractures. The tests were carried out at the Laboratory of Fracture Mechanics of the Politecnico di Torino, Italy. By subjecting quasi-brittle materials such as granitic rocks to compression tests, for the first time the bursts of neutron emission during the failure process is observed, necessarily involving nuclear reactions, besides the well-known acoustic emission (AE), and the phenomenon of electromagnetic radiation (EM), which is highly suggestive of charge redistribution during material failure and at present
under investigation.

[] We are treating with inert, stable and non-radioactive elements at the beginning of the experiments (iron), as well as after the experiments (aluminum). Neither radioactive wastes, nor gamma emissions were recorded, but only thermal and fast neutron emissions. As confirmation of this observation, the results of Energy Dispersive X-ray Spectroscopy (EDS), performed on samples coming from the Luserna stone, a metamorphic rock deriving from a granitoid protolith, specimens used in the experiments, show that, on the fracture surfaces, a considerable reduction in the iron content (-25%) is counterbalanced by an increase in Al, Si and Mg concentrations.

[] Classically during the process of nuclear fission, a neutron strikes a heavy nucleus that splits into two lighter fragments. Each of the two fragments consists of a nucleus with roughly half the neutrons and protons of the original nucleus. This fission process releases a large amount of energy and gamma rays are emitted as well as two or more neutrons that are no longer bound by the fission fragments.

Instead, piezonuclear fission reactions consist in new nuclear reactions produced by new methods such as pressure, fracture or cavitation. Even small deviations from classical assumptions, e.g., from the concept of average bond energy per nucleon, could explain these new phenomena. It would suffice to assume a weak section within the nucleus, as it happens in very hard and strong rocks, that nevertheless cleave under very low stresses. Moreover, the main and peculiar characteristic of piezonuclear reactions is neutron production without gamma emission. This physical phenomenon could be the signature of a new physics of nuclear interactions, as it is theoretically and experimentally discussed in the literature.

[] Energy Dispersive X-ray Spectroscopy (EDS) was performed on different samples of external or fracture surfaces belonging to granite specimens used in the piezonuclear tests. For each sample, different measurements of the same crystalline phases (phengite or biotite) were performed in order to get averaged information of its chemical composition and to detect possible piezonuclear transmutations from iron to lighter elements. Considering the results for phengite and biotite, and also their abundances in the Luserna stone composition, a considerable reduction in the iron content (∼25%) is observed. This iron decrease is consistently counterbalanced by an increase in aluminum, silicon and magnesium. In particular, the increase in aluminum content corresponds to 85% of the iron decrease. Therefore, the following piezonuclear fission reactions should have occurred in granitic rocks during the piezonuclear tests:

Fe 56/26 → 2Al 27/13 + 2 neutrons, (1)
Fe 56/26 → Mg 24/12 + Si 28/14 + 4 neutrons. (2)

[] It has been recently reported that electromagnetic phenomena take place in a wide frequency range prior to an earthquake, and these precursory seismo-electromagnetic effects are expected to be useful for the mitigation of earthquake hazards. The generation of electromagnetic emissions during earthquakes has been verified also in laboratory experiments involving fracturing of quartz-bearing rocks.

Similar to the case of EME coming from fracture phenomena, the neutron emissions involved in piezonuclear reactions have been detected not only in laboratory experiments but also at the Earth’s crust scale. Recent neutron emission detections [] have led to consider also the Earth’s crust, in addition to cosmic rays, as being a relevant source of neutron flux variations. Neutron emissions measured near the Earth’s surface exceeded the neutron background by more than three orders of magnitude in correspondence to seismic activity and rather appreciable earthquakes. This relationship between the processes in the Earth’s crust, EM emissions and neutron flux variations has allowed to develop new methods for short-term prediction and monitoring of earthquakes.

Taking into account that granite is a common and widely occurring type of intrusive, sialic, igneous rock, and that it is characterized by an extensive concentration in the rocks that make up the Earth’s crust (∼60% of the Earth’s crust), the piezonuclear fission reactions considered above can be generalized from the laboratory to the Earth’s crust scale, where mechanical phenomena of brittle fracture, due to fault collision and subduction, take place continuously in the most seismic areas of the globe. This hypothesis seems to find surprising evidence and confirmation from both the geomechanical and the geochemical points of view.

The present natural abundances of aluminum (~8%), silicon (∼28%) and magnesium (∼1.3%) and scarcity of iron (∼4%) in the continental Earth’s crust are possibly due to the piezonuclear fission reactions (1 and 2) expressed above. In addition, considering the percentage mass concentrations of other chemical elements, such as Na (∼2.9%), Ni (∼0.01%), and Co (∼0.003%), in the continental crust, it is possible to conjecture additional piezonuclear fission reactions that could have taken place in correspondence to plate collision and subduction:

Co 59/27 → Al 27/13 + Si 28/14 + 4 neutrons (3)
Ni 59/28 → 2Si 28/14 + 3 neutrons, (4)
Ni 59/28 → Na 23/11 + Cl 35/17 + 1 neutron. (5)

The large concentrations of granite minerals, such as quartz and feldspar (SiO2,Al2O3) in the Earth’s crust, and to a lesser extent of magnesite, halite, and zeolite (MgO, Na2O, Cl2O3), and the low concentrations of magnetite, hematite, bunsenite and cobaltite minerals (composed predominantly of Fe, Co, and Ni), could be ascribed to piezonuclear reactions (1,2,3,4 and 5) due to tectonic and subduction phenomena.

[] The localization of Al and Fe mineral reservoirs seems to be closely connected to the geological periods when different continental zones were formed. This fact would seem to suggest that our planet has undergone a continuous evolution from the most ancient geological regions, which currently reflect the continental cores that are rich in Fe reservoirs, to more recent or contemporary areas of the Earth’s crust where the concentrations of Si and Al oxides present very high mass percentages. [] The geographical locations of main bauxite mines show that the largest concentrations of Al reservoirs can be found in correspondence to the most seismic areas of the Earth []. The main iron mines are instead exclusively located in the oldest and interior parts of continents (formed through the eruptive activity of the proto-Earth), in geographic areas with a reduced seismic risk and always far from the main fault lines. From this point of view, the close correlation between bauxite and andesitic reservoirs and the subduction and most seismic areas of the Earth’s crust provides very impressive evidence of piezonuclear effects at the planetary scale.

[] Evidence of piezonuclear reactions can be also recognized considering the Earth’s composition and its evolution throughout the geologic eras. In this way, plate tectonics and the connected plate collision and subduction phenomena are useful to understand not only the morphology of our planet, but also its compositional evolution.

From 4.0 to 2.0 Gyr ago, Fe could be considered one of the most common bio-essential elements required for the metabolic action of all living organisms. Today, the deficiency of this nutrient suggests it as a limiting factor for the development of marine phytoplankton and life on Earth. Elements such as Fe and Ni in the Earth’s protocrust had higher concentrations in the Hadean (4.5–3.8 Gyr ago) and Archean (3.8–2.5 Gyr ago) periods compared to the present values. The Si and Al concentrations instead were lower than they are today.

[] A clear transition from a more basaltic condition (high concentrations of Fe and Ni) to a Sialic one (high concentrations of Al and Si) can be observed during the life time of our planet. The most abrupt changes in element concentrations [] appear to be intimately connected to the tectonic activity of the Earth. The vertical drops in the concentrations of Fe and Ni, as well as the vertical jumps in the concentrations of Si and Al, 3.8 Gyr ago, coincide with the time that many scientists have pointed out as the beginning of tectonic activity on the Earth. The subsequent abrupt transitions 2.5 Gyr ago coincide with the period of the Earth’s largest and most intense tectonic activity. [] the decrease in the mass concentration of iron and nickel is balanced by the increase in Al and Si and assuming an increase in Mg, according to reaction (2), equal to that of Si over the Earth’s lifetime. [] a total decrease of ∼7% in Fe and Ni concentrations and a consistent increase of ∼7% in the lighter chemical element concentrations (Mg, Al and Si) between the Hadean period (Hadean Eon, 4.5–3.8 Gyr ago) and the Archean period (Archean Eon, 3.8–2.5 Gyr ago) []. Similarly, a decrease of ∼ 5% in the heavier elements (Fe and Ni) and a related increase (∼5%) in the concentrations of lighter ones (Mg, Al and Si) can be considered between the Archean period (Archean Eon, 3.8–2.5 billion years ago) and more recent times. The Earth’s protocrust in the Hadean era was strongly basaltic, with a composition similar to that of the proto-planets (chondrites).

[] As a matter of fact, Mg is not only a resulting element, as shown by piezonuclear reaction (2), but can also be considered as a starting element of another possible piezonuclear reaction:

Mg 24/12 → 2C 12/6. (6)

Reaction (6) could be very important for the evolution of both the Earth’s crust and the Earth’s atmosphere, and considered as a valid explanation for the high level of CO2 concentration (∼15%) in the Archean Earth’s atmosphere. In addition, the large amount of C produced by Mg transformation (∼3.5% of the Earth’s crust) has undergone a slow but continuous diminishing in the CO2 composition of the Earth’s atmosphere, as a result of the escape which also involves other atmospheric gases like He and H.

Piezonuclear reaction (6) can also be put into correlation with the increase in seismic activity that has occurred over the last century. Very recent evidence has shown CO2 emissions in correspondence to seismic activity: significant changes in the emission of carbon dioxide were recorded in a geochemical station at El Hierro, in the Canary Islands, before the occurrence of several seismic events during the year 2004. Appreciable precursory CO2 emissions were observed to start before seismic events of relevant magnitude, and to reach their maximum values some days before the earthquakes.