Denis Stanić

Radon anomaly in soil gas as an earthquake precursor

The mechanical processes of earthquake preparation are always accompanied by deformations; afterwards, the complex short- or long-term precursory phenomena can appear. Anomalies of radon concentrations in soil gas are registered a few weeks or months before many earthquakes. Radon concentrations in soil gas were continuously measured by the LR-115 nuclear track detectors at site A (Osijek) during a 4-year period, as well as by the Barasol semiconductor detector at site B (Kasina) during 2 years. We investigated the influence of the meteorological parameters on the temporal radon variations, and we determined the equation of the multiple regression that enabled the reduction (deconvolution) of the radon variation caused by the barometric pressure, rainfall and temperature. The pre-earthquake radon anomalies at site A indicated 46% of the seismic events, on criterion M>or=3, R<200 km, and 21% at site B. Empirical equations between earthquake magnitude, epicenter distance and precursor time enabled estimation or prediction of an earthquake that will rise at the epicenter distance R from the monitoring site in expecting precursor time T.

Measurements of neutron radiation in aircraft

Radiation environment is a complex mixture of charged particles of the solar and galactic origin, as well as of secondary particles created in an interaction of galactic cosmic particles with the nuclei of the Earths atmosphere. A radiation field at aircraft altitude consists of different types of particles, mainly photons, electrons, positrons and neutrons, with a large energy range. In order to measure a neutron component of the cosmic radiation, we investigated a few combinations of a track etch detector (CR-39, LR-115) with a plastic converter or boron foil. Detector calibration was performed on neutrons coming from the nuclear reactor, as well as in the CERN-EU high-energy Reference Field (CERF) facility. From November 2007 to September 2008, the neutron dose equivalent was measured by the track detectors during five aircraft flights, in the north geographical latitude from 21° to 58°; the respective average dose rate, determined by using the D-4 detector (CR-39/B), was Ḣ(n)=5.9 μSv/h. The photon dose rate, measured by the electronic dosimeter RAD-60 SE, had the average value of Ḣ(f)=1.4 μSv/h.

Anisotropic transport properties of the Al13TM4 and T-Al–Mn–Fe complex metallic alloys

Anisotropy of the transport properties (electrical resistivity, ρ(T), thermoelectric power, S(T), and thermal conductivity, κ(T)) of the Al76Co22Ni2 (Y-Al–Ni–Co), o-Al13Co4 and T-Al72.5Mn21.5Fe6.0 complex metallic alloys was investigated experimentally. These compounds belong to the class of approximants in decagonal quasicrystals phases with stacked-layer crystallographic structure and enabled us to study the evolution of transport properties with increasing structural complexity and the unit cell size. For Y-Al–Ni–Co and o-Al13Co4, the anisotropic electronic transport coefficients were analyzed theoretically by Boltzmann transport theory and ab initio calculated anisotropic Fermi surface. The non-metallic anisotropic electrical resistivity of the T-Al72.5Mn21.5Fe6.0 may be analyzed in a semi-quantitative way by the theory of quantum transport of slow charge carriers.

Hall effect in Taylor-phase and decagonal Al3(Mn,Fe) complex intermetallics

Abstract The Hall coefficient (RH) of Al73Mn27–xFex (x = 0, 2, 4 and 6) complex metallic alloys has been measured in the temperature interval from 90 to 400 K. All the alloys are T (Taylor) phase except Al73Mn21Fe6 that is a decagonal (d) quasicrystal. The Hall coefficients of all the samples are positive and they decrease strongly with the increase of temperature according to the Curie-Weiss [C/(Tθ)] law. Therefore, for the separation of the normal (R0) and anomalous (RS) Hall coefficients, the results for the paramagnetic susceptibility (χ) in the corresponding temperature interval have been used. The values deduced from RH(χ) plots are about –2 × 10–10 m3 C–1 for R0, and about 5 × 10–7 m3 C–1 for RS. When the possible dependence of RS on temperature, that is due to the temperature dependence of the electrical resistivity ρ(T), is taken into account the values are about zero for R0, and about 3 × 10–7 m3 C–1 for RS (295 K). No significant composition dependence of R0 has been detected.

Identification and mapping of radon-prone areas in Croatia—preliminary results for Lika-Senj and the southern part of Karlovac counties

Long-term indoor radon measurements performed by LR 115 track etched detectors in Croatian homes during 2003-04 showed that the arithmetic means of radon concentrations in Lika-Senj and the southern part of Karlovac counties were three times higher (198 Bq m(-3)) than in houses at national level (68 Bq m(-3)). Recently, indoor radon measurements in randomly selected houses were investigated. The obtained values in these new measurements have confirmed the values obtained 10 y ago (the average radon value in 225 investigated houses in this area is 223 Bq m(-3)). Radon concentrations in soil gas were measured in September and October 2012 and 2013 with the AlphaGUARD measuring system. Areas with both elevated indoor radon levels and radon in soil gas were identified (some micro locations in Korenica, Ličko Lešće, Generalski Stol, Slunj and Ogulin) and visually presented in the form of maps using the inverse distance weighting approach.

Electrical, magnetic and thermal properties of the δ-FeZn10 complex intermetallic phase

We report the electrical, magnetic, and thermal properties of the δ-FeZn10 phase in the zinc-rich domain of the Fe-Zn system. The δ-FeZn10 phase possesses high structural complexity typical of complex metallic alloys: a giant unit cell comprising 556 atoms, polyhedral atomic order with icosahedrally coordinated environments, fractionally occupied lattice sites, and statistically disordered atomic clusters that introduce intrinsic disorder into the structure. Structural disorder results in suppression of the electrical and heat transport phenomena, making δ-FeZn10 a poor electrical and thermal conductor. Structural complexity results in a complex electronic structure that is reflected in the opposite signs of the thermoelectric power and the Hall coefficient. The δ-FeZn10 phase is paramagnetic down to the lowest investigated temperature of 2 K with a significant interspin coupling of antiferromagnetic type. Specific heat indicates the formation of short-range-ordered spin clusters at low temperatures, very likely a precursor of a phase transition to a collective magnetic state that would take place below 2 K. The magnetoresistance of δ-FeZn10 is sizeable, amounting to 1.5% at 2 K in a 9-T field. The electrical resistivity exhibits a maximum at about 220 K, and its temperature dependence could be explained by the theory of slow charge carriers, applicable to metallic systems with weak dispersion of the electronic bands, where the electron motion changes from ballistic to diffusive upon heating.

Electrical, magnetic and thermal properties of the d-FeZn 10 complex intermetallic phase

We report the electrical, magnetic, and thermal properties of the δ-FeZn10 phase in the zinc-rich domain of the Fe-Zn system. The δ-FeZn10 phase possesses high structural complexity typical of complex metallic alloys: a giant unit cell comprising 556 atoms, polyhedral atomic order with icosahedrally coordinated environments, fractionally occupied lattice sites, and statistically disordered atomic clusters that introduce intrinsic disorder into the structure. Structural disorder results in suppression of the electrical and heat transport phenomena, making δ-FeZn10 a poor electrical and thermal conductor. Structural complexity results in a complex electronic structure that is reflected in the opposite signs of the thermoelectric power and the Hall coefficient. The δ-FeZn10 phase is paramagnetic down to the lowest investigated temperature of 2 K with a significant interspin coupling of antiferromagnetic type. Specific heat indicates the formation of short-range-ordered spin clusters at low temperatures, very likely a precursor of a phase transition to a collective magnetic state that would take place below 2 K. The magnetoresistance of δ-FeZn10 is sizeable, amounting to 1.5% at 2 K in a 9-T field. The electrical resistivity exhibits a maximum at about 220 K, and its temperature dependence could be explained by the theory of slow charge carriers, applicable to metallic systems with weak dispersion of the electronic bands, where the electron motion changes from ballistic to diffusive upon heating.

Anisotropic electrical and thermal conductivities of the Al76Co22Ni2 decagonal approximant

Abstract The electrical (σ) and thermal conductivity (λ) of Al76Co22Ni2 decagonal approximant has been measured along three orthogonal directions a*, b and cof the Al76Co22Ni2 unit cell, where (a, c) monoclinic atomic planes are stacked along the perpendicular b direction. Electrical conductivity is relatively high in all crystalline directions, appearing in the order σb >> σc > σa*. Thermal conductivity appears in the same order λb > λc > λa*, so that b is the most conducting direction for both electricity and heat. The results are compared to the reported anisotropic electrical and thermal conductivity of the d-Al–Ni–Co decagonal quasicrystal.

Thermal and electrical conductivities in Al-based complex metallic alloys

A study is reported of the heat transport of AlPd(Mn, Fe, Co, Rh) complex metallic alloys that belong to an interesting class of Al-based alloys characterized by giant unit cells with quasicrystal-like cluster substructure. The electrical and thermal conductivity were investigated in the temperature range 8–300 K, in order to see how the exceptional structural complexity and the coexistence of two competing physical length scales affect the transport properties of these materials. The alloys have electrical conductivity typical of metallic alloys, and low thermal conductivity which is at room temperature comparable to that of thermal insulators, e.g. amorphous SiO2 and Zr/YO2 ceramics.

Assessing the radiological load on the environment in the middle Danube river basin on the basis of a study of the Kopački Rit Nature Park, Croatia

A study of the environmental radioactivity in the Kopački Rit Nature Park, Croatia, is presented. This wildlife reserve is part of the Middle Danube River Basin, and it is exposed to various pollutants due to a number of human activities in the surroundings, where there is a nuclear power plant and also urban centres and areas of intense agricultural production. Results for the activity concentrations of soil and surface water samples do not indicate any elevated radioactivity level, which is confirmed by on-site measurements of ambient dose rate equivalent. An assessment of the radiological load on the local biota, carried out using the ERICA tool, implies an overall low radiological risk even if conservative values of the risk quotient are used. Therefore, human activities do not have a significant effect on the radiological load on the Kopački Rit area. A similar conclusion might be made with regard to numerous similar environments in the Middle Danube River Basin.