Fe Melting Transition: Electrical Resistivity, Thermal Conductivity, and Heat Flow at the Inner Core Boundaries of Mercury and Ganymede

The electrical resistivity and thermal conductivity behavior of Fe at core conditions are important for understanding planetary interior thermal evolution as well as characterizing the generation and sustainability of planetary dynamos. We discuss the electrical resistivity and thermal conductivity of Fe, Co, and Ni at the solid–liquid melting transition using experimental data from previous studies at 1 atm and at high pressures. With increasing pressure, the increasing difference in the change in resistivity of these metals on melting is interpreted as due to decreasing paramagnon-induced electronic scattering contribution to the total electronic scattering. At the melting transition of Fe, we show that the difference in the value of the thermal conductivity on the solid and liquid sides increases with increasing pressure. At a pure Fe inner core boundary of Mercury and Ganymede at ~5 GPa and ~9 GPa, respectively, our analyses suggest that the thermal conductivity of the solid inner core of small terrestrial planetary bodies should be higher than that of the liquid outer core. We found that the thermal conductivity difference on the solid and liquid sides of Mercury’s inner core boundary is ~2 W(mK)−1. This translates into an excess of total adiabatic heat flow of ~0.01–0.02 TW on the inner core side, depending on the relative size of inner and outer core. For a pure Fe Ganymede inner core, the difference in thermal conductivity is ~7 W(mK)−1, corresponding to an excess of total adiabatic heat flow of ~0.02 TW on the inner core side of the boundary. The mismatch in conducted heat across the solid and liquid sides of the inner core boundary in both planetary bodies appears to be insignificant in terms of generating thermal convection in their outer cores to power an internal dynamo suggesting that chemical composition is important.

Radiation shielding and gamma ray attenuation properties of some polymers

In the present work we investigated the gamma radiation parameters as mass attenuation coefficients ?/?, the total atomic scattering cross-sections ??, the electronic scattering cross-sections se, the effective atomic numbers Zeff, and the effective electron densities Neff for some polymers such as polyoxymethylene (CH2O), poly acrylonitrile (C3H3N), natural rubber (C5H8), poly ethyl acrylate (C5H8O2), polyphenyl methacrylate (C10H10O2), and polyethylene tetraphthalate (C10H8O4). The gamma ray photons were detected by NaI(Tl) detector with resolution of 8.2 % at 662 keV, using radioactive gamma ray sources 57Co, 133Ba, 137Cs, 54Mn, 60Co, and 22Na at energies 122, 356, 511, 662, 840, 1170, 1275, and 1330 keV. Values of ?/? for the chosen polymers decrease with increasing energy. The results of investigated data are useful in plastic industry, building materials, agriculture fields radiation shielding, accelerator centers, polymer industry, medical field, etc.

Atypical thermal transport in Cu nanorods in the diffusive–ballistic crossover

We propose a simple theoretical calculation scheme based on the phenomenological Fourier heat-flow formalism to study thermal transport behaviors in nanoscale copper rods. The axial heat transport is characterized by a new super-oscillatory feature along with small-amplitude heat spikes. It is anticipated that these atypical spikes are generated by accumulation of localized “hotspots” that have low heat dissipation characteristics. In the case of radial transport, we witness the existence of three distinct heat regimes owing to buildup of hot electrons after experiencing ballistic scattering events. It is important to note that, even though the nanorod diameter is comparable to or smaller than the electron mean free path length, λmfp ∼ 30 nm; multiple ballistic electronic scattering from the outer surface of the nanorods and subsequent accrual into several layers through secondary collisional events has led to concentric heat zones. The hotspots disappear when the nanorod diameter exceeds λmfp.