Direct Absorption Of Radiation Research Articles

Still potentially deadly after all these years: how to safely handle and display radioactive dinosaurs and other fossils

Most curators and collection managers responsible for a geological collection will be aware of the risk posed by rocks and minerals which emit ionising radiation and will have put measures in place to reduce this risk to collection users. However, fewer people are aware that fossils, ranging from fish to dinosaurs, and even coprolites can be radioactive too. A fossil may be radioactive if it has been exposed to uranium-bearing fluids during diagenesis and fossilisation processes. Any uranium-enriched groundwater moving through nearby porous deposit can contaminate the rocks and fossils with radioactive elements. Over time the skeletons or other remains being fossilised incorporate these elements into their min- eral structure, such that the concentration of radioactive elements in fossils may be greater than that in the host rock. The greater the volume of fossil material, e.g. a large dinosaur bone, the greater the potential for higher levels of radioactivity, and a greater risk to hu- mans (although some small specimens can be highly radioactive). Whilst most radioactive fossils may not present a danger to health through direct absorption of radiation, unless there is prolonged exposure at close quarters (e.g. hundreds of hours), a risk is posed by the ingestion or inhalation of small radioactive particles derived from the specimen. Here, we describe what measures can be taken to reduce these risks and also provide a list of locations around the world known to yield radioactive fossils, which we hope can be augmented by others. The general principles discussed here are widely applicable, but it is recommended that specialist advice is sought to comply with national regulations in each instance. In ad- dition to the health risks posed by these specimens, there are also legal penalties for failing to comply with regulations.

Contribution of Topical Antioxidants to Maintain Healthy Skin—A Review

The skin is constantly exposed to various environmental stresses, in particular to the damage caused by pollution and ultraviolet radiation (UV), and as a consequence, the horny extract can be negatively impacted by the harmful influence of some of its surface components. The mechanisms involved in the degradation processes promoted by UV radiation are driven by the direct absorption of radiation via cellular chromophores, the formation of excited states and the consequent chemical reactions, or even by the photosensitization mechanisms, in which UV light is absorbed by the sensitizers that are excited and their reactions promote the formation of reactive oxygen species (ROS). The mechanisms of polluting agents are not yet fully understood, however, they indicate that one of the main mechanisms involved is oxidative stress by lipid peroxidation, with the ability to promote damage to the composition of sebum, the quality of the stratum corneum and also, promote aging skin. Recent studies demonstrate the potential of antioxidant agents, with an emphasis on products of natural origin, which try to promote the maintenance of the physiological balance of the skin.

First experimental studies of solar redox reactions of copper oxides for thermochemical energy storage

Thermochemical redox processes are currently considered one of the most promising methods for thermal storage of solar energy. Among the different types of materials available for this purpose, metal oxides allow higher operation temperatures in CSP systems. This is in agreement with the new R&D trends that focus on increasing the temperature to augment the efficiency. Copper oxide was previously proposed as a valid metal oxide for thermochemical storage. However, no demonstrative experiments had been carried out so far under solar radiation. In this work, the suitability of copper oxide was proved in a solar furnace. The employed solar reactor was a rotary kiln device with direct radiation absorption on reactive particles, which is a configuration that guarantees higher operation temperatures than other types of solar reactors. Given results include the performance of the CuO reduction in the rotary kiln under argon atmosphere and the cyclability of the pair CuO/Cu2O in air.

Scaling and direct stability analyses of natural convection induced by absorption of solar radiation in a parallelepiped cavity

The present study considers the early stage of the flow development in a water-filled, three-dimensional parallelepiped cavity subject to solar radiation. The thermal structure consists of an upper stable stratification due to internal heating, provided by the direct absorption of radiation, and a bottom potentially unstable boundary layer due to the absorption and re-emission of the residual radiation by the bottom boundary. The growth of the competing thermal layers and the stability properties of the bottom thermal boundary layer are investigated by means of a scaling analysis and a direct stability analysis based on three-dimensional numerical simulation. The scaling relations are benchmarked against the numerical simulation, and the effects of the normalised water depth, the Rayleigh number and the box aspect ratio on the thermal instability are studied.

Relaxation of H2O from its /04>- vibrational state in collisions with H2O, Ar, H2, N2, and O2.

We report rate coefficients at 293 K for the collisional relaxation of H2O molecules from the highly excited /04>(+/-) vibrational states in collisions with H2O, Ar, H2, N2, and O2. In our experiments, the mid R:04(-) state is populated by direct absorption of radiation from a pulsed dye laser tuned to approximately 719 nm. Evolution of the population in the (/04>(+/-)) levels is observed using the combination of a frequency-quadrupled Nd:YAG laser, which selectively photolyses H2O(/04>(+/-)), and a frequency-doubled dye laser, which observes the OH(v=0) produced by photodissociation via laser-induced fluorescence. The delay between the pulse from the pump laser and those from the photolysis and probe lasers was systematically varied to generate kinetic decays. The rate coefficients for relaxation of H2O(/04>(+/-)) obtained from these experiments, in units of cm3 molecule(-1) s(-1), are: k(H2O)=(4.1+/-1.2) x 10(-10), k(Ar)=(4.9+/-1.1) x 10(-12), k(H2)=(6.8+/-1.1) x 10(-12), k(N2)=(7.7+/-1.5) x 10(-12), k(O2)=(6.7+/-1.4) x 10(-12). The implications of these results for our previous reports of rate constants for the removal of H2O molecules in selected vibrational states by collisions with H atoms (P. W. Barnes et al., Faraday Discuss. Chem. Soc. 113, 167 (1999) and P. W. Barnes et al., J. Chem. Phys. 115, 4586 (2001).) are fully discussed.

Endothermic reactors for an ammonia based thermochemical solar energy storage and transport system

The ammonia dissociation reaction is one of a number of reactions which has been investigated for use in closed loop solar thermochemical energy storage systems, over a period of nearly two decades. A recent series of experiments with an electrically heated high pressure ammonia dissociation reactor has validated a two dimensional pseudo-homogenous theoretical reactor model, established rate parameters for the catalyst used, paved the way for a closed loop demonstration and simulated operation of a receiver/reactor under solar operation. The model has subsequently been used to investigate full sized receiver/reactor options for a 20 m 2 paraboloidal dish. Technically feasible designs based on: directly irradiated catalyst filled tubes, sodium reflux heat transfer to catalyst tubes and direct absorption of radiation using a windowed pressure vessel, have been identified.

High-resolution far-infrared observations of the Ring Nebula

High spatial resolution 50 and 100 micron observations of the Ring Nebula reveal a far-infrared emission peak close to the center of the nebula where atomic and molecular emission is at a minimum. Dust in this central peak emission region is heated by direct absorption of radiation from the central star. While the dust temperature in the central peak region is about 50 K (dust emissivity index of 1.5), the temperature of the bulk of the dust located in the regions of the ionized nebular core and the neutral molecular gas is on average lower than 50 K. Ly(alpha) photons are sufficient for heating the dust grains within the nebular core. Far-infrared emission is also found from grains mixed with the molecular gas outside the main ionized nebular core.

An action spectrum for ultraviolet radiation-induced membrane damage in Escherichia coli K-12.

AbstractA wild‐type Escherichia coli K‐12 strain was irradiated using monochromatic radiation in the range 254 to 405 nm. A measure of the cell membrane damage induced at each wavelength was investigated by comparing cell viability after irradiation on nutrient agar and on minimal medium containing either a low or high inorganic salt concentration. An action spectrum for lethality and for cell membrane damage was then determined. From 254 to 310 nm lethality closely corresponded to the absorption spectrum of DNA, and there was no indication of membrane damage. However, above a wavelength of 310 nm, the direct absorption of radiation by DNA could not account for the sensitivity observed. Moreover, at wavelengths longer than 310 nm, cell membrane damage was induced and by an increasing factor up to a peak at 334 nm. At the longer wavelengths of 365 and 405 nm, there was a gradual decrease from the peak of damage to cell membranes induced by 334 nm radiation. These results indicate that cell membrane damage may contribute significantly to near‐UV radiation‐induced cell lethality in wild‐type E. coli K‐12.

Generation of oxygen O2(1.DELTA.g) by direct absorption of radiation by ground-state oxygen

Generation of oxygen O2(1.DELTA.g) by direct absorption of radiation by ground-state oxygen

The action spectrum (313-435 nm) for killing Hoechst 33258 treated Chinese hamster ovary cells containing bromodeoxyuridine substituted DNA.

Abstract— The action spectrum (313–435 nm) for killing Chinese hamster ovary cells containing bromo‐deoxyuridine substituted DNA and treated with Hoechst 33258 was very similar to the absorption spectrum of the dye bound to chromatin, indicating that sensitization was mediated through direct absorption of radiation by the dye. The ratio of sensitization cross sections for 365 nm (plus dye) to 313 nm (no dye) was approx. 30 while this ratio for strand breakage was about one. These results are in agreement with the hypothesis that strand breaks are not the major class of lethal photoproducts induced via Hoechst 33258 sensitization.

Anionic Polymerization of β-Nitrostyrene under the Influence of High Energy Radiation

Abstract β-Nitrostyrene (βNS) was polymerized in aprotic solvents. The rate of polymerization increased in the series dimethyl sulfoxide ≈ dimethylformamide < N-methylpyrrolidone < hexamethylphosphoric triamide (HMPT). From copolymerization experiments with α-methylstyrene and methacrylonitrile, evidence for an ionic mechanism was obtained. Electron scavengers inhibited the polymerization. Thus it was concluded that in dilute solution the initiation comprises the thermaliza-tion of electrons which become solvated and react with β NS to form the radical anion βNS. Pulse radiolysis experiments were carried out in HMPT. The spectrum of an intermediate (presumably -βNS−) was recorded. By measuring the rates of the formation of -βNS− and of the decay of solvated electrons the rate constant k e (9 ± 3) × 109 liter/mole-sec was determined. At higher monomer concentrations the polymerization was autoinhibited which is probable due to the fact that direct absorption of radiation by the monomer becomes important.