Radiation, concentrated

The presence of radiation in the workplace - which is an inevitable consequence of the radioactivity of uranium - requires that additional safety precautions be taken over and above those observed in other similar workplaces. There are generally three sources from which radiation exposure may occur (i) radiation emitted from uranium ore in-situ and/or during handling (ii) airborne radiation resulting from the decay of radon gas released from the ore and uranium dust and (iii) contamination by ore dust or concentrate. Radiation levels around uranium mining and milling facilities are quite low - for the most part only a few times the natural background levels - and they decrease rapidly as the distance from... 

Study of the behavior of biomass subjected to concentrated radiation (solar pyrogasification). Determination of the conditions enhancing the production of either oils or gases for electricity generation or chemical preparation. 

Siddiqi MA, Bothe E (1987) Single- and double-strand break formation in DNA irradiated in aqueous solution Dependence on dose and OH radical scavenger concentration. Radiat Res 112 449-463... 

The specific heat at constant pressure, Cpf of the HIP-treated sample with nominal composition LaVg 25 0,7504 was measured over the temperature range 4-400 K by the heat pulse method in a calorimeter that incorporates a feedback system to regulate the temperature of concentric radiation shields surrounding the sample (9). The Cp values are accurate to within 1%, as determined by calibration runs using a polycrystalline copper sample and a sapphire single crystal sample. 

The detector of GB-A-2260218 comprises a photo-responsive material and an array of planar antennae formed thereon which concentrate radiation in fringe fields at antenna edges and extremities interacting with the photo-responsive material. This structure allows the photo-responsive material to be formed thinly, which reduces volume-dependent generation-recombination noise with consequent increase in responsivity and detectivity. Furthermore, reduced element thickness allows higher element resistance. 

An alternative concept is the so-called direct absorption concept, which applies solar-receiver reactors. According to this concept a solar reformer was developed by DLR in the SOLASYS project (Tamme, 2003) based on earlier experiences in the projects SCR and CAESAR (Bauer, 1994). It allows the concentrated radiation to penetrate through a transparent aperture into the reformer, where it is absorbed directly by the irradiated absorber. The reaction gases pass through the absorber which serves simultaneously as a heat transfer unit and as support for the catalyst. The quartz window, used as aperture closure, enables the reformer to be operated under pressure. A schematic of the solar receiver is shown in Figure 3 (right). The reformer was operated up to 0.9 MPa and 780°C. The pilot reformer was tested at a power level of about 300 kW(th) at the solar tower of the Weizmann Institute of Science in Rehovot, Israel. In a follow-up project SOLREF (Moller, 2006), the operation conditions will be about 1.5 MPa and 950°C. 

Boutin O, Lede J, Use of a Concentrated Radiation for the Determination of the Elementary Mechanisms of Cellulose Theima] Decomposition , these proceedings. 

Fig. 4 reports the theoretical variations of q , q y and q as a function of Tw The limit of char formation determined in the present work (qi = 9 x 10 W ra ) is also represented. It can be seen that ablation is the most efficient process of heating during which char would be formed only at low wall temperatures (< 800 K). Gas exchange and non concentrated radiation lead to the lowest values of q and as a matter of fact, char is usually observed when each of these two situations occurs separately. 

Cellulose can be pyrolysed under well characterised conditions of absorbed heat flux densities by using a concentrated radiation. Experiments have been performed with cellulose pellets submitted to controlled times of irradiation at the focal zone of an image furnace. 

Fig. 5.66 a Flat radiation shields between two flat parallel walls 1 and 2. b Concentric radiation shields between concentric spheres or very long cylinders 1 and 2... 

Another possibility lies in the use of equipment being developed by Manowitz and co-workers (H2). The equipment, called a continuous calciner, converts aqueous slurries to compact fused salts. One source of fission products of high specific activity would be the Mn02 scavenge cake used in separations processes, to remove most of the fission products in a head-end treatment prior to a solvent extraction process. Mn02 may be dissolved in fused caustic in a continuous calciner to form a highly concentrated radiation source. 

In the AAS method a solution is vaporized in an acetylene-oxygen flame so that the atoms of the unknown element are present in the flame. If, for instance, the intention is to determine the molybdenum concentration, radiation emitted from a cathode ray lamp with a molybdenum electrode is allowed to pass through the flame. 

Using this approach, we can now measure pressure, temperature, ion and gas concentration, radiation level, and other important process variables with sensors that directly incorporate all circuitry needed to self-compensate for environmental changes and to... 

The schematic of a standard on-top bath cryostat [8] is shown in Figure 3.5.3. Radiation shields and a fN2 tank surround the inner fHe tank. At the bottom of the IHe tank, the microscope is suspended by springs and radiation cooled by two concentric radiation shields that are connected to the f He and fN2 tanks, respectively. For fast conductive cooling, the microscope is pressed against the base plate of the f He reservoir. After cooling down, the microscope is released from the base plate for better vibration isolation [8j. The helium consumption of such a cryostat is about 0.11 h [12]. 

Recently, the photochemical attachment of n-alkanes with 8,19, 20, 21, 24, and 28 carbon atoms and 1-eicosene to pyrene has been investigated. The dependence of attachment selectivity (based on the degree of retention of the pyrenyl aromatic system in the products and the fraction of them in which attachment is at the 1-position of the -alkane and the 1-position of pyrene) and efficiency (based on the relative yields of attached products when irradiations were performed under conditions of constant flux) on solvent phase, pyrene concentration, radiation wavelength (above and below 300 nm), and alkane chain length was explored. Without exception, attachment was more efficient and selection was greater in the solid than in the liquid phases of the alkanes. Also, the efficiency decreased significantly when initial pyrene concentrations were > 10" M. Reactions in the sohd state of solid -alkanes with >21 carbon atoms yielded l-(n-alkyl)pyrenes almost exclusively when the radiation wavelength was >300 nm. This behavior was attributed, in part, to the location of the pyrene molecules at the interfaces between alkane lamellae. 

Non-concentrating photoreactors have no moving parts or solar tracking devices (see Fig. 7.3c). This kind of reactor does not concentrate radiation, and because of this, efficiency is not limited by factors connected with reflection, concentration, or solar tracking. In this system, optical efficiency is higher as compared with concentrating reactors. Moreover, non-concentrating system can utilize the diffuse and direct portion of the solar UVA [182]. One-sun collectors are usually cheaper than PTCs because their elements are simpler, and the surface required for their installation is smaller [178]. 

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