Irradiation materials

Radioactive Gemstones. Zircon can contain radioactive elements, but the amount in jewelry-grade material is insignificant. Some of the treatments of Table 3 may leave irradiated material radioactive. Such gemstones have been released on rare occasions without the required cooling-off period (10). 

PL can be used as a sensitive probe of oxidative photodegradation in polymers. After exposure to UV irradiation, materials such as polystyrene, polyethylene, polypropylene, and PTFE exhibit PL emission characteristic of oxidation products in these hosts. The effectiveness of stabilizer additives can be monitored by their effect on PL efficiency. 

The energy available in various forms of irradiation (ultraviolet, X-rays, 7-rays) may be sufficient to produce in the reactant effects comparable with those which result from mechanical treatment. A continuous exposure of the crystal to radiation of appropriate intensity will result in radiolysis [394] (or photolysis [29]). Shorter exposures can influence the kinetics of subsequent thermal decomposition since the products of the initial reaction can act as nuclei in the pyrolysis process. Irradiation during heating (co-irradiation [395,396]) may exert an appreciable effect on rate behaviour. The consequences of pre-irradiation can often be reduced or eliminated by annealing [397], If it is demonstrated that irradiation can produce or can destroy a particular defect structure (from EPR measurements [398], for example), and if decomposition of pre-irradiated material differs from the behaviour of untreated solid, then it is a reasonable supposition that the defect concerned participates in the normal decomposition mechanism. 

Depth of EB penetration The depth of penetration of energetic electrons into a material at normal angle of incidence is directly proportional to the energy of the electrons and inversely proportional to the density of the material [49,50]. The depth is expressed as a product of penetration distance and the density of the material (i.e., 1 g/cm = 1 cm X 1 g/cm ). The radiation energy and thus the type of electron accelerator to be used are dependent on the required penetration depth, the density of the irradiated material, and the chosen irradiation system. If one measures the density (d) in gram per cubic centimeter (g/cm ) and the layer thickness (T) in millimeter (mm), one can determine the radiation energy ( ) necessary for optimal homogeneity from [40] ... 

Absorbed Dose—The energy imparted to matter by ionizing radiation per unit mass of irradiated material at the place of interest. The unit of absorbed dose is the rad. One rad equals 100 ergs per gram. In SI units, the absorbed dose is the gray which is 1 J/kg (see Rad). 

Peng, F., Wang, H., Yu, H. and Chen, S. (2006) Preparation of aluminum foil-supported nano-sized ZnO thin films and its photocatalytic degradation to phenol under visible light irradiation. Materials Research Bulletin, 41, 2123-2129. 

Perhaps the most fruitful of these studies was the radiolysis of HCo(C0)4 in a Kr matrix (61,62). Free radicals detected in the irradiated material corresponded to processes of H-Co fission, electron capture, H-atom additions and clustering. Initial examination at 77 K or lower temperatures revealed the presence of two radicals, Co(C0)4 and HCo(C0)4 , having similar geometries (IV and V) and electronic structures. Both have practically all of the unpaired spin-density confined to nuclei located on the three-fold axis, in Co 3dz2, C 2s or H Is orbitals. Under certain conditions, a radical product of hydrogen-atom addition, H2Co(C0)3, was observed this species is believed to have a distorted trigonal bipyramidal structure in which the H-atoms occupy apical positions. 

Rp)max w ich stays nearly constant up to 40% conversion. It decreases later on because of mobility restriction brought upon by gelation and solidification of the UV-irradiated material. This behavior is best illustrated in Figure 4 where the instant rate of polymerization (Rp), calculated from the slope of the curve recorded by RTIR spectroscopy, was plotted as a function of the exposure time. 

The choice of material for SG is very important and was first reported a decade ago by Brodeur and Chin [21, 75] using a femtosecond laser in condensed media. They observed that spectral broadening of the white light depends on the band-gap of the irradiated material [75]. Furthermore, they found the existence of a band gap threshold, 4.7eV, below which a medium... 

Mechanical Property Testing. Mechanical tests were performed on both unirradiated and irradiated materials at -157°C, 24°C, and 121°C. Specimens were kept dry prior to testing in an environmental chamber mounted in a tensile testing machine. Tensile test specimens of [0]4, [10]4, [45]4, and [90]4 laminates were cut from 4-ply composite panels. All specimens were straight-sided coupons. For tension and shear tests the length/width aspect ratio was 8. For the compression tests the aspect ratio was 0.25 and the unsupported length was 0.64 cm. The [0]4 laminates were used to measure the ultimate tension and compression strength, Xit the axial... 

Electron irradiation causes chain scission and crosslinking in polymers. Both of these phenomena directly affect the glass transition temperature (Tg) of the materials. Thermomechanical (TMA) and dynamic-mechanical analysis (DMA) provide information about the Tg region and its changes due to radiation damage. Therefore, DMA and TMA were performed on all irradiated materials. 

Absorbed dose Energy imparted to matter by ionizing radiation per unit mass of irradiated material at the place of interest in that material expressed in rad units. 

The sensitivity to temperature is reminiscent of that seen in Ron s study (188) of o-methoxy-m-cinnamic acid, 129. When crystals of this substance are exposed to light at low temperatures (< — 80°C), there occurs a gradual isomerization of the molecules to the trans form, 130, with formation of a little of the (2 + 2) photodimer, 131, of the latter. If this irradiated material is warmed in the dark to + 60°C, recooled, and reirradiated for a short while, there is a jump in the amount of dimer. This behavior is interpreted as follows ... 

This useful technique has made many contributions to radio- and nuclear chemistry, although primarily for investigational purposes rather than those of separation for its own ends. Thode and his co-workers have made many investigations into the inert gases produced in fission and it was by these means that the fine structure of fission was first discovered (79), (121). Since then several other elements, the rare-earths, strontium, caesium, zirconium, and molybdenum (35), (50), (132) have been investigated, and the isotopic ratios obtained provide relative values of fission-yields which are more accurate than can be obtained by standard radiochemical means. The latter technique, however, requires rather less heavily irradiated material than the former. 

In the first attempts to overcome the background problem using decay time, the variation of the fluorescence decay time as a function of wavelength across the entire emission profile for a variety of materials have been used (Measures 1985). For a variety of rocks and minerals, it was proved that this information represents a new kind of signature, the so called fluorescence decay spectrum, that possesses considerable discrimination power, being able to characterize the irradiated material with far superior precision than the normal luminescence spectrum (Fig. 7.2). 

In this condition, Bethe formulated the stopping power for electron according to the Born approximation. Stopping power is a property of irradiated materials and gives the amount of energy deposited per unit path length, —dU/dx. 

Where, E is the energy, x is the length, and e are the rest mass and charge of electrons, respectively, v is the velocity of electron, N and Z are the number of atoms in unit volume and atomic number of the irradiated material, respectively, and /I is the relative velocity represented by v/c, where c is the velocity of light. 

Photocatalytic bactericidal activity experiments were performed using E. coli with untreated and TiO -coated fabric and aluminum foil (Fig. 1.6) and with or without UV-A irradiation. Photocatalytic bactericidal properties of TiO -coated fabric and foil were observed after 30 min. The most distinctive difference between coated and UV-irradiated materials was observed initially. This is a clear demonstration of the photocatalytic ability of TiO and accelerated surface decontamination. We observed complete bacteria killing only on aluminum foil coated with TiO, and partial killing on the coated fabric. These results suggest that TiO coated materials have bactericidal properties. 

The energy deposited in the irradiated material causes a temperature rise (AT), which depends on absorbed dose and specific heat ... 

Absorbed dose The amount of energy absorbed per unit mass of the irradiated material. 

Dose In the context of chemicals, the temi dose means the amount, quantity, or portion of the chemical exposed to or applied to the target (e.g., a human being). It may also refer to a consistent measure used in toxicological testing to determine acute and chronic toxicities. An alternate definition is die amount of ionizing radiation energy absorbed per unit mass of irradiated material at a specific location, such as a part of die human body, measured in REMS, or an inanimate body, measured in rads. 

---