Radiations ionizing

Gamma radiation is the most convenient type of high-energy radiation for initiating polymerization because its high penetrating power affords uniform irradiation of the system. Because gamma rays are absorbed to the same extent by solids as by liquids, solid monomers can be polymerized readily. This allows polymerization of many monomers at low temperatures. 

The chemical effects of the different types of radiation on molecules are qualitatively the same, though there are quantitative differences. Molecular excitation may occur with the subsequent formation of radicals in the same manner as in photolysis, but ionization of a compound by ejection of an electron is more probable because of the higher energies of these radiations. (For this reason such radiations are termed ionizing radiations.) Thus a compound C, on excitation, may yield a radical-cation C by ejecting an electron, 

The radical-cation can propagate at the radical and positive centers depending on reaction conditions. It may also dissociate to form separate radical and cationic species  

The initially ejected electron may be attracted to the cation A with the formation of another radical  

The ejected electron may also be captured by the component C forming an anion C which may or may not be excited depending on the energy of the electron, and may further dissociate producing radicals and ions  

TL has been used to study radiation damage (38) and also the radioactivity of certain minerals (106, 111, 128, 129). 

There is not much agreement on the name for this phenomenon. Ashby (136) and others used the term oxylumineseence Barker et al. (139) called it thermochemiluminescence (TCL) David (50) used photothermal analysis (PTA) Wynne and Wendlandt (142) called it light emission (LE) and Stivala (160) called it chemiluminescence (CL). The term employed here will be oxylumineseence (OL) although chemiluminescence would probably be just as appropriate. 

As pointed out in Chapter 1, ionizing radiation includes high-energy electrons (electron beam), y-rays, and x-rays. These not only are capable of converting monomeric and oligomeric liquids into solids, but also can produce major changes in properties of solid polymers. Also, in comparison to UV and visible radiation, they can penetrate considerably deeper into the material. 

Coating materials — Methods for testing the resistance of coatings to ionizing radiation in nuclear plants 

Electrical insulating materials — Determination of the effects for ionizing radiation (lEC 60544) German version EN 60544 1996-2011 

Electrical insulating materials — Determination of the effects of ionizing radiation 

Determination of long-term radiation ageing in polymers 

The actual species responsible for cationic polymerizations initiated by ionizing radiation is not established. The most frequently described mechanism postulates reaction between radical-cation and monomer to form separate cationic and radical species subsequently, the cationic species propagates rapidly while the radical species propagates very slowly. The proposed mechanism for isobutylene involves transfer of a hydrogen radical from monomer to the radical-cation to form the r-butyl carbocation and an unreactive allyl-type radical  

The evidence for this mechanism is based on mass spectroscopy of the gas-phase radiolysis of isobutylene, which may not be applicable to the typical liquid-phase polymerization system. Initiation in condensed systems may follow the same course as electroinitiation— coupling of radical-cations to form dicarbocations. 

Cationic polymerization initiated by ionizing radiation is markedly different from other cationic polymerizations in that the propagating species is a free ion remote from a counterion. Overall electrical neutrality is maintained by electrons trapped by the monomer. 

The initiator ion pair (consisting of the carbocation and its negative counterion) produced in the initiation step (Eq. 5-4) proceeds to propagate by successive additions of monomer molecules 

This addition proceeds by insertion of monomer between the carbocation and its negative counterion. 

Since DNA is a highly charged polyanion, it is always hydrated by water molecules [in the dry state (under moist air) it contains 12 water molecules per nucleotide subunit]. In a cellular environment, proteins (histones in eukaryotic cells) are always attached to DNA or are at least surrounded by proteins as in viruses. In order to attack DNA, radicals have to be sufficiently mobile in such a partially hydrophilic environment. For this reason, typical lipid radicals confined to the membranes will not be discussed here, although one must keep in mind that small fragments of free-radical nature maybe able to escape the lipid environment and can, in principle, also react with DNA. 

To understanding the basis of radiation chemistry, it seems appropriate to recall some important aspects of the physics of energy absorption and the ensuing radiation chemistry, but for details the reader is referred to some textbooks, e.g., Henglein et al. (1969) Farhataziz and Rodgers (1987) von Sonntag (1987) Spinks and Woods (1990) Jonah and Rao (2001). 

The water radical cation, produced in reaction (1), is a very strong acid and immediately loses a proton to neighboring water molecules thereby forming OH [reaction (3)]. The electron becomes hydrated by water [reaction (4), for the scavenging of presolvated (Laenen et al. 2000) electrons see, e.g., Pimblott and LaVerne (1998) Pastina et al. (1999) Ballarini et al. (2000) for typical reactions of eaq, see Chap. 4], Electronically excited water can decompose into -OH and 11- [reaction (5)]. As a consequence, three kinds of free radicals are formed side by side in the spurs, OH, eaq , and H . To match the charge of the electrons, an equivalent amount of ED are also present. 

Since a spur can contain more than one free-radical pair, there is always the possibility that they interact with one another [cf. the higher yields of eaq and OH 

Often it is desirable to study the reaction of OH without a contribution of eaq. For this purpose, eaq- is usually converted into further -OH by saturating the solution with N20 [reaction (11), k = 9.1 x 109 dm3 mol-1 s-1 [N20] at saturation = 2.2 X 10-2 mol dm-3]. 

Beginning early in the twentieth century, physicians recognized that 

Smaller nuclear accidents included the Hanford, California, americium incident in 1976. In an explosion, a laboratory worker was exposed to radiation that required years of treatment (Breitenstein 1991 Brown 1983). Posttraumatic stress symptoms did not develop. Protective characteristics of the person included being a male older than 40 years and having occupational experience, above average intelligence, no history of mental health problems, religious belief, 

The Chernobyl accident in Russia released radioactive iodine, cesium, strontium, and plutonium over major European countries. The disaster disrupted life in the Ukraine, Belorussia, and Russia, causing deaths, disease, environmental damage, lifestyle changes, and physical and psychiatric stress in hundreds of thousands of victims and rescuers (Darby and Reeves 1991 Torubarov 1991). More than 4 million people lived in the contaminated area 130,000 required immediate evacuation, and 1 million became involved in the cleanup. A 30-km forbidden area exists around the site, and 300,000 live in strict control zones that require constant monitoring (van den Bout et al. 1995). 

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Pu (86 years) is formed from Np. Pu is separated by selective oxidation and solvent extraction. The metal is formed by reduction of PuF with calcium there are six crystal forms. Pu is used in nuclear weapons and reactors Pu is used as a nuclear power source (e.g. in space exploration). The ionizing radiation of plutonium can be a health hazard if the material is inhaled. 

The flexible large area screen with photostimulable phosphor called the imaging plate, which temporarily stores the image induced by the ionizing radiation, e g. by X-rays, electrons or other charged particles ... 

A monochromator is useful not only for removing unwanted lines from the X-ray source but also for narrowing the otherwise broad lines. For example, each of the MgXa and AlXa doublets is unresolved and about 1 cY wide at half-intensity. A monochromator can reduce this to about 0.2 cY This reduction of the line width is very important because in an XPS specttum, unlike an ultraviolet photoelectron specttum, the resolution is limited by the line width of the ionizing radiation. Unfortunately, even after line narrowing to 0.2 cY... 

As already mentioned, fhe resolution in XPS is usually limited by fhe line widfh of fhe ionizing radiation. In UPS fhe obfainable resolution depends on such factors as fhe... 

The chemical shift is related to the part of the electron density contributed by the valence electrons, ft is a natural extension, therefore, to try to relate changes of chemical shift due to neighbouring atoms to the electronegativities of those atoms. A good illustration of this is provided by the X-ray photoelectron carbon Is spectmm of ethyltrifluoroacetate, CF3COOCH2CH3, in Figure 8.14, obtained with AlXa ionizing radiation which was narrowed with a monochromator. 

If monochromatic X-rays are used as the ionizing radiation the experimental technique is very similar to that for XPS (Section 8.1.1) except that it is the kinetic energy of the Auger electrons which is to be measured. Alternatively, a monochromatic electron beam may be used to eject an electron. The energy E of an electron in such a beam is given by... 

Ionization gauges Ionization potentials Ionizing radiation... 

Polyimide. Polyimide is a biaxiaHy oriented high performance film that is tough, flexible, and temperature- and combustion-resistant. Its room temperature properties compare to poly(ethylene terephthalate), but it retains these good characteristics at temperatures above 400°C. Its electrical resistance is good and it is dimensionally stable. The principal detriment is fairly high moisture absorbance. The main uses are for electrical insulation, particularly where high temperatures are prevalent or ionizing radiation is a problem. The films may be coated to reduce water absorption and enhance... 

Octafluoronaphthalene [313-72-4] is prepared in 53% yield by defluorination of perfluorodecahydronaphthalene [306-94-5] over iron or nickel at 500°C. Exchange fluorination of octachloronaphthalene with KE in sulfolane (235°C) gave 60% yield of octafluoronaphthalene. This product exhibits good StabiHty to ionizing radiation (274). 

Copolymerization is effected by suspension or emulsion techniques under such conditions that tetrafluoroethylene, but not ethylene, may homopolymerize. Bulk polymerization is not commercially feasible, because of heat-transfer limitations and explosion hazard of the comonomer mixture. Polymerizations typically take place below 100°C and 5 MPa (50 atm). Initiators include peroxides, redox systems (10), free-radical sources (11), and ionizing radiation (12). 

Addition reactions between isoprene and tetrahalomethanes can be induced by peroxides, high energy ionizing radiation, or other radical-generating... 

Microwaves may be used to ionize gases when sufficient power is apphed, but only through the intermediate process of classical acceleration of plasma electrons. The electrons must have energy values exceeding the ioniza tion potential of molecules in the gas (see Plasma technology). Ionizing radiation exhibits more biological-effect potential whatever the power flux levels (2). 

Polybutene can be cross-linked by irradiation at ambient temperature with y-rays or high energy electrons in the absence of air. The performance of articles manufactured from polybutene is only slightly affected by ionizing radiation at doses below 30 kGy (3 Mrad) (26). PMP is also relatively stable to P-and y-radiation employed in the sterilization of medical suppHes (27). 

Table 5. Ionizing Radiation Interactions with Polymeric Substrates. ...

A. F. Readdy, Jr., "AppHcation of Ionizing Radiations in Plastics and Polymer Technology," Plastic Report R41, Plastics Technical Evaluation Center, Picatinny Arsenal, Dover, N.J., 1971. 

U.S. radiation protection guidelines are estabHshed by the National CouncH on Radiation Protection and Measurement (NCRP) and are based on the recommendations of the International Commission on Radiological Protection (ICRP). The National Research CouncH also sponsors a report from its advisory committee on the biological effects of ionizing radiations (20). 

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