60Co y-radiation

In tbe first attempt to prepare a two-dimensional crystalline polymer (45), 60Co y-radiation was used to initiate polymerization in monolayers of vinyl stearate (7). Polymerization at the air-water interface was possible but gave a rigid film. The monomeric monolayer was deposited to give X-type layers that could be polymerized in. ////. fills polymerization reaction, quenched by oxygen, proceeds via a free-radical mechanism. 

Pulse radiolysis has been used to afford the radical cations of thioanisole, p-methylthioanisole, and benzyl phenyl sulfides. The absorption spectra of these radicals and their reaction with a number of nucleophiles and electron donors are reported.302 Exposure of trimethylphosphine sulfide to 60Co y-radiation at 77 K gave the radical anion Me PS , identified by its ESR spectrum, from which other radicals, including Me2PS, were formed at higher temperatures.303... 

Sterilization of tylon Enzyme Electrodes. Sterilization of in vivo electrodes is essential for clinical use and advisable for applica-tions in the food industry. It was thus of interest to study the behaviour of various carbohydrate sensor membranes before and after irradiation with 60Co-y radiation (Figure 1). Thus, after each membrane calibration in a batch mode, the membrane was detached, placed in a sealed glass tube with phosphate buffer (pH 7) and irradiated to set doses. The membrane was then reattached to the... 

Cholest-4-en-3/3-ol and its 5a-A6- and 5a-A7-isomers gave complex mixtures of oxidation products on treatment with 60Co y-radiation in air. Reaction paths are discussed and compared with those occurring in photosensitized and free-radical oxidations.119 1-Methyl-11-oxo-oestrone (107) is converted by DDQ in 1% aqueous dioxan into the 9/3-hydroxy-derivative (108), apparently by hydration of an intermediate quinone methide.120... 

Packer and Richardson (1975) and Packer et al. (1980) made use of the fact that electrons can be generated in water by y-radiation from a 60Co source (Scheme 8-29) to induce a free radical chain reaction between diazonium ions and alcohols, aldehydes, or formate ion. It has to be emphasized that the radiolytically formed solvated electron in Scheme 8-29 is only a part of the initiation steps (Scheme 8-30) by which an aryl radical is formed. The aryl radical initiates the propagation steps shown in Scheme 8-31. Here the alcohol, aldehyde, or formate ion (RH2) is the reducing agent (i.e., the electron donor) for the main reaction. The process is a hydro-de-diazoniation. 

There is in addition to the pulse radiolysis technique the classical continuous radiation method. This later procedure uses either the 60Co-y sources or in the case of Pu the self a irradiation due to the radioactive decay. 

Early in the 1950s, Stacey was successful in his negotiations to have a 60Co source of y-rays installed in his laboratory. Then, in collaboration with Barker and Bourne, a series of investigations of the effects of y-radiation on saccharides was started. Both polymer formation from simple sugars and the degradation of polysaccharides were studied. 

It is clear from this discussion that the dose requirement and unit cost will be lower if the material has a higher molar mass M and the reaction has a high G value. Thus, the best candidates will be a polymeric material and a chain reaction. Quite often, a free-radical irradiation is used. The radiation source of choice is usually a 60Co - y facility, although electron beam irradiation is also used. Since most radiation-chemical reactions used in industry can also be brought about by other conventional means such as thermal, or photochemical processes, the processing cost must be below 10irradiation cost one has to include the cost of operation, maintenance, and the like. (Danno, 1960). 

Ionizing radiation. Further studies on the effects of ionizing radiation such as 60Co y-ray radiation and ion beams on polysilanes have been reported.295 304-306 Both positive and negative resist properties can be shown, depending on the side-chain type, branch density, and the presence or absence of radical initiators. 

Cobalt-60 y-Radiolysis Studies. Samples of PIPTBK powder were sealed under vacuum and exposed to 60Co 7-radiation at the National Bureau of Standards in Washington D.C. The samples received 0, 6, 12, and 20 Mrads and the number-average and weight-average molecular weight of each polymer, relative to polystyrene, were determined in THF by GPC. The scission efficiency and the cross-linking efficiency were determined from... 

The monomer 1 was polymerized by heating the crystals in a vacuum vessel below the melting point or by y-ray or UV irradiation of the crystals at room temperature. 60Co y-ray irradiation with a dose rate of 0.1 Mrad h 1 or a high-pressure mercury lamp (200 W) without filter was used as the radiation sources for the polymerization the conversion ratio was determined by extraction of residual monomer with ethanol. A comparison of the polymerization rates indicates that 60C y-ray irradiation is much more efficient than UV irradiation in inducing polymerization. 

Table 2.1. Radiation-chemical yields (G values units 10-7 mol J-1) of water radicals, ions and molecular products at a scavenger capacity of ca. 2 x 10s s-1 under the conditions of sparsely ionizing radiation (60Co-y-rays, high-energy electrons) in the presence of different saturating gases (von Sonntag 1987)...

Similarly Abou Zeid and co-workers made a detailed study on LDPE film, irradiated with different types of radiation such as 60Co y-rays, thermal and fast neutrons, and electron beam irradiation [19]. The structural changes of PE films with thickness varying from 8 to 24 pm, were characterised by FT-IR spectroscopy. The characteristic FT-IR absorption bands of unirradiated, y-irradiated and reactor irradiated LDPE film are presented in Table 5.1. 

The reactor for radiation chemical synthesis with an agitator (about 200 rotations per minute) is located in the operation chamber. Inside the reactor there is a cavity for introducing sources of y-radiation. The role of the radiation source is played by 60Co in airproof stainless steel ampules the activity of 60Co radiation is about 3000 eq Ra. The consumption degree of the energy of radiation when the sources are placed in the cavity, or the radiation coefficient of efficiency, varies from 17 to 19%. The equipment is encased in a special box made of stainless steel and plexiglass the box has intensive ventilation. 

The effect of radiation damage has been studied of the solvents using y rays from 60Co. The results show that the solvents are not degraded by exposing to the y radiations up to 1 x108 rad, which is more than 100 times of the dose resulted from the treatment of the HLW. 

Ni(CO)4 is not affected by intense 60Co-y-irradiation and can be looked upon as one of the most radiation stable compounds 44>. A study of the radiolysis of mixtures of cyclohexane and/or benzene and Ni(CO)4 has demonstrated its protective properties. Probably, energy transfer to Ni(CO)4 and the reversible dissociation... 

For radiation curing, a sealed tube containing the blend film was placed in the y-ray (60Co source) radiation chamber at the dose rate of 1.32 x 10 R/min. for 30 minutes. 

Irradiation. The samples were irradiated with 60Co y-rays at 77 °K. in ampoules sealed at 10"4-10 5 torr. The ampoules were made from Suprasil quartz which on irradiation gave an ESR signal which was very small compared with the intensity of the sample absorption. The dose rate of the radiation source varied within 300-350 krads/hour. The dose was 3.4 Mrads for most of the experiments. The dose dependence of the radical formation was investigated in the dose range 0.02-10 Mrads. 

The experiments involved the use of y-radiation of 60Co. The dose rate was commonly equal to — 1016 e.v./ml. sec. The dosimetry was made by the ferrosulfate method. The calculation of the dose was performed while taking into account the difference in electron densities of the dosimetric and investigated solutions. 

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