Cobalt gamma radiation

Solution polyacrylamides can also be prepared at high polymer soHds by radiation processes (80,81). Polyacrylamides with molecular weights up to 20 million can be prepared by inradiation of acrylamide and comonomers in a polyethylene bag with cobalt-60 gamma radiation at dose rates of 120-200 J/kg-h. The total dose of radiation is controlled to avoid cross-linking. 

An extractive study of one can enamel in the presence of food-simulating solvents to determine how gamma radiation from a cobalt-60 source altered the nature and amount of extractives of this enamel. 

Irradiation Conditions. The gamma (cobalt-60) radiation facility and the source calibration are described by Holm and Jarrett (4). Irradiation doses were 3-4 Mrad and 6-7.5 Mrad at 9 X 102 rads per second for the screening study. Irradiation temperatures were 5, —30, and — 90°C. The gamma source was calibrated with the ferrous sulfate-cupric sulfate dosimeter. 

Gamma knife A device that uses multiple converging beams of gamma radiation from cobalt-60 to highly focus radiation on small tumors within the brain. 

High-energy radiation may be classified into photon and particulate radiation. Gamma radiation is utilized for fundamental studies and for low-dose rate irradiations with deep penetration. Radioactive isotopes, particularly cobalt-60, produced by neutron irradiation of naturally occurring cobalt-59 in a nuclear reactor, and caesium-137, which is a fission product of uranium-235, are the main sources of gamma radiation. X-radiation, of lower energy, is produced by electron bombardment of suitable metal targets with electron beams, or in a... 

The increase in the modulus for Bis A PSF and Hq/Bp PSF with irradiation indicated that crosslinking predominated for both polymers and that the crosslink structures were probably basically similar. Hq/Bp(50) PSF was considerably more radiation resistant than Bis-A PSF, as shown by the rate of decrease in the elongation at failure. For both polymers, there was an initial rapid decrease in the elongation at failure followed by a slower decrease. This effect was also demonstrated by the variation in the fracture toughness (KI(.) with irradiation for Bis-A PSF. This work with cobalt-60 gamma radiation complements earlier studies of these materials using high dose rate electron beam irradiation (6). 

Sinanoglou, V. J., Batrinou, A., Konteles, S., and Sflomos, K. (2007). Microbial population, physicochemical quality, and allergenicity of molluscs and shrimp treated with cobalt-60 gamma radiation. J. Food Prot. 70, 958-966. 

Radioisotopes are also used in radiation therapy to treat cancer. The goal in radiation therapy is to kill malignant cells, while protecting healthy tissue from radiation effects. Radioisotopes such as yttrium-90, a beta emitter, may be placed directly in the tumor. Alternatively, the diseased tissue may be subjected to beams of gamma radiation. Cobalt-60 used in radiation therapy is prepared by a series of transmutations ... 

Irradiation Conditions and Dosimetry. All irradiations were carried out in the gamma-radiation field of either a nominally 10 or 18 kilocurie cobalt-60 source. Dosimetry of the gamma-radiation field was carried out using the Fricke method (ASTM test D 1671-59). Since the effective mass absorption coefficient for y-rays of this energy is nearly equal for the polymer and for the dosimetric solution, no correction was made for the change in media. 

A cobalt source was used to provide gamma radiation for a powdered polymer sample under a nitrogen atmosphere. A total dose of 20 Mrad was applied. Solutions with 1.0 dl/g were made of the initial and exposed polymer in THF at 30 °C. In the usual fashion, the reduced viscosity, risp/c was calculated for each. From an original value of 1.81, the i)sp/c fell to 0.14 after irradiation. 

Systems using either gamma radiation from cobalt 60 or electron beams have been used for vulcanization. The electron beam method has been used for curing silicone rubbers. 

T.D. Phillips, Effect of Gamma Radiation from Cobalt 60 on the Mechanical Properties of AHH and ARP Double-Base Solid Propellants , NPP TMR-159, Naval Powder Factory, Indian Head... 

Impulseless resonance absorption of y-quants (gamma radiation) from a radioactive isotope, here Cobalt 57Co 57Fe + y (main quant 122 keV quant used for spectroscopy has a different energy)... 

Radiation-Density Gauges Gamma radiation may be used to measure the density of material inside a pipe or process vessel. The equipment is basically the same as for level measurement, except that here the pipe or vessel must be filled over the effective, irradiated sample volume. The source is mounted on one side of the pipe or vessel and the detector on the other side with appropriate safety radiation shielding surrounding the installation. Cesium 137 is used as the radiation source for path lengths under 610 mm (24 in) and cobalt 60 above 610 mm. The detector is usually an ionization gauge. The absorption of the gamma radiation is a function of density. Since the absorption path includes the pipe or vessel walls, an empirical calibration is used. Appropriate corrections must be made for the source intensity decay with time. 

This discussion is not intended to be an exhaustive review of the wood-polymer literature, but rather an overview of the processing procedures used today. In general, the free radicals used for the polymerization reaction come from two sources, temperature sensitive catalysts and Cobalt-60 gamma radiation. In each case a free radical is generated by the process, but from that point the vinyl polymerization mechanism is the same. Each... 

J. Hubbal, P. MiDauro, et al., Developments in crosslinking of stationary phases for capillary gas chromatography by cobalt-60 gamma radiation, J. Chromatogr. Sci., 22 185-191 (1984). 

The emulsion polymerization of vinyl chloride, initiated by gamma radiation from a Cobalt-60 source, has been studied in detail. Good conversions to high yields were obtained. 

Figure 3. Sensitivity to gamma radiation (Cobalt source) CO, G(s) 5.1 O PMMA, G(S) 0.8.

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