Gamma Radiations

With respect to radiation protection, absorbers of low atomic numbers Z are most useful for absorption of P radiation, for instance perspex or almninium of about 1 cm thickness. 

The absorption of y rays and X rays is, in principle, different from that of a or rays. While the latter lose their energy by a succession of collisions, y-ray photons give off their energy mostly in one process. Because they do not carry a charge, then-interaction with matter is small. For the absorption of y rays an exponential law is valid  

The relation between the energy of y radiation and its absorption is characterized by the half-thickness ii/2, i e. the thickness of the absorber by which the intensity of the y radiation is reduced to half of it. Introducing I — h/2 in eq. (6.18) gives  

Instead of the linear absorption coefficient, the mass absorption coefficient n/p (cm /g) is often used  

In the first place, the absorption of y radiation depends on the density of the absorber, similarly to the absorption of a or radiation. In Table 6.3 the mass absorption coefficients for various absorbers and various energies of y radiation are listed. 

In some applications, particularly in the nuclear industry, medical instrumentation and food sterilisation, plastics are subjected to damage, which is associated with a loss in molecular weight and deterioration of some physical properties, such as impact strength and colour change upon exposed the plastics to gamma rays [65, 66]. 

It can be seen in Table 8.4 that several polymers such as polystyrene (PS), polyether ether ketone (PEEK) and polyether-imide (PEI) enjoy an excellent resistance to gamma rays, whilst a wide range of polymers have very good resistance to gamma rays. 

reinforced polyimide (PI) upon exposure to gamma rays had a decay of short term shear strength for a zero dose value of 87.1 to 79.3 MPa after cohalt 60 irradiation to 1,000 kGy 

LDPE Low-density polyethylene PA Polyamide PAI Polyamide imide PC Polycarbonate PET Polyethylene terephthalate PMMA Polymethyl methacrylate PP Polypropylene PTFE Polytetrafluoroethylene PU Polyurethane XPE Crosslinked polyethylene Source Author s own files  

An electron that comes from a nucleus is called a P particle, and an x-ray that comes from the nucleus is called ay-ray. Physically, these are identical however, the names are different to denote where they originated from. 

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For this kind of case, a modification of the dilution method is being developed. Instead of using an external fixed-geometry measurement chamber, a suitable part of the process, e.g. a stretch of pipe, is used. A radiation detector is mounted on the outside of the pipe, and a tracer emitting sufficiently hard gamma radiation is used. As sufficient mixing can be achieved by injecting upstream the separator the radiation level found will be strictly proportional to the concentration and thus inversely proportional to the true flow rate. 

In situ measurement of the concentration of radioactive tracers in the different phases requires that the phases are separated and arranged according to density difference over the measurement cross section in a horizontal pipe. In general, the measurements are performed with two spectral gamma radiation detectors placed on top and bottom of the pipe respectively. 

Laboratory tests indicated that gamma radiation treatment and cross-linking using triaHylcyanurate or acetylene produced a flexible recycled plastic from mixtures of polyethylene, polypropylene, general-purpose polystyrene, and high impact grade PS (62). 

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. 

Both side-chain and main-chain scission products are observed when polyacrylates are irradiated with gamma radiation (60). The nature of the alkyl side group affects the observed ratio of these two processes (61,62). 

PCTFE plastic is compatible withHquid oxygen, remains ductile at cryogenic temperatures (16—22), and retains its properties when exposed to either uv or gamma radiation. PCTFE exhibits a refractive iadex of 1.43 (ASTM D542) and an amorphous sheet can provide over 90% transmittance. 

The synthesis of the high molecular weight polymer from chlorotrifluoroethylene [79-38-9] has been carried out in bulk (2 >—21 solution (28—30), suspension (31—36), and emulsion (37—41) polymerisation systems using free-radical initiators, uv, and gamma radiation. Emulsion and suspension polymers are more thermally stable than bulk-produced polymers. Polymerisations can be carried out in glass or stainless steel agitated reactors under conditions (pressure 0.34—1.03 MPa (50—150 psi) and temperature 21—53°C) that require no unique equipment. 

Medical and health-care related appHcations consume about 21,000 t of polycarbonate aimuaHy. Polycarbonate is popular because of its clarity, impact strength, and low level of extractable impurities. Special grades have been developed to maintain clarity and resistance to yeHowing upon gamma radiation sterilization (qv) processes. Leisure and safety appHcations are many and varied, accounting for about 22,000 t of consumption aimuaHy. The... 

PC—copolyester better processibihty, hydrolytic, and gamma radiation resistance than PC sterilizable apphcations 43,109... 

Polysulfones also offer desirable properties for cookware appHcations, eg, microwave transparency and environmental resistance to most common detergents. Resistance to various sterilizing media (eg, steam, disinfectants, and gamma radiation) makes polysulfones the resin family of choice for many medical devices. Uses in the electrical and electronic industry include printed circuit boards, circuit breaker components, connectors, sockets, and business machine parts, to mention a few. The good clarity of PSF makes it attractive for food service and food processing uses. Examples of appHcations in this area include coffee decanters and automated dairy processing components. 

Similar to pure polyglycoHc acid and pure polylactic acid, the 90 10 glycolide lactide copolymer is also weakened by gamma irradiation. The normal in vivo absorption time of about 70 days for fibrous material can be decreased to less than about 28 days by simple exposure to gamma radiation in excess of 50 kGy (5 Mrads) (35). 

Gamma radiation produces free carriers much as does visible light (36). High energy protons and electrons produce defects that reduce minority carrier lifetime according to equation 8 ... 

For color removal, ozonization has achieved the greatest practical importance as seen by the plethora of articles and patents on this method (147—163). Ozonization in combination with treatments such as coagulation, flocculation, carbon adsorption, uv irradiation, gamma radiation, and biodegradation significantly and successfully remove dye wastes and reduce costs (156,164—170). 

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 radi-... 

Radiographic examination is either by x-rays or by gamma radiation. The former has greater penetrating power, but the latter is more portable. Few x-ray machines can penetrate beyond 300-mm (12 -in) thickness. 

Density Gauges These are used to measure the density or suspended solids content of the feed and underflow streams. Gamma radiation devices are the most commonly used for automatic control, but ultrasonic devices are effective in the lower range of slurry density. Marcy pulp density scales are an effective manually operated device. A solids mass flow indication is usually obtained by combining a density gauge output with the output from a flowmeter. 

For example, a 1 MeV point isotropic source of gamma-radiation has a buildup factor ol 2.1 when penetrating a mean-free thickness of water. If the build-up factor is ignored, equation 8.3-11 is exp(-l) = 0.36. Hence, 36% of the radiation passes through the shield. But when the buildup factor is included, 2.1 0.36 = 76% of the radiation penetrates the shield. 

Rontgen The amount of x-ray or gamma radiation that produces one unit of charge in 1 cc of dry air. 

Gamma Radiation Induced Preparation of Polyelectrolytes and Its Use for Treatment of Waste Water... 

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