SUBJECTS radiation sensitizers

The anodized surface is often subjected to additional treatment before the radiation-sensitive coating is appHed. The use of aqueous sodium siUcate is well known and is claimed to improve the adhesion of diazo-based compositions ia particular (62), to reduce aluminum metal-catalyzed degradation of the coating, and to assist ia release after exposure and on development. Poly(viQyl phosphonic acid) (63) and copolymers (64) are also used. SiUcate is normally employed for negative-workiag coatings but rarely for positive ones. The latter are reported (65) to benefit from the use of potassium flu o r o zirc onate. 

During the sterilization procedure the radiation dose should be measured. For this purpose, dosimeters that are independent of dose rate should be used, giving a quantitative measurement of the dose received by the product itself. Dosimeters should be inserted in the load in sufficient number, and dose enough together to ensure that there is always a dosimeter in the chamber. Where plastic dosimeters are used, they should be used within the time-limit of their calibration. Dosimeter absorbances should be read within a short period after exposure to radiation. Biological indicators may be used only as an additional control. Radiation-sensitive colour discs may be used to differentiate between packages that have been subjected to irradiation and those that have not they are not indicators of successful sterilization. The information obtained should constitute part of the batch record. 

Handling procedures should prevent any mix-up between irradiated and non-irradiated materials. Each package should cany a radiation-sensitive indicator to show whether or not it has been subjected to radiation treatment... 

Materials handling procedures should prevent mix-up between irradiated and non-irradiated materials. Radiation sensitive colour disks should also be used on each package to differentiate between packages which have been subjected to a irradiation and those which have not... 

Care must be taken to distinguish between materials which have been irradiated and those which have not Design of plant, and the use of radiation-sensitive discs, can ensure this. To this end each package should carry a radiation-sensitive disc to indicate whether it has been subjected to radiation treatment. These discs are not quantitative in their... 

Radiotoxicity depends on energy deposition in tissue or organs by the radionuclide, the specific tissue exposed to the radionuclide, and the tissue radiation sensitivity. Energy deposition by a radionuclide is a function of its emitted radiations and half-life. Biokinetic studies have identified for most radionuclides of interest the pattern of movement through the body and the effective turnover rate (the sum of the biological and radioactive turnover rates). Biokinetic information also identifies the appropriate type of sample to be collected among blood, urine, feces, saliva, breath, hair, teeth, nasal swipes, and tissue obtained incidental to unrelated operations, and collection frequency. The measured radionuclide concentrations are combined with biokinetic information to calculate the committed dose equivalent, the indicator of radiation impact on the subject (NCRP 1987b). 

The intrinsic HPGe detector now has replaced the Ge(Li) detector. This detector is made of sufficiently pure germanium that does not require lithium drifting for its radiation-sensitive properties. The HPGe is not subject to adverse effects if allowed to come to room temperature, but must be cooled to liquid-nitrogen temperature during use to achieve good resolution. 

Energy Transfer and Dissipation. From early times it was recognized that the presence of small concentrations of certain structures in a material can lead to a pronounced decrease in the radiation sensitivity of the material as a whole. The earliest observations of this type were of the evolution of gases from mixtures of small aromatic and aliphatic molecules. For example, Manion and Burton (18) reported in 1952 that the yields of reactions in irradiated mixtiu-es of cyclohexane and benzene were reduced significantly compared to the yield expected from the linear addition of the yields of the pure individual molecules. This led to the concept of protection effect, in which the introduction of aromatic groups results in significant protection of the surrounding aliphatic stmctin-es. The mechanism of protection afforded by the aromatic molecules has been a subject of considerable discussion. 

Heat sensitive materials need to be stored away from heat sources such heaters and windows where they are subject to solar radiation. 

The properties of such materials are not measurably altered until subjected to doses in excess of a million rads. At these higher doses, the principal changes are due to chem decompn which, with very few exceptions, resnlt in a decrease in sensitivity to mechanical stimulus and also in a dimunition of expl output. The radiation doses normally encountered in neutron activation procedures range from a few rads for 14 MeV fast neutron activation to several thousand rads for thermal neutron activations in a nuclear reactor. Thus, such doses are well under the limit at which measurable changes can occur... 

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