Self-attenuating materials

The most acceptable ways of modification of aromatic polyesters aimed to get self-attenuating materials of improved resistance to aggressive media are the condensation of polymers from halogen-containing monomers. 

The question of improving fire-resistance of aromatic polyesters is paid more attention last time. Polymeric materials can be classified on criterion of combustibility noncombustible, hard-to-bum and combustible. Aromatic polyesters enter the combustible group of polymers self-attenuating when taken out of fire. 

This result demonstrates that the self-spreading dynamics are controllable by tuning the bilayer-substrate interactions. The above-mentioned electrolyte dependence is an example of this fact. Considering that there are many parameters that alter the bilayer-substrate interaction, a diverse approach can be proposed. For example, Nissen et al. investigated the spreading dynamics on the substrate coated with polymetic materials [48]. They found that insertion of a hydrophilic and inert polymer layer under the self-spreading lipid bilayer strongly attenuated the bilayer-substrate interaction. 

Self-shadowing and resonance capture effects. The use of small samples and standards so that the neutron flux is not appreciably attenuated between the exterior and interior of the irradiation unit is to be desired. When large samples are used or appreciable high cross section material is present in the matrix, it is important that the standard be prepared with a matrix physically and chemically similar to that of the sample. 

Look up the density (note that the density x container height = area mass) and the gamma-ray mass attenuation factor of commonly counted materials to compare the influence on the self-absorption factor of density and atomic number (i.e., electrons per atom). 

Although gamma rays are much less subject to attenuation than alpha and beta particles, a density correction is needed if the density of the sample deviates significantly from the density of the calibration standards. The effect of density on self-absorption for both the standard and the sample is estimated by Eq. (7.2) [x for this purpose is the photon attenuation coefficient in cm /g and x is the sample area density in g/cm. Values for ix in some common materials are listed in Table 2.2 and in its cited reference. If a large set of samples with consistent density is analyzed, it may be possible to prepare radioactivity standards at the same density to avoid the need for correction. Interpolating efficiency values as a function of density is feasible at energies above 0.1 MeV because the effect of minor density difference on counting efficiency is small. 

Reducing the sample mass and the amount of materials between the sample and the detector reduces radiation attenuation 1. This effort is most important for alpha particles and least important for energetic gamma rays, as discussed in Chapter 7. The fractional self-absorption within the sample can be estimated for beta particles and gamma rays by using Eq. (7.2). The fractional attenuation of gamma rays in... 

The HT architecture fortuitously balances several factors in poly(3-alkylthiophene)s. Defects engage steric mechanisms that distort conformation, attenuate orbital overlap and disrupt packing. Their elimination from the HT architecture affords a material prone to planarization and self-assembly, leading to organized aggregates and, ultimately, domains with high intermolecular orbital overlap. 

Beta rays can be attenuated or even completely stopped by the sample itself (self-absorption), by the wall of the sample vessel, by the air layer between the sample and the counter, and by the window material of the counter. On the other hand, P rays can be detected with higher eflSciency and lower background than y rays. Various types of measurement of P rays are described below. 

By use of shielding layers produced from different materials (lead, copper, iron, etc.), the dose calculation must take into account the buildup of lower energy photons together with attenuation in the shielding materials, including air and self-absorption of the human body (Wood 1982). 

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