Magnitude Of Change In Properties Research Articles

Gamma photon techniques for detection of nucleation in superheated emulsion detectors for neutron dosimetry

Application of transmission and scattering gamma photon techniques for calibration of superheated emulsion detectors used for neutron dosimetry is described. The bubbles nucleated in the detector due to neutron exposure generate detectable changes in both attenuation and scattering properties of the medium, and the magnitude of change in properties depends on population density of bubbles nucleated and in turn is proportional to neutron dose. The experimental set-up consists of (137)Cs and (241)Am sources and an HPGe detector-based gamma-ray spectrometer. An indigenously developed bubble detector and a commercially available one (BTI, Canada) are used in the present study. Theoretical models for the variation in transmitted and scattered intensities through the bubble detector as a function of neutron dose are formulated, and the experimental results obtained are found to be in good agreement with the models. In the neutron dose region studied, the transmission technique shows better sensitivity than scattering technique.

Effects of electronic and recoil processes in polymers during ion implantation

It has been shown that ion implantation produces remarkable improvements in surface-sensitive mechanical properties, as well as other physical and chemical properties in polymers. To understand mechanisms underlying such property changes, various polymeric materials were subjected to bombardment by energetic ions in the range of 200 keV to 2 MeV. The magnitude of property changes is strongly dependent upon ion species, energy, and dose. Analysis indicated that hardness and electrical conductivity increased by employing ion species with larger electronic cross sections and with increasing ion energy and dose. The results showed that electronic stopping or linear energy transfer (LET, energy deposited per unit track length per ion) for ionization was the most important factor for the enhancement of hardness, while nuclear stopping or linear energy transfer for displacement generally appeared to reduce hardness.

Ion beam application for improved polymer surface properties

Various polymeric materials were subjected to bombardment by different energetic ions with energies ranging from 200 to 1000 keV. Tests showed substantial improvements in hardness, wear resistance, oxidation resistance, resistance to chemicals, and electrical conductivity. The magnitude of property changes was strongly dependent upon ion species, energy, dose, and polymer structure. Both hardness and electrical conductivity increased with ion energy and dose. These properties were apparently related to the effectiveness of cross-linking. Ion species with a large electronic stopping cross-section are expected to produce more cross-linking. It is believed that the polymer property improvements are commensurate with the extent of cross-linking, which is responsible for the formation of three-dimensionally-connected, carbon-rich, rigid networks.

Solution‐induced changes in the properties of polyethylenes

AbstractThe chain entanglement states in high density, linear low density, and low density polyethylenes (HDPE, LLDPE, and LDPE) have been modified by recovering the polymers from solutions in trichlorobenzene (TCB) and p‐xylene. In the thermodynamically good solvent, TCB, the entanglement density is assumed to be sharply reduced, a condition which is carried over to the corresponding solids. These display transient, but large increments in tensile moduli, slight changes in stress at rupture, and decreases in dynamic mechanical parameters and in elongation at rupture. Scanning calorimetry also shows these solids to have reduced crystallinity. Much smaller property modifications are noted in corresponding samples recovered from p‐xylene. This liquid is a poorer solvent, particularly for HDPE and LLDPE. The results indicate that property modifications due to deliberate changes in the entanglement states of the polymers are a general phenomenon in the polyethylenes, and the magnitude of property changes depends on parameters of the molecular weight distribution. Chain branching does not seem to be a leading factor in the sensitivity of properties to modifications in the entanglement states. The property modifications produced by the present solution treatments are viewed as guides to the magnitude and duration of shear refining effects to be expected in HDPE, LLDPE, and LDPE polymers.