Microfilters for biomedicine obtained by swift ion processing.
Swift ions with 50 MeV energy are used to irradiate bio-polymeric films. Lithium, carbon and oxygen beams, with fluencies ranging between 10(8) and 10(13) ions/cm2, are swept on large surfaces of hydrogenated and fluorated polymers. The electronic stopping power of the ion induces high rates of ionization, excitation and radical formation along the ion path with production of chain-scission and cross-linking processes which can be investigated by the molecular emission from the irradiated polymer. The radiation damage increases the chemical solubility of the material around the ion track up to distances of the order of 100 nm. A suitable chemical etching removes the damaged material leaving micrometric holes in the polymeric film. This process gives rise to micro-perforated films which can be used as microfilters, with sub-micrometric pore dimension, high selectivity and controllable porosity. Their use is very interesting for special applications in ultra- and microfiltration of biological liquids.
RADIATION EFFECTS OF KEV-MEV ION IRRADIATED PVDF
Abstract Polyvinilydene fluoride (PVDF) is a fluoropolymer very useful in the manufacture of synthetic bio-membranes through processes of ion energy deposition. Semicrystalline PVDF, irradiated with different ions in the range 100 keV-100 MeV, exhibits a strong change of crystalline structure, as detected by X-ray diffraction measurements as well as calorimetric analysis. PVDF ion irradiation produces a strong molecular emission for masses 2, 19 and 20, as detected “in situ” by a mass quadrupole spectrometer. At low ion doses, in the range 100–300 kGy, the diffraction analyses show a structure reordering along the (020) atomic plane. At high ion doses, the fluoropolymer shows a degradation of the crystalline structure which consists in radiation damage, reduction of hydrogen and fluorine concentration and formation of carbon reticulation. A phenomenological model, based on the ion track picture, is proposed to explain the experimental data.
The laws of Cnut and the history of Anglo-Saxon royal promises
The ‘first’ and ‘second’ law codes of Cnut are the last surviving codes issued in the name of an Anglo-Saxon king.They are the final fruit of the interest in kingship and law and in the inter-relationship of the two which characterized the period following the monastic revival in England and which is especially associated with the name of Wulfstan, archbishop of York. Although they are far from being complete codifications of Anglo-Saxon law, they draw extensively on earlier legislation. They are different in kind from much tenth-century law, which is usually more limited and administrative in content and character, and their nature and purpose invite further consideration.