Lewis T. Chadderton

Anion voidage and the void superlattice in electron irradiated Caf2

Abstract Anion voidage and anion void lattice formation in electron irradiated (100 keV–1 MeV) fluorite (CaF2) has been investigated by in situ transmission electron microscopy. At low fluences (≲1 dpa) the damage consists of randomly distributed anion voids and large bubble-like defects associated with fluorine gas. At higher fluences (≳ 1 dpa) the anion voids form a three-dimensional ordered superlattice with a simple cubic structure, whose axes are commensurate with those of the matrix. The superlattice has a unit cell parameter A0 in the range 15–30 nm and a ratio A0/R(superlattice parameter/anion void radius) in the range 3–6. The fully ordered superlattice “crystallizes” from randomly distributed anion voids by an ordering process in which locally ordered areas grow together after a fashion similar to that of epitaxy, leaving distorted superlattice regions between individual, fully ordered blocks. The basic radiation damage events are radiolytic and confined to the anion sublattice. Damage processes...

Fullerene formation in the tracks of energetic ions

Chromatographic analyses of solvent extracts from graphite bombarded with 130 MeV/amu 161 Dy 22+ ions, and polyimide (kapton) bombarded with 5 MeV 6 Li 1+ ions, give clear evidence for the in situ synthesis of buckminsterfullerene −C 60 . The role played by the production of highly confined, dense assemblies of energetic electrons in this phase change is discussed

Axisymmetric vibrational modes of fullerene C60

Abstract Axisymmetric vibrations for fullerenc C 60 , are examined, naively modelling the molecule as a thin spherical shell. It is shown that the observed frequency pattern for the experimentally active Raman and i.r. modes reflects two branches, a n and b n , of the fundamental, thin shell dispersion curve. There is satisfactory agreement between normalized frequencies calculated for a total of four Raman and four characteristic i.r. modes, and correspondingly strong resonances observed in practice. Six experimentally weaker, five-fold degenerate H g Raman active modes are not predicted. The four distinctly characteristic i.r. active, axisymmetric vibrations of the isolated C 60 , molecule are essentially preserved on crystallization into fee fullerite, though a fundamental gap or potential i.r. “window” inherent to the model is not realized. The possible influence of Coriolis forces is briefly considered. The model, though simple, may have applications to the higher order symmetric fullerenes and, suitably modified as a solid sphere of constant density, to the more recently observed “nested” fullerenes.

On the lithium uptake of MeV ion irradiated polymer foils from a LiCI solution

Abstract Commercial polyimide (PI, ‘kapton) and polycarbonate (PC, ‘makrofol) foils have been irradiated with 135 MeV Ar5+ and 340 MeV Xe7+ ions, respectively, and subsequently boiled in a 5 mole/ltr LiCI solution for different times. The depth distributions of Li diffused into the foils suggest that the doping proceeds via regular diffusion, into both unirradiated bulk and into tracks. Low fluence irradiations appear to lead to a compaction or densification of the polymer matrix. One consequence of this is a decreasing Li uptake with increasing fluence. For higher ion fluences the Li uptakeproportional to track densitybecomes dominant. It is possible to define, to first order, a mean ‘effective track radius’ for the average amount of lithium taken up per track, and this can be shown to be of the order of only an A. The diffusional behaviour of lithium suggests that tracks in 340 MeV Xe ion irradiated polyimide act as open micropores for diffusing dopants. Conversely, in 135 MeV Ar irradiated PC, the do...

Optical properties of the phthalocyanines

Abstract The optical properties of some of the phthalocyanines have been investigated for molecules in different degrees of association. If the spectral shifts arising from temperature dependence and the broadening due to crystal field effects are accounted for there appears to be a one-to-one correspondence between peaks observed in vapour, sublimed film, and single crystal absorption spectra. It is proposed that the simple band model offers a reasonably good description of crystalline copper, platinum, and metal-free phthalocyanines. The sharp energy levels of the free molecule transform into broad quasi-continuous bands on crystallization.

Depth distribution of infrared absorption of ion irradiated PETP

Abstract The depth distributions of infrared absorption of PETP (polyethyleneterepthalate, ‘mylar) were measured for a number of different ion irradiation conditions. It turned out that at low fluences the depth profiles resemble the ones of the transferred electronic energy distribution. With increasing fluence the depth profiles of IR absorption approach the ones of the transferred nuclear energy distribution, thus reflecting the increasing polymer destruction. The earlier assumed correlation of the depth profile shapes with the ratio of electronic to nuclear energy transfer can thus be ruled out.

On the correlation of nuclear track effects with basic track parameters

Abstract The formation of nuclear tracks in polymers in acompagnied by radiochemical, structural, electronic and optical changes that show up macroscopically above specific threshold values. The correlation of these effects with both the average transferred electronic energy density ϱ e and with ϱ e S e (S e = electronic stopping power) is examined in this work. Scaling with ϱ e S e yields in general better results: The consequence for the choice of the corresponding track model is discussed.

On the uptake of water vapor by ion irradiated polyimide

Abstract It is known that ion-irradiated polymers are capable to adsorb dopants from solid, liquid or gaseous phases. For simple ambient atmosphere exposures, oxygen and water vapor are the most prominent dopants. Though the quantity of the latter one is not sufficient to be probed by conventional spectroscopic techniques, it can be detected indirectly via its ionic conductivity on applying a strong electric field along the track direction, as long as it is not yet masked by the intrinsic ion track conductivity, which is the case for low-fluence polymer irradiation. The conductivity is of similar order for most low-fluence irradiated polymers examined – namely 10−15−10−13 Ω−1 cm−1. Water vapor uptake – as determined via the ion track conductivity – sensitively depends on the ambient air humidity, so that fresh low fluence irradiated polymers can act as humidity sensors. Aging however leads to rapid deterioration of this property within a week exposure time at ambient room temperature and pressure. The wat...

On an application of the fission track method to botany

Abstract A fission track analysis has been used to determine uranium abundances in certain Himalayan plant species. Lexan polycarbonate detectors have been used to register the tracks made by fragments from thermal neutron induced fission of uranium. The results show that the plants possess a low content of uranium by comparison with that found in minerals, and in fossil bones from the same orogeny.

On the annealing behaviour of fission tracks in zeolites

Abstract The fission-track method has been employed in a study of the annealing behaviour of zeolites, in particular the mineral chabazite. Variations of fission-track density with etching time and at different annealing temperatures make it possible to interpret annealing data for the mineral in terms of the paleoisotherm of its intrinsic fission-track clock. Extrapolation of the experimental data suggests that a temperature of 149°C, enduring for one million years, is needed for all fission tracks in chabazite to be erased. Experiments directed at an evaluation of the use of optical absorption spectroscopy as a means of determining the degree of fission fragment induced crystal lattice damage in chabazite are also described.