Morten Eldrup

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Positronfit: A versatile program for analysing positron lifetime spectra

COMPUTER PROGRAMS/POSITRONFIT, for analysis of positron lifetime spectra, in FORTRAN for B6700 or... more

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Oxygen diffusion in copolymers of ethylene and norbornene

by Morten Eldrup and I. Zebger

MACROMOLECULES, 2003

Oxygen diffusion coefficients, D, have been measured as a function of temperature over the range ... more

Positronium formation at low temperatures: the role of trapped electrons

Radiation Physics and Chemistry, 2000

Measurements have been carried out of electron spin densities (by electron spin resonance techniq... more Measurements have been carried out of electron spin densities (by electron spin resonance technique) and positronium (Ps) formation probability as functions of Co-60 g-irradiation dose in poly(methyl methacrylate) and linear poly(ethylene) at 77 K. We observe a linear relationship between the enhancement of the Ps formation and the density of trapped electrons in both polymers. This clear correlation strongly supports the previous suggestion by the authors that the increase in Ps formation with time (that has been observed at low temperatures for a number of polymers) can be explained as a reaction of free positrons with trapped electrons produced by the previously injected positrons. 7

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Free volume sizes in intercalated polyamide 6/clay nanocomposites

Polymer, 2005

The effect of incorporating modified clay into a polyamide 6 (PA6) matrix, on the free volume cav... more The effect of incorporating modified clay into a polyamide 6 (PA6) matrix, on the free volume cavity sizes and the thermal and viscoelastic properties of the resulting nanocomposite, was studied with positron annihilation lifetime spectroscopy, differential scanning calorimetry and dynamic mechanical analysis. At low concentrations of clay the fraction of PA6 crystals melting close to 212°C was increased, while the

Nanoscopic properties of silica filled polydimethylsiloxane by means of positron annihilation lifetime spectroscopy

Polymer, 2004

Positron annihilation lifetime spectroscopy (PALS) was performed on a series of polydimethylsilox... more Positron annihilation lifetime spectroscopy (PALS) was performed on a series of polydimethylsiloxane (PDMS)/fumed silicon dioxide (SiO 2 ) composites at temperatures between K185 and 100 8C to study the effect of filler content and filler particle size on the free volume properties and the positron annihilation characteristics. The glass transition behavior of the PDMS/SiO 2 composites was determined with differential scanning calorimetry. A clear influence on the o-Ps lifetime (t 3 ) in the polymer upon addition of nano-sized fumed SiO 2 was observed at all temperatures. The observed o-Ps lifetime behavior was related to filler content and filler particle size. A transition in the temperature dependence of the o-Ps lifetime was observed close to K35 8C above which temperature PDMS exhibits long o-Ps lifetimes. A relationship between t 3 and the surface tension, equivalent to the behavior of ordinary molecular liquids was observed in this temperature region. The o-Ps yield was strongly reduced in the crystallization region and by addition of SiO 2 . The reduction due to filler addition did, however, in the case of nano-sized SiO 2 not follow a linear relationship with filler weight, which was observed for micron-sized fillers. The nonlinear relationship between filler weight and o-Ps yield could be due to out-diffusion of positrons and/or o-Ps from the filler particles to the matrix. q

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Positron Annihilation Study of Defects in Succinonitrile

Physical Review Letters, 1979

Positron lifetime and angular correlation measurements have been made on the plastic crystal succ... more Positron lifetime and angular correlation measurements have been made on the plastic crystal succinonitrile. They confirm the phase transition at 234 +/- 1 K. In the plastic phase the average orthopositronium lifetime increases with temperature and saturates at the highest temperatures. This is interpreted as orthopositronium trapping in thermally created defects, probably vacancies. A defect formation energy of 0.36 +/- 0.1 eV is deduced. This is lower than predicted values of the vacancy formation energy.

Diffusion of nanosized sodium inclusions in platinum

by Andy Horsewell and Morten Eldrup

Journal of Physics: Condensed Matter, 1994

AbstracL Na inclusions with diameters in the range from 2 nm to 15 nm have been made by ion impla... more AbstracL Na inclusions with diameters in the range from 2 nm to 15 nm have been made by ion implantation of Na into 70 ntn thick singlecrystalline pt foils followed by annealing. The s t " of solid inclusions and the diffuslon of molten inclusions have been studied by " i s s i o n electron microscopy. At room t e m p " the inclusioos are faceted and crystalline with a BCC structure and they are aligned topotactically with the pf (KC) ma@ix. The diffusion of inclusions in the liquid state was investigated by annealing at temperatures of 1227 K, 1432 K and 1534 K. The diffusion coefficient was found to have a dependence on the inclusion radius and an activation energy of 2.8 0.2 eV, this being consistent with a mechanism by which volume self-diffusion of Fl controls the diffusion rate of the inclusions. Diffusion of pf at the interfaces between the pt matrix and the Liquid Na inclusions was found to be strongly inhibited compared with the free surface self-diffusion of pt The resnlts are used to propose a method to produce sources for positron annihilation spectroscopy at high tempenrurrs.

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Fundamental aspects of inert gases in solids

by Andy Horsewell, Jan Skov Pedersen, and Morten Eldrup

Journal of Nuclear Materials, 1992

The NATO Advanced Research Workshop on Fundamental Aspects of Inert Gases in Solids, held at Bona... more

Review: Evolution of stacking fault tetrahedra and its role in defect accumulation under cascade damage conditions

by Morten Eldrup, D.j Edwards, and S. Golubov

Journal of Nuclear Materials, 2004

In order to help understand the evolution of stacking fault tetrahedra (SFTs) in a cascade produc... more In order to help understand the evolution of stacking fault tetrahedra (SFTs) in a cascade producing irradiation environment, the available information on the behaviour of SFTs observed under different experimental conditions has been briefly reviewed. Effects of thermal annealing and irradiations on the stability of pre-existing SFTs produced by quenching and aging are also included in the review. Some results on the effects of thermal annealing of irradiationinduced SFTs are presented and discussed. The analysis of these observations leads to three significant conclusions: (a) during irradiation SFTs produced in the cascades are likely to interact with vacancies, self-interstitial atoms (SIAs) and SIA clusters, (b) interaction with SIAs and their clusters may cause both shrinkage and transformation of SFTs into Frank loops and (c) both during irradiation and annealing the lifetime of SFTs is determined not only by their thermal stability but also by their stability against transformation to loops. These facts must be taken into account in the theoretical treatments of damage accumulation. Published by Elsevier B.V.

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Fission neutron irradiation of copper containing implanted and transmutation produced helium

by Andy Horsewell, F. Garner, and Morten Eldrup

Journal of Nuclear Materials, 1992

Hngh purity copper containing approximately 100 appm hehum was produced in two ways In the first,... more Hngh purity copper containing approximately 100 appm hehum was produced in two ways In the first, hehum was nmplanted by cyclotron at Harwell at 323 K In the second method, helium was produced as a transmutation product in 800 MeV proton irradnatnon at Los Alamos, also at 323 K The dlstnhutnon~ of helium prior to fission neutron nrradxatxon were determined by a combination of transmission electron mncroscopy (TEM) and posnron anmhflation techniques (PAT) These speomens, together wtth pure copper, were then wradlatcd with fi,,snon neutro~ m a single capsule in fast flux test facihty (FFFF) at ~686 +_5 K to a dose level of -48 dpa (77x102~' nm -2, E>0.1 MeV) Investngauon of the void and dnslocahon mncrostructures m the three specnmens by TEM showed large differences between the speomens m void size and swelhng The observed differences as well as the effect of the presence of other transmutation produced impurity atoms in the 800 MeV proton Irradiated copper will be discussed

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Positronfit extended: A new version of a program for analysing position lifetime spectra

Computer Physics Communications, 1974

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Program system for analysing positron lifetime spectra and angular correlation curves

Computer Physics Communications, 1981

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Positronfit extended: A new version of a program for analysing positron lifetime spectra

Computer Physics Communications, 1984

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Positronfit: A versatile program for analysing positron lifetime spectra

Computer Physics Communications, 1984

In a condensed material positrons may annihilate at several different characteristic rates. A mea... more In a condensed material positrons may annihilate at several different characteristic rates. A measured positron lifetime spectrum will therefore consist of a sum of decaying exponential functions with different decay rates, smeared somewhat owing to the finite time resolution of the measuring system and superimposed on a constant background.

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PATFIT-88: A data processing system for positron annihilation spectra on mainframe and personal computers

Abstract. A data processing system has been developed for analyzing positron annihilation lifetim... more

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A small-angle neutron scattering and transmission electron microscopy study of krypton precipitates in copper

by Andy Horsewell, Jan Skov Pedersen, and Morten Eldrup

Journal of Physics: Condensed Matter, 1996

The annealing behaviour of bulk copper containing 2.6 at.% krypton has been studied by small-angl... more The annealing behaviour of bulk copper containing 2.6 at.% krypton has been studied by small-angle neutron scattering (SANS) and transmission electron microscopy (TEM). In addition positron annihilation spectroscopy (PAS) and mass-density measurements (MDM) were made. In the as-prepared and annealed material a high density of krypton precipitates ('bubbles') exists. Special emphasis is put on different approaches to the analysis of the SANS data. Differences between the results from the various analyses are pointed out and discussed. Polydisperse models clearly give the most extensive information, i.e. the size distribution of the Kr bubbles and integral parameters derived from it (i.e. bubble volume, total surface area and average radius). It is demonstrated that a correct choice of form factor is important for the reliability of the derived size distribution. In TEM a high degree of overlap of bubble images is observed and corrected for. Good agreement between the shapes of SANS and TEM size distributions is found, while differences in amplitude are ascribed to experimental uncertainties. Average krypton densities in the bubbles as well as fractional cavity volumes derived from PAS and MDM are found to be in good agreement, but the cavity volumes are clearly larger than the total bubble volumes obtained from the SANS and TEM size distributions. Above roughly 300 • C bubble growth takes place. Two different mechanisms for the initiation of growth are discussed. At the higher annealing temperatures the growth in bubble size and total volume fraction is explained by bubble migration and coalescence followed by absorption of thermal vacancies.

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