Jerzy Kansy

Point Defect Study in Fe72Al28 Alloy as a Function of Thermal Treatment by Positron Lifetime Spectroscopy

The defect structure of Fe28Al samples is examined with the Positron Annihilation Lifetime Spectroscopy. The studies are carried out for samples in as-cast state and after heat treatments: annealing for 24 hours at 900°C (or 1050°C) and either slow cooling with furnace or quenching to oil. The PALS spectra are analyzed using two-state trapping model. Only one type of defects is detected. The positron lifetime in these defects (V) suggests that they are quenched-in Fe-monovacancies (VFe). The vacancy concentration strongly depends on the rate of cooling. Besides, V also depends slightly on the rate of cooling of the material. This fact suggests, according to the predictions of latest theoretical calculations, that V is sensitive to the atomic configuration in the nearest neighborhood of VFe, which give hope to estimate the degree of atomic ordering in alloys by the PALS technique.

Positron Irradiation Effects in HDPE during PAL Measurement at Ambient Temperature

The positron irradiation effect in high density polyethylene at ambient temperature is studied by positron annihilation lifetime method. The positron spectra are analyzed with a model which takes into account positron trapping and so called delayed formation of positronium (DFP). A good relationship is noticed between the rate of positron trapping and the rate of DFP.

A Study of Point Defects in the B2-Phase Region of the Fe-Al System by Mössbauer Spectroscopy

In this work, Mössbauer spectroscopy and X-ray powder diffraction (XRD) are used in a study of point defect formation in intermetallic phases of the B2 structure of the Fe-Al system as a function of Al concentration. The results are compared with the concentrations of point defect determined from positron annihilation data. In the Mössbauer effect, two types of samples are investigated: Fe-Al alloys with few additives obtained by induction melting and Al-rich metallic powders produced by the self-decomposition method and intensive grinding of high energy in the electro-magneto-mechanical mill. The work presents the values of the 57Fe isomer shift and quadruple splitting for the components describing the point defect in the local environment of a Mössbauer nuclide. The concentration of the Fe vacancies and Fe atoms substituting Al (Fe-AS) are determined. The results show that an increase in Al content causes an increase in vacancy and Fe-AS concentration.

Positronium Thermalization Process in Nanoporous Materials and its Influence on the Shape of PALS Spectrum

A new method of analysis of PALS spectra of porous materials is proposed. The model considers both the thermalization process of positronium inside the pores and the pore size distribution. The new model is fitted to spectra of mesoporous silica MCM-41 and MSF. The resulting parameters are compared with parameters obtained from fitting the “conventional” models, i.e. a sum of exponential components with discrete or/and distributed lifetimes.

Thermalisation of Positronium in Polymers

A new model is presented which describes the annihilation of positronium (Ps) in polymers. Ps is formed in the bulk and is trapped into the free volume holes with epithermal initial energy and it thermalises towards its ground state during its lifespan through elastic collisions with the inner walls, This thermalisation is characterised by an asymptotic Ps-decay constant lambda(po)(infinity), an energy ratio parameter xi and by a relaxation parameter, from which the free volume hole size R, the effective recoiling mass M, and the quenching probability per collision mu can be obtained, We have verified this model on a set of cross-linked PMMA samples.