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a b s t r a c tWe present here the first results obtained employing the Timepix3 for the detection and tagging of annihilations of low energy antiprotons. The Timepix3 is a recently developed hybrid pixel detector with advanced Time-of-Arrival and Time-over-Threshold capabilities and has the potential of allowing precise kinetic energy measurements of low energy charged particles from their time of flight. The tagging of the characteristic antiproton annihilation signature, already studied by our group, is enabled by the high spatial and energy resolution of this detector. In this study we have used a new, dedicated, energy selection beamline (GRACE). The line is symbiotic to the AEgIS experiment at the CERN Antiproton Decelerator and is dedicated to detector tests and possibly antiproton physics experiments. We show how the high resolution of the Timepix3 on the Time-of-Arrival and Time-over-Threshold information allows for a precise 3D reconstruction of the annihilation prongs. The presented results point at the potential use of the Timepix3 in antimatter-research experiments where a precise and unambiguous tagging of antiproton annihilations is required.

The exact solution of a diffusion−reaction model for the trapping and annihilation of positrons in small extended spherical defects (clusters, voids, small precipitates) with competitive rate-limited trapping in vacancy-type point defects is presented. Closed-form expressions are obtained for the mean positron lifetime and for the intensities of the two positron lifetime components associated with trapping at defects. The exact solutions can be conveniently applied for the analysis of experimental data and allow an assessment in how far the usual approach, which takes diffusion limitation into account by means of effective diffusion-trapping rates, is appropriate. The model is further extended for application to larger precipitates where diffusion-and reaction limited trapping is not only considered for the trapping from the matrix into the precipitate−matrix interface but also for the trapping from inside the precipitates into the interfaces. This makes the model applicable to all type of composite structures where spherical objects are embedded in a matrix irrespective of their size and their number density.

The design of specific material properties of aluminum alloys demands for a detailed understanding of clustering and precipitation processes occurring during heat treatments. Positron lifetime spectroscopy in combination with high-precision dilatometry measurements were taken, allowing for a comprehensive analysis of the aging mechanisms occurring on different timescales and in different temperature regimes, during artificial aging. From the results, unambiguous experimental evidence for the following three main steps of the precipitation process is obtained. In the first seconds of artificial aging, a competitive process of dissolution and growth of different cluster types occurs. Subsequently, clusters start to transform into coherent precipitates, which are mainly responsible for the hardening effect. For prolonged artificial aging, the number density of the coherent precipitates increases, while positron lifetime spectroscopy already reveals the simultaneous formation of less coherent precipitates.