Intense Pulsed Positron Beam Research Articles

Defect dynamics studies during heat treatments in plastically deformed metals predicted for nuclear applications

We report on defects dynamics during heat treatment in plastically deformed metallic materials using positron annihilation lifetime spectroscopy carried out on the intense pulsed positron beam. The conducted experiment allowed us to observe the changes in the concentration and sizes of vacancy-like defects observed during in situ annealing. We monitored heat treatments up to 300 °C in hydrostatic extruded Ti and cavitation peened V–4Cr–4Ti alloy. We were able to track the recovery processes in Ti and redistribution of large voids at the surface of cavitation peened V–4Cr–4Ti alloy. The relaxation time during recovery was about 20 min. Performed experiments show that in cold-worked metallic materials significant changes in vacancy clusters concentrations occur at mildly elevated temperatures. The presented results give opportunity to the application of in situ observation of defects dynamic to similar problems related to thermomechanical processing of metallic materials.Graphical abstract

Hydrogen‐induced defects in Pd films

AbstractHydrogen absorbed in crystalline solids causes a lattice expansion and the formation of hydride phases. Contrary to free standing bulk samples, thin films are fixed at substrates, which prevent their in‐plane expansion. This makes hydrogen‐induced expansion of thin films highly anisotropic and leads to the formation of high stresses in hydrogen loaded thin films. As a consequence, lattice defects may be created in thin films loaded with hydrogen. This work reports about defects created by hydrogen loading in epitaxial Pd films deposited on Al2O3 substrates by cold cathode beam sputtering. Hydrogen‐induced defects are characterized by positron annihilation spectroscopy performed with variable energy slow positron beams. Extended studies of defect depth profile and its development with increasing concentration of hydrogen are performed by measurement of Doppler broadening of annihilation profile using a continuous positron beam. Selected states are investigated also by positron lifetime spectroscopy on an intense pulsed positron beam. Firstly, the microstructure of virgin films is characterized. Subsequently, the hydrogen concentration in the films is increased step‐by‐step by electrochemical charging. The development of the film microstructure and the evolution of defects are investigated. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A positron lifetime spectroscopy apparatus for surface and near-surface positronium experiments

A positron lifetime spectroscopy apparatus, which utilizes an intense pulsed positron beam generated by an electron linear accelerator, is presented. Using this apparatus we can measure positron lifetime spectra with variable energy, high count rate, wide measurable time range, and high peak-to-background ratio. These features are suitable for surface and near-surface positronium experiments.

Production and application of pulsed slow positron beam using an electron linac

Slow positron beam is quite useful for non-destructive material research. At the Electrotechnical Laboratory (ETL), an intense slow positron beam line has been constructed by exploiting an electron linac in order to carry out various experiments on material analysis. The beam line can generate pulsed positron beams of variable energy and variable pulse period. Various capabilities of the intense pulsed positron beam is presented, based on the experience at the ETL, and the prospect for the future is discussed.

Control and measurement system for positron experiments at the ETL linac facility

A control and measurement system for positron experiments in the Electrotechnical Laboratory (ETL) slow positron facility has been developed. The system acquires both monitor signals from the ETL electron linac and time spectrum data from the positron experimental apparatus. Furthermore, this system enables us to control both the linac and positron experimental apparatus remotely and semi-automatically. Using this system we can perform positron lifetime measurements as well as positron annihilation-induced-Auger electron spectroscopy with an intense pulsed positron beam with minimum labor.

Generation of an intense pulsed positron beam for positron lifetime and TOF experiments

Recent advances in the intense slow positron beam line at the Electrotechnical Laboratory are reported. Several improvements on the beam line have been made in order to carry out high count-rate positron lifetime spectroscopy and TOF experiments with a wide spectral range. We report the present status of the intense positron beam, high count-rate (∼10 5 cps) time-spectrum measurement system, and design of a new linear storage section which generates an intense beam of low energy spread.

An intense pulsed positron beam

A positron pulsing system for an intense positron beam generated by an electron linac is reported. The pulsing system generates an intense pulsed positron beam of variable energy and variable pulse period. The pulsed positron beam is used as a non-destructive probe for various material research. In this paper, we also discuss applications of the pulsed positron beam: positron lifetime spectroscopy, age-momentum correlation spectroscopy, positronium time-of-flight measurement, and positron annihilation-induced Auger electron spectroscopy with a time-of-flight technique.