Positron Anihilation Spectrometers

Positron lifetime spectrometer of fast-fast type comprising BaF2 scintillators and XP2020Q photomultipliers with time resolution 260 ps.

The 30-μCi activity positron source containing 22Na isotope enveloped in 7-μm thick kapton foil is used in the measurements. Positron lifetime spectroscopy has been used to study vacancies, vacancy clusters and dislocations in metallic samples, free volumes in polymers and pores (open and closed) in porous materials. The software necessary for processing the experimental data is available.

Doppler broadening spectrometer comprising coaxial HpGe detector with energetic resolution 1.44 keV interpolated for 511 keV.

The spectrometer enables us to measure the contribution to the spectrum originating in positron annihilation with low momentum electrons in the sample. This contribution is correlated with structural changes and presence of point defects of vacancy type. The so called S-parameter measurement is a standard procedure. However, the measurement set-up can be modified so that the germanium detector working in coincidence with NaJ(Tl) scintillation detector registers spectra with reduced background. The peak to background ratio is equal to 1000:1 for 22Na source and 5000:1 for 68Ge source. This type of measurements reveals the positron annihilation with electrons of ion cores.

Long slit positron annihilation apparatus.

The set-up is used for measurement of the peak height of the angular correlation curve as a function of temperature in temperature range 20-300°C. It enables us to detect the changes of vacancy or vacancy clusters concentration with temperature, which are connected with such processes as thermal generation of vacancies or annealing of vacancies during or recovery recrystallization. The set-up is used also for the study of vacancy - impurity interaction in low-melting metals and alloys.

Positron implantation profile spectrometer.

The measurement set-up based on the HpGe detector is used for detection of positron profile for positrons emitted from radioactive sources with the spatial resolution 50 μm. The positron linear absorption coefficient for different materials may be determined with the accuracy of a few percent. We use the 22Na source of activity 0.1 μCi and 68Ge source of activity 0,2 μCi. The set-up was successfully applied for the measurement of defect depth profile of vacancy type created by the mechanical processing of the surface. The method takes advantage of the change of the positron annihilation line shape with the depth, where the positrons annihilate.

Photos

Department in which the equipment is in use:

Positron Annihilation Laboratory (Department of Structure Research of Condensed Matter)