To the theory of Ps formation. New interpretation of the lifetime spectrum in water

Investigation of the Ability to Detect Electrolyte Disorder Using PET with Positron Annihilation Lifetime Spectroscopy

Various concentrations (8-300 mmol/L) of NaCl, KCl, and NaCl + KCl aqueous solutions were investigated using positron annihilation lifetime spectroscopy (PALS). A strong dependence of the o-Ps intensity as a function of the solution concentration was demonstrated. On this basis, the mean positron lifetime and the sum of counts in a selected time interval were proposed as reliable parameters for detecting disturbances in the ion balance of living organisms. The use of these parameters for differentiating healthy and cancerous tissues allows for the development of auxiliary diagnostic methods in a new generation of PET scanners equipped with a PALS detection module.

Microstructural free volume and dynamics of cryoprotective DMSO–water mixtures at low DMSO concentration

This work investigates the free-volume properties of the dimethyl sulfoxide (DMSO)–water mixtures by positron annihilation lifetime spectroscopy over a wide temperature range of 20–320 K. The processes of melting and solidification of the water, DMSO and the DMSO–water mixtures at 1.8, 2.0 and 10% vol. DMSO respectively were studied. It was found that the recrystallization during heating of the water–DMSO cryoprotective mixtures above 160 K at low DMSO concentrations is affected by the amount of DMSO in the mixture. The amount of amorphous phase formed during cooling influences the hysteresis between cooling and heating cycles which could be crucial for cell survival. Experiments also show the time dependence of crystallization which indicates that rapid heating can suppress this secondary crystallization which is undesirable during the cell thawing process. Similar concentrations of DMSO (1.8% and 2% vol. DMSO in water) where a 2% vol. DMSO mixture secures cell survival but 1.8 vol% does not, showed differences in structural and dynamic properties that are key factors in cell survival. These results were supported by differential scanning calorimetry and low frequency dielectric spectroscopy measurements. The obtained data are in strong agreement with the observed cryoprotective efficacy of the DMSO–water mixtures on living cells.

Positron annihilation lifetime spectroscopy reveals changes in the DMSO–water microstructure in low concentrations of DMSO (1.8%, 2.0% and 10% v/v) that have a great impact on the cryoprotective effect during the cryopreservation of cells.

Solid Eu(III) complexes studied by positron annihilation, optical and Mössbauer spectroscopies: insights on the positronium formation mechanism

In this work, positron annihilation lifetime (PALS), Doppler broadening annihilation radiation lineshape (DBARL), Mössbauer and optical spectroscopies measurements were performed in Eu(III) dipivaloylmetanate complex, Eu(dpm)(3), at 295 and 80 K. The Eu(dpm)(3) complex is not luminescent at 298 K and does not form positronium. On the other hand, it is highly luminescent at 80K, but still does not form positronium. The absence of positronium formation at 80K cannot be explained by a ligand/metal charge transfer process. We found strong evidences that the electronic delocalization does not occur at both temperatures. Despite the Mössbauer results being inconclusive regarding the Eu(III)/Eu(II) reduction hypothesis, previous results showing positronium formation in other Eu(III) complexes suggest that this process is not occurring. Thus, more studies are needed to explain the absence of positronium in Eu(III) complexes.