An introduction to the subject is given, the principle of lifetime measurements is discussed and the experimental apparatus described. A computer program used for data analysis is described and the problems involved in the analysis discussed. All lifetime spectra are resolved into three components. For H2O the long lifetime, attributed to ortho-positronium, is 0.68 usee inicebetween -196°C and -100°C, increases to 1.12 nsec at 0°C and abruptly to 1.86 nsec upon melting. Its relative intensity is 52% in ice and 27% in water. Spectra for heavy ice are identical with those for light ice, whereas heavy water gives 2.01 nsec, 22%. The increase in lifetime in ice above -100°C is attributed to trapping of positronium in temperature-created defects. Spectra for frozen aqueous soluotions of concentrations above 10-7 mole fraction contain at -160°C a longlived component attributed to the trapping of positronium. Very good agreement with the trapping model is obtained for HF solutions, both fast frozen
and annealed. An irreversible change in the spectrum takes place by heating a fast frozen HF solution approx. -125°C.
|Place of Publication||Roskilde, Denmark|
|Publisher||Risø National Laboratory|
|Number of pages||115|
|Publication status||Published - 1971|
|Series||Denmark. Forskningscenter Risoe. Risoe-R|
- Risø report 254