| Popis: |
The annihilation scheme of positrons in liquid helium at 4.2\ifmmode^\circ\else\textdegree\fi{}K was studied. Three components in the decay were observed with mean lives: ${\ensuremath{\tau}}_{1}l5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$ sec, ${\ensuremath{\tau}}_{2}=(2.6\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$ sec, and ${\ensuremath{\tau}}_{3}=(1.2\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$ sec. The abundance of the ${\ensuremath{\tau}}_{3}$ component is (16\ifmmode\pm\else\textpm\fi{}2)% of all positrons which annihilate in the liquid. Three-quantum annihilation occurs in about 15% of all positron annihilations. This leads to the conclusion that the three components are due to parapositronium, free positron annihilation, and orthopositronium. |
