Jain, P. C.7; Eldrup, Morten Mostgaard5; Pedersen, Niels Jørgen5; Sherwood, J. N.8
1 Nano-Microstructures in Materials, Materials Research Division, Risø National Laboratory for Sustainable Energy, Technical University of Denmark2 Materials Research Division, Risø National Laboratory for Sustainable Energy, Technical University of Denmark3 Risø National Laboratory for Sustainable Energy, Technical University of Denmark4 University of Delhi5 Department of Energy Conversion and Storage, Technical University of Denmark6 University of Strathclyde7 University of Delhi8 University of Strathclyde
Positron annihilation angular correlation curves have been measured as a function of temperature for trimethylacetic (pivalic) acid in both the brittle and plastic phases. A simple fitting of the data to a sum of three gaussians shows the presence of a narrow component due to para-positronium (p-Ps) annihilation. In the brittle phase the intensity of the narrow component is inconsistent with previous positron lifetime data. A more detailed analysis, requiring consistency with the lifetime data, results in the determination of the shapes of the angular correlation components for free positron-, pick-off-, and p-Ps intrinsic annihilation. The p-Ps component has a width (fwhm) of 3.75 mrad in the brittle phase, probably due to Ps self-trapping or trapping in defects smaller than molecular vacancies. In the plastic phase the width (fwhm) is 3.25 mrad which is ascribed to Ps localization in vacancies and divacancies in accordance with positron lifetime data.
Chemical Physics, 1986, Vol 106, Issue 2, p. 303-313