E. Hamadaa,1, N. Oshimab, K. Katoha, T. Suzukic, H. Kobayashic, K. Kondoc, I. Kanazawad and Y. Itoe
aDepartment of Radiological Sciences, Ibaraki Prefectural University of Health Sciences Ami, Ibaraki 300-0394, Japan
bAtomic Physics Laboratory, The Institute of Physical and Chemical Research (RIKEN) Wako, Saitama 351-0198, Japan
cHigh Energy Accelerator Research Organization (KEK) Tsukuba, Ibaraki 305-0801, Japan
dDepartment of Physics, Tokyo Gakugei University, Koganei, Tokyo 184-0015, Japan
eResearch Center for Nuclear Science and Technology, The University of Tokyo Tokai, Ibaraki 319-1106, Japan
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A pulsing system for a slow-positron beam was applied to study the region near the surface of low-density polyethylene film using positron-annihilation lifetime measurement. The lifetime and intensity of ortho-positronium near the surface were measured as a function of the incident positron energy (1.6-9.1 keV). The size of intermolecular spaces in the surface region (~1500 nm) was larger than that in the bulk region. This tendency was especially strong in the region around 200 nm below the surface. On the other hand, the intensity of ortho-positronium decreased at lower incident positron energies, which was attributed to a decrease in the density of the spur electrons and/or an increase in the number of reemitted positrons from the surface.
1corresponding author
DOI: 10.12693/APhysPolA.99.373
PACS numbers: 78.70.Bj