POSITRON IRRADIATION EFFECTS ON POSITRONIUM FORMATION IN POLYCARBONATES DURING A POSITRON-ANNIHILATION EXPERIMENT |
| T. Suzukia, K. Kondoa, E. Hamadab and Y. Itoc aHigh Energy Accelerator Research Organization (KEK) Tsukuba, Ibaraki 305-0801, Japan bDepartment of Radiological Sciences, Ibaraki Prefectural University of Health Sciences Ami, Ibaraki 300-0394, Japan cResearch Center for Nuclear Science and Technology, The University of Tokyo Tokai, Ibaraki 319-1106, Japan |
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| The positron-irradiation effect on polycarbonate during a positron-annihilation lifetime spectroscopy experiment was investigated using different intensities of 22Na positron sources and γ-irradiated samples. The decrease in I3 was larger for a larger intensity of positron sources. In the case of a weak source (~140 kBq), I3 did not change with the elapsed time for non-irradiated samples. However, for 1 MGy irradiated samples, I3 measured with the weak source increased with the elapsed time. This can be attributed to a decrease in the radicals induced in the irradiated samples by γ-irradiation. In order to explain the change in I3 measured at room and liquid-nitrogen temperatures, several effects, such as radicals, cross-linking, structure change, and charging, need to be considered. Also, it is difficult to explain the change in I3 using only one of these effects. |
| DOI: 10.12693/APhysPolA.99.515 PACS numbers: 78.70.Bj |