Experimental model of positron lifetime spectrometer with β+-γ coincidence

A positron lifetime method is a unique method for sensitive detection of hole, aggregate and dislocation in the crystal and distinguishing them as a kind and a quality. The β+-γ coincidence measurement method is able to observe the positron lifetime under the condition of the sample separated from the radiation source. 68Ge (about 3MBq) was used as the radiation source of positron. An annealing pure Cu sample was observed at room temperature. The results showed the main component (91.6%) 123±2ps and the second one (8.4%) 1087±20ps. The former value agreed with the result of the usual method (γ-γ coincidence method), although the spectrum was less S/N, higher back ground and much more amount of long life components than that of usual method. When the positron energy was selected by electromagnet, the full widths at half maximum (FWHM) changed from 283 ps to 192 ps. The fact enabled the effective control of the resolving power decreasing. (S.Y.)