1.Measurements The experiments were performed on 400 kV Cockcroft-Walton acceleratorof Nanjing University,using the T(d,n)~4He reaction to produce 14.6MeVneutrons.The energy of the incident deuterons was 200keV,the deuteroncurrent was 40μA,and the neutron yield was about 2×10~8 n/s.The ZnS neu-tron detector was used as flux monitor.Each sample to be measured was packedtogether in two standard sample foils of the same dimensions(2×1cm~2 rectang-lar foils and purities better than 99.5%)to form a sandwich so that they areirradiated in the same geometry.The γ-ray activities of the irradiated samplesand monitor foils were measured with a GEM-25210 type HPGe γ-spectrometer.The efficiency of this detector was determined with aEu standard γ source.