DETERMINATION OF PHOTON-EMISSION PROBABILITIES OF RADIONUCLIDES USING A SI(LI) DETECTOR CALIBRATED BY THE PRIMARY STANDARD SOURCE, BESSY

BESSY is an electron storage ring which is optimized for use as a primary radiometric standard source for the infrared to X-ray region. The relative uncertainty of the spectral photon flux Phi(E) is less than 0.45% (1 sigma) in the spectral range 5<E<15 keV. Measurements in undispersed synchrotron radiation produced a quantum detection efficiency for a Si(Li) detector with relative uncertainties of less than 0.5%. The calibrated detector was used to measure the photon flux of radioactive standards of known activity Co-57, Zn-65 and Y-88) in the photon energy range from 5 to 15 keV. From these measurements, the K-alpha X-ray and gamma-ray emission probabilities p(E) of the radionuclides were deduced. Our results for the K-alpha X-ray lines of Co-57, p(6.4 keV)= 0.501(5) and Zn-65, p(8.0 keV)= 0.346(3) and for the ratio p(Co-57; 14.4 keV)/p(Y-88; 14.1 keV)= 0.179(4) have small uncertainties and are not affected by uncertainties in the fluorescence yields. They confirm recommended data.