Abstract
Since the electron storage ring BESSY is suitable for use as a calculable radiation standard of extremely low photon flux, currents below 1 nA have to be measured exactly. For this we installed two different photon detection systems for monitoring the stepwise decrease in the photon flux as the number of stored electrons is reduced one by one. The performances of a photon counter, accepting a large solid angle of the visible and near-UV synchrotron radiation, and an array of photodiodes, sensitive mostly in the soft X-ray region, were investigated for different operational conditions of the storage ring. With a computerized data analysis routinely up to 1000 electrons are counted unambiguously allowing the determination of electron currents up to 0.77 nA with an uncertainty of 3 × 10 −7 of the measured current.
Published Version
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