Simple source preparation and disintegration rate measurement of56Co and its use for efficiency calibration

In order to precisely determine the γ-ray detection efficiencies in the energy region above 1500 keV, sources of 56Co, which emit many γ-rays with well determined emission probabilities in that energy region, have been prepared and used. After proton irradiation of natural iron foils, thin foils with 10-μm thickness were sandwiched with two metallised VYNS films and thick foils were treated by ion exchange after dissolving. Although 55Fe was produced by a secondary reaction, the disintegration rates of 56Co sources were successfully determined by means of the 4πβ–γ coincidence method. The absolute detection efficiency was determined and the emission probabilities for four weak γ-rays of 56Co were measured.