Calibration of Cf-252 sources by neutron counting and gamma-ray spectrometry

Kamel Abbas - European Commission, Joint Research Centre
Davide Bertolotti - Nuvia Italia, Via Fermi, Ispra (VA), Italy
Stephen Croft - Lancaster University, Bailrigg, Lancaster (UK)
Riccardo Ferretti - European Commission, Joint Research Centre, Ispra (VA), Italy
Marc Looman - Consultant Nuvia Italia, Via Fermi, Ispra (VA), Italy
Giovanni Mercurio - European Commission, Join Research Centre
Stefan Nonneman - European Commission Joint Research Centre
Josef Zsigrai - European Commission, Joint Research Centre, Karlsruhe, Germany
Andrea Favalli - European Commission, Joint Research Centre

252Cf is a transuranium radionuclide which is well established as a consumer product in many application domains. It has found important uses in numerous industries including the nuclear sector being common place in nuclear safeguards, security, and research. It also plays a unique role in medicine either for diagnosis or in the therapy of diseases. 252Cf is commercially available in the form of sealed neutron sources from a number of suppliers and is usually delivered with nominal certification on the neutron emission rate, often given with large uncertainties (up to 30%), together with a statement of the isotopic composition of Cf (252Cf, 251Cf, 250Cf, 249Cf) and the date of the last radiochemical separation (from 248Cm). However, for some research and analysis applications it is necessary to know the neutron source output with more stringent uncertainties, 1% or less, and this is usually generally achieved only by the manganese bath technique which is available in only a limited number of metrology laboratories around the world. It is interesting to ask whether alternative methods can be used to characterize and calibrate 252Cf-sources to adequately meet local needs in a technically defensible way. This paper addresses this quest. It presents preliminary results of work carried out for the determination of neutron source activity and the neutron emission rate of physically small sealed 252Cf-sources using both high-energy resolution gamma-ray spectrometry with HPGe and high-level neutron coincidence counting (HLNCC). The measurements were performed in the PERLA laboratory of the Joint Research Centre (Ispra, Italy) using a set of sources spanning a wide dynamic range, and which have recently been certified in the manganese bath at the National Physical Laboratory (UK).