The NPL air kerma primary standard PS5-1/PS5-2 for 137Cs and 60CO: summary of factors

Since the 1950s the UK primary standard for the realisation of air kerma for high energies consisted of three graphite-walled cylindrical cavity ionisation chambers. These chambers have become increasingly unreliable in recent years and a project was started at the National Physical Laboratory to replace them. Spherical graphite-walled cavity ionisation chambers PS5-1 and PS5-2 have been constructed and commissioned and this report summarises the factors for the new chambers.