Revised correction factor for the UK national primary standard for air kerma for¹³⁷Cs and⁶⁰Co gamma-rays

From 1 May 2009 the United Kingdom National Physical Laboratory (NPL) has changed its air kerma standards for Cs-137 and Co-60 gamma-rays. Adoption of the new correction factors results in an increase in the NPL air kerma standard by similar to 1% for both Cs-137 and Co-60 gamma-rays. All NPL secondary standard calibrations issued after 1 May 2009 contain the revised correction factor.