Secondary standards for 223Ra revised

• The new NIST primary standard for Ra-223 is transferred to secondary measurements.
• Dose calibrator calibration factors first reported in 2010 are revised.
• New experiments confirm the validity of the data reevaluations.

Dose calibrator dial settings reported by NIST in 2010 (ARI, v. 68, p. 1367) are now known to give erroneously low (by 10%) activity readings. The original determinations were based on a chain of calibrations; a broken link in this chain was recently discovered. New calibration factors (i.e., dial settings), directly linked to updated NIST primary standards, are reported here. In addition, the raw data used to derive the factors reported in 2010 are revisited. The validity of the reevaluation is established via comparison with the new experiments and revised calibration factors for numerous clinical geometries are reported. The main conclusions of the 2010 report regarding geometry effects remain valid.