The air-kerma strength per unit activity is estimated based on the Monte Carlo calculated fluence spectra around the four types of sources. The uncertainty is 1 standard deviation of statistical uncertainty. On the source surface the air-kerma strength is lower than at distances from 1 cm and up. This is explained from the geometry of the source being a line and not a point.
All angles are in radians.
At distances from 1 cm and up, this value is approximately 1.0 except for the VariSource for which the distance must be 5 cm to consider it a point source. The ratios of the air-kerma strength at the source surface to that at 1 cm distance for the four sources are 0.372, 0.273, 0.270 and 0.081, respectively. The difference from the theoretical value is the influence of absorption and scatter in the core and in the encapsulating material. At these distances the geometry factor is approximately 1. This work Glasgow et al.