Determination of the photon-contribution of a $^(238)$Pu-Be source

Gamma radiation of a $^(238)$Pu-Be source at CERN was measured with two neutron insensitive ionisation chambers, i.e. a graphite chamber filled with CO//2 and a steel chamber filled with argon, in order to determine the photon-contribution to ambient dose equivalent. These straightforward measurements were confronted with a novel method using a recombination chamber, with which a coarse spectrum in LET of the mixed radiation field can be obtained. The lowest LET part of the spectrum corresponds to the photon-contribution to the absorbed dose of mixed radiation. The comparison of the different methods showed very good agreement within the measurement uncertainties.