Dose measurements of Bremsstrahlung-produced neutrons from thick targets at the Advanced Photon Source

Bremsstrahlung is produced in the Advanced Photon Source storage ring when the positron beam interacts with the storage ring components or with the residual gas molecules in the storage ring vacuum. This bremsstrahlung has an energy range of zero to 7.0 GeV, which is the maximum energy of the positron beam. Bremsstrahlung photons of sufficiently high energy can interact with beam line components such as beam stops and collimators, generating neutrons of varying energies. This paper presents the results of simultaneous measurements, conducted at the Advanced Photon Source, of bremsstrahlung and the corresponding photoneutron production from thick targets of iron, copper, tungsten and lead, which allow one to correlate photoneutron dose rates from these metals as a function of bremsstrahlung power. The average photoneutron dose equivalent rates, normalised to the bremsstrahlung power, are measured as 2.7 +/- 0.5 rem/h/W for iron, 3.2 +/- 0.5 rem/h/W for copper, 3.9 +/- 05 rem/h/W for tungsten and 4.6 +/- 0.8 rem/h/W for lead targets. These are measured at 80 cm lateral from the centre of the targets, perpendicular to the photon beam direction.