Dosimetry of high-energy electron linac produced photoneutrons and the bremsstrahlung gamma-rays using TLD-500 and TLD-700 dosimeter pairs

The neutron and gamma doses are crucial to interpreting the radiation effects in microelectronic devices operating in a high-energy accelerator environment. This report highlights a method for an accurate estimation of photoneutron and the accompanying bremsstrahlung (gamma) doses produced by a 450MeV electron linear accelerator (linac) operating in pulsed mode. The principle is based on the analysis of thermoluminescence glow-curves of TLD-500 (Aluminium Oxide) and TLD-700 (Lithium Fluoride) dosimeter pairs. The gamma and fast neutron response of the TLD-500 and TLD-700 dosimeter pairs were calibrated with a (CO)-C-60 (gamma) and a Am-241-Be (alpha,n) neutron standard-source, respectively. The Kinetic Energy-Released in Materials (kerma) conversion factor for photoneutrons was evaluated by folding the neutron kerma (dose) distribution in (LiF)-Li-7 (the main component of the TLD-700 dosimeter) with the energy spectra of the Am-241-Be (alpha, n) neutrons and electron accelerator produced photoneutrons. The neutron kerma conversion factors for Am-241-Be neutrons and photoneutrons were calculated to be 2.52 x 10(-3) and 1.37 x 10(-3) mu Gy/a.u. respectively. The bremsstrahlung (gamma) dose conversion factor was evaluated to be 7.32 x 10(-4) mu Gy/a.u. The above method has been successfully utilised to assess the photoneutron and bremsstrahlung doses from a 450 MeV electron linac operating at DESY Research Centre in Hamburg, Germany. (c) 2005 Elsevier B.V. All rights reserved.