Helmut W Fischer et al 2006 Phys. Med. Biol. 51 N461 doi:10.1088/0031-9155/51/24/N02
Helmut W Fischer1, Ben E Tabot1,2 and Björn Poppe2
Show affiliationsActivation products have been identified by in situ gamma spectroscopy at the isocentre of a medical linear accelerator shortly after termination of a high energy photon beam irradiation with 15 × 15 cm field size. Spectra have been recorded either with an open or with a closed collimator. Whilst some activation products disappear from the spectrum with closed collimator or exhibit reduced count rates, others remain with identical intensity. The former isotopes are neutron-deficient and mostly decay by positron emission or electron capture; the latter have neutron excess and decay by β− emission. This new finding is consistent with the assumption that photons in the primary beam produce activation products by (γ, n) reactions in the treatment head and subsequently the neutrons created in these processes undergo (n, γ) reactions creating activation products in a much larger area. These findings are expected to be generally applicable to all medical high energy linear accelerators.
Issue 24 (21 December 2006)
Received 27 September 2006, in final form 25 October 2006
Published 30 November 2006
Helmut W Fischer et al 2006 Phys. Med. Biol. 51 N461
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