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Predicting Induced Activity in the Havar Foils of the 18F Production Targets of a PET Cyclotron and Derived Radiological Risk

Martinez-Serrano, J. Javier*; Diez de los Rios, Antonio

doi: 10.1097/HP.0000000000000064
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Abstract: The PET cyclotron at the Centre of Molecular Imaging of the Universidad de Malaga (CIMES) is a 16.5 MeV GE PETtrace cyclotron working at dual beam (40 μA beam−1). The cyclotron is dedicated mainly to 18F production. The 18F target has two thin circular foils composed of a metal alloy (Havar), that are highly activated by the proton beam and secondary neutrons. The main purpose of this study is to assess induced activity radiological risk derived from the Havar foils activation. Induced activity in Havar foils was estimated by two procedures. One consisted in estimating neutron and proton fluxes with MCNPX and using them as inputs in the activation code ACAB. Alternatively, given the regular periodicity of the irradiation cycles, an analytical expression was derived to estimate activity concentrations of activation products using production rates calculated with MCNPX. Large differences were found in the induced foil activities predicted by the two procedures. Therefore, an irradiated vacuum foil was measured with a Ge detector to analyze activity levels. Cobalt-58 (58Co) and 56Co activities calculated with ACAB match well with measurements. Cobalt-60 (60Co) activity estimated with the alternative method agrees acceptably with the measured activity, and 58Co activity is slightly overestimated. Cobalt-57 (57Co) is the activation product of concern in the long term. The vacuum and window foils will be exempted in 3.3 y and 5.5 y, respectively, after replacement. Calculated effective dose with MCNPX and ICRP reference HML phantoms in the foils replacement operation is 0.34 mSv, and annual effective dose would be 2.1 mSv, which is below the annual limits.

*Departamento de Física Aplicada I, Facultad de Ciencias, Boulevar Louis Pasteur s/n, Universidad de Malaga, 29010, Malaga, Spain; †Departamento de Radiología y Medicina Física, Facultad de Medicina, Boulevar Louis Pasteur 32, Universidad de Malaga, 29010, Malaga, Spain.

The authors declare no conflicts of interest.

For correspondence contact: J. Javier Martínez Serrano, Departamento de Física Aplicada, Facultad de Ciencias, Boulevar Louis Pasteur s/n, Universidad de Malaga, 29010, Malaga, Spain, or email at javiermserrano@uma.es.

(Manuscript accepted 29 October 2013)

© 2014 by the Health Physics Society