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Monte Carlo Study to determine the Monte Carlo Study to determine the Neutron Fluence spectrum for a Neutron Fluence spectrum for a
water Phantom: Preliminary Resultswater Phantom: Preliminary Results
University of the Western Cape
Energy Postgraduate Conference 2013
Presenter: Makhubela MathewsSupervisor: Mark Herbert
Co-Supervisor: Andrew Esau
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Introduction• In neutron therapy facility, neutron beam are used to
irradiate cancer cells.
• Consequently, prior knowledge of the neutron fluence is required for calculation of absorption dose in human tissue.
• During previous experimental studies, neutron fluence spectra inside a water phantom were experimentally measured at iThemba Labs.
• The current study was undertaken to investigate the feasibility of using neutron threshold spectrometry to determine the neutron fluence spectrum as an alternative technique.
• The Monte Carlo neutron Transport code Mcnpx Was used for Simulations.
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Material and Methods• Seven foils shown in table.1 were chosen as activation
detectors due to the availability of cross section data in Mcnpx libraries[1]
[1] Zhonglu Wang, Nolan E. Herbert, and Eric Burgett , Fermilabs Neutron Therapy Facility Neutron Spectrum Determination by Threshold Foils. International Workshop ON Fast Neutron
Detectors University of Cape Town, South Africa, April 3-6,2006
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Material and Method• Activation reaction selection criteria
Fig.2. cross section plots for activation foilsFig.1. example of a decay scheme
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Material and Methods• Reaction rates for bare
foils placed at different position in a water phantom were calculated using Mcnpx.
Fig.4. Activation foil positions inside a water phantom
dEEF )(4
dEEECFM )()(
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Response Matrix Calculations• Each foil is characterized by a response as a function of
incident energy, The response for each foil was calculated at different positions in a water phantom.
• The result were binned into 43 bines from 5.23 to 67Mev these was done using the FT special treatment card which bines the responses by incident energy groups.
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Neutron spectrum unfolding
• The spectrum adjustment code Maxed[2] solves the inverse of the matrix shown in previous slide to obtain the spectral distribution.
• Maxed uses a priori information to choose the solution which best fits the activation data from a infinite number of solution.
• Herbert et al measurement were use as estimates for the a priori information.
[2] M.REGGINATO, The ”Few-Channel” Unfolding Programs in the UMG package: MXD_fc33,GRV_FC33 and IQU_FC33,UMG package, Version3.3-release
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Results
Fig.5:Comparison of the unfolded spectrum and measurement, Measured Default spectrum.
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conclusion• The unfolded spectrum agree well with Measurement.
• Although it is clear that the shape of the final spectrum depends on the shape of the a priori spectrum.
• Introducing high energy threshold reaction in our simulations might improve the quality of the spectrum.
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Acknowledgements
• Manus & Matsci• E-HCD & KG• Immanuel Mulaudzi• Vusi Masondo