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The Water Equivalence of Organic Liquid Scintillators for Proton Dosimetry

S Ingram

W S Ingram*, D Robertson, S Beddar, UT M.D. Anderson Cancer Center, Houston, TX

SU-E-T-116 Sunday 3:00:00 PM - 6:00:00 PM Room: Exhibit Hall

Purpose: Torganic liquid scintillators are currently under investigation for use in proton dosimetry. The purpose of this work is to evaluate the water equivalence of these materials as a preliminary step to identify scintillators that are well-suited to this purpose.

Methods: Stopping powers were calculated for 0.001-1000 MeV protons in water, polystyrene, and two organic liquid scintillators: BC-531 and OptiPhase 'Hi-Safe' 3 at 0%, 25%, and 50% concentrations of water. Angular scatter was quantified by theta0, a characteristic multiple Coulomb scattering angle analogous to the standard deviation of a Gaussian distribution of proton angles relative to the incident beam axis. Theta0 was calculated as a function of depth over the range of 200 MeV protons in these materials.

Results: Collisional stopping power in BC-531 ranged from +44% to +1% of that in water. It remained within 6% from 2-600 MeV. OptiPhase ranged from +24% to -2%, with smaller deviations at increased water concentrations. At all concentrations, OptiPhase showed smaller deviations than polystyrene and BC-531 and remained within 1% of water from 2-600 MeV.

Theta0 was very similar for all materials, with deviations from water of 5 milliradians or less over the majority of the proton range. BC-531 showed deviations of 10 milliradians or more in the last few millimeters of the range. OptiPhase showed smaller deviations than BC-531 or polystyrene, and these deviations decreased with increasing water concentration.

Conclusions: OptiPhase was found to be more water equivalent than BC-531 or polystyrene in stopping power and angular scatter, and increased water concentration improved both quantities. Large deviations in stopping power were only found below 2 MeV for any material, where proton range is less than 0.1 millimeter. The deviations from water found in angular scatter were less significant, and probably too small to affect measurement.

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