User's manual for PHOEL-2: a Monte Carlo computer code for calculating energies of photoelectrons and Compton electrons in water

A Monte Carlo computer code, PHOEL-2, is described for generating the energies of photoelectrons and Compton electrons in water irradiated uniformly by photons having an arbitrary energy spectrum. The code treats input photons individually on the basis of the energy-dependent cross sections for Compton scattering and for the photoelectric effect. Options exist for following each photon through successive Compton scattering events until it disappears by photoelectric absorption or allowing at most only a single Compton scattering event per input photon. The photoelectric effect can be turned on or off with either option. If energetically possible, the photoelectron is assumed to come from the oxygen K shell; otherwise, it originates in the L shell. An Auger electron of energy 0.508 keV is assumed to be emitted following the creation of a K vacancy. The basic numerical data used in PHOEL-2, their mathematical treatment, and the operation of the code are described. Detailed comparisons made with work for 60Co, and monoenergetic x rays confirm the numerical validity of results obtained with the code. Some of the data of Cormack and Johns are extended by including successive Compton scatterings for the same photon and by including the photoelectric effect and Auger electrons. PHOEL-2 can be obtained from the Radiation Shielding Information Center at Oak Ridge National Laboratory. The new version differs from the old by employing a more realistic handling of the photoelectric cross section as a function of energy, compiling electron spectra instead of storing the energies of every electron produced, eliminating some former input restrictions, and using a different random number generator. PHOEL-2 does not treat pair production, which should be included for water at photon energies above about 2000 keV. 5 figures, 4 tables