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Determination of the source position for the electron beams from a high‐energy linear accelerator
Author(s) -
Jamshidi Abolghassem,
Kuchnir Franca T.,
Reft Chester S.
Publication year - 1986
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.595823
Subject(s) - physics , linear particle accelerator , scattering , full width at half maximum , electron , electron scattering , collimated light , photon , atomic physics , advanced photon source , computational physics , optics , particle accelerator , nuclear physics , beam (structure) , laser
We have investigated the energy and field‐size dependence of the source position of the electron beams from a Varian Clinac‐2500 accelerator. Three independent experimental methods were used: (1) multipinhole camera (MPC), (2) back projection of the full width at half maximum (FWHM), and (3) the inverse square law (ISL). The positions of the virtual and effective sources were calculated using the multiple Coulomb scattering (MCS) formalism. The results obtained from the MPC agree, within the experimental uncertainties, with the calculated values for the virtual source position. Similarly, the results from the FWHM method agree with the calculations with the exception of those for small field sizes at the lower energies. This is consistent with the fact that both kinds of measurements are not very sensitive to scattering in the photon and electron collimators. In contrast, the source position determined by the ISL method shows strong dependence on field size and energy, and does not agree with the values predicted by the MCS formalism. This is due to contamination from electrons scattered in the x ray and electron collimation system. The techniques and results reported here should be generally applicable to other scatter foil linear accelerators.