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Displacement Effect of Thimble Chambers Exposed to a Photon or Electron Beam from a Betatron

Displacement Effect of Thimble Chambers Exposed to a Photon or Electron Beam from a Betatron FROM THE RADIATION PHYSICS DEPARTMENT (DIRECTOR : ASSOC. PROF. G . HETTINGER), UNIVERSITY OF UME.~, SWEDEN. DISPLACEMENT EFFECT OF THIMBLE CHAMBERS EXPOSED TO A PHOTON O R ELECTRON BEAM FROM A BETATRON G. HETTINGER, PETTERSSON H. SVENSSON C. and Depth doses of high-energy photons and electrons from a betatron are often determined with the aid of ionization chambers in a water phantom. The ratio between the dose absorbed in water and ionization in the air cavity must then be known, however. This ratio depends on the radiation energy and thus in the case of electrons on the depth at the point of measurement. This ratio has been studied in a number of experimental and theoretical investigations recently performed. When the centre of the thimble chamber is selected as the measurement point, the dose/ionization ratio has to be corrected for displacement of phantom material by the air cavity (JOHNS 1961, SPIERS MEREDITH & 1962). SKAGGS (1949) pointed out that the effective measurement point of a cylindrical chamber exposed to electrons from a betatron is just beyond the front wall of the chamber. If no correction for displacement is applied at electron radiation, the error in the dose/ionization ratio may http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Acta Radiologica Informa Healthcare

Displacement Effect of Thimble Chambers Exposed to a Photon or Electron Beam from a Betatron

Abstract

FROM THE RADIATION PHYSICS DEPARTMENT (DIRECTOR : ASSOC. PROF. G . HETTINGER), UNIVERSITY OF UME.~, SWEDEN. DISPLACEMENT EFFECT OF THIMBLE CHAMBERS EXPOSED TO A PHOTON O R ELECTRON BEAM FROM A BETATRON G. HETTINGER, PETTERSSON H. SVENSSON C. and Depth doses of high-energy photons and electrons from a betatron are often determined with the aid of ionization chambers in a water phantom. The ratio between the dose absorbed in water and ionization in the air cavity must then be known, however. This ratio depends on the radiation energy and thus in the case of electrons on the depth at the point of measurement. This ratio has been studied in a number of experimental and theoretical investigations recently performed. When the centre of the thimble chamber is selected as the measurement point, the dose/ionization ratio has to be corrected for displacement of phantom material by the air cavity (JOHNS 1961, SPIERS MEREDITH & 1962). SKAGGS (1949) pointed out that the effective measurement point of a cylindrical chamber exposed to electrons from a betatron is just beyond the front wall of the chamber. If no correction for displacement is applied at electron radiation, the error in the dose/ionization ratio may
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