Spectrometric investigation of scattering contribution in photon fields of Cs-137 and Co-60 sources

For calibrating photon dosemeters monoenergetic photon fields with known properties at the point of interest are needed. Usually encapsulated Cs-137 and Co-60 sources are used to determine the response of the dosemeters in dependence on the energy. Due to this encapsulation the photon spectra emitted from the source will be changed. This means that the knowledge of the spectral distribution of the incoming photons at the point of calibration is necessary for determining their contribution to the total kerma. Moreover it is also of interest to know the amount of wall-scattered photons in the calibration fields. With a Ge(Li)- and a 3'' x 3'' NaI(Tl) detector these influences were investigated. For unfolding of the pulse height spectra of the NaI(Tl) detector the response function of Berger and Seltzer were used. From this unfolded energy distribution of the photons the kerma in air was determined by means of the mass energy transfer coefficients of Hubbell. These values were then compared with the reading of a spherical ionization chamber in the same fields. The measurements were carried out in two different rooms and the distance between source and detector was varied. (orig.)