A generalised algorithm for spectral reconstruction in Compton spectroscopy with corrections for coherent scattering.

Reconstruction of primary-photon energy spectra from pulse-height distributions obtained in a Compton spectrometer has earlier been performed under the assumption that coherent scattering in the scatterer is negligible. This holds for most clinical x-ray units operated in the range 40-150 kV. In mammography, and to some extent in dental radiography, the relatively high frequency of low-energy photons (less than 30 keV) in the primary beam makes it necessary to extend the algorithms to allow for significant contribution of coherent scattering.

Measurement of absolute energy spectra from a clinical CT machine under working conditions using a Compton spectrometer.

Absolute measurements of photon energy spectra (keV-1 sr-1 mA-1 s-1) from a clinical CT machine have been performed under normal working conditions (140 mA tube current) using a Compton spectrometer. The inaccuracy of the measured spectra is estimated to be +/- 6%, determined by uncertainties in dead-time corrections and in the parameters of the geometrical set-up. Absorbed doses measured in thermoluminescent LiF dosimeters agree within this uncertainty with calculated ones derived from measured spectra (80 kVp, 120 kVp and 140 kVp) and tabulated mass energy absorption coefficients for LiF.

Compton spectroscopy in the diagnostic x-ray energy range. II. Effects of scattering material and energy resolution.

The overall performance of a Compton spectrometer and, in particular, its energy resolution are investigated both experimentally and theoretically for different scattering materials. Using low-Z (less than or equal to 8) scatterers of moderate sizes (scatterer diameter d less than or equal to 5 mm), there are negligible disturbances due to coherent and/or multiple scattering at 90 degrees scattering angle and photon energies above 20 keV. Two factors contribute to decreasing the energy resolution compared with that in direct measurements: (i) the velocity distribution of the electrons in the scatterer and (ii) the scattering geometry.

Compton spectroscopy in the diagnostic x-ray energy range. I. Spectrometer design.

The optimal design of a Compton spectrometer for measuring photon energy spectra from x-ray tubes in a clinical laboratory is analysed. The demands are: (i) coherent and multiple scattering distort the measurements and must be avoided; (ii) the measuring time should be as short as possible to avoid unnecessary wear on the x-ray tube; and (iii) the impairment in energy resolution due to the scattering geometry should be kept minimal. A scattering angle of 90 degrees is advocated.