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

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Abstract
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' is advocated. Scatterers (of low-atomic-number material) in the shape of long circular rods (0.5-4 mm diameter, 20-40 mm long) are preferable to scattering foils. Use of a short focus-scatterer distance ( approximately 200 mm) is to be preferred compared to using a large detector are a (>or=4 mm diameter) in order to establish a sufficiently high count rate in the detector. Short focal distances and a 90' scattering angle are advantages in measuring energy spectra in the gantry of CT machines where the available space is limited. To limit the geometrical energy broadening to less than 1 keV, the spread in scattering angles of registered photons must not exceed 1-2' for incident photon energies of 100-150 keV.