A 41-channel Xe detector array was developed for use in a fan-beam CT [computed tomography] scanner. Each channel is split into a front and rear detector producing 2 signals for each ray through the patient. Since the front and rear detectors measure different photon energies of the X-ray spectra, dual energy information is obtained from a single CT scan. This information can be used to determine electron density and effective atomic number images of the patient and correct spectral artifacts. A plexiglas cylinder 7.7 cm in diameter, filled with water and various plastics, was scanned. With this phantom, electron density was determined to an accuracy of 2% and effective atomic number to 4%. Details of the detector design and calibration are discussed and electron density, effective atomic number, and spectral artifact corrected images are presented.