Speaker
Mr
Angelo La Manna
(DIFTER University of Palermo)
Description
Abstract
X-ray spectra and dosimetry information are very important for quality assurance in
X-ray diagnostic systems. Several semiconductor detectors (Si, Ge) have been
proposed
for medical X-ray measurements [1,2]. Recently, cadmium telluride (CdTe)
semiconductor is promising X-ray detector and is suitable for portable systems. The
number of papers investigating the physical and the spectrometry properties of CdTe
detectors [3] has increased many times in the course of the 90s and keeps on
growing.
The high atomic number (Cd: 48, Te: 52) and the high density (~ 5.9 g cm-3) of CdTe
crystals ensure high detection efficiency for photons with energy below 100 keV even
for thin detectors; the wide band gap (EG ~ 1.5 eV) enables CdTe detectors to be
operated at room temperature without cryogenics. In this work a CdTe portable
apparatus for X-ray spectroscopy and dosimetry is described. The system is able to
directly measure (count mode of operation) X-ray spectra and X-ray fluence at high
photon count rate, as typical of medical X-ray diagnostic systems. The portable
device
consists of four blocks: a detector case (detector and preamplifier), a shaping
amplifier, an ADC card and a notebook computer. Schottky contacts and a
thermoelectric cooling (-30° C) of both the CdTe crystal and the preamplifier input
FET ensure low noise and good stability in the X-ray measurements. The output
preamplifier pulses are processed by the shaping amplifier and then are recorded by
a
12 bit ADC card with a 10 MHz sampling rate. A dedicated software calculates the
incident photon count and the energy spectrum by analyzing the sampled output of
the ADC
card.
Good system response to monoenergetic photons was measured using X-ray and gamma-ray
calibration sources (109Cd e 241Am). Measured molybdenum X-ray tube spectra show the
good spectral system ability in mammographic energy range (1-30 keV) also at high
photon fluence rates (~ 106 counts/mm2 s). Dosimetry measurements have been made
using radioactive sources and a molybdenum X-ray tube. The system compactness and
its
easy operation, in addition to good energy and time resolution, make the system
suitable for medical X-ray spectroscopy under clinical conditions.
Keywords: X-ray spectroscopy, dosimetry, semiconductor detectors, CdTe
References
[1] Birch, R., Marshall, M., Computation of bremmstrahlung x-ray spectra and
comparison with spectra measured with a Ge(Li) detector, Phys. Med. Biol., 24, p.
505-517 (1979).
[2] Aoki, K., Koyama, M., Measurement of diagnostic x-ray spectra using a
silicon
photodiode, Med. Phys., 16 (4), p. 529-536 (1989).
[3] 11th International Workshop on Room Temperature Semiconductors and
Associated
Electronics, Nucl. Instr. and Meth. A 458 (2001) 1-603.
Author
Mr
Leonardo Abbene
(DIFTER University of Palermo)
Co-authors
Mr
Angelo La Manna
(DIFTER University of Palermo)
Prof.
Francesco Fauci
(DIFTER University of Palermo)
Prof.
Gaetano Gerardi
(DIFTER University of Palermo)
Prof.
Giuseppe Raso
(DIFTER University of Palermo)
