Page 55 - 00. Complete Version - Progress Report IPEN 2014-2016

Application of Ionizing Radiations | Progress Report 55

Development of the inorganic scintillator using the Bridgman technique. In this tech-
crystals used as radiation detector nique, the charge is maintained at high tem-
perature for 10 h for the material melting
The Laboratory of scintil- and complete reaction, using a quartz cruci-
lator crystal growth devel- ble in vacuum atmosphere. The temperature
ops pure and doped crys- gradient 21° C/cm and 1 mm/h descending
tals for the construction of velocity were chosen as technique parame-
radiation detectors. Inor- ters. After finishing the growth, the furnace
ganic scintillators play an is cooled at a rate of 20° C/h to room tempera-
Figure 10. pure CsI crystals important role in the de- ture. The best doping element concentration
tection and spectroscopy is studied. The main used dopants are thal-
lium (Tl), bromine (Br), lead (Pb) and lithium
(Li). The grown crystals are subjected to heat
treatment. In this procedure, it is used vacu-
um of 10-6 mbar and continuous tempera-
ture of 350º C, for 24 hours. Figures 10 and 11
shows pure CsI crystal and the bromine doped
Figure 11 shows the bromine doped cesium iodine crystals CsI:Br) cesium iodine crystals (CsI:Br), respectively.

of gamma and X-rays, as well as in neutrons For the detection system, crystals are cou-
and charged particles. For a variety of appli- pled optically with the photocathode. The
cations, new inorganic scintillation materials bright photons move the electrons of photo-
are being studied. New scintillation detector cathodes and these are accelerated by a se-
applications arise continuously and the inter- ries of electrodes (dynodes) inside the photo-
est in the introduction of new fast scintilla- multiplier tube. In the scintillation detection
tors becomes relevant. Scintillation crystals process, the proportionality is maintained in
based on cesium iodide (CsI) have relatively each step, that is, the number of photons re-
low hygroscope, easy handling and low cost, leased by the crystal is proportional to the en-
features that favor their use as radiation de- ergy released in crystal, from the incident ra-
tectors. Pure and doped CsI crystals are grown diation. The number of displaced electrons in

Figure 12. Pulse height obtained for gamma radiation from Figure 13. Pulse height obtained for gamma radiation from
54Mn (835 keV) source with crystals of CsI: Br and pure CsI 137Cs (662 keV) source with crystals CsI:Br and pure CsI