Page 9 - PR 2014 2016 03 Applications of Ionizing Radiations

Applications of Ionizing Radiations | Progress Report 51

Radiation Detectors Bil 3

Before After
Purification and Growth of Semiconductor
Crystals for Applications as Room
Temperature Radiation Detectors
TlBr
Before After
A great interest has been focusing on the
development of a room temperature radia-
tion detector, using semiconductor materi-
als that have high atomic number and wide
band gap, due to its applicability as X ray
Figure 8. Pictures of the BiI and TlBr crystals without and after
and gamma ray spectrometer, operating at three purifications. 3
room temperature. Layered semiconductor
materials have a number of properties that
make them attractive for such application. The impurities identified for both crystals as
However, the role of crystal impurities on well as the tendency of the impurity concen-
the detector performance is crucial, and, trations to decrease in function of the purifi-
consequently, improvements on the chem- cation number are presented in Fig.9. The seg-
ical purification and the impurity reduction regation of most of the total impurities to the
analysis should be achieved. To accomplish beginning or end of the crystal indicates that
this goal, the Repeated Vertical Bridgman the purification method established in this
technique was established for previous pu- work was effective. After three purifications,
rification of the raw materials before their most of the impurities for both crystals were,
growth, in order to obtain the single crystals practically, removed in the middle region.
of high-purity and highest crystal quality, Thus, Repeated Vertical Bridgman showed
whose characteristics are required for X and to be an efficient technique for purification
gamma rays detection. In this work, the BiI of BiI and TlBr powders, with potential to be
3 3
and TlBr powders with nominal purity of used in the radiation semiconductor detector
99.99% were used as used as raw material development.
and the efficiency of the Repeated Vertical
Bridgman technique for removing impurities
was evaluated by the measurements of the
impurity concentrations in the crystals after
different purification number. For the BiI
3
crystals, previously purified, a blackish gray
coloration and glossy surface were observed,
while crystal grown without prior purifica-
tion presented a non-uniformity opaque gray
color, being more accentuated in the upper
region (Fig. 8). The formerly purified TlBr crys-
tals presented a fully translucent yellow color,
while crystals grown without purification Figure 9. Reduction trend of the impurities concentration in
showed non-uniformity darker yellow color function of the number of purifications (once, twice and three
times purifications).The colored lines are a guide to the vision,
with dark residue in the upper region. evidencing this tendency.