Page 54 - 00. Complete Version - Progress Report IPEN 2014-2016

54 Application of Ionizing Radiations | Progress Report

Radiation Detectors moving impurities was evaluated by the mea-

surements of the impurity concentrations in
Purification and Growth of Semiconductor the crystals after different purification num-
Crystals for Applications as Room ber. For the BiI3 crystals, previously purified,
Temperature Radiation Detectors a blackish gray coloration and glossy surface

were observed, while crystal grown without
A great interest has been focusing on the prior purification presented a non-unifor-
development of a room temperature radia- mity opaque gray color, being more accen-
tion detector, using semiconductor materi- tuated in the upper region (Fig. 8). The for-
als that have high atomic number and wide merly purified TlBr crystals presented a fully
band gap, due to its applicability as X ray and translucent yellow color, while crystals grown
gamma ray spectrometer, operating at room without purification showed non-uniformi-
temperature. Layered semiconductor mate- ty darker yellow color with dark residue in
rials have a number of properties that make the upper region.
them attractive for such application. Howev-
er, the role of crystal impurities on the detec- The impurities identified for both crystals as
tor performance is crucial, and, consequently, well as the tendency of the impurity concen-
improvements on the chemical purification trations to decrease in function of the puri-
and the impurity reduction analysis should fication number are presented in Fig.9. The
be achieved. To accomplish this goal, the Re- segregation of most of the total impurities to
peated Vertical Bridgman technique was es- the beginning or end of the crystal indicates
tablished for previous purification of the raw that the purification method established in
materials before their growth, in order to ob- this work was effective. After three purifica-
tain the single crystals of high-purity and tions, most of the impurities for both crys-
highest crystal quality, whose characteristics tals were, practically, removed in the mid-
are required for X and gamma rays detection. dle region. Thus, Repeated Vertical Bridgman
In this work, the BiI3 and TlBr powders with showed to be an efficient technique for pu-
nominal purity of 99.99% were used as used rification of BiI3 and TlBr powders, with po-
as raw material and the efficiency of the Re- tential to be used in the radiation semicon-
peated Vertical Bridgman technique for re- ductor detector development.

Bil3

Before After

TlBr
Before After

Figure 9. Reduction trend of the impurities concentra-
tion in function of the number of purifications (once,
Figure 8. Pictures of the BiI3 and TlBr crys- twice and three times purifications).The colored lines
tals without and after three purifications. are a guide to the vision, evidencing this tendency.

Instituto de Pesquisas Energéticas e Nucleares