**1. Introduction**

176 Heat Treatment – Conventional and Novel Applications

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Ionizing radiation dosimetry plays a very important role in several fields, useful in the ordinary life, such as radiotherapy, nuclear medicine diagnosis, nuclear medicine, radioisotope power systems, earth science, geological and archaeological dating methods, etc.

The phenomenon of Thermoluminescence (TL) has been known since 1663, when Robert Boyle notified the "Royal Society" in London, which observed the emission of light by a diamond when it was heated in the dark [1]. Afterwards, a large number of scientists began to work with TL; as did Henri Becquerel, whose work described IR measurements spectra [2] and the effect of TL, too. Marie Curie, in 1904, noted that the TL properties of the crystals could be restored by exposing them to radiation from the radio element mentioned in her doctoral thesis. In the middle of the 1930's and 1940's, Urbach performed experimental and theoretical work with TL [1] and in 1945 Randall and Wilkins developed a first theoretical model [3] of thermoluminescent emission kinetics.

The use of thermoluminescence in dosimetry date from 1940, when the number of people working on places with radiation sources such as hospitals, nuclear reactors etc. exposed to ionizing radiations (γ-rays, X rays, α and β-particles, UVA and UVB) increased and efforts to develop new types of dosimeters began [4]. Among the pioneers of TLD we have Daniels,

© 2012 Tatumi et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Tatumi et al., licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### 178 Heat Treatment – Conventional and Novel Applications

1953, with LiF, Bjarngard, 1967 with CaSO4 and Ginther and Kirk (1957) with CaF2. After these works search in other materials such as natural fluorides or synthetic as, LiBO3:Mn, CaF2:Dy, CaSO4 and MgSiO4:Tb. They usually obtained as monocrystalline samples Czochralski, Bridgmann, etc.

Effects of Heat Treatments on the Thermoluminescence and Optically Stimulated

Luminescence of Nanostructured Aluminate Doped with Rare-Earth and Semi-Metal Chemical Element 179

LiAlO2:Tb, Li2Al2O4:Tb, Mg2SiO4:Tb, Mg2SiO4:Tb, Co CaSiO3:Tb [25]. Some morphological studies was introduced in the science of OSL materials, using high-resolution microscope (TEM) coupled to punctual electron diffraction analysis in nanoscale, showed that dopants formed nanocrystalline structure located at surface of the matrix elements as Al2O3:Mg,

Nowadays, luminescent dosimetry materials can be used in personal dosimetry, radiotherapy, nuclear medicine and diagnostic and environmental dosimetry they are widely used due to high sensitivity, linear response to the dose, the response is independent

The aim of this chapter is to present a very comprehensive research about new materials consisting in aluminate crystals doped with rare-earths, for radiation dosimetry using TL

Some features on fabrication of aluminates dosimeters will be shown relating the luminescence response according to the relative concentration of several rare-earths and transition metals. A study in nanoscale effects, size, shape and surface morphology using TEM, SEM, EDS and electron diffraction measurements will be shown too. The physicochemical properties of the doped materials are strongly related to the fabrication process as well the experimental parameters as temperature of thermal treatments,

As materials science has developed down to nanoscale, the exceptional properties of nanoscaled rare-earth materials are only now being recognized and performed intentionally.

Polycrystalline powder samples of α-Al2O3:Er, Yb; Mg; Tb and Nd were obtained by sol-gel and Pechini process. In the sol-gel procedure stoichiometric amounts of tri-sec-butoxide of aluminum was dissolved in distilled water and hydrochloric acid. The dopants Er, Yb, Nd and Tb oxides were added during the sol stage, with different concentrations. Some portions of the resulting powder were calcinated at different temperature from 1200 to 1600 °C. Experimental parameters of the calcination process, as heating and cooling rates and set

Pechini is a chemical routine that produces, at the end of the stage, an organic polymer with metallic ions, which will be responsible for the formation of the desired material. The polymer is obtained after low temperature reaction among ethylene glycol, citric acid and aluminum nitrate. Once the polymer is ready, a number of heat treatments are carried out in order to (1) collapse the polymeric structure and allow the gradual oxidation reaction of the metallic ions with atmospheric oxygen, and (2) obtain the desired structure of the material. This technique is known to obtain uniform composition and controlled grain size distribution, due to the slow oxidation reaction and the viscosity of the polymer, which

point values were varied, in order to verify the effect on the luminescence response.

with radiation energy (within a certain range), their reusability, etc.

Yb:Er, Nd and KAlSi3O8:Mn [26-30].

calcination time, heating rates, etc.

**2. Experimental part** 

avoid precipitation.

and OSL.

However, Cameron, 1961, with their research on the application of LiF: Mg and Ti obtained the first thermoluminescence dosimeter (TLD-100) [5], which is still one of most popular TLD phosphor, due to tissue equivalent Zeff = 8.04, which is an important characteristic for personal dosimetry. Akselrod et al., 1990 [6] carried out studies on TL properties of carbon doped Al2O3 (TLD-500), a very sensitive material to radiation exposure, showing few TL peaks, with dose interval of detection between 0.05 µ to 10 Gy and fading rate of 3% by year (when kept in the dark). This high sensitivity of the material is attributed to oxygen vacancies created during the crystal growth procedure; the electrons can be trapped at these vacancies creating F and F+ centers, which act as recombination centers yielding a bright emission.

In order to increase the luminescence emission response with dose of some thermoluminescence dosimeters (TLD), heat treatments procedures were frequently performed. Halperin et al., 1959, [7] noted that the thermal treatment enhanced the intensity of various TL glow peaks of NaCl by factors of a few thousands; on prolonged heat treatment. They observed that the intensity of TL peaks locate above RT decreased, while those at lower temperatures continued to grow even after 80 hours of heat treatment at 550 °C. Mehendru, 1970 [8], studied the effects of heat treatment on the TL response of pure KCl; they associated the peaks at 95, 135, and 190 °C with the F centers, these last created due to the background divalent cation impurities, and with the first- and the second-stage F centers, respectively. Kitis et al., 1990 [9], studied the sensitization of LiF:Mg, Ti as a function of irradiation at elevated temperatures, pre-irradiation annealing, and post irradiation annealing between 150–400 ° C; the results showed that the first and third conditions cause an enhancement of the sensitivity; after more two works about preheating and high temperature annealing on TL glow curves of LiF:Mg, Ti [10] and in LiF TLD100 [11] were published. Holgate, 1994, [12] investigated TL and radioluminescence (RL) spectra of calcium fluoride samples doped with neodymium and variations of spectra with Nd concentrations and thermal treatments were observed. Nowadays, it is possible to find oxides, sulfates, sulfides and alkali haloids doped with rare-earths and transition metals as commercial dosimeters.

The optically stimulated luminescence (OSL) was pioneered used to determine environmental radiation dose received by geological samples [13]. However, the idea of using OSL dosimetry was first suggested in 1956 [14]. The first experience was made using MgS, CaS, SrS and SrSe phosphors doped with different rare-earths [15,16]. Nanto et al., 1993 [17], investigated the OSL properties of single crystals of KCl:Eu; after, Akselrod et al. 1998 [18], proposed the use of Al2O3:C for OSL dosimetry, because the high sensitivity of the crystal to visible light. At the present time, the crystal is the principal OSL dosimeter [19-22]. Currently, there are various materials proposed for OSL dosimetry as KBr:Eu [23,24], LiAlO2:Tb, Li2Al2O4:Tb, Mg2SiO4:Tb, Mg2SiO4:Tb, Co CaSiO3:Tb [25]. Some morphological studies was introduced in the science of OSL materials, using high-resolution microscope (TEM) coupled to punctual electron diffraction analysis in nanoscale, showed that dopants formed nanocrystalline structure located at surface of the matrix elements as Al2O3:Mg, Yb:Er, Nd and KAlSi3O8:Mn [26-30].

Nowadays, luminescent dosimetry materials can be used in personal dosimetry, radiotherapy, nuclear medicine and diagnostic and environmental dosimetry they are widely used due to high sensitivity, linear response to the dose, the response is independent with radiation energy (within a certain range), their reusability, etc.

The aim of this chapter is to present a very comprehensive research about new materials consisting in aluminate crystals doped with rare-earths, for radiation dosimetry using TL and OSL.

Some features on fabrication of aluminates dosimeters will be shown relating the luminescence response according to the relative concentration of several rare-earths and transition metals. A study in nanoscale effects, size, shape and surface morphology using TEM, SEM, EDS and electron diffraction measurements will be shown too. The physicochemical properties of the doped materials are strongly related to the fabrication process as well the experimental parameters as temperature of thermal treatments, calcination time, heating rates, etc.

As materials science has developed down to nanoscale, the exceptional properties of nanoscaled rare-earth materials are only now being recognized and performed intentionally.
