ANEXO I

Algunas Estructuras Cristalinas de Compuestos Relacionados con este Trabajo de Tesis

Las estructuras presentadas en este anexo se muestran desde dos puntos de vista: el primero está

basado en los elementos constituyentes en la celda unitaria, tal y como se esquematizan

comúnmente en los libros de texto: mediante proyecciones del plano xy a lo largo del eje z;

siendo el valor de este la coordenada z de la proyección. El segundo se basa en el apilamiento de

capas bidimensionales con empaquetamiento compacto. En este último la posición de las capas

en el apilamiento se denota por la posición de los intersticios A, B o C generados por la capa

precedente [2].

Figura:

A.1 (a). Estructura cristalina de CaF2 (fluorita).

A.1 (b). Estructura cristalina de CaF2 (fluorita).

A.2 (a). Estructura cristalina cúbica tipo C.

A.2 (b). Estructura cristalina cúbica tipo C (con empaquetamiento compacto).

A.3 (a). Estructura cristalina de TiO2 tipo Rutilo.

A.3 (b). Estructura cristalina de TiO2 tipo Rutilo.

A.4. Estructura cristalina hexagonal tipo Hematita.

Z = 0 1/4 2/4

3/4 4/4 5/4

6/4 7/4 8/4

Figura A.1 (a). Estructura cristalina de CaF2 (fluorita).

: Ca; : F

Figura A.1 (b). Estructura cristalina de CaF2 (fluorita).

: Ca; : F

: sitio A : sitio B : sitio C

Ca (C) F (B)

F (B) Ca (A)

F (C) Ca (B) F (A)

F (B) Ca (A) F (C)

F (A) Ca (C) F (B)

F (C) Ca (B) F (A)

Z = 0 1/8 2/8

3/8 4/8 5/8

6/8 7/8 8/8

Figura A.2 (a). Estructura cristalina cúbica tipo C.

: M; : O

1 2 3

4 5 6

7 8 9

Figura A.2 (b). Estructura cristalina cúbica tipo C (con empaquetamiento compacto).

: M ; :O

Z = 0, 1 Z = ½

A.3 (a). Estructura cristalina de TiO2 tipo Rutilo.

: Ti ; : O

A.3 (b). Estructura cristalina de TiO2 tipo Rutilo.

: Ti ; : O

: sitio A : sitio B : sitio C

O (A) ½ Ti (C) O (B) ½ Ti (C) O (A) ½ Ti (C) O (B)

A.4. Estructura cristalina hexagonal tipo Hematita.

: Fe ; : O

: sitio A : sitio B : sitio C

O (A)

2/3 Fe(C)

O (B)

2/3 Fe(C)

O (A)

2/3 Fe(C)

O (B)

2/3 Fe(C)

O (A)

2/3 Fe(C)

O (B)

2/3 Fe(C)

O (A)

ANEXO II

Publicación Relacionada con esta Tesis de Maestría

Thermoluminescence of Sc2O3 exposed to beta-particle irradiation

F. Browna, V. E. Alvarez-Montañoa, V. R. Orante-Barróna, C. Cruz-Vázqueza, H. A. Borbón-Nuñeza

, I. C. Muñozb, V. M. Castañoc, R. Bernald,* aDepartamento de Investigación en Polímeros y Materiales, Universidad de Sonora, Rosales

y Luis Encinas s/n, Hermosillo, Sonora 83000 México. bDepartamento de Ciencias Químico Biológicas, Universidad de Sonora, Rosales y Luis

Encinas s/n, Hermosillo, Sonora 83000 México. cCentro de Física Aplicada y Tecnología Avanzada, Instituto de Física de la Universidad

Nacional Autónoma de México, Apartado Postal 1-1010, Querétaro, Querétaro 76000 México

dDepartamento de Investigación en Física, Universidad de Sonora. Apdo. Postal 5-088, Hermosillo, Sonora 83190 México.

*Corresponding author. E-mail: rbernal@gimmunison.com Abstract In this work, the thermoluminescence (TL) features of Sc2O3 exposed to beta particle irradiation in the dose range from 0.08 to 150 Gy are reported. Characteristic glow curves exhibit two main TL maxima, located at 74 and 192 °C when a 2 °C/s heating rate is used. The TL response as a function of dose exhibits a linear behavior for doses below 70 Gy. We conclude that Sc2O3 is a promising phosphor material for using as TL dosimeter. Keywords: Thermoluminescence dosimetry; Sc2O3; beta particle radiation. 1. Introduction Scandium oxide (Sc2O3), also named Scandia, is a white crystalline powder inert to environmental conditions, non-toxic and insoluble in water. It is a wide band gap insulator (Eg = 6.0 eV) [1]. Its crystal structure, under environmental conditions of pressure, is cubic C-type with lattice constant a = 0.98450 nm [1]. Scandia has been proposed as a promising material for laser optical coating due to its suitable refractive index for antireflection in the UV spectral range [2]. Very efficient Sc2O3 coatings for superluminescent light-emitting diodes were reported by Ladany et al. [3]. Furthermore, stimulated luminescence emissions of Sc2O3 have been attributed to radiative recombination processes of the excited donor-acceptor pairs Sc3+−O2- originated from intrinsic defects such as oxygen vacancies [4]. On the other hand, thermally stimulated luminescence, or thermoluminescence (TL), has been widely accepted as an useful and reliable technique to study defects in insulators and semiconducting materials, nevertheless, its most known successful application is in the field of radiation dosimetry [5]. Despite the luminescent features as well as the previous knowledge about solid state defects of scandium oxide mentioned above, there are no investigations regarding the thermoluminescence characterization of this ceramic oxide. In this respect, thermoluminescence features of commercial powder of Sc2O3 aimed at proposing this material for radiation dosimetry applications are presented in this work for the very first time.

2. Experimental Powdered commercial Sc2O3 (Rare Metallic Co. Ltd, 99.9 %; Japan) was used for this study. Prior to TL characterization, Sc2O3 powder placed inside a high-alumina crucible was submitted to thermal annealing at 850 °C during 24 h in air using a Thermolyne 46100 furnace. The purpose of this annealing was to get rid of the humidity excess from the powder, even though it is not hygroscopic under environmental conditions.

A Risø TL/OSL model TL/OSL-DA-15 equipped with a 90Sr beta source was employed to perform both beta-particle irradiations and TL measurements. Aliquots of 30 mg of Sc2O3 powder in stainless steel cups were used for the readouts. All irradiations were accomplished using a 5 Gy/min dose rate at room temperature (ca. 22 °C). The TL measurements were carried out from room temperature (22 °C) up to 450 °C under N2 atmosphere using a heating rate of 2 °C/s. 3. Results and discussion Figure 1 shows the thermoluminescence (TL) glow curves of Sc2O3 as obtained after exposure to beta particle irradiation in the dose range from 0.08 up to 10.67 Gy. Two maxima can be observed, located at 76 and 192 °C, respectively. The lower temperature maximum is not considered as suitable for TL dosimetry applications, but the second one is located at a temperature currently expected to assure thermal stability of the TL signal if the irradiated sample is stored at standard environmental conditions [5]. The whole glow curve shape looks quite complex, revealing that it is composed by the superposition of overlapped individual TL peaks. No change in the glow curve shape neither in the maxima positions is observed as dose changes, indicating that first-order kinetics processes are involved. The integrated TL as a function of dose exhibits a linear dependence, without any evidence of saturation (figure 2).

Figure 3 shows the TL glow curves evolution as dose increases from 5 up to 150 Gy. As in figure 1, it can be seen that the shape of the thermograms remain unchanged, but are more evident shoulders between 250-275 °C and 350-375 °C. No shift is observed for the TL maximum position. Figure 4 shows the integrated TL as a function of dose, displaying a linear response for doses below 80 Gy. The linear behavior in the mentioned dose interval is of interest for some important dosimetry applications, as in clinical dosimetry [6]. The origin of the TL in Sc2O3 could be related with F centers formed during irradiation by electron trapping in anion vacancies in tetrahedral sites of the crystal structure [7]. Figure 5 shows the glow curves as obtained from four different samples. It can be seen that similar samples gives similar TL response if exposed to the same radiation dose. Since Sc2O3 powders studied here are commercially available, it is worth to mention that this material is a reliable phosphor to be used as a TL dosimeter. The glow curves obtained for the same sample exposed to ten consecutive irradiation - TL readout cycles, using a 50 Gy dose for each irradiation, are displayed in figure 6. It can be seen an increase in the TL emission at the lower temperatures interval (below 130 °C), and a decrease in the emission at temperatures above the TL maximum. These changes are greater during the first cycles. However, the height of the TL maximum exhibits a remarkable stability. For dosimetry purposes, the intensity of the TL maximum could be used as a measure of dose. On the other hand, a pre-irradiation thermal annealing should be investigated in order to eliminate the changes in the TL emission below and above the TL maximum. Currently, several

thermal treatments applied to commercial dosimetric materials improve the sensitivity and other TL features. Figure 7 shows the glow curves of Sc2O3 exposed to 50 Gy of beta particle irradiation, obtained at different time intervals elapsed between irradiation and the corresponding TL readout. As the low temperature TL exhibits a fading as expected from the TL mathematical models for the thermal fading, the intensity of the TL maximum initially increases and it begins to diminish after 28 h. Since this sensitization was not observed in the TL - dose response, which is linear for doses below 70 Gy, could be associated to charge carrier transfer from deep trapping states which are not thermally released during the TL readouts. In this concern, a systematic investigation is needed to determine a pre-irradiation annealing protocol to fix this issue. As a result of the anomalous behavior of the TL glow curves displayed in figure 7, the integrated TL as a function of the time interval elapsed between irradiation and TL readout looks as in figure 8. 4. Conclusions The thermoluminescence (TL) features of commercially available Sc2O3 exposed to beta particle irradiation in the dose range from 0.08 to 150 Gy were investigated. The glow curves display two maxima, located at 74 °C and 192 °C, respectively, when a 2 °C/s heating rate is used. No shift of the TL maxima is observed as dose changes, indicating that first-order kinetics processes are involved. The integrated TL as a function of dose displays a linear behavior for doses below 70 Gy. In spite that further research is necessary to fix some issues, such as the anomalous TL fading; from the experimental evidence here exposed we conclude that Sc2O3 is a promising phosphor material for TL dosimetry applications. Acknowledgements The authors gratefully acknowledge the financial support for this work from CONACYT (México), under Grant CB-106041. References: [1] A. V. Emeline, S. V. Petrova, V. K. Ryabchuk, and N. Serpone, Chem. Mater. 10 (1998) 3484-3491. [2] W. Heitmann, Appl. Opt. 12, (1973) 394-397. [3] I. Ladany, P. J. Zanzucchi, J. T. Andrews, J. Kane, and E. DePiano, Appl. Opt. 25, (1986) 472-473. [4] O. M. Bordun, Journal of Applied Spectroscopy 68, (2001) 304-307. [5] S. W. S. McKeever, Thermoluminescence of Solids, Cambridge: Cambridge University Press, 1985. [6] S. W. S. McKeever, M. Moscovitch, P. D. Townsend, Thermoluminescence Dosimetry Materials: Properties and Uses, Nuclear Technology Publishing, 1995. [7] A. F. Wells, Structural Inorganic Chemistry, fourth ed., Clarendon Press, Oxford, 1975.

Figure Captions

Figure 1. Thermoluminescence glow curves of Sc2O3 commercially available samples, exposed to beta particle irradiation in dose range from 0.08 to 10.7 Gy. Figure 2. Integrated thermoluminescence of Sc2O3 exposed to beta particle irradiation in the dose range from 0.08 to 10.7 Gy. Figure 3. Thermoluminescence glow curves of Sc2O3 commercially available samples, exposed to beta particle irradiation in dose range from 5.0 to 150 Gy. Figure 4. Integrated thermoluminescence of Sc2O3 exposed to beta particle irradiation in the dose range from 5.0 to 150 Gy. Figure 5. Thermoluminescence glow curve of four Sc2O3 samples exposed to 50 Gy of beta particle irradiation. Figure 6. Thermoluminescence glow curves of Sc2O3 obtained in 10 consecutive irradiation - TL readout cycles. For each irradiation, 50 Gy were delivered. Figure 7. Thermoluminescence glow curves of Sc2O3 exposed to 50 Gy of beta particle irradiation, as obtained at different elapsed time intervals between irradiation and the corresponding TL readout. Figure 8. Integrated thermoluminescence of Sc2O3 exposed to 50 Gy of beta particle irradiation, as a function of the elapsed time interval between irradiation and the corresponding TL readout.

0 100 200 300 4000.0

8.0x104

1.6x105

2.4x105

TL

Inte

nsity

(arb

. u.)

Temperature (°C)

0.08 Gy 0.17 Gy 0.33 Gy 0.67 Gy 1.33 Gy 2.67 Gy 5.33 Gy 10.67 Gy

Figure 1

0 2 4 6 8 100.0

6.0x106

1.2x107

1.8x107

2.4x107

3.0x107

Inte

grat

ed T

L (a

rb. u

.)

Dose (Gy)

Figure 2

50 100 150 200 250 300 350 400 4500

1x106

2x106

3x106

4x106

5x106

TL

Inte

nsity

(arb

. u.)

Temperature (°C)

5 Gy 10 Gy 25 Gy 50 Gy 75 Gy 100 Gy 150 Gy

Figure 3

0 20 40 60 80 100 120 140 160

1x108

2x108

3x108

4x108

5x108

Inte

grat

ed T

L (a

rb. u

.)

Dose (Gy)

Figure 4

0 100 200 300 4000.0

4.0x105

8.0x105

1.2x106

1.6x106

TL

Inte

nsity

(arb

. u.)

Temperature (°C)

Sc2O3 ~ 30 mg Sc2O3 ~ 30 mg Sc2O3 ~ 30 mg Sc2O3 ~ 30 mg

Figure 5

0 100 200 300 4000.0

3.0x105

6.0x105

9.0x105

1.2x106

1.5x106

T

L In

tens

ity (a

rb. u

.)

Temperature (°C)

Cycle (1) Cycle (2) Cycle (3) Cycle (4) Cycle (5) Cycle (6) Cycle (7) Cycle (8) Cycle (9) Cycle (10)

Figure 6

50 100 150 200 250 300 350 400 4500.0

2.0x105

4.0x105

6.0x105

8.0x105

1.0x106

T

L In

tens

ity (a

rb. u

.)

Temperature (°C)

0 h 1.5 h 3 h 6 h 12 h 24 h 48 h 96 h

Figure 7

0 20 40 60 80 1008x107

9x107

1x108

1x108

1x108

1x108

Inte

grat

ed T

L (a

rb. u

.)

Time (h)

Figure 8