Thermoluminescence properties of Al2O3:Tb nanoparticles irradiated by gamma rays and 85 MeV C6+ ion beam

Journal of Luminescence 167 (2015) 59–64

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Thermoluminescence properties of Al2O3:Tb nanoparticles irradiated by gamma rays and 85 MeV C6 þ ion beam Numan Salah a,n, Najlaa D. Alharbi b, Sami S. Habib a, S.P. Lochab c a

Center of Nanotechnology, King Abdulaziz University, Jeddah 21589, Saudi Arabia Sciences Faculty for Girls, King Abdulaziz University, Jeddah 21589, Saudi Arabia c Inter-University Accelerator Centre, Aruna Asaf Ali Marg, New Delhi 110067, India b

art ic l e i nf o

a b s t r a c t

Article history: Received 15 April 2015 Received in revised form 30 May 2015 Accepted 3 June 2015 Available online 15 June 2015

Carbon ions beam is recently recognized as an ideal cancer treatment modality, because of its excellent local tumor control. These ions have a high relative biological effectiveness resulting from high linear energy transfer (LET) and their sharp Bragg peak. However, the dose of those energetic ions needs to be measured with great precision using a proper dosimeter. Aluminum Oxide (Al2O3) is a highly luminescent phosphor widely used for radiation dosimetry using thermoluminesence (TL) technique. In this work nanoparticles of this material activated by different elements like Eu, Tb, Dy, Cu and Ag were evaluated for their TL response to gamma rays irradiation. Tb doped sample is found to be the most sensitive sample, which could be selected for exposure to 85 MeV C6 þ ion beam in the fluence range 109–1013 ions/cm2. The obtained result shows that C ion beam irradiated sample has a simple glow curve structure with a prominent glow peak at around 230 °C. This glow curve has a dosimetric peak better than those induced by gamma rays. This glow peak exhibits a linear response in the range 109–1011 ions/cm2, corresponding to the equivalent absorbed doses 0.285–28.5 kGy. The absorbed doses, penetration depths and main energy loss were calculated using TRIM code based on the Monte Carlo simulation. The wide linear response of Al2O3:Tb nanoparticles along with the low fading makes this low cost nanomaterial a good candidate for C ion beam dosimetry. & 2015 Elsevier B.V. All rights reserved.

Keywords: Nanomaterials Al2O3:Tb nanoparticles Carbon ions beam Thermoluminescence

1. Introduction Nanostructured materials have attracted huge attention by a large number of researchers. That is because of their superior unique properties. Different nanostructures were produced and their properties like structural, electrical, optical, magnetic, mechanical and dosimetric were studied [1–6]. Moreover, large number of these nanostructures were evaluated for different applications. In the field of ionizing radiation dosimetry, a good number of these nanostructures were produced and studied for their response to both sparsely and densely ionizing radiations [7–20]. These nanostructures were found to have excellent thermoluminescent (TL) dosimetric properties, particularly their response in a wide span of exposures. However, testing these nanostructures for their response to C ion beam, which is recommended for cancer treatment, rarely appears. Energetic heavy ion beams were recently recognized to be effective in radiotherapy and diagnostic applications [21–23]. n

Corresponding author. Fax: þ 966 2 6951566. E-mail addresses: [email protected], [email protected] (N. Salah).

http://dx.doi.org/10.1016/j.jlumin.2015.06.004 0022-2313/& 2015 Elsevier B.V. All rights reserved.

These highly energetic ion beams have several advantages for cancer treatment in comparison with the conventional photons irradiation [24–26]. “The physical advantage is a significantly more favorable dose deposition profile. Whereas with conventional irradiation the dose deposition decreases in proportion to the penetration depth, with ion beams it gradually increases, and then declines rapidly beyond a sharply defined maximum known as the Bragg Peak near the end of range of ion beam. Therefore, the penetration depths of those ions can be projected to have a maximum absorption at the tumors' positions” [27]. Carbon ions were identified to be the most suitable ions because they cause a different type of cellular damage than protons and photons do [27]. They deliver a larger mean energy per unit length (Linear Energy Transfer: LET) of their trajectory in the body. This unique property provides high local tumor control when used in radiotherapy. Carbon ions directly cleave double-stranded DNA at multiple sites even at low oxygen content, which allows access to hypoxic parts of tumors that would be resistant to low LET radiotherapy [28,29]. However, the dose of those energetic ions needs to be measured with great precision and accuracy, especially, while dealing with human body.

N. Salah et al. / Journal of Luminescence 167 (2015) 59–64

TL dosimeters might be a good choice for dose verification in heavy ions irradiation, particularly C ion. Such TL materials exhibit differences in dose response between sparsely ionizing radiation like X-ray or γ-ray and densely ionizing radiation like heavy charged particles (HCP). This is due to different spatial dose distribution, which causes saturation effects in the case of densely ionizing radiation [30]. On the other hand several nanostructure materials showed saturations at only very high doses [7–20] and thus might be the ultimate choice for ion beam dosimetry mainly carbon ions beam. Aluminum oxide is a highly sensitive TLD material, commonly used for ionizing radiation dosimetry [31–33]. Its TL properties have been tried to be improved through several studies [34–36]. Most of the work was focused on Al2O3 TL response to relatively low doses. In this work nanoparticles of Al2O3 activated by different elements like Eu, Tb, Dy, Cu and Ag were synthesized by the chemical combustion (propellant) method and characterized by different techniques. Then they were evaluated for their TL response to gamma rays irradiation. Tb doped sample is found to be the most sensitive sample, which then could be selected for exposure to 85 MeV C6 þ ion beam in the fluence range 109–1013 ions/cm2.

2. Experimental Nanoparticles of Al2O3 activated with Eu, Tb, Dy, Cu and Ag were synthesized by the method described earlier by Salah et al. [37]. They were produced by the propellant chemical combustion method. The used concentration of these dopants is 0.2 mol% except that of Tb, where different concentrations were used. The synthesized materials were characterized by SEM using a field emission scanning electron microscopy (FESEM), JSM-7500 F (JEOL-Japan). The XRD of pure Al2O3 powder sample was also recorded, using an Ultima-IV (Rigaku, Japan) diffractometer with Cu Ka radiation, while the phase transition was investigated using Shimadzu DSC-60, Japan. Photoluminescence (PL) emission spectra of the as-synthesized nanoparticles of pure and doped Al2O3 samples were recorded using a fluorescence spectrofluorophotometer, model RF-5301 PC, Shimadzu. The excitation wavelength is 325 nm. TL glow curves were recorded on a Harshaw TLD reader, Model 3500. For TL measurement 5 mg of sample was taken each time and carried out the measurement under nitrogen atmosphere. The heating rate was kept constant at 5 °C/s. For C ion beam irradiation the powder samples were prepared in pellet form. The procedure for making pellets and ion beam irradiation was described earlier [12]. The prepared pellets were of 0.66 mm (660 μm) thickness and 10 mm diameter. They were prepared by taking 100 mg of the sample and 2 mg of Teflon powder. Then, they were mixed together, put in a die, and a pressure of 0.2 t/cm2 was applied by a manual hydraulic press. The formed pellets were annealed at 600 °C for 1 h in nitrogen atmosphere. This annealing is useful to anneal out the deformations, if any, due to applied stress. The ion beam range was 109–1013 ions/cm2. For taking TL of the C ion beam irradiated samples the irradiated surface of the pellet was kept facing upward toward the detector of the Harshaw TLD reader.

reported earlier [37]. From the dosimetry point of view these individual nanoparticles are much better than those in cluster form to avoid overlapping of radiation tracks [12]. The XRD diffraction pattern of Al2O3 powder in nanoparticles form is shown in inset a of Fig. 1. The main diffracted peaks are clearly shown with the corresponding hkl values. Moreover, it is obvious from this pattern that the prepared nanomaterial has stabilized α phase of alumina [38]. A clear broadening in the diffracted peaks can also be seen, which is due to the reduction in the particle size [36]. The crystallite sizes calculated with the Scherrerformula are around 30 nm, which are close to those observed by SEM (Fig. 1). DSC measurement for pure Al2O3 nanoparticles was measured in the range of 30–600 °C. The result is presented in inset b of Fig. 1. This result shows that there are no endo- or exothermic peaks in this range, which means that pure Al2O3 nanostructure has only a single phase. The material is therefore thermally stable in this range, which is useful for dosimetry using TL technique. Normally, oxide materials are thermally stable with no phase change at temperatures lower than 500 °C. Therefore, it is expected that Al2O3 nanoparticles will be very stable as a dosimeter using TL technique. Fig. 2 shows the PL emission spectra of pure (curve a) and doped Al2O3 nanoparticles. They were doped with Ag, Cu, Eu, Dy

Fig. 1. SEM image of the as-synthesized Al2O3 nanoparticles. XRD pattern and DSC plot for the as-synthesized Al2O3 nanoparticles are shown in the insets a and b.

350 300 250 200 150 100 50 0

PL Intensity (Arb. units.)

60

3. Results and discussion SEM image of the as-synthesized Al2O3 nanoparticles is presented in Fig. 1. The particles are of spherical shapes with diameters in the range 20–70 nm. These nanoparticles are well defined without any clusters. This result is almost similar to that

400

500

600

700

800

Wavelength (nm) Fig. 2. PL emission spectra of the as-synthesized pure and doped Al2O3 nanoparticles (Impurities concentration is 0.2 mol%).

N. Salah et al. / Journal of Luminescence 167 (2015) 59–64

and e), but with lower PL intensities. The emission spectrum of Ag doped sample (curve b) shows broad emission between 400 and 470 nm. This emission might be due to the increase in absorption and quantum yield due to the surface plasmon resonance of Ag ions [42]. In case of Cu doped sample (curve c), there is a weak emission at around 420 nm. This emission might be of Cu2 þ ions [43,44]. TL glow curves of Al2O3 nanoparticles doped with different elements are presented in Fig. 3. The samples were exposed to 100 Gy of gamma-rays from a 137Cs source. As can be seen in this figure that all the doped samples showed poor TL sensitivity with two humps at around 150 and 260 °C (curves b, c, d and e), except that of Tb dopant (curve a). The glow curve of Al2O3:Tb has three major peaks; the highest is located at around 370 °C and the second one is peaking at 230 °C. The third peak is almost of two components located at around 125 and 90 °C. This glow curve structure has not been reported earlier. Single prominent glow peak is reported in pure Al2O3 obtained by sol–gel [45]. Doped samples with Tb and Tm prepared by combustion method were reported by Barros et al. [36] to have a linear response in a very small range i.e. 0.05–5 Gy. They reported that “annealing effect at temperatures in the range 1000–1400 °C on the TL intensity was found to enhance the TL of Tm doped sample, while that of Tb has less improvement. At this high temperature it is possible that a phase transition from γ to α has taken place, but the new phase is suitable for Tm dopants and results in TL improvement”. In the present material mainly of Tb doped samples were annealed at 850 °C, which is much below the γ-α phase transition, therefore Tb doped sample have the highest TL intensity. This result is of

and Tb (curves b, c, d, e, and f, respectively) at a concentration of 0.2 mol%. Pure sample has almost no emission band (curve a), while the most intense emission is observed in Tb doped one (curve f). The latter has an emission spectrum of two strong sharp emissions at 488 and 544 nm beside two smaller ones at around 585 and 620 nm, which are the well-known emissions of Tb3 þ ions. They can be assigned to the 5D4-7F6, 5D4-7F5, 5D4-7F4, and 5 D4-7F3 transitions of Tb3 þ ion, respectively [39]. The emission bands of Eu3 þ [40] and Dy3 þ [41] were also observed (curves d 5

TL Intensity (arb. units)

4x10

a b c d e

5

3x10

a

5

2x10

5

1x10

ce d b

0 50

100

150

200

250

300

350

400

0

Temperature ( C) Fig. 3. TL glow curves of doped Al2O3 nanoparticles exposed to 100 Gy of gamma rays.

137

Cs

Fig. 4. TL glow curves of Al2O3:Tb nanoparticles exposed to different exposures of function of impurity concentration is shown in inset b.

61

137

Cs gamma rays. The TL response curve is shown in inset a, while the TL intensity as a

62

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90

great importance to test the glow curve structure under exposure to different doses. Fig. 4 shows the TL glow curves of Tb doped Al2O3 nanoparticles exposed to different exposures of 137Cs gamma rays. They were exposed to gamma rays in the range of 10 Gy–10 kGy (curves a–f). Quite stable glow curves are observed with no significant change in the glow curve structure or peak position. The TL response curve of nanocrystalline Al2O3:Tb powder to different doses in the range 10 Gy–10 kGy is presented in inset a of Fig. 4. It was plotted by calculating the integrated area under the curve. As can be seen in this figure that the response curve is almost linear in the dose range 10–1000 Gy; it has a sublinear behavior beyond this range. This TL result is much better than that reported by Barros et al. [36] on Tb doped Al2O3. This might be due to the annealing treatment around the phase transition temperature for their sample as mentioned above. The optimum Tb concentration for maximum TL in Al2O3 nanoparticles was studied and found to be 0.2 mol%. This result is shown in inset b of Fig. 4. These results show that this nanostructure is a good candidate for exposures to different fluences of C ion as it showed excellent TL characters. The nanoparticles of Al2O3:Tb at a dopant concentration of 0.2 mol% were prepared in the form of pellets as described in the experimental section and exposed to different fluences of 85 MeV C6 þ ion beam. The result presented in Fig. 5 shows TL glow curves of this nanomaterial exposed to C ion beam in the fluence range 109–1013 ions/cm2 (curves a–f). The glow curves show a prominent peak at around 230 °C beside smaller one at 370 °C. Small hump is also observed at around 125 °C. Almost no variation has been observed in the glow curve structure or peak position by varying the ion beam fluence. This glow curve structure has not been reported earlier. The TL response curve of Al2O3:Tb nanoparticles to 85 MeV C6 þ ion beam is shown in inset of Fig. 5. This curve shows a linear behavior in the fluence range 109–1011 ions/cm2; beyond that it saturates. The fading effect of the glow curve in the Al2O3:Tb nanoparticles exposed to 1010 ions/cm2 was studied over a month. The result is presented in Fig. 6. The total fading over this period of storage was around 4%. It is worth to mention that the absorbed doses by the given fluences are high. The equivalent absorbed doses were calculated by using TRIM code based on the Monte Carlo simulation [46]. The following formula was used to calculate these doses:

80

D (Gy) = 1.602 × 10−10 ×

70

In this formula the macroscopic dose at the irradiated volume is expressed in Gy. The ion fluence, ϕ , is measured in cm  1, ρ is the density of the irradiated nanomaterial in g cm  3 (it is around 1.93 g cm  3 for the pellets of Al2O3:Tb nanoparticles) and the main energy loss (dE/dx) is calculated using the TRIM code [46] in units of MeV cm  1. In addition to the absorbed doses, the penetration depths and main energy loss were also calculated using TRIM code and the result is tabulated in Table 1. TRIM code

Fig. 5. TL glow curves of Al2O3:Tb nanoparticles exposed to different fluences of 85 MeV C6 þ ion beam. The TL response curve is shown in the inset.

Area under the curve (Normalized)

130 120 110 100

60 0

5

10

15

20

25

30

Storage time (days) Fig. 6. Fading in TL glow curve of Al2O3:Tb nanoparticles exposed to 1  1010 ions/cm2 of 85 MeV C6 þ ion beam over a month.

1 (dE/dx)(MeV cm2 . g) × ϕ (ions/cm2) ρ (1)

Table 1 TRIM calculations on the irradiated Al2O3 nanoparticles using 85 MeV C6 þ ion beam. The equivalent absorbed doses by this nanomaterial as a function of the ion beam fluences are also shown. Beam

(dE/dx)e (MeV mm  1)

(dE/dx)n (MeV mm  1)

Ion range (μm)

Fluences (ion/cm2)

Equivalent dose (kGy)

85 MeV C6 þ

338

0.17

159.5

1  109 5  109 1  1010 1  1011 1  1012 1  1013

0.285 1.425 2.85 28.5 285 2850

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Fig. 7. Schematic diagram of multilevel TL model for competing trapping and luminescent. centers due to (a) gamma irradiation and (b) 85 MeV C6 þ ion beam for Al2O3 nanoparticles.

calculations presented in Table 1 shows that the penetration depth (159.5 μm) is covering a good portion of the Al2O3:Tb pellets (the pellet thickness is 660 μm), which can reflect a good TL response. These calculations show that the major energy lost by the used 85 MeV C6 þ ion beam in Al2O3 nanoparticles pellet is electronic in nature. This perhaps could influence the initial energy band structure and the trapping and recombination mechanism. It is slightly different than that in the case of gamma irradiated Al2O3 nanoparticles. The change in the population of luminescent/traps centres (LCs/TCs) due to the use of gamma rays and 85 MeV C6 þ ion beam might be explained using the proposed model presented in Fig. 7. In case of gamma rays irradiated sample the observed glow curve has three peaks as shown in Figs. 3 and 4. The high temperature peak is more prominent, which might be due to the formation of high density traps as proposed in Fig. 7a. The other peaks perhaps could be induced from the shallow and medium traps resulting on the low and medium temperature glow peaks. However, with the use of high energetic C ion (Fig. 7b) the population of these formed traps perhaps could be greatly influenced. The density of the medium traps becomes higher than the corresponding traps of gamma rays irradiated sample. The wide response of nanostructure materials was explained in an earlier work [7,8,12,37] and could be attributed to the tiny size of the nanostructures. These ultrafine sizes perhaps could minimize tracks overlapping. From the application point of view Al2O3 nanoparticles showed a good linear response for C ion in the range 109–1011 ions/cm2, corresponding to the equivalent absorbed doses 0.285–28.5 kGy as mentioned above. For dosimetric purpose this property along with the low fading makes these low cost nanomaterials a good candidate for C ion beam dosimetry. However, the reusability might be a question, which will be addressed in further work.

4. Conclusions Nanoparticles of Al2O3 have been successfully evaluated for their TL response to carbon ions beam. This nanomaterial was doped with different elements like Eu, Tb, Dy, Cu and Ag. The most sensitive sample to gamma rays radiation was found to be the Tb doped one, which could be selected for exposure to 85 MeV C6 þ ion beam in the fluence range 109–1013 ions/cm2. The obtained result showed that C ion beam irradiated sample has a prominent TL glow peak at around 230 °C, which is simpler than that induced by gamma rays. Moreover, this glow peak exhibits a linear

response in the range 109–1011 ions/cm2. The absorbed doses, penetration depths and main energy loss were calculated using TRIM code based on the Monte Carlo simulation. These results showed that it is quite possible to use Al2O3:Tb nanoparticles as a dosimeter for C ion beam due to its wide linear response along with the low fading. Moreover, even if the reusability is questionable, the low cost of this nanomaterial beside its simple method of preparation can solve this problem and make Al2O3:Tb nanoparticles a good candidate for C ion beam dosimetry that has been recommended for radiotherapy.

Acknowledgments Thanks are due to King Abdulaziz City for Science and Technology, Riyadh, Saudi Arabia, for providing financial assistance in the form of Research Project “A-T-32-72.”

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