Radiation Physics and Chemistry 86 (2013) 52–58

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Radiation Physics and Chemistry

0969-80

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TL response of nanocrystalline MgB4O7:Dy irradiated by 3 MeV proton beam,50 MeV Li3þ and 120 MeV Ag9þ ion beams

Numan Salah a,n, Sami Habib a, Saeed S. Babkair b, S.P. Lochab c, Vibha Chopra c

a Center of Nanotechnology, King Abdulaziz University, Jeddah 21589, Saudi Arabiab Center of Nanotechnology, Department of Physics, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabiac Inter-University Accelerator Centre, Aruna Asaf Ali Marg, New Delhi 110067, India

H I G H L I G H T S

c TL response of nanocrystalline MgB4O7:Dy irradiated by ion beams is studied.c Proton beam as well as Li3þ and Ag9þ ion beams irradiated samples showed different TL responses.c This nanomaterial has highest the TL sensitivity to Li3þ , then Ag9þ ions and finally protons.c TRIM code is used to calculate the absorbed doses, penetration depths and main energy loss.

a r t i c l e i n f o

Article history:

Received 24 October 2012

Accepted 24 January 2013Available online 9 February 2013

Keywords:

Nanoparticles

MgB4O7:Dy

Ion beams

Thermoluminescence

6X/$ - see front matter & 2013 Elsevier Ltd.

x.doi.org/10.1016/j.radphyschem.2013.01.034

esponding author.

ail addresses: nsalah@kau.edu.sa, alnumany@

a b s t r a c t

Magnesium borate (MgB4O7) is a highly sensitive phosphor commonly used in a thermoluminescence

(TL) dosimeter. In this work we report on TL response of nanocrystalline MgB4O7:Dy irradiated by

3 MeV proton beam as well as 50 MeV Li3þ and 120 MeV Ag9þ ion beams in the fluence range of

1�1011–1�1015 ions/cm2. The induced TL glow curves were compared with that of gamma rays

irradiation. A single glow peak is observed at around 430 K in the samples irradiated by Li3þ and Ag9þ

ions, while that exposed to proton beam has an extra one at 525 K. This nanomaterial has maximum

sensitivity to Li3þ , then Ag9þ ions and finally protons. The TL response curves of the samples exposed

to these radiations are linear/sublinear at the lower fluences, while at higher values they saturate.

These variations in the glow curve structure and TL response could be attributed to the modifications

created in the traps/luminescent centres. TRIM code was also used to calculate the absorbed doses,

penetration depths and main energy loss. The results show that this nanomaterial might be useful for

the dosimetry of heavy charged particles such as Li3þ and Ag9þ particularly at low fluences, while in

case of proton beam the TL glow curve is greatly altered and shows poor sensitivity.

& 2013 Elsevier Ltd. All rights reserved.

1. Introduction

Nanoscale materials are defined as the materials with grainsize in the nanometer scale. The surface to volume ratio is so largethat the electron behaviour differs from that of bulk materials.This characteristic leads to a beneficial modification of optical,electrical, magnetic, and other physical and chemical propertiesof the materials. These nanomaterials have attracted large num-ber of researchers from different areas, especially from the field ofluminescence. Recent reports on different luminescent nanoma-terials showed that they have a potential application in dosimetryof ionizing radiations for the measurements of high doses using

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the thermoluminescence (TL) technique, where the conventionalmicrocrystalline phosphors saturate (Salah et al., 2006a, 2006b,2008b, 2009, 2011a, 2011b; Salah, 2008a; Sahare et al., 2007;Lochab et al., 2007a, 200b; Salah, 2011c). The use of nanoscalematerials has solved this problem to a major extent. The reportedresults of the nanomaterials have presented excellent character-istics such as high sensitivity and saturation at very high doses.

Recently, the use of TL technique in measuring the doses from theconventional radiation beams has been increased. Ion beams ofcharged particles become a powerful technique for cancer diagnosisand therapy (Barth et al., 2003; Strehl, 1999). There are a number ofcommercial TL dosimeters (TLD) which are readily available to theusers and researchers but in spite of this, efforts are still being madeby the research community to improve the TL characteristics ofdifferent materials (Madhusoodanan et al., 1999; Shinde et al., 2001;Lakshmanan et al., 2002; Kim et al., 2004) for specific applications.

N. Salah et al. / Radiation Physics and Chemistry 86 (2013) 52–58 53

Magnesium borate (MgB4O7) is a highly sensitive phosphorcommonly used for medical dosimetry using the TL technique.The preparation of polycrystalline MgB4O7 activated by dyspro-sium (Dy) was reported in 1974 (Kazankaya et al., 1974). It is anear tissue equivalent material with an effective atomic numberfor photoelectric absorption equal to 8.4 compared to 7.4 forwater and soft biological tissue. The dosimetric characteristics ofMgB4O7:Dy were systematically reported in 1982–1983 (Barbinaet al., 1982; Driscol et al., 1983). Later on this material was dopedwith extra dopants like sodium (Na; Furetta et al., 2000) andreported to be a useful TLD material particularly in individualmonitoring and in various medical dosimetry purposes. Thenanostructure form of this material was studied for its TLresponse to gamma rays in 2007 (Lochab et al., 2007b). Theyfound that the nanomaterial has a linear TL response for highdoses, poor fading and excellent reusability features. Theseexcellent TL characters have encouraged further investigationsabout this nanomaterial. Recently, the nanocrystalline form ofMgB4O7:Dy,Na was exposed to gamma rays and 150 MeV protonbeam, and studied for its TL response (Bahl et al., 2013). Theauthors reported that the TL response curve of gamma rays islinear in a good range of exposure (0.1–1000 Gy), but protonbeam irradiated materials shows early saturation (o350 Gy).However, this nanomaterial has not been tested for its TLresponse to other ionizing radiations like heavy ions.

In the present work we report on the TL response of nano-crystalline MgB4O7:Dy irradiated by 3 MeV proton beam as wellas 50 MeV Li3þ and 120 MeV Ag9þ ion beams in the fluence rangeof 1�1011–1�1015 ions/cm2. The induced TL glow curves arecompared with that of gamma rays irradiation. Initially thenanomaterials were synthesised by the combustion method andcharacterized by the X-ray diffraction (XRD), field emissionscanning electron microscopy (FESEM) and energy dispersivespectroscopy (EDS) techniques. Then their pellets forms wereirradiated by proton beam as well as Li3þ and Ag9þ ion beamsusing a 16 MV Tandem Van de-Graff-type electrostatic pelletronaccelerator at the Inter-University Accelerator Center (IUAC), NewDelhi, India. The obtained TL results are studied in detail.

2. Experimental procedure

2.1. Methods of preparation

Nanostructure form of MgB4O7:Dy is synthesized bya combus-tion method similar to that produced and described earlier(Lochab et al., 2007b). In this method the starting mixture witha molar ratio of Mg(NO3)2:H3BO3:NH4NO3:Urea¼1.0:3.2:10.2:10.2, and appropriate amount of DyCl3 (for Dy concentration of1000 ppm) were put in a large quartz crucible and introduced in amuffle furnace preheated to 550 1C. The mixture undergoessmoldering (flameless) combustion to produce the borate nano-material. Stoichiometric composition of the redox mixture wascalculated based on the total oxidizing and reducing valenciesof the oxidizer (O) and the fuel (F), keeping the O/F ratio unity(Patil et al., 1997).

2.2. Characterization

To confirm the formation of the compound, the X-ray diffrac-tion pattern was studied at room temperature by X-ray diffrac-tion, using an Ultima-IV (Rigaku, Japan) diffractometer withCu Ka radiation, while the morphology of these nanostructureswas analyzed with a field emission scanning electron microscope(FESEM), JSM-7500F (JEOL-Japan) operated at 13 kV. The chemicalcompositions of the synthesised material were measured by the

energy dispersive spectroscopy (EDS) technique using EDAX,Oxford. Pellets of the prepared nanopowder with 1 mm thicknessand 10 mm diameter were prepared taking 100 mg of the sampleand 2 mg of Teflon powder, mixing together, putting in a die, andapplying 0.1 t/cm2 pressures each time by a hydraulic press. Thepellets were again annealed at 973 K for 1 h in argon atmosphereand quenched rapidly to anneal out the deformations, if any, dueto applied stress.

Small pieces (approximately 5 mg) of the pellets were exposedto g-rays from a 137Cs source for various doses in the range of100 Gy–20 kGy. The samples in the form of pellets were irra-diated at room temperature by proton beam as well as Li3þ andAg9þ ion beams at energies of 3, 50, and 120 MeV, respectively,for different ion fluences in the range of 1�1011–1�1015 ions/cm2, using a 16 MV Tandem Van de-Graff-type electrostaticpelletron accelerator at the Inter-University Accelerator Center(IUAC), New Delhi, India. The full details of this setup aredescribed earlier (Kanjilal et al., 1993). The samples weremounted on a copper target ladder with a silver paste givinggood thermal and electrical conductivity between them. Thisprevents sample heating during heavily charged irradiation. Theion beams were magnetically scanned on a 10�10 mm2 area onsamples surfaces for a uniform irradiation and their spot sizeswere 2.5 mm2. Three pellets were exposed to the same fluence,every time. For taking TL the irradiated surface of the pellet waskept facing upward toward the detector (photomultiplier tube) ofthe TLD reader. Three glow curves were recorded for each sampleto confirm uniform irradiation. TL glow curves were recordedusing a Harshaw TLD reader (model 3500). The heating rate was5 K s�1.

3. Results

3.1. Crystal structure and particle size

The formation of MgB4O7:Dy compound was confirmed bystudying the X-ray diffraction (XRD). Fig. 1(a) shows the XRDpattern with hkl values of the as-synthesized sample. The dif-fracted peaks show that the compound exhibits an orthogonalstructure. These peaks are similar to those given in the PowderDiffraction File (PDF) ‘‘card number:01-076-0666’’. This PDF is adatabase for X-ray powder diffraction patterns maintained by theInternational Center for Diffraction Data (ICDD). The result shownin Fig. 1(a) shows a considerable broadening in the X-ray diffrac-tion lines. This might be due to the reduction in particle size.These results are similar to those reported earlier (Lochab et al.,2007b). SEM image for the as synthesized MgB4O7:Dy is pre-sented in Fig. 1(b). It shows nanoparticles with tubular shape.Their approximate diameter is in the range of 30–50 nm withlength around 100 nm. The particle size distribution is almostuniform. These results are in agreement with those reportedearlier (Lochab et al., 2007b). The chemical composition of theas synthesized MgB4O7:Dy nanoparticles has also been studiedusing energy dispersive spectroscopy (EDS). The experimentalquantitative and qualitative analysis results are presented inFig. 2. All the elements forming the MgB4O7:Dy nanoparticlesare present in almost their respective concentrations. The theo-retical values for the atomic percentage are also shown in thisfigure. They are close to the obtained experimental results. Theused dysprosium (Dy) as a dopant is also shown in these results.

3.2. TL glow curves

Fig. 3 shows typical TL glow curves of MgB4O7:Dy nanoparti-cles, irradiated with 1�1011 protons/cm2 of 3 MeV proton beam

N. Salah et al. / Radiation Physics and Chemistry 86 (2013) 52–5854

(curve a), 1�1011 ions/cm2 of 50 MeV Li3þ and 120 MeV Ag9þ

ion beams (curves b and c, respectively). The TL glow curve of thesample irradiated by 1 kGy of 137Cs gamma rays is also shown inthis figure (curve d). The TL glow curves structures of the samplesirradiated by Li3þ and Ag9þ ions are similar with a single peak ataround 430 K, while that exposed to proton beams has an extra

20 30 40 60500

20

40

60

80

100

(015

)

(332

)

(311

)

(031

)

(321

)(3

02)

(221

)

(120

)(0

20)(3

00)

2θ(Degree)

Inte

nsity

(a.u

.)

Fig. 1. (a) XRD pattern and (b) SEM image of the as-synthesized nanocrystalline

MgB4O7:Dy.

Fig. 2. EDS quantitative and qualitative results for the as-synthesised MgB4O7:Dy n

prominent one at 525 K. The latter has a TL glow curve similar tothat exposed to gamma rays, but the intensities of its peaks arealmost equal. It is clear from Fig. 1 that the position of the firstband in all the presented glow curves shows a small variation byaround 77 K. Fig. 3 also shows that the MgB4O7:Dy nanoparticleshave different TL sensitivities to these ionizing radiations. TheMgB4O7:Dy nanoparticles have the highest sensitivity to Li3þ

ions, then Ag9þ and finally proton beam.Figs. 4–7 show the recorded TL glow curves of MgB4O7:Dy

nanoparticles exposed to different doses/fluences of these ioniz-ing radiations. TL glow curves of this sample irradiated withdifferent doses of 137Cs gamma rays in the range of 100 Gy–20 kGy are presented in Fig. 4. There is no significant change inthe glow curve structure or peak position. The TL response curveof MgB4O7:Dy nanoparticles is shown in the inset of Fig. 3. Itshows a linear response in the range of 100 Gy–15 kGy. Thenbeyond that it saturates. These results are in agreement withthose reported earlier (Lochab et al., 2007b). The linearity/sub-linearity or supralinearity in all the response curves of thesamples irradiated by different ionizing radiations in this studyis presented in the following sections.

The TL result of the samples of MgB4O7:Dy nanoparticles exposedto different fluences of proton as well as Li3þ and Ag9þ ion beamsshows similar behaviour to those of gamma rays irradiation (Figs.5–7, respectively). There is no change in the glow curve structure or

anoparticles. The theoretical values for the atomic percentage are also shown.

350 400 450 500 550 600

0.0

2.0x108

4.0x108

6.0x108

dc

b

a

x2

x0.05

x0.02

TL In

tens

ity (a

.u.)

Temperature (K)

Fig. 3. TL glow curves of MgB4O7:Dy nanoparticles samples exposed to (a) 1�

1011 protons/cm2 of 3 MeV proton beam, 1�1011 ions/cm2 of (b) 50 MeV Li3þ ,

(c) 120 MeV Ag9þ ion beams and to 1000 Gy of 137Cs g-rays (d). The ordinate is to

be multiplied by the numbers at the curves to get the relative intensities.

350 400 450 500 550 600

0.0

2.0x109

4.0x109

6.0x109

8.0x109

0.1 1 10

108

109

1010

TL R

espo

nse

(a.u

.)

Dose (kGy)

g

f

e

d

cba

a- 100 Gy b- 500 Gyc- 1 kGy d- 5 kGye- 10 kGyf- 15 kGyg- 20 kGy

TL In

tens

ity (a

.u.)

Temperature (K)

Fig. 4. TL glow curves of MgB4O7:Dy nanoparticles irradiated with different doses

of 137Cs g-rays.

350 400 450 500 550 600

0.0

2.0x107

4.0x107

6.0x107

100 101 102 103 104

106

107

108

109

Dose (kGy)

TL R

espo

nse

(a.u

.)

ed

cb

a

a- 1x1011

b- 1x1012

c- 1x1013

d- 1x1014

e- 1x1015

TL In

tens

ity (a

.u.)

Temperature (K)

Fig. 5. TL glow curves of MgB4O7:Dy nanoparticles irradiated with 3 MeV proton

beam at different fluences.

350 400 450 500 550 600

0.02.0x108

4.0x108

6.0x108

8.0x108

1.0x109

1.2x109

101 102 103 104

108

109

1010

Dose (kGy)

TL R

espo

nse

(a.u

.)

gfed

cb

a

a- 1x1011

b- 3.3x1011

c- 1x1012

d- 3.3x1012

e- 1x1013

f- 3.3x1013

g- 1x1014 TL In

tens

ity (a

.u.)

Temperature (K)

Fig. 6. TL glow curves of MgB4O7:Dy nanoparticles irradiated with 50 MeV Li3þ

ion beam at different fluences.

300 350 400 450 500 550 600

0.0

4.0x106

8.0x106

1.2x107

1.6x107

103 104 105

106

107

108

TL R

espo

nse

(a.u

.)

Dose (kGy)

fe

dc

ba

a- 3.3x1010

b- 1x1011

c- 3.3x1011

d- 1x1012

e- 3.3x1012

f- 1x1013

Temperature (K)

TL In

tens

ity (a

.u.)

Fig. 7. TL glow curves of MgB4O7:Dy nanoparticles irradiated with 120 MeV Ag9þ

ion beam at different fluences.

N. Salah et al. / Radiation Physics and Chemistry 86 (2013) 52–58 55

peaks positions, except that of Li3þ ion beam; there is a small shift inthe peak position to the lower temperature side by around 10 K. TheTL response curves are presented in the insets of these figures. In caseof proton beam and Li3þ ion beams irradiated samples the response

curves are linear/sublinear in the range of 1�1011–1�1013 proto-ns or ions/cm2, then beyond that they saturate, while that of Agirradiated samples is linear/sublinear only in a smaller range of3.3�1010–1�1011 ions/cm2.

Table 1TRIM calculations on the irradiated MgB4O7:Dy nanoparticles using 3 MeV proton

beam, 50 MeV Li3þ and 120 MeV Ag9þ ions beams. The equivalent absorbed doses

by this nanomaterial as a function of the ion beam fluences are also shown.

Beam (dE/dx)e (dE/dx)n Ionrange

Fluences Equivalentdose

(MeV mm�1) (MeV mm�1) (lm) (proton orion/cm2)

(kGy)

3 MeVproton

116.7 0.0649 151.25 1�1011 1.5579

1�1012 15.579

1�1013 155.79

1�1014 1557.9

1�1015 15,579

50 MeVLi3þ

546 0.0282 527.98 1�1011 7.289

3.3�1011 24.054

1�1012 72.89

3.3�1012 240.54

1�1013 728.9

3.3�1013 2405.4

1�1014 7289

120 MeVAg9þ

69430 263 27.72 3.3�1010 305.741

1�1011 926.49

3.3�1011 3057.41

1�1012 9264.9

3.3�1012 30,574.1

1�1013 92,649

10-1 100 101 102 103 1040.0

0.4

0.8

1.2

1.6

2.0

dcb

a

Supr

alin

earit

y fu

nctio

n

Exposure (kGy)

a Gamma raysb Proton beamc Li3+ ionsd Ag9+ ions

Fig. 8. Supralinearity function for the peak at 430 K of MgB4O7:Dy nanoparticles

as a function of exposures of (a) 137Cs g-rays, (b) 3 MeV proton beam, (c) 50 MeV

Li3þ ion beam and (d) 12 MeV Ag9þ ion beam.

N. Salah et al. / Radiation Physics and Chemistry 86 (2013) 52–5856

3.3. TRIM code calculation based on the Monte Carlo simulation

The TRIM code (Ziegler et al., 1985) based on the Monte Carlosimulation is used in this study to calculate some ion beamparameters. The values for the equivalent absorbed dose, D, dueto ions beams irradiation for MgB4O7:Dy nanoparticles werecalculated and are tabulated in Table 1. The following relation isused for calculating the values of D (Geiß et al., 1998):

D¼ 1:602� 10�10 1

rdE

dx

� �n. . .. . .. . .: ð1Þ

where the macroscopic dose at the irradiated volume is expressedin Gy, the particle fluence, n, is measured in cm�1, r is the densityof the irradiated material in g cm�3 ( it is around 1.2 g cm�3) andthe main energy loss (dE/dx) is calculated using the TRIM code(Ziegler et al., 1985) in units of MeV cm�1. The calculated para-meters using TRIM code are electronic main energy loss (dE/dx)e,nuclear main energy loss(dE/dx)n and the range of ions for thepellets of MgB4O7:Dy nanoparticles. They were calculated andtabulated in Table 1.

3.4. Supralinearity function

Linearity, sublinearity and supralinearity of the TL responsecurves of MgB4O7:Dy nanoparticles irradiated by gamma rays,proton beam as well as Li3þ and Ag9þ ion beams have beenstudied using the supralinearity function, f(D), defined as

f ðDÞ ¼FðDÞ=D

FðDnÞ=Dn

. . .. . .. . .. . .. . .: ð2Þ

where F(D) is the intensity of the TL signal at dose D and Dn

represents sufficiently low doses at which the detector responseis linear (Mahajna and Horowitz, 1997; Horowitz et al., 2001). Thefunction f(D) is equal to unity in the linear region, greater thanunity in the supralinear region and lower than one followingsaturation. The supralinearity function has been normalized todata taken in the linear part of the peak. Fig. 8 shows the values off(D) as a function of doses of gamma rays and proton beam as well

as Li3þ and Ag9þ ion beams (curves a, b, c and d, respectively). Itis clear from this figure that in case of gamma rays irradiatedsample the value of f(D) equals 1 in the dose range of 100 Gy–10 kGy, indicating a linear response (curve a); then it becomesslightly supralinear (f(D)41) up to 15 kGy, and finally showssublinearity (f(D)o1) above this value. In case of proton beam,Li3þ and Ag9þ ion beams the results show sublinear behavior(f(D)o1) in the whole studied ranges. The present MgB4O7:Dynanoparticles show early saturation in the selected ranges ofexposures, particularly those exposed to proton beams as well asLi3þ and Ag9þ ion beams. It is clear that the equivalent doses inGy due to irradiation by these protons as well as Li3þ and Ag9þ

ions are almost higher than the saturation value of gamma raysdoses (Table 1). Probably at lower values of exposures thelinearity, sublinearity and supralinearity behaviors of theresponse curves of ion beams irradiated samples might be similarto that of gamma rays.

4. Discussion

In the present study the induced TL glow peaks in MgB4O7:Dynanoparticles due to proton and ion beams irradiation areessentially similar to those of gamma rays irradiated sample(Fig. 3). This indicates that they have emerged from the sameenergy levels and traps/luminescent centres (TCs/LCs). But theseTCs/LCs might get modified by these energetic ions. Thesesignificant modifications induced in the TCs/LCs perhaps couldchange their populations. These modifications might be more incase of heavier ions such as Li3þ and Ag9þ . This might be thecause of missing the TCs/LCs of the second TL glow peak ofMgB4O7:Dy nanoparticles irradiated by Li3þ and Ag9þ ion beams(Fig. 3 curves b and c). The TCs/LCs responsible for the secondpeak at 525 K probably become optically non-active.

Sparsely ionizing radiations like protons or gamma rays showalmost similar TL results. The used protons perhaps could notinduce much modification in the TCs/LCs compare to those of theother used heavier ions (i.e. Li3þ and Ag9þ). Proton is a very tinyparticle compared with these ions; therefore, the number ofelectrons excited/trapped in these TCs/LCs might be small in caseof proton beam irradiated sample (Fig. 3, curve a). This might leadto a poor TL intensity in comparison with those of the other ionbeams. The TL intensity in case of Ag9þ irradiated sample is also

N. Salah et al. / Radiation Physics and Chemistry 86 (2013) 52–58 57

not high (Fig. 3, curve c) compare to that of Li3þ irradiated sample(Fig. 3, curve b). This might be due to the small penetration depthof Ag9þ in the MgB4O7:Dy pellet. TRIM code calculations (Ziegleret al., 1985) show that the penetration depth of 120 MeV Ag9þ

ions in the MgB4O7:Dy pellet is only 27.72 mm, while that of Li3þ

is 527.98 mm (Table 1). This means that there is only a small layerof MgB4O7:Dy pellet contributing to the TL emission in case ofAg9þ ions irradiated sample.

TRIM code calculations given in Table 1 show that more than99.9% of energy lost by the used 3 MeV proton beam as well as50 MeV Li3þ and 120 MeV Ag9þ ion beams in 1 mm thickMgB4O7:Dy pellets is electronic in nature, which perhaps influ-ences the initial energy band structure and the trapping andrecombination mechanism. Similar effects were also observed inour earlier studies (Sahare et al., 2005; Salah, et al., 2006a) whichcould be attributed to the change in the population of LCs/TCs;during irradiation by highly energetic ions. But this loss in theenergy is much higher in case of Ag9þ irradiated sample than thatof Li3þ and proton beams irradiated pellets. Though Ag9þ ion hashigher energy its size is much larger than those of Li3þ andproton; therefore its impact collision will be higher. Ion size andits energy are critical factors determining the amount of trapped/excited electrons and then amount of TL emission. Moreover,impacts of heavy ions on the trapping and luminescent centersmight influence these LCs/TCs, changing their populations andgiving rise to a different TL response of the respective peaks. Thepenetration depth is also another factor affecting the TL response.It is normally smaller in case of heavier ions than that of lighterions, but the induced deep TL emissions might get self-absorbedby the material itself and cannot significantly contribute to the TLintensity.

From the above results, it is obvious that irradiation by theseenergetic ions is the cause for these variations in the LCs/TCs,changing their populations and giving rise to a different behaviorthan those of gamma rays irradiated materials, particularlyheavier ions (i.e. Li3þ and Ag9þ). On the other hand, ionsimplantations might take place inside the host of these materials,which might also induce permanent defects, giving rise to thechange in the population of the LCs/TCs, and then, changing therelative intensity of their respective glow peaks. TRIM codecalculations given in Table 1 show that all of the used ions getimplanted inside MgB4O7:Dy pellets. Sometimes such ion implan-tation inside the host induces new TL glow peaks (Sahare et al.,2005). From the application point of view the presented nano-material might be useful for the dosimetry of heavy ions like Li3þ

and Ag9þ particularly at low fluences. There are no significantvariations in the glow curve structures or peak positions ofMgB4O7:Dy nanoparticles exposed to these ions. Moreover, theglow curve simply has a single peak, which is preferred inradiation dosimetry. In case of proton beam irradiated materialthe TL glow curve is greatly altered and shows early saturationand poor sensitivity, which are undesirable in radiation dosime-try. These results on proton beam irradiation are similar to thatreported in MgB4O7:Dy,Na (Bahl et al., 2013). Proton beamirradiated MgB4O7:Dy,Na nanomaterial showed early saturation(o350 Gy) with a significant variation in the glow curve struc-ture. This variation is observed in both low energy (i.e. 3 MeV inthe present study) as well as high energy protons (150 MeV in theTL result of MgB4O7:Dy, Na nanomaterial; Bahl et al., 2013).

The observed early saturation of TL response in case of theseions (Figs. 5–7) is expected as observed in earlier studies (Sahareet al., 2005). But it occurs at higher doses compared to that ofgamma rays irradiations (Table 1). The absorbed equivalent dosesby the material according to the given fluences are relatively higheven at low fluences (Table 1). The nanomaterial is expected tohave linear behavior below these doses. This saturation might be

explained in the framework of track interaction model (Horowitzet al., 2001). According to this model, at low fluences, therecombination of TCs/LCs occurs entirely within the tracks ofthese ions. The TL signal/peak, therefore, is simply proportional tothe number of ion beam tracks (the fluence). At higher fluences,the distance between the neighboring tracks decreases and theelectrons escaping the track can reach the neighboring track,resulting in the increased recombinations of the luminescentcenters leading to greater TL intensity. The sublinearity/saturationoccurs due to more overlapping of the tracks at much higherfluences. The nanomaterial has a small particle size. Thus, even athigher fluences when the distance between the nearest neighbor-ing tracks is small, it is less probable for electrons of one track torecombine with another track since the possibility of the neigh-boring track to be in a different particle altogether would be veryhigh as a result of the tiny size of the nanomaterials. Therefore,the TL saturation occurs at only high exposures.

5. Conclusions

The TL response of nanocrystalline MgB4O7:Dy irradiated by3 MeV proton beam as well as 50 MeV Li3þ and 120 MeV Ag9þ

ion beams in the fluence range of 1�1011–1�1015 ions/cm2 hasbeen demonstrated. The induced TL glow curves are almostsimilar to that of gamma rays irradiation. Single glow peak ataround 430 K is observed in the samples irradiated by Li3þ andAg9þ , while that exposed to proton beams has an extra band at525 K. This nanomaterial has the highest sensitivity to Li3þ ions,then Ag9þ and finally proton beam. The observed variations in theTL glow curve structure and response could be attributed to themodifications in the traps/luminescent centres. The ion size andpenetration depths are the main factors affecting the TL response.TRIM code calculations were also used to calculate the equivalentabsorbed dose, penetration depths and main energy loss. Theseresults suggest that this nanomaterial might be useful for thedosimetry of heavy ions particularly at low fluences.

Acknowledgments

This project was funded by the Deanship of Scientific Research(DSR), King Abdulaziz University, Jeddah, under Grant No. 74/135/1432. The authors, therefore, acknowledge with thanks DSRtechnical and financial support.

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