TL dosimetry of nanocrystalline Li2B4O7:Cu exposed to 150 MeVproton, 4 MeV and 9 MeV electron beam

Vibha Chopra a,n, Lakhwant Singh a, S.P. Lochab b, V.E. Aleynikov c, Arun S. Oinamd

a Department of Physics, Guru Nanak Dev University, Amritsar, Punjab 143005, Indiab Inter University Accelerator Center, Aruna Asaf Ali Marg, P.O. Box 10502, New Delhi 110067, Indiac Joint Institute for Nuclear Research, Dubna 141980, Russiad Department of Radiotherapy, Post Graduate Institute of Medical Education and Research, Chandigarh 160012, India

H I G H L I G H T S

� TL properties of Li2B4O7:Cu exposed to 150 MeV proton beam have been studied.� TL properties of Li2B4O7:Cu exposed to 4 MeV electron beam have been studied.� TL properties of Li2B4O7:Cu exposed to 9 MeV electron beam have also been studied.

a r t i c l e i n f o

Article history:Received 19 April 2013Accepted 3 April 2014Available online 13 April 2014

Keywords:Li2B4O7:CuThermoluminescenceProton therapyCancer treatment

a b s t r a c t

Nanocrystals of the Li2B4O7:Cu were synthesized by a combustion method using 1000 ppm and2500 ppm concentrations of Cu. TL characteristics of the synthesized Li2B4O7:Cu material doped withCu of concentration 1000 ppm and 2500 ppm were studied using 150 MeV proton beam, 4 MeV and9 MeV electron beam. It is observed that Li2B4O7:Cu doped with Cu (both 1000 ppm and 2500 ppm)exhibits a linear response in the range 1�100–3�101 Gy for exposure to 150 MeV proton beam.Nanocrystalline Li2B4O7:Cu, doped with 1000 ppm and 2500 ppm Cu, shows a linear TL response in therange 1�10�1–1�101 Gy for 4 MeV and 9 MeV electron beam. Fading of phosphors was also studiedand it was found that Li2B4O7:Cu is quite suitable for proton and electron beam dosimetry.

& 2014 Elsevier Ltd. All rights reserved.

1. Introduction

Borates are of considerable interest in thermoluminescence(TL) dosimetry, because borates are relatively stable chemicalcompounds and respond without serious problems when attempt-ing to dope them with TL sensitizers such as rare earth, copper ormanganese ions. Materials such as Li2B4O7, MgB4O7 have a closetissue equivalence and are thus worth considering for their TLproperties. Indeed the lithium borate (Li2B4O7) dosimeters aresuperior to lithium fluoride (LiF) in terms of tissue equivalence.When these materials are doped, they show some desirablefeatures for TL in terms of high sensitivity, linearity and storage.Crystalline Li2B4O7 is of considerable interest due to its practicalapplications in thermoluminescence dosimetry of X-ray, gammaray and neutron radiation (Furetta and Wang, 1998; Mahesh et al.,1989; Dolzhenkova et al., 2001). Lithium borate, a tissue equiva-lent material (Jayachandran et al., 1968) with an effective atomic

number, Zeff¼7.3 was first investigated as a TLD in 1965 (Schulmanet al., 1965). The detailed TL properties of Li2B4O7 doped with Cuwere studied by different workers (Furetta et al., 1996; Watanbeet al., 1996; Thanh et al., 2008). The thermoluminescence proper-ties of different preparations of lithium borate have been studied(Wall et al., 1982; Takenaga et al., 1983). The TL properties of threepowder preparations, Li2B4O7, Li2B4O7:Mn, and Li2B4O7:Cu werecompared (Driscoll et al., 1983) and it was observed that Li2B4O7:Cu had an advantage over Li2B4O7:Mn in situations where dosesdown to about 20 μGy need to be measured. Second, Li2B4O7:Cuwas observed to have appreciable fading if exposed to light forperiod exceeding an hour. The previous work on Li2B4O7 led to theconclusion that it shows a useful TL feature of perfect linearity inits TL response, with dose up to 103 Gy followed by sublinearbehavior without any supralinearity (Srivastava and Supe, 1989).Different methods have been developed to prepare Li2B4O7 givingdifferent TL characteristics (Kutomi et al., 1986; Soramasu andYasuno, 1996; Martini et al., 1993). The comparative study ofLi2B4O7:Cu, Ag, P and LiF: Mg, Cu, Na, Si with well known typeLiF: Mg, Ti detector (TLD-100) was presented. LiF: Mg, Cu, Na,Si was found to have sensitivity 75 times higher than TLD-100

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Radiation Physics and Chemistry

http://dx.doi.org/10.1016/j.radphyschem.2014.04.0050969-806X/& 2014 Elsevier Ltd. All rights reserved.

n Corresponding author.E-mail address: vibhachopra04@gmail.com (V. Chopra).

Radiation Physics and Chemistry 102 (2014) 5–10

and Li2B4O7:Cu, Ag, P has 5 times higher sensitivity than that ofLiF: Mg, Ti (Miljanic et al., 2006). Further a Li2B4O7 dosimeter with0.3 wt% (weight percentage) of Mn impurity concentration wasprepared for high dose level (in the range 1–30 kGy) for gammairradiation applications (Sharifzadeh and Gorjifard, 2008). Thedosimetric properties of synthesized microcrystalline Li2B4O7:Cuwere studied. This material shows a linear TL behavior in therange 10�3–103 Gy of gamma radiations. Therefore the preparedphosphor was found to be useful for personal dosimetric mea-surements and environmental applications, but the material wasfound to be light sensitive (El-Faramawy et al., 2000). Later thedifferent concentrations of copper were added to Li2B4O7 to get agood dosimeter compatibility with the commercial one. Further,a comparative study of undoped and Cu doped Li2B4O7 to TLD-100,TLD-700, TLD-700H and Al2O3: Mg, Y (D-3) using low and highlinear energy transfer (LET) radiations and mixed radiation fields(Photon and thermal neutrons) was reported (Fernandes et al.,2008). It shows that Li2B4O7:Cu is 50 times more sensitive togamma radiation than undoped Li2B4O7 and 5 times more sensi-tive as compared to TLD-100. Li2B4O7:Cu was found to be 5 timesless sensitive to thermal neutrons than pure Li2B4O7.

There is a growing demand for dosimetry of beams of chargedparticles since they are increasingly being used for diagnostic andtherapeutic purposes (Barth et al., 2003; Strehl, 1999; Pandey et al.,2011). Particle-therapy is recognized as having the most favorabledose deposition properties possible with external beam techni-ques. With respect to a role in radiation therapy, ion beams havetwo important features arising both from the physical aspects oftheir dose distribution in the patient and from potentially advan-tageous biological phenomena resulting from their high rate ofenergy deposition (high linear energy transfer (LET)) over aportion of the particle track which can often be located in thetumor volume. The interest in this application field is welldocumented by the growing number of facilities in the worldand by the number of patients already treated successfully withthis method (Gehanne et al., 2005).

The overall literature review of Li2B4O7 compounds reveals thatnot much work has been done in the metal doping of thesematerials and no work is yet reported for proton and electroninduced modifications of the respective materials. So, we havedecided to work in this field so as to apply these materials inradiation dosimetry.

2. Experimental

Li2B4O7:Cu nanophosphor has been synthesized by using thecombustion method (Singh et al., 2011; Chopra et al., 2013). Thephosphor obtained by the combustion method was then crushedto get the powder form. Finally the nanocrystalline powder wasannealed at 300 1C for 10 min in crucible in the presence of air andwas quenched by taking the crucible out of the furnace andplacing it on a metal block. The synthesized phosphor was thenused for studying its TL properties.

To study TL properties, the annealed samples were thenirradiated with electron beam of energies 4 MeV, 9 MeV for doseranging 1�10�2–1�101 Gy, each using a Dual energy Clinac DHXlinear accelerator (Varian medical system, Palo Alto, CA, USA) atPGIMER, Chandigarh (India). We have used solid water (RW3)phantom. The density of medium was 1.003 g/cc and the scatter-ing, absorption and attenuation of electron beam energy in solidwater phantom, nearly equal to that of water. Since TLD powderwas spread over the phantom in a thin layer, it provided BraggGray Cavity condition at the depth of charge particle equilibrium.Source to surface distance of phantom for exposure of TLD wasR50¼100 cm (“R50¼” should be read as “SSD¼” that is source to

surface distance) for each electron beam of 4 and 9 MeV. Thedepth of dose measurement was performed for field size of 15�15 cm2 at the reference depth defined by

dref ¼ 0:6 R50�0:1 gm=cm2

which is beyond depth of dose maximum.TLD was exposed under the condition of charge particle equili-

brium at the depth of reference depth. The synthesized samples werealso irradiated with proton beam of energy 150MeV for dose ranging1�100–1�102 Gy using a Phasotron at the Joint Institute for NuclearResearch, Dubna, Russia. Beam energy was defined from proton rangein water (R¼200mm of water). Depth–dose distributions weremeasured by means of a semiconductor Si detector in a waterphantom. Energy of the beam at the beam entrance at the procedureroom was 150MeV. Additional energy PMMA moderator equivalentto 40 mm water was placed before the final collimator. Dosimetrycalibration at the each point of detectors irradiations was performedby means of an ionization chamber and clinical dosimeter KD-27012(Kovar et al., 1993). Sets of detectors were exposed behind additionaldegrader equivalent to 150mm of water at the Spread out Bragg peak(SOBP). Dose rate at the point on the exit windows behind additionaldepth 4 mm PMMA was measured by a dosimeter with a diamonddetector. Dose rate in this point was 8.184 Gy/min or 491.04 Gy/h.

TL glow curves were then recorded using a Harshaw TLD reader(Model 3500) fitted with a 931B photo-multiplier tube (PMT)(having PMT tube Model: R268HA of Bicron, USA, and Serial no.AA4324) at IUAC, New Delhi. The heating rate was 5 K/s and theamount of 5 mg of the sample was taken for each TL recording.

3. Results

The TL properties of synthesized Li2B4O7:Cu (doped with1000 ppm and 2500 ppm Cu), irradiated with proton beam ofenergy 150 MeV, electron beam of energies 4 MeV and 9 MeV havebeen studied and the results are shown in Table 1. TL propertiesexamined in this study include TL glow curves, TL response curvesand fading. These results may be helpful in the development oftissue equivalent TL nanocrystalline detectors best suited for widerange of proton and electron beam exposures.

3.1. TL glow curves

TL glow curves of synthesized nanocrystalline Li2B4O7:Cu(doped with 1000 ppm Cu), exposed to proton beam of energy150 MeV of different doses in the range 1�100–1�102 Gy, areshown in Fig. 1(a) and those of Li2B4O7:Cu (doped with 2500 ppmCu) are shown in Fig. 1(b). Fig. 1(a) reveals that for a dose of3�101 Gy, the nanophosphor shows one prominent peak at 486 K.With increase in dose to 6�101 Gy, the TL intensity keeps onincreasing and there is a small shift in peak. On further increasingthe dose to 1�102 Gy, the TL intensity still keeps on increasing,the prominent peak is observed at 490 K and a small peak isobserved at 434 K. Fig. 1(b) reveals that for a dose of 1�100 Gy,the nanophosphor shows prominent peak at 548 K. With increasein dose to 5�100 Gy, the peak at 443 K becomes prominent andthat of 548 K becomes small. When the dose is increased further,the intensity of the prominent peak keeps on increasing and thatof small peak keeps on decreasing. For increase in dose up to1�102 Gy, the main peak is shown at 443 K and small humps at492 K and 550 K.

Fig. 2(a) and (b) shows the TL glow curves of Li2B4O7:Cu (dopedwith 1000 ppm and 2500 ppm Cu respectively), exposed to 4 MeVelectron beam of different doses in the range 1�10�2–1�101 Gy.Fig. 2(a) reveals that for a dose of 1�10�2 Gy, the nanophosphorshows a prominent peak at 603 K. With increase in dose to

V. Chopra et al. / Radiation Physics and Chemistry 102 (2014) 5–106

1�10�1 Gy, the peak intensity of prominent peak decreases and asmall hump is shown at around 471 K. It is also found that withincrease in dose to 2�100 Gy, the intensity of prominent peak athigher temperature keeps on decreasing and that of small peak atlower temperature increases. With increase in dose to 1�101 Gy,

the prominent peak shifts to 482 K, and small peak to 609 K.Further Fig. 2(b) presents the similar trend for Li2B4O7:Cu (dopedwith 2500 ppm Cu) in which the prominent peak becomes thesmall peak and small peak becomes the prominent peak withincrease in dose. Finally at a dose of 1�101 Gy, the prominentpeak is observed at 465 K, a small hump at 514 K and the smallpeak is observed at 609 K.

TL glow curves of Li2B4O7:Cu (doped with 1000 ppm and2500 ppm Cu), exposed to 9 MeV electron beam of different doses

400 450 500 550

0.05.0x1041.0x1051.5x1052.0x1052.5x1053.0x1053.5x1054.0x1054.5x1055.0x1055.5x1056.0x1056.5x1057.0x1057.5x1058.0x1058.5x105

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Fig. 1. TL glow curves of Li2B4O7:Cu: (a) doped with 1000 ppm Cu and (b) dopedwith 2500 ppm Cu, irradiated to proton (150 MeV) beam.

Table 1TL properties of synthesized Li2B4O7:Cu (doped with 1000 ppm and 2500 ppm Cu), irradiated with proton beam and electron beams of different energies.

Beam Observations Results of LiB4O7:Cu (1000 ppm) Results of LiB4O7:Cu (2500 ppm)

150 MeV proton beam (a) Dose range 1�100–1�102 Gy 1�100–1�102 Gy(b) Peak position for highest dose Prominent peak—490 K

Small peak—434 KProminent peak—443 KSmall peak—492 K, 550 K

(c) TL response Linearity—1�100–3�101 Gy Linearity—1�100–3�101 GySupralinearity up to 6�101 Gy Supralinearity up to 6�101 Gy

(d) Fading 6.8% in month 7.85% in month

4 MeV electron beam (a) Dose range 1�10�2–1�101 Gy 1�10�2–1�101 Gy(b) Peak position for highest dose Prominent peak—482 K Prominent peak—465 K

Small peak—609 K Small hump—514 KSmall peak—609 K

(c) TL response Linearity—1�10�1–1�101 Gy Linearity—1�10�1–1�101 Gy(d) Fading 7.2% in month 7.55% in month

9 MeV electron beam (a) Dose range 1�10�2–1�101 Gy 1�10�2–1�101 Gy(b) Peak position for highest dose Prominent peak —475 K Prominent peak—461 K

Small hump—540 K Small hump—511 KSmall peak—615 K Small peak—592 K

(c) TL response Linearity—1�10�1–1�101 Gy Linearity—1�10�1–1�101 Gy(d) Fading 7% in month 7.3% in month

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Fig. 2. TL glow curves of Li2B4O7:Cu: (a) doped with 1000 ppm Cu and (b) dopedwith 2500 ppm Cu, irradiated to electron (4 MeV) beam.

V. Chopra et al. / Radiation Physics and Chemistry 102 (2014) 5–10 7

in the range 1�10�2–1�101 Gy are presented in Fig. 3(a) and (b)respectively. Fig. 3(a) and (b) reveals that for a dose of 1�10�2 Gy,the nanophosphor Li2B4O7:Cu (doped with 1000 ppm Cu) showsa prominent peak at 603 K and the nanophosphor Li2B4O7:Cu(doped with 2500 ppm Cu) shows a prominent peak at 610 K.With increase in dose to 1�10�1 Gy, the peak intensity ofprominent peak decreases and a small hump is observed at around478 K in Fig. 3(a) and at 465 K in Fig. 3(b). It is also found that withincrease in dose to 5�10�1 Gy, TL intensities of the prominentpeak at higher temperature keep on decreasing and those of smallpeaks keep on increasing. Finally with increase in dose to1�101 Gy, the prominent peak is observed at 475 K, hump at540 K, and the small peak at 615 K in Fig. 3(a) and prominent peak,small hump and small peak are observed at 461 K, 511 K and 592 Krespectively in Fig. 3(b).

3.2. TL response

TL response of Li2B4O7:Cu (doped with 1000 ppm and2500 ppm Cu) exposed to proton for doses in the range of1�100–1�102 Gy is shown in Fig. 4. It has been found thatLi2B4O7:Cu nanophosphor irradiated with 150 MeV proton beamexhibits a linear response in the range 1�100–3�101 Gy. Withfurther increase in dose to 6�101 Gy, supralinear behavior hasbeen noticed. This linearity over a wide range of dose is found withan uncertainty of 77% (with almost 3% uncertainty in protonirradiation, 2% uncertainty in weighing the sample and 2% uncer-tainty of the TLD reader. On the basis of these calculations theerror has been calculated and marked as error bars in themeasurements). This shows that synthesized nanophosphorLi2B4O7:Cu (doped with both 1000 ppm and 2500 ppm Cu) canbe used as a TL dosimeter within a range of 1�100–3�101 Gy ofproton beam (150 MeV).

Figs. 5 and 6 show the TL response of Li2B4O7:Cu (dopedwith 1000 ppm and 2500 ppm Cu) exposed to electron beam of

energy 4 MeV and 9 MeV respectively for doses in the range1�10�1–1�101 Gy. It has been found that Li2B4O7:Cu nanopho-sphor irradiated with 4 MeV and 9 MeV electron beam exhibits alinear response in the range 1�10�1–1�101 Gy. This linearityover a wide range of dose is found with an uncertainty of 78%(with almost 4% uncertainty in electron irradiation, 2% uncertaintyin weighing the sample and 2% uncertainty of the TLD reader).Fig. 5 reveals that TL sensitivity of Li2B4O7:Cu (doped with2500 ppm Cu) is found to be less than that of Li2B4O7:Cu (dopedwith 1000 ppm Cu) for lower doses, as the dose increases TLsensitivity of Li2B4O7:Cu (doped with 2500 ppm Cu) is found tohave sharp decrease. Whereas Fig. 6 reveals that TL sensitivity ofLi2B4O7:Cu (doped with 2500 ppm Cu) is also found to be less thanthat of Li2B4O7:Cu (doped with 1000 ppm Cu) for lower doses butas the dose increases both are found to have equal TL sensitivity.This shows that synthesized nanophosphor Li2B4O7:Cu (doped

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Fig. 3. TL glow curves of Li2B4O7:Cu: (a) doped with 1000 ppm Cu and (b) dopedwith 2500 ppm Cu, irradiated to electron (9 MeV) beam.

100 101 102

104

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espo

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Li B O : Cu doped with 1000 ppm Cu 2500 ppm Cu

Fig. 4. TL response of Li2B4O7:Cu (doped with 1000 ppm and 2500 ppm Cu)irradiated to proton (150 MeV) beam.

10-1 100 101

102

103

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espo

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Doping concentration of Cu in Li B O : Cu 1000 ppm 2500 ppm

Fig. 5. TL response of Li2B4O7:Cu (dopedwith 1000 ppm and 2500 ppm Cu) irradiatedto electron (4 MeV) beam.

10-1 100 101102

103

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Doping concentration of Cu in Li B O : Cu1000 ppm2500 ppm

Fig. 6. TL response of Li2B4O7:Cu (doped with1000 ppm and 2500 ppm Cu) irradiatedwith electron (9 MeV) beam.

V. Chopra et al. / Radiation Physics and Chemistry 102 (2014) 5–108

with both 1000 ppm and 2500 ppm Cu) can be used as a TLdosimeter for electron beam of energies 4 MeV and 9 MeV in thedose range of 1�10�1–1�101 Gy.

3.3. Fading

The results of fading of synthesized nanocrystalline Li2B4O7:Cuirradiated to 150 MeV proton beam of dose 6�101 Gy, 4 MeVelectron beam of dose 5�100 Gy, 9 MeV electron beam of dose5�100 Gy are presented in Figs. 7-9 respectively. Fig. 7 revealsthat in case of samples doped with 1000 ppm Cu, the fading onthird day is 3.6%, on 7th day it is 5% and on 15th day it is 6.5%,whereas in one month the total fading recorded is 6.8%. The fadingrecorded in the samples doped with 2500 ppm of Cu on 3rd day is4.5%, on 7th day it is 5.8% and on 15th day it is 7.1%, whereas in onemonth the total fading recorded is 7.8%. The maximum fading

recorded in our system is seen in first week after exposure of thesamples.

Fig. 8 reveals that in case of Li2B4O7:Cu doped with 1000 ppmCu, the fading on third day is 3.6%, on 7th day it is 5% and on 15thday it is 6.5%, whereas in one month the total fading recorded is7.2%. The fading recorded in the samples doped with 2500 ppm ofCu on 3rd day is 4.5%, on 7th day it is 5.8% and on 15th day it is6.8%, whereas in one month the total fading recorded is 7.5%.

Further it is observed from Fig. 9 that in case of Li2B4O7:Cudoped with 1000 ppm Cu, the fading on third day is 4.5%, on 7thday it is 5.2% and on 15th day it is 6.2%, whereas in one month thetotal fading recorded is 7%. The fading recorded in the samplesdoped with 2500 ppm of Cu on 3rd day is 5.2%, on 7th day it is 6%and on 15th day it is 6.6%, whereas in one month the total fadingrecorded is 7.3%.

4. Discussion

TL glow curves of synthesized nanocrystalline Li2B4O7:Cu(doped with 1000 ppm Cu) exposed to proton beam of energy150 MeV show the prominent peak at 490 K and a small peak isobserved at 434 K. The appearance of two peaks at higher doses inthe glow curve of nanophosphor indicates that there are possiblytwo kinds of trapping sites, one which is shallower leading to thepeak at lower temperature and the other which is deeper leadingto the peak at higher temperature (Lochab et al., 2007). In the caseof nanoparticles the surface to volume ratio is high which resultsinto a high surface barrier energy. Therefore the low doses ofradiation are unable to create enough defect states to produce TL.On increasing the dose the total energy density will overcome thesurface barrier to produce more defects states and enhance the TLintensity. The occurrence of various peaks, changes in theirintensities and the linearity over a wide range of doses for thesynthesized nanocrystalline material are explained using themodel shown in previous work (Salah et al., 2007). The linearbehavior of synthesized nanomaterial over a wide range of dosescan be explained on the basis of a track interaction model (TIM)(Mahajna and Horowtz, 1997; Horowitz et al., 2001). According tothis model, the number of traps generated by the high energyradiation in a track depends upon the cross section and the lengthof the track inside the matrix. In case of nanomaterials the lengthof the track generated by high energy radiation is of the order offew tenths of nanomaterials. At the low doses there exist few trapcenters. As the dose increases, the TL intensity increases as stillsome particles exist that would have missed while targeting by thehigh energy radiation, owing to the small size of particles. Thisgives good linearity over a wide range of dose (Vij et al., 2009). Asthe dose increases, the average distance between the nearestneighbor tracks decreases and electron escaping the parent trackcan reach the luminescent center in neighboring tracks, thusresulting in increased production of light leading to supralinearity.

The better response for only 1000 ppm and 2500 ppm Cudoped samples may be due to the ordering of atoms that mayoccur at this particular concentration of dopant, which may lead tothe enhancement of TL intensity. Doping with Cu introducespredominantly deeper trapping levels in Li2B4O7 and also theenhancement in TL intensity. The change in trap distributions maybe due to the lattice perturbation caused by incorporation of Cu inLi2B4O7 (Kumar et al., 2009). The change in the behavior of the TLglow curves for 1000 ppm and 2500 ppm doped samples may bedue to change in the population of luminescent/trapping centers,as a result of addition of impurities in different concentrations.

Li2B4O7:Cu (doped with 2500 ppm Cu), when irradiated with4 MeV electron beam, shows the prominent peak at 465 K, a smallhump at 514 K and the small peak is observed at 609 K. Since the

0 5 10 15 20 25 30

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Fig. 7. Fading of synthesized nanocrystalline Li2B4O7:Cu irradiated to proton(150 MeV) beam.

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Fig. 8. Fading of synthesized nanocrystalline Li2B4O7:Cu irradiated to electron(4 MeV) beam.

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Fig. 9. Fading of synthesized nanocrystalline Li2B4O7:Cu irradiated to electron(9 MeV) beam.

V. Chopra et al. / Radiation Physics and Chemistry 102 (2014) 5–10 9

nanocrystalline structure of the phosphor is more conducive to thecreation of shallow traps in the phosphor, thus the nanophosphorgives its major peak at the lower temperature of 465 K. In case ofthe nanophosphor the deeper traps act as a reservoir for theshallow traps and therefore some electrons from the deeper trapsmove to the conduction band on thermal stimulation via theshallow traps. This enhances the number of filled shallow traps atrelatively lower temperatures, thus resulting in a substantialincrease in the intensity of the lower temperature peak.

5. Conclusions

Nanocrystalline Li2B4O7:Cu (doped with 1000 ppm and 2500 ppmCu) shows a linear response in the range 1�100–3�101 Gy forexposure to 150 MeV proton beam and in the range 1�10�1 –1�101 Gy for 4 MeV and 9 MeV electron beam. So this material can beused as a radiation dosimeter for the treatment of skin cancer atdifferent depths using an electron beam and treatment of deeptumors using a proton beam.

Acknowledgments

We are grateful to Dr. Sundeep Chopra of Inter UniversityAccelerator Center, New Delhi for providing necessary facilitiesto carry out this work. We are thankful to Dr. Numan Salah fromCenter for Nanotechnology, Saudi Arabia for valuable discussions.

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