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Nuclear Engineering and Design 285 (2015) 31–38

Contents lists available at ScienceDirect

Nuclear Engineering and Design

jou rn al hom ep age: www.elsev ier .com/ locate /nucengdes

orrelation of gamma ray shielding and structural properties ofbO–BaO–P2O5 glass system

ulwinder Kaur, K.J. Singh ∗, Vikas Anandepartment of Physics, Guru Nanak Dev University, Amritsar 143005, India

i g h l i g h t s

Transparent glass samples of the system 55PbOxBaO(45 − x)P2O5 (x = 1 up to 5) have been prepared in the laboratory.Gamma ray shielding properties improve with the addition of BaO.Number of non-bridging oxygens decrease with the increase in the content of BaO.Investigated glass system can be potential candidate as an alternate to conventional radiation shielding ‘concrete’.

r t i c l e i n f o

rticle history:eceived 13 August 2014eceived in revised form9 November 2014

a b s t r a c t

The presented work has been undertaken to evaluate the applicability of BaO doped PbO-P2O5 glasssystem as gamma ray shielding material in terms of mass attenuation coefficient and half value layer atphoton energies 662, 1173 and1332 keV. A meaningful comparison of their radiation shielding properties

ccepted 26 December 2014has been made in terms of their mass attenuation coefficient and HVL parameters with standard radiationshielding concrete ‘barite’. The density, molar volume, XRD, FTIR, Raman and UV–visible techniques andmechanical properties (by Yamane and Mackenzie’s procedure) have been used to study the structuralproperties of the prepared glass system in order to check the possibility of their commercial utility asalternate to conventional concrete for gamma ray shielding applications.

© 2015 Elsevier B.V. All rights reserved.

. Introduction

Developments in the several sectors including agriculture,edicine and industry have involved the excessive use of gamma

ay isotopes. These radiation sources are very harmful not only foruman life but also, for sensitive laboratory equipment. In ordero handle this situation, search for a viable and efficient shielding

aterial is a necessity. Concrete is the most commonly used shieldaterial in nuclear reactors because it is inexpensive and adapt-

ble for any construction design. Concrete has acceptable strengthnd density for attenuation of gamma rays. However concrete hasany drawbacks (Lee et al., 2007) such as: (1) crack formation

fter the prolonged exposure to nuclear radiations (2) variabilityn its water content due to evaporation of water at high gamma

ay energies which leads to uncertainty in calculations for shieldesign and (3) non-transparency to visible light due to which it isot possible to see through concrete based shield design. In the

∗ Corresponding author. Tel.: +91 8427106016.E-mail address: kanwarjitsingh@yahoo.com (K.J. Singh).

ttp://dx.doi.org/10.1016/j.nucengdes.2014.12.033029-5493/© 2015 Elsevier B.V. All rights reserved.

light of this situation, it is necessary to develop better gamma raymaterial which can act as an alternate to concrete. Glass can be agood alternate for the concrete as gamma ray shielding material.There are several types of nuclear radiations in nuclear reactorsincluding gamma rays. Gamma rays are absorbed effectively byheavy elements. In order to make an effective gamma-ray shield,shield material should accommodate heavy elements. Glass can betransparent to visible light and their chemical composition can alsobe varied to accommodate large quantity of heavy metals (Singhet al., 2003). On the other hand, glasses are brittle in nature whichrestricts their practical utility. In the light of this situation, inves-tigation of structural properties of potential gamma ray shieldingglasses is an important area of research which may provide theclues to improve the brittle properties of the gamma ray shieldingglasses.

Silica based glasses are widely used for commercial applications.Poor chemical durability, high hygroscopic and volatile nature of

phosphate glasses have restricted their use as compared to silicateglasses (Kaewkhao and Limsuwan, 2010). However, these proper-ties can be improved by addition of suitable oxides in the phosphateglasses (Ardelean et al., 2005; Majhi et al., 2009; Ohishi, 2008;

3 ering a

PwllWc(

afffflcpwgigcarstu1

2

2

(pPmi2ufisa

2

rssieetl

�

wz

V

2 K. Kaur et al. / Nuclear Engine

isarska, 2009; Watanabe et al., 2001). Also, phosphate glasses haveell established properties of high thermal expansion coefficients,

ow preparation temperatures and good transparency to visibleight (Chanthima et al., 2012; Im et al., 2010; Kirdsiri et al., 2011;

ilder, 1980). In the light of this situation, phosphate glassesan be potential candidates for applications as shielding materialsKaewkhao et al., 2010).

The purpose of this work is to study the gamma ray shieldingnd structural properties of BaO doped PbO-P2O5 glass system asunction of composition. Glasses containing phosphorus as a glassormer and alkali and alkaline earth metals as modifiers have beenound to be stable (Sene et al., 2004). Phosphorus is a strong glassormer which participates with polymer like structure of regu-ar tetrahedron of PO4

3− groups which are linked together withovalent bonding in chains or rings. These chains or rings of phos-hate have been subjected to modifications to various extentsith addition of modifier. Change in structure has been investi-

ated FTIR, UV–visible and Raman spectroscopy techniques. Thiss accompanied by determining the shielding properties of thelass system in terms of the values of the mass attenuation coeffi-ient and half value layer parameters at photon energies 662, 1173nd 1332 keV. The values have been compared with conventionaladiation shielding concrete ‘barite’ by using WinXCom computeroftware (Gerward et al., 2004). Moreover, mechanical proper-ies of the glass system have been determined theoretically bysing Yamane and Mackenzie’s procedure (Yamane and Mackenzie,974).

. Materials and methods

.1. Sample preparation

Glass samples of the system xBaO·(45 − x)P2O5·55PbOx = 1–5 wt%) are prepared by melt quenching technique. Appro-riate amounts of AR grade chemicals of NH4H2PO4, BaCO3 andbO are used to prepare the samples. NH4H2PO4 is used as sourceaterial for P2O5 component. 20 g batch of each composition

s mixed well and melted in porcelain crucible above 950 ◦C for h until homogeneous mixture is obtained. Further, annealing isndertaken around 350 ◦C in pre-heated copper mold for 30 minollowed by slow cooling to room temperature in order to removenternal stress. Cylindrical shape samples are grounded for mea-urements. Chemical composition of the prepared glass samplesre provided in Table 1.

.2. Density and molar volume studies

This is the simple but powerful tool to study the changes occur-ing in structure of glasses. These parameters are affected by thetructural softening or compactness. Density of prepared glassamples is calculated by Archimedes principle using benzene asmmersion liquid. Archimedes principle is a well-established tool tovaluate the density values of the glass samples (Limkitjaroenpornt al., 2011). Density of prepared glass samples is calculated byhe above mentioned principle using pure benzene as immersioniquid. Density (�) is calculated as per the following relation:

={

W1

(W1 − W2)

}× �benzene (1)

here W1 = weight of sample in air; W2 = weight of sample in ben-ene; �benzene = density of benzene at room temperature.

Measured density values are reported in Table 1.

Molar volume (Vm) of glass is obtained by

m = M

�(2)

nd Design 285 (2015) 31–38

where � is the density of the glass samples calculated byArchimedes principle and M is the molar mass of the prepared glasssamples.

2.3. XRD studies

XRD study of prepared samples has been undertaken by BrukerD8 Focus. Cu K� lines were the source of X-rays with high inten-sity. Wavelength (∼1.54 A) at scanning rate of 2◦/min in the angle(2�) range 10◦ to 70◦ has been used for identification of amorphousnature of samples.

2.4. FTIR studies

FTIR study of prepared samples has been undertaken by PerkinElmer spectrometer (C92035) at the room temperature in the rangeof 400 to 3600 cm−1. Hydraulic press was employed to prepare pel-lets of sample powder with KBr in the ratio (1:100). FTIR study isan important tool to identify the various bands present in the glasssystem (explained in Section 4.2.2).

2.5. Raman studies

Raman study of prepared samples has been undertaken by Ren-ishaw InViva Raman microscope with 488 nm laser in the range30–1600 cm−1 at the room temperature. Raman study has beenused to identify the chemical changes in the structure by identi-fying the presence of different modes (stretching or vibrations) inthe investigated system (explained in Section 4.2.3).

2.6. UV–visible studies

Optical absorption measurements were performed on pre-pared glass samples exposed to UV–visible radiations in the range200–800 nm with CECIL UV–visible spectrophotometer. Obtaineddata has been used to calculate optical band gap using Tauc’s plots(Abdelghany et al., 2011) (explained in Section 4.2.5).

3. Theory/calculation

3.1. Gamma ray shielding properties

Mass attenuation coefficient (�/�) of prepared samples can bedetermined theoretically by using mixture rule and XCOM com-puter software (Gerward et al., 2004) developed by NIST. Massattenuation coefficient can be evaluated by using the followingrelation:

Mass Attenuation Coefficient =∑

wi

(�

�

)i

(3)

where wi is weight fraction of the constituent elements and (�/�)iis mass attenuation coefficients of the constituent elements. Thevariation of mass attenuation coefficient with wt% of BaO for ourglass system is given in Fig. 1.

Half value layer (HVL) parameter of the samples can be eval-uated by using the linear attenuation coefficient (�) as per theformula given below:

HVL = 0.693�

(4)

with the help HVL value, it is possible to determine the thickness ofmaterial required for gamma ray shielding applications. HVL is the

thickness of a shielding material required to reduce the intensityof gamma rays by half. Smaller HVL values of our prepared glasssamples than barite concrete shows that the volume requirementsof our glass system for shielding will be lesser.

K. Kaur et al. / Nuclear Engineering and Design 285 (2015) 31–38 33

Table 1Chemical composition (in wt%), density (�) and molar volume (Vm) of investigated glass samples.

Sample code Composition in wt% Density (�) (g/cm3) Molar volume (Vm)(cm3)

PbO BaO P2O5

PbBaP1 55 1.0 44 4.415 40.27PbBaP2 55 2.0 43 4.512 39.43

42

41

40

poc2Rec

3

meb

m

wngc

3

v

n

wtd

PbBaP3 55 3.0PbBaP4 55 4.0

PbBaP5 55 5.0

Effective atomic number (Zeff) is a fundamental property of com-ounds and mixtures. Investigated glass system belongs to categoryf mixtures and effective atomic number of such glass systems isalculated by using user-friendly software auto-Zeff (Taylor et al.,012) developed by Medical Radiation Physics Research Group ofMIT University for the robust, energy-dependent computation offfective atomic number. The variation of effective atomic numberomputed using software is shown in Fig. 3.

.2. Average coordination number

A chemical change occurs in glass network with addition ofodifier. Therefore, average coordination number of constituent

lements also changes. This change in average coordination num-er is given by

=[∑

ncixi

](5)

here nci is the coordination number of each cation. Coordinationumbers for Ba, P and Pb are 6, 4 and 6, respectively. Octahedraleometry of Pb and Ba and tetrahedral geometry of P have beenonfirmed from FTIR spectra (Shih, 2003).

.3. Bond density

Addition of metal oxide affects the number of bonds per unitolume (nb) which is calculated as

b =(

NA

Vm

)∑ncxi (6)

here NA is the Avogadro’s number, Vm is the molar volume, nc ishe coordination number of cation and xi is the mole fraction ofifferent oxides.

Fig. 1. Mass attenuation coefficient of prepared samples and barite concrete.

4.610 38.624.780 37.294.865 36.67

3.4. Packing density

It is an important parameter to describe the packing of atoms.Packing density (Vt) is calculated as

Vt =∑ ViXi

Vm(7)

where Vi is the packing factor for each component. xi is the molefraction of different oxides and Vm is the molar volume of the pre-pared samples. Vi is calculated by using “Pauling ionic radii” forcations and anions in the system (Makishima and Mackenzie, 1973).For example, if AmOn is the compound then its Vi can be calculatedby using the following formula:

Vi =(

43

)× II × N∗

A

[mR3

A + nR3O

](8)

where NA is Avogadro’s number and RA and Ro are the Pauling ionicradii of cation and anion for each component of prepared glasssample, respectively.

3.5. Elastic properties

Glass is considered as elastic substance. Mechanical propertiesfor prepared glass samples can be characterized through elas-tic properties like modulus of elasticity, compressibility, Poisson’sratio etc. (Sidek et al., 2012). In the presented work, elastic prop-erties for our glass system have been calculated by using Yamaneand Mackenzie’s procedure (Yamane and Mackenzie, 1974).

3.5.1. Poisson’s ratioThe Poisson’s ratio (�) is the ratio of the transverse to linear

strain for a linear stress. The concentration of bonds resist-ing a transverse deformation decrease as per the followingorder for different type of networks (three dimensional < twodimensional < one dimensional) (Damodaran and Rao, 1989). It iscalculated by using the relation

� = (0.5) − 1(7.2Vt)

(9)

3.6. Refractive index

From UV–visible studies, band gap has been calculated usingTauc’s plots (Abdelghany et al., 2011). Plot has been drawn for(˛h�)1/2 as function of h�. Here ˛, h and � are absorption coefficient,Planck’s constant and frequency of UV–visible radiation. Intercepton the energy (h�) axis of the above mentioned plot provides thevalue of band gap (Eg). Details of the calculation procedure are pro-vided in Singh et al. (2014). Values of band gap have been used tocalculate the refractive index (n) using the equation:(

n2 − 1) (

Eg)

(

n2 + 2) = 1 − sqrt

20(10)

where Eg is the band gap obtained from optical absorption data andtheir values are provided in Table 6.

34 K. Kaur et al. / Nuclear Engineering and Design 285 (2015) 31–38

Table 2Mass attenuation coefficient of glass samples and barite concrete.

Sample code Mass attenuation coefficient (�/�) (cm2/g)

662 keV 1173 keV 1332 keV

PbBaP1 0.09364 0.05994 0.05529PbBaP2 0.09365 0.05989 0.05524PbBaP3 0.09366 0.05984 0.05519PbBaP4 0.09367 0.05979 0.05514

3

e

R

wr

3

˛

4

4

4

mopm(rMf

oX(‘ofe

oat

4

tTm

aH

Table 3Half value layer (HVL) parameter of glass samples and barite concrete.

Sample code Half value layer (HVL) (cm)

662 keV 1173 keV 1332 keV

PbBaP1 1.71 2.67 3.03PbBaP2 1.67 2.62 2.97PbBaP3 1.57 2.46 2.79PbBaP4 1.54 2.42 2.74

4.2.2. FTIR studiesFig. 5 shows the FTIR spectra of investigated samples. The spec-

tra shows sharp absorption band at 893–699 cm−1 due to formation

PbBaP5 0.09369 0.05974 0.05509Barite concrete 0.0780 0.0565 0.0528

.7. Molar refraction

Molar refraction (RM) is calculated by using Lorentz–Lorentzquation (Duffy, 2002)

M =[(

n2 − 1)(

n2 + 2)]

× (Vm) (11)

here the factor (n2 − 1)/(n2 + 2) is called refraction loss. Values ofefractive index and molar refraction are provided in Table 6.

.8. Cation polarizability

Cation polarizability (˛) is calculated by using the equation

= 3RM

4IINA(12)

Cation polarizability has been expressed in Å3.

. Results and discussion

.1. Gamma ray shielding properties

.1.1. Mass attenuation coefficientMass attenuation coefficient is an important parameter to esti-

ate gamma ray shielding properties of the glass systems. Detailsf exact version of XCOM software and its link to the website arerovided in Berger et al. (2010). Many researchers have evaluatedass attenuation coefficient experimentally of several materials

including glasses) and compared their results with the theoreticalesults obtained by XCOM (Kaundal et al., 2010; Kharita et al., 2012;edhat, 2009; Singh et al., 2005, 2006, 2008). Good agreement was

ound between experimental and calculated values.In the presented work, mass attenuation coefficient values for

ur glass system has been obtained by using computer programCOM developed by National Institute of Standards and Technology

NIST). Results have been compared with the values of concretebarite’ at the same photon energies as given in Table 2. It has beenbserved that the values of mass attenuation coefficient parameteror our glass system are much higher than ‘barite’ at same photonnergies.

Comparative results have been shown in Fig. 1. It has beenbserved that with the increase in the weight fraction of BaO, massttenuation of glass samples also increase which may be attributedo increase in content of heavy metals in the glass samples.

.1.2. Half value layerHalf value layer (HVL) is also very useful parameter to iden-

ify the suitable specimen for gamma ray shielding applications.he glass sample having lower value of HVL is the better shielding

aterial in terms of thickness requirements.Values for our glass system are compared with ‘barite’ concrete

t same photon energies given in Table 3. It has been observed thatVL values of our glass system are smaller than ‘barite’ concrete at

PbBaP5 1.51 2.37 2.69Barite concrete 2.54 3.50 3.75

same photon energies. HVL values decrease with increase in weightfraction of BaO in the system (as shown in Fig. 2) due to increase inmass attenuation coefficient and corresponding density values ofthe system. Therefore, it is evident that higher value of weight frac-tion of BaO improves the gamma ray shielding properties in termsof mass attenuation coefficient and half value layer parameters.

4.1.3. Effective atomic numberIt has been observed that there is decrease in effective atomic

number values for all the glass systems with increase in photonenergy from 662 to 1173 and further to 1332 keV which can bedue to dependence of cross-section of photoelectric process whichvaries inversely with the incident photon energy as E3.5 (Sharmaet al., 2012).

Among the above investigated samples, PbBaP5 has maximumvalue of effective atomic number as shown in Fig. 3. This behaviorcan be explained as follows. Cross-section for Compton scatteringdepends on Z and the PbBaP5 sample has highest value of weightfraction of all heavy atomic number compounds. This also explainsthe increase in Z effective values from sample PbBaP1 to PbBaP5 atall the investigated gamma ray energies.

4.2. Structural properties

4.2.1. XRD studiesXRD patterns of investigated samples are shown in Fig. 4.

Absence of sharp peaks confirms the amorphous nature of samples.A small hump at 2� of 25–30◦ is due to loss of heat and formationof some nucleation sites. During the quenching of melt into coppermold, some of the atoms of the melt get aligned in periodic way atthe walls of the mold.

Fig. 2. Half value layer graph of prepared samples and barite concrete.

K. Kaur et al. / Nuclear Engineering and Design 285 (2015) 31–38 35

Table 4Observed FTIR peaks as function of wave number.

Wave number (cm−1) Structural units References

3400–3450 Bending and stretching vibrations of water molecules Le Saoût et al. (2002)1600–1650 Bending and stretching vibrations of water molecule Dayanand et al. (1996), Sene et al. (2004)1300–1400 Transformation of PO4

3− units to PO3− groups Sene et al. (2004)

1234 Due to presence of P O and P O− groups Le Saoût et al. (2002)1100 Partial breakdown of phosphate chains or rings with

addition of modifier, formation of M O P bond where(M = Ba or Pb)

Le Saoût et al. (2002), Sene et al. (2004), Shih(2003)

1080–980 Ionic character of PO43− Dayanand et al. (1996)

Near 900 Symmetric vibrations of P O P Le Saoût et al. (2002)893–699 P O P Le Saoût et al. (2002)Near 700 Anti-symmetric vibrations of P O P Le Saoût et al. (2002)

F

otPbgsa3tid1gi

ig. 3. Variation of Z effective with photon energy for prepared glass samples.

f P O P structure. Band near 900 cm−1 is due to symmetric vibra-ions and near 700 cm−1 is due to anti symmetric vibrations of

O P structure. Absorption peak in the range 1080–980 cm−1 cane assigned to ionic character of PO4

3− which is present in all P2O5lasses (Dayanand et al., 1996). Maximum intensity near 1100 cm−1

uggest partial break down of phosphate chains or rings withddition of modifier. Peaks in the region of 1600–1650 cm−1 and400–3450 cm−1 is due to bending and stretching vibrations of con-aminated water having no role in glass structure. This involves onlyntermolecular hydrogen bonding. Absorption peak at 1234 cm−1 isue to presence of P O and P O− groups. A small peak in the region

300–1400 cm−1 is due to transformation of PO4

3− units to PO3−

roups with the addition of modifier (Sene et al., 2004). Therefore,t can be estimated that phosphate glasses consist of a sequence

Fig. 4. XRD patterns of prepared samples.

Fig. 5. FTIR spectra of prepared samples.

of PO43− tetrahedrons and single PO4

3− unit which can be linkedto three other P O P linkages. Conversion of PO4

3− to PO3− units

may be done due to the breaking of P O P bonds due to additionof some cations like Ba2+ (Sene et al., 2004) (Table 4).

4.2.3. Raman studiesFig. 6 presents Raman spectra of investigated samples. Both

polar and non-polar vibrations of phosphates lattices are active ininfrared as well as in Raman spectra. Phosphorus is a strong glassformer participating with polymer like structures of regular tetra-hedron of PO4

3− groups which are linked together with covalentbonding in chains or rings. In Raman spectra, the bands appearedat 695 cm−1 due to vibrations of P O P chain and at 1064 cm−1

due to the stretching modes of P O− group which are formed dueto breaking of P O P chains with addition of modifier. The highestintensity in the band at 1144 cm−1 is due to PO2 groups. The band

Fig. 6. Raman spectra of prepared samples.

36 K. Kaur et al. / Nuclear Engineering and Design 285 (2015) 31–38

Table 5Observed Raman peaks as function of wave number.

Wave number (cm−1) Structural units References

1144 Presence of PO2 groups Le Saoût et al. (2002)1064 Stretching modes of P O− group Smith et al. (2014)

l with

bifiS

4

Divsa

4

p2tBi

4

bpetieedpieac2

aotweau(towTem

estp

695 P O P chain

327 Bending modes of phosphate polyhedra

ecome broader with the increase in the weight percentage of BaOn the prepared glass sample because it acts as the network modi-er and it results in the broadening of bands in Raman spectra (Leaoût et al., 2002) (Table 5).

.2.4. Density and molar volume measurementsResults of density and molar volume are provided in Table 1.

ensity of the system increases and molar volume decreases withncrease in wt% of BaO in the prepared samples. Decrease in molarolume with increase in the content of BaO may be attributed to thetructural changes occurring in the coordination of phosphorousnd lead in glass network.

.2.5. UV–visible studiesResults of optical studies are provided in Table 6. Band gap of the

repared samples is obtained from Tauc’s plot (Abdelghany et al.,011). Increase in value of band gap and decrease in value of refrac-ive index and molar refraction is observed with increase in wt% ofaO in prepared samples which can be related to structural changes

n lead and phosphorus.

.2.6. Calculated parametersAbove inferences about structural properties are also supported

y the calculated parameters. Table 6 shows the variation of opticalarameters with composition. From the tabulated values, it can bestimated that with the increase in the content of BaO from 1 wt%o 5 wt%, optical band gap increases from 2.88 to 3.07 eV whichndicate decrease in non-bridging oxygens in the system (Novatskit al., 2008). Refractive index is also an important parameter tolucidate the structure of glasses. The value of refractive indexepends upon the individual ions present in the glass and cationolarizability. Value of refractive index increases with increase

n ratio of non-bridging oxygens to bridging oxygens (Bhardwajt al., 2014) and it also increases cation polarizability (Dimitrovnd Sakka, 1996). Cation polarizability (˛) has important chemi-al implications, therefore, it is subject of various studies (Duffy,002).

In the presented glass system, the value of cation polariz-bility decreases from 10.91 A3 to 9.81 A3 (Table 6). The valuef refractive index also decreases indicating the decrease inhe number of non-bridging oxygens (Sastry and Rao, 2014)ith increase in wt% of BaO. The molar refraction is consid-

red as the sum of the contributions of the cationic refractionnd oxygen ionic refraction (Bhardwaj et al., 2014). The val-es of molar refraction decrease with the addition of BaOTable 6). The value of average coordination number of the sys-em increases with increase in wt% of BaO. Increasing contentf BaO results in increase in the number of bridging oxygenshich in turn decreases the number of non-bridging oxygens.

his leads to change in the glass structure. Glass is considered aslastic substance. This property of glasses is governed by elasticoduli.Table 7 shows compositional dependence of the elastic prop-

rties with change in the content of BaO. Packing density of theystem increases with increase in wt% of BaO (Table 7). This revealshat BaO acts as network modifier and enhances the rigidity of pre-ared samples. Poisson’s ratio also gives the idea of the rigidity

Le Saoût et al. (2002) addition of modifier Le Saoût et al. (2002), Smith et al. (2014)

of the glass samples. It is the measure of cross-link density. Forsystems having high cross link density, Poisson’s ratio lies in therange 0.1–0.2 and for low cross link density, value lies in the range0.3–0.5 (Gowda et al., 2005). In our glass samples, the value ofPoisson’s ratio is found to be in the range 0.269–0.280 (Table 7).The results of Poisson’s ratio show the tightening in the bonds ofglass structure and hence the increase in the rigidity of glass struc-ture. When an oxide is introduced in the system, the strength ofthe structure depends on the field strength of the cation. As BaOfavors the mechanical properties (Kityk et al., 2002), therefore,increase in the weight fraction of BaO content in the glass systemhas resulted in increasing of elastic moduli values (Table 7). Thisindicates the resistance to deformation at higher content of BaOwhich is due to presence of large number of covalent bonds (Sideket al., 2012).

In the earlier reported glass systems, it has been observedthat gamma ray shielding properties improve and elastic prop-erties deteriorate with the addition of heavy metal oxides whichrestricts the selection of compromising composition for gamma rayshielding applications. In the presented glass system (BaO dopedPbO-P2O5 glass system), it has been estimated that both gammaray shielding and elastic properties improve at the higher contentof heavy metal oxide. This result indicate that in the presented glasssystem, the glass sample with higher content of BaO can be idealcomposition for gamma ray shielding applications. Earlier reportedrestriction for selection of compromising composition has beenremoved in the barium oxide doped lead oxide phosphate glasssystem.

Better values of gamma ray shielding parameters in terms ofmass attenuation coefficient and half value layer of our glass sys-tem as compared to barite concrete indicate that our glass samplescan be possible candidate for gamma ray shielding applications.Reported glass samples have been found to be transparent to visi-ble light which further enhances their chance for utility as nuclearreactor shield. The addition of BaO has increased the values of den-sity of the system and simultaneously decreased the molar volumevalues. This observation can be related to increase in the com-pactness of the glass structure which can be further correlatedto the decrease in bond length or interatomic spacing betweenatoms of glasses (Bürger et al., 1992; Singh et al., 2012). Additionof BaO affects the number of bonds per unit volume. It has beeninferred from bond density data that with addition of the contentof BaO, bonds per unit volume increase. This reveals that BaO acts asnetwork modifier. Packing density data of the studied glass struc-ture shows increasing rigidity of the structure with the increasein the content of BaO. These inferences are supported by Pois-son’s ratio results which also give the idea of rigidity of structure.Obtained results show tightening in the bonds of glass structureand hence, increase in rigidity of the structure at higher contentof BaO. Increase in strength of glass structure and hence, rigiditycan lead to modification in mechanical properties. FTIR, Raman andUV–visible techniques have also been used to investigate the struc-tural properties of our glass system. Above mentioned techniques

indicate that number of non-bridging oxygens decrease with theincrease in the content of barium oxide which may further lead tothe formation of more number of covalent bonds. Therefore, boththeoretical and experimental results are complimentary to each

K. Kaur et al. / Nuclear Engineering and Design 285 (2015) 31–38 37

Table 6Optical properties of prepared glass samples.

Sample code Cationpolarizability(˛) (Å3)

Optical bandgap (Eg) (eV)

Refractiveindex (n)

Molar refraction (RM)(cm3)

Average coordinationnumber (m)

Bond density (nb)(×1029) (m−3)

PbBaP1 10.91 2.88 2.73 27.50 4.90 0.717PbBaP2 10.66 2.92 2.72 26.85 4.92 0.735PbBaP3 10.41 2.96 2.71 26.23 4.94 0.783PbBaP4 10.01 3.04 2.70 25.23 4.97 0.804PbBaP5 9.81 3.07 2.69 24.72 5.00 0.823

Table 7Elastic properties of prepared samples.

Sample code Packing density (Vt) Poisson ratio (�) Modulus of elasticity(E) (GPa)

Modulus of compressibility (K)(GPa)

Modulus of elasticity inshear (G) (GPa)

PbBaP1 0.602 0.269 49.30 35.47 20.72PbBaP2 0.609 0.272 49.67 36.17 20.83

obo

5

(

(

(

A

fSp7

PbBaP3 0.616 0.275 50.02PbBaP4 0.626 0.278 50.37

PbBaP5 0.631 0.280 50.51

ther and support the inference that there is decrease in the num-er of non-bridging oxygens and hence, high rigidity at high contentf barium oxide.

. Conclusions

From above discussion, it can be concluded that:

1) The BaO doped PbO-P2O5 glass system may be treated as thepotential candidate for gamma ray shielding applications dueto better values of mass attenuation coefficient and half valuelayer parameters as compared to ‘barite’ concrete. Transpar-ent natures of prepared samples also support the usefulness ofsamples for the aforesaid purpose.

2) Results of several experimental techniques employed includingFTIR, Raman and UV–visible indicate the decrease in the num-ber of non-bridging oxygens with the addition of the content ofBaO in the glass system. This inference is supported by severalcalculated parameters such as Poisson’s ratio, packing density,elastic moduli, average co-ordination number, bond density etc.

3) In terms of HVL parameter, PbBaP5 is the best sample amongthe prepared glass samples. It has the least average HVL valuewhich is 2.19 cm. On the other hand, barite concrete has theaverage HVL value of 3.26 cm. This result indicate that lesservalue of thickness is required for producing the gamma rayshielding material from PbBaP5 glass composition as comparedto barite concrete. Barium has the maximum content as ele-ment in barite concrete and Pb has the maximum content aselement in our glass samples. Moreover, barium in barite con-crete is used as barium sulphate (Akkurt et al., 2005) and inour glass samples, lead is used as lead oxide. Price of the PbOis cheaper than BaSO4 for same purity level. In the light of thissituation, it is imperative that production cost will be lesser fordeveloping the gamma ray shield from the glass compositioncorresponding to PbBaP5 sample than barite concrete. Trans-parency to visible light for the glass sample can be advantageduring its use.

cknowledgements

The authors Kulwinder Kaur and Vikas Anand are grate-

ul to the financial assistance provided by the Department ofcience and Technology, New Delhi (India) through INSPIRErogram [IF-120620] and UGC, New Delhi (India) JRF (NET) [F.17-4/2008(SA-I)], respectively.

36.86 20.9337.73 21.0138.13 21.04

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