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Journal of the Australian CeramicSociety ISSN 2510-1560 J Aust Ceram SocDOI 10.1007/s41779-017-0172-1

Theoretical and experimental study ofPbO-SiO2-Sb2O3 glasses as gamma rayshielding materials

Negin Allahmoradi, Saeid Baghshahi &Masoud Rajabi

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RESEARCH

Theoretical and experimental study of PbO-SiO2-Sb2O3 glassesas gamma ray shielding materials

Negin Allahmoradi1 & Saeid Baghshahi1 & Masoud Rajabi1

Received: 11 June 2017 /Revised: 11 December 2017 /Accepted: 19 December 2017# Australian Ceramic Society 2018

AbstractInvestigation and application of high energy radiations require the availability of radiation shields. In this research, glasses withthe composition of 0.65PbO.(0.35-x)SiO2.xSb2O3 (x = 0, 0.01, 0.02, 0.03, 0.04, 0.05) were fabricated and characterized usingdensitometry, XRD, UV-Vis spectrophotometry and gamma ray spectrometry. The theoretical attenuation coefficient of thesamples was calculated using WinXCom software. It was observed that although PbO strongly increased the mass attenuationcoefficient for Co-60 radiation of glass, its substitution by Sb2O3 initially increased the parameter from 0.0609 to 0.0621, due tothe dominant effect of Sb2O3 on bubble removal. The results also showed that there was an inconsistency between the theoreticaland empirical results, that is, with increasing Sb2O3 content of the samples, the attenuation coefficient initially increased and thendecreased, while the theoretical calculations predicted a continuous decline. It appears that the disagreement is mainly due to thefining effect of Sb2O3 and its effects on the bubble content. The WinXCom software is designed to work solely based on themixture law. The sample 0.65PbO.0.34SiO2.0.01Sb2O3 showed the highest mass attenuation. The coefficient was 0.0621 and0.0609 in 1.250 MeV for the samples with x = 0 and 0.01.

Keywords Gamma ray shielding .WinXCOM . Lead glass . Sb2O3 addition . Attenuation coefficient

Introduction

Increased industrial, agricultural, and pharmaceutical applica-tion of gamma ray emitting isotopes necessitates the study ofthe attenuation coefficients of various materials. There is al-ways a need to develop new materials which could withstandthe nuclear rays, for radiation shield application [1]. Most ofthe nuclear ray shields are comprised of different layers ofconcretes with different compositions and densities.However, the change in the water content of the concretescould be a source of error in the calculation of mass attenua-tion coefficient. Moreover, concretes are neither transparentnor homogenous in terms of composition and density. Theseare the necessary requirements for shield materials. Thus,glasses are promising choices for such applications. Nuclear

engineering glasses are transparent against visible light, butabsorb gamma and neutron rays. A suitable glass shield musthave a highly reactive cross section and retain its mechanicaland optical properties while absorbing emissions [1].

It has been demonstrated that glasses containing heavymetals have great potentials for emission shield applications[2]. The effect of lead oxide in borate [1, 3–5], phosphate [6],and silicate [7] glasses have been investigated. In all the cases,higher concentrations of lead oxide enhance the attenuationproperties of the glass. Higher lead content in PbO-B2O3

glasses results in a linear increase in the mass attenuationcoefficient [1]. Lead containing glasses with more than 25%lead show better shielding properties in comparison to thecommonly used concrete.

Marzouk et al. [8] demonstrated that borate-aluminumglasses show good protection properties in gamma ray envi-ronment, as do glasses containing heavy metal cations such aslead or bismuth. On the other hand, Sb2O3 is commonly addedto the glasses as a gas bubble removal agent [9, 10].

Mass attenuation coefficient, effective atomic number, andeffective electron density are important factors in determiningthe gamma photon penetration in materials [2]. The linearattenuation coefficient (μ) can be calculated from Lambert-

* Saeid Baghshahibaghshahi@eng.ikiu.ac.ir

1 Department of Materials Science and Engineering, School ofEngineering, Imam Khomeini International University, Qazvin, Iran

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Beer law (Eq. 1) by dividing the number of passed photons inthe presence of the shield to the number of passed photons inits absent (the original photon count):

II0

¼ e−μx ð1Þ

where I0 and I are the incident intensity and intensity aftershielding respectively, x (cm) is the thickness of the absorbingmedium, and μ (cm−1) is the linear attenuation coefficient [4].The attenuation coefficient depends on temperature, heat treat-ment, and the light wavelength and is generally independentof the glass thickness [11].

The linear attenuation coefficient changes with the densityof the absorbent. It is true even when the absorbent material isconstant. It severely limits the use of this coefficient. That iswhy the mass attenuation coefficient is more extensively used.This coefficient is defined by Eq. 2:

mass attenuation coefficient ¼ μρ¼ ln I0=Ið Þ

ρtð2Þ

where ρ is the density (g/cm3) of the medium [12]. For acertain gamma ray energy level, the mass attenuation coeffi-cient does not depend on the physical state of the absorbent.For instance, it is the same for both liquid and vapor of thesame material.

Mass attenuation coefficient of a compound or mixture ofelements could be derived from the mixture law (Eq. 3) [12]:

μρ

� �c¼ ∑Wi

μρ

� �i

ð3Þ

where Wi is the mass fraction of the element indexed i in themixture or compound, and (μ/ρ)i is the mass attenuation co-efficient of the element indexed i [4].

X-rays and gamma rays have high penetration powers, butwhile passing through materials, the energy of the beams dis-sipates or the wave diminishes completely. One way to de-scribe the penetration power of a beam is using the estimate ofthe shield thickness. For each material, half value layer (HVL)is the material thickness which could cut the beam intensity tohalf in a shield. Equation 4 shows the relation between HVLand the mass attenuation coefficient [1]:

HVL ¼ 0:693

μð4Þ

The molar volume of the glass could be derived using Eq. 5[7]:

Vg ¼ Mρ

ð5Þ

In this equation, ρ is the glass density and M is the molarmass of the glass which could be derived by Eq. 6:

M ¼ 0:65M 1 þ 0:35‐xð Þ M 2 þ x M 3 ð6Þwhere M1, M2, and M3 are molar masses of PbO, SiO2, andSb2O3, respectively. Equation 6 uses the molar mass of theoxides. The excess volume in this case is determined using Eq.7:

Ve ¼ Vg− 0:65VPbO þ 0:35−xð ÞVSiO2 þ xVSb2O3½ � ð7Þ

The molar volume of the oxide constituents of glass isemployed in Eq. 7.

Silicate glasses are the most common type of glasses, sincethey are easily produced and highly transparent against visiblelight [7]. Lead oxide act as a network modifier in low concen-trations and as network former in higher concentrations [5].Antimony oxide has a dual contribution. It is traditionallyadded to the glass batch as a refining agent for reducing thebubble content. On the other hand, due to its high atomicnumber, antimony oxide is expected to enhance the gammaray attenuation abilities of these glasses. In this paper, theshielding potentials of Sb2O3 containing lead silicate glasseshave been investigated. The goal of this study was to investi-gate the interaction between PbO-SiO2-Sb2O3 glass and gam-ma ray beam (in 1250 keVenergy level) and measurement ofthe mass attenuation coefficient of this glass.

Experimental procedure

In order to prepare the samples, analytical grade PbO (Chem-Lab), SiO2 (Merck), and Sb2O3 (Merck) were used. Sampleswith the general composit ion of 0.65PbO.(0.35-x)SiO2.xSb2O3 (x = 0, 0.01, 0.02, 0.03, 0.04, 0.05) were for-mulated (Table 1). The batches were milled with the speed of120 rpm for an hour in a planetary ball mill. The powders werethen transferred into alumina crucibles and melted in an elec-trical furnace at 1100 °C for 2 h. The obtained melt waspoured into a steel mold, which was previously preheated at300 °C for 30 min in another furnace. For stress releasing ofthe as-cast samples, they were kept at the 300 °C for an hour.Then, the furnace was switched off and the samples werenaturally cooled down to the room temperature. Thereafter,the properties of the manufactured glass samples wereinvestigated.

XRD analysis (APD-2000, GNR, Italy, operated at 40 kW,with Cu-kα) was used to verify the amorphous structure of theglasses or the crystal phases of the devitrified samples.

The density of the samples was measured at 25 °C usingArchimedes method, by which the molar volume was alsocalculated. The results are reported in Table 1.

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To measure the bubble content of the glasses, samples withthickness of about 5 mm were observed under optical micro-scope. To measure the gamma ray shielding properties, Co60gamma ray source, Picker V9 emission system (which pro-duced a 4.99 mGy/min output in 80 cm distance and a 10 ×10 cm2 field), Farmer type 0.6 cm3 ionization module mea-surement system, and a PTW-Vnidos electrometer were used.

To analyze the absorption of spectra, a Rayleigh (1800UV)spectrophotometer was used which covers 190 to 1100 nmwavelength range. The absorption and transmission spectrawere measured for all the samples.

Results and discussion

Table 1 shows the appearance, density, molar volume, and ex-cess volume of the samples. All the samples except for S4 andS5 were transparent. The XRD examinations showed that onlysample Sb5 was devitrified and contained Pb2Sb2O7 (JCPDS:00-042-1355) and PbSb2O4 (JCPDS: 00-021-0937) as shown inFig. 1. It is noteworthy that Sb ions are present as Sb5+ inPb2Sb2O7 and as Sb3+ in PbSb2O4. Also the diffuse peaks cen-tered at around 30 and 50° are due to the glass structure.

The fact that Sb4 was opaque and not devitrified might bedue to metastable phase separation, shown in the Sb2O3-SiO2

phase diagram [13].Figure 2 shows the density and molar volume of the sam-

ples versus the molar percent of Sb2O3. Increase in the molarconcentration of Sb2O3 resulted in a lower molar concentra-tion of silicon. The density increased with Sb2O3 concentra-tion, because the molar mass of Sb2O3 is higher than that ofthe SiO2. Molecular mass was used to calculate the molarvolume. Excess molar volume decreased when Sb2O3 contentwas lower (Table 1). Excess molar volume is a measure of thedifference between the molar volume of the glass specimenand that of the crystalized structure. Excess molar volumecould be used to determine the network openness [7].Table 1 shows that 0.65PbO 0.35SiO2 had the most openstructure. This has been reported to be 1.67 cm3/mol in previ-ous works [7]. In addition, the molar volume of the specimenshowed the expansion in the structure of the glass, which is inaccordance with Singh’s report [3].

The optical images of the transparent samples are shown inFig. 3. The bubble content of the samples was measured usingthe ImageJ software and the results are shown in Fig. 4.

It seems that the addition of 2% molar fraction of Sb2O3

decreased the volume percentage of bubbles by more than

Table 1 Chemical composition,molar volume, and density of thesamples

Sample Mole fraction Appearance Density(g/cm−3)

Molar volume(cm3/mol)

Excess volume(cm3/mol)

PbO SiO2 Sb2O3

Sb0 0.65 0.35 0 Transparent 6.54 25.42 + 2.12

Sb1 0.65 0.34 0.01 Transparent 6.58 25.59 + 2.09

Sb2 0.65 0.33 0.02 Transparent 6.63 25.75 + 1.92

Sb3 0.65 0.32 0.03 Transparent 6.74 25.66 + 1.51

Sb4 0.65 0.31 0.04 Opaque 6.85 25.60 + 1.22

Sb5 0.65 0.30 0.05 Opaque 6.95 25.57 + 0.85

0

100

200

300

400

500

600

700

800

900

0 10 20 30 40 50 60 70 80 90

Inte

nsity

(a.

u.)

2 (o)

Pb2Sb2O7

PbSb2O4

Fig. 1 The XRD patterns ofsample Sb5

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50%. But adding more than 2% molar fraction of Sb2O3 ad-versely increased the number of gas bubbles. The initial de-crease in the amount of bubbles can be ascribed to the effect ofSb2O3 as the fining agent. However, at higher contents, Sb2O3

played the role of a network former or results in phase sepa-ration [7]. However, in the sample with 5% molar fraction ofSb2O3, devitrification decreased the fining effect of Sb2O3 andincreased the amount of bubbles in the structure.

UV-Vis absorption spectra of the specimens are shown inFig. 5. Samples Sb4 and Sb5 showed high absorption in thevisible region of light and absorb almost the entire incidentlight. In fact, these two specimens were opaque.

No peaks could be seen in the visible region for Sb0, Sb1,Sb2, and Sb3 (Fig. 5), which shows that they are transparentand colorless. The absorption edge for these samples wasaround 420 nm. The absorption edge is the wavelength in

which no transmission occurs. As observed, the addition ofantimony oxide to the base glass decreased the absorptionedge and made the glasses more transparent. The glass con-taining 1%molar fraction of Sb2O3 showed the lowest absorp-tion edge wavelength. A higher Sb2O3 concentration led to ahigher wavelength absorption edge, but in the infrared region,glasses containing antimony oxide transmitted the infraredlight better. The base glass shows a sudden increase in absorp-tion in 945 nm, which seems to be due to the grating change inthe spectrophotometer.

Apparently, adding 1%molar fraction of antimony oxide tothe base glass led to stronger bonds which in turn resulted inan increase in the energy required for electron interactions anddecrease in the absorption edge, but further antimony oxideincreased the absorption edges, which means a lower bondstrength and higher non bridging oxygen concentration.

The blue spectrum begins at 450 nm. The absorption edgeof the glasses was in this area. In transparent materials, thecolor of the materials depends on the passing wavelengths.

a b

dc

Fig. 3 The optical images of cross section of the samples of ~ 5 mmthickness: a Sb0, b Sb1, c Sb2, d Sb3

25.3

25.4

25.5

25.6

25.7

25.8

25.9

6.4

6.5

6.6

6.7

6.8

6.9

7

0 1 2 3

mol

ar v

olum

e (c

m3 /

mol

)

Den

sity

(g/

cm3 )

Sb2O3 (mol %)

density Molar volume

Fig. 2 The effect of Sb2O3 on the molar volume and the glass density ofthe samples

0

1

2

3

4

5

6

7

8

9

10

370 470 570 670 770 870 970

Absorb

ance (

%)

Wavelenght (nm)

Sb0

Sb1

Sb2

Sb3

Fig. 5 The UV-Vis absorption spectra of the samples

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 1 2 3 4

Bub

ble

Co

nte

nt

(vo

l %

)

Sb2O

3Content (mol % )

Fig. 4 The effect of antimony oxide on the bubble content of the samples

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These glasses absorb blue lights and let other wavelengthspass. The combination of the transmitted red and green lightsproduced a yellow color.

Figure 6 shows the transmission of the light by samples.Between 16 and 24% of the received light was transmitted bythe glass. For wavelengths up to 500 nm, transmission washigher in the glasses without antimony oxide, but for longerwavelengths, the glass containing 3%molar fraction of Sb2O3

showed the highest transmission. The sample containing 2%molar fraction of Sb2O3 showed the lowest transmission in allwavelengths. Microstructural investigations showed that thisspecimen contained the minimum amount of bubbles.Figure 4 shows that the transmission of Sb2 is less than theother samples. Less bubbles, on the one hand, means lessscattering sites in the glass, and on the other hand, less densityand absorption. Since the size of the bubbles was too large tomake scattering dominant, Sb2 showed the least transmission.

Figure 7 shows the variation in the theoretical, empirical,and normalized mass attenuation coefficient of the samples asa function of antimony oxide content. The theoretical resultswere calculated using WinXCom software [14]. The experi-mental results were normalized to rule out the presence ofdifferent bubble contents in the samples, that is, the measured

values were divided by (1-y), where y is the bubble percent.As observed, normalization did not change the results much,since the bubble content was not considerable.

As observed in Fig. 7, the addition of 1% molar fraction ofantimony oxide to the glass increased the mass attenuationcoefficient, but further addition of antimony oxide had a re-verse effect. The mass attenuation coefficient decreased rap-idly at first, but the rate of decrease slowed down later.Figure 7 demonstrates that the mass attenuation coefficientchanged slowly with the change of composition. Since theatomic number of silicon is moderate, 1% molar fractionchange did not create much difference.

The difference between the theoretical and the experimen-tal results is because of the decrease in the lead oxide molarcontent. It happens when the antimony oxide content in-creases. It can be shown mathematically that when antimonyoxide is added, even though the molar content of the leadoxide is the same, the weight fraction of this oxide actually

0

20

40

60

80

100

380 580 780 980

Tra

nsm

issi

on (

%)

Wavelenght (nm)

Sb0 Sb1

Sb2 Sb3

Fig. 6 UV-Vis transmission spectra of the samples

0

0.5

1

1.5

2

2.5

3

3.5

4

40

45

50

55

60

65

70

75

0 0.5 1 1.5 2 2.5 3 3.5

Bubble

Conte

nt

(%

)

Mas

s A

tten

uat

ion C

oef

fici

ent

(×10

3m

2g)

Sb O Content (mol%)

Experimental Att. Coef.

Normalized Att. Coef.

Theoretical Att. Coef.

Bubble Content

Fig. 7 The variation of porosity,theoretical, experimental, andnormalized attenuationcoefficients as a function ofSb2O3 content of the samples at1250 keV

1.69

1.7

1.71

1.72

1.73

1.74

1.75

0 1 2 3 4

HV

L (

cm)

Sb2O3 (mol%)

Fig. 8 The change of HVL with the change in the molar percent ofantimony oxide

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decreases. Hence, as the lead oxide is the primary attenuatingagent in the glass, the mass attenuation coefficient decreases.In the software, the calculation is based on the mixture law(Eq. 3), in which the weight fraction of the materials is incor-porated. In the abovementioned papers, all the calculationswere based on the molar fraction, but the change in the weightfraction in these studies were not so high to reveal this prob-lem with the WinXCom software. Therefore, as theWinXCom results show, the attenuation coefficient must de-crease when the molar fraction of antimony oxide increases(which results in a decrease in the lead oxide fraction).However, it is apparent in the diagram that in practice, theattenuation coefficient increases at first and then declines.

The second problem with the WinXCom software is thatthe software does not consider the effect of materials on themicrostructure of the shield. For instance, in this study,Sb2O3 not only changed the weight percent and molarcomposition, but also affected the microstructure of thematerial. Sb2O3 reduced the number of bubbles in theglass. Adding 2% molar fraction of this oxide minimizedthe bubble content. Bubbles have a very lower density incomparison to the glass matrix so they have much lessattenuation potential relative to the glass structure whichis comprised of heavier atoms such as lead, antimony, oreven silicon. The higher the atomic number, the more at-tenuation potential an element has. Thus, air bubbles atten-uate the beam much less than the glass matrix. In fact,removing bubbles from the structure increases the massattenuating coefficient.

Adding 2% antimony oxide increased the attenuation coef-ficient by decreasing the bubbles, but on the other hand, thedecrease of lead oxide as the primary factor in beam absorp-tion resulted in lower attenuation coefficient of Sb2 comparedto Sb1. A higher bubble content in Sb3, together with thedecrease in the lead oxide concentration, was the reasons forthe lower mass attenuation coefficient of this sample.

Commercial shield glasses usually contain 20–30% PbO,54–58% SiO2, and 14% basic materials. Since lead is the maincomponent in emission shields, the composition must be set tomaximize the lead content. The attenuation coefficient for aglass with 30% PbO, 14% Na2O, and 56% SiO2 have beencalculated theoretically to be 0.0862 and 0.0595 in 662 keVand 1173 keV, respectively [7]. This coefficient was 0.0621and 0.0609 in 1250 keV for Sb1 and Sb0, respectively, but in1173 keV for a composition similar to Sb0, the attenuationcoefficient was measured to be more than 0.063 [7].

Mass attenuation coefficient for Sb1 was 0.062 cm2/g in1.25 MeV. It is higher than the ferrite concrete [15], whichshows the highest mass attenuation properties in 1.173 MeV.

To have a better emission shield, a high attenuation coeffi-cient and a low HVL is desirable. Figure 8 illustrates the HVLthickness versus molar percent of antimony oxide, which is indesirable range.

Conclusions

The addition of Sb2O3 to a silicate glass composition hadpositive outcomes. The most important role of Sb2O3 wasrefining of the glass microstructure and removal of air bub-bles. The decrease in the air bubbles increased the transmis-sion and lowered the scattering of visible light. This led to amore transparent glass in comparison to the base glass. Inshorter wavelengths of gamma range, increasing the densityand removal of bubbles enhanced the attenuation properties ofthe glass.

The important point is that increasing the molar percent ofSb2O3 resulted in the decrease of the weight percent of PbO.Since lead is the primary attenuating agent (because of its highatomic number), a decrease in its molar percent must linearlydecrease the mass attenuating coefficient. However, the bub-ble removal and refining effect of Sb2O3 resulted in a higherattenuation coefficient. The interaction of these two factorscaused Sb1 to show the highest mass attenuation coefficientamong the samples. It must be noticed that the WinXComsoftware is inefficient in calculating the attenuation coeffi-cient, because it works solely based on the mixture law. Theeffect of materials on the microstructure of the shield must betaken into account in the design of this software.

Acknowledgements This research work received financial support fromIran National Science Foundation (INSF) (contract number 93006640).Hereby, the authors would like to appreciate the INSF for this support.

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