Mass Attenuation Coefficients of Li2o- B2O3 Glass System at 0.662 and 1.25 Mev Gamma Energies

XI Radiation Physics & Protection Conference, 25-28 November 2012, Nasr City - Cairo, Egypt

Mass attenuation coefficients of Li2O- B2O3 glass system at 0.662 and 1.25 MeV gamma energies

H.E. Donya* Faculty of Science, Physics Department, Menoufia University, Egypt. *Hossam Elsayed Donya ([email protected]), Tel: 00201004164148

ABSTRACT Borate glasses are very promising materials for the radiation dosimetry

applications in view of the fact that their effective atomic numbers (Zeff) are very close to that of human tissue and having a high ability of hosting activators. The total mass attenuation coefficients, partial interactions and

Zeff of glass system (100-x)B2O3-xLi2O (where x=5, 10, 15, 20, 25, 30, 35 and 40 mole %) have been calculated at photon energies 0.662 and 1.25 MeV using WinXCom software on the basis of mixture rule. Results indicated that the total mass attenuation coefficients showed a decrease with increasing the

Li2O content, due to a decrease in Compton scattering probability, which gave a dominant contribution to the total mass attenuation coefficients for the studied glass samples at both energies. However, the photoelectric absorption and coherent scattering showed an increase with increasing the

Li2O, concentrations at same energies. For a comparison, the total mass attenuation coefficients of the glass system had lower values at the energy

1.25 MeV than that at 0.662 MeV. Zeff was found to increase linearly with the increase of Li2O concentrations. It was concluded that low Li2O concentrations in glass system, under study, have Zeff closed to that of biological tissue (Zeff=7.42) and have higher total absorption coefficients at energy of 0.662 MeV than that at 1.25 MeV. These results are very useful in designing gamma radiation detectors using thermoluminescence technique.

Therefore, it is recommended to use low Li2O content in Li2O-B2O3 glass system which makes it suitable for radiation detection purposes in medical applications.

Keywords: Borate glasses/Effective atomic number/Mass attenuation coefficients /Thermoluminescence.

1. INTRODUCTION New thermoluminescent (TL) materials are suitable for radiation detection in the last several years that have been produced and studied. Special attention was given to different glass systems by our group because of their high TL sensitivity and their negligible fading (1- 3) (1) . In our previous paper , it is showed that Li2O-B2O3 glass system has good TL properties

191 XI Radiation Physics & Protection Conference, 25-28 November 2012, Nasr City - Cairo, Egypt

to be considered as a new added candidate to the member of the currently being used dosimetric tree. The response of a thermoluminescent material to γ- ray detection depends on the atomic number of its constituents; then it is important to know first the effective atomic number of such material, Zeff, for obtaining its expected TL response at different energies. This was carried out by calculating the strength of different interaction probabilities (cross- sections) between gamma rays and the studied materials (detectors) (4).

2. METHOD OF CALCULATION

The effective atomic number, Zeff of a thermoluminescent material (a composite) can be calculated according to the following equation (5, 6):

b bb Zeff=++aZ 1 1 aZ 2 2 ...... (1) with

nZ() anNZ==ii , iiAinZ() ∑i ii where a1, a2,… are the fractional contents of electrons belonging to different elements of atomic number Z1, Z2, ….etc in the composite, ni is the number of electrons, in one mole, belonging to each element Zi and NA is the Avogadro's number. The values of b are in the range from 2.94 to 3.5.

The total mass attenuation coefficient of a mixture or compound (µ/ρ)m has been calculated by WinXCom, based on the mixture rule (7), where

⎛⎞μ n ⎛⎞μ ⎜⎟= ∑w i ⎜⎟ (2) ⎝⎠ρ mii ⎝⎠ρ

(µ/ρ)i is the mass attenuation coefficient for the individual element in each component and wi is the fractional weight of the element in each component. This equation is valid when the effects of molecular binding, chemical and crystalline environment are negligible. Berger and Hubbell developed XCOM for calculating the total mass absorption coefficients or photon interaction cross- sections for any element, compounds or mixtures in a wide range of photon energies (from 1keV to 100 GeV). Recently, XCOM was transformed to the Windows platform by Gerward et al. (8), called WinXCom and our calculations were extracted using this software.

3. RESULTS AND DISCUSSIONS

In this study, the (100-x)B2O3-xLi2O glass system (where x=5, 10, 15, 20, 25, 30, 35 and 40 mole %) was converted to weight fraction and given in table (1). For an example LiB5 sample refers to the composition 95B2O3-5Li2O.

192 XI Radiation Physics & Protection Conference, 25-28 November 2012, Nasr City - Cairo, Egypt

Table (1). Chemical composition of samples and compound mole fraction of each in the mixture of the studied glass systems

Sample B2O3 (Mol. %) Li2O (Mol. %)

LiB5 95 5 LiB10 90 10 LiB15 85 15 LiB20 80 20 LiB25 75 25 LiB30 70 30 LiB35 65 35 LiB40 60 40

The total mass attenuation coefficients, of the studied glass systems were calculated at two photon energies 0.662 (137Cs-source) and 1.25 MeV (average energy of 60Co-source) using the WinXCom software on the basis of mixture rule.

ph 3.1 Photoelectric mass absorption cross section ( μm ) ph Based on our calculations, it was found that the photoelectric cross section ( μm ) of the studied glass system at 0.662 and 1.25 MeV showed a decrease with increasing the Li2O concentrations (see Fig. 1).

1.30 0.662 MeV 1.20 1.25 MeV

/g) 1.10 2

1.00 y=-3E-08x + 1E-05 (cm

-5 R² = 1 0.90

0.80

0.30

0.25

0.20

0.15 y = -5E-09x + 2E-06 Photoelectric interaction x 10 interaction Photoelectric R² = 0.99 0.10 5 10152025303540 % LiB 5-40

Fig. (1). The photoelectric mass absorption coefficient of (100-x) B2O3-xLi2O glass system (where x=5, 10, 15, 20, 25, 30, 35 and 40 mole %).

193 XI Radiation Physics & Protection Conference, 25-28 November 2012, Nasr City - Cairo, Egypt

ph It is clear from Fig. 1 that the values of μm at low photon energy (0.662 MeV) are higher ph than those at high energy (1.25 MeV). In addition, the slope of the straight line between μm and x at 0.662 MeV is higher than that at 1.25 MeV. Therefore, the effect of increasing Li2O, ph and accordingly decreasing the B2O3 concentrations, showed a decrease in the μm values of the studied glass systems at both energies.

3.2 Compton and coherent scattering cs Compton scattering mass attenuation coefficients ( μm ) of the studied glass system were cs calculated using WinXcom software. Results are given in Fig. 2 where μm values show an cs observed decrease with increasing Li2O concentration. Also, values of μm at 0.662 MeV are ph cs higher than those at 1.25 MeV. Therefore, both μm and μm values are more effective at low energy value, i.e at 0.662 MeV.

7.90 7.88 0.662 MeV 7.86 7.84 1.25 MeV 7.82

/g) 7.80 2 7.78

(cm 7.76 y = -3.3E-05x + 0.07865 -2 7.74 R2=0.997 7.72 7.70

5.65 5.60 5.55 5.50 y = -2.3E-5x + 0.05555 5.45 Compton Interaction x 10 R2=0.994 5.40 5.35 5 10152025303540 % LiB 5-40

Fig. (2) The Compton scattering, interaction of (100-x) B2O3-xLi2O glass system (where x=5, 10, 15, 20, 25, 30, 35 and 40 mole %).

ch The Coherent scattering mass attenuation coefficients ( μm ) of the studied glass system ch were also calculated and results are represented in Fig. 3. μm shows (see Fig.3) a decrease ch with increasing Li2O concentration. The rate of increase in μm is obvious at energy of 0.662 ch MeV where values of μm are higher than those at 1.25 MeV.

194 XI Radiation Physics & Protection Conference, 25-28 November 2012, Nasr City - Cairo, Egypt

0.160 0.155 0.662 MeV 0.150 1.25 MeV 0.145 y = -3.6E-7 x + 1.435E-4 /g)

2 R² = 0.999 0.140

(cm 0.135 -3 0.130

0.055

0.050 0.045 y = -8E-08x + 3E-05 0.040 R² = 0.999 0.035 0.030 Coherent interaction interaction x 10 Coherent 0.025

5 10152025303540 % of LiB 5-40

Fig. (3) The coherent scattering mass attenuation coefficient of (100-x) B2O3-xLi2O glass system (where x=5, 10, 15, 20, 25, 30, 35 and 40 Mol. %).

From the above calculations of photoelectric, Compton and coherent interaction, the total mass absorption coefficient were calculated and illustrated in Table 2.

Table (2). Total absorption coefficient values of the studied glass system.

Sample Energy Coherent Compton (cm2/g) Photoelectri Sum 2 -4 -2 -6 2 -2 LiB5 0.60 1.42×10 7.85×10 9.56×10 7.86×10 1.25 3.27×10-5 5.54×10-2 1.98×10-6 5.55×10-2 -4 -2 -6 -2 LiB10 0.60 1.40×10 7.83×10 9.43×10 7.84×10 1.25 3.23×10-5 5.53×10-2 1.87×10-6 5.53×10-2 -4 -2 -6 -2 LiB15 0.60 1.38×10 7.82×10 9.30×10 7.83×10 1.25 3.19×10-5 5.52×10-2 1.93×10-6 5.52×10-2 -4 -2 -6 -2 LiB20 0.60 1.36×10 7.80×10 9.17×10 7.81×10 1.25 3.15×10-5 5.51×10-2 1.82×10-6 5.51×10-2 -4 -2 -6 -2 LiB25 0.60 1.35×10 7.78×10 9.04×10 7.80×10 1.25 3.11×10-5 5.50×10-2 1.88×10-6 5.50×10-2 -4 -2 -6 -2 LiB30 0.60 1.33×10 7.77×10 8.91×10 7.78×10 1.25 3.06×10-5 5.49×10-2 1.77×10-6 5.49×10-2 -4 -2 -6 -2 LiB35 0.60 1.31×10 7.75×10 8.78×10 7.76×10 1.25 3.02×10-5 5.48×10-2 1.83×10-6 5.48×10-2 -4 -2 -6 -2 LiB40 0.60 1.29×10 7.73×10 8.65×10 7.74×10 1.25 2.98×10-5 5.46×10-2 1.72×10-6 5.46×10-2

195 XI Radiation Physics & Protection Conference, 25-28 November 2012, Nasr City - Cairo, Egypt

From table (2), one can notice that the total absorption coefficient closes to the Compton interaction values. To confirm the obtained values of the attenuation coefficient of the studied glass, the effective atomic number (Zeff ) should be calculated and compared the obtained data by the attenuation coefficient of the element with Z has the same or near Zeff .

4. ZEFF –CALCULATION

Zeff was calculated for the studied glass samples [LiB(5-40)] and given in Table 3 using Eq. (2). Column 1 gives the glass composition, element under study is given under column 2, the atomic weight, A and atomic number Z are given under columns 3 and 4, respectively. Weight fraction, w, and the total number of electrons per gm, NAZw/A are displayed under columns 5 and 6 respectively. The fraction number of electrons due to each element in the composition is then calculated and given under column 7 and denoted by a.

The values of aZb were then calculated and given under the last two columns where x takes the values 2.94 and 3.5. Finally, values of Zeff were calculated and given in the last row of each glass composition. For example, Zeff values of LiB5 glass composition were found to be 7.33 and 7.39 with a percentage difference of about 0.8% and of an average of 7.36.

196 XI Radiation Physics & Protection Conference, 25-28 November 2012, Nasr City - Cairo, Egypt

Table (3). Zeff calculation for our studied glass samples [LiB(5-40)].

2.94 3.5 Element A Z W NAZ W/A a a Z a Z 22 LiB5 B 10.81 5 0.295 8.19×10 0.279 31.719 78.118 O 16 8 0.684 2.06×1023 0.702 317.203 1016.407 Li 6.941 3 0.021 5.47×1021 0.019 0.472 0.872 Sum 1 2.93×1023 1 349.394 1095.397 Zeff 7.329 7.387 22 LiB10 B 10.81 5 0.27781 7.738×10 0.264 29.991 73.861 O 16 8 0.67318 2.027×1023 0.692 312.833 1002.404 Li 6.941 3 0.049 1.275×1022 0.043 1.101 2.037 Sum 1 2.928×1022 1 343.925 1078.302 Zeff 7.290 7.354 22 LiB15 B 10.81 5 0.265 7.35×10 0.252 28.576 70.376 O 16 8 0.674 2.03×1023 0.694 313.582 1004.804 Li 6.941 3 0.061 1.59×1022 0.054 1.374 2.542 Sum 1 2.92×1023 1 343.532 1077.722 Zeff 7.287 7.352 22 LiB20 B 10.81 5 0.245 6.824×10 0.234 26.573 65.442 O 16 8 0.65714 1.979×1023 0.679 306.809 983.105 Si 6.941 3 0.09742 2.536×1022 0.087 2.199 4.068 Sum 1 2.915×1022 1 335.582 1052.616 Zeff 7.230 7.303 22 LiB25 B 10.81 5 0.235 6.52×10 0.224 25.412 62.584 O 16 8 0.664 2.00×1023 0.686 309.937 993.125 Li 6.941 3 0.101 2.63×1022 0.090 2.283 4.223 Sum 1 2.91×1023 1 337.632 1059.931 Zeff 7.245 7.318 2.94 3.5 Element A Z W NAZ W/A a a Z a Z 22 LiB30 B 10.81 5 0.21347 5.946×10 0.205 23.243 57.241 O 16 8 0.64128 1.931×1023 0.665 300.562 963.084 Li 6.941 3 0.1452 3.779×1022 0.130 3.290 6.0873 Sum 1 2.903×1023 1 327.095 1026.412 Zeff 7.167 7.251 22 LiB35 B 10.81 5 0.205 5.68×10 0.196 22.227 54.740 O 16 8 0.654 1.97×1023 0.678 306.268 981.368 Li 6.941 3 0.141 3.67×1022 0.126 3.197 5.915 Sum 1 2.90×1022 1 331.692 1042.023 Zeff 7.201 7.282 22 LiB40 B 10.81 5 0.18194 5.068×10 0.175 19.892 48.989 O 16 8 0.62565 1.884×1023 0.652 294.451 943.504 Li 6.941 3 0.19242 5.008×1022 0.173 4.378 8.100 Sum 1 2.891×1023 1 318.721 1000.593 Zeff 7.104 7.198

197 XI Radiation Physics & Protection Conference, 25-28 November 2012, Nasr City - Cairo, Egypt

The variation of the mean values of Zeff of the present glass system with Li2O is given in Fig. 4. It is clear that (see Fig. 4), Zeff decreases with increasing the Li2O concentration and their values range from 7.15 to 7.36. This variation is represented by an excellent linearity form with R2=0.99.

Fig(4) The effective atomic number of (100‐x) B2O3‐ xLi2O glass system (where x=5, 10, 15, 20, 25, 30, 35 and 40 mole %).

From the Zeff calculations, one can notice that, the Zeff for the studied glass are decreased from 7.35 to 7.15. So, the attenuation coefficient can be compared by an element closes to this range as Nitrogen atom (9) which has an attenuation coefficient value of 0.081 and 0.057 at gamma energies of 0.66 and 1.25 MeV respectively which is in a good agreement with our data (see table 2). Zeff of LiB glass system have the same as soft tissue (Zeff = 7.30 ± 1.25%) (10), which is recommended for dose measurements using insertion of LiB TL-detectors in various phantoms [1].

5. CONCLUSION

The total mass attenuation coefficients and partial interactions at photon energies 0.662 and 1.25 MeV (100-x) B2O3-xLi2O glass system (where x=5, 10, 15, 20, 25, 30, 35 and 40 mole %) have been investigated using the WinXCom software. Results showed that total mass attenuation coefficients decreased with increasing Li2O concentration, due to a decrease in Compton scattering of glass samples which contribute dominantly to the total interaction.

Although, the coherent scattering showed a decrease with increasing Li2O concentrations but it has lower values than Compton scattering. The photoelectric interaction has a slight influence in these glass samples on comparison to the effects of other two interactions. In addition, the Zeff values of our studied glasses showed a decrease with increasing Li2O

198 XI Radiation Physics & Protection Conference, 25-28 November 2012, Nasr City - Cairo, Egypt

concentration and found to have values from 7.15 to 7.35. Results recommend Li2O-B2O3 glass system as a TL γ-dosimeter especially at low Li2O content. In addition the low Li2O content in the glass system makes it very close to tissue equivalent material. Therefore, it is recommended to use low Li2O content in Li2O-B2O3 glass system as good gamma detectors at energy of 0.66 MeV.

6. REFERENCE

(1) A. El-Adawy, N. E. Khaled, A. R. El-Sersy, A. Hussein, and H. Donya, Appl. Radiat. Isot., 68 – 6 (2010) 1132. (2) N.E.Khaled, A.R.El-Sersy, H. M. El-samman, A.Hussein, A. El-Adawy and H. Donya, World Acad. of Sci. Eng. and Techn., 76 (2011) 894. (3) H. Donya, H.M. El-Samman, A. El-Adawy A. Hussein, A.R. El-Sersy and. N.E. Khaled , Tenth Radiation Physics & Protection Conference, EG1100464, 42(33) (2011) 135 www.iaea.org/inis/collection/NCLCollectionStore/Public/42/076/42076638.pdf (4) A.R. El-Sersy, A. Hussein, H.M. El-Samman, N.E. Khaled, , A. El-Adawy and H. Donya, J. of Anal. and Nucl. Chem., 288 (2010) 65. (5) P.R. González, , C. Furetta, B. E. Calvo, M. I. Gaso, E. Cruz-Zaragoza , Nucl. Inst. & Meth. Phys. Res. B 260 (2007) 685. (6) C. Furetta, B.E. Calvo, M.I. Gaso, E. Cruz-Zaragoza, Mod. Phys. Lett. B, 22(2008) 1997. (7) D.F. Jackson, D.J. Hawkes, Phys. Rep. 70 (1981) 169. (8) L. Gerward, N. Guilbert, K.B. Jensen, H. Levring, Radiat. Phys. Chem. 60 (2001) 23. (9) http://physics.nist.gov/PhysRefData/XrayMassCoef/tab3.html (2013). (10) Faiz M. Khan, “The Physics of Radiation Therapy” Lippincott Williams & Wilkins , 3rd ed., 2003.

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