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Results in Physics
journal homepage:www.elsevier.com/locate/rinp
Er
2
O
3
e
ffects on photon and neutron shielding properties of TeO
2
-Li
2
O-ZnO-Nb
2
O
5
glass system
O. Agar
a, E. Kavaz
b, E.E. Altunsoy
c,d, O. Kilicoglu
d,e, H.O. Tekin
d,f,⁎, M.I. Sayyed
g, T.T. Erguzel
h,
Nevzat Tarhan
i,jaKaramanoglu Mehmetbey University, Department of Physics, 70100 Karaman, Turkey bAtaturk University, Faculity of Science, Department of Physics, 25240 Erzurum, Turkey
cUskudar University, Vocational School of Health Services, Medical Imaging Department, Istanbul 34672, Turkey dUskudar University, Medical Radiation Research Center (USMERA), Istanbul 34672, Turkey
eUskudar University, Department of Nuclear Technology and Radiation Protection, Istanbul 34672, Turkey fUskudar University, Vocational School of Health Services, Radiotherapy Department, Istanbul 34672, Turkey gUniversity of Tabuk, Physics Department, Tabuk, Saudi Arabia
hUskudar University, Faculty of Engineering and Natural Sciences, Department of Software Engineering, Istanbul 34672, Turkey iNPIstanbul Hospital, Department of Psychiatry, Istanbul, Turkey
jUskudar University, Faculty of Humanities and Social Sciences, Department of Psychology, Istanbul, Turkey
A R T I C L E I N F O Keywords: Radiation shielding Er2O3 Tellurite glass MCNPX code A B S T R A C T
In this study, a series of 75TeO2-5Li2O-10ZnO-(10-x)Nb2O5-(x)Er2O3(where x = 0, 0.5, 1.0, 1.5, 2.0 and 2.8 mol
%) glasses have been surveyed in terms of photon and neutron shielding characteristics. For this aim, 3 × 3 inch NaI(Tl) detector has been simulated in order to detect photons. Afterwards, the mass attenuation coefficients (μ/ ρ) and some shielding quantities such as half-value layer (HVL), tenth value layer (TVL), mean free path (MFP), effective atomic number (Zeff), effective electron density (Nel), equivalent atomic number (Zeq) and exposure
build-up factor (EBF) have been calculated. The obtained MCNPX results of all the glasses have been compared and approved with those of XCOM program. Also, their gamma ray buildup factors have been determined in a wide energy range of 0.02–20 MeV for penetration depths up to 15 mfp. Moreover, neutron attenuation abilities of glasses have been evaluated by estimating neutron total effective removal cross section. The results showed that Er2O3partial replacement of Nb2O5in 75TeO2-5Li2O-10ZnO-(10- x)Nb2O5-(x)Er2O3glass system enhances
photon and neutron attenuation characteristics. It can be deduced that obtained results from the present in-vestigation can be useful to understanding of influence of Er2O3on nuclear radiation shielding properties of
tellurite glasses.
Introduction
In the last few decades, there has been increasing interest in tellurite oxides (TeO2)-doped glasses on account of their promising magnetic, electrical, optical, mechanical and physical features. Additionally, TeO2 based glasses exhibit the excellent chemical and physical durability such as large third order non linear optical (NLO) susceptibilities, large refractive indices, low phonon energy, low melting temperature (800 °C) and high dielectric permittivities[1–3]. It is well-known that the present oxide does not has glass formation ability (GFA) on its own under normal quenching conditions, therefore, it is necessary to the addition with different modifiers namely rare earth oxides, alkali earth metal or transition metal to easily form a glass. It has been found that
the doping of niobate (Nb2O5) as a network modifier to tellurite glasses stabilize the glass host and may enhance a double role in glass network alteration as a network former as well as modifier[4]. On the other hand, in order to improve the chemical durability of glass, it can be inserted Er2O3which acts rare earth, owing to both its lower oxidizing in air and stability. Having such properties lead to be used in various application areas e.g., medical, optoelectronics and glassfibers[5,6]. An insertion of ZnO that behaves as a network modifier gives rise to wider glass forming compositional zone, extended optical transparency and low Tg[7,8]. Finally, it is recognized that the inclusion of Li2O alkali oxide as network modifier to tellurite glasses composes more non-bridging oxygen's (NBO's) and thereby, decreasing the glass strength [9]. The combination of all these characteristics in a glass system makes
https://doi.org/10.1016/j.rinp.2019.102277
Received 23 February 2019; Received in revised form 4 April 2019; Accepted 5 April 2019
⁎Corresponding author at: Uskudar University, Medical Radiation Research Center (USMERA), Istanbul 34672, Turkey.
E-mail address:huseyinozan.tekin@uskudar.edu.tr(H.O. Tekin).
Available online 08 April 2019
2211-3797/ © 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/BY-NC-ND/4.0/).
it a unique material for various advanced application areas, particularly in laser and photonics. As well-known, glasses are in particular alter-native matrices compared to conventional materials in shielding due to absorbing high-energy radiation and transparency to visible light. A great number of studies have been employed on radiation shielding effectiveness of TeO2- based glasses[10–15]. Beyond all that the above-mentioned optical and structural features, TeO2-Li2O-ZnO-Nb2O5-Er2O3 glass system can be considered as a quite attractive material to at-tenuate the high energetic X/gamma ray photons and neutron radia-tion. According to our knowledge, any works on the shielding perfor-mance of the selected glasses have not been done. The present research aims to report the results on evaluation of photon and neutron shielding parameters for erbium-doped tellurite glasses. The obtained results from the present investigation can be useful to understanding of in-fluence of Er2O3on nuclear radiation attenuation features of tellurite based glasses.
Material and methods
Shielding parameters
Table 1 presents glass codes, densities and compositions of CeO2 incorporated 75TeO2-5Li2O-10ZnO-(10-x)Nb2O5-(x)Er2O3 in composi-tion of x = 0, 0.5, 1.0, 1.5, 2.0 and 2.8 mol%) glass systems[1].
The linear attenuation coefficients of any absorber (μ, expressed in cm−1) describe a measure of the probability of photon interaction when radiation passes through a target material, depending on the thickness of the physical absorber[16]:
= − μ x I I 1 ln 0 (1)
where I0 and I show intensities of the original and the attenuated gamma rays, respectively. t denotes the thickness of the absorber. The ratio I/I0is called the transmission factor. The ratio of the μ to the density can be entitled the mass attenuation coefficient (μ ρ/ , cm2/g)
and expressed as the effective cross-sectional area of electrons per unit mass[17]. Theμ ρ/ values for the chosen glasses can be determined by using mixture rule[18]:
∑
= μm w μ ρ( / ) i i i (2) where wishows the fraction by weight and (μ ρ/ )irepresentsμ ρ/ of the ithelement by using WinXCOM[19–21].The mean free path (MFP) changes with linear distance and is the mean distance at which a single particle passes through the sample before interacting it with the material. It can be obtained by the fol-lowing relation[22]:
=
MFP (1/ )μ (3)
Half value layer (HVL) for the absorber defines the thickness that attenuated one-half of the radiation inserting it. In addition, Tenth-value layer specifies the average thickness material that diminished the photon to the tenth of the initial intensity [23]. HVL and TVL are computed by the following relations[24]:
=
HVL (ln 2/ )μ (4)
=
TVL (ln 10/ )μ (5)
The effective atomic number (Zeff) indicating the photon interaction in different situations for multicomponent materials is calculated using the direct method with the following equation[25,26]:
Table 1
Glass code, composition and density of the TLZNE glasses.
Glass sample code Composition (mol %) Density (ρ, g/cm3)
TeO2 Li2O ZnO Nb2O5 Er2O3 TLZNE1 75 5 10 10 0.0 4.12 TLZNE2 75 5 10 9.5 0.5 4.21 TLZNE3 75 5 10 9.0 1.0 4.24 TLZNE4 75 5 10 8.5 1.5 4.53 TLZNE5 75 5 10 8.0 2.0 4.71 TLZNE6 75 5 10 7.2 2.8 4.83
Fig. 1. (a) Simulation setup for mass attenuation coefficients studies (b) 3-D view of modeled 3x3 inch NaI(Tl) detector obtained from MCNPX Visual Editor (VE X_22S).
=∑ ∑ Z f A μ f μ ( ) ( ) eff i i i ρ i j j A Z ρ j j j (6)
where fi denotes the proportional by mole of the individual element providing that∑i if =1AiandZjrepresent the weight and the number of atoms, respectively.
The effective electron density (Nel), described in electron numbers per unit mass can be calculated by the following relation[27,28]:
= 〈 〉 N N Z A (electrons/g) e A eff (7) where〈 〉A shows the mean mass of atoms in the absorber.
On other hand, the effective removal cross section (∑R) corresponds to the total cross section of all the atoms constituting a given material in a cubic centimeter.∑Rvalues of a given material can be obtained with the instruction of the weight percentages wiand the values of (∑R)ifor each of the component of the material[29]:
Table 2
Mass attenuation coefficients of the TLZNE glasses calculated with both MCNPX code and XCOM.
Energy(MeV) TLZNE1 TLZNE2 TLZNE3
MCNPX XCOM R.D. MCNPX XCOM R.D. MCNPX XCOM R.D.
0.020 27.563 25.309 8.91 27.564 25.314 8.89 27.567 25.317 8.89 0.060 4.985 4.918 1.36 4.986 5.022 0.72 5.196 5.124 1.41 0.080 2.315 2.291 1.05 2.357 2.341 0.68 2.385 2.390 0.21 0.122 0.795 0.784 1.40 0.816 0.801 1.87 0.817 0.817 0.00 0.356 0.124 0.122 1.64 0.125 0.123 1.63 0.125 0.124 0.81 0.511 0.091 0.089 2.25 0.092 0.090 2.22 0.092 0.090 2.22 0.662 0.076 0.075 1.33 0.077 0.075 2.67 0.077 0.075 2.67 1.173 0.055 0.054 1.85 0.055 0.054 1.85 0.055 0.054 1.85 1.250 0.051 0.052 1.92 0.052 0.052 0.00 0.052 0.052 0.00 1.330 0.049 0.050 2.00 0.051 0.050 2.00 0.051 0.050 2.00 5.000 0.035 0.033 6.06 0.035 0.033 6.06 0.035 0.033 6.06 8.000 0.034 0.033 3.03 0.035 0.033 6.06 0.035 0.033 6.06 10.000 0.035 0.034 2.94 0.036 0.034 5.88 0.036 0.034 5.88 15.000 0.037 0.037 0.00 0.037 0.037 0.00 0.037 0.037 0.00 20.000 0.040 0.039 2.56 0.040 0.039 2.56 0.040 0.039 2.56
Energy(MeV) TLZNE4 TLZNE5 TLZNE6
MCNPX XCOM R.D. MCNPX XCOM R.D. MCNPX XCOM R.D.
0.020 27.570 25.318 8.89 27.572 25.322 8.89 27.599 25.325 8.98 0.060 5.246 5.225 0.40 5.345 5.326 0.36 5.505 5.486 0.35 0.080 2.416 2.439 0.94 2.499 2.487 0.48 2.555 2.564 0.35 0.122 0.832 0.833 0.12 0.850 0.849 0.12 0.877 0.875 0.23 0.356 0.125 0.125 0.00 0.126 0.126 0.00 0.127 0.127 0.00 0.511 0.092 0.090 2.22 0.092 0.091 1.10 0.094 0.091 3.30 0.662 0.077 0.075 2.67 0.077 0.076 1.32 0.077 0.076 1.32 1.173 0.055 0.054 1.85 0.055 0.054 1.85 0.055 0.054 1.85 1.250 0.052 0.052 0.00 0.052 0.052 0.00 0.052 0.052 0.00 1.330 0.051 0.050 2.00 0.051 0.050 2.00 0.051 0.050 2.00 5.000 0.035 0.033 6.06 0.035 0.033 6.06 0.035 0.033 6.06 8.000 0.035 0.033 6.06 0.035 0.034 2.94 0.035 0.034 2.94 10.000 0.036 0.034 5.88 0.036 0.035 2.86 0.036 0.035 2.86 15.000 0.037 0.037 0.00 0.037 0.037 0.00 0.038 0.037 2.70 20.000 0.040 0.040 0.00 0.040 0.040 0.00 0.041 0.040 2.50
Fig. 3. The linearity ofμ/ρMCNPXandμ/ρXCOMof the glasses as a function of
Er2O3content.
∑
= ρ ρ ΣR (Σ / ) i i R i (8) whereρ and(Σ / )Rρidenote the densities and the removal cross-sections of the individual component.The gamma ray build factor describes a multiplier quantity that is utilized to get the real response to un-collided gamma rays with the inclusion of the contribution of the scattered photons. Energy absorp-tion buildup factor (EABF) denotes the stored energy for a material which interacts with the photon. Exposure buildup factor (EBF) is a parameter that determines the absorption of air[30]. The EBF of glass samples can be obtained by applying the Geometrical Progression (G-P) fitting parameters as described below. Firstly, the equivalent atomic number (Zeq) is found by determining the ratio of the interaction coefficients of the substance to μ ρ( / )Compton/( / )μ ρTotal) the element having the ratio of the interaction coefficients corresponding to this in the same energies. The geometric progression parameters for exposure build-up factors (EBF) can be calculated using an interpolation proce-dure. G-P fitting parameters are taken from the standard reference database ANSI / ANS-6.4.3[31]. Then, these values are used for EBFs from the G-Pfitting relation[32]:
= + ≠ B(E,X) 1 b - 1 K - 1(K - 1) for K 1 x (9) = + = B(E,X) 1 (b - 1)x for K 1 (10) where, = + for ⩽
K(E,x) cx dtanh(x/X - 2) - tanh(- 2)
1 - tanh(- 2) x 40mfp
a k
(11) whereEand x represent the original photon energy and the pene-tration depth, a,b,c,d andXkshow the G-Pfitting parameters and also, b denotes the buildup factor at 1 mfp.
Monte Carlo simulations using MCNPX version 2.6.0
Recently, the frequency of applications in mathematical techniques is increasing to solve different physical problems such as radiation-matter interactions as well as material optimization for optimum shielding properties. The Monte Carlo simulation simulates the ex-perimental area while considering different geometrical and physical properties of cross-section values and tools. Various databases have been found from experimental works. On the other hand, these simu-lations can provide an important outcome of optimum radiation pro-tection abilities of investigated material among the studied chemical combinations by minimizing the amount of time, cost and radiation exposure. In this study, one of well-known Monte Carlo codes in the
literature namely MCNPX (version 2.6.0)[33] has been carried out many investigations[34–36]ofμ ρ/ values and transmission factors of investigated glasses encoded TLZNE1, TLZNE2, TLZNE3, TLZNE4, TLZNE5 and TLZNE6, respectively. The generic appearance of MCNPX simulation setup for calculation of µ/ρ with designed equipment such as glass samples as a shielding material, point radioactive isotropic source and Pb shield for 3x3 inch NaI (Tl)[37]detector to avoid from the back-scattered photons is exhibited inFig. 1a. Moreover,Fig. 1b ex-hibits the 3-D version of modeled 3x3 inch NaI (Tl) with help of MCNPX Visual Editor (VE X_22S). To detect the photon inter the detector per MeV·cm2·s−1, the 3x3 inch NaI (Tl) detector was placed at the same line with a distance of 70 cm from radioactive point isotropic source. The studied glass sample was located between the source and detectionfield for a distance of 50 cm.
Results and discussion
In the present work, the TeO2based glasses have been consisted of Li2O, ZnO, Nb2O5and Er2O3oxides. The codes, chemical composition and density of the chosen glass samples are tabulated inTable 1. The structural and optical features on the glass systems in the composition 75TeO2-5Li2O-10ZnO-(10-x)Nb2O5-(x)Er2O3 (where x = 0, 0.5, 1.0, 1.5, 2.0 and 2.8 mol%) have been studied by Elkhoshkhany et al.[1]. Thus, the chemical compositions of the TLZNE glasses in their in-vestigations have been taken notice. Theμ/ρ express the total possibi-lities of the interaction mechanisms between photon and matter. When a narrow beam of photons with original intensity of I0pass on any glass having thickness of x, the intensity of the attenuated photon (I) is es-timated according to Lambert-Beer rule[38–40]. Theμ/ρ values for TLZNE1–TLZNE6 glasses containing different amounts of Er2O3have been calculated over photon energies of 0.2–20 MeV exploiting MCNPX simulation code and graphically demonstrated inFig. 2. The variation of theμ/ρ values against the photon energy refers to different photon interaction mechanism which is effective at various energy regions. Photoelectric absorption (PE) and Compton scattering (CS) processes prevail at the low and intermediate energies, respectively, whereas in higher photon energy regions, pair production (PP) is predominant. It can be detailed as follows: the whole energy of photon is absorbed in the PP mechanism. On other hand, the incident photons cannot be entirely absorbed in CS as well as PP processes. The attenuation values thence decreased depending on the increment in the photon energy. It is obvious that the effect of adding network modifier in μ/ρ is re-markable at low energies, whereas there is comparatively no influence or quite low for intermediate or higher energies. It is observed that the μ/ρ rises from 2.315 to 2.564 cm2/g with the increment in Er
2O3from 0 (TLZNE1) to 2.8 mol% (TLZNE6) at 0.08 MeV, while changing only from 0.049 to 0.050 cm2/g at 1.33 MeV. The reason of this difference can be attributed the dependence of the cross-sections of PE and PP processes on the atomic number as Z4 and Z2, respectively. Various researcher have found similarfindings for the dependence of Zeffon the energy of the photon for tellurite[41], germinate[42]and borate[43] glasses.
The theoreticalμ/ρ values were also determined with help of XCOM software. The comparison of computational and theoretical values de-pending on Er2O3 concentrations with x = 0, 0.5, 1.0, 1.5, 2.0 and 2.8 mol% has been tabulated inTable 2and indicated graphically in Fig. 3. It can be easily seen that the change ofμ/ρMCNPXandμ/ρXCOM coincides with each other for all the contents. Moreover, it seems from Fig. 3that the attenuation results of the glasses are proportional to the increment of Er2O3 amount while reducing with the rise in photon energy. This increase inμ/ρ by the increment in Er2O3content results from the increment in the mole fraction of the higher Z element namely Er with Z = 68 compared to the other constituent (Nb, Z = 41). In order to approval the linearity between results of the MCNPX code and XCOM software, correlation theory has been exploited. The relative deviation (R.D.) between the MCNPX and XCOM results can be
calculated by the following relation[44]: ⎜ ⎟ = ⎛ ⎝ − ⎞ ⎠ ∗ R D μ ρ μ ρ μ ρ . . / / / 100 XCOM MNCPX XCOM (12)
The obtained R.D. values in MCNPX and XCOM results are given in Table 2 and in the range of 0–8.91%, 0–8.89%, 0–8.89%, 0–8.89%, 0–8.89% and 0–8.98% for TLZNE1, TLZNE2, TLZNE3, TLZNE4, TLZNE5 and TLZNE6 glass samples, respectively. The difference is less than 6.06% with exception of R.D. values at 0.020 MeV. It is
understandable that the results of these methods are in a satisfactory matching. On other hand, the effective atomic number (Zeff) for the TLZNE glasses was estimated to evaluate their shielding characteristics. More detail on the formula utilized in Zeffcalculations is described in many of our previous works[45]. The Zeffof each sample of interest was calculated in this way for all the possible element rare earth compound combination. The obtained Zeffresults of the selected glasses depending on the photon energies of 0.2–20 MeV have been presented graphically inFig. 4. Thisfigure revealed that the values of Zeffare related to the energy of photon and thus, exhibit different behaviors in
different energy regions. Moreover, it can be easily said that the results increase with the insertion of Er2O3as network modifier. This indicates that the TLZNE6 sample including the largest amount (x = 2.8 mol%) of Er2O3has the largest Zeffvalues, hence can attenuate more incident photon than the rest of other glasses. Similarly, the effective electron density (Neff) for the TLZNE glasses was calculated. As can be seen in Figs. 4 and 5, the dependences of Zeffand Neffquantities for the present glasses on photon energy are nearly similar to each other. It is due to fact that the curve of Nel can be provided by Zeff for mixtures and compounds since atomic number Z explains knowledge on proton (or electron) numbers of any elements. The photon shielding performance of a given absorber or target can be determined through another quantities such as MFP, HVL and TVL. From the shielding point of view, the lower the values of MFP, HVL and TVL, the better a suitable ab-sorber reduces more photon. The MFP, HVL and TVL results for TLZNE glasses with different concentrations of Er2O3against photon energies between 0.2 and 20 MeV have been plotted inFig. 6(a–c), respectively. It is obviously evident that the inclusion of a rare earth metal oxide to glass system provides a reduction in HVL over all photon energies. It is well-known that the photon attenuation capability of any glass is strongly related to its density. It can be deduced that the insertion of
Fig. 7. Comparison of MFPs for these glasses with different commercial glasses and standard concretes.
Table 3
Effective removal cross sections for the glasses.
TLZNE1 (density = 4.12 g cm−3) TLZNE2 (density = 4.21 g cm−3) TLZNE3 (density = 4.24 g cm−3) Element ∑R/ρ(cm2 g−1) Fraction by weight (%) Partial Density (g cm−3) ∑R (cm−1) Fraction by weight (%) Partial Density (g cm−3) ∑R (cm−1) Fraction by weight (%) Partial Density (g cm−3) ∑R (cm−1) Li 0.084 0.00446 0.01838 0.00154 0.00441 0.01857 0.00156 0.00441 0.01870 0.00157 O 0.0405 0.22063 0.90900 0.03681 0.21877 0.92102 0.03730 0.21695 0.91987 0.03725 Zn 0.0183 0.04194 0.17279 0.00316 0.04178 0.17589 0.00322 0.04162 0.17647 0.00323 Nb 0.0153 0.11919 0.49106 0.00751 0.11283 0.47501 0.00727 0.10646 0.45139 0.00691 Te 0.0134 0.61378 2.52877 0.03389 0.61154 2.57458 0.03450 0.60922 2.58309 0.03461 Er 0.0115 0 0 0 0.01067 0.04492 0.00052 0.02134 0.09048 0.00104 TOTAL 0.08292 0.08436 0.08461
TLZNE4 (density = 4.53 g cm−3) TLZNE5 (density = 4.71 g cm−3) TLZNE6 (density = 4.83 g cm−3) Element ∑R/ρ (cm2 g−1) Fraction by weight (%) Partial Density (g cm−3) ∑R (cm−1) Fraction by weight (%) Partial Density (g cm−3) ∑R (cm−1) Fraction by weight (%) Partial Density (g cm−3) ∑R (cm−1) Li 0.084 0.00441 0.01998 0.00168 0.00437 0.02058 0.00173 0.00437 0.02111 0.00177 O 0.0405 0.21515 0.97463 0.03947 0.21332 1.00474 0.04069 0.21047 1.01657 0.04117 Zn 0.0183 0.04146 0.18781 0.00344 0.04130 0.19452 0.00356 0.04105 0.19827 0.00363 Nb 0.0153 0.10017 0.45377 0.00694 0.09396 0.44255 0.00677 0.08403 0.40586 0.00621 Te 0.0134 0.60698 2.74962 0.03684 0.60481 2.84866 0.03817 0.60123 2.90394 0.03891 Er 0.0115 0.03183 0.14419 0.00166 0.04224 0.19895 0.00229 0.05885 0.28425 0.00327 TOTAL 0.09003 0.09321 0.09496
Fig. 8. Effective removal cross-section values of the glasses.
Fig. 10. (a-f). The exposure buildup factors in the energy region 0.015–15 MeV up to 15 mfp for the glasses.
Er2O3as network modifier to glasses enhances the better attenuation effectiveness of photon. Moreover, it is clear from these figures that MFP, HVL and TVL results are nearly stationary up to 0.1 MeV and then, increase with an increase in the energy of the photon. It means the chosen glasses possess superior radiation shield performance at lower energies.
Photon attenuation capabilities of the TLZNE glass samples have been compared with various types of glasses[46]and concretes[47]. It can be viewed from Fig. 7that the TLZNE glasses have lower MFP values than RS-253-G18 and RS-360 glasses as well as barite and chromite concretes at all energies. Otherwise, the MFP results of TLZNE samples are almost same to that of ferrite doped concrete while having higher MFP values than that of RS-520 glass. Through theΣR/ρof the elements forming the material, the ΣR values of the glass under in-vestigation have been computed as follows[48]:
∑
=∑
W(∑
/ )ρ R i i R i (13) where ∑R/ρ and Wi denote the mass removal cross-section and the partial density of the individual constituent element, respectively. The ΣR/ρvalues of the elements have been listed inTable 3 [49]and shown inFig. 8. It is obvious that theΣRvalues of the glasses vary in range of 0.08937 to 0.12117 cm−1. This plot shows that theΣRvalues are pro-portional to the increase in the amount of Er2O3, which may be on account of the higher density of the glasses with a high concentration of Er2O3. The calculated result refers that the neutron attenuation e ffec-tiveness of the TLZNE glasses enhance with the addition of rare metal oxide to the glass.EBFs of the glasses have been discussed depending on chemical composition, photon energy and penetration depth.Fig. 9indicates the variation of equivalent atomic number (Zeq) of the glasses with photon energy. It is clearly seen that 2.8 mol% Er2O3 added TLZNE6 glass possesses highest Zeqvalues.Fig. 10(a–f) shows the variations of EBF for the glasses with photon energy within the range from 0.015 to 15 MeV at penetration depths 1–15 mfp. With increasing photon energy, it can appear fromFig. 10(a–f) that EBF values reach to a highest value in the intermediate energies for all glass samples and then begin to decrease. At the low and high energies, respectively, PE and PP processes are dominant. These events cause the photons to be completely absorbed, so that the photons possess less life in the material; consequently, the values EBF are decreased. On the other hand, photons are not entirely eliminated at the mid-energies in which CS dominate. However, their energies are reduced resulting in the buildup of photons. Due to the photons being left in the material for longer periods, a large number of scattered photons are formed. This increases the photon buildup in the substance. EBF increases again at very high energy, and large pene-tration depth due to PP process varies as∼Z2. Additionally, two sharp peaks in EBF values are clearly observed at 40 and 60 keV as demon-strated inFig. 10(a–f) which might be due to K-absorption edge of Te and Er at around 31.81 and 57.48 keV, respectively. The variations of EBF with penetration depth are indicated in Fig. 11(a–d) at several photon energies of 0.015, 0.15, 1.5 and 15 MeV. There are large EBF variations for samples at 0.015 MeV, which represents a very low en-ergy region. However, there is no dependence of the chemical compo-sition of the glasses. The EBF mainly depends on the chemical com-position at 0.15 MeV (Fig. 11b). It can be viewed that the values of EBF are quite small at low and intermediate energies (0.15 and 1.5 MeV) and for all penetration depths of the glasses with higher Zeq, and also proportional to the penetration depthes. It can be said that as the Er2O3 content increases in the TLZNE glasses, the radiation shielding cap-abilities are positively affected. EBF values for TLZNE6 glass are found to be the highest at 15 MeV (Fig. 11d). FromFig. 10(a–f), one can also seem that EBF values increase beyond 5 MeV at 15 mfp due to the basis of dominance of PP at higher energies. For low penetration depths, the electron–positron pair may leave the substance. However, when the penetration depth is high, secondary gamma photons (extinction
radiation) contribute to photon buildup. Conclusion
Photon and neutron shielding features of 75TeO2-5Li2 O-10ZnO-(10- x)Nb2O5-(x)Er2O3(where x = 0, 0.5, 1.0, 1.5, 2.0 and 2.8 mol%) glasses were evaluated. The following conclusions have been briefly summarized:
- Theμ/ρ and other related parameters such as Zeff, Nel, HVL, MFP, TVL as well as EBF have been found apparently depend on both incident photon energy and chemical compositions constituting glass.
- The insertion of Er2O3content leads to an increase ofμ/ρ; a decrease of HVL and EBF. Therefore, TLZNE6 appears as best gamma ray shielding glass due to higher values for mass attenuation coefficient and lower values of both HVL and MFP compared the rest of the TLZNE glasses.
- The estimated MFP results for TLZNE glasses have been compared with some commercial shielding glasses and previous studied con-cretes. The shielding capacity for the investigated glasses has ob-served comparable to those of the glasses and concretes. The Er2O3 doped tellurite glasses may be alternative and innovative as Pb-free photon shielding materials.
- Finally, theΣRvalues of the glasses are proportional to the Er2O3 concentration in the glass. Among the TLZNE glasses, TLZNE6 sample is the most effective glass in terms of neutron shielding. - The presented data exhibit that the selected glasses may be offered
as an alternative shielding material to attenuate radiations such as gamma ray photon and neutron.
Acknowledgement
The authors express their gratitude to the NP Istanbul Hospital for support in the present investigation.
Conflict of Interest
There are no conflicts of interest to declare. References
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