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Results in Physics
journal homepage:www.elsevier.com/locate/rinp
Shielding features of concrete types containing sepiolite mineral:
Comprehensive study on experimental, XCOM and MCNPX results
M.I. Sayyed
a, H.O. Tekin
b, O. K
ılıcoglu
c, O. Agar
d, M.H.M. Zaid
e,⁎aDepartment of Physics, Faculty of Science, University of Tabuk, Tabuk, Saudi Arabia
bUskudar University, Vocational School of Health Services, Radiotherapy Department, Istanbul 34672, Turkey
cUskudar University, Vocational School of Health Services, Department of Nuclear Technology and Radiation Protection, Istanbul, Turkey dKaramanoğlu Mehmetbey University, Department of Physics, 70100 Karaman, Turkey
eDepartment of Physics, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia
A R T I C L E I N F O Keywords: Sepiolite Radiation shielding Attenuation coefficients MCNPX XCOM A B S T R A C T
Natural sepiolite mineral is a naturally occurring clay form belonging to a part of layered silicate. Because of its advantages such as low production cost, light-weight and convenient, it may be selected as an alternative shielding material to others. Radiation shielding performances of some concretes to sepiolite and B4C addictive
have been researched reported in a wide energy region of 0.08–1.333 MeV using experimental data, MCNP and XCOM. The simulated data obtained by MCNPX are discussed and compared with the experimental results as well as with the XCOM results. The simulations match the experiments very well except for S3 sample. From the measurement, the maximum gamma-ray attenuation was detected in the concrete specimen with 10% sepiolite (S1) while the minimum attenuation of gamma-ray was noted in the concrete specimen with 30% sepiolite (S3). The addition of sepiolite mineral to concretes may be an alternative option that can be used in several radiation protection applications.
Introduction
As well-known, one of the traditional shielding materials is lead (Pb) material with the purpose of the protection of both public and equipments from harmful effect of ionizing radiation. However, the use of Pb should be avoided due to some disadvantages such as toxic, heaviness for transportation and storage, high production cost and harmful effects on human body. Therewithal, building and construction materials are commonly used as an alternative gamma ray shielding material to Pb in wide spread applications of nuclear science and technology such as high-energy particle laboratories, medical facilities, power plants, high-level waste dry casks, hot cells and nuclear research center using nuclear tools [1]. Among construction materials, the concretes with inexpensive cost, versatile, high mass attenuation property and low maintenance requirement have been of interest as an adequate shielding material as well as its excellent structural char-acteristic [2]. Moreover, concretes having thinner thicknesses and higher attenuation coefficient may be produced by varying the percent of composition in material with additives of various specific densities to increase the radiation shielding performance[3].
Many studies of radiation shielding effectiveness for concretes
doped with special additives have been reported by several researchers [4–10]. Natural sepiolite mineral is chemically know as magnesium hydrosilicate with a needle-like morphology and has the chemical for-mula (Si12)(Mg9)O30(OH6)(OH2)4·6H2O It is a light-weight, porous and
non-swelling clay with a large specific surface area. Its specific density ranges between about 2–2.5 g/cm3. Besides, sepiolite mineral is
pre-sently used in a wide variety offields which take advantage of the great absorption capacity, action of the clay as well as rheological behavior catalytic[11–13].
The attenuation (the scattering and the absorption) of high-energy photons are directly proportional to the density and atomic number of any target. The information of their photon interaction properties such as mass attenuation coefficients (μm), total atomic (σa)and electronic
cross-sections (σe), the effective atomic (Zeff) and electron numbers
(Neff), half-and value layer (HVL) play a significant role for estimating
their chemical and physical properties[14]. The accurate data of ra-diation shielding performance for material of interest are extremely necessary for various areas such as, dosimetry, medical, nuclear and radiation physics, industrial and agricultural applications. Also, the experimental investigations of photon attenuation coefficients should be supported by those of theoretical and computational methods.
https://doi.org/10.1016/j.rinp.2018.08.029
Received 27 July 2018; Received in revised form 14 August 2018; Accepted 15 August 2018
⁎Corresponding author.
E-mail address:mhmzaid@upm.edu.my(M.H.M. Zaid).
Results in Physics 11 (2018) 40–45
Available online 22 August 2018
2211-3797/ © 2018 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/BY/4.0/).
In our previous work, several concrete types including natural se-piolite mineral and boron carbide (B4C) were prepared. The μm
ex-perimentally at different photon energies has been measured[10]. The main of this work is to compare and validate the results of the previous paper using MNCPX computer code and XCom software for determining the radiation shielding performance with higher accuracy. The photon interaction parameters of these concrete samples such as Zeff, Neff, HVL,
mean free path (MFP), tenth value layer (TVL) and radiation protection efficiency (RPE) which will help in exploring its possible use in radia-tion protecradia-tion applicaradia-tions have been calculated.
Materials and methods
Theoretical calculations
The µmis used to estimate the capability of any absorber to
at-tenuate the photons of certain energies. The attenuation of gamma ray photons can be expressed by the next equation[15,16]:
μ (1) = − xρ lnI I0 (1) where x is the material’s thickness, I0and I represent the incident and
transmitted photon intensities, respectively, ρ is the density of the target (g/cm3).
Theoretically, the µm values of a composite mixture of different
elements and compounds are defined by the mixture rule namely[17]:
∑
⎜ ⎟ = ⎛ ⎝ ⎞ ⎠ μ w μ ρ m i i (2)where wiis the weight fraction of the mass of composition ith.
Some absorption parameters such as total atomic and electronic cross-section, the effective atomic number and electron density can be determined using theμmvalue. The total atomic cross section (σa,cm2/ atom) can be determined using the following equation[18]:
= ∑ ∑ σ μ N n a m n A i i i i i (3) where N is the Avogadro constant,wiis the fractional weight of the ith
constituent in the mixture, and Aiis the atomic weight of ith element.
The total electronic cross-section (σe, cm2/electron) can be written
as follows[19]:
∑
= σ N μ f A Z 1 e i i i i i (4)where fi is the fractional abundance of the ith element and Zi is the
atomic number of the ith element.
The Zeff(which is dimensionless quantity) is directly proportional to
σaandσenamely[20]: = Z σ σ eff a e (5)
Also, the Neff(electron/g) is can simply derived using theμmandσe
described above[18]: = N μ σ e m e (6)
The HVL and TVL are the thickness of a homogeneous absorber that attenuates the narrow beam intensity to 50% and 90% of the incident intensity, respectively. The relationship between these values and the attenuation coefficient can be written as[21]:
= HVL ln μ 2 (7) and = TVL ln μ 10 (8) The MFP denotes the average distance between two successive in-teractions of gamma rays; the following equation has been used to calculate the MFP for the present concretes[22]:
= MFP
μ 1
(9) The radiation protection efficiency (RPE) of any absorber is given by: ⎜ ⎟ = ⎛ ⎝ − ⎞ ⎠ RPE I I 1 . 100 0 (10) Experimental details
To investigate the gamma radiation shielding performance for the proposed samples, two different sets of concretes with different ratios of aggregate, sepiolite mineral and boron carbide (B4C) were prepared for
the shielding tests in this work. Thefirst set has been formed by mixing sepiolite mineral in fractions of 10%, 20%, 30%, 40% and 50% by weight in concrete, which is tagged as S1, S2, S3, S4 and S5 respec-tively. Other set has been made of mixing sepiolite mineral and B4C
additives in fractions of 10% + 1, 10 + 3% and 10 + 5% by weight in concrete, which is tagged as S6, S7 and S8, respectively. The SEM images have been given in the previous work by Agar[10]as the evi-dence that there is a uniform distribution and good dispersion of the sepiolite and B4C additives within the samples. As given inTable 1, the
densities of samples are 2.26, 1.97, 1.81, 2.19, 1.99, 2.28, 2.26 and 2.27 g/cm3for S1, S2, S3, S4, S5, S6, S7 and S8, respectively.
The gamma ray spectra of the prepared concrete samples have been obtained using high resolution spectrometers equipped with high purity germanium detectors (HPGe). The standard radioactive point sources with the different photon energies22
Na (1275 keV),60Co (1173 and 1333 keV),133Ba (81, 276, 303, 356 and 384 keV) and137Cs (662 keV)
have been utilized in the linear attenuation coefficient measurements. The detailed experimental procedure can be found in Ref's[10].
MNCPX code
Monte Carlo N-Particle Transport Code System-extended (MCNPX) version 2.6.0 (Los Alamos National Laboratory, USA) is a general-pur-pose Monte Carlo code to simulate various physical interactions at wide energy range[23]. MCNPX are well suited and useful code for nuclear applications such as criticality safety analyses, detector modeling, and radiation shielding and dosimetry calculations in complicated three-dimensional geometries [24]. In the literature, there are various MCNPX studies on radiation shielding effectiveness for different ma-terials in recent years[25–27]. This code has been carried out to esti-mate the photon shielding characteristics of concretes mentioned in the previous section. The total simulation geometry ofμmcalculations is shown inFig. 1. To determine theμmvalues of various concrete sam-ples, chemical compositions and geometrical features of each sample
Table 1
The codes and mixture proportions of the produced concretes.
Sample Code w/c Aggregate Sepiolite B4C ρ(g/cm3)
S1 0.5 90 10 – 2.26 S2 0.5 80 20 – 1.97 S3 0.5 70 30 – 1.81 S4 0.5 60 40 – 2.19 S5 0.5 50 50 – 1.99 S6 0.5 89 10 1 2.28 S7 0.5 88 10 2 2.26 S8 0.5 87 10 3 2.27
have been described in inputfile. The elemental compositions of the samples have been measured by using Energy-dispersive X-ray spec-troscopy (EDX) technique (Fig. 2). The sample has been designed as an absorber between source and detection area. Also, a radioactive point source was placed at a certain distance from the sample. Besides that, 108particles have been tracked as the number of particles (NPS
vari-able). All MCNPX calculations have been performed by using Intel® Core™ i7 CPU 2.80 GHz computer hardware.
XCOM software
Theoreticalμmvalues can be obtained from the database by Hubbell and Seltzer. Berger and Hubbell developed XCOM software to estimate
μm values or photon interaction cross-sections of a single element, compound or composite mixture in wide energy region of 1 keV–100 GeV[27]. Different parameters such as interaction coeffi-cients and total attenuation coefficients are determined as sums of the corresponding amounts for the various chemical compositions. The total amounts of the corresponding quantities for the atomic con-stituents can be referred to calculate the interaction coefficients and total attenuation coefficients for compounds or the mixtures. The weighting factors, that is, the fractions by weight of the constituents, are calculated by XCOM from the chemical formula entered by the user. However, the user must supply the fractions by weight of the various components to measure the amount in the mixtures [28]. Recently,
several studies have been used the XCOM software in order to calculate the values forμmin the shielding materials[29–33]. In this study, the calculations are made by using chemical results of EDX for concretes as seen inFig. 2.
Results and discussions
The µmfor concrete samples with different ratios of aggregate,
se-piolite mineral and boron carbide (B4C) were estimated using MCNPX
code at nine photon energies (in the range of 0.08–1.33 MeV). The MCNPX results were compared with the experimental values[10]and the XCOM results[27].
The MCNPX values of µmare summarized inTable 3 along with
those calculated theoretically using XCOM software and measured in the lab. Generally, the MCNPX µmvalues show a good agreement with
the XCOM and experimental values. The discrepancies between the experimental µmvalues and the theoretical values were noticed for S3
and S4 at all energies. These disagreements can be attributed to the oxygen vacancies in image of S3 sample. The oxygen amount of S3 sample in the elemental compositions with EDX (Table 2) is, in parti-cular, notable. So, a uniform distribution and good dispersion of the addictive within the material may be related to alteration in the gamma ray shielding effectiveness.
On the other hand, in the lower energy region (< 0.1 MeV) of gamma ray spectrum, it's hard tofit the peak of Ba-133 radioactive point source at 0.08 MeV due to X-ray and background peaks during spectrum analyzing. Therefore, this difference between the experi-mental and XCOM results is associated with more precise analysis of the spectrum in the experimental measurements. Besides, it is clear from Table 3that the experimentally determined µmvalues are lower than
Fig. 1. MCNPX simulation geometry.
Fig. 2. The EDX spectrum of S5 concrete sample. Table 2
The chemical compositions of the selected concrete types (weight %).
Element S1 S2 S3 S4 S5 S6 S7 S8 O 42.43 53.01 54.77 54.2 53.31 41.89 45.55 48.39 Si 5.39 10.5 23.42 17.13 18.06 10.88 11.2 19.21 S 0.21 0.29 1.06 1.06 0.87 0.81 0.67 0.63 K 1.18 0.82 1.1 1.05 0.73 1.85 1.45 1.22 Ca 50.37 18.6 9.81 17.51 11.56 36.14 32.48 29.91 Fe 0.42 0.74 – – – – 2.01 0.63 Na – 0.92 – 0.19 – – 0.43 – Mg – 0.91 0.35 0.53 0.21 0.3 – 0.01 C – 14.22 9.48 8.32 9.51 8.04 6.21 – Al – – – – 5.71 – – – F – – – – – 0.1 – –
the results obtained from XCOM and MCNPX. This might be attributed to the crystalline nature of the molecular arrangement of detector source which can make incident beam geometry narrow, possibly re-ducing the µmvalues[34].
The maximum attenuation of photon intensity was for the concrete sample with 10% sepiolite (i.e. S1), whereas the minimum attenuation was for the concrete samples with 70% and 50% sepiolite (i.e. S3 and S5). The maximum attenuation of S1 concrete sample may be attributed to the fact that S1 contains highest weight fraction of20Ca (50.3%),
while the low weight fraction of20Ca in S3 and S5 samples leads to reduce the attenuation for these two samples, then it can be concluded that among the prepared concretes, S1 is the most effective to attenuate the incoming photons thus has superior radiation shielding perfor-mance.
It is evident fromTable 3that at low photon energies (between 0.08 and 0.383 MeV), the µmdecreases dramatically with the increment of
photon energy for S1–S8 concretes. This trend in the µmat these low
photon energies can be ascribed to preeminence of photoelectric ab-sorption (PE) mechanism[35]. The effective cross section of PE is in-versely proportional to the photon energy as E−3.5and related directly to atomic number as Z4for low energy region and Z5for high energy region. From this we can understand the highest differences noticed in μ/ρ values between different concretes in this energy zone and also this explained the higher values ofμ/ρ for S1 which contains large amount of high Z element (i.e20Ca). On the other hand, for 0.662, 1.17, 1.27
and 1.33 MeV photon energies, it is clear fromTable 3that the values of µmdecrease at a slow rate with the increase in the photon energy (i.e.
show less dependent on the energy) and also show less dependence on the atomic number Z, hence we can see from Table 3 that all the samples have almost the same µmvalues at these high energies. This less
dependence of the µmon the atomic number and the energy may be
explained depending on the Compton scattering (CS) mechanism which overcome the PE mechanism at these energies, and it is known that cross section of CS is proportional to the atomic number and the energy as Z and E−1respectively.
These results are also confirmed by Elmahroug et al. work con-firmed that the highest differences occur in µmvalues for Bi2O3-V2O5
-TeO2glass system occurs in PE energy range, while in the authors
re-ported that in CS zone, the Bi2O3-V2O5-TeO2glasses have almost the
same µmvalues[36]. The obtained µmthen used to evaluate the Zefffor
S1–S8 concrete samples using Eqs.(3)–(5)and the calculated Zeffas a
function of energy is illustrated inFig. 3. All the samples (S1–S8) have the same behavior via radiations, since they consist of the same ele-ments in different proportions. The Zeffvalues of all concretes were
noticed initially decreasing with the photon energy up to 0.356 MeV, then Zeffvalues tend to be constant thereafter. This is due to the linear
Z-dependence of Compton scattering (CS), and as mentioned in the previous paragraph, CS is the most important mechanism in this energy zone. Maximum values of Zefffor the prepared concretes were seen for
S1 sample (which contains 10% sepiolite). It may be due to the reason that S1 has the maximum µmvalues, so from the prepared samples S1
seems to be the best gamma ray radioprotective.
On the other hand, the values of Zefffor the prepared concretes lie in
the range of 14.21–12.05, 10.38–9.15, 10.12–9.30, 10.70–9.57, 10.23–9.36, 12.55–10.71, 12.57–10.65, and 12.69–11.06 for S1–S8, respectively. The variation of Neffshown in Fig. 4 is similar to the
Table 3
The experimental, XCOM and MCNPX mass attenuation coefficient (cm2/g) of the sepiolite concretes.
Energy (MeV) S1 S2 S3 S4
XCOM Exp.* MCNPX XCOM Exp. MCNPX XCOM Exp. MCNPX XCOM Exp. MCNPX
0.08 0.2742 0.191 ± 0.014 0.2753 0.2145 0.190 ± 0.004 0.2152 0.2023 0.105 ± 0.003 0.2032 0.2141 0.149 ± 0.004 0.2041 0.276 0.1134 0.117 ± 0.016 0.1145 0.1115 0.112 ± 0.009 0.1125 0.1113 0.072 ± 0.003 0.1124 0.1116 0.099 ± 0.005 0.1113 0.302 0.1091 0.105 ± 0.004 0.1094 0.1076 0.104 ± 0.003 0.1082 0.1074 0.062 ± 0.002 0.1082 0.1077 0.092 ± 0.002 0.1082 0.356 0.1017 0.101 ± 0.003 0.1021 0.1007 0.098 ± 0.001 0.1014 0.1006 0.060 ± 0.001 0.1003 0.1008 0.085 ± 0.002 0.1004 0.383 0.0986 0.095 ± 0.007 0.0998 0.0978 0.092 ± 0.005 0.0979 0.0977 0.057 ± 0.004 0.0983 0.0978 0.085 ± 0.006 0.0986 0.662 0.0775 0.078 ± 0.001 0.0789 0.0773 0.077 ± 0.001 0.0782 0.0773 0.052 ± 0.001 0.0783 0.0773 0.069 ± 0.001 0.0783 1.17 0.0589 0.057 ± 0.001 0.0592 0.0588 0.056 ± 0.001 0.0593 0.0588 0.039 ± 0.002 0.0593 0.0588 0.050 ± 0.001 0.0591 1.27 0.0565 0.054 ± 0.001 0.0571 0.0564 0.054 ± 0.001 0.0571 0.0564 0.033 ± 0.001 0.0571 0.0564 0.047 ± 0.001 0.0574 1.33 0.0552 0.054 ± 0.001 0.0557 0.0551 0.053 ± 0.003 0.0564 0.0551 0.036 ± 0.001 0.0563 0.0551 0.048 ± 0.001 0.0562 Energy (MeV) S5 S6 S7 S8
XCOM Exp. MCNPX XCOM Exp. MCNPX XCOM Exp. MCNPX XCOM Exp. MCNPX
0.08 0.2039 0.163 ± 0.002 0.2491 0.2484 0.154 ± 0.004 0.2491 0.2493 0.155 ± 0.002 0.2499 0.2427 0.182 ± 0.005 0.2436 0.276 0.1111 0.118 ± 0.009 0.1133 0.1126 0.102 ± 0.008 0.1133 0.1125 0.102 ± 0.007 0.1144 0.1124 0.105 ± 0.008 0.1133 0.302 0.1073 0.097 ± 0.004 0.1092 0.1085 0.093 ± 0.003 0.1092 0.1083 0.094 ± 0.004 0.1096 0.1083 0.103 ± 0.003 0.1093 0.356 0.1005 0.094 ± 0.002 0.1021 0.1013 0.087 ± 0.002 0.1021 0.1012 0.094 ± 0.001 0.1024 0.1012 0.094 ± 0.001 0.1033 0.383 0.0975 0.091 ± 0.003 0.0985 0.0982 0.089 ± 0.005 0.0985 0.0981 0.086 ± 0.004 0.0993 0.0982 0.092 ± 0.007 0.0994 0.662 0.0772 0.076 ± 0.001 0.7791 0.0774 0.072 ± 0.001 0.7791 0.0773 0.072 ± 0.001 0.0779 0.0774 0.075 ± 0.001 0.0779 1.17 0.0587 0.054 ± 0.001 0.0591 0.0588 0.050 ± 0.002 0.0591 0.0588 0.053 ± 0.002 0.0593 0.0588 0.056 ± 0.001 0.0594 1.27 0.0563 0.052 ± 0.002 0.0559 0.0564 0.049 ± 0.001 0.0559 0.0564 0.049 ± 0.003 0.0571 0.0564 0.054 ± 0.003 0.0578 1.33 0.0550 0.052 ± 0.002 0.0544 0.0552 0.049 ± 0.001 0.0544 0.0551 0.054 ± 0.008 0.0563 0.0551 0.053 ± 0.003 0.0562
* Data of previous work[10].
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 9 10 11 12 13 14 15 Zef f E (MeV) S1 S2 S3 S4 S5 S6 S7 S8
variation in Zeff, i.e. the Neffdecreased towards higher photon energies
up to 0.356 MeV, and then Neffbecomes almost constant after there.
The radiation protection efficiency (RPE) is a very important para-meter to compare the effectiveness of shielding materials under in-vestigation. The shielding efficiencies (%) of the sepiolite concretes are demonstrated in Fig. 5. According to this figure, S1 sample possess capable of stopping between 84 and 42% for photon energy range of 80–1332 keV, which has the maximum values. Therefore, it supports the better performance of S1 sample among the samples.
HVL, TVL and MFP are appropriate quantities to estimate the shielding performance of any material.Figs. 6–8show the variation of these quantities with the energy in the energy range 0.08–1.33 MeV. It is worth mention that the lower the HVL, TVL and MFP values, the less energy passes through the concrete sample.Figs. 6–8indicate that S1 and S3 are the best and the worst for photon shielding material re-spectively amongst the prepared concretes in the energy range under investigation. Also, the HVL, TVL and MFP are found to increase with increase in the photon energy. This means that the photons with low energy are more attenuated (or, photons with high energy can pene-trate the sample easily).
Conclusions
Through calculations with theoretical (XCOM) and simulation
(MCNP5 code), the mass attenuation coefficients (μm) and other
shielding parameters of concrete doped with sepiolite and B4C have
been estimated for photons of 0.08, 0.276, 0.302, 0.356, 0.383, 0.662, 1.17, 1.27 and 1.332 MeV energies and compared with experimental results of previous work. According to the obtained results, XCOM and MNCPX data were found to be quite close to those of experimental except for S3 sample. The Zeffand Neffvalues decreased with the
in-crease of photon energy because of the decreasing photon interaction possibility. Among different concrete forms, S1 sample has demon-strated the best HVL value which defines the required volume in the shield design. It is concluded from this research that the doping of se-piolite mineral in concretes may be an alternative choice that can be used for the aims of radiation shielding.
Acknowledgements
This work was supported by Karamanoglu Mehmetbey University (Project Numbers: 13-M-17) and thefinancial support from Universiti Putra Malaysia (UPM) under Inisiatif Putra Muda (IPM) are gratefully acknowledged. 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 3.0 3.1 3.2 3.3 3.4 3.5 3.6 Nef f *10 23 E (MeV) S1 S2 S3 S4 S5 S6 S7 S8
Fig. 4. The effective electron density of the sepiolite concretes.
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 30 40 50 60 70 80 90 RPE E (MeV) S1 S2 S3 S4 S5 S6 S7 S8
Fig. 5. The radiation protection efficiency of the sepiolite concretes.
S1 S2 S3 S4 S5 S6 S7 S8 0 2 4 6 HV L (cm) Concrete sample 0.08 MeV 0.276 MeV 0.302 MeV 0.356 MeV 0.383 MeV 0.662 MeV 1.17 MeV 1.27 MeV 1.33 MeV
Fig. 6. The half value layer of the sepiolite concretes.
S1 S2 S3 S4 S5 S6 S7 S8 0 5 10 15 20 TVL (cm) Concrete sample 0.08 MeV 0.276 MeV 0.302 MeV 0.356 MeV 0.383 MeV 0.662 MeV 1.17 MeV 1.27 MeV 1.33 MeV
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