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Results in Physics
journal homepage:www.elsevier.com/locate/rinp
Photon and neutron shielding characteristics of samarium doped lead
alumino borate glasses containing barium, lithium and zinc oxides
determined at medical diagnostic energies
M. Almatari
a, O. Agar
b, E.E. Altunsoy
c,d, O. Kilicoglu
e, M.I. Sayyed
a,⁎, H.O. Tekin
d,f aPhysics Department, University of Tabuk, Tabuk, Saudi ArabiabKaramanoğlu Mehmetbey University, Department of Physics, Karaman, 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, Vocational School of Health Services, Department of Nuclear Technology and Radiation Protection, Istanbul 34672, Turkey fUskudar University, Vocational School of Health Services, Radiotherapy Department, Istanbul 34672, Turkey
A R T I C L E I N F O Keywords: XCOM Glasses MCNPX Attenuation Gamma photon Neutron A B S T R A C T
In the present work, we studied the radiation shielding parameters such as mass attenuation coefficients, ef-fective atomic number, half value layer, mean free path, macroscopic effective removal cross-sections and neutron transmission function for samarium doped lead alumino borate glasses containing barium, lithium and zinc oxides at medical diagnostic energies (between 20 and 150 keV) using MCNPX code. The results showed that the photon attenuation depends on the type of modifier used (i.e. ZnO, BaO or Li2O) and also, upon the
energy of the photon. The higher mass attenuation coefficients were found for the glass containing BaO. The results also revealed that the glass containing Li2O has the maximum effective atomic number between 20 and
40 keV. In addition, some important neutron shielding parameters such as macroscopic effective removal cross-sections (ΣR) and neutron transmission function (N/N0) have been calculated for investigated glass samples.
Introduction
Worldwide, human beings are being exposed to natural and man-made sources of ionization radiations. These harmful radiations are frequently utilized in many medical areas such as radiotherapy, cardi-ology, computerized tomography, mammography, nuclear medicine therapy, diagnostic radiology and several other medicalfields. For ex-ample, one of the most common use of the ionization radiation (namely X-ray) is to detect whether bone are broken. Another application of x-ray is known as cardiology, where particular x-x-ray pictures are taken of the heart. Besides, ionization radiations are utilized in different kind for medical imaging and for treatment of disease or cancer[1].
International radiation organizations have suggested some princi-ples to diminish and decrease the hazards of the radiation on the human organs and tissues. The most common radiation protection principles are MIRD (Medical Internal Radiation Dose) and ALARA (As Low As Reasonably Achievable)[2].
ALARA (As Low As Reasonably Achievable) is a sound radiation safety principle which based on the minimization of radiation doses by taking into the account three factors (distance, time and shielding).
Briefly, reducing the time of exposure can reduce radiation dose, maximizing the distance between the worker or patient and the radia-tion source will reduce exposure, andfinally using convenient shielding material (such as lead or lead equivalent shielding)[2–4].
Developing a novel shielding material for diagnosis radiology rooms is of considerable significance to the future of the radiological field. The most important features of the material to be used as protection ma-terial are to attenuate the gamma photons, and this can be achieved by utilizing materials with high atomic number elements thus having high density values. The other important features of the novel protection material are the easiness in shaping and manufacturing the sample according to the required parts of the workstations. These features can be found in several glass systems which have the aforementioned abilities[5–15].
In order to examine the possibility of utilizing any glass sample as photons protection material, there is a requirement of methodical and detailed work in terms of some photon shielding quantities. One of these quantities is the mass attenuation coefficient (μ/ρ), which gives information about the number of scattered or absorbed photons by the interacting material. Theμ/ρ parameter is considered as an essential
https://doi.org/10.1016/j.rinp.2019.01.094
Received 7 January 2019; Received in revised form 29 January 2019; Accepted 31 January 2019
⁎Corresponding author.
E-mail address:mabualssayed@ut.edu.sa(M.I. Sayyed).
Available online 06 February 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/).
or expensive lab materials or hard to be conducted in some research premises. Also, it is useful and helps in testing certain glass system before preparing the glass to estimate the attenuation features of the glass sample in order to save materials and efforts.
There is a number of works dealing with the estimation of µ/ρ for different glass systems such as barium–bismuth–borosilicate [18], heavy-metal oxide [19], silicate glasses [20], lead borate [21]and phosphate glasses [22]. Most of these works, reported the radiation shielding parameters of different glasses at moderate and high energy values, while in the literature there are only minimal works which tried to study the gamma and neutron shielding parameters on different glass systems at the medical diagnostic energies. Therefore, understanding the photon and neutron properties with the glass at the medical diag-nostic energies has become essential for many biological and medical applications. The present work deals with radiation shielding para-meters such as mass attenuation coefficients effective atomic number, half value layer, mean free path, macroscopic effective removal cross-sections and neutron transmission function for samarium doped lead alumino borate glasses containing barium, lithium and zinc oxides at medical diagnostic energies. The obtained theoretical results are com-pared with those of MCNPX code.
Materials and methods
The frequency of use of numerical models is increasing day-by-day in order to determine and optimize the properties of radiation shielding materials. When it comes to medical radiationfields, the importance of numerical models increases due to the fact that the structure is viable tissue that can be affected by the source of medical radiation. In this work, samarium doped lead alumino-borate glasses incorporated with three modifiers (BaO, Li2O and ZnO) have been selected as shown in
Table 1 [23]. The weight fraction, density and the code for the samples are given in this table. The µ/ρ for the samples were calculated at dif-ferent energies (20 keV, 30 keV, 40 keV, 60 keV, 80 keV, 100 keV and 150 keV). These energies are used usually in diagnostic radiology. To determine the µ/ρ values for the present glass systems in the range of diagnostic radiology energies, Monte Carlo N-Particle Transport Code System-extended (MCNPX) was carried out. The cross-sectional MCNPX 3-D view of radiation attenuation scheme with several simulation equipments namely the glass sample as absorber, a point radioactive source, lead (Pb) collimator for primary radiation beam, Pb blocks to prevent from the scattered photons and F4 tally mesh detectionfield is
flux in F4 tally mesh by the mean value of neutron flux in the uniform detection field. Two detection fields are placed in front and behind of the glass in order to carry out this formulation into MCNPX code. While detecting the intensity of primary neutrons at thefirst detection area placed in front of the glass material, the intensity of attenuated neutrons passing through the glass was detected in those of the detection region behind the glass. The MCNPX simulation layout of neutron transmission factor is visualized in Fig. 2.
Results and discussion
Fig. 3shows the energy dependence of the obtainedμ/ρ calculated at several energies used usually in diagnostic radiology for the PAB, ZPAB, LPAB and BPAB glasses. As it is seen in thisfigure, the photon attenuation depends on the type of modifier used (i.e. ZnO, BaO or Li2O) and depends also on the energy of the photon. The trend shown in
this figure for the μ/ρ is similar to the results reported for different materials such as rocks[28], biological compounds[29]and glasses [30]. For the glasses under study, theμ/ρ follows the trend BPAB > ZPAB > LPAB > PAB. The higherμ/ρ value for BPAB is mainly due to Ba content in this glass sample, since Ba has higher atomic number than Li and Zn. In addition, it is clear that theμ/ρ decreases as the energy of the photon increases from 20 keV to 150 keV. This decrease in the at-tenuation is clear significantly between 20 and 60 keV, while by in-creasing the energy from 60 keV to 150 keV theμ/ρ decreases in lower rate. It is worth mention that at very low energy, the photoelectric absorption is the dominating attenuation mechanism; the cross section of this mechanism which represents the probability of the interaction to occur is directly proportional to Z4-5, whereas inversely to E3.5. Hence,
we can see fromFig. 3 that the μ/ρ attains the maximum value at 20 keV and abrupt reduction in the attenuation values occur as the energy increase in the low energy zone (from 20 keV to 60 kev). For example, the μ/ρ for the ZPAB sample at 20 keV and 60 keV are 37.19 cm2/g and 2.45 cm2/g, respectively. For the same sample, theμ/ρ values are 1.22 cm2/g and 0.89 cm2/g at 80 keV and 150 keV (the
dif-ference is only 0.33) and this can attributed to Compton scattering which becomes the dominating mechanism between these energies [31]. The cross section of this mechanism varies with Z and E−1and this explains the slow change in the attenuation for E > 60 keV.
Moreover, theμ/ρ values calculated by XCOM software and MCNPX code are graphically demonstrated inFig. 4for the purpose of com-parison between results of different methods. As can be seen inFig. 4,
Table 1
The weight fractions and densities of the samarium doped lead alumino borate glasses containing barium, lithium and zinc oxides.
Code B O Al Sm Pb Zn Li Ba Density g/cm3
PAB 0.140269 0.391106 0.050736 0.028273 0.389616 0 0 0 3.53
ZPAB 0.118628 0.357070 0.050180 0.027964 0.385352 0.060806 0 0 3.98
LPAB 0.124595 0.375033 0.052705 0.029371 0.404738 0 0.013558 0 3.54
there is a stationary agreement between theoretical and computational results. The relative deviation of the MCNPX results with respect to XCOM [RD = (μ/ρXCOM-μ/ρMCNPX) × 100/μ/ρXCOM] has been calculated
and found to below ± 7.01% except for 15.04%, 18.97% and 19.68% at 80 keV for PAB, LPAB and ZPAB, respectively. The XCOM's results have been taken into account in the calculation of the related shielding parameters.
The effective atomic number (Zeff) is an important parameter to
figure out the photon attenuation properties of the glasses. The Zeffhas
been obtained from the theμ/ρ according to the next relation[32]:
= ∑ ∑
( )
( )
Z f A f eff i i i μ ρ i j j A Z μ ρ j j j (1)where fidenotes the fractional abundance of the element i. The Zefffor
the present samples are exhibited inFig. 5. The highest Zefffor all
samples is found at 20 keV (71.36, 66.30, 69.99 and 71.83 for PAB, ZPAB, BPAB, and LPAB respectively). The Zeff of all the glasses
de-creased with the increase in the energy, except at 100 keV. The abrupt rise in the Zeffat 100 keV could be due to k edge absorption energy of
lead (88 keV). It has been shown that LPAB has the maximum Zeffvalue
between 20 and 40 keV, while BPAB has the maximum Zeffvalue from
E > 40 keV. The explanation of high Zeffvalue for LPAB for the energy
range 20–40 keV is most probably due to photoelectric absorption probability, which is very high at lower energies and for high atomic number elements and it is also clear fromTable 1 that this sample contains the highest percentage of lead.
One interesting parameter that used frequently to estimate the suitable thickness to attenuate the incoming gamma photons is the half value layer (HVL). It is defined as the thickness of the sample where 50% of the original photons can transmit through the glass sample. HVL is related with the density, and denser glass indicates better attenuation ability. The following relation can be used to obtain the HVL for the present samples[33]:
(a) (b)
Fig. 1. (a) MCNPX simulation setup of recent investigation (b) 3D view of MCNPX simulation setup obtained from MCNPX Visual Editor (version X22_S).
Fig. 2. MCNPX simulation scheme for neutron TF calculations.
Fig. 3. The mass attenuation coefficients (cm2/g) of samarium doped lead
=
HVL μ
0.693
(2) Fig. 6 demonstrates the effect of the energy on HVL of the four glasses under study. Generally, the HVL values are increasing with in-creasing the energy from 20 keV to 80 keV. This result reveals that the four PAB, ZPAB, BPAB, and LPAB samples are able to attenuate the photons at low energy, and the ability of the samples to reduce more photons decreases with the rise of the energy of the photon. In contrast, at 100 keV, the HVL decreases which is due to the behavior ofμ/ρ at this energy as we discussed in previous paragraph. PAB sample (has lowest density, 3.53 g/cm3) has the highest HVL followed by LPAB (ρ = 3.54 g/cm3). This means PAB and LPAB possess worse attenuation
features in comparison to ZPAB and BPAB. A conclusion can be reached from this conclusion that the density has a considerable influence on
the gamma photon attenuation for the sample.
Further parameter was evaluated to verify the effectiveness of the present samples as gamma shielding material at the medical diagnostic energies namely mean free path (MFP). It denotes the mean distance that before being interacted, a photon can travel in any shielding ma-terial and is obtained from theμvalue by the following equation[34]:
=
MFP μ
1
(3) Fig. 7shows the comparison of MFP for the PAB, LPAB, ZPAB and BPAB glasses with other commonly used shielding materials namely ordinary concrete[35], polymer[36], and three commercial glasses [37]. It can be viewed that all the MFP values arise with increasing the photon energy. On other hand, the glasses under investigation have the lower MFP values than those of ordinary concrete, PMMA and
RS253-Fig. 4. Theoretical and computational mass attenuation coefficient values for the selected glasses with photon energy.
Fig. 5. The effective atomic number of samarium doped lead alumino-borate glasses barium, lithium and zinc oxides.
Fig. 6. The half value layer (cm) of samarium doped lead alumino-borate glasses barium, lithium and zinc oxides.
G18 glass samples while possessing higher MFP values than RS-520 glass sample. In addition, the MFP results in this study are quite close to that of RS-360 glass sample.
On the other hand, some important neutron shielding parameters such as macroscopic effective removal cross-sections (ΣR) and neutron
transmission function (N/N0) have been calculated for investigated
glass samples. The term of macroscopic effective removal cross sections for fast neutrons ΣR(cm−1) is known as the possibility of a neutron
undergoing certain reaction per unit length when moving through the shielding medium [38]. In this study, calculation of macroscopic ef-fective removal cross-sections (ΣR) of investigated glasses were
calcu-lated by using the equation in below[39]:
= W
ΣR Σ i(ΣR ρ i/ ) (4)
The calculatedΣRvalues for fast neutrons of the selected glasses are
graphically indicated inFig. 8. It can be obviously viewed from this figure that the ΣRvalues of the glasses containing barium, lithium and
zinc oxides are in increase order of BPAB (0.099 cm−1) < PAB (0.1047 cm−1) < LPAB (0.1054 cm−1) < ZPAB (0.1123 cm−1). The higher value ofΣRfor ZBAP glass sample may be ascribed to possess
large elemental composition of low-Z and highest density of 3.98 g/cm3
(seeTable 2). Moreover, as demonstrated inFig. 9, these results are highly supported by the obtained TF values of glasses according to glass thicknesses.Fig. 9revealed that the TF values of the studied glasses decrease linearly with increment of thickness and ZPAB has the lowest TF values. Hence, ZBAP glass is the best neutron shielding material among other glasses containing other oxides.
Conclusion
The feasibility of using samarium doped lead alumino borate glasses including BaO, Li2O and ZnO in medical applications as gamma and
X-ray shielding material at various photon energies between 20 and 150 keV has been reported. The estimated theoreticalμ/ρ values were found to be very close to those of MCNPX code. These results exhibited that the by the addition of barium, lithium and zinc oxides to the se-lected glasses, the higher density they have and the superior radiation absorption it provide. Moreover, the shielding features of the studied glasses are better than the concretes, polymers and basic conventional shielding glasses except for RS-520 glass sample according to MFP re-sults. Besides, the highestΣRvalue was found for ZPAB glass samples so
it is a superior material for neutron shielding applications. This kind of glasses may be used for the applications namely x-ray diagnostic and
Fig. 7. Variation of mean free path (cm) with photon energy for the glasses along with comparison to other materials.
Fig. 8. The fast neutron removal cross sections for the studied glasses.
Table 2
Calculations ofΣR(cm−1) of the studied glasses.
PAB (density = 3.53 g/cm3) ZPAB (density = 3.98 g/cm3) LPAB (density = 3.54 g/cm3) BPAB (density = 3.69 g/cm3) Element Fraction by Weight (%) Partial Density (g/ cm3) ∑R (cm−1) Fraction by Weight (%) Partial Density (g/ cm3) ∑R (cm−1) Fraction by Weight (%) Partial Density (g/ cm3) ∑R (cm−1) Fraction by Weight (%) Partial Density (g/ cm3) ∑R (cm−1) Li 0 0 0 0 0 0 0.013558 0.04799532 0.004026807 0 0 0 B 0.140269 0.49514957 0.0284711 0.118628 0.47213944 0.027148018 0.124595 0.4410663 0.025361312 0.11119 0.4102911 0.023591738 O 0.391106 1.38060418 0.055914469 0.35707 1.4211386 0.057556113 0.375033 1.32761682 0.053768481 0.334681 1.23497289 0.050016402 Al 0.050736 0.17909808 0.005247574 0.05018 0.1997164 0.005851691 0.052705 0.1865757 0.005466668 0.047034 0.17355546 0.005085175 Zn 0 0 0 0.060806 0.24200788 0.004428744 0 0 0 0 0 0 Ba 0 0 0 0 0 0 0 0 0 0.119694 0.44167086 0.005675471 Sm 0.028273 0.09980369 0.001207625 0.027964 0.11129672 0.00134669 0.029371 0.10397334 0.001258077 0.026211 0.09671859 0.001170295 Pb 0.389616 1.37534448 0.014303583 0.385352 1.53370096 0.01595049 0.404738 1.43277252 0.014900834 0.36119 1.3327911 0.013861027 TOTAL 0.105144351 0.112281746 0.10478218 0.099400108
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