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ORIGINAL ARTICLE
Year : 2019  |  Volume : 42  |  Issue : 1  |  Page : 47-56  

Lead nitrate loaded, novel clay-based bricks as radiation shielding materials for building applications


Department of Physics, Osmania University College for Women, Koti, Hyderabad, Telangana, India

Date of Submission04-Jun-2018
Date of Decision19-Jul-2018
Date of Acceptance19-Mar-2019
Date of Web Publication3-Jun-2019

Correspondence Address:
Madhuri Dumpala
Department of Physics, Osmania University College for Women, Koti, Hyderabad - 500 001, Telangana
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/rpe.RPE_36_18

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  Abstract 


A new class of clay bricks designed, developed, and tested for their radiation shielding efficiency. The bricks were prepared using natural clay, lake clay, and lightweight clay and loaded with different concentrations of Pb (NO3)2. The gamma-ray shielding parameters were measured for these bricks with a transmission type of good geometry setup and operated at 511 and 662 keV energies. The gamma-ray spectrometer consists of a 2“×2” NaI (Tl) detector, 8K multichannel analyzer. The 22Na and 137Cs point isotropic gamma-ray sources were used in this study. To evaluate the efficiency of these bricks, various shielding parameters, such as linear attenuation coefficient, mass attenuation coefficient, mean-free path, half-value layer and tenth-value layer were calculated. The X-COM software was used to calculate these parameters theoretically, and both the experimental and theoretical values were compared, and they are in good agreement. These results suggest that the clay bricks prepared with the natural and lake clay attenuate more radiation than the lightweight clay bricks. It is also observed that the lightweight bricks prepared with the solutions with higher loadings of lead nitrate showing increased attenuation, this may be attributed to the reason that at higher loadings of LN, the porous gaps of lightweight bricks are being filled by the LN particles and contributed to the attenuation of radiation.

Keywords: Clay bricks, gamma-ray attenuation coefficient, radiation shielding materials, radiation shielding parameters


How to cite this article:
Dumpala M. Lead nitrate loaded, novel clay-based bricks as radiation shielding materials for building applications. Radiat Prot Environ 2019;42:47-56

How to cite this URL:
Dumpala M. Lead nitrate loaded, novel clay-based bricks as radiation shielding materials for building applications. Radiat Prot Environ [serial online] 2019 [cited 2019 Oct 14];42:47-56. Available from: http://www.rpe.org.in/text.asp?2019/42/1/47/259668




  Introduction Top


Exposure to ionizing radiation, for longer times, is hazardous to human beings. Therefore, there is a need to develop new class of shielding materials, time to time, to protect them from direct exposure to the harmful radiation. One such requirement is to develop building materials with high radiation shielding efficiency for residential buildings. At the same time, the use of radioactive isotopes has been increasing, drastically, in the fields of medicine, industry, defense and in other applications.[1] The exposure to radiation causes damage not only to the cells in living organisms but to the sensitive laboratory equipment as well. The effect of the radiation could be minimized by three common methods, namely (i) time, (ii) distance, and (iii) shielding. The most effective method among these for attenuation of radiation is shielding and measurement of these attenuation coefficients of materials was published by Hubbel.[2]

The measurement of accurate values of photon interaction parameters, such as mass attenuation coefficients in materials, are required in solving different problems in radiation physics, radiation protection, radiation dosimetry, nuclear diagnostics (computerized tomography), nuclear medicine, gamma-ray fluorescence, shielding, security screening and research and development etc.[2],[3],[4],[5],[6],[7],[8] Gamma-ray attenuation measurements, compilations and calculations in different elements have been published.[9],[10],[11],[12],[13],[14],[15],[16],[17],[18],[19],[20],[21],[22],[23]

Understanding the influence of the radiation shielding is important in building materials. Heavy metals such as lead or tungsten are ideal materials to be used in radiation shielding. On the other hand, they cannot be used directly in building construction due to durability and also cost. The design of shielding material depends on various parameters like type and the cost of material and the facilities available. The clay brick is one of the main materials used in building construction, even though it is less effective shielding material than lead (Pb) and tungsten (W), for example, lead (Pb) and tungsten (W) compounds can be used for the shielding from X- and γ rays directly or by adding some shielding materials. These materials have an important role in the development of shielding technology. Since clay bricks alone are not good shielding materials there is a need to improve the shielding properties of materials. Different loadings of lead (Pb) and tungsten (W) compounds were added to pure clay bricks to improve their shielding efficiency. The Pb (NO3)2 is also an alternative material that can be used as an aggregate in the clay brick to improve radiation shielding properties, those are presented in terms of mass attenuation coefficient (μ/ρ, linear attenuation (μ), mean-free path (MFP) (1/μ), half-value layer (HVL) (ln 2/μ) and tenth-value layer (TVL) (ln 10/μ).

The mass attenuation coefficients of normal clay bricks[24],[25] are around 10% lower than the theoretical mass attenuation coefficient of water for those energies (511–1333 kev). Hence, it is concluded that the normal clay brick is attenuating less than the water for the incident radiation. Hence, we test bricks loaded with different concentrations of lead nitrate for higher attenuation of incident radiation and studying the gamma-ray shielding parameters, which has become an important[26],[27],[28] method to assess them.

A systematic study has been undertaken to develop clay-based bricks with improved radiation protection and tested at the energies 511 and 662 keV. We are presenting these results of gamma-ray interactions with and without Pb (NO3)2 concentration clay bricks prepared with different types of clay by measuring gamma-ray shielding parameters at different photon energies.

Theory and computation

If matter is exposed to gamma radiation beam, the intensity of the beam will be attenuated as per the Beer–Lambert Law. The gamma-ray attenuation coefficient in a particular medium is measured by

I = Io e-μt (1)

Where, I and Io are the initial and final intensities of interacting photons, respectively. μ is linear attenuation coefficient of the sample and “t” is the thickness of a material.

A correction term, known as the “Buildup factor” (B) need to be incorporated in the above Equation 1 for any breach of conditions and hence, the Beer–Lambert Law now becomes I = Io Be-μt.[29]

Then the buildup factor is given by

B = I/Ioeμt (2)

Where “B” is buildup factor of the sample

The linear attenuation coefficient (μ) is given by

μ =1/t ln (Io/I) (3)

Linear attenuation coefficients are very apt for developing engineering applications. The density of absorber, which does not contain a unique value always, but it depends, to certain extent, on the physical state of the material. To eliminate this density dependency and to utilize the mass attenuation coefficients (μ/ρ which, if μ is in cm−1 and ρ is in g/cm3, will be in the customary units of cm2/g. The mass attenuation coefficients (μ/ρ is expressed as

μ/ρ =1/ρt 1n (Io/I) (4)

Where “t” is the sample thickness (cm), and “ρ” is material density (g/cm3), Io and I are the net counts under the photopeak, without sample and with sample, respectively. Io and I were obtained for the same counting time and experimental conditions. Interpolations from tabulated theoretical values of the mass attenuation coefficients for clay bricks were obtained using XCOM.[30]

An average distance traveled by a photon between successive interactions is known as MFP, and it is given by

MFP = 1/μ (5)

The material thickness that reduces the intensity of the photon beam to half of its original value is known as HVL a material. The HVL is represented by

HVL = ln 2/μ(6)

The material thickness that reduces the intensity of the photon beam to one-tenth of its original value is known as TVL a material. The TVL is represented by

TVL = ln 10/μ (7)


  Materials and Methods Top


In the present study, clay was collected from different geographical locations, sources and the bricks were made with different concentrations of lead nitrate loading. These clay bricks were prepared with water, collected from different sources.

Materials used

The following types of clay materials were used in the present study: (a) natural clay which is used in preparing normal clay bricks, (b) lake clay was collected from lake at near pochampally village, and (c) lightweight clay. The lightweight clay contains natural clay, fly ash and husk, and the ratio is 4:2:1, respectively. The groundwater from different sources was collected and stored in clean bottles for mixing clay. AR grade of lead nitrate (Pb [NO3]2) compound was purchased from Hychem Laboratories, Hyderabad, India.

Preparation methods

Different concentrations of lead nitrate solutions are prepared in the following method. Six liters of water were taken in a beaker and heated up to 70°C. At this temperature, the lead nitrate was added to water and stirred thoroughly for uniform mixing. In this way, different concentrations of lead nitrate solutions were prepared for making clay brick and they are as follows:

  • LNC0-0th concentration prepared without any lead nitrate compound (LNC).
  • LNC1-1st concentration prepared with 94 g of LNC diluted in 6 L of water
  • LNC2-2nd concentration prepared with 188 g of LNC diluted in 6 L of water
  • LNC3-3rd concentration prepared with 375 g of LNC diluted in 6 L of water
  • LNC4-4th concentration prepared with 750 g LNC diluted in 6 L of water
  • LNC5-5th concentration prepared with 1.5 kg LNC diluted in 6 L of water
  • LNC6-6th concentration prepared with 3 kg LNC diluted in 6 L of water
  • LNC7-7th concentration prepared with 6 kg of LNC diluted in 6 L of water.


The clay bricks were prepared with different concentrations of lead nitrate solutions separately as mentioned above. A set of four bricks were prepared for each type of solution.

The density of the clay bricks is measured as

Density = mass/volume

The mass of the brick is measured with electronic balance and the volume calculated as

Volume of a brick = length × width × height (l × h × w)

The error in measuring the density is <2%.

Experimental

Different shielding parameters were determined using gamma-ray source and transmission experiments in narrow beam geometry set up[25] as shown in [Figure 1]. In these experimental methods, fairly good amount of thick lead sheet was used as shielding around the source and the detector to prevent detection of scattered radiation from surroundings. For the low energy measurements, the probability of coherent scattering interactions is relatively high and so very good collimation is required to reduce the contribution of Rayleigh scattered photons reaching the detector. A tight collimation reduces the absolute detection efficiency so that high activity sources must be employed, that is around 10 mCi strength. At higher energies, the probability of elastic scattering becomes much smaller and so scattered radiation is less important which reduces the need for such close collimation quantify higher energies. Furthermore, Compton scattering would lead to scattered component. Therefore, source strengths in the range 10–20 μCi were found to be adequate for the higher energy measurements. The radioactive sources of strength around 10 μCi were procured from BRIT, Mumbai, India, and details of the radioactive sources are given in [Table 1].
Figure 1: Block diagram of the experimental setup. S: Source, D: Detector, T: Target, Slit diameters: a: 4 mm, b: 10 mm. Length of the collimators: L1: 8 cm, L2: 5 cm

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Table 1: Radioactive isotope used in the present work

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A NaI (Tl) crystal detector of size 2“×2” with the energy resolution of 8% at the 662 keV and 8K multi-channel analyzer plug-in-card were used with associated electronics to measure the pulse-height of gamma-radiations emanated by radioactive sources. The densities of the clay bricks were calculated and summarized in the [Table 2].
Table 2: Densities of the clay bricks for different thicknesses and concentrationsa

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Elemental analysis of the prepared samples was done by using EDAX (measured with Carl Zeiss EVO 15, scanning electron microscope). The percentage of elemental compositions of the investigated clay bricks are given in [Table 3].
Table 3: Percentage of various elemental compositions of clay bricks under study

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For each sample, counts were taken in the following sequence, background, no sample, sample, sample, no sample, and so on.[28] Different parts of the sample are exposed to the beam. The counting sequence was continued in most cases until counting statistics contributed <0.5% error. The errors in the present investigations are due to (i) counting statistics, (ii) nonuniformity of the sample, (iii) density measurements, and (iv) scattered radiation reaching the detector within the accepted maximum angle of scattering. In the present investigation, this angle was around 3° and the error is due to this factor was about 0.3%. The counting statistics were such that the error is <0.5%. The fractional error arising due to nonuniformity of the sample was estimated to be in the order of 0.2%. The error in the density measurement is <2%. After considering the error due to density, the overall error in the presented work is <2.82% (that means the consolidated error of my experimental calculations are <2.82%). The theoretical gamma-ray shielding parameters of prepared samples were estimated by using mixture rule.


  Results and Discussions Top


In the present work, the results of the theoretical and experimental values of different radiation shielding parameters (mass attenuation, linear attenuation, MFP, HVL, TVL and Buildup factor) for different type clay bricks (natural, lake and lightweight) with different concentrations of Pb (No3)2 loadings, at 511 and 662 keV energies were presented and the same was summarized as [Table 4] and [Table 5], respectively.
Table 4: Radiation shielding parameters in different types of clay bricks at 511 keV energy

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Table 5: Radiation shielding parameters in different types of clay bricks at 662 keV energy

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Mass attenuation coefficients

With the exponential increase of lead nitrate concentration in clay bricks, it was observed that there was a slow increase in the mass attenuation coefficients and it is decreased with increasing of photon energy, which is presented in [Figure 2]a and [Figure 3]a. There is good agreement between the theoretical and experimental values of mass attenuation coefficients. From the graph, the mass attenuation coefficients of different type clay bricks (natural, lake, and lightweight clay) are nearly equal at all concentrations. Therefore, the values of mass attenuation coefficients are not changing with the clay type used in the present study.
Figure 2: Variation of various shielding parameters of the clay bricks under study at 511 keV energy: (a) Mass attenuation coefficients (b) Linear attenuation coefficients (c) Mean-free path (d) half-value layer (e) tenth-value layer (f) Buildup factor. N9 cm: Natural clay brick with 9 cm, Th: Theoritical value, N7 cm: Natural clay brick with 7 cm, L9 cm: Lake clay brick with 9 cm, L7 cm: Lake clay brick with 7 cm, LT9 cm: Lightweight clay brick with 9 cm, LT7 cm: Lightweight clay brick with 7 cm

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Figure 3: Variation of various shielding parameters of the clay bricks under study at 662 keV energy: (a) Mass attenuation coefficients (b) Linear attenuation coefficients (c) mean-free path (d) half-value layer (e) tenth-value layer (f) buildup factor. N9 cm: Natural clay brick with 9 cm, Th: Theoritical value, N7 cm: Natural clay brick with 7 cm, L9 cm: Lake clay brick with 9 cm, L7 cm: Lake clay brick with 7 cm, LT9 cm: Lightweight clay brick with 9 cm, LT7 cm: Lightweight clay brick with 7 cm

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At LNC7 concentration the mass attenuation coefficients of different type clay brick at 511 and 662 keV are nearly equal to the theoretical value of mass attenuation coefficients of LNC and it is 0.130 and 0.098 g/cm2, respectively. For 9 cm thickness, the experimental mass attenuation coefficients of lead nitrate clay brick at 511 and 662 keV are 0.119 and 0.097 g/cm2, respectively.

Linear attenuation coefficients

Linear attenuation coefficient increases with the increasing of lead nitrate concentration. [Figure 2]b and [Figure 3]b show how the linear attenuation coefficients vary with the increase of lead nitrate concentrations in the clay bricks. From the graphs, it is clear that, for all concentrations, the linear attenuation coefficients of natural and lake clay bricks are nearly equal but for the lightweight clay brick deviated from them. Comparatively natural and lake clay brick, lightweight clay brick have low density and the linear attenuation is directly proportional to density.

Mean-free path

The variation of MFP values of different types of clay bricks is shown in [Figure 2]c and [Figure 3]c. From the figure, it is clear that the MFP decreases with the increasing of lead nitrate concentration in clay bricks. The linear attenuation is inversely proportional to MFP.

Half-value layer

HVL decreases with the increasing of lead nitrate concentration in clay bricks, as shown in [Figure 2]d and [Figure 3]d.

Tenth-value layer

From [Figure 2]e and [Figure 3]e, it is clear that the TVL decreases with the increasing of lead nitrate concentration in clay bricks.

Buildup factor

Buildup factor were calculated as per the formula[29] and shown as [Figure 2]f and [Figure 3]f.


  Conclusions Top


A new class of clay-based bricks for building material was developed with enhanced radiation shielding properties. These clay bricks were prepared with clay collected from different sources, loaded with different concentrations of LN, were studied for their radiation shielding efficiency. These bricks showed enhanced radiation shielding properties. Experimental measurements were taken using good geometry setup at energies 511 and 662 keV to measure various radiation shielding parameters. The mass attenuation coefficients of different types bricks prepared using natural, lake clay and lightweight bricks are nearly equal at all concentrations. Therefore, it is concluded that the mass attenuation coefficient is not changing with the type of clay used. The Linear attenuation coefficients of natural and lake clay bricks at all concentrations are nearly equal but lightweight clay deviated with natural and lake clay bricks at all concentrations. MFP, HVL and TVL of natural and lake clay bricks at all concentrations are equal, lightweight clay brick is deviated from them at all concentrations. Mean-free path, HVL and TVL are reciprocal of linear attenuation coefficients. Among all, the clay bricks prepared with LNC7 using natural and lake clay showed low HVL and TVL values and high mass attenuation values, indicating that these bricks demonstrated improved shielding properties and are suitable for radiation shielding applications. It is observed that for the lightweight clay bricks are not suggestible for radiation shielding as they show poor radiation shielding properties compared to the brick prepared using natural and lake clay, in spite of the fact that at higher loadings of LN in lightweight clay bricks, the radiation shielding has been increased, this may be due to the reason that at higher loadings of LN in the lightweight clay bricks, the porous gaps of lightweight bricks are being filled by the LN particles and contributed to the attenuation of radiation from LNC3 (third concentrations) onwards. Therefore, the shielding parameters measured in this study, reveals that the bricks prepared with natural and lake clay showed higher attenuation compare to lightweight clay bricks.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

  [Figure 1], [Figure 2], [Figure 3]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]



 

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