a research on the radiation shielding effects of clay silica fume and cement samples
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Article about different types of shielding protection, based upon a series of new materials and mixesTRANSCRIPT
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A research on the radiation shielding effects ofclay, silica fume and cement samples
Suat Akbulut, Arvin Sehhatigdiri, Hayrettin Eroglu,Semet Çelik
PII: S0969-806X(15)30028-1DOI: http://dx.doi.org/10.1016/j.radphyschem.2015.08.003Reference: RPC6885
To appear in: Radiation Physics and Chemistry
Received date: 23 August 2014Revised date: 29 July 2015Accepted date: 4 August 2015
Cite this article as: Suat Akbulut, Arvin Sehhatigdiri, Hayrettin Eroglu and SemetÇelik, A research on the radiation shielding effects of clay, silica fume andcement samples, Radiation Physics and Chemistry,http://dx.doi.org/10.1016/j.radphyschem.2015.08.003
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A research on the radiation shielding effects of clay, silica fume and
cement samples
Suat AKBULUTa, Arvin SEHHATİGDİRİ
a, Hayrettin EROGLU
b,*, Semet
ÇELİKc
aAtaturk Universty, Graduate School of Natural and Applied Sciences,
Department of Nanoscience and Nanoengineering, 25240 Erzurum, Turkey
b,*Ataturk Universty, Faculty of Engineering, Department of Biomedical
Engineering, 25240, Erzurum, Turkey
c Ataturk Universty, Faculty of Engineering, Department of Civil Engineering,
25240, Erzurum, Turkey
*Corresponding author
E-mail : [email protected]
Tel : +90 442 231 4547
Fax : +90 442 231 2766
2
Abstract
Nowadays, as the application areas of nuclear technology increases, protection
from radiation has become even more important. Especially, the importance of
radiation-shielding is important for the environment and employees which are
in close proximity. Clays can be used as additives for shielding the radioactive
materials. In this study, the shielding properties of micronize clay-white
cement, clay-silica fume, gypsum, gypsum-silica fume, cement, white cement,
cement-silica fume, white cement-gypsum, white cement-silica fume, red mud-
silica fume, silica fume and red mud at different energy levels were examined.
Additionally, compaction and unconfined compression tests were carried out
on the samples. The results of clays and other samples were compared with
each other. As a result, it was found that clays, especially clay-white cement
mixture were superior than other samples in radioactive shielding.
Keyword: Clay, Silica fume, Cement, Radiation Shielding.
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1. Introduction
Radiation is defined as the emission and transmission of atomic energy by
electromagnetic waves or particles in vacuum. It can also be defined as a type
of energy ranging from long radio waves to cosmic rays. The usage areas of
radiation, mainly used to be medical and industrial fields, nowadays has
significantly widened to cover various environments and fields [1].
Radiation's presence was first perceived with Wilhelm Roentgen's discovery of
X-rays and with the proof of the existence of radioactivity in 1902 by the Curie
couple, it has begun to be used in many research areas including medical
science, agriculture and industry, and it has been used for nearly 100 years at
an increasing rate. Although the information regarding its existence is
considerably new, the usage area of radiation has increasingly become
widespread. In addition to its benefits, radiation has significant hazards to
living organisms. X, α, β and γ rays which are known as ionized radiation can
become important threats for living organisms if required precautions are not
taken. These rays may cause biological, chemical and physical changes in
living organisms. All these changes may be temporary or permanent
depending on the type, duration and density of exposure to ionized radiation
[2,3].
In nature, there are no living cells immune to radiation and there hardly exists a
radiation-free place. Each person living on earth is exposed to radiation
originating from cosmic rays, radioactive sources or artifical sources of daily
life. 78 % of the public doze is caused by the natural sources, 20.7 % by
medical irradiators and the rest is caused by occupational irradiators and
artificial sources [1]. It should be noted that these numbers may show little
variations and are expected to be location-dependent.
There are three main elements of radiation protection. These are necessity,
optimization and personal dose limitations. The purpose of radiation protection
is to prevent deterministic effects and to keep the probability of harmful effects
at an acceptable level by limiting the exposed dose to below certain threshold
4
values. In practice, important protection measures such as duration, distance
and shielding can be taken for radiation-protection [1,4].
The dose of radiation received is directly proportional to duration of the
exposure, and inversely proportional to the square of the distance from the
source. Additionally, the most important and effective way of preventing the
radiation hazard is shielding. Placing a barrier between the radiation source and
the employee provides a reduction in radiation intensity. In this process,
radiation attenuation property of the substances is utilized so that the working
duration around the source can be extended. Shielding can be in various
shapes and thicknesses depending on the radiation type and energy. α rays can
be stopped by a paper or body skin, whereas β rays require 2.5 cm thickness
and γ rays require large amounts of lead or concrete [1,5]
Shielding is especially important in places where radiation is used and the
vicinity of radioactive area is covered with lead or concrete bricks in order to
protect the working environment from the harmful effects of radiation.
However, this type of shielding has high costs and is very cumbersome.
In recent years, numerous studies have been made in the building materials,
especially by using nanotechnology in cement-based materials. Nano building
materials, which have self-cleaning, dirt-repellent, flame-retardant, sound
insulating and light control film properties bring a different perspective to
conventional building materials [6-8]. Clay minerals are very tiny crystalline
substances evolved primarily from chemical weathering of rock-forming
materials [9]. In recent years, the researchers have been interested in
surfactants and polymers to modify clays for improving their engineering
properties. Some researchers have indicated that the geotechnical properties of
organoclays show significant change when compared to natural clay [10,11]. In
these studies it was obtained that the specific gravities, unconfined
compression strengths, cohesions and maximum dry densities of cationic and
anionic organoclays were decreased [10,11]. Additionally, optimum moisture
content and swelling pressure values were decreased in cationic surfactant
5
modified clays. However, optimum moisture content and swelling pressure
values of anionic surfactant clays are increased. Indicated that, clays modified
with zwitterion, nonionic and anionic surfactants gave the lowest contact
angles compared to those for natural clay; however, the clays modified with
cationic surfactants gave the highest contact angles. Similarly, the
electrokinetic properties (zeta potential, electrical conductivity, pH and cation
exchange capacity) of surfactant modified clays were changed when compared
with natural clay [10,11].
Many researchers have used various oxides on the nanoscale (such as nano-
SiO2, nano-TiO, nano FeO2) to improve the chemical and physical properties
of the concrete. The use of these small grains helps to improve the shielding
properties of concrete [6-8].
In this study, the effect of nanoscale clays and clay reinforced mixtures on
shielding is investigated. The studies show that clay materials improve the
shielding effect and decrease the radiation permeability. Hence, it can be
considered as an alternative solution in shielding problems.
2. Materials and Method
2.1. Materials
In this study, mechanical features and radioactivity shielding performances of
micronize clay, natural red clay, natural yellow clay, gypsum, cement, white
cement, silica fume, red mud, and some mixtures of these materials are
investigated.
Radioactivity sources at different energy levels including 99m
Tc (Technetium-
99m), 241
Am (Americium-241), 109
Cd (Cadmium-109), 131
I (Iodine-131) are
used for the calculation of radiation permeability of the materials prepared for
radiation shielding. The energy levels of these sources are given in Table 1.
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Table 1.
2.2. Sample Preparation
Red clay, yellow clay, micronize clay, gypsum, cement, white cement, silica
fume and red mud samples and some mixtures of these samples were prepared
for testing. These mixtures and their ratios are given in Table 2.
Table 2.
Each mixture shown in Table 1. were compacted by using modified proctor test
(MPT). As a result of MPT, optimum water content and maximum dry unit
weight were obtained. The maximum dry unit weight is obtained when
compaction is performed at optimum water content. Unconfined compression
tests and measurement of radiation permeability were performed on samples
compacted in the optimum water content.
The samples obtained from compaction were placed into the mold by using
shielding mold. The samples became ready for the tests after leaving the mold
in the oven for 24 hours.
2.3. Compaction test
The Proctor compaction test is a laboratory method of experimentally
determining the optimal moisture content at which a given soil type will
become most dense and achieve its maximum dry density. The term Proctor is
in honor of R. R. Proctor, who in 1933 showed that the dry density of a soil for
a given compactive effort depends on the amount of water the soil contains
during soil compaction [12]. His original test is the most commonly referred to
as the standard Proctor compaction test; later on, his test was updated to create
the modified Proctor compaction test.
In this study, modified proctor test were implemented on samples according to
ASTM D 1557. This test method is a compaction method used to determine
the relationship between water content and dry unit weight of soils compacted
7
in 101.6 mm diameter mold with a 44.5 N rammer dropped from a height of
457 mm. As a result of the test, optimum water content and maximum dry
unit weight values of the samples were determined.
2.4. Unconfined compression test
Unconfined compression tests were carried out according to ASTM D 2166.
Compacted specimens, which were prepared with optimum water content and
maximum dry unit weight, were used in this study. Undisturbed samples were
collected from compacted soil in proctor mold. Samples having a diameter (D)
of 38 mm and a height (H) of 76 mm were prepared for unconfined
compressive tests. In the test procedure, for the determination of unconfined
compressive strength of soil samples, cylindrical soil sample were first
subjected to load in axial direction only and then unconfined compressive
strength of soil samples were determined.
2.5. Measurement of radiation permeability
Measurements of radiation permeability were performed on compacted soil
sample. Undisturbed soil sample were collected from mold. 99m
Tc, 241
Am,
109Cd,
131I which radiate gamma rays at different energy levels were used for
the calculation of radiation permeability of the samples. Biodex, Atomlab 400
model dose calibrator were utilized for the measurement of radiation
permeability from these radioactive sources. Dose Calibrators are an integral
part of any nuclear medicine department. An ionization chamber is an
instrument constructed to measure the number of ions within a medium.
Ionization chambers are used in nuclear medicine to determine the exact
activity of radioactive dose administered to the patients. First, the energy levels
of radioactivity sources were measured in a lead container open on one side.
Then, the open side of the lead container was closed with the prepared building
materials and the energy levels were measured again. Finally, the radiation
8
permeability of these materials are measured using these values.
The linear attenuation coefficient (µ) describes the fraction of a beam of x-rays
or gamma rays that is absorbed or scattered per unit thickness of the absorber.
Linear attenuation coefficients depend on the composition of the attenuating
material, water content of material, and photon energy [13]. Linear attenuation
coefficient is expressed in equation 1.
(
)
( ) 1
Where, Io is the incident intensity, I is the intensity after passing a material of
thickness “ ”, and is the linear attenuation coefficient.
The radiation attenuation percentages of the materials are calculated with;
(
) 2
3. Result and Discussion
The results of compaction, unconfined compression, and measurement of
radiation permeability tests are shown below.
3.1. Compaction Test Results
The optimum water content and maximum dry unit weight values of samples
determined according to modified proctor test are given in Table 3. The
changes in maximum dry unit weights of the samples are given in Figure 1.
Table 3.
Figure 1:
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3.2. Unconfined Compression Test Results
The unconfined compressive strength of the samples were determined with
unconfined compression test carried out on undisturbed samples compacted at
optimum water content at modified proctor energy. Figure 2 shows the changes
in the unconfined compressive strength of the samples.
Figure 2:
It was found that there were significant increases in unconfined compressive
strength values of N4 (micronize clay - white cement), N7 (gypsum - silica
fume), N10 (cement - silica fume), N11 (white cement-gypsum) mixtures (50%-
50%), compared to pure clays. There were significant decrease in unconfined
compressive strength values of N9 (white cement) (100%), N12 (white cement -
silica fume) (50% -50%), N14 (red mud) (100%), N15 (red mud - silica fume)
(50% -50% ) mixtures, compared to pure clays. The maximum unconfined
compressive strength values were determined in N4 (micronize clay - white
cement) and N7 (gypsum - silica fume).
3.3. Shielding test results
Shielding test results were carried out with 99m
Tc, 241
Am, 109
Cd, 131
I at different
energy intervals. As a result of these tests, attenuation percentages and linear
attenuation coefficients of samples against different radioactive substances
were obtained. The results are shown in Figure 3 and Figure 4.
Linear attenuation coefficients of the samples for 99m
Tc, 241
Am, 109
Cd, 131
I is
calculated by using equation (1) and the results is shown in Figure 3.
Figure 3:
According to these results, it was seen that clays and clay mixtures (especially
clay and white cement) have higher linear attenuation coefficients than those of
10
the other samples. Also, N4 sample in which micronize clay and white cement
is used have higher linear attenuation coefficient than those of the other
samples for all energy levels studied. It was determined that N4 has a linear
attenuation coefficient of 0.7736 cm-1
at Am-241, 0.3779 cm-1
at Cd-109,
0.0772 cm-1
at Tc-99m and 0.0264 cm-1
at I-131.
It was seen that these materials are more suitable as radiation protective
materials in low energy radiations by examining their linear attenuation
coefficients and attenuation percentages. The dose levels of the sources were
used for the calculation of linear attenuation coefficients of samples for
radiation sources with different energies.
Radiation attenuation percentages of the samples for 99m
Tc, 241
Am, 109
Cd, 131
I
are determined by using equation (2) and shown Figure 4.
Figure 4:
According to these results, it was seen that clays and clay mixtures (especially
micronize clay and white cement) have higher attenuation percentages than
those of the other samples. Also, N4 sample in which micronize clay and white
cement is used have higher attenuation percentages than those of the other
sample for all energy levels studied. It was determined that N4 had attenuation
percentages of 77% at Am-241, 51.23% at Cd-109, 13.64% at Tc-99m and
4.9% at I-131.
4. Conclusion
In this study, geotechnical and shielding tests were carried out on clays and
other materials for the shielding of radioactive substances. Generally, until
today, in radiation shielding studies, it was focused on metal or concrete
materials and polymer-reinforced concrete. In this study, it was focused on
11
clays.
In the study, maximum dry unit weights, optimum water content, unconfined
compressive strength, attenuation percentages and radiation permeability
coefficients of clays and other materials were determined. The results of
experimental studies are listed below.
- The highest unconfined compressive strength values were determined in N4
(micronize clay - white cement) and N7 (gypsum - silica fume) samples.
- Clay and clay reinforced white cement samples gave the maximum
attenuation percentages.
- The highest linear attenuation coefficient was obtained for micronize clay and
white cement mixture sample.
- It was found that using clay had a very important effect on shielding the
radioactive substances.
- Even in radioactive substances with high energy such as Iodine-131, the best
results were obtained in clays and especially micronize clay- white cement
mixtures.
It is observed that as the energy of the radioactive substance increases, the
attenuation percentage decreases.
In the light of these results, using clay and clay reinforced white cement is the
best option in radiation shielding for places working with radiation. These
materials are advised to be used because they are environment-friendly, easy-
to-build, widely available and have low production costs.
5. References
[1] Berk, F., 2002. Sterilization of disposable medical products with gamma
radiation and comparison with other techniques. Hacettepe University Institute
of health sciences. M.Sc. Thesis. Ankara.
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[2] Öztürk, E., 2010. Ammonia Nitrogen Removal from Aqueous Solution by
Ultrasonic Radiation, leyman Demirel niversity rad ate chool of
Applied and Natural Sciences Department of Environmental Engineering.
M.Sc. Thesis. Isparta.
[3] Görpe, A., Cantez, ., . ratik kleer . İstan l ak ltesi
Vakf . Istanbul.
[4] Murray, R.L., Holbert, K,E. 2015. Nuclear Energy: An Introduction to the
Concepts, Systems, and Applications of Nuclear Processes, Radiation
protection. B-H, USA.
[5] Kowalsky, R.J., Perry, J.R., 1987. Radiopharmaceuticals in Nuclear
Medicine Practice. Appleton & Lange. California.
[6] F. Pacheco-Torgal and Said Jalali, 2011. Nanotechnology: Advantages and
drawbacks in the field of construction and building materials. Constr. Build.
Mater. 25, 582–590.
[7] Hanus, M. J., Harris, A.T., 2013. Nanotechnology innovations for the
construction industry, Prog.Mater. Sci. 58, 1056–1102.
[8] Chen, J., Poon, C., 2009. Photocatalytic construction and building
materials: From fundamentals to applications. Build. Environ. 44, 1899–1906.
[9] Holtz, R.D., Kovacs, W.D., 1981. An Introduction to Geotechnical
Engineering. Prentice Hall. New Jersey.
[10] Akbulut, S., Arasan, S., Kurt, Z. N., 2010. Some Geotechnical Properties
of Two Organoclays. Indian Geotechnical Conference. 605-608.
[11] Akbulut, S., Kurt, Z. N., Arasan, S., 2012. rfactant modified clays’
consistency limits and contact angles. Earth. Sci. Res. J. 16, 13-19.
[12] Day, R.W., 2001. Soil Testing Manual: Procedures, Classification Data,
and Sampling Practices. McGraw Hill. New York.
[12] Yaltay, N., Ekinci, C.E., Çak r T., Oto, B., 2015. Photon attenuation
properties of concrete produced with pumice aggregate and colemanite
addition in different rates and the effect of curing age to these properties.
Progress in Nuclear Energy. 78, 25-35.
13
[13] Eckerman K.F, Endo A.2007.MIRD: Radionuclide Data and Decay
Schemes, Society for Nuclear Medicine. Virginia.
[14] Marie-Martin Be, Venassa Chiste et al.2010. Table of Radionuclides
(Comments on evaluation). Bureau International Des Poids Et Mesures.
Sèvres.
FIGURE CAPTIONS
Figure 1: Maximum dry unit weights of samples.
Figure 2: Unconfined compressive strength of samples determined by
unconfined compression test
Figure 3: Linear attenuation coefficients of the samples for different
radioactive sources.
Figure 4: The radiation attenuation percentages of the samples for different
radioactive sources.
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TABLES
Table 1. Some of the radioactive properties of radioactive sources used
[14,15].
Radioactive
Isotopes
Half-Life Decay Gamma
energy (keV)
99mTc
6,01
hours
Isomeric
Transition 140,511
241Am
432,2
years Alpha 59,541
109Cd
462,6
days
Electron
Capture 88,040
131I
8,02
days Beta 364,489
15
Table 2. Percentage of composite samples used in the test
Sample code Materials Mixture percentages
(%)
N1 Micronize clay 100
N2 Red clay 100
N3 Yellow clay 100
N4 Micronize clay – white cement 50-50
N5 Micronize clay – silica fume 50-50
N6 Gypsum 100
N7 Gypsum – silica fume 50-50
N8 Cement 100
N9 White cement 100
N10 Cement - silica fume 50-50
N11 White cement - gypsum 50-50
N12 White cement - silica fume 50-50
N13 Silica fume 100
N14 Red mud 100
N15 Red mud - silica fume 50-50
16
Table 3. Optimum water content and maximum dry unit weight values of the
samples
FIGURES
. N1 N2 N3 N4 N5 N6 N7 N8 N9 N10 N11 N12 N13 N14 N15 .
Samples
12
13
14
15
16
17
18
19
20
21
22
Maxim
um
dry
unit w
eig
ht,
kN
/m3
Figure 1.
Sample
code
Optimum moisture
content (%)
Maximum dry unit
weight (kN/m3)
N1 22 15.99
N2 24 15.20
N3 26 17.66
N4 23 15.70
N5 27 19.23
N6 20 20.31
N7 24 13.93
N8 28 18.34
N9 30 19.42
N10 27 12.75
N11 26 19.91
N12 24 17.46
N13 20 13.93
N14 27 20.80
N15 26 20.21
17
. N1 N2 N3 N4 N5 N6 N7 N8 N9 N10 N11 N12 N13 N14 N15 .
Samples
0
1000
2000
3000
4000
5000U
nco
nfine
d c
om
pre
ssio
n s
treng
th,
kP
a
Figure 2.
Samples
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Lin
ear
attenuation c
offic
ients
, cm
-1
. N1 N2 N3 N4 N5 N6 N7 N8 N9 N10 N11 N12 N13 N14 N15 .0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
Lin
ear
attenuation c
offic
ients
, cm
-1
Am-241 Cd-109
I-131 Tc-99m
18
Figure 3.
Samples
0
10
20
30
40
50
60
70
80
90
Ra
dia
tio
n a
tte
nu
atio
n p
erc
en
tag
es,%
. N1 N2 N3 N4 N5 N6 N7 N8 N9 N10 N11 N12 N13 N14 N15 .0
2
4
6
8
10
12
14
16
Ra
dia
tio
n a
tte
nu
atio
n p
erc
en
tag
es,
%
Am-241
Cd-109
I-131
Tc-99m
Figure 4.
Highlights
The strength and radiation shielding properties of clay and some soils were
examined.
All tests were performed on compacted soil in optimum water content.
Clay-white cement mixtures have the highest unconfined compression
strength.
Clay-white cement mixtures have the highest linear attenuation coefficient.
Clay-white cement mixture can be used as building materials in radioactivity
places.