Author’s Accepted Manuscript

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

This is a PDF file of an unedited manuscript that has been accepted forpublication. As a service to our customers we are providing this early version ofthe manuscript. The manuscript will undergo copyediting, typesetting, andreview of the resulting galley proof before it is published in its final citable form.Please note that during the production process errors may be discovered whichcould affect the content, and all legal disclaimers that apply to the journal pertain.

www.elsevier.com/locate/radphyschem

1

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 : heroglu@atauni.edu.tr

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.

3

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.

6

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:

9

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.

12

[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.

14

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.