Isobe et al.

Note

Radiation Safety Management Vol. 22 (1–6)

Shielding Ability of a Novel Iron Ceramic Material for Gamma-Rays
Midori ISOBE1), Hiroyuki MORI2), Narufumi OKADA2), Yuriko MANNAMI2),
and Hiroaki TERATO1)*
1)

Advanced Science Research Center, Okayama University, 2-5-1 Shikata-cho, Kita-ku, Okayama 700-8558, Japan2)
Mitsuishi Taika Renga Co. Ltd., 868 Mitsuishi, Bizen 705-0132, Japan
Received Aug. 9, 2023; accepted Oct. 16, 2023    Radiation shielding is one of the necessary procedures in radiation protection. The lead blocks arecommonly used to shield against gamma- and X-rays. However, due to lead’s biotoxicity, the development ofalternative materials is required. We developed a novel ceramic product as a non-biotoxic shielding material
composed mainly of iron (III) oxide. In this study, the radiation shielding performance against gamma-rays wasevaluated and its potential as a radiation shielding material was investigated. We measured the gamma-ray amounttransmitted through the ceramic specimens using a NaI scintillation counter with three different gamma sources(133Ba, 137Cs, and 60Co). The order of shielding ability of the sample with the same volume was lead > iron > theceramics. The effects of piling the blocks and the type of jointing agent used in the gaps on the shielding ability
were also observed for considering actual use.
      Key Words: gamma-rays, shielding, attenuation, half-value layer, ceramics[doi:10.12950/rsm­.230809]

1.   Introduction

radiation-controlled areas because it takes advantage of the

avoid unnecessary external exposure. There are various ways toshielding material should be selected according to the type andOne of the most important aspects of radiation work is toachieve this object, such as using tongs and remote control tokeep distance from the source, rational experimental design,and skill training to reduce exposure time and shielding withattenuation of radiation. As mentioned above, the appropriate
energy of the radiation. For shielding against gamma- andX-rays, lead has been most used, and lead blocks are often
piled together in front of any radiation source.1) Concrete andappropriate materials.

iron have been used for shielding walls and other large-areathat between radiation and the atom or molecule, while theshielding ability than lead, so it must be thicker for shielding

The microscopic aspect of radiation-matter interaction ismacroscopic aspect is the attenuation of radiation passing

through the matter. The manner of attenuation depends largely

applications for cost reasons. However, concrete has a weakeruse. Among these three materials, lead has the highest shielding
ability, but lead has a biotoxicity as well known.2) For thison the type and energy of the radiation and material

reason, the use of lead is becoming contraindicated.3) The

and activation occurs, in which the material becomesabundant element in nature. It is also easily processed andcharacteristics. In some cases, secondary radiation is generated,radioactive.

Shielding is one of the procedures necessary for work in* Advanced Science Research Center, Okayama University, 2-5-1
Shikata-cho, Kita-ku, Okayama 700-8558, Japansecond highest shielding ability is iron. Iron is the mostinexpensive and is often used as a shielding material. The
weakness of iron is that it rusts. To avoid this, the surface may
E-mail: hiroakiterato@okayama-u.ac.jp
Tel: +81-86-235-7496

1

A Novel Ceramic Shielding

A

B

C

D

Fig. 1. The plate materials in this study. These are the ceramic (A), iron (B), lead (C), andconcrete (D). These are squares with 10 cm on each side. The thicknesses are 1 cm for theceramic, iron, and lead plates, and 5 cm for the concrete one.

be painted. However, it is difficult to use outdoors where it may

blocks are often covered with a jointing agent in common

Based on the above, various efforts are being made regarding

surface of the block was also examined, and the difference in

get wet.

radiation shielding materials. For example, in various concrete,heavy concrete is used as shielding material. Ceramics is also
4)tested to find more optimal materials.5) We developed a ceramic

blocks. Therefore, the jointing agent that fills the contact
shielding ability between the different types of jointing agentswas also studied.

made with iron (III) oxide (Fe2O3) expected to be a novel toxic-2.   Materials and Methods

already in practical use, though chemical analysis of its

the previously reported procedure, whose main ingredient isperformance of this material against gamma-rays was evaluatedbelow. A powder containing 99% iron oxide was fabricated into

free shielding material named RASHIX.6) This material isproperties is still needed. In this study, the radiation shielding

in detail, and its potential as a radiation shielding material was
examined. As a result, this ceramic was found to be useful as an

The ceramic products used in this study were produced byiron (III) oxide.6) A brief description of how to make it is given
specimens by pressing gently into an iron mold, and then it was

pushed and hardened with 3 MPa/cm2. The specimen wasalternative shielding material to lead.

subjected to a firing process up to 1,320°C and then cooled atshielding material near the source of radiation. There is a risk

preparation are referred to our previous report.6)

The shielding material is often used by piling up blocks ofof radiation leakage through gaps between the blocks. In thisstudy, two approaches were taken to address this issue. One isroom temperature for 10 days. Other details related to sample
To investigate the shielding ability, plate-like samples of

1 cm in thickness and 10 cm in height and width were prepared,

to change the shape of the blocks. The contact surface between

and the required number of plates were piled on top of eachblocks with a mountain-shaped concave-convex contact surface

were lead and iron plates of the same shape and a piece ofblocks is flat in general blocks (straight gap). Here we created(offset gap) and evaluated the radiation leakage. Gaps between

2other. Controls for the shielding ability evaluation experiments
concrete of 5 cm in thickness, 10 cm in height and width (Fig.

Isobe et al.

1). To evaluate the effect of block piling, the ceramic blocks

aperture with a side length of 2 cm using a lead block, and thecomparison of radiation leakage during the piling gap, 5 cm inradiation source and the detector was 20 cm. The detector usedwith 5 cm thick, 10 cm height, and 20 cm width were used. For
length was prepared and used for piling. The blocks were piledin three differently shaped blocks without a gap, with a straight

gap, and an offset gap (Fig. 2). The offset between the centerand both ends of the block is 5 mm.

The jointing agents used were prepared by mixing theradiation dose was measured. The distance between thefor the measurements was a Nal (Tl) detector (Universal Scaler
TPC-501, Aloka, Japan) with a diameter of 5 cm. The
measurement time was 30 seconds, and measurements weretaken 10 times for the same sample.

The sample was 1 cm-thick ceramic plates as mentioned

materials listed below. Epoxy resin was purchased fromabove, and the amount of the radiation that passed through

Crucible Co., Ltd., Japan. Fuji Light#10 and Sealex were made1 cm to 10 cm. Similarly, the shielding ability of 1 cm-thick

Konishi Co., Ltd., Japan. Super3000SW was from Nippon
by Fujikawa Kenzai Co., Ltd., Japan. The sticky rice was from

Okayama Pearl Rice Co., Ltd., Japan. Iron sand was from Kato
Hikinzoku Kogyo Co., Ltd., Japan. Borax sand and Boric acid

were from Borax Tech, United States, and Ohara & Co., Ltd.,
Japan, respectively.
andThree different gamma-ray sources including 133Ba, 137Cs,
60

Co were used to determine the radiation penetration

them was measured when the thickness was increased fromsteel, lead, and 5 cm-thick concrete plates were compared bymeasuring the amount of radiation that passed through them atsimilar thicknesses. Ten measurements were taken at a time,

and the mean value and standard deviation were calculated. The
obtained values were statistically processed and examined fortheir certainty.

The amount of radiation passing through the gap between

ability. The radio activities of these gamma sources were

the blocks was measured when the 5 cm-thick ceramic blocks

attenuation calculation obtained these radio-activities values onblocks without or with different gaps as mentioned above (Fig.

1,028.7 kBq, 3,598.0 kBq, and 154.3 kBq, respectively. The
September 1st, 2019. These gamma sources were obtained fromJapan Radioisotope Association, Japan. The energies of the
gamma-rays from133

Ba and137

Cs are 356 keV and 662 keV,

respectively. 60Co releases two gamma-rays with 1,173 and1,333 keV. Therefore, the average of these two gamma-rays,
1,253 keV, is used in the discussion. The radiation beam fromthe radiation source was guided to the sample through a squareA

B

were piled. The blocks were piled in three differently shaped2). The offset between the center and both ends of the block is 5

mm. For using those shaped blocks, the amount of radiation
leaking through the gaps between the blocks was compared. We

also measured the amount of radiation that passed through thegaps between the blocks when they were filled with jointing

agents. The jointing agents used were (1) epoxy resin, (2)Super3000SW, (3) Fuji Light #10, (4) sticky rice, (5) epoxy

CFig. 2. The block-shaped ceramic used in this study. The size of each block is 18 cm(width)×10 cm (height)×5 cm (depth). We used three types of blocks without a gap (A),with a straight gap (B), and an offset gap (C). The offset between the center and both endsof the block is 5 mm.

3A Novel Ceramic Shielding

resin (90%) + iron sand (10%), (6) Super3000SW (80%) + ironsand (20%), (7) Fuji Light #10 / Sealex, (8) Fuji Light #10 /A

100000

Sealex (60%) + iron sand (40%), and (9) sticky rice / borax /10000

boric acid.

Count

1000

3.   Results and Discussion

The shielding ability of the novel ceramic material was100

examined using three different sources emitting gamma-rays

10

ceramic, we used iron, lead, and concrete for references. We set

1with different energies. To compare the shielding ability of the
1 cm thick plates (Fig. 1) made of them between the gamma

source and detector, and the shielding ability was evaluated bymeasuring the dose of gamma-rays that passed through the

B

10000

source decreased (Fig. 3). This phenomenon was similar for all

1000

Count

piled, the dose of gamma-rays reaching the detector from thecalculated the half-value layers and used them to compare the10highest shielding ability for all three different gamma-rays,

1of each material for each gamma-ray show that lead has thefollowed by iron, then the ceramic, and finally concrete (Table

and 662 keV, respectively, while 60Co emits gamma-rays of

C

10

12

0

2

4

6

8

10

12

10

12

1000

Count

The measured densities of lead, iron, the ceramic, and concrete

8

10000

proportional to the strength of the gamma-rays. From thethe shielding ability was proportional to the respective density.

6

Thickness (cm)Thickness (cm)

1,173 keV and 1,333 keV. The half-value layer was naturally
shielding material’s point of view, the trend of the strength of

4100

shielding ability of respective materials. The half-value layers

1). The gamma-rays emitted from 133Ba and 137Cs are 356 keV

2100000plates and reached the detector. As more and more plates wereradiation types and all shielding materials. From these plots, we0100

are 1104.8, 798.6, 493.4, and 228.9 kg/m3, respectively. The

10

45% that of lead and 2.2 times that of concrete. The linear

1

iron oxide ceramic whose density is 62% that of iron. It is also
attenuation coefficient (μ) for60

Co gamma-rays is 0.162 and0.254 for the ceramic and iron, respectively. Dividing these by

their respective densities to obtain the mass attenuation
coefficients (μ/ρ), the results are 0.033 and 0.032 for theceramic and iron, respectively, which are in close agreement.

This means that the ceramic consists of pure iron (III) oxide(Fe2O3) and that the shielding ability is almost the same for thesame mass. The above suggests use of the ceramic as a
substitute for other shielding materials.

Lead and concrete blocks used for shielding are usually

piled on top of each other. In such cases, radiation leakage fromgaps between the blocks becomes a problem. We here

compared and quantified the leakage of radiation from two

4

0

2

4

6

8

Thickness (cm)Fig. 3. Shielding capacities of plate samples for gamma-rays
133
137
60
from Ba (A), Cs (B), and Co (C). The plots are the ceramic(open circle), iron (closed triangle), lead (closed rectangle),and concrete (closed circle), respectively. Each count is themean of 10 independent experiments, with standard deviations
shown as bars, although some of the standard deviations are
small and hidden by markers. The counts were obtained from30-second measurements. Each value is from ten independent
experiments, and the representation consists of the average ±standard deviation.

Isobe et al.

Table 1

Half-value layers of plate materials.

Shield material

Ba-133

Cs-137

Co-60

The ceramic

0.935±0.018

2.066±0.017

4.038±0.033

Iron

0.282±0.011

1.176±0.021

2.496±0.082

Lead

0.199±0.003

0.533±0.006

1.272±0.078

Concrete

2.964±0.028

4.868±0.044

8.729±0.298

Footnote: The half-value layers are expressed in terms of length (cm) in this table. The
respective values are from the ten independent experiments, and the representationconsists of the average±standard deviation.

different types of gaps with the piled ceramic blocks and6.0

compared two types of piling, one with a straight gap and theother with an offset gap (Fig. 2). We also used one without a
gap as a control. The results of the experiment showed that theshape with no gaps had the lowest radiation leakage for all
three types of gamma-rays, followed by the mountainous shape,

and the straight shape had the highest radiation leakage (Fig.
4). The shielding capacities for 133Ba gamma-rays were 88.7%

and 51.2%, respectively, with no gaps as 100%. The capacity
for

137

Cs gamma-rays was 89.0% and 67.2%, respectively. And

the capacity for60

Co gamma-rays, 85.8%, and 78.7%,

respectively. Although the offset gap had a higher shielding
capacity compared to the straight shape, it still showed anincrease in leakage of more than 10% compared to the no-gap

shape. This will be discussed later in the jointing agent
experiments.

When the effect of piling blocks on shielding was examined

Half value layer (cm)examined the effect of radiation leakage on the shielding. We

5.0
4.0
3.0
2.0
1.0
0.0

Ba-133

Cs-137

Co-60

Fig. 4. The half-value layers of piled block samples werecompared for the respective type of gamma radiations,
133
137
60
Ba,
Cs, and Co. The shape of the piling are straightgap (closed bar), offset gap (gray bar), and no gap (openbar). The exact shape is in Fig. 2. Each value is from ten
independent experiments, and the representation consists of
the average ± standard deviation.

in the last experiment (Fig. 4), an increase in leakage dose ofagents that most improved the shielding ability were Fuji Light

gap. Although it cannot be used for various experiments in

gamma-rays. The improvement ratio was 1.1 to 1.3 times,

reduction could be achieved by filling the gaps with a jointing

forming in this study. This means that offset molding and themore than 10% was observed regardless of the shape of theirradiation chambers, it was considered that the leakage dose
agent when used in a fixed condition, such as an internal
shielding material in a wall. Therefore, we observed the effectof jointing agents on shielding by filling the gaps in the straightshape of the ceramic blocks with various jointing agents. The#10 for 133Ba and 137Cs gamma-rays and sticky rice for 60Co

which was almost the same as that of the straight-to-offset
use of jointing agents have almost the same effect, suggestingthat there is little need for the former, which is more cost andtime-consuming in process and storage.

In the above, we measured the gamma shielding ability of a

jointing agents were epoxy resins and other commercially

new iron oxide ceramic material and discussed its ability as aExperimental results showed that the jointing agents could

field,6) and the fact that we were able to confirm its accurate

available products, either alone or mixed (Table 2).
improve shielding capacity, although the effectiveness variedamong the different types of jointing agents. The jointing

shielding material. This new material is already in use in theshielding capability in this study may provide importantsuggestions for the rationalization of shielding in the future. On

5

A Novel Ceramic Shielding

Table 2

EŠect of jointing agents for half-value layers of block materials.
Jointing agents

Ba-133

Cs-137

Co-60

Control (no ˆlling)

1.825±0.015

3.074±0.023

5.133±0.101

Epoxy resin

1.662±0.014

2.890±0.022

4.742±0.087

Super3000SW

1.793±0.020

3.075±0.020

5.029±0.141

Fuji Light #10

1.356±0.012

2.745±0.013

4.592±0.082

Sticky rice

1.669±0.013

2.792±0.013

4.590±0.070

Epoxy resin＋iron sand (9:1)

1.799±0.016

3.068±0.025

5.065±0.112

Super3000SW＋iron sand (8:2)

1.837±0.016

3.106±0.030

5.142±0.139

Fuji Light #10/Sealex

1.767±0.017

2.966±0.050

4.801±0.134

Fuji Light #10/Sealex＋iron sand (6:4)

1.808±0.023

3.042±0.014

5.049±0.087

Sticky rice/Borax/Boric acid

1.412±0.032

2.908±0.014

4.733±0.097

Footnote: The half-value layers are expressed in terms of length (cm) in this table. The respective values arefrom the ten independent experiments, and the representation consists of the average±standard deviation.

the other hand, further study is needed to safely put thismaterial to practical use. For example, studies on the generationof secondary radiation when high-energy beta-rays passthrough it and on its activation when neutron-rays pass throughit. Despite the remaining issues, the ceramic material examinedin this study can be used as one of the new non-toxic and usefulshielding materials.

4.   Acknowledgments

This research was conducted under the joint research

agreement between Okayama University (HT) and Mitsuishi
Taika Renga Co., Ltd. We thank Dr. Toshiro Ono (Okayama

Healthcare Professional University as current affiliation) and
Dr. Naoyuki Osada (Osaka University as current affiliation) for
their preliminary experiments during their tenure at Okayama
University.

6

References

1. Thoraeus, R.: Attenuation of gamma radiation from 60Co, 137Cs,
192
Ir, and 226Ra in various materials used in radiotherapy. Acta
Radiol., 3, 81–86 (1965).

2. Environmental Health Criteria 85, Lead—Environmental Aspects:
World Health Organization (1989).
3. Tajani, A., Maasikas, M.: Directive (EU) 2017/2102 of theEuropean Parliament and of the council. Off. J. Eur. Union,
32017L2102 (2017).
4. Mostofinejad, D., Reisi, M., Shirani, A.: Mix design effective
parameters on γ-ray attenuation coefficient and strength of normal
and heavyweight concrete. Construct. Building Materials, 28,
224–229 (2012).
5. Jawed, A. A., Demirkol, N., Gunoglu, K., Akkurt, I.: Radiation
shielding properties of some ceramic wasted samples. Internat. J.
Environment. Sci. Technol., 16, 5039–5042 (2019).

6. Mori, H., Oku, Y., Mannami, Y., Kunisada, T.: Iron (III) oxidebased ceramic material for radiation shielding. Ceramics, 3, 258–
264 (2020).