Radiation Environment and Medicine 2023 Vol.12, No.1 74–79

ReportEstimation of Radiation Field Produced by a Coin-shaped Naturally
Radioactive Source and Its Application to School Education
Hiromi Koike1*, Takao Kawano2 and Takeshi Iimoto1
Department of Environment Systems, Graduate School of Frontier Science, The University of Tokyo,
5-1-5, Kashiwanoha, Kashiwa-shi, Chiba 277-8563, Japan
2
Japan Shield Technical Research Co., Ltd.; 276, Motomiyaboyashiki, Motomiya-shi, Fukushima 969-1113, Japan
1

Received 16 May 2022; revised 21 November 2022; accepted 22 November 2022

Naturally radioactive sources were developed using three easily available and familiar substances:
potassium chloride, instant coffee, and kelp. The radiation fields that they generated were actual
measurements using various instruments to adapt the sources to school radiation education. It wasquantitatively found that the potassium chloride source can be used for qualitative experimentson β -rays. The latest national Courses of Study published by the Ministry of Education, Culture,
Sports, Science, and Technology (MEXT) have been applied since 2020. By the results of ourmeasurements with the Courses of Study, an example of experimental training using naturally
radioactive sources: “Absorption training Experiment of β -rays Using Shielding Materials” wasdeveloped. We believe that the widespread application of naturally radioactive sources made offamiliar materials will make it easier for schoolteachers to carry out radiation experiments in theirclasses and contribute to establishing the publicʼs literacy on radiation.
Key words: radiation education, naturally radioactive source, National Courses of Study, Naturally
occurring radioactive materials (NORM)

1. Introduction
Radiation is relevant to many fields, including energy,
medicine, and industry, and is of interest from a varietyof perspectives, not only as a target for active use but
also as a potential source of risk. The Japanese Ministryof Education, National Culture, Sports, Science, andTechnology (MEXT) was preparing to strengthenradiation education based on the National Coursesof Study, which was enforced in 2012, and to provide*Hiromi Koike: Department of Environment Systems, Graduate School of Frontier
Science, The University of Tokyo, 5-1-5, Kashiwanoha, Kashiwa-shi, Chiba 2778563, Japan
E-mail: 7712372897@edu.k.u-tokyo.ac.jp
https://doi.org/10.51083/radiatenvironmed.12.1_74
Copyright © 2023 by Hirosaki University. All rights reserved.

educational guidelines from kindergarten to high school.
At that time, radiation-related topics were mostly coveredin science, but in response to the situation after the
Fukushima Daiichi Nuclear Power Plant accident in2011, the policy was changed to cover radiation not only
from the scientific perspective but also from the disasterprevention and morality ones. The status of radiation
education in schools is revealed in a survey conductedby MEXT covering elementary schools and juniorhigh schools, high schools, and special-needs schools
throughout Japan (2019 - 2020)1).
There is no doubt that experiments in education
generally play a major role in effective learning and deep
understanding. The general theory should also be applied
to radiation education. However, one of the reported
problems relating to radiation experiments in schools

Hiromi Koike et al./ Radiation Environment and Medicine 2023 Vol.12, No.1 74–79

is that they require a radioactive source2). For school
teachers who do not have access to radiation facilities, it
may not be practical to obtain so-called artificial radiation
sources. Even for low-activity sources, which are exempt
from the law, the law does not require the control of thetotal quantity of sources in the establishment, detailed
records of storage, use, disposal, and training for users, butsome source distributors require these actions, thereby
making their use in schools more difficult in Japan3). In
addition, it is hard to get many of them from the market.
As an example of the solution to this problem, the authors
considered developing a radiation source made fromvarious materials found around us. Specifically, dried kelp
and potassium chloride were powdered and compressedin a doughnut-shaped mold for science experiments4). The
materials are readily available and can be produced stably
without chemical manipulation to increase radioactivity
and minimize shape quality5-9). In addition, the use offamiliar materials makes it possible to use the productregardless of people and places, thereby overcoming the
major problems mentioned above. In this study, the fields
created by several naturally radioactive sources developedby the authors were evaluated by actual measurements
using various measuring instruments; and the possibilityof their application to radiation education at school sites
was examined. The target audience for this research
was junior high school and high school students. By
combining these results with the latest Japanese Coursesof Study, which will be applied from the 2020 - 2022 school
year, and by proposing specific experimental practices
using naturally radioactive sources, we aim to expand
the possibilities of implementing radiation education,
especially experimental practices, in schools and othereducational institutions. From a global perspective, Japan
has a good education system, and the same can be said
about radiation education. Therefore, we can demonstrate
the usefulness of this source by showing the possibility
to construct experiments that satisfy this curriculum
guideline and provide a high level of radiation education.
2. Examination of radiation fields produced bynaturally radioactive sources
2.1. Nuclides contained in naturally radioactive sources
and counting rate
The materials for sources selected in this study are (a)potassium chloride (purity 99.5% or higher) (YONEYAMAKAGAKU KOGYO KAISHA, LTD.), (b) instant coffee(Ajinomoto AGF, Inc.), and (c) dried kelp (Kitamae
Bussan). Other candidates include radon daughter
nuclides in air, which are α -emitting nuclides withrelatively short half-lives. However, it is difficult to apply
our source fabrication method detailed in this study to air
as a medium, and we are investigating the possibility of75

Table 1. Radionuclide and counting rate of each material
Material

Radionuclide

Counting rate [cpm/g]

Instant coffee
Kelp
Potassium chloride

K-40

0.048
0.088
0.66

Fig. 1. Naturally radioactive sources(1) Potassium chloride, (2) Instant coffee, (3) Dryed kelp
(Diameter 30 mm, thickness 10 mm)

using them in radiation education in a different system.
To identify the nuclides and calculate the specificcounting rate per minute, each material was powderedand sealed in a U8 type container of 5 cm in height.
The γ -ray energy distribution was measured by apulse height analyzer calibrated at 0.5 keV/ch usinga Ge semiconductor detector (CANBERRA GC2017).
The weights of potassium chloride, instant coffee, anddried kelp samples were 107.62 g, 60.43 g, and 85.20 g,
respectively. The corresponding measurement times were
21600, 518400, 345600 seconds to obtain 10,000 counts
as a peak channel. The measurements were performed
following “Gamma-ray Spectrometry using Germanium
Detector (5th edition)”, the series of environmental
radioactivity measuring methods published by Nuclear
Regulation Authority in Japan10). The obtained results
are shown in Table 1. A strong peak of 40K was observed
at 1461 keV for potassium chloride, instant coffee, anddryed kelp. Each counting rate per 1 g was 0.66 cpm/
g, 0.048 cpm/g, and 0.088 cpm/g in that order, and theirstandard uncertainties were also about 2.5%10). Uranium
and thorium series nuclides were below the backgroundand not detected. The isotopic abundance ratio of 40K in
nature is estimated to be about 0.0117%11), and it is obviousthat potassium chloride chemicals commonly found inschool science laboratories are good source candidates.
It is generally known that kelp contains large amounts ofpotassium as a mineral and dried and concentrated coffee

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Hiromi Koike et al./ Radiation Environment and Medicine 2023 Vol.12, No.1 74–79

beans also have a higher potassium concentration.
2.2. Investigation of radiation field by actual measurement
The selected naturally radioactive sources are shown in
Figure 1. They are fabricated as 1 cm thick flat cylindersof 3 cm diameter and weigh approximately 15 g. For
instant coffee and dryed kelp, if there is no hygiene
problem, by crushing the source and tasting the coffee
after the experiment, or by using the kelp for cooking,we can emphasize the fact that familiar materials emit
radiation. We do not expect the dose to be sufficientenough for quantitative consideration as a radiation
source. Educational tools which expose students to thefact that radiation exists in nature are important, andwe do not completely rule out the use of these sourcesin the school setting. In this study, the emphasis is on
experimentally reproducing and quantitatively discussing
radiation-specific phenomena such as the inverse
square law of distance and transmission. Therefore, therepresentative material is potassium chloride, which has
the highest counting rate, as a source containing 40K.
The changes in radiation flux at different distanceswere evaluated by actual measurements. An end-window
GM survey meter (HITACHI TGS-1146) and a 5 mm
thick aluminum plate were used for γ -rays and an endwindow GM survey meter for β -rays. Assuming a realistic
measurement time for the practical training, the averagevalue was calculated by setting the measurement time to
1 minute and the number of measurements to 3 times perdata set.
This source emits β -rays of 1.312 MeV (max) from40
K. In the case of β -rays, significant counts about six
times higher than the background were shown. Distancedependence on the counting rate of the γ -ray could not beshown in practice due to the competition with backgroundradiation. Emphasizing and recognizing this difference
between β and γ rays can also lead to understanding
the competition between background radiation and net
radiation from the source, i.e., the lower detection limit inradiation measurements, and the difference in detection
efficiency between β and γ rays with the GM survey
meter.
3. Effective use of naturally radioactive sources
following positioning of “radiation” in school
education of Japan
In Japan, school curriculum is based on the Coursesof Study, and classes are also taught according to it.
Therefore, it is necessary to use this radioactive sourcein the school setting based on this curriculum, so weorganize the treatment of radiation in the Courses ofStudy and show that a wide range of experiments can be
conducted according to the studentʼs level of proficiency.

3.1. Environment surrounding radiation as an educational
theme
It is well known that educators in elementary, junior high,and high schools may not have received any radiation
education as students themselves. Therefore, they do nothave sufficient knowledge about radiation or sufficientconfidence in their teaching due to the generally sensitivesocial context of radiation12). Under these circumstances,even if education only using textbooks based on the
Courses of Study by MEXT is implemented at schools, it
is concerning that the content of the textbooks will not
be sufficiently retained, as they only provide superficial
knowledge and information. This paper proposes the useof naturally radioactive sources as an educational tool toovercome this problem. Our goal is to ensure that bothstudents and educators acquire radiation knowledge
appropriate to their level of proficiency and purpose in
the process of using this tool in the field. Specifically, theauthors intend to clarify the relationship between thevarious radiation phenomena observed in experimentswith sources and the descriptions in the Courses of Studyand to make appropriate and effective use of them inschools.
Various studies have been conducted on radiation
education in the Courses of Study. Most of them havefocused on science, especially physics, chemistry, or social
studies13-15), and comparisons have been made between
the old and the new Courses of Study. The descriptionsof radiation in the new Courses of Study are not limited
to physics, chemistry, and social studies, but can also befound in earth science, health and physical education, andhome economics. It should be noted that radiation-related
topics are now positioned as a comprehensive educational
subject, including disaster prevention and morality, in thecurrent trend toward cross-subject education.
3.2. Three pillars of the Courses of Study
The Courses of Study were revised around three pillars
related to student qualities and abilities16, 17). These threepillars are: first, knowledge and skills to live and workin society and daily life; second, the ability to think,judge, and express to cope with unknown situations;and third, the ability to apply what one has learned tolife and society. All subjects emphasize the importanceof balancing knowledge acquisition, application, andexploration to develop abilities and qualities that
address contemporary issues. In radiation education, it isimportant to confirm basic phenomena through classroom
learning and experiments; to “acquire” knowledge andunderstand the relationship between familiar technology
and radiation; to “utilize” it and experience how thetechnology can be used in society; and to “explore” it. In
other words, the combination of authorized textbooks
based on the Courses of Study, the training of teachers

Hiromi Koike et al./ Radiation Environment and Medicine 2023 Vol.12, No.1 74–79

on their use, and practical tools such as experiments withnaturally radioactive sources as described herein will
facilitate a smooth flow and maintain a stable balance
between study and practice.
For example, in science and mathematics education,
students are required not only to acquire knowledge
through classroom lectures, but also to collect data andanalyze them by themselves using statistics, to draw
graphs by making full use of computers to develop theability to utilize information, to actively collect information
to solve problems and to present to others, and so on.
Active learning approaches, such as the use of a computer,or a computer program that uses a computer as a learning
tool, are introduced. In addition, the perspective of disasterprevention and safety education was also emphasizedin the science curriculum, for example, by enhancing
content related to natural disasters. The authors believethat the stakeholders in radiation education should beconstantly aware of this kind of trend in school education,
which is the core foundation of national literacy. Devisingand providing tools and modules that fit the current
trends in the educational field will be a steady path toachieving our goals.
3.3 Radiation education content by grade level
The following content is a summary of the experimental
practices related to each grade and subject based on thelearning items in each subject18). We particularly focus
on junior high and high school students. In junior highschool, there are descriptions of radiation in science,
health and physical education, industrial arts, and home
economics. In science, radiation is treated from the aspectof science. Health and physical education, industrial artsand home economics deal with radiation in terms ofhealth and hygiene. In high school, there are descriptionsof radiation in Basic Chemistry, Basic Physics, Physics,
Geology, Home Economics, and Health and Physical
Education. The main focus of Basic Chemistry, Basic
Physics, and Physics is on the scientific characteristicsof radiation and radionuclides themselves. For example,
the properties and half-lives of γ-rays and other types ofradiation, and the decay of atomic nuclei exist. Geology
focuses on age determination while home economics
and health and physical education focus on the uses ofradiation such as food storage and radiation therapy aswell as the risks to life and health. However, the study
is always treated as scientific knowledge and principles
and its utilization across various subjects. We have theimpression that the explanations of each subject should
not stop at the knowledge of radiation, but focus on
the use of the knowledge and the measures to solve
problems. Scientific experiments are important for
acquiring knowledge, but the experimental design should
be carefully planned so that the content includes the77

Fig. 2. Schematic View of Experiment Proposed for Radiation
Education

Fig. 3. Relationship between Al Thickness and Counting Rateexistence of radiation around us.
In this section, we present a β -ray absorption
experiment using a shielding material as an example.
The experiment plan and discussion points are presented
with the descriptions in the Courses of Study, assuming
application in junior high and high schools. First, theequipment used and the experimental procedure areshown. These items are common to both middle and highschool courses. Figure 2 shows a schematic view of theexperiment.
Equipment- A naturally radioactive source (potassium chloride)- End-window type GM survey meter or educational
instrument for detecting β and γ -rays (GM survey meteris used this time)- Aluminum foil (12 µm thick)Experimental Procedure(1) Turn on the end-window type GM survey meter.
(2) Set the time constant to 30 seconds.
(3) Without placing the source, wait for about 1.5 minutes
and measure the background counting rate after itstabilizes.
(4) Place the source and detector such that the distance
between the source and the detector surface is 0 cm
and then count without aluminum foil.

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Hiromi Koike et al./ Radiation Environment and Medicine 2023 Vol.12, No.1 74–79
Table 2. Original Data of β-ray Absorption Experiment by Shielding
Number ofaluminum foil
2
4
8
16
24
32
40
42
48
56
64
72
74
76
78
80
82
88
90
Background [cpm]Al
thickness[µm]
24
48
96
192
288
384
480
504
596
692
788
884
908
932
956
980
1004
1056
1080

Net counting rate [cpm]Number of measurements
1
2
3
69
70
86
64
73
47
55
61
43
49
47
48
36
32
42
39
33
39
19
26
34
26
21
33
16
29
17
32
12
23
17
2
14
12
5
2
6
7
18
10
10
4
13
8
4
8
10
14
12
7
9
10
4
6
6
3
0
24

(5) Place a piece of aluminum foil between the naturally
radioactive source and the measuring plane and count.
(6) Stack several aluminum foils.
(7) Place the stacked aluminum foil between the source
and the measuring plane and count.
(8) Repeat steps (6) and (7) for varying distances between
source and detector surface
Naturally radioactive sources are less radioactive thanartificial sources. Therefore, the time constant was set
as long as 30 seconds to minimize the fluctuation of thevalue and to read the counting rate accurately.
In junior high school, there are units on distanceattenuation and naturally occurring radiation andradioactive materials in second and third-grade science;and on food safety and health in industrial arts, home
economics, and health and physical education. The
Understanding to the principles of radiation and thephysical phenomena produced by fields around thesource is not necessarily required. Since it is sufficient
to recognize the fact that the counting rate decreases
as the thickness of the shielding increases, it is notnecessary to take detailed measurement points, andabout 10 measurement points should be sufficient. In thediscussion, the students are made aware that the counting
rate decreases as the thickness of the aluminum foil
increase, in other words, the phenomenon of shielding in
addition to radiation transparency. For this purpose, thestudents are asked to pay attention to the shape of thegraph and note that it is a rightward sloping graph. Using
the resulting graph to measure thin aluminum sheets of

Average
75
61
53
48
37
37
26
27
21
22
11
6
10
8
8
11
9
7
3

Std.error
9
8
7
7
6
6
5
5
5
5
3
3
3
3
3
3
3
3
2

unknown thickness also contributes to the study of theprinciples of thickness gauge. The process of recording
data is also effective for learning basic experimental
data handling through the calculation of uncertainty andaverages of radiation measurements and graphing of data.
The content of study in high school is more scientificallyand technologically advanced. In physics, for example, one
can relate radiation shielding to the interaction of nuclei
with the matter, understand the shape of the decay curve,
and read its principle. Here, the measurements weretaken every 48 µm, which is equivalent to four aluminum
foils, after a thickness of several hundred µm, where theeffects of bremsstrahlung begin to be seen under thisexperimental system; and every 96 µm, equivalent toeight aluminum foils, in the other parts of the specimen.
Figure 3 and Table 2 show an example of the relationshipbetween the thickness of the aluminum foil and thenet counting rate excluding the effect of backgroundcounting, as well as the original data. According to thisexperimental situation, the counting rate decreases
almost linearly up until 700 μm, but after 700 μm, it
gathers around 9 cpm and does not reach 0 cpm. Thisis due to the counting of bremsstrahlung from β -rays.
Students can calculate the coordinates of the intersection
with the x-axis from the slope of the measurement points
in the range where the effect of bremsstrahlung is small
and can estimate the range of the β -rays. Radionuclides
in naturally radioactive sources and their β -ray energies
can also be examined, and the information can be used
to determine the maximum range within the shielding
body. Thus, by appropriately combining classroom

Hiromi Koike et al./ Radiation Environment and Medicine 2023 Vol.12, No.1 74–79

lectures using textbooks based on the Courses of Studyand experiments such as those proposed in this paper,radiation education of high quality and depth can be
developed. Even if the same sources and tools are used,
it should be possible to construct an educational modulethat matches the proficiency level of the students andthe purpose of education by devising the experimental
procedures and the content of the discussion.
The detailed relationship between the lineup of
school experiments organized by proficiency level andthe descriptions in the Courses of Study, including theexample using these sources presented in this paper, will
be published in a separate report shortly.

References
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4. Conclusion
Naturally radioactive sources were developed using
potassium chloride, instant coffee, and dried kelp. Theircharacteristics as radiation sources are presented. The
materials contained mainly 40K, but it was quantitatively
clear that potassium chloride sources could be used for β-ray experiments.
If naturally radioactive sources made from familiar
materials become more widely available, radiation
experiments in schools will become easier to conduct,
which will contribute to the expansion of radiation
education. The results also suggest that the use of thissource can provide a high level of radiation education andthat it is possible to teach about β radiation in a way thatsatisfies the Courses of Study in Japan.
In the future, we would like to enhance educational
programs, worksheets, and manuals so that school
teachers can easily understand and conduct theexperiments. We hope that these naturally radioactive
sources and their application will increase the number ofteachers and students who are interested in radiation.
Acknowledgments
We would like to express the heartfelt thanks to Mr.
Toshiaki Hagiwara, Mr. Takuya Shiina, Mr. Shogo
Akabori, Mr. Takahiro Yamashita, and Ms. Natsumi
Asano of the Japan Radioisotope Association for theirsupport for various measurements in conducting thisstudy, and Mr. Tomohisa Kakefu and Mr. Taichi Kato of
the Japan Science Foundation for advice on the status ofradiation education at schools. The authors would like toexpress their sincere appreciation for their cooperation.
This work was partially supported by ERAN Y-21-13.
Conflict of interest
The authors declare that they have no conflict of interest.

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