Basic Knowledge ofRadiation and Radioisotopes(2019)(Scientific Basis, Safe Handling ofRadioisotopes and Radiation Protection)

Japan Radioisotope Association

Contents

I. Introduction............................................................................................... 1
1. The Role of Radiation Workers ................................................................ 1
II. Scientific Basis .......................................................................................... 3
1. Structure of Atom..................................................................................... 3
2. Structure of Atomic Nucleus ................................................................... 5
3. Isotopes.................................................................................................... 6
4. Radioisotopes and Radioactivity .............................................................. 8
5. Half-Life of a Radioisotope ..................................................................... 9
6. Types of Radioactive Decay......................................................................11
7. X-Rays ................................................................................................... 19
8. Accelerators ............................................................................................ 21
9. Types of Radiation ................................................................................. 22
10. Quantities and Units Related to Radiation .............................................. 24
III. Safe Handling.......................................................................................... 29
1. Who is the Radiation Protection Staff? ................................................. 29
2. Protection Against External Exposure.................................................... 31
3. Protection Against Internal Exposure ..................................................... 33
4. Attitude when Handling Radioisotopes and Radiation ............................ 37
5. Radiation Monitoring ............................................................................. 39
6. Education and Training .......................................................................... 47
7. From Procurement to Waste Management of Radioisotopes ................... 49
8. Usage of Radioisotopes and Radiation Generating Apparatuses.............. 51
9. Storage of Radioisotopes ......................................................................... 53
10. Discharge of Radioisotopes from Facilities and Radioactive Waste
Management ........................................................................................... 55
11. Record Keeping (Radioisotopes Tracking) ............................................. 57
12. Record Keeping (Dose)........................................................................... 59
13. Health Surveillance ................................................................................ 61ⅰ14. Procedures at the Time of on an Accident or Emergency .................... 63
15. Procedures in the Event of Excess Exposure or Contamination............ 65
IV. Biological Effects of Radiation ............................................................... 67
1. Classification of Radiation Effects on the Human Body............................ 67
2. Acute Effects ......................................................................................... 68
3. Late Effects............................................................................................ 69
4. Heritable Effects..................................................................................... 70
5. Biological Effects Depend on the Dose Received .................................. 71
6. Effects from External and Internal Exposures ....................................... 73
7. What is Equivalent Dose? ...................................................................... 75
8. What is Effective Dose?......................................................................... 77
9. Assessment of Internal Dose ................................................................. 80
10. Natural Radiation and Artificial Radiation ............................................. 82
11. Radiation and Health Effects ................................................................. 84
12. Exposure Categories .............................................................................. 86
13. Risk........................................................................................................ 88
14. Limits on Personal Exposure ................................................................. 90
V. The Act and Regulations............................................................................... 93

1. Act on the Regulation of Radioisotopes, etc. ................................................. 93
2. Hierarchy of the Act and Relevant Regulations.............................................. 95

3. Acts and Regulations Concerning Radiation................................................ 97

4. What is the Act on the Regulation of Radioisotopes, etc.? ......................... 99
5. Acts and Regulations to Protect Workers ........................................................ 100
6. Who are Radiation Workers?

.................................................................... 102

7. Who are Radiation Protection Supervisors? ..................................................... 104
8. What is Radiation under Acts and Regulations? .............................................. 106
9. What is Radioisotopes? ...................................................................................... 108
10. What is Radiation Generating Apparatus? ........................................................ 109
11. What are Sealed Radioisotopes? ............................................................... 110

ⅱ

12. What is the Controlled Area? ................................................................................ 112
13. What is meant by“Radiation Levels outside Controlled Areas”? ..........................................114
14. Secure Specified Radioisotopes Manager............................................................. 115
VI. Radiation Hazards Prevention Program ............................................................... 116
1. What is the Radiation Hazards Prevention Program? .......................................... 116

Appendix1. Sign ..............................................................................................................120iii

Ⅰ. Introduction

Ⅰ.Introduction

1.

The Role of Radiation Workers

The purpose of “the Act on the Regulation of Radioisotopes, etc.”, with
relevant Cabinet order, Enforcement regulation and Notification etc. (hereinafterreferred to as “the Acts and Regulations”), is not only to minimize the radiation
exposure of individual workers and the public, but also to ensure the safety ofpeople by preventing contaminations in both the workplace and the generalenvironment. To satisfy this purpose, it goes without saying that facilities andequipments should be well maintained. But there are many areas where little canbe achieved without the cooperation of the radiation workers themselves. That is
to say, it is difficult to attain the purpose of the Act without appropriate handling ofradiation and radioisotopes by radiation workers, no matter how much effort is put
into maintaining facilities and equipments. Being aware of how to protect
themselves, as well as the significance of their role in radiation protection
management, each radiation worker must cooperate with others at his or her
workplace.
1-1. What knowledge must radiation workers have?
In order to deal with radiation and radioactive materials safely at theirworkplace and to attain the goal of radiation protection, radiation workers must
understand at least the following:
1)
2)
3)
4)
5)

Basic provisions of the Act on the Regulation of Radioisotopes, etc.;
Basic physics of the radioactive materials that they handle;
Biological effects of radiation;
Techniques for preventing contamination;
Methods for radioactive waste management; and6) How to deal with abnormal and emergency situations.

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I. Introduction

Fig. 1 What knowledge must radiation workers have?

2

II.

Scientific Basis

Ⅱ. Scientific Basis
1.

Structure of Atom
The structure of an atom is similar to that of the solar system.

All objects are composed of atoms. At the center of each atom is a nucleus
with a positive electric charge, around which electrons with the negative charge aremoving along fixed orbitals. These electrons are called orbital electrons. This
structure can be compared to the solar system, where planets are orbiting aroundthe sun.
Normally, the positive charge of the atomic nucleus is equal to the total
negative charge of the orbital electrons, and the atom as a whole is electricallyneutral. When external energy is applied to an atom, an orbital electron may bekicked out of its orbital, becoming a free electron no longer bound to the nucleus.
The atom then remains as a positively charged ion. This phenomenon is called
ionization.
Sometimes, the application of external energy may cause an orbital electron
to move to an orbital further from the nucleus, leaving the nearer orbital position
vacant. Such an atom is said to be excited.
The diameter of an atomic nucleus ranges from 10-15 to 10-14 m, with theorbitals of the electrons extending much further out. The size of the entire atom
is of the order of 10-10 m. If, for example, the atomic nucleus is pictured as being
the size of a tennis ball, then the orbital electrons would be as far as 5 kilometers
away.

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Scientific Basis

Fig. 2 Structure of a helium (He) atom: The charge (e) on each electron iscalled elementary electric charge. The helium nucleus has a positive charge
twice that of the elementary electric charge, balancing the two orbital electrons.

Fig. 3 Ionization and excitation of a beryllium atom

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Scientific Basis

2. Structure of Atomic Nucleus
The atomic nucleus consists of two kinds of particles, protons andneutrons.
The atomic nucleus consists of protons, which are positively charged, andneutrons, which have no charge. The positive charge of a proton is equal, but
opposite, to the negative charge of an electron. The mass of a proton isapproximately 1,840 times that of an electron; the mass of a neutron is almost thesame as, but slightly larger than, that of a proton. Thus, because an electron isso much lighter than either a proton or a neutron, the mass of an atom can bedeemed to be essentially equal to the mass of its nucleus.
The particles that make up the nucleus, i.e. the protons and neutrons, are called
nucleons. Nucleons are held together by what is called the nuclear force, which
overcomes the naturally repulsive tendency of the positively charged protons.
The number of protons in a nucleus is normally the same as the number oforbital electrons around the nucleus. The chemical nature of an atom is determinedby the number of protons in its nucleus. This number is called the atomic number,and it defines a chemical element.
Atomic number = number of protons in an atomic nucleus= number of orbital electrons in a neutral atom

Fig. 4 Just as a drop of water looks like a single structure but actuallyconsists of a great number of molecules, the atomic nucleus is composed ofindividual protons and neutrons.

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Scientific Basis

3. Isotopes
Isotopes are atomic brothers.
The type of an atomic nucleus is determined by the number of its protons andneutrons. When two atoms have the same number of protons but a different numberof neutrons, they have different masses, but the same chemical nature. That is tosay, they are the same element. These atoms are like brothers, and are calledisotopes.
In order to distinguish among isotopes, the total number of protons andneutrons (called the mass number) is shown at the upper left of theelement's symbol. The atomic mass is roughly expressed by the mass
number.
Mass number = number of protons + number of neutrons
Hydrogen (H, atomic number 1) is an element with one proton, and exists inthree isotopes: 1H, 2H and 3H. 2H is called deuterium (D), also known as heavyhydrogen, and 3H is called tritium (T).
In elements having smaller atomic number, light elements, the number ofneutrons is more or less equal to the number of protons, but, in elements having
larger atomic number, heavy elements, the number of neutrons exceeds the numberof protons. For example, the nucleus of 16O consists of eight protons and eightneutrons, but the nucleus of 226Ra (atomic number 88) has 88 protons and 138
neutrons.

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Scientific Basis

Fig. 5 Hydrogen isotopes: In all cases, the nucleus has one proton.

Fig. 6 Oxygen isotopes: In all cases, the nucleus has eight protons.

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Scientific Basis

4. Radioisotopes and Radioactivity
Isotopes that spontaneously give off radiation and whose nuclei decay
into other types of nuclei are called radioisotopes. Instead of the“radioisotope”, the terms “radionuclide” or “radioactive nuclide” are often
used.
Among isotopes, there are some in which the nucleus emits radiation and isconverted into another type of nucleus spontaneously, i.e. without the applicationof any external condition, such as pressure, temperature, chemical treatment, etc.
These are called radioisotopes. This property is called radioactivity, and theconversion of the nucleus is called radioactive decay or disintegration. Emitted
radiation can be in the form of alpha rays, beta rays, gamma rays, or others. The
nucleus before decay is called the parent, and the one after decay is called theprogeny (or daughter).
Approximately 70 kinds of radioisotopes exist in nature. These include
uranium, thorium, radium, and potassium( 40K). In addition, there areapproximately 3,000 kinds of radioisotopes that have been created artificiallyusing nuclear reactors or accelerators.
The term “activity” is used to describe the magnitude of radioactivity, theunit for which is the becquerel (Bq), the number of decay events per second.
1 becquerel = 1 decay event per second
The old unit of activity curie (Ci), which was defined originally based on theactivity of 1 gram of 226Ra, is related to the becquerel as shown in the following
equations:
1 Ci = 3.7 × 1010 Bq
1 Bq = 0.2702…× 10-10 Ci ≈ 27 pCi

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Scientific Basis

5. Half-Life of a Radioisotope
A radioisotope has an inherent half-life.
Let us think of a group of atoms of a radioisotope. As the individual
atoms decay (i.e., as their nuclei decay), they are converted into another type of
atom. The time required for the number of atoms of the radioisotope to become
half their original number, namely, for half of them to be converted into anothertype of atom, is called the “half-life”. The activity of a certain amount of theradioisotope is in proportion to the number of original atoms remaining.
Half-life is inherent to a radioisotope, and is not affected by external
conditions, such as temperature or pressure. Half-lives vary among the kinds ofradioisotopes, from more than several billion years to only a very small fraction of
a second.
Fig.7 shows the decrease in activity over time. Activity measured as 1MBq
becomes 0.5 times of 1 MBq after one half-life; 0.25 times of 1 MBq after two
half-lives; and 0.125 times of 1 MBq after three half-lives.

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Scientific Basis

Fig. 7 Decrease in activity: Activity is reduced by half with the passageof each half-life (T).

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Scientific Basis

6. Types of Radioactive Decay
6-1. Alpha rays are fast helium nuclei emitted from atomic nuclei.
In one type of radioactive decay, a set of two protons and two neutrons, i.e. ahelium nucleus, is emitted at high speed from a heavy nucleus consisting of a large
number of protons and neutrons, such as uranium or thorium. Such emissions arecalled alpha (α) rays, which are said to consist of alpha particles.
After an alpha particle is emitted, there remains an atomic nucleus with two protons
and two neutrons less than the original nucleus (see Fig. 8). This type of decay iscalled alpha decay.
6-2. Beta rays are fast electrons emitted from atomic nuclei.
In another type of radioactive decay, a neutron changes to a proton in the
nucleus, and an electron is emitted. Such emissions are called beta (β) rays,
which consist of beta particles. After a beta particle is emitted, there remains a
nucleus with one proton more and one neutron less than the original nucleus (seeFig. 9). This type of decay is called beta decay.

The words “decay” and “disintegration” suggest that the atomic nucleus is destroyed or falls into
pieces. Actually, the nucleus is merely converted into a different kind of nucleus.

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226Ra

Fig. 8

Scientific Basis

222Rn

Decay of 226Ra(radium-226): 226Ra(radium-226) becomes 222Rn(radon222 ) by emitting an alpha particle.

3H

3He

32P

32S

Fig. 9 Decay of 3H(tritium) and 32P (phosphorus-32): 3H changes to3
He(helium-3) by emitting a beta particle, and 32P changes to 32S(sulphur-32)
by emitting a beta particle. In beta decay, one neutron in the nucleus changes
into a proton and an electron, and the electron is emitted.

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Scientific Basis

6-3. A positron sometimes emerges from a nucleus.
In another type of radioactive decay, a proton in the nucleus changes into aneutron and a positron (or a positive electron) is emitted. Positrons are described as
beta-plus (β+) rays, and this type of decay is called positron decay or β+ decay*(see Fig. 10). Positrons have the same mass as electrons, and the same but
opposite electric charge. After a positron is emitted, there remains a nucleus
with one proton less and one neutron more than the original nucleus. Positrons are
attracted easily to any available negative electron, whereupon the electron and thepositron―being in fact the anti-particles of each other―annihilate. Thisannihilation process produces electromagnetic waves (two photons of 0.51 MeVeach) emitted in opposite directions with energy equal to the mass of theelectron pair (see Fig. 11). Such waves are called annihilation radiations.

11B

11C

Fig. 10 Positron decay of 11C（carbon-11）: 11C becomes 11B(boron-11) by emitting
a positron. In positron decay, one proton in the atomic nucleus changes into
both a neutron and a positron.

Fig. 11 Production of annihilation radiation: A positron and an electron
meet and annihilate, and two waves (photons) of annihilation radiation are
emitted 180 degrees apart.
* In contrast to β decay, usual beta decay may be expressed as β decay, and, in contrast to β rays,−
usual beta rays are described as β rays.
+

−

13

+

II.

Scientific Basis

6-4. An orbital electron is sometimes captured by a nucleus.
When a proton in the nucleus captures an orbital electron and changes into aneutron, this type of decay is called orbital electron capture (EC). After an EC
decay, a nucleus is left which has one proton less and one neutron more than theoriginal nucleus (see Fig. 12).

201Tl

201Hg

Fig. 12
Orbital electron capture in 201Tl(thallium-201): A 201Tl nucleus
becomes a 201Hg(mercury-201) nucleus after capturing one orbital electron.
As this leaves a vacancy among the orbital electrons, emission of thecharacteristic X-rays of mercury follows. In orbital electron capture, one
proton in the nucleus captures an orbital electron and changes to a neutron.

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6-5.

Scientific Basis

Gamma rays are electromagnetic waves emitted from an excitednucleus, and are essentially the same as X-rays.

A nucleus after decay may often be unstable, i.e., the nucleus is in an excitedstate. It becomes stable by emitting its extra energy in the form of electromagnetic
waves, usually within a very short period of time (see Fig. 13). In this case, theelectromagnetic waves emitted from the nucleus are called gamma (γ) rays. Suchemissions do not cause the nucleus to change further into another type, and, forthis reason, the term ‘gamma decay’ is not used.
Gamma rays and X-rays are both electromagnetic waves and are distinguished
not by their energy (wave length), but by their origins. High energy
electromagnetic waves (photons) other than gamma rays are categorized to be Xrays.
Sometimes, instead of emitting a gamma ray, an excited nucleus transfers its
extra energy to one of its orbital electrons, and that electron is emitted, i.e.
knocked out of the atom. This phenomenon is called “internal conversion”, andthe emitted electron is called an “internal conversion electron”..
6-6. Gamma rays are sometimes emitted with delay.
Sometimes the excited nucleus is not extremely unstable but has a finite
period of life. In such a case, the excited nucleus is said to be a “ nuclear
isomer”, and is designated by adding ‘m’ at the end of its mass number, e.g.,
99m

Tc(technetium-99m). Nuclear isomers have their own half-lives. They become
stable by emitting gamma rays in a process known as “isomeric transition” (IT).
＊Electromagnetic waves: X-rays/gamma rays are electromagnetic waves like radio waves, infrared rays,
visible light and ultraviolet rays, but their wavelength is very short. Electromagnetic waves sometimes
behave as particles. When electromagnetic waves are considered to be a stream of particles, theparticles are called photons. The shorter the wavelengths are, the larger the photon energy is.

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60

Co(cobalt-60)
Proton 27
Neutron 33

60

Scientific Basis

60

Ni(nickel-60)
Excited state

Ni(nickel-60)
Ground state

Proton 28
Neutron 32

Proton 28
Neutron 32

Fig. 13 Gamma ray emissions: Nuclei are left excited after decay, andbecome stable by emitting their extra energy as gamma rays.

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Scientific Basis

6-7. Sources and action of neutrons with matter.
As we know, neutrons are generally produced by fission of heavy nuclei suchas U (uranium-235) irradiated with low-energy neutrons, a familiar process
occurring in the nuclear reactor.
235

There exist, however, some radioisotopes whose nucleus splits automaticallyinto two fragments and at the same time emits several high-energy neutrons. This
process is called the “spontaneous fission (SF)”. The most widely used neutron
source of such type is 252Cf (californium-252).
Another type of neutron sources is those using nuclear reaction such as(α,n)
reaction. The 241Am/Be neutron source is an example.
The interaction of neutrons with other materials is very different from that ofalpha and beta rays. Moreover, the action of neutrons varies greatly depending on
their speed (kinetic energy). See Fig. 14.
Because the neutron has no electric charge, it can easily approach an atomic
nucleus without electrically interacting with charged nuclei. Slow neutrons arereadily absorbed by the nucleus. When a neutron is thus captured by a nucleus, thenucleus becomes an isotope of the same element with the mass number greater by
1. Such an isotope may often be radioactive. For example, stable 59Co(cobalt-59)
becomes radioactive 60Co by capturing a neutron. Most radioisotopes are produced
in nuclear reactors by using this process of “neutron capture”.

Fig. 14 Neutron capture by a nucleus: When a neutron is captured by anatomic nucleus, the nucleus becomes an isotope of the same element. Slowneutrons are captured more easily than fast neutrons.

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Scientific Basis

Table 1 shows a comparison of the properties of alpha, beta, gamma (Xrays) and neutrons.
Table 1 Types of radiation and their properties
Properties

Alpha rays

Beta rays

Gamma rays

Neutrons(X-rays)HeliumElectronElectromagnetic Neutron

nucleus

Positronwave (photon)

Mass

Large

Very small

None

Large

Electric charge

+ 2e

– 1e

None

None

Nature+1ePenetration

Small

Medium

Large

Large

Photographic effectLarge

Medium

Small

Small

Fluorescence effectLarge

Medium

Small

Small

Ionization effectLarge

Medium

Small

Small

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Scientific Basis

7. X-Rays
There are two types of X-rays: bremsstrahlung and characteristic X- rays.
X-rays are electromagnetic waves like visible light and radio waves. X-ray
tubes are used to generate X-rays (see Fig.15). Electrons emitted from a heatedfilament in a vacuum are accelerated toward an anode by high voltage. Whenthey strike the metal anode, X-rays are generated. This is because, as the electrons
are passing by atomic nuclei of the atoms of the anode, the electric force
between the nuclei and the electrons exerts a strong braking action on the electrons,
and their kinetic energy is partially converted to X-rays (see Fig.16). X-rays
generated in this way are called bremsstrahlung ( a German term meaning braking
radiation).

Fig. 15 X-ray tube:Fast electrons collide with the metal anode andgenerate X-rays.
Additionally, when fast electrons cause the atoms of the anode to become
excited or ionized, and electrons from outer orbitals move to vacant inner orbitals,
energy equal to the energy difference between the outer and the inner orbit isemitted as electromagnetic waves (see Fig.17). Such electromagnetic waves haveenergy specific to the kind of atom, and are called “characteristic X-rays” (seealso Fig. 12). Instead of the emission of characteristic X-rays, sometimes one of
the electrons in an outer orbit is given excitation energy and kicked out of theatom. This electron is called the “ Auger electron” which is derived from French
physicist Prof. Pierre Auger.

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Scientific Basis

Fig. 16 Generation of bremsstrahlung: When moving electrons arebraked, X-rays are generated.

Fig. 17 Emission of characteristic X-rays or Auger electrons: When an
electron in an outer orbit moves to a vacancy in an inner orbit, a characteristic
X-ray or an Auger electron are emitted.
Eb: Energy necessary to release an orbital electron from the atom(binding
energy of an orbital electron to the nucleus).

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Scientific Basis

8. Accelerators
Accelerators are used to generate various kinds of radiation and to
produce radioisotopes.
Because electrons and protons are electrically charged, they can be
accelerated in a vacuum by application of electric force and given high kinetic
energy. An accelerator is a device to produce fast streams of electrons, protons, orother charged particles. Various types of accelerators are used in academic studies,and for the production of high energy X-rays or radioisotopes for industrial andmedical purposes. These accelerators are legally classified as radiation generating
apparatuses.

Fig. 18 Small-size cyclotron: Used to produce very short-lived
radioisotopes for medical use

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Ⅱ.

9.

Scientific Basis

Types of Radiation
There are many types of what we commonly call “radiation”.

As has been explained so far, radiation includes X-rays, alpha rays, betaminus rays, beta-plus rays, gamma rays, neutrons, electrons, protons and cosmic
rays. Major types of radiation can be classified by their characteristics as shownin the table below. Radiation that exists in the environment is called “naturalradiation”. Radiation created artificially is called “artificial radiation”.
“Radioactivity” and “radiation” are similar words and are often confused -- but
the meanings are different. When a radioisotope is likened to an electric lamp,
for example, radiation is the light emitted from the lamp, while radioactivity is theproperty of the lamp that emits light.
Radiation is the product of anything that is radioactive. It does not comeonly from radioisotopes, but also from accelerators and nuclear reactors, as wellas cosmic rays.
Table 2 Major types of radiation

Electromagnetic
radiation(photons)

X-rays (Bremsstrahlung, characteristic X-rays,
generated by phenomena occurring outside ofnuclei)
Gamma rays (generated by changes in theenergy states of nuclei)
Beta-minus rays (electrons emitted from nuclei)
Beta-plus rays (positrons emitted from nuclei)
Electrons (produced by accelerators)

Radiation

Alpha rays (helium nuclei emitted from nuclei)
Charged particles

Protons (produced by accelerators)
Deuterons (produced by accelerators)
Various heavy ions and mesons (produced byaccelerators)

Uncharged
particles

Neutrons (produced by reactors, acceleratorsand radioisotopes)

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Scientific Basis

Fig. 19 Relationship among radioactivity, radiation and radioisotopes

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Ⅱ.

10.

Scientific Basis

Quantities and Units Related to Radiation

The basic unit of energy is the joule (J); however, the usual measure ofradiation energy is the electron volt (eV). The kinetic energy gained by an electron
when it is accelerated by a potential difference of 1 volt is defined as 1 eV. The
relationship between the electron volt and the joule is,
1 eV = 1.6022×10-19 J
1 eV×103 and 106 are called 1 keV and 1 MeV, respectively. For example,
60
Co emits gamma rays of 1.17 MeV and 1.33 MeV after emitting beta rays witha maximum energy of 0.32 MeV.
In assessing the effect of radiation on humans, three quantities: absorbed dose,
equivalent dose and effective dose, are considered. The equivalent dose and theeffective dose are used for the ICRP’s system for radiation protection and called
the “protection quantities”.

10-1. KERMA
The KERMA (Kinetic Energy Released in MAterial) is the given kinetic
energy (J) per unit mass of the material (1kg) by the interaction between radiationand material. The KERMA is used for uncharged radiation or particles such as γ-,
x-ray or neutron. The unit is the gray (Gy). When the material is air, that is called“Air KERMA”.
10-2. Absorbed dose
As a result of interaction between radiation and material (receptor), the energy
absorbed per unit mass of the material is called the absorbed dose. The absorbed
dose is a fundamental dosimetric quantity, and can be considered regardless of thekind of radiation or the kind of material. The unit for absorbed dose is the gray(Gy). An absorbed dose of one gray means that one joule of energy is absorbed
per one kilogram of the material.
When using the absorbed dose, it should be mentioned what the absorber is,
because in a radiation field the absorbed dose will vary depending on the absorber.
For radiation protection purposes, air, water, and soft tissue are usually regarded as
the absorber.

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Scientific Basis

10-3. Equivalent dose
When the human body is exposed to radiation, the degree of biological effects
will differ depending on the type and energy of the radiation, even in cases
where the absorbed dose is the same. This is because the damage to DNA due tothe energy deposited by radiation is more difficult to repair as the density of energy
deposition becomes greater.
The concept of equivalent dose was created as a common index for
calculations of risk to the human body from radiation under different conditions.
This concept of equivalent dose is used only in the context of radiation
protection calculations.
The relationship between equivalent dose and absorbed dose in a particular
tissue or organ is described by the following formula:
Equivalent dose in Sv = Absorbed dose in Gy×radiation weighting factor (wR)
The radiation weighting factor assumes that the degree of biological effectdiffers depending on the ionization density (linear energy transfer, LET) ofradiation and determined by the ICRP based upon theoretical and experimental
data and considering practical applications. Radiation weighting factors of 1 forbeta rays (electrons) and gamma rays (X-rays), and 20 for alpha rays are currently
used. For neutrons the value varies with their energy ranging 2.5 to about 20.
When the gray is used as the unit for absorbed dose, the unit for equivalentdose is the sievert (Sv). The millisievert (mSv, 10-3 Sv) and the microsievert (µSv,
10-6 Sv) are also used.
10-4. Tissue equivalent dose and effective dose
Equivalent dose for a particular tissue or organ T is called tissue equivalentdose HT. When the human body is exposed to radiation, how the effects (in thiscase, incidence of fatal cancer or severe genetic diseases) appear depends on tissueor organ. In order to assess the total of such effects on various tissues and organs
throughout the body, effective dose is used. To get the effective dose, tissue
equivalent doses are multiplied by tissue weighting factors and then summed up foreach exposed tissue and organ throughout the body. Tissue weighting factors (Table9) are estimated from clinical data, followup studies of Atomic bomb survivors, andstudies with experimental animals. The unit of effective dose is also Sv (See also
Ⅳ 7 and 8).

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Ⅱ.

Scientific Basis

Tissues or organs
Equivalent dose:
How much is the effect ontissues or organs?

Human body
Effective dose:
How much is the effect on thewhole human body?

Fig. 20 Absorbed dose, equivalent dose and effective dose: The absorbed
dose is a measure of how much energy is absorbed in material, regardless ofthe type of radiation or material; the equivalent dose is a measure of
biological effects of radiation on tissues or organs in the human body. The
effective dose is a measure of total effects on the whole body. The tissue
equivalent dose and the effective dose are used solely in the context ofradiation protection calculations.

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Scientific Basis

10-5. Operational dose quantities and units
The tissue equivalent dose and the effective dose are almost impossible to bemeasured because it would require dosimeters inside of the body. Therefore, inpractice, operational dose quantities are defined as substitutes for them forexternal irradiation. These operational dose quantities were provided by theInternational Commission on Radiation Units and Measurements (ICRU).
For the measurements of effective dose rate in a workplace, dose rate meters
calibrated with the ambient dose equivalent (designated as 1 cm dose equivalentin Japanese regulations) are used which is defined by the dose at a point of 1 cm
depth in a sphere of 30 cm diameter made of tissue equivalent material (ICRU
sphere).
For the measurements of skin equivalent dose in a workplace, dose rate meters
calibrated with the directional dose equivalent (designated as 70μm dose
equivalent) are used.
For the measurement of personal dose, personal dosimeters calibrated with thepersonal dose equivalent are used.
The units of these dose equivalents are also Sv.

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Scientific Basis

Table 3 Quantities and units related to radiation
Item

Unit

SymbolDefinition

Remarks

KERMA

gray

Gy

Kinetic Energy Released in
MAterial. Used for uncharged
particles such as γ, x ray orneutron.1 Gy corresponds to one
joule per kilogram of material.

absorbed dose

gray

Gy

1 Gy corresponds to absorbed

SI unit:energy of one joule per kilogramof material

J/kg

Absorbed dose (Gy) ×

SI unit:radiation weighting factor

J/kg∑(Equivalent dose for a tissue ×

SI unit:tissue weighting factor)

J/kg

equivalent dose

effective dosesievertsievert

Sv

Sv

SI unitJ/kg

activitybecquerel

Bq

One decay event per second

SI unit: s-1

radiation energy

electron volt

eV

Kinetic energy gained by anelectron when it is accelerated by

SI unit: Ja potential of one volt28

Ⅲ. Safe HandlingIII. Safe Handling
1. Who is the Radiation Protection Staff?
Those who support the practice of radiation protection at a facility are called
the radiation protection staff. This is not a legally defined occupation, but nofacility can be operated without someone who actually supports radiation workers
to practice the radiation protection. The number and positions of radiation
protection staff will differ according to the size and nature of the facility. The scopeof work of radiation protection staff ranges from controlling the access of radiation
workers to environmental monitoring, and to personal exposure control.
1-1. Responsibilities of radiation protection staffs and their relationships
with radiation workers
The position within the organization, scope of work, and responsibilities of aradiation protection staff member will differ according to the facility, and be
defined in the Radiation Hazards Prevention Program of the facility (see Chapter Ⅵ).
There may be a misunderstanding among radiation workers that the work ofradiation control can be left in the hands of the radiation protection staff. In
reality, actual radiation control cannot be done only by radiation protection
supervisors (see Chapter Ⅴ 7) and radiation protection staff, but requires theactive participation of the radiation workers themselves.
1-2. Keeping close contact with radiation protection staff
Because the radiation protection staffs at each facility are most knowledgeable
about radiation control at that location, radiation workers should feel free to talk tohim or her even about routine operations. Of course, whenever anything abnormal
occurs－particularly any kind of accident －radiation workers must contact anyoneof the radiation protection staff members promptly, and follow his or her
instructions.

29

Ⅲ. Safe HandlingI will do my bestwith the help of theradiation workers

I want you to support
the radiation workers
for safety control at
this facility

Fig. 21

Radiation protection staff

30

Ⅲ. Safe Handling2.

Protection Against External Exposure
Measures for protection against external exposure should focus on thethree principles: shielding, distance and time.
2-1. Shielding
Dose rate in any workplace should be reduced by shielding radiation sources
with lead, iron or concrete for gamma rays, and plastics or water for neutrons.
Specific measures will vary according to the type and energy of radiation.
Shielding can generally be done more easily and more economically as dose to
the radiation source as possible.
2-2. Distance
It is important to work as far as possible from the radiation source.

If theradiation source is a point source, such as a gamma ray source, the dose rate is ininverse proportion to the square of the distance.

For example, if the dose rate ata point one meter from the point source of gamma ray is 100 mSv/h, it will be
one fourth, or 25 mSv/h, at a point two meters away, and only one hundredth, or
1 mSv/h, at a point ten meters away. The exposure can be substantially reduced
by using remote handling equipment such as tongs.
2-3. TimeBy shortening exposure time, the exposure can be reduced.

Radiation

workers should review operational procedures in advance, and work efficiently.
Time reduction, however, should be looked to only after the best measures forshielding and distance have been taken.

31

Ⅲ. Safe HandlingFig. 22 Three principles for protection against external exposure: Those
who handle radiation must always keep in mind the three principles ofshielding, distance and time.

32III. Safe Handling

3. Protection Against Internal Exposure
Protection against internal exposure can be attained by faithfully
observing all rules and guidelines for operations with unsealed radioisotopes.
Radioisotopes can enter the body through the following three intake routes:(1) through the respiratory system;(2) through the digestive system; and(3) through the skin, especially a wound.

Fig. 23 Intake routes of radioisotopes into the Body
Generally, intake through the respiratory system―inhalation―is the mostsignificant. In order to prevent radioisotopes from entering the body, it is importantto keep equipment and the workplace orderly, to work efficiently, and to faithfully
observe all rules for operation.
In a facility where radioisotopes are handled, it is necessary to put on
special working clothes. When leaving a controlled area, those clothes should be
removed, hands should be well washed, and contamination on the hands, feet andclothes should be checked for by using a body surface monitor (a Hand-foot- clothes
monitor). Whenever anything is brought out of the controlled area, it should bechecked for radioactive contamination with appropriate measuring equipment.
Continuous care must be taken in regard to radioactive air contamination andsurface contamination on floors, tables, etc., in the working environment.

33

III. Safe Handling

When working in an area of possible air contamination, workers need towear a protective mask to avoid inhalation of radioactive aerosol.

Fig. 24
In order to prevent radioactive contamination when handlingunsealed radioisotopes, special working clothes, slippers and rubber gloves
should be worn. When leaving the controlled area, working clothes should be
removed, hands washed well, and contamination checked for by a body surface
monitor.

34

III. Safe Handling

When airborne dust, gas or vapor can be produced, unsealed radioisotopes
should be handled under a hood (see Fig. 25). It is sometimes necessary tohandle them in a fully airtight space, such as a glove box (see Fig. 26).
Eating, drinking, smoking and wearing make-up must not be done in aworkroom where isotopes are handled. Nothing should be sucked through apipette by mouth.
In order to prevent radioisotopes from adhering to the body, special clothes,a cap, footwear and rubber gloves should be worn. If circumstances so require, arespirator or, sometimes, an airline suit should be worn.

ConduitFig. 25 Oak-Ridge-type hood35III. Safe HandlingFig. 26 Glove box

36III. Safe Handling

4. Attitude when Handling Radioisotopes and Radiation
When handling radioisotopes and radiation, for protection against both
external and internal exposure, the basic three-point attitude is: “Don't be afraid;
don't panic; but don't take it lightly”. For that, it is necessary to have an accurate
understanding of radioisotopes and radiation.
In addition, when commencing a new task, it is of course necessary to plan
the work carefully. It is also of great benefit in the prevention of accidents topractice the necessary operations several times without using real radioisotopes
or radiation (cold run), in order to become familiar with the steps and procedures,and to modify them if necessary.

Fig. 27 Attitude when handling isotopes and radiation

37

III. Safe Handling

Actual operation

Fig. 28 Working without a rehearsal could cause an accident

38

III. Safe Handling

5. Radiation Monitoring
Radiation cannot be felt or detected by our senses, but its existence andamount can be determined with appropriate methods.
5-1. Personal monitoring instruments(1) External exposure
Thermoluminescent dosimeters (TLD), fluoroglass dosimeters (FLD),
optically stimulated luminescence (OSL) dosimeters and electronic personal
dosimeters are all instruments to measure personal dose equivalent from external
exposure (see Fig.29). These dosimeters are worn on the chest (or on the abdomen
for women of reproductive age). If there is any possibility of substantial exposure
to other parts of the body, for example, the fingertips, those have to be monitoredwith special monitors such as ring badges.
(2) Internal exposure
To assess doses from internal exposure, the kind of radioisotopes and theiramount of intake must be known. There are several methods for determining theintake of an isotope. Intake can be determined externally by means of a wholebody counter (Fig.30), by measuring activity concentration in the air at workplace
and working time, or by the method of bioassay, i.e. radiochemical analysis ofexcreta. The internal dose can then be calculated based on radioisotope intake as
obtained by any of these methods.
When using a whole-body counter, the amount and distribution of gamma rays
can be determined by measuring gamma rays emitted by the radioisotope
distributed in the body from outside. In contrast to this, in the bioassay method,
radioisotope contained in urine, feces or, in cases of handling tritium, breath is used
to estimate the amount of radioisotope in the body. The bioassay is appropriate toassess the intake of radioisotopes emitting only beta rays or alpha rays, but it takes
much effort and time.

39III. Safe HandlingFig. 29 There are a variety of instruments to measure personal external
exposure, which are used separately or jointly.

Fig. 30 Whole-body counter : This device is sensitive to gamma rays enoughto easily detect even the slight amount of potassium (40K) that is naturally
present in the body.

40III. Safe Handling

5-2. Workplace monitoring
Using survey meters, it is easy to measure the dose rate in working areas.
Geiger-Mueller (GM) counters, ionization chambers and scintillation counters arecommon types of survey meters, and each have their own strengths and weaknesses(see Fig. 31).

Fig. 31
(1)
(2)
(3)
(4)

Major types of survey meters
Ionization chamber type
GM counter type
Scintillation counter type
Neutron survey meter

In order to measure activity concentration in the air or in water, various
kinds of sampling equipment and radiation measuring instruments are used, in
accordance with the specific needs of that measurement.
Radiation monitors, such as area monitors, water monitors and gas monitors,
are placed at specified locations to continuously measure and monitor the amount ofactivity concentration at that spot.

41III. Safe Handling
5-3. Monitoring of surface contamination
Survey meters can sometimes be used to check for surface contamination
on a floor, tables and any other goods, but when the dose rate in the vicinity is high,e.g., in the case of a container of gamma ray sources, contamination on the surface
can often not be measured accurately. In such cases, wipe tests are used. In thatmethod, extraneous matter on the tested surface is wiped off with filter paper(see Fig.32). Radioactivity on the paper is then measured to detect and assess
surface contamination.
For contamination on workers’ bodies, body surface monitors are used at theexit of controlled areas.

Fig. 32 Collecting a sample for a wipe test42III. Safe Handling

5-4. External exposure measurement

External exposure refers to exposure when the radiation source is outside
the human body. Exposure levels depend on the type and energy of the radiation.
Low-penetrating radiations such as alpha rays and low-energy beta rays are blockedfrom reaching the body by the air, by clothes, or by the surface layer of the skin.
For low-penetrating radiation, the dose equivalent at a depth of 70μm is measured
and used to assess the skin equivalent dose. Otherwise, 1-cm dose equivalent must
be measured to assess the effective dose.
(1) Methods for measuring external exposure
External exposure can be assessed either by measuring the radiation level inthe working environment or by measuring the exposure of an individual radiation
worker. Measurement and assessment of individual dose are done continuously by
personal dosimeters (Fig. 29) while working in the controlled area. When thewhole body is evenly exposed, the instruments should be worn on the chests formen, while on the abdomen for women.
(2) When exposure is uneven
Sometimes, because of uneven distribution of radiation, only a part of the
body receives significant exposure to radiation, for example, in the case of
exposure to X-rays or beta rays from small sources, or by wearing a protective
apron. In such situations, tissue equivalent doses should be considered for thethree regions of the body shown in Fig. 33.
(3) When measuring dose is difficult
It is sometimes difficult to measure and assess dose with personal dosimeters.
In such a situation, a survey meter or other radiation measuring instrument is used.
If this, too, is difficult, assessment based on calculations is permissible.
(4) Surface contamination on the skin and clothing
Usually hand-foot-clothes monitors are used.

43III. Safe Handling

OSL dosimeter

Fig. 33 Measuring external exposure

44III. Safe Handling

5-5. Internal exposure and its assessments
Internal exposure refers to the exposure when radiation sources are inside
the body, i.e. when any radioisotope has somehow entered the body. With
internal exposure, unlike with external exposure, exposure to alpha rays or lowenergy beta rays becomes significant.
(1) Routes for internal exposureRadioisotopes can enter the body by inhalation, by ingestion, or through theskin, especially through a wound, all of which are referred to as intake.
Radioisotopes move through the body along different routes, depending on their
physical and chemical characteristics, and are eventually excreted from the bodyby urine and feces, and sometimes by exhalation.
(2) Methods for assessing internal exposure
The intake of radioisotopes can be assessed by external measurement of
gamma rays emitted by the radioisotopes within the body. For this, a whole-bodycounter is used.
The bioassay method indirectly measures the intake of radioisotopes bymeasuring their presence in samples of excreta, such as urine and feces. For this,biokinetic models are necessary, which allow assessments of the amount ofradioisotopes deposited in various organs. This method is useful in analyzing
radioisotopes that emit only alpha or beta rays.
Calculations based on measured concentrations of radioisotopes in the air
involve many variables, including the amount of inhalation, breathing rate, and how
long one stays in the place. Despite these difficulties, the method is widely used.
(3) Implementation of the assessments
The calculation of internal exposure is done for an individual who may takein radioisotopes inadvertently. In actual practice, the appropriate method or45

III. Safe Handlingcombination of the methods is determined based on a judgment of cost, labour, thekind of radioisotopes handled, the nature of the work operation, and the working
environment. When the inhaled or ingested amount becomes known, assessment ofeffective dose or tissue equivalent dose is done by using dose-to-intake conversion
coefficients given by the ICRP. These coefficients are also given in the
Notification by the NRA. The Act on the Regulation of Radioisotopes, etc. requires
determination of internal exposure at least once every three months for thoseworkers who work in the area where radioisotope intake may occur.
Intake through inhalation or ingestion

Fig. 34

Measuring internal exposure46

III. Safe Handling

6．Education and Training
It is essential for radiation protection that radiation workers be aware ofradiation-control requirements, and that they be fully cooperative. To this end,
radiation workers are required, through education and training, to understand theimportance of radiation control and specific protection measures, and to have basic
knowledge about biological effects of radiation. Education and training arenecessary before a radiation worker deals with radiation or radioisotopes for the
first time, and regularly thereafter at least once a year.
6-1. Timing of education and training
Education and training for a radiation worker must be provided before theworker enters a controlled area for the first time, and, after the worker has entered acontrolled area, within one year from the beginning day of the fiscal year following
the fiscal year of the day on which previous education and training were provided.
Through re-education, radiation workers obtain the latest knowledge on radiation
effects and techniques for safe handling, as well as have the opportunity toreconfirm regularly the importance of safe handling.
6-2. Topics to be learned through education and training
For inexperienced radiation workers, items to be taught and required hours areclearly established, as shown in the Table 4. These are minimum requirements,
with each facility providing its own education and training curriculum, taking its
own situation into account. Programs often go beyond mere lectures, and include
opportunities to improve the skills of safe handling in realistic situations. It is also
important that radiation workers learn from their more experienced colleagues andfrom radiation protection staffs－which is to say, on-the-job training, or OJT.

47

III. Safe Handling

Table 4

Required items and length of education/training before enteringa controlled area
Item / Classification

minimum requirements

Effects of radiation on human body

30 min.

Safe handling of radioisotopes, etc. or radiation
generating apparatuses

1 hr.

Acts and regulations on the prevention of radiation
hazards and a radiation hazards prevention program

30 min.

not apply to use, storage and transport in accordance with the conditions forcertification for approved devices with a certification label, etc.

Fig. 35 Education and training48

III. Safe Handling

7. From Procurement to Waste Management of Radioisotopes
At any facility dealing with radioisotopes, there are various steps fromprocurement of radioisotopes to pre-disposal of them. Vital parts of each of thesesteps are safe handling, control and recording. Especially, the types and amountsof sealed radiation sources being brought in and taken out must be balanced.
To accomplish this, at each step－procurement, storage, use, transportation,and disposal－safety control and accurate record-keeping are essential.
7-1. Procurement
Only permitted radioisotopes and their quantities for which there has been
proper notification may be received. Usually the type and quantity of theradioisotopes that can be used in each workplace are limited, so it is necessary totalk with the radiation protection supervisor and radiation protection staffs before
receiving them.
It is also important that more radioisotopes than necessary are not purchased,
as this will only increase the management burden.
7-2. Storage
When the radioisotopes are delivered, they are usually put into a storage
facility, where they are recorded in a logbook.
7-3. Use
Prior to actual use, it is recommended that a cold run be undertaken in exactly
the same way as the operation to be performed. An amount as close as possible
to the exact amount required should then be taken out of storage, and any leftovershould be returned to storage, with the appropriate recording entries made.
7-4. Transportation
When radioisotopes (including materials contaminated by radioisotopes) aretransferred outside the facility, the type and quantity should be recorded, and theyshould be transported in accordance with the requirements for transportation49

III. Safe Handlingstandards. No one should bring any radioisotope out of a facility without
instructions or the approval of the radiation protection supervisor.
7-5. Waste disposal
Solid and liquid radioactive waste produced as a result of testing, etc., should
be sorted according to the categories, Table 5, in the room where the radioisotopes
are being used, and then transferred to a radioactive waste-storage facility. The
waste should be classified accurately into the prescribed categories.
7-6. Restrictions on transfer, procurement and possession of radioisotopes
License users are not allowed to transfer any radioisotopes beyond what isstated in the permit to any other user, seller or waste management operator, nor toaccept or hold radioisotopes in excess of the capacity of the facility as mentioned
in the permit.

50III. Safe Handling

8. Usage of Radioisotopes and Radiation Generating Apparatuses
The application of radioisotopes and radiation generating apparatuses varies
significantly depending on the nature of the radiation source. Radiation sources canbe broadly classified as sealed sources, unsealed sources, and radiation generating
apparatuses. Proper handling and radiation control also differ according to thesources.
8-1. Use of sealed sources
The followings are the principal advantages of using sealed sources: (1)There is no risk of leakage or damage during use under normal conditions. (2)There is no risk of the radioisotopes being scattered and causing contamination asa result of leakage, etc. Sealed radiation sources, however, do have the potential tocause radioactive contamination if there is a problem with the sealing. To avoid this,
it is necessary to check periodically for contamination.
8-2. Use of unsealed sources
Unsealed radiation sources should be handled only in a ‘workroom’. The
inside walls and floors of the workroom, which may become contaminated, must
be constructed with a minimum of protuberances, depressions, cavities and joints.
Materials should be flat and smooth, and resistant to infiltration and corrosion. The
radiation source itself should be handled in a hood or a glove box.
8-3. Use of radiation generating apparatuses
In case where induced radioactivity is not produced by the use of radiation
generating apparatuses, it is sufficient to control external exposure in the samemanner as for sealed radiation sources. On the other hand, if an activation productis generated, controls similar to those for an unsealed radiation source aresometimes required.

51

III. Safe HandlingFig. 36 Usage of radioisotopes and radiation

52

III. Safe Handling

9. Storage of Radioisotopes
When radioisotopes are not being used, usually they should be put in an
appropriate container and stored in a fireproof storage room. Sealed sources,
however, can be stored in fire-proof containers in a storage facility.
9-1. Requirements for storage facilities
The main structure of the storage facility has to be of fireproof construction,and radioisotopes beyond the approved storage capacity should not be stored
there. Radioisotopes should be put into containers and stored in a fireproof storage
room or storage box, in such a way that they cannot be taken out easily without
permission. Special fire doors should be used at the storage room entrance, andlocks and other security equipment should be installed.
9-2. Requirements for storage containers
Containers for radioisotopes have to meet the following requirements:
1) They should be air-tight so as to prevent contamination of the outsideair.
2) Containers for liquid radioisotopes have to be suitably impermeable anddesigned so that spilling is avoidable.
3) If there is any danger that a container for liquid or solid radioisotopes
might become cracked or broken, it should be used with a saucer, absorber
or other means to absorb and prevent the spread of the radioisotope.
9-3. Requirements for waste-storage facilities
The above requirement are also applicable to the technical requirements for
waste-storage facilities.

53

III. Safe HandlingFig. 37 Storage of radioisotopes

54III. Safe Handling

10. Discharge of Radioisotopes from Facilities and Radioactive Waste
Management
The Act and relevant Ordinances regulate the discharge of radioisotopes
from facilities and radioactive waste management.

10-1. Procedures for discharging radioactive materials in exhaust and rainage
Radioactive materials in exhaust are mostly discharged into the atmosphere
within the radioactivity concentration not exceeding the limit specified by the NRA,
through an exhaust (or ventilation) system equipped with a high-efficiency filtering
unit to remove radioactive particulate.
Drainage with lower radioactive concentration are collected in a reservoir,
diluted with non-radioactive drain water and discharged with the radioactivity
concentration not exceeding the limit specified by the NRA to the public sewage
system.

10-2. Radioactive waste management (Pre-disposal of liquid and solid wastes)
Liquid materials of higher radioactive concentration are treated by the several
methods of processing; e.g. 1) after evaporation or coprecipitation to reduceradioactive concentration, and then the liquid phase is discharged to the publicsewage system, the residue being treated as solid waste, 2) after being sealed in acontainer, which is solidified with solidification materials and stored for disposal
in a waste-storage facility, 3) are incinerated to reduce volume, the residue being
treated as solid waste.
Solid radioactive wastes have to be stored in waste-storage facilities until awaste management operator collects the wastes. Solid wastes should be divided
into several categories and put into separate containers for the convenience of
which method of pretreatment will be used afterwards.
10-3.

An example of the categorization of Radioactive wastes

An example of the categorization of solid wastes is shown in Table 5. These
categories apply to the collection of wastes from radioisotope users by the Japan
Radioisotope Association.

55

III. Safe Handling

Table 5 An example of waste categories for separate
collection by the Japan Radioisotope Association
Classification

Items

Combustible TypeⅠ

Paper, clothes, wood pieces

Combustible TypeⅡ

Plastic tubes, plastic vials, polyethylene sheets,
rubber gloves

Incombustible(Compressible)

Glass vials, other glass equipment, injection

Incombustible

Soil, sand, iron bars, pipes, concrete pieces,(Incompressible)

castings, clock parts, large amounts of TLC

needles, vinyl chloride pipes, vinyl chloride

plate, machinery and equipment
Animal carcasses

Animals after being dried

Inorganic liquids※1

Fluids after testing

Combustible filters※2

HEPA filters, pre-filters, charcoal filters

Containers are normally 50-liter drums.
※1 Inorganic liquids are put first in 25-liter polyethylene bottles, which are then put into 50liter drums. Adjust the pH to between 2 and 12, do not use HCl to adjust pH.
※ 2 Filters are packed in corrugated cardboard, polyethylene-sheets.

56III. Safe Handling

11. Record Keeping (Radioisotopes Tracking)
The amounts of radioisotopes used and the waste management should be
accurately entered in a logbook. The purpose of such entries is to ensure themanagement of radioisotopes facilities, by recording each step in the process fromprocurement of radioisotopes to radioactive waste management. The records must
be maintained for a prescribed period of time.
11-1. Entry items
Table 6 below shows the items that are legally required to be entered. Entries
make it possible to confirm the location of radioisotopes and how they are being
handled at each step in the process from procurement of radioisotopes to radioactive
waste management, for all radioisotopes at the facility. Entry is a very importanttask from the viewpoint of radiation source control at a facility.
Table 6 Items to be entered by radioisotope or radiation generating
apparatuses users
Entry Items
1. Use of radioisotopes
2. Operation of radiation generating apparatuses
3. Storage of radioisotopes
4. Transportation of radioisotopes
5. Radioactive waste management radioisotopes
6. Inspection of radiation facilities
7. Education and training
11-2. Who should make entries?
There are two kinds of entries-those made by radiation protection staff andthose made by radiation workers. Radiation workers, in principle, record the use
and storage of radioisotopes, as well as transfer of radioisotopes and materials
contaminated by radioisotopes. Because information relating to radioisotopes, fromprocurement of radioisotopes to radioactive waste management, amounts to a kindof “registry” for the radioisotope, record keeping should be done accurately. The
format of the logbook may be decided by each facility, so as to make its use easy

57III. Safe Handlingfor the radiation workers, taking into consideration the nature of the work in thefacility. To ensure accuracy, an entry should be made every time a radioisotope isused, stored or transferred.

Accurate and timely entries should be made, not only during periods ofnormal operation, but when accidents or emergencies occur, updated regularly.
11-3. Custody period for entries
Logbooks should be closed annually, and then be maintained for five years.

Fig. 38

Record Keeping

58III. Safe Handling

12. Record Keeping (Dose)
Records should be kept on the results of all legally required measurements.
Such measurements relate to the working environment and to personal exposure.
Recording is thus for the purpose of controlling personal exposure.
12-1. Items to be measured
Items legally required to be measured are: 1) For places where there is a
probable radiation hazard, the level of radiation and the state of contamination fromradioisotopes (measurement of the working environment). 2) For those who enterradiation facilities, the dose received and state of contamination by radioisotopes(assessment of personal dose).
12-2. Measurements and recording of external exposure
External dose must be measured, and the results recorded, for the three-month
periods starting on each April 1, July 1, October 1 and January 1, and for oneyear periods starting each April 1. For pregnant women, measurements must be
made and recorded every month. Items to be recorded are: 1) name of worker
measured, 2) name of person doing the measurement, 3) type of the personal
dosimeter used, 4) measurement method, and 5) body parts measured and results ofthe measurements.
12-3. Measurements and recording of internal exposure
Internal dose to workers who enter places where there is a possibility ofinternal exposure must be assessed at least once every three months (at least once
every month for pregnant women), and the results of those assessments must berecorded each time. Items to be recorded are: 1) date of assessment, 2) name ofworker being measured, 3) name of person doing the assessment, 4) kind andtype of radiation measuring equipment, 5) assessment method and, 6) results.

59III. Safe Handling

12-4. Custody Period for Records
Records of measurements of the working environment must be kept for five
years. Records on the exposure and health surveillances of radiation workers must
be kept permanently. It is recommended that records of accidents andemergencies also be kept permanently.

Fig. 39 Recording60III. Safe Handling

13. Health SurveillancesThose who are to be assigned to deal with radiation and radioisotopes must be
checked to see if they are suitable for the job from the viewpoint of their health.
The radiological health surveillance is in contrast to an ordinary healthsurveillance given to every worker in the facility. There are two kinds ofradiological health surveillances－one prior to starting work as aradiation

worker and those given periodically thereafter.
13-1. Why is the health surveillance necessary?
Each organization conducts two kinds of health surveillances－routine healthsurveillances for every worker, and radiological health surveillances exclusively forradiation workers. The purposes in both cases are not only to improve the health of
the workers and allow them to work without anxiety, but to discover any healthrelated abnormalities as early as possible so that they can be treated properly.
13-2. Medical examination items legally required
Radiological health surveillances consist of oral interviews, medical
examinations and tests. Medical examination and test items are shown in the tablebelow. These were determined from past experience and are based on a knowledgeof radiation hazards and radiation effects.
Test and Medical Examination Items
1)

Amount of hemoglobin, the counts of erythrocyte and leukocyte andthe percentage of each subtype of leukocyte in the peripheral blood

2)

Skin

3)

Eyes

4)

Any other parts of the body, or items, designated by the Nuclear
Regulation Authority

61III. Safe Handling

13-3. When are health surveillances given?
According to the Regulations on Prevention of Ionizing Radiation Hazards
under the Labor Standards Act, radiological health surveillances should be
conducted before starting the handling of the worker's first handling of radiation orradioisotopes, and every six months thereafter. If certain required conditions aremet, however, radiation health surveillances can be omitted. On the other hand,
whenever there has been any abnormal radiation exposure (exposure to radiationin excess of the effective dose limit) or abnormal contamination, workers must be
examined by a doctor.
13-4. How to interpret the results of health surveillances?
If radiation and radioisotopes are controlled according to all applicable
rules, radiation workers will not have any related health problems. Moreover,because the dose to each radiation worker is controlled by personal monitoring,
there is practically no chance that a worker will be found in a medical examination
to exhibit any abnormal values as a result of his or her normal radiation work.
Results of blood counts, one of the items in a radiological health surveillance,
commonly fluctuate for a variety of reasons. Thus, if an abnormal value is found,
it is entirely possible that the body has a problem due to a cause other thanradiation. The health of radiation workers should be evaluated based on the resultsof both radiological health surveillances and general medical tests.

62III. Safe Handling

14. Procedures at the Time of an Accident or Emergency
14-1. What is an accident and what is an emergency?
When radioisotopes are stolen, missing, leaked or unplanned exposure, thesituation is referred to as an accident. When there is a danger of a radiation
hazard, or when it actually occurs, the situation is referred to as an emergency.
14-2. Principles for immediate measures at the time of an accident
When the whereabouts of a radioactive source becomes unknown, the worker
should make contact with a radiation protection staff member and ask for
instructions on measures to be taken.
14-3. Principles for immediate measures at the time of an emergency.
Immediate measures to be taken by a radiation worker at the time of an
emergency are: 1) avoid endangering him- or herself, or others, and ensure
safety, 2) promptly notify others about the occurrence of the emergency, and 3) takemeasures to prevent contamination from spreading and to prevent the situationfrom worsening. It is necessary for radiation workers to learn about possible
emergency situations in detail, through education and training, so that they will beable to accurately assess them and implement all needed measures immediately andeffectively.
14-4. To whom and how to notify?
It is essential for radiation workers to immediately let the people around themknow that an accident has occurred, in order to secure their safety and to preventthe spread of contamination. They should also notify a radiation protection staff
member of the accident and ask for instructions. Procedures for notification are
posted at various locations where radiation workers can easily see them, such as at
the entrances to controlled areas.
When notifying, the radiation workers should calmly state 1) when, 2) where,
3) what, and 4) why. When a fire occurs, the radiation protection supervisor or theoperator is required to contact the fire department, and to report to the NRA.

63

III. Safe Handling

14-5. Specific measures to prevent worsening of an accident
The way to prevent an accident from worsening depends on the situation. In
the event of contamination with unsealed sources, identifying and clearly marking
off the contaminated area is the key to preventing contamination from spreading.
14-6. Preventing reoccurrence of an accident
In order to prevent the reoccurrence of an accident, it must be analyzed
carefully to accurately determine its cause. Then, anything needed to improve thefacility, equipment or method of handling should be done as promptly as possible.
For the investigation to be effective, the cause of the accident and the responsibility
for it should be pursued separately.

64III. Safe Handling

15. Procedures in the Event of Excess Exposure or Contamination
If excess exposure or contamination occurs, radiation workers should
immediately report to the radiation protection staff to ask for appropriate
instructions. When an accident does occur, however, avoiding danger to thebody and preventing spread of contamination are the first priority.
15-1. What is excess exposure?
When exposure exceeds the dose limit for occupational exposure, it is called
excess exposure. Such a dose limit is not the limit of safety, however, and aradiation hazard does not necessarily exist even at excess exposure.
15-2. Measures in the event of excess exposure
If there is any possibility that a radiation hazard involving excess exposure
exists, it is necessary to see a doctor without delay. The cause of the accident
should then be investigated to avoid reoccurrence.
15-3. What is contamination?
Contamination refers to the existence of radioisotopes where they should
not be. Contamination can occur on floors, table surfaces where radioisotopes arebeing handled, or on the surface or inside of the body. Radiation workers shouldmake it a routine to check their workplace frequently with, for example, a survey
meter, both before and after handling of radioisotopes, in order to detect
contamination. Radiation workers should also check for contamination with ahand-foot-clothes monitor in a contamination monitoring room when leaving acontrolled area.
15-4. Measures in the event of contamination
In order to prevent contamination from spreading, decontamination should be
carried out immediately, after clearly identifying the contaminated area. Radiation
workers have to notify a radiation protection staff member of the contamination andask for instructions on the most suitable method of decontamination under thecircumstances.

65

III. Safe Handling

15-5. Transfer of a radiation worker who received excess exposure
Whenever necessary, transferring a radiation worker who experienced excess
exposure to a different department, or restricting his or her access to the controlledarea, should be considered.

Fig. 40 Notification

66

Ⅳ. Biological Effects of Radiation

IV. Biological Effects of Radiation
1.

Classification of Radiation Effects on the Human Body

Effects of radiation on the human body can be categorized into those thatappear in the person who are exposed and those that appear in his / her offspring.
The former is called somatic effects; the latter is called heritable effects.
Somatic effects are further categorized into acute effects and late effects,
based on the time from radiation exposure to the appearance of the effect. Acuteeffects appear within a relatively short time after exposure, usually in several weeks.
Late effects appear in several years to decades. The period until the effect appears
is called the latent period.
Even when total dose is the same, severity of the effect differs depending onwhether the exposure was all at one time (acute exposure), or multiple occasions
over a long period of time (chronic exposure). This is because, in the latter case,the body is able to exercise its inherent ability of recovery in between exposures.
Effects also differ between whole-body exposure and partial exposure (see Fig.
41).

Fig.41 Whole-body exposure and partial exposure. Radiation effect appears
on radiosensitive organs by whole-body exposure whereas only on the exposedorgans by partial exposure.

67

IV.

2.

Biological Effects of Radiation

Acute Effects

Acute effects by single whole-body exposure with gamma rays (X-rays) are
shown in Table 7 . No clinical symptoms are recognized at doses of 0.25 Gy or
lower. A dose of 0.5 Gy causes a temporary reduction in the number of leukocytes,
but it returns to the normal level thereafter. Radiation sickness to 50%, including
a hangover-like symptoms, occurs by an exposure of 1.5 Gy or higher. A dosearound 4 Gy brings death to 50% of exposed individuals in 60 days without
appropriate medical care. At 7 Gy, the probability of death is almost 100%.

Table 7 Dose-dependent symptoms of acute effects(Whole-body, single exposure to gamma rays (or X-rays))
Dose (Gy)0.25 or less
0.5
1

Symptoms
Almost no clinical symptoms
Temporary reduction of leukocyte(lymphocytes)
Nausea, vomiting, whole-body languor,
substantial reduction of lymphocytes

1～2

Death to 10% within 60 days*

1.5

Radiation sickness to 50%～4Death to 50% within 60 days*

5～7

Death to 90% within 60 days*

7～10

Death to 50% within 2 weeks*) without medical care (aseptic treatment, bone-marrow transplantation etc.)
In this table, absorbed dose (in Gy) is used instead of equivalent dose oreffective dose (in Sv). That is because the radiation weighting factors (see 7-2)
recommended by the ICRP are based on the stochastic effects such as cancer
induction and not applicable to the deterministic effects.

68

IV.

3.

Biological Effects of Radiation

Late Effects

The latent period of late effects can be up to decades. Typical late effects
are cancer and cataracts.
The length of latent period for cancer differs by exposed organ or tissue, age
at the time of exposure and dose, although it ranges from several years to decades.
The probability of cancer incidence also varies depending on the organ or tissue
and age. According to the ICRP Publication 103 (2007), the approximated overall
fatal risk coefficient of cancer is 5% per Sv on which current international radiation
safety standards are based.
The latent period for cataracts, the clouding (opacification) of the lens of
the eye, ranges from several years to a few decades. The minimum dose to cause
cataracts is considered as 0.5 Gy.
As many factors are involved in the onset of cancer and cataracts, it is difficult
to distinguish whether these diseases are the result of radiation exposure or not.

Fig. 42 Today in Japan, cancer is the leading cause of death. Various
factors are involved in cancer incidence, and radiation is only one of them.
It is not possible to distinguish cancer caused by radiation from cancer
arising from other causes.

69

IV.

4.

Biological Effects of Radiation

Heritable Effects

Heritable effects caused by radiation have not been verified in humanbeings.
The heritable effects of radiation have been studied for a long time, and there
continues to be no direct evidence that exposure of parents to radiation leads toexcess heritable disease in offspring including children of atomic bomb survivors
in Japan. In 2001, the United Nations Scientific Committee on the Effects ofAtomic Radiations (UNSCEAR) reported this issue by using the method of
doubling dose which is the dose to induce the same number of spontaneous
mutations in one generation.
Because there are no data on frequency of radiation-induced mutations inhumans, the doubling dose has been estimated using spontaneous mutation rates ofhuman genes and radiation-induced mutation rates of mouse genes by low dose,sparsely ionizing radiation of the order of 1Gy. On the basis of the report, ICRP
estimates genetic risks to second generation of about 0.2% per Gy.

70

IV.

5.

Biological Effects of Radiation

Biological Effects Depend on the Dose Received

Radiation effects on the human body can also be categorized into
stochastic effects and deterministic effects, depending on the relationshipbetween the radiation dose and the rate of occurrence.
A threshold value identifies a dose below which there is no radiation effect,
whereas the occurrence frequency and severity of radiation effects increases
starting around the threshold dose (Fig.43, left panel). All of the acute effects andcataracts are considered to have their own threshold value and are called asdeterministic effects.
In contrast, risks of cancer including leukemia and heritable effects simply
increase with the dose. No threshold values are assumed to exist, and the severityof the effect dose not change by the dose received (Fig.43, right panel). These
effects are called as stochastic effects.
Classification of biological effects of radiation by using categorizations
described above are shown in Table 8.
The relative contribution of a specified organ or tissue to the overall radiation
detriment from stochastic effects, as a result of systemic irradiation, is called thetissue weighting factor (W T, see also Table 9) for tissue(T). Effective dose(E) isdefined by the following formula:
𝐸𝐸 = � 𝑊𝑊T ・𝐻𝐻T
𝑇𝑇

Here, HT is the equivalent dose for tissue T.
Within the low-dose range of exposure with properly implemented radiation
protection, the occurrence of deterministic effects in radiation workers are virtually
negligible. There must be concern, however, about stochastic effects. Thus,
radiation monitoring and dose evaluation are very important for radiation
protection.

71

IV.

Biological Effects of Radiation

Fig. 43 Schematic expression of variations for occurrence and severity ofdeterministic effects (left) and stochastic effects (right)

Table 8 Classification of biological effects of radiation
Erythema on the skin
Acute

Loss of haireffects

Reduction of leukocytes

Radiation effects

Somatic

Infertility, etc.

effects

Deterministic
effects

Cataracts
Late

Effects on embryos, etc.

effects

Leukemia
Cancer

Stochastic effects

No evidence in human
Heritable effects

72

IV.

6.

Biological Effects of Radiation

Effects from External and Internal Exposures

In planning and implementing measures for radiation protection, it isimportant to distinguish external exposure and internal exposure - that is,
exposure from radiation sources outside the body and exposure fromradioisotopes within the body.
When handling sealed radiation sources or operating radiation generating
apparatuses that do not produce radioisotopes, only external exposure is to beconsidered. When handling unsealed radioisotopes emitting low energy beta-raysor alpha-rays only, internal exposure is generally considered (though this depends
also on the handling method and conditions). Otherwise, both external and internal
exposures should be considered.
In the case of external exposure, strongly penetrating radiation such as gamma
rays (or X-rays) or neutrons, is the main concern. In contrast, with internal
exposure, radiation with low penetration power, such as alpha-rays and beta-rays,
are the crucial problem.
The radioactivity taken into the body decreases in accordance with its inherent
physical half-life Tp. The activity in the body is also reduced by metabolism. The
reduction is assumed to be expressed by a simple exponential function and the“biological half-life” Tb is defined. Thus, the body burden radioactivity is reducedin accordance with the effective half-life Teff, as shown by the following formula:1
1
1－ = － + －
Tp
Tb
Teff
For evaluation of internal doses, more precise biokinetic model is constructed
for major individual radioisotope in any physical and chemical forms. Based on themodel, the conversion coefficients of committed effective dose per unit intake,“dose coefficients”, are obtained. Examples are shown in Table 10.

73

IV.

Biological Effects of Radiation

The intake of radioisotopes by ingestion may be negligible because eating
and smoking should be strictly prohibited in any controlled area where unsealed
radioisotopes are handled.
Regardless of external or internal, the severity of health effect is assumed tobe the same if the received effective dose is the same.

exposure

exposure

Fig. 44 In implementing measures for radiation protection, it is importantto understand radiation environment where the worker is subject to external
or internal exposure.

74

IV.

7.

Biological Effects of Radiation

What is Equivalent Dose?

Equivalent dose is the basic dose concept used in radiation protection, theunit is the sievert (Sv). Regardless of the type of radiation, when the equivalentdose to a particular tissue is the same, the radiation effects to the tissue areassumed to be the same. Equivalent dose can be obtained by multiplying
absorbed dose (a mean energy imparted to tissue) by a radiation weighting
factor, which is a function of the type and energy of the radiation.
7-1. Protection quantity in tissue level
Radiation can be easily measured based on physical property, such as
ionization effect. However, the effect on human body differs by the type ofradiation. In order to use the measured quantity to assess the effect on the human
body, the values of radiation weighting factors (WR) in different radiation types
are selected by judgement on the basis of broad range of experimental relative
biological effectiveness(RBE) data which are relevant to stochastic effects. The
result obtained by multiplying the absorbed dose by the radiation weighting factor
is defined as the equivalent dose. Equivalent dose is the basic protection quantity
in tissue level.
7-2. Radiation weighting factors
In ICRP 2007 Recommendations, the following radiation weighting factors
are recommended:
1 for photons (gamma-rays and X-rays) and electrons (beta-rays)
2 for Protons
20 for alpha-rays
2.5 to about 20 for neutrons (a continuous function of neutron energy)
Equivalent doses corresponding to 1 mGy from gamma-rays and 1 mGy fromalpha-rays are, 1 mSv and 20 mSv, respectively.
7-3. Assessing Equivalent Dose
Equivalent dose is used in assessment of the effect at a specific part of the
body and is measured by using various kinds of personal dosimeters (see III.5).

75

IV.

Biological Effects of Radiation

For assessment of the dose to the skin, the personal dose equivalent with
70µm depth dose equivalent can be used.
.

Fluorescent glass
dosimeter

Fig. 45 Measurements of 1cm- and 70µm depth dose equivalents

76

IV.

8.

Biological Effects of Radiation

What is Effective Dose?

Effective dose is a concept quantifying radiation risk of stochastic effects.
Sievert (Sv) is also the unit of effective dose. Equivalent dose for each tissueor organ is multiplied by the tissue weighting factor W T (Table 9), and thesum is performed over all organs and tissues to obtain the effective dose. The
dose limit of 50 mSv/y and 100 mSv/5y for radiation workers, specified in
Chapter Ⅴ, is expressed by effective dose.
8-1. Accounting for the radiation sensitivity of each tissue or organ
Even if the equivalent dose is the same, the probability that stochastic effects
will appear depends on irradiated tissue or organ because of different sensitivity
to radiation. Effective dose was therefore created to represent overall radiation
detriment from stochastic effects. The unit is sievert (Sv). The unit is the samefor equivalent dose as well as for some operational quantities. Effective dose isused in implementation of the radiation protection system.
8-2. Applicable regardless of exposure type
By using effective dose, the risks of stochastic effects by external exposure,regardless of whole body or local, and internal exposure can be combined to assessoverall effects.
8-3. Use of operational quantities for measurements of external dose
Effective dose and equivalent dose are called as protection quantities and are
not measurable. Therefore, operational quantities are used for assessment ofeffective dose or mean equivalent doses in tissues or organs by which area
monitoring and individual monitoring of external exposures are performed. For
assessment of effective dose, the personal dose equivalent with a depth of 1cm
dose equivalent is used. Operational quantities are defined by the International
Commission of Radiation Units and Measurements (ICRU) with simplified sourcedetector geometry to avoid underestimation of both equivalent dose and effective
dose.

77

IV.

Biological Effects of Radiation

Table 9 Tissue weighting factors provided in the 2007 Recommendations of the
ICRP

Oesophagus*Remainder Tissues (14 in total): Adrenals, Extrathoracic (ET) egion, Gall bladder,
Heart, Kidneys, Lymphatic nodes, Muscle, Oral mucosa, Pancreas, Prostate, Small
intestine, Spleen, Thymus, Uterus/cervix.

78

IV.

Biological Effects of Radiation

Table 10 Some examples of effective dose coefficients for inhalation
NuclidesChemical form

Dose coefficients (mSv/Bq)

H

Elementary
MethaneWater
Organic compounds except methane
Other compounds

1.8×10-12
1.8×10-10
1.8×10-8
4.1×10-8
2.8×10-8

14Gaseous organic compounds
Carbon monoxide
Carbon dioxide
Methane

5.8×10-7
8.0×10-10
6.5×10-9
2.9×10-9P

Compounds except tin phosphates
Tin phosphates

1.1×10-6
2.9×10-6

Co

Compounds except oxides, hydroxides,
7.1×10-6
halogenides, nitrates
Oxides, hydroxides, halogenides, nitrates 1.7×10-5

3

C

32

60

131

I

Elementary
Methyl iodide
Compounds except methyl iodide

2.0×10-5
1.5×10-5
1.1×10-5

137

Cs

All compounds

6.7×10-679IV.

Biological Effects of Radiation

9. Assessment of Internal DoseRadioisotopes taken into the body by inhalation or by ingestion are
excreted or remain in the body as radiation sources until the they completely
decay or are excreted. Dose from such remaining radioisotopes is estimatedtaking future dose into account. This is called committed equivalent dose to
the relevant tissue or organ. The committed effective dose is a total sum ofthese committed equivalent doses multiplied by the tissue weighting factor foreach tissue or organ.
9-1. Exposure from radioisotopes taken into the bodyRadioisotopes taken into the body are either excreted from the body mainly
in urine and feces, or remain in the body while irradiating the tissues emitting until
they completely decay.
9-2. Committed dose is used for internal exposure
The internal radioactivity may give rise to doses to body tissues for many
months or years after the intake. The need to regulate exposures to radionuclides
and accumulation of radiation dose over extended periods of time has led to thedefinition of committed dose quantities. The time integral of the equivalent dose
rate in a particular tissue or organ that will be received following intake ofradioisotopes into the body is called committed equivalent dose. The sum of the
products of the committed organ or tissue equivalent doses and the appropriate
tissue weighting factors is called committed effective dose. When the committed
period is not specified, it is taken to be 50years from the intake for adults (including
radiation workers) and 70 years old of age for infants and children.
9-3. Assessments of committed equivalent dose and effective dose
Assessments of committed dose is based on the amount of intake and thereference dose coefficient. The dose coefficients for specified radionuclides andtheir physical/chemical forms (Sv/Bq) were calculated by using defined biokinetic
and dosimetric models, and were published by the ICRP.

80

IV.

Fig. 46 Committed dose

81

Biological Effects of Radiation

IV.

Biological Effects of Radiation

10. Natural Radiation and Artificial Radiation
Between natural and artificial radiations, there is no difference inbiological effects on human body.
From the point of view of the effects on human body, whether it is naturalradiation or artificial radiation does not matter. Natural and artificial radiations of
the same type and with the same energy have the same effect on the body.

Fig. 47 Natural and artificial radiations

People living on the earth are inevitably exposed to naturally occurring
radiation. Exposure to artificial radiation for medical purposes would be added
depending on the person. Average of annual dose from various radiation sources
are shown in Fig. 48 and Table 11.

82

IV.

Biological Effects of Radiation

Fig. 48. Average of annual effective dose (mSv) in worldwide and Japan(‘Environmental Radiation in Life’ by the Nuclear Safety Research Association 2011)

Table 11 Typical estimated values of annual effective
dose to people in the world (UNSCEAR 2008)
Average per person (mSv)

Naturalbackground
2.4 mSv

Artificial
exposure
0.6 mSv

Inhalation (Radon)

1.26

Ingestion

0.29

Terrestrial gamma rays

0.48

Cosmic rays

0.39

Medical exposure (diagnosis)

0.6

Atmospheric weapon testing

0.005

Occupational exposure

0.005

Nuclear power generation

0.000283

IV.

Biological Effects of Radiation

11. Radiation and Health Effects
Effects that can clearly be attributed to radiation do not occur unless one
is exposed to a large amount of radiation due to, for example, an accident.
In addition, a person's recovery from the effects of radiation exposure depends
on the dose received. When the dose is small, effects are temporary and disappear
after some time. The higher the dose becomes, however, the more serious the effects
are, and the more difficult to recover from them.
For example, assume that the skin is exposed partially in an accident to alarge amount of weakly penetrating radiation such as beta rays or soft X-rays (lowenergy X-rays). If the dose is 3 to 5 Gy*, the skin will become red and hair will fallout. These effects are not temporary, however, and the skin will return to normal inseveral months. If the dose is 5 to 10 Gy, blisters will form, as when the skin isburned, but here, too, it may recover in several months. On the other hand, if thedose exceeds 25 Gy, the exposed skin will become ulcerated and never return tohealthy structure. The surface of the skin (epidermis) will become thinner, and thetissues beneath (dermis) become harder and thicker, and the skin appears blotchy.
The important thing to remember is that the dose needed to cause suchdeterministic effects is far higher than the dose limit for the skin (0.5 Sv/y) forradiation workers.
Additionally, there is no evidence that radiation workers catch colds moreeasily or become physically weaker during normal operations. Easily catching colds
and being weak physically are in large part related to the body's immune mechanism.
Immune system consists of various kinds of immune cells, such as lymphocytes,
monocyte/macrophages, and polymorphonuclear leukocytes, which are generated
in the bone marrow. Unless the bone marrow is exposed to radiation with doses, thenumber of these cells do not change. Thus, there is no risk of affecting the immune
system when engaging in normal radiation work.
* Here absorbed dose (Gy) is used instead of equivalent dose (Sv), because tissue weighting factor
recommended by the ICRP is applicable only to low dose where stochastic effects are relevant.

84

IV.

Biological Effects of Radiation

Fig. 49 Radiation and health effects

85

IV.

Biological Effects of Radiation

12. Exposure Categories
12-1. Occupational exposure
Occupational exposure is defined as all radiation exposure of workers incurred
as a result of their work. Doses from occupational exposure varies depending on thetask and the type of radiation source. The average exposure dose per person forvarious occupational fields excluding workers in Nuclear Power Plants is surveyed
by the Council on Personal Dosimetry Service every year. The results of 2017 areshown in Table 12. Workers of Non-destructive Testing received the largest
exposure dose, with an average dose of 0.392 mSv. In contrast, workers in researchand education area received the lowest dose at 0.022 mSv. According to the statistics
for nuclear workers in 2017 by the Radiation Effects Association, the annual average
effective dose per person was 0.7 mSv.
Table 12 Annual average dose per person (mSv) (Japan FY 2017)
Occupational Field

Effective Dose (mSv)

Number ofworkers

Medicine

0.339

360,123

Dentistry

0.026

23,929Veterinary Medicine

0.031

16,151

Non-destructive Testing

0.392

3,678

General Industry

0.067

67,256

Research and Education

0.022

66,078

Nuclear Power Plant

0.7

67,00486

IV.

Biological Effects of Radiation

12-2. Medical Exposure
Medical exposure is incurred by patients as part of their own medical or dental
diagnosis or treatment. There are increasing cases to receive diagnostic radiationsuch as X-ray examinations, computerized X-ray tomography (CT scans),
interventional radiology (IVR), and radioisotope examinations. In addition,
radiation therapy is one of the major options for cancer treatment. Medical exposure
also includes the exposure of volunteers in a program of biomedical research.

12-3. Public Exposure
Public exposure is incurred by members of the public from radiation sources,
excluding any occupational or medical exposure and the normal local natural
background radiation. Public exposure is mainly attributable to atmospheric nuclear
weapon testing, nuclear power generation as shown in Table 11.

87

IV.

Biological Effects of Radiation

13. Risk
The use of radiation and radioisotopes brings various benefits to our daily
lives. The use of radiation in medicine contributes significantly to keeping us
healthy. Radiation and radioisotopes thus contribute positively to human society;yet exposure to radiation itself is considered harmful to the body. Harmful effects,
however, do not necessarily appear whenever one is exposed to radiation. In
particular, the dose a person receives daily is so small that it is not clear whether
there are any harmful effects.
The degree of harmful effects that may occur as a result of usage of radiation.
The probability of the occurrence of the effects, is called risk. Risk does not meanthat harmful effects will occur; it just means the possibility that they may occur.

88

IV.

Biological Effects of Radiation

Fig. 50 Double-edged sword

89IV. Biological Effects of Radiation

14. Limits of Personal Exposure
Exposure dose of radiation workers is controlled to remain below acertain level. This level is the dose limit. The tissue equivalent dose and theeffective dose limit are specified in the Enforcement Regulation.
14-1. Dose limit for radiation workers
The dose for radiation workers should be controlled so as not to exceed thespecified limits for either effective dose or tissue equivalent dose. The effective
dose limit and tissue equivalent dose limit are both controlled based on one-year
periods starting April 1, except in the case of women. Values are shown in
Table 13.

90

IV. Biological Effects of Radiation
Table 13 Effective dose limits and tissue equivalent dose limits
for radiation workers

Item

Radiation Worker

Effective dose limits(1) 100 mSv/5 years*1(2) 50 mSv/any single year*2(3) Female worker*3 5 mSv/3 months*4(4) Pregnant worker
The internal exposure limit set forthis woman is 1mSv for a period
starting from the time when her
employer and others are informed ofher pregnancy by her reporting or
any other means up to the time ofthe delivery of the baby

*2, *5(1) The lens of the eye 150 mSv/year(2) SkinEquivalentdose limits

500 mSv/year*2(3) Abdomen surface 2 mSv for a period of time starting fromof pregnant worker the time when her employer and others
are informed of her pregnancy by herreporting or any other means up to thetime of the delivery of the baby

* 1: Each period of time derived from the division of years from April 1, 2001 into
increments of 5 years* 2: The time span of 1 year with April 1 as the starting date
* 3: Excluding those who were diagnosed as being unable to achieve a pregnancy,
those who made an offer of having no intention of becoming pregnant inwriting, and those who are currently pregnant* 4: Three-month periods each with the starting date set on April 1, July 1, October
1 and January 1* 5: This dose limit is in revision. The new dose limit will be set at 100mSv in 5
years and 50mSv in any single year.

91IV. Biological Effects of Radiation

14-2. Application of dose limit
According to the Act on the Regulation of Radioisotopes, etc., electrons and
X-rays devices with energy less than 1 MeV are not subject to regulation, but
exposure dose from such radiation devices must be included in total
personal exposure. Radiation doses from medical exposure and natural radiation
exposure are not subject to the dose limits.
14-3. Equivalent dose limits other than those mentioned above
Dose limit for radiation workers engaging in emergency operations inradiation facility is stipulated as 100 mSv in the Act; this is limited to men and to
women who are diagnosed as infertile.

92

V. The Act and Regulations

V. The Act and Regulations
1.

Act on the Regulation of Radioisotopes, etc.

“Act on the Regulation of Radioisotopes, etc. including its Enforcement
Regulations and notifications etc. (Acts and Regulations)” apply uniformly
regardless of the nature of the facility. It is appropriate to think of them as
stipulating the minimum standards that the facility and the radiation workers
must observe, and, accordingly, each facility, while of course meeting thelegally prescribed standards, should implement radiation control appropriate
for its own activities.
1-1. Why is control based on the Acts and relevant Regulations necessary?
Radiation and radioactive materials may be causes of hazardous effects.
When people attempt to use them, their use should always be controlled.
1-2. Historical background for the Act and Regulations concerning
radiation hazards in Japan
Radiation, especially X-rays, came into use relatively early in the medical andresearch fields. It wasn't until the mid-1950s that the use of radiation andradioisotopes in areas other than medicine and research began. In response to thenew developments, the Atomic Energy Basic Act and the Act on Prevention ofRadiation hazards due to Radioisotopes, etc., and relevant Ordinances were passed
in 1955 and 1957, respectively. Both have been revised many times since then,based on the latest scientific and technological knowledge. Because the Act on
Concerning Prevention of Radiation Hazards (former Act on the Regulation ofRadioisotopes, etc.) was drafted and modified in line with recommendations of the
ICRP, its provisions on radiation control are not significantly different from thosein other countries.
1-3. Characteristics of the Act
The purpose of the Act on the Regulation of Radioisotopes, etc. is to prevent
radiation hazards due to such activities, to secure specified radioisotopes and toensure public safety. In order to attain this purpose, the Act provides for the93

V. The Act and Regulations

regulation of facilities (requirements for facilities) and for the regulation of people's
actions, etc. (requirements for actions).

Fig. 51 Role of the Act and the Regulation

94

V. The Act and Regulations

2.

Hierarchy of the Act and Relevant Regulations

Act is enacted by the National Diet, which is the national legislative body.
Various administrative bodies are then empowered to establish statutory
instruments - Cabinet Order, Enforcement Regulations, and Notifications by
any minister directly to the public. In this chapter, these are collectively called
Acts and regulations.

2-1. Relationship among Acts and Regulations
An example of the relationships among Acts and Regulations is shown in
Table 14. Acts are enacted by the Diet, establishing fundamental principles. Details
are then provided in enforcement ordinances, enforcement regulations, andpublic notices.
2-2. Administrative GuidanceDespite the existence of Acts and Regulations, many actual situations
involving radiation may not be adequately dealt with by specific provisions.
Therefore, administrative bodies sometimes provide guidance in the form ofguidelines and notifications, in order to attain the administrative purpose.
2-3. Rules in each facility
Each facility is required to establish local rules called Radiation Hazards
Prevention Program, in accordance to the Act on the Regulation of Radioisotopes,
etc. and the Enforcement Regulation. Under the Act for the Regulation of Nuclear
Source Materials, Nuclear Fuel Materials and Reactors, they are called Security
Rules.
Many facilities, moreover, in addition to their rules, maintain their own
radiation control manuals, which can be revised as appropriate at any time.

95

V. The Act and Regulations
Table 14 Hierarchy of the Act and the Regulation

Acts and Regulations

Diet

Act

Act on the Regulation of Radioisotopes, etc.

Cabinet Cabinet Order

Order for Enforcement of the Act on theRegulation of Radioisotopes, etc.

NRA*

Enforcement
Regulations

Ordinance for Enforcement of the Act on theRegulation of Radioisotopes, etc.

NRA*

Notifications

Notification to Specify Standards for theAmount, etc. of Radioisotopes

NRA*

Announcement

For example, Safety for Incineration of Waste
Liquid Scintillator

Facility

Internal
practices

Radiation Hazards Prevention Program*NRA: Nuclear Regulation Authority

96

V. The Act and Regulations

3. Acts and Regulations Concerning Radiation
In order to prevent radiation hazards for radiation workers and thegeneral public, while furthering the use of radiation and radioisotopes, many
Acts and Regulations have been enacted from various points of view, and thefacilities where radiation and radioisotopes are used are regulated by theseActs and Regulations.
3-1. Acts and Regulations concerning radiation
Acts and Regulations concerning radiation include the Atomic Energy Basic
Act, which deals with the development and use of nuclear power; the Regulations
on Prevention of Ionizing Radiation Hazards, concerned with the protection ofradiation workers at radiation facilities; the Medical Care Act, regulating the useof radiation for diagnosis and therapy; and the Rules to Manufacture and Handle
Radioactive Pharmaceuticals, on the production of radiopharmaceuticals.
3-2. Acts and Regulations to promote the use of atomic energy
The principal Act governing promotion of research and development, and theuse of nuclear power, is the Atomic Energy Basic Act. Under the Act, research anddevelopment, and use of atomic energy, are limited to peaceful purposes, withassured safety, independent operations, government oversight results madeavailable to the public, and a commitment to international cooperation.
The Atomic Energy Basic Act also provides for the separate enactment of the
Act on the Regulation of Radioisotopes, etc. to prevent such hazards and ensure
public safety; and of the Act on the Regulation of Nuclear Source Materials,
Nuclear Fuel Materials and Reactors (shortly, the Nuclear Reactor and Fuel
Regulation Act), to regulate safety control in regard to nuclear materials and reactor
operations.

97

V. The Act and Regulations

4. What is the Act on the Regulation of Radioisotopes, etc.?
Pursuant to the Atomic Energy Basic Act, the Act was enacted to prevent
radiation hazards and ensure public safety, by regulating the use of radiation
and radioisotopes, and management of contaminated objects. Originallyenacted in 1957, it has been revised in accordance with recommendations of the
ICRP.
4-1. Requirements for facilities
Prior to the use of radiation or radioisotopes, permission or notification to
the Nuclear Regulation Authority (NRA) is required. Upon granting permission,
the NRA confirms that the location, structure and equipment of facilities to be used,
for storage and to manage wastes meet the technical standards (standards forfacilities) prescribed in the Act and Regulation. Even after permission is granted,
the NRA conducts regular periodic inspections of all facilities handlingradioisotopes in excess of a defined quantity, to see that the technical standards
are maintained (regular periodic inspections, etc.).
Table 15 Standards for facilities requiring permission or notification
Permission User

Notification User

The use of radioisotopes or radiation The use of sealed radiation sources of thegenerating apparatus (excluding those quantity exceeding the exemption limit but
for which the notification requirement not exceeding 1,000 times the lower boundapplies)quantity

4-2. Requirements for actions
Permission or Notification users must comply with a series of standards
for safety control, in order to prevent radiation hazards. Specific standards apply
in the following areas: education and training, measurement of personal dose,
health surveillances shall be provided for any radiation workers who enter acontrolled area. Dose rate at places where there is risk of radiation hazard shall bemeasured.

98

V. The Act and Regulations

4-3. Local Rules on Radiation Safety Control
Detailed rules on radiation safety control, in accordance with the conditions
and circumstances of the facility, must be provided in each facility's Radiation
Hazards Prevention Program.

99

V. The Act and Regulations

5. Acts and Regulations to Protect Workers
Regulation on Prevention of Ionizing Radiation Hazards was establishedunder the Industrial Safety and Health Act, solely to protect workers at
working sites from radiation hazards. Similar regulations are establishedunder different Acts for seamen, government employees, self-defense-force
members, miners, and others.
5-1. A Regulation of the Ministry of Health, Labor and Welfare:“the Regulations on Prevention of Ionizing Radiation Hazards”
The Regulations on Prevention of Ionizing Radiation Hazards was establishedunder the Industrial Safety and Health Act providing for regulations based on theprinciple that employers (operators) should try to minimize ionizing radiation towhich workers are exposed in the course of their jobs.
An industrial physician and a safety supervisor must be appointed under the
regulations. Safety supervisors deal with technical matters associated with safe
operations of X-ray apparatuses such as X-ray analyzers and X-ray diffraction
devices.
These regulations, unlike the Act on the Regulation of Radioisotopes, etc.,
cover X-rays and electrons with energy less than 1 MeV, and the mining of nuclear
source materials.
5-2. Working Environment Measurement Act
This Act, together with the Industrial Safety and Health Act, stipulates
qualifications of experts and organizations for monitoring.
5-3. Rules of the National Personnel Authority
The Rules of the National Personnel Authority 10-5 (Prevention of Radiation
Hazards for Employees) were established under the National Public Service Act,to protect regular government employees from radiation hazards. The contents arealmost the same as those of the Regulations on Prevention of Ionizing Radiation
Hazards that are not applicable to government officials.

100

V. The Act and Regulations

Fig. 52 Working Environment Measurement Act and Regulation on
Prevention of Ionizing Radiation Hazards

101

V. The Act and Regulations

6. Who are Radiation Workers?
Those who handle radiation generating apparatus or radioisotopes mainly incontrolled areas are called “radiation workers” under the Act on the Regulationof Radioisotopes, etc. Because radiation workers handle radiation andradioisotopes, which are considered to be harmful materials, such workers
must fully understand the basic concepts regarding radiation and its
deleterious effects, and observe the provisions in Acts and Regulations and in
the Radiation Hazards Prevention Program at their facility.
6-1. Why is it necessary to specifically identify “radiation workers”?
Radiation and radioisotopes are considered harmful, and should not be handled
by just anyone. Only those who have completed specific steps to work incontrolled areas are allowed to use radiation or radioisotopes - i.e., to become asradiation workers. Radiation workers, in the course of their handling of radiation
and radioisotopes, are concurrently subject to necessary regulations control(education and training, exposure control and health surveillance).
6-2. Steps in becoming a radiation worker
Only those who have had required education and training and have had healthsurveillances, are allowed to enter controlled areas as radiation workers. Educationand training are given to radiation workers to ensure that they have the enoughknowledge and skills required as radiation workers. Health surveillances are
required to determine if the individual is medically suitable for assignments
involving the handling of radiation and radioisotopes.
If a radiation worker has experience handling radiation at, for example,
another facility, his or her previous exposure dose records must be checke102

V. The Act and Regulations

6-3. Regulations
Workers designated as “radiation workers” may handle radiation andradioisotopes in controlled areas according to all applicable rules and procedures.
Radiation workers receive on a regular basis: 1) education and training, 2)
health surveillances, and 3) personal monitoring in controlled areas. Radiation
workers must be informed of the results of their personal monitoring each time, andthey themselves should make a habit of confirming such results.

103

V. The Act and Regulations

7. Who are Radiation Protection Supervisors?
In order to conduct appropriate and thorough radiation safety control ata facility, it is necessary to have a management structure or mechanism inplace that is responsible for radiation protection control within the facility. Insuch a situation, the radiation protection supervisor is playing a key role. The
radiation protection supervisor makes the radiation protection programs forthe facility, taking its nature and specific circumstances into consideration,and over sees operations to make sure the programs are implemented properly.
7-1. Who are radiation protection supervisors?
Radiation protection supervisors are the person responsible for supervisingefforts to prevent radiation hazards. They are appointed at any facility whereradiation or radioisotopes are handled in the course of using, selling, or leasing, ofthem and waste management.
7-2. Role of radiation protection supervisors in the facility
Radiation protection supervisors are responsible for supervising all mattersassociated with radiation control and radiation safety in their facility. Radiation
workers must follow the instructions of the radiation protection supervisor
concerning radiation safety control. The employer must also pay serious attention
to the decisions of the radiation protection supervisor on matters necessary forradiation safety control.
7-3. Categories of radiation protection supervisor certificate
To be qualified as a radiation protection supervisor, a person must complete
required pass a national examination and training courses. The certificate are threeclasses of radiation protection supervisors - first class to third class. Which class isrequired by a particular facility depends on the kind and level of radiation orradioisotopes handled. Radiation protection supervisors must attend periodic
training on an on-going basis, in order to always have the latest information in thefield of radiation protection.

104

V. The Act and Regulations

7-4. Cooperation with radiation protection supervisors
The radiation protection supervisors are responsible for supervisingradiation safety control at a facility. Good radiation safety control will be
implemented by good communication among radiation protection staff andradiation workers under a leadership of the radiation protection supervisors (seeⅢ1).
7-5. Periodic Training for Radiation Protection Supervisors
A radiation protection supervisor must attend periodic training within one
year from the day of the appointment as a radiation protection supervisor (however,persons are excluded, who have received periodic training for radiation protection
supervisors within a period of one year prior to the appointment as a radiation
protection supervisor). Moreover, the radiation protection supervisors who received
periodic training, must receive periodic training within a period of three years,(within a period of five years for a notification seller or a notification lessor) startingfrom upcoming fiscal year in Japan; that is April 1.

Fig. 53 Radiation protection supervisor

105

V. The Act and Regulations

8. What is Radiation under Acts and Regulations?
“Radiation” as used in Acts and Regulations does not mean radiation
as the word is understood in physics; rather, it means radiation as specified in
the Atomic Energy Basic Act. Among the many kinds of electromagnetic
waves and particles, the Act defines radiation as alpha rays, gamma rays andother radiations with the ability to directly or indirectly ionize the air.
8-1. There are various types of radiation
Radiation broadly means all electromagnetic waves and corpuscular beams.
X-rays from X-ray generating apparatus, alpha and beta rays emitted during the
decay of atomic nuclei, and gamma rays, are all well-known types of radiation.
Particles emitted during nuclear reactions, mutual transformations of elementary
particles, and cosmic rays are also type of radiation.
Legally, however, radiations generated artificially and that have the ability
directly or indirectly to ionize air are defined as “radiation”, as shown below.
The radiation defined in the Cabinet Order for the Definition of Nuclear
Source Material, Nuclear Fuel Material and Nuclear Reactor is:1) Alpha rays, deuterons, protons and other heavy charged-particles,
and beta rays;
2) Neutrons;3) Gamma rays and characteristic X-rays (limited to characteristic X-rays
generated at the time of electron capture); and
4) Electrons and X-rays with energy of 1 MeV or more.
8-2. Definitions of radiation in other Acts and Regulations
According to the Laws and Regulations, electrons and X-rays with energy
over 1 MeV are classified as “radiation”, whereas the Medical Care Act regulates
X-ray generating apparatus with a tube voltage of 10 kV or more. Also, under the
Regulations on Prevention of Ionizing Radiation Hazards by the Ministry of Health,Labour and Welfare (MHLW), although the regulations do not specify an energy limit,
and the MHLW has decided that X-ray generating apparatus with tube voltage of 10
kV or more must be regulated for the purpose of radiation protection.

106

V. The Act and Regulations

8-3. Radiation subject to dose evaluation
Electrons and X-rays less than 1 MeV are not “radiation as defined by the
Act on the Regulation of Radioisotopes, etc., and the Nuclear Reactor and Fuel
Regulation Act, whereas they are included in the Regulations on Prevention of
Ionizing Radiation Hazards.
However, when dose is assessed, exposure to such radiation is to be added
to exposure from other legally defined “radiation”.

Fig. 54 Various types of radiations

107

V. The Act and Regulations

9.

What are Radioisotopes?
Legally, “radioisotopes” are isotopes emitting radiation, compounds ofthem, and materials containing them (including those equipped in instruments), in
quantities or concentrations exceeding those stipulated by the Cabinet Order.
Such quantities or concentrations are called “exemption limit”, becauseradioisotopes below the limit quantity or concentration are exempted from
regulations for radioisotopes.
Table 16 shows examples of the exemption limit for radioisotopes frequently
used in laboratories and factories. This means that anyone who has no experience
to deal with radioisotopes can have or use 108 Bq or 105 Bq/g of tritium of any
form without permission by or notification to the NRA.
It should be noted that the exemption level is not the activity level for
disposing of radioactive wastes without permission nor notification (clearance).
Table 16 Quantities and concentrations of main radioisotopes
above which are subject to regulations
Radioisotopes

Activity(Bq)

Activity concentration(Bq/g)

3

1×109

1×106

1×107

1×104

P

1×105

1×103

Co

1×105

1×101

131

I

1×106

1×102

Cs

1×104

1×101

H

14

C

32
60

137

108

V. The Act and Regulations

10.

What is Radiation Generating Apparatus?

At present, many kinds of radiation generating apparatus are in use.
There are substantial differences in capacity among such equipment, and theapplicable Acts differ. Under the Act on the Regulation of Radioisotopes, etc.,
several types of devices, including cyclotrons and linear accelerators, aresubject to regulation.
10-1. Radiation generating apparatus under Acts and Regulations“Radiation generating apparatus” covered by the Acts and Regulations
includes such devices as cyclotrons or synchrotrons generating radiation byaccelerating charged particles, as shown in the Table 17. Ordinary X-ray generating
apparatus for health surveillances are not included because the X-ray energy is
below 1 MeV. Also, when the maximum equivalent dose rate at a point 10 cm awayfrom the surface of the equipment is 600 nSv/h or less, such equipment is notincluded.
10-2. Use of radiation generating apparatus
At the entrance to a room where radiation generating apparatus is operated,
there must be automatic display systems which shows whether the apparatus is inoperation or not, and additionally there must be interlocking systems at the entrance.
Table 17

Radiation generating apparatus under the Act on theRegulation of Radioisotopes, etc.,*
Radiation Generating Apparatus

1.
2.
3.
4.
5.
6.
7.
8.

Cyclotron
Synchrotron
Synchro-cyclotron
Linear accelerator
Betatron
Van de Graaff accelerator
Cockcroft-Walton accelerator
Other type of radiation generating apparatus by accelerating charged
particles, specified by the NRA: transformer-type accelerator,
microtron, and plasma generating equipment capable of attaining a
critical plasma condition for the D-T reaction*Equipment for which the l cm depth dose equivalent at a point 10cm away from the surface ofthe equipment is 600 nSv/h or less are excluded.

109

V. The Act and Regulations

11. What is Sealed Radioisotopes?
Radioisotopes are classified into two categories for the purpose of control— sealed radioisotopes (sealed sources) and unsealed radioisotopes (unsealed
sources). Included in the sealed sources are sources for radiation therapy,
industrial sources, calibration sources, and sources for electron-capture
detectors for gas chromatography. Sealed sources present no danger inregard
to contamination, but external exposure must be a concern.
11-1. Safe handling of sealed sources
Sealed radioisotopes are basically used in circumstances that involve nodanger of their being opened or damaged under normal conditions, and they present
no risk of the contents being scattered and causing contamination as a result ofleakage, infiltration, etc. It is, however, always important to prevent overexposure
by taking appropriate measures for protection, regardless of the size or natureof the source. Also, leak testing should be done regularly, though it is not required
legally.
One of uses of sealed sources is in “Approved device with a certification
label”. These are instruments that the NRA has recognized as meeting technicalstandards in their mechanisms for the prevention of radiation hazards. One example
is an electron capture detector (ECD) for gas chromatography. In handling an ECD,
there is no danger of overexposure and the controlled area does not extend outside
the cabinet of the chromatography device, but it is important to always control thewhereabouts of the sources.
11-2. Management of disused sealed sources
Management of sealed sources that are no longer needed may be different
from the handling of radioisotope waste because a radioisotope contained in asealed source is usually high in activity and has a long half-life. Therefore, recovery
of disused sealed sources, including those installed in devices, should be asked ofthe manufacturer or of the Japan Radioisotope Association.

110

V. The Act and Regulations

Fig. 55 Return of sealed sources

111

V. The Act and Regulations

12. What is the Controlled Area?
At any facility where radiation or radioisotopes are dealt with, any area
where there is a possibility that the level of radiation or the concentration ofradioisotopes in the air or on surface might rise above a specified level isdesignated a controlled area, and access to that area must be restricted.
When unsealed radioisotopes are used, they must be used in a “workroom”,
where measures for cleaning the exhaust air, the floor and the wall areprovided.
12-1. Radiation levels in controlled areas
At frequently entered places (e.g., “workroom”) within controlled area, inorder to maintain total effective dose from external and internal exposure atunder 1 mSv per week, shielding material should be installed and working hours
restricted when necessary.
In addition, outside the boundary of the controlled area, effective dose fromexternal radiation must not to exceed 1.3 mSv per 3 months. Radiation levels inareas where people live are requested to be the same as those at the boundary of thesite of facility, i.e., 250 µSv per 3 months.
The radiation levels to be maintained are shown in Table 18. At the entranceof a controlled area, a notice required to prevent radiation hazards is to be posted atclearly visible locations in usage facilities or in a controlled area.

12-2. Radiation work in controlled areas
When unsealed radioisotopes are handled at a facility, it must be done in a
specifically provided “workroom”. Because such a “workroom” is a place wherea person can regularly enter within radiation facilities, the radiation level is controlled
not to exceed 1mSv per week and the surface density of radioisotopes on the objects
shall be kept not exceeding the limit of surface density.

112

V. The Act and Regulations

12-3. Contamination inspection room
At any facility where unsealed radioisotopes are used, a contamination
inspection room has to be provided near the entrance/exit regularly used by workers.
In the contamination inspection room, there are washing facilities, a place to change
clothes, radiation measuring equipment, etc. When workers leave the controlledarea where radioactive contamination may occur, they must confirm that theirbodies are not contaminated.
When skin contamination is detected, it must be removed (decontaminated)using the washing facilities. If any significant contamination still remains on theskin after the decontamination procedure as instructed, radiation protection staff
member shall be notified of the matter.
Table 18 Radiation limit to be maintained in andaround a controlled area
Area/Item
Effective dose

Frequently entered place
within a controlled area
1 mSv per week

Outside boundary ofa controlled area
1.3 mSv per 3 months

Concentration of Average concentration for 1
radioisotopes in week: as mentioned in column
the air
4 of Table 2 attached to the
Notification on Quantity ofRadioisotopes*

1/10 of the values in theleft column

Concentration of Radioisotopes emitting alphasurface density rays: 4 Bq・cm-2 or less;1/10 of the values in theleft column

Radioisotopes not emittingalpha rays: 40 Bq・cm-2 or less* Specifying Standards for the Quantities, etc. of Radiation-Emitting Isotopes

113

V. The Act and Regulations

13. What is meant by “Radiation Levels outside Controlled Areas”?
In order to prevent hazards to the public and non-radiation workers fromradiation and radioisotopes, limits for radiation levels apply to various areas otherthan controlled areas. Pursuant to the Acts and Regulations, limits for radiationlevels around the controlled areas and area for residence inside of factory or place ofbusiness are set.
Radiation levels are also regulated at the boundary of the place of business,to ensure the safety of the public, separately from regulations for the safety ofradiation workers working in controlled areas. Limits for radiation levels outside
the controlled areas of a facility are shown in Table 19.
Table 19 Limits for radiation levels at various locations
outside controlled areas
Item

Locations

Effective dose from Outside the boundary of the place of business: 250 µSv
external and internal for 3 months;
exposure
residence inside of factory or place of business: 250 µSv
for 3 months;
Sickrooms in hospitals and clinics: 1.3 mSv for 3
monthsAverageconcentration ofradioisotopes in theexhaust or air

Average concentrations for 3 months are the same as
those mentioned in column 5 of Table 2 attached to the
Notification

Averageconcentration ofradioisotopes inliquid discharge ordrain water

Average concentrations for 3 months are the same as
those mentioned in column 6 of Table 2 attached to the
Notification

114

V. The Act and Regulations

14. Secure Specified Radioisotopes Manager
To prevent radiation hazards caused by those radio activities, to secure
specified radioisotopes and to ensure public safety, specified radioisotope security
manager is appointed from among the persons who satisfy the requirements
provided for in the NRA Regulation concerning the knowledge on handling ofspecified radioisotopes, etc., in order to have the manager supervise uniformly theduties on the security of specified radioisotopes, pursuant to provisions of the NRARegulation.
Moreover, the facility prepares specified radioisotope security program, andthey have to take periodic training for specified radioisotope security managers.

Fig. 56 Boundary of a place of business115

Ⅵ.. Radiation Hazards Prevention Program

Ⅵ. Radiation Hazards Prevention Program
1.

What is the Radiation Hazards Prevention Program?

The Radiation hazards prevention Program is the basis for radiation protection
at a facility. In the Program, the basic concepts of radiation protection at thefacility, the safety control structure, and specific practices that radiation workers
must adhere to, are all spelled out. The operating management of the facility,
the radiation protection supervisor, radiation protection staffs and radiation workers
must thoroughly understand and observe the Radiation Hazards Prevention
Program.
For radiation workers, an explanation of the Radiation Hazards
Prevention Program is required to be given prior to the actual start of work in thecourse of education and training.
1-1. The Radiation Hazards Prevention Program
The Radiation Hazards Prevention Program is a specific rules for the
implementation of radiation safety control and the prevention of radiation hazards
at each facility.
The Radiation Hazards Prevention Program is the pledge regarding radiation
control at the facility. The responsibilities of the operating management of the
facility, the radiation protection supervisor, radiation protection staffs, and radiation
workers are prescribed.
Items legally required to be included in the Radiation Hazards Prevention
program are listed below.
1-2.

Relationship between radiation workers and the programBecause the rules at each facility are based on the Act on the Regulationof Radioisotopes, etc., radiation workers are not required to know all the detailsof the Act itself. However, they must fully understand all items in the Radiation
Hazards Prevention Program relating to what they themselves must do.

For thisreason, lectures on the program are included within the education and training
curriculum provided prior to the worker's handling of radiation or radioisotopes forthe first time.

116

Ⅵ. Radiation Hazards Prevention Program
Items to be covered in the Radiation Hazards Prevention Program(1) matters concerning the duties and organization of radiation protection
supervisors and other persons engaged in safety management in handling ofradioisotopes, etc. or radiation generating apparatuses (including the duties andorganization of persons engaged in handling of radioisotopes, etc. or radiation
generating apparatuses);(2) matters concerning of a deputy of a radiation protection supervisor;(3) matters concerning the maintenance and management of radiation facilities(including management of persons who enter the area deemed not to be controlledarea as special exception of a controlled area pertaining to radiation generating
apparatus (Article 22-3 Paragraph 1) and the inspection of radiation facilities(controlled area in cases where a notification user uses sealed radioisotopes ormanages disused sealed radioisotopes or wastes contaminated with radioisotopes);(4) matters concerning the use of radioisotopes or radiation generating apparatuses(including matters pertaining to the method for confirmation of the quantity of
unsealed radioisotopes in the case where outside a usage facility a permission user
uses unsealed radioisotope of the quantity not exceeding the lower bound quantity per
day (Article 15 Paragraph 2);(5) matters concerning receipt, delivery, storage, transport or waste management ofradioisotopes, etc. (for a notification lessor, including measures taken whenradioisotopes leased to a permission or notification user are not properly stored);(6) matters concerning measurements of the quantity of radiation and condition ofcontamination by radioisotopes and the measures for the prepare books and therecords of results of the measurements (Items of Article 20 Paragraph 4);(7) matters concerning education and training required to prevent radiation hazards;(8) matters concerning health surveillance;(9) matters concerning measures necessary for the health of a person who has
suffered or is likely to suffer radiation hazards;(10) matters concerning preparation and storage of books as obligation to prepare
books (Article 25 of the Act);(11) matters concerning measures to be taken when an earthquake, fire or other117

Ⅵ. Radiation Hazards Prevention Program
disaster occurs (excluding measures pursuant to the provisions of the following
Items);(12) matters concerning emergency measures;(13) matters concerning provision of information in cases where radiation hazards
are likely to occur or have occurred;(14) matters concerning required items to take measure emergency responses as
emergency measures prescribed in Article 29 Paragraph 1 of the Act that those set
forth in the following Items (limited to using radioisotopes or radiation generating
apparatus provided for the NRA),a. matters concerning the duties and organization of persons engaged measured
to emergency responses,
b. matters concerning maintenance of required facilities or equipment engaged
measured to emergency responses,c.

matters concerning procedure for implementation of emergency responses,d.

matters concerning enforcement of training about emergency responses,

e. matters concerning cooperation with prefectural police, fire services andmedical institution or other related organs;(15) matters concerning business improvement for prevent radiation hazards (limited
to specified permission user or permission waste management operator);(16) matters concerning report of status of radiation control;(17) matters concerning measures to be taken for prevention of radiation hazards
according to the decay of radioactivity in burial wastes that are buried in waste burialsite (limited to the case where waste burial is conducted);(18) other necessary matters concerning prevention of radiation hazards.

118

119

Appendix 1(Sign)
Radioisotope Use RoomRadiation Generating
Apparatus Use RoomRadioactive Waste
Repacking Room

Waste Management
Workroom

Contamination Inspection
Room

Activated Objects Storage
Equipment (No Entry
without Permission)

Container Prepared in an
Activated Objects Storage
Equipment

Storage Room (No Entry
without Permission)

Storage Box (No Touch
without Permission)

120

Container Prepared in a
Storage Facility(Radioisotopes)

Container prepared in a
Storage Facility(Radioactive Waste)

Exhaust Equipment (NoTouch without Permission)

Drainage Purification Tank (No Entry without Permission
or No Touch without Permission)

Predisposal Equipment (NoEntry without Permission)

Container Prepared in a
Predisposal Equipment

Usage Facility(No Entry
without Permission)

121

Storage Facility(No Entry without
Permission)Waste Management Facility(No Entry without
Permission)

Waste Repacking Facility(No Entry without
Permission)

Controlled Area (Place of
Use of Radioisotopes) (No
Entry without Permission)

Controlled Area (Place of
Use of Radiation Generating
Apparatus) (No Entry
without Permission)

122

Waste Storage Facility(No Entry without
Permission)

Basic Knowledge of Radiation and Radioisotopes（2019）©Japan Radioisotope Association,1997/2003/2005/2016/2019

第 5 版（2019 年版）は大学等放射線施設協議会の監修協力により改訂を行いました。ここに記して感謝の意を表します。
担当
1・5・6 章 Appendix1
2章
3章
4章

監修協力（敬称略）
桧垣正吾（東京大学）
柴田理尋（名古屋大学）
平田雄一（北海道大学）
松田尚樹（長崎大学）

Basic Knowledge of Radiation and Radioisotopes (2019)(Scientific Basis, Safe Handling of Radioisotopes and Radiation Protection)
1997 年 11 月 21 日 初版発行
2003 年 9 月 8 日 改訂版発行
2005 年 6 月 30 日 第 3 版発行（2005 年 6 月に施行された放射線障害防止法関係法令に準拠）
2016 年 2 月 1 日 第 4 版発行
2019 年 10 月 30 日 第 5 版発行（2019 年 9 月に施行された放射性同位元素規制法関係法令に準拠）
編 集

公益社団法人 日本アイソトープ協会

発 行
113-8941 東京都文京区本駒込二丁目 28 番 45 号
TEL
E-mailURL© Japan Radioisotope Association, 1997/2003/2005/2016/2019

03 - 5 3 9 5 - 8 0 35

s-shogai@jrias.or.jp
https://www.jrias.or.jp＊著作権法により本書の著作権は日本アイソトープ協会に帰属します。転載を希望される方は上記メールアドレスまでご連絡ください。

ISBN978-4-89073-273-9 C2040