In 1955, the United Nations General Assembly established theScientific Committee on the Effects of Atomic Radiation (UNSCEAR)
to collect and evaluate information on the levels and effects of­ionizing radiation.

This publication attempts to present objectively the latest­ nowledge on radiation levels and effects in a way that is ­accessiblekto the general reader. It is based on UNSCEAR’s scientific reports,
which are used as the main source of information.

RADIATION EFFECTS and SOURCES

This was in response to concerns about the effects of ionizing
radiation on human health and the environment as at that time
fallout from atmospheric nuclear weapon tests was reaching­people through air, water and food. UNSCEAR’s first report laid the­scientific grounds on which, in 1963, the Partial Test Ban Treaty
prohibiting atmospheric nuclear weapon testing was negotiated.

RADIATION
EFFECTS and SOURCES

What is radiation?
What does radiation do to us?
Where does radiation come from?

›1 000 mSv

100 mSv

Dose used in radiotherapy

Astronaut dose
(4 months)

10 mSv

CT scan of the abdomen

1 mSv

Worker dose in nuclear industry(1 year)

0.1 mSv

Chest X-ray or flight (20 hours)

0.01 mSv

Dental X-ray

0.001 mSv

Brazil nuts (30 g)

United Nations Environment ProgrammeRADIATIONEFFECTS and SOURCES
What is radiation?
What does radiation do to us?
Where does radiation come from?

United Nations Environment Programme

DISCLAIMER
This publication is largely based on the findings of the United Nations ScientificCommittee on the Effects of Atomic Radiation, a subsidiary body of the United
Nations General Assembly and for which the United Nations Environment
Programme provides the secretariat. This publication does not necessarily
represent the views of the Scientific Committee or of the United Nations
Environment Programme.
The designations employed and the presentation of the material in this publication do not imply the expression of any opinion whatsoever on the part of theUnited Nations Environment Programme concerning the legal status of any
country, territory, city or area or of its authorities, or concerning delimitation of
its frontiers or boundaries.
This publication may be reproduced in part and in any form for educational or
non-profit purposes without special permission from the copyright holder,provided acknowledgement of the source is made. The United Nations
Environment Programme would appreciate receiving a copy of any print material
that uses this publication as a source.
No use of this publication may be made for resale or for any other commercial
purpose whatsoever without prior permission in writing from the United Nations
Environment Programme.
The United Nations Environment Programme promotes environmentally soundpractices globally and in its own activities. This publication was printed onr ecycled paper, 100 per cent chlorine free. UNEP’s distribution policy aims to
reduce its carbon footprint.
Cataloguing: Radiation: effects and sources, United Nations Environment
Programme, 2016
ISBN: 978-92-807-3517-8
Job No.: DEW/1937/NA
Copyright © United Nations Environment Programme, 2016
Corrected electronic version

RADIATIONEFFECTS and SOURCES
What is radiation?
What does radiation do to us?
Where does radiation come from?

United Nations Environment Programme

ACKNOWLEDGEMENTS
This booklet is largely based on the findings of the United Nations Scientific Committee
on the Effects of Atomic Radiation and on the United Nations Environment Programme
publication Radiation: doses, effects, risks, initially edited in 1985 and 1991
by Geoffrey Lean.
Technical editing: Malcolm Crick and Ferid Shannoun
Text editing: Susan Cohen-Unger and Ayhan Evrensel
Graphics and layout: Alexandra Diesner-Kuepfer
Furthermore, the following persons provided valuable contribution and comments on
this booklet:
Laura Anderson, John Cooper, Susan Cueto-Habersack, E­ milie van Deventer, Gillian Hirth,David Kinley, Vladislav Klener, Kristine Leysen, Kateřina Navrátilová-Rovenská,
Jaya Mohan, ­Wolfgang-Ulrich Müller, Maria Pérez, Shin Saigusa, Bertrand Thériault,­Hiroshi Yasuda and Anthony Wrixon.

FOREWORD
Hiroshima, Nagasaki, Three Mile Island,
Chernobyl and Fukushima-Daiichi: thesenames have become associated withthe public’s fear of radiation, either fromuse of nuclear weapons or accidents at
nuclear power plants. In fact, p­ eopleare much more exposed daily to radiation from many other sources, including
the atmosphere and the Earth as well asfrom applications used in medicine andindustry.
In 1955, nuclear weapon tests raised
public concerns about the effects ofatomic radiation on air, water and food. In response, the United Nations
General Assembly established the United Nations Scientific ­Committee
on the Effects of Atomic Radiation (UNSCEAR) to collect and evaluate information on the levels and effects of radiation exposure. The C­ ommittee’s
first report laid the scientific grounds for negotiating the ­Partial Test
Ban Treaty in 1963 that prohibited atmospheric nuclear weapon testing. Since then, it has continued to ­produce high-profile reports onradiation exposure, including from the accidents at the Chernobyl and
Fukushima-Daiichi nuclear power plants. The Committee has consistently delivered work of great value both to the scientific c­ ommunity andpolicymakers.
While the scientific community has published information on radiation sources and effects, it has tended to be technical and perhaps­difficult for the general public to understand—which has often confused,rather than informed, the public, meaning that the fear and confusion
engendered decades ago prevails. This publication tackles the issue by
detailing the most up-to-date scientific information from UNSCEAR—
on the types of r­ adiation, their sources and effects on humans and theenvironment—and making it accessible to the general reader.
Today, the UNSCEAR secretariat operates under the auspices of theUnited Nations Environment Programme (UNEP), which helps countries
implement environmentally sound policies and practices. Helping the
public understand radiation and how it affects life on this planet lies
within the core mandate of UNEP.

I am very pleased to ­congratulate all those who have ­contributed tothis publication, as well as all the m­ embers of the Committee and theirdelegations, who have worked so diligently for the past six decades onthese critical issues.

Achim Steiner
UNEP Executive Director andUnder-Secretary-General of the United Nations

CONTENTS
INTRODUCTION

1

1. WHAT IS RADIATION?

3

1.2. Some basics
				Radioactive decay and half-lives
				Radiation units

4
6
7

1.1.

1.3.

Some history

Penetration power of radiation

39

2. WHAT DOES RADIATION DO TO US?

11

2.2. Effects on animals and plants

22

2.3. Relationship of radiation doses and effects

24

2.1. Effects on humans
				Early health effects
				Delayed health effects
				Effects on offspring

13
14
15
18

3. WHERE DOES RADIATION COME FROM?

27

3.2. Artificial sources
				Medical applications
				Nuclear weapons
				Nuclear reactors
				Industrial and other applications

32
33
37
39
48

3.1. Natural sources
				Cosmic sources
				Terrestrial sources				 Sources in food and drink

3.3. Average radiation exposure to public and workers

28
28
29
32

54

INTRODUCTION
Before we begin, we need to distinguish between ionizing and nonionizing radiation. Ionizing radiation has enough energy to liberate
electrons from an atom, thereby leaving the atom charged, whereas
non-ionizing radiation, such as radio waves, visible light or ultra-violet
radiation, does not. This publication is about the effects of radiation
exposure from both natural and artificial sources. However, the word
radiation, throughout, refers only to ionizing radiation.

Examples of different applications using radiation
4

Radiospectrum

Microwave

Visible Ultra- X-rays Gamma Cosmic
light violet
rays
rays
Ionizing radiation

Infrared(eV) (Hz)Non-ionizing radiation

Frequency

104 105 106 107 108 109 1010 1011 1012 1013

1014 1015 1016 1017 1019 1021 1023

Energy10-10 10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1

1

101

102

104

106 108 1010

Non-ionizing radiation does not have enough energy—measured in electron volts (eV)—to make changes to atoms or molecules.

Today, we know more about the sources and effects of exposure toradiation than to almost any other hazardous agent, and the scientificcommunity is constantly updating and analysing its knowledge. Most
people are aware of the use of radiation in the nuclear power production of electricity or in medical applications. Yet, many other uses ofnuclear technologies in industry, agriculture, construction, research andother areas are hardly known at all. To someone who is reading about
the topic for the first time, it may come as a surprise that the sourcesof radiation causing the greatest exposure of the general public are notnecessarily those that attract the most attention. In fact, the greatest
exposure is caused by natural sources ever present in the environment,
and the major contributor to exposure from artificial sources is the use of
INTRODUCTION1

r­ adiation in medicine worldwide. Moreover, everyday experience such as
air travel and living in well-insulated homes in certain parts of the world
can substantially increase exposure to radiation.
This publication is an attempt by the United Nations Environment­ rogramme (UNEP) and the secretariat of the United Nations ScientificP
Committee on the Effects of Atomic Radiation (UNSCEAR) to help raiseawareness and deepen understanding on the sources, levels and effects
of exposure to ionizing radiation. Bringing together leading scientists
from 27 Member States of the United Nations, UNSCEAR was set up by
the United Nations General Assembly in 1955 to evaluate radiation­exposures, effects and risks on a worldwide scale. However, it does not
set, or even recommend, safety standards; rather it provides scientificinformation that ­enables national authorities and other bodies to do so.
UNSCEAR’s ­scientific evaluations over the past sixty years are the main
source of information for this ­publication.

2

1. WHAT IS RADIATION?
To be able to talk about the levels, effects and risks of radiation exposure, we first need to address some basics of radiation science. Bothradioactivity and the radiation it produces existed on Earth long before life
emerged. In fact, they have been present in space since the beginning of
the universe and radioactive material was part of the Earth at its very formation. But humanity first discovered this elemental, universal phenomenon
only in the last years of the nineteenth century and we are still learning new
ways of using it.

1.1. Some history
In 1895, Wilhelm Conrad Roentgen, a German physicist, discovered
radiation—which he called X-rays—that could be used to look into thehuman body. This discovery heralded the medical uses of radiation,
which have been expanding ever since. Roentgen was awarded the firstNobel Prize in physics in 1901 in recognition of the extraordinary services
he had rendered to humanity. One year after Roentgen’s discovery, Henri
Becquerel, a French scientist, put some photographic plates away in adrawer with fragments of a mineral containing uranium. When he developed them, he found to his surprise that they had been affected by radiation. This phenomenon is called radioactivity and occurs when energy
is released from an atom spontaneously and is measured today in units
called becquerels (Bq) after Henri Becquerel. Soon afterwards, a young
chemist, Marie Skłodowska-Curie, took the research further and was thefirst to coin the word radioactivity. In 1898, she and her husband Pierre
Curie discovered that as uranium gave off radiation, it mysteriously
turned into other elements, one of which they called polonium, after
her homeland, and another they called radium, the “shining” ­element.

Wilhelm C. Roentgen (1845–1923)

Marie Curie (1867–1934)

Henri Becquerel (1852–1908)

WHAT IS RADIATION?

3

Marie Curie shared the Nobel Prize in physics in 1903 with Pierre Curie
and Henri ­Becquerel. She was the first woman to win the Nobel Prize asecond time in 1911 for her discoveries in radiation chemistry.

1.2. Some basics
The scientists’ quest was to understand the atom and, more ­particularly,
its structure. We now know that atoms have a tiny, positively-charged
nucleus surrounded by a cloud of negatively-charged electrons. The nucleus
is only about one hundred thousandth of the size of the entire atom, but itis so dense that it accounts for almost the entire mass of the atom.
The nucleus is generally a cluster of particles, protons and neutrons,
clinging tightly to each other. Protons have a positive electrical charge
while neutrons have no charge. Chemical elements are determined by the
number of protons in their atoms (e.g. boron has an atom with 5 ­protons
and uranium has an atom with 92 protons). Elements with the same
number of protons but a different number of neutrons are called ­isotopes(e.g. uranium-235 and uranium-238 differ in three ­neutrons in their
nuclei). An atom as a whole is normally neither positively nor ­negatively
charged because it has the same number of negatively-charged electrons
as it has positively-charged protons.

The atomAtomic number
Symbol5

B- numberof electrons- numberName BORON 0f protons

electron

protonneutronAn atom is composed of a nucleus of uncharged neutrons and positively-charged protons
surrounded by a cloud of negatively-charged electrons. In uncharged atoms, the numberof electrons and protons is equal, representing the atomic number of the element.

4Some atoms are naturally stable while others are unstable. Atoms
with unstable nuclei—which spontaneously transform, releasing energy
in the form of radiation—are known as radionuclides. This energy caninteract with other atoms and ionize them. Ionization is the process
by which atoms become positively or negatively charged by gainingor ­losing electrons. Ionizing radiation carries enough energy to knock­electrons out of their orbit resulting in the creation of charged atoms
called ions. The emission of two protons and two neutrons is referred toas alpha decay and the emission of electrons as beta decay. Frequently,
the unstable nuclide will be so energized that the emission of particles
is not sufficient to calm it down. It then gives off a vigorous burst ofenergy in the form of electromagnetic waves as photons called gamma
rays.
X-rays are also electromagnetic radiation like gamma rays but withlower energy photons. An X-ray spectrum with different energies is­produced in a vacuum tube made of glass when an electron beam, emitted by a cathode, is fired at target material called an anode. The X-ray
spectrum depends on the anode material and the accelerating energyof the electron beam. Thus, X-rays can be generated artificially exactly
when they are needed, which is very advantageous in industrial andmedical applications.

X-ray tube
Electron beam
Glass (vacuum)

Anode

+

Cathode–––X-rays

WHAT IS RADIATION?

5

Radioactive decay and half-lives
While all radionuclides are unstable, some are more unstable thanothers. For example, the particles in the nucleus of a uranium-238 atom(with 92 protons and 146 neutrons) are only just able to cluster together.
Eventually, a clump of two protons and two neutrons will break away
and leave the atom as an alpha particle, turning the uranium-238 into­thorium-234 (with 90 protons and 144 neutrons). But thorium-234 is also
unstable, and transforms by a different process. By emitting high-energy
electrons as beta particles and converting a neutron into a proton, it
becomes protactinium-234, with 91 protons and 143 neutrons. This, inturn, is extremely unstable and soon becomes uranium-234, and so theatom goes on shedding particles and transforming itself until it finallyends up as lead-206, with 82 protons and 124 neutrons, which is stable.
There are many such sequences of transformation, or radioactive decay
as it is called.

238U

234U

years
illion4.5 b

Uranium-238—radioactive decay chain

1.17 min

80 000
years
214Po

214Bi

Different types of decay and their half-lives

218Po

3 min

210Bi

214Pb

22
yea
rs

gamma
decay

in

beta
decay

27 m

alpha
decay

ays
138 d

3.8 days

5 da
ys

19.7
m

222Rn

234Th

210Po

1 602 years

in

24
day
s

226Ra

ec

230Th

s
160 μ

234Pa

250 000 years

210Pb

206Pb Stable

The period it takes half of any amount of an element to decay is
known as its half-life. After one half-life, out of one million atoms on
average 500 000 will decay into something else. During the next halflife about another 250 000 atoms will decay, and so on, until all havedecayed. After 10 half-lives, only about a thousand remain of the original
million (i.e. about 0.1 per cent). In the example given above, it would

6

take a little over a minute for half of the atoms of protactinium-234 to
decay to ­uranium-234. In contrast, for uranium-238 it would take fourand a half billion years (4 500 000 000) for half of the atoms to decay to­thorium-234. That said, only relatively few radionuclides occur naturally
in the environment.

Radiation units
Today we know that the energy of radiation can damage living tissue,
and the amount of energy deposited in living tissue is expressed in terms ofa quantity called dose. The radiation dose may come from any radionuclide,or a number of radionuclides, whether they remain outside the body or irradiate it from inside, for example after being inhaled or ingested. Dose quantities are expressed in different ways depending on how much of the bodyand what parts of it are irradiated, whether one or many persons are
exposed, and the length of the period of exposure (e.g. acute exposure).
The amount of radiation energy absorbed
per kilogram of tissue is called the absorbed
dose and is expressed in units called grays(Gy) named after the English physicist andpioneer in radiation biology, Harold Gray.
But this does not give the full picture because
the same dose from alpha particles can domuch more damage than that from beta particles or gamma rays. To compare absorbed
doses of different types of radiation, theyneed to be weighted for their potential tocause certain types of biological damage.
This weighted dose is called the equivalentdose, which is evaluated in units called sieverts(Sv), named after the Swedish scientist Rolf
Sievert. One sievert is 1 000 millisieverts, justas one litre is 1 000 millilitres or one meter is
1 000 ­millimetres.

Harold Gray (1905–1965)
Rolf Sievert (1896–1966)

Another consideration is that some partsof the body are more vulnerable than ­others.
For example, a given equivalent dose of radiation is more likely to cause cancer in thelung than in the liver, and the reproductive
organs are of particular concern because
WHAT IS RADIATION?

7

of the risk of heritable effects. Thus, in order to compare doses when­different ­tissues and organs are irradiated, the equivalent doses to­different parts of the body are also weighted, and the result is called theeffective dose, also expressed in sieverts (Sv). However, the ­effective
dose is an indicator of the likelihood of cancer and genetic effects­following lower doses and is not intended as a measure of s­ everity ofeffects at higher doses.
This complex system of radiation quantities is necessary to bringthem into a coherent structure, allowing radiation protection experts torecord individual doses consistently and comparably, which is of major
importance for people working with radiation and who are ­occupationally
exposed.

Radiation quantities
Physical quantity
Activity

The number of nuclear transformations of energy perunit of time. It is measured as decays per second andexpressed in becquerels (Bq).

Absorbed dose

The amount of energy deposited by radiation in a unit
mass of material, such as a tissue or organ. It is
expressed in grays (Gy), which corresponds to joules
per kilogram.

Calculated quantity

8

Equivalent dose

The absorbed dose multiplied by a radiation factor (wR)that takes into account the way different types ofradiation cause biological harm in a tissue or organ.
It is expressed in sieverts (Sv), which corresponds tojoules per kilogram.

Effective dose

The equivalent dose multiplied by organ factors (wT)that take into account the susceptibility to harm­of different tissues and organs. It is expressed insieverts (Sv), which corresponds to joules per ­kilogram.

Collective ­effective dose

Sum of all effective doses of a population or group ofpeople exposed to radiation. It is expressed in
man-sieverts (man Sv).

This, however, describes only doses to individuals. If we add up all
the effective doses received by each individual in a population, the result
is called the collective effective dose or simply collective dose, and this isexpressed in man-sieverts (man Sv). For example, the annual collective
dose to the world population is over 19 million man Sv corresponding toan annual average dose per person of 3 mSv.

1.3. Penetration power of radiation
In short, radiation may take the form of particles (including alpha,beta and neutron particles) or of electromagnetic waves (gamma rays
and X-rays), all with different amounts of energy. The different emitting­energies and particle types have different penetrating power—and sohave ­different effects on living material. Since alpha particles are made up
of two positively-charged protons and two neutrons, they carry the mostcharge of all radiation types. This increased charge means that they interact to a greater extent with surrounding atoms. This interaction rapidly
reduces the energy of the particle and therefore reduces the penetrating
power. Alpha particles can be stopped, for example, by a sheet of paper.
Beta particles, made up of negatively-charged electrons, carry less charge
and are therefore more penetrating than alpha particles. Beta particles
can go through a centimetre or two of living tissue. Gamma rays and X-rays

Penetrating power of different types of radiationalphaparticlebeta
particle
X-rays
gamma
rays
electron
protonneutronneutronparticle

Paper

Body

Steel

Concrete

WHAT IS RADIATION?

9are extremely penetrating and will go through anything less dense thana thick slab of steel. Artificially produced neutrons are emitted froman unstable nucleus as a result of atomic fission or nuclear fusion.
­Neutrons can also occur naturally as a component of cosmic radiation.
Because neutrons are electrically neutral particles, they have a very high­penetrating power when interacting with material or tissue.

102. WHAT DOES RADIATION DO TO US?
Before going into more detail about the effects of radiation exposure, we should recall the pioneers in radiation science introduced­earlier. Soon after Henri Becquerel’s discovery, he himself experienced
the most troublesome drawback of radiation—the effect it can have on
living ­tissues. A vial of radium that he had put in his pocket damaged
his skin.
Wilhelm Conrad Roentgen, who discovered X-rays in 1895, died ofcancer of the intestine in 1923. Marie Curie, who was also exposed toradiation throughout her working life, died of a blood disease in 1934.
It is reported that by the end of the 1950s, at least 359 early radiation
workers (mainly doctors and other scientists) had died from their­exposure to radiation, unaware of the need for protection.
It is not surprising that those involved in applying radiation to patientswere the first to develop recommendations for ­radiation protection ofworkers. By 1928, the Inter­national X-ray and Radium Protection Committee was set up during the ­second International Congress of ­Radiology inStockholm and Rolf Sievert was elected as its first chair. After the ­Second
World War—to take account of new uses of radiation outside medicine—it was restructured and renamed as the International Commission on
Radiological Protection. Later on, between 1958 and 1960, Rolf Sievert
was the fourth chair of UNSCEAR, at a time when there was particularconcern about the genetic effects on humans from atomic weapon­testing.
With the growing awareness of the risks associated with exposure toradiation, the twentieth century witnessed the development of intensive
research on the effects of radiation on humans and the environment. The
most important evaluation of population groups exposed to radiation is
the study of approximately 86 500 survivors of the atomic bombings of­Hiroshima and Nagasaki at the end of the Second World War in 1945
(henceforth referred to as the survivors of the atomic bombings). ­Further,reliable data on the subject comes from experience with irradiatedpatients, and with workers after accidental exposure (e.g. Chernobyl
nuclear power plant accident), and from animal and cell ­experiments inlaboratories.

WHAT DOES RADIATION DO TO US?

11

Sources of information on radiation effects

Population studies

Animal experiments

Clinical investigations

Cell experiments

UNSCEAR evaluates scientific information on effects of radiation exposure on humans and the environment and tries to work out, as ­reliably as
possible, what effects can be associated with different ­levels of radiation
exposure. As mentioned earlier, radiation exposure depends on the typeof radiation, the time over which it is delivered and the amount of energy
deposited in the material. For its evaluations, UNSCEAR currently uses theterm low dose to mean levels below 100 mGy but greater than 10 mGy andthe term very low dose for any levels below 10 mGy.

Dose bands used by UNSCEAR

12High dose

More than ~1 Gy

Severe radiation accidents(e.g. firemen at the Chernobyl
accident)

Moderate dose~100 mGy to ~1 Gy

Recovery operation workers
after the Chernobyl accident

Low dose~10 mGy to ~100 mGy

Multiple computer tomography(CT) scans

Very low doseLess than ~10 mGy

Conventional radiography(i.e. without CT)

2.1. Effects on humans
Since the discovery of radiation, more than a century of radiation
research has yielded extensive information on the biological mechanisms by which radiation can affect health. It is known that radiation
can produce effects at the level of cells, causing their death or modification usually because of direct damage to deoxyribonucleic acid (DNA)strands in a chromosome. If the number of damaged or killed cells islarge enough, it may result in organ dysfunction and even death. Also,
other damage to DNA may occur that does not kill the cell. Such d­ amageis usually repaired completely but if not, the resulting modification—
known as cell mutation—will be reflected in subsequent cell divisions
and may ultimately lead to cancer. If the cells modified are those transmitting hereditary information to descendants, genetic disorders may
arise. Information on biological mechanisms and on heritable effects isoften gained from laboratory experiments.

Radiation damage to DNA strand
Single breakβγDouble breakα

α = alpha particle, β = beta particle and γ = gamma rays.

On the basis of the observation of their occurrence, health effects
following radiation exposure are defined here as either early or delayed
health effects. Generally, early health effects are evident through diagnosis of clinical syndromes in individuals, and delayed health effects—
such as cancer—through epidemiological studies by observation ofincreased occurrence of a pathology in a population. Further, special
attention is paid here to effects on children and on embryos/fetuses,
and to ­heritable effects.
WHAT DOES RADIATION DO TO US?

13

Early health effects
Early health effects are caused by extensive cell death/damage.
Examples are skin burns, loss of hair and impairment of fertility. These
health effects are characterized by a relatively high threshold that must
be exceeded over a short period before the effect occurs. The severity ofthe effect increases with increasing dose after the threshold has been
exceeded.
Generally, acute doses higher than 50 Gy damage the central nervous
system so badly that death occurs within a few days. Even at doses lower
than 8 Gy, people show symptoms of radiation sickness also known asacute radiation syndrome, which could include nausea, vomiting, diarrhoea, intestinal cramps, salivation, dehydration, fatigue, apathy, listlessness, sweating, fever, headache and low blood pressure. The term acuterefers to medical problems that occur directly after exposure rather thanones that develop after a prolonged period. However, victims may survive at first only to die from gastrointestinal damage one to two weeks
later. Lower doses may not inflict gastrointestinal injury but still cause
death after a few months, mainly from damage to the red bone marrow.
Still lower doses will delay the onset of sickness and produce less severe
symptoms. About half of those who receive doses of 2 Gy suffer fromvomiting after about three hours, but this is rare for doses below 1 Gy.

Accidental exposure in medicine

Radiotherapy involves
the delivery of high doses
to patients. Therefore,
prevention of
acute effects isa priority.

14

Fortunately, if the red bone marrow and the rest of the blood-forming
system receive less than 1 Gy, they have a remarkable capacity for regeneration and can completely recover—although there will be a higher riskof developing leukaemia in later years. If only part of the body is irradiated, enough bone marrow will normally survive unimpaired to replace
what has been damaged. Animal experiments suggest that even if only
a tenth of the active bone marrow escapes irradiation, the chances ofsurvival are nearly 100 per cent.
The fact that radiation can directly damage cell DNA is applied todeliberately kill malignant cells with radiation in cancer treatment known
as radiotherapy. The total amount of radiation applied in radiotherapy
varies depending on the type and stage of cancer being treated. ­Typicaldoses for solid tumour treatments range from 20 to 80 Gy to the tumour,which would endanger the patient if delivered as a single dose. Thus, inorder to control the treatment, radiation doses are applied in repeatedfractions of maximally 2 Gy. This fractionation allows cells of normal­tissue to recover, while tumour cells are killed because they are ­generally
less efficient at repairing after radiation exposure.

Delayed health effects
Delayed health effects occur a long time after exposure. In general,most delayed health effects are also stochastic effects, i.e. for which theprobability of occurrence depends on the radiation dose received. These
health effects are believed to be caused by modifications in the genetic
material of a cell following radiation exposure. Examples of delayed
effects are solid tumours and leukaemia occurring in exposed persons
and genetic disorders occurring in the offspring of persons who were
exposed to radiation. The frequency of occurrence—but not the severity—of these effects in a population appears to increase with larger doses.
Epidemiological studies are of great importance in understanding
delayed health effects after radiation exposure. Such studies use statistical methods to compare the occurrence of a health effect (e.g. cancer) inan exposed population with that in an unexposed population. If a considerable increase is found in the exposed population, it may be that it
is associated with the radiation exposure for the population as a whole.
The most important long-term evaluation of populations exposed
to radiation is the epidemiological study of the survivors of the atomic
bombings. This is the most comprehensive study ever conducted because
WHAT DOES RADIATION DO TO US?

15

of the large number of people, essentially representative of the general
population, receiving a wide variety of doses spread fairly evenly over the
body. Estimates of the doses received by this group are also relatively
well known. So far, the study has revealed a few hundred more cancer
cases than would be expected in this group if they had not been exposed
to radiation. Because many of the survivors of the atomic bombings arestill alive, studies are continuing in order to complete the evaluation.
CancerCancer is responsible for about 20 per cent of all fatalities and is themost common cause of death in industrialized countries after cardio­
vascular disease. About four out of ten persons in the general population
are expected to develop cancer during their lifetime even in the absenceof radiation exposure. In recent years, the most common cancers among
men have been lung, prostate, colorectum, stomach, and liver cancer
and among women they have been breast, colorectum, lung, cervix, andstomach cancer.
The development of a cancer is a complex process, consisting of a n­ umberof stages. An initiating phenomenon, most probably affecting a single cell,appears to start the process, but a series of other events seem to be necessary before the cell becomes malignant and the tumour d­ evelops. Cancer

Occurrences

Cancer appearance after radiation exposure

Solidcancers(except
thyroid)

Leukaemia

0

10

20
Years after exposure

16

30

40

becomes evident only long after the first damage is done, following a periodof latency. The probability of cancer occurring following radiation exposure
is a major concern and could be calculated for a group if it were exposed toa ­sufficiently high level of radiation to cause an increased occurrence of cancer that would overcome the statistical and other uncertainties. However,
the real contribution of radiation as a cause of cancer remains unknown.
Leukaemia, thyroid cancer and bone cancer first appear within a few
years of exposure to radiation, while most other cancers are not expresseduntil at least 10 years, often several decades, after exposure. However,no single type of cancer is uniquely caused by exposure to radiation so it
is impossible to distinguish radiation-induced tumours from those arising from many other causes. Nevertheless, it is important to estimate theprobability of getting cancer after certain doses of radiation in order toprovide a sound scientific basis for setting exposure limits.
Studies of people who received medical treatment using radiation,
people occupationally exposed, and—above all—the survivors of theatomic bombings build the foundation of the knowledge about the relationship between cancer and radiation exposure. These studies coverlarge samples of people who received exposure over many parts ofthe body and who were followed up over reasonably long periods. But
some studies have major drawbacks, mainly a different age distribution
from that of the normal population and the evidence that many of thethese patients were already sick when irradiated and had already been­receiving treatment for cancer.
More fundamentally still, almost all the data are based on the studyof people whose tissues have received quite high doses of radiation, one
gray or more, either as a single dose or over relatively short periods. Thereis little information on the effects of receiving low doses for a long time—
just a few studies on the effects of the range of doses normally received
by people working with radiation, and there is practically no direct information about the consequences of exposure to which the general public
are routinely subjected. Studies would need to track a large number ofpeople over a long period and eventually may still be too weak to observe
increases in occurrence of cancer compared to the baseline cancer rates.
UNSCEAR conducted comprehensive reviews of the occurrence ofc­ancer in populations exposed to radiation, and estimated that the­additional chance of dying of cancer due to radiation exposure above
100 mSv was about 3 to 5 in a hundred per sievert.
WHAT DOES RADIATION DO TO US?

17

Other health effects
High radiation doses to the heart increase the probability of cardio­
vascular diseases (e.g. heart attacks). Such exposure may happen d­ uring
radiotherapy, although treatment techniques nowadays result in lower cardiac doses. However, there is no existing scientific evidence to conclude
that exposure to low doses of radiation causes cardiovascular diseases.
UNSCEAR recognized that there was an increased occurrence of cataracts among Chernobyl emergency workers, possibly associated withhigh doses of radiation. Further, UNSCEAR has also studied the effects ofradiation on the human immune system in survivors of the atomic bombings, in emergency workers at the Chernobyl nuclear power plant and inpatients undergoing radiotherapy treatment. The effects of radiation on
the immune system are assessed by estimating changes in cell numbers or
by using a variety of functional analyses. High doses of radiation s­ uppress
the immune system mainly because of damage to lymphocytes. Their­reduction is currently used as an early indicator to determine the radiationdose after acute exposure.

Effects on offspring
If radiation damage occurs in reproductive cells, the sperm or ovum,
it can lead to heritable effects in descendants. Moreover, radiation candirectly damage an embryo or fetus already developing within the womb.
It is important to distinguish between radiation exposure of adults,­children and embryos/fetuses. UNSCEAR has conducted comprehensive
reviews of health effects, including heritable effects, in these groups.
Effects on children
Health effects in humans depend upon a number of physical factors.
Because of their anatomical and physiological differences, the impactsof radiation exposure on children and on adults are different. Further,because children have smaller bodies and are less shielded by overlying
tissues, the dose to their internal organs will be higher than that for adults
for a given external exposure. Also, children are shorter than adults, so they
may receive higher doses from radionuclides deposited on the ground.
Regarding internal exposure, because of the smaller size of c­ hildren,and because their organs are, thus, closer together, radionuclides­concentrated in one organ irradiate other organs more than would be the18case for adults. There are also many other age-related factors involving
metabolism and physiology that make a substantial difference in dose atdifferent ages. Several radionuclides are of particular concern regarding
internal exposure of children. Accidents involving releases of radioactive
iodine-131 can be significant sources of exposure of the thyroid. For agiven intake, the dose to the thyroid for infants is about nine times higher
than that for adults. Studies of the Chernobyl nuclear power plant accident have confirmed the link between thyroid cancer and iodine-131,
which concentrates mainly in this organ.
Epidemiological studies have shown that young people under 20 yearsof age appear to be about twice as likely as adults to develop leukaemia following the same radiation exposure. ­Further, children under 10 years are
particularly susceptible; some other s­ tudies suggest that they are three
to four times more likely to die of leukaemia than adults. Other studies
have also shown that girls exposed at under 20 years of age are about
twice as likely to develop breast cancer as adult women. Children are
more likely than adults to develop cancer after ­radiation exposure, but
it may not emerge until later in life when they reach an age at which thecancer normally becomes evident.
UNSCEAR has reviewed scientific material indicating that cancer
occurrence in children is more variable than in adults and depends ontumour type, and on the child’s age and sex. The term ­radiosensitivity

Particularly radiosensitive organs in children
Brain
Skin

Thyroid
BreastBone marrow

Children exposed
to radiation at ages
below 20 years
are about twice as likely
to develop brain cancer
as adults exposed tothe same dose.
A similar association
was noticed forbreast cancer when girls
were exposed at ages
below 20 years.

WHAT DOES RADIATION DO TO US?

19

with regard to cancer induction refers to the rate of tumours causedby irradiation. Studies on the differences in radiosensitivity between
adults and children have found that children are more sensitive for the­development of thyroid, brain, skin and breast cancer, and leukaemia.
Differences in early health effects on children following high doses(such as those received in radiotherapy) are complex and can be explainedby the interaction of different tissues and biological mechanisms. Some
effects are more evident for exposure in childhood than in adulthood (e.g.
brain defects, cataracts and thyroid nodules); and there are a few effects
for which children’s tissues are more resistant (e.g. lungs and ovaries).
Effects on the unborn childAn embryo or fetus can be exposed through radioactive materialtransferred by the mother via food and drink (internal exposure) or
directly through external exposure. Because a fetus is protected in theuterus, its radiation dose tends to be lower than the dose to its motherfor most radiation exposure events. However, the embryo and fetus
are particularly sensitive to radiation, and the health consequences of
exposure can be severe, even at radiation doses lower than those that
immediately affect the mother. Such consequences can include growth
retardation, malformations, impaired brain function and cancer.

Radiation exposure pathways for embryos

Internal exposure
through mothers ingesting
radiopharmaceuticals
or radioactive (contaminated)food or drink.
External exposure
through mothers being
exposed to X- or gamma rays.

X- or gamma rays

20

The development of mammals in the womb falls roughly into threestages. It is known that radiation might kill an embryo in the womb inthe first stage, which lasts from conception to the point when it settles
into the wall of the womb, and covers the first two weeks of pregnancy
in humans. It is very hard to study what happens at this stage; however,information mainly from animal experiments confirms the fatal effect on
the early embryo of radiation doses above certain thresholds.
During the next stage, lasting from the second to the eighth week inhumans, the main danger is that radiation will lead to the growing organs
becoming malformed and, perhaps, cause death at around the time ofbirth. Animal experiments have shown that organs (e.g. eyes, brain,­skeleton) are particularly susceptible to malformation if irradiated just at
the point when they are developing.
The greatest damage seems to occur in the central nervous systemafter the eighth week, when the third and last stage of pregnancy begins.
Much progress has been made in understanding the effects of radiation
exposure on brains of unborn children. As an example, 30 children of
the survivors of the atomic bombings out of about 1 600 exposed before
birth to a dose of 1 Gy had extreme intellectual disability.
There has been controversy about whether radiation exposure ofembryos can cause cancer later in life. Animal experiments have failed
to show any particular relationship. UNSCEAR has tried to estimate theoverall risks to unborn children for a number of effects of irradiation—
death, malformation, intellectual disability and cancer. In all, it reckons
that no more than two out of every 1 000 live-born children who havebeen exposed to a dose of a hundredth of a gray in the womb might beaffected—compared with the 6 per cent who develop the same effects
naturally.
Heritable effects
Radiation might modify cells transmitting hereditary information todescendants, which may cause genetic disorders. The study of such disorders is difficult because there is very little information on what genetic
damage humans sustain through radiation exposure, partly because thefull tally of heritable effects takes many generations to show, and partly
because—as for cancer—these effects would be quite indistinguishable
from those occurring from other causes.
WHAT DOES RADIATION DO TO US?

21

Many of the severely affected embryos and fetuses do not survive. It
has been estimated that about half of all miscarriages have an abnormal
genetic constitution. Even if they do survive to birth, babies with genetic
disorders are about five times more likely to die before their fifth birthday
than are normal children.
Heritable effects fall into two main categories: chromosomal aberrations involving changes in the number or structure of chromosomes,
and mutations of the genes themselves. They can appear in subsequent­generations, but will not necessarily do so.
Studies of children whose parents were survivors of the atomic bombings have failed to find observable heritable effects. This does not meanthat no damage has been sustained; just that moderate radiation exposure of even a relatively large population has no observable impact.
­However, experimental studies, in plants and animals exposed to highdoses, have clearly demonstrated that radiation can induce heritableeffects. Humans are unlikely to be an exception.
UNSCEAR has concentrated only on severe heritable effects and estimated that the total risk is about 0.3–0.5 per cent per gray—which is lessthan one-tenth of the possibility of occurrence of fatal cancer—to the first
generation following radiation exposure.

2.2. Effects on animals and plants
Effects of radiation exposure on animals and plants are receiving
more attention than previously. In past decades, the prevailing view wasthat if human life were adequately protected, both plants and animals
would be similarly protected. UNSCEAR evaluated the effects of radiation exposure on plants and animals and found that a theoretical dose
range of 1–10 Gy was unlikely to result in effects on animal and plant
populations and that individual responses to radiation exposure varied(mammals are the most sensitive of all animals). Those effects that arelikely to be significant at the population level concern fertility, mortality
and the induction of mutations. Reproductive changes, such as in thenumbers of offspring, are a more sensitive indicator of radiation effects
than mortality.

22

Lethal doses represent doses at which 50 per cent of the exposed
subjects would die. For plants exposed in a relatively short time (acute),
these have been noted to range from less than 10 to about 1 000 Gy. In
general, larger plants are more radiosensitive than smaller ones. Lethal
doses range from 6 to 10 Gy for small mammals and are about 2.5 Gy
for larger ones. Some insects, bacteria and viruses can tolerate doses ofover 1 000 Gy.

Ranges of acute lethal doses for some animals and plants
Viruses
Bacteria
Insects
ReptilesFish
Higher plants
Birds
Mammals
1

10

100

1 000

10 000

Acute lethal dose (Gy)A main source of information has been the observations obtained
from radiation exposure of animals and plants in the areas around theChernobyl nuclear power plant. UNSCEAR evaluated pathways throughwhich the environment was exposed, and developed new approaches forassessing the potential effects of such exposure.
Recently, UNSCEAR estimated doses and associated effects of radiation exposure for selected animals and plants after the Fukushima-Daiichi
nuclear power station accident and concluded that the exposures were,in general, too low for acute effects to be observed. However, changes inbiomarkers, which are indicators of a particular disease or physiologicalstate of an organism—in particular for mammals—could not be ruled out,
but their significance for the population integrity of those organisms was
unclear.
WHAT DOES RADIATION DO TO US?

23

It is important to note that protective and remedial action conducted toreduce radiation exposure to humans can have a significant wider impact.
For example, it can affect environmental goods and services, resources
used in agriculture, forestry, fisheries and tourism, and ­amenities used in
spiritual, cultural and recreational activities.

2.3. Relationship of radiation doses and effects
When summarizing the relationship between radiation doses andhealth effects, UNSCEAR has stressed the importance of distinguishing
between observations of existing health effects in exposed populations,and theoretical projections of possible future effects. For both s­ ituations,
it is important to take into account any uncertainties and inaccuracies—
whether in radiation measurements, statistical considerations or otherfactors.
Given the present state of knowledge, observed health effects canbe confidently attributed to radiation exposure if early effects (e.g. skinburns) occur in individuals after high doses above 1 Gy. Such doses
might arise in radiation accidents, such as those received by emergency­workers during the Chernobyl nuclear power plant accident or by patientsduring accidents in radiotherapy.
It is possible, using epidemiological methods, to attribute anincreased occurrence of delayed health effects (e.g. cancer) in a population exposed to moderate radiation doses if the observed increaseis high enough to overcome any uncertainties. However, there are no­biomarkers presently available to distinguish whether a cancer has beencaused by radiation exposure or not.
Where the level of radiation exposure was low or very low—moret­ ypical of environmental and occupational radiation exposure—changes
in the occurrence of delayed health effects have not been confirmed,
given the statistical and other uncertainties. Nevertheless, such effects
cannot be ruled out.
With regard to possible health effects in the future, there is an understanding of how to estimate the probability of the occurrence of theseeffects for high and moderate doses. However, at low and very low doses,
it is necessary to make assumptions and use mathematical models to estimate the probability of any health effects resulting in values that are very
uncertain. Consequently, for low and very low radiation doses, UNSCEAR

24

WHAT DOES RADIATION DO TO US?

25

100%

0%

Very low

Natural background,
occupational doses

Low

Biologically plausible

Chernobyl childthyroid doses

Moderate

Statistical limitations

Increasing risk of cancer
about 5% per Sv

Statistically observable in populations(epidemiology)

Relationship of radiation doses and health effects

Probability of effect

High

Dose

Clinically observablein individuals

Chernobyl
firemenBurns,
radiation sickness
and deathhas chosen not to use such models in their assessments—­following, forexample, the Chernobyl and Fukushima-Daiichi accidents—to ­project
numbers of health effects or deaths because of the unacceptable uncertainties in the predictions. Nevertheless, for public health comparisons orradiation protection purposes, it may be useful to make such calculations
providing that the uncertainties are taken into account and the limitations
are clearly explained.

26

3. WHERE DOES RADIATION COME FROM?
We are continuously exposed to radiation from many sources. All
species on Earth have existed and evolved in environments where they
have been exposed to radiation from the natural background. Morerecently, humans and other organisms have also been exposed to artificial sources developed over the past century or so. Over 80 per centof our exposure is from natural sources and only 20 per cent is humanmade from artificial sources—mainly from radiation applications usedin medicine. Radiation exposure is categorized in this publication by its
sources, with a focus on what the general public receive. For regulatory
purposes (e.g. radiation protection) radiation exposure is addressedfor different groups. Therefore, additional information is provided hereon patients—who are exposed due to medical use of radiation—and on­people exposed at workplaces.
Another way to categorize radiation exposure is how it irradiates us.
Radioactive substances and radiation in the environment may irradiate
our body from the outside—externally. Or we may inhale the substancesin air, swallow them in food and water or absorb them through skin andwounds, and then they irradiate us from inside—internally. Considered
globally, doses from internal and external exposure are about the same.

Worldwide distribution of radiation exposure
Art
ific
ial

Cosmic | 13%

Medical | 20%

Exte
rn

Soil | 16%

s
dose
al

Radon | 42%

Inte
rn

doses
al
Food | 9%

WHERE DOES RADIATION COME FROM?

27

3.1. Natural sources
Since the creation of the Earth, its environment has been exposed
to radiation both from outer space and from radioactive material in its
crust and core. There is no way to avoid being exposed to these natural sources, which, in fact, cause most of the radiation exposure of theworld’s population. The global average annual effective dose per person
is about 2.4 mSv and ranges from about 1 to more than 10 mSv depending on where people live. Buildings may trap a particular radioactive gas,called radon, or the building material itself may contain radionuclides
that increase radiation exposure. Although the sources are natural, ourexposure can be modified by choices we make, such as how and where
we live or what we eat and drink.

Cosmic sources
Cosmic rays are a major natural source of external exposure to radiation. Most of these rays originate from deep in interstellar space; someare released from the sun during solar flares. They irradiate the Earth
directly, and interact with the atmosphere, producing different typesof radiation and radioactive material. They are the dominant radiation
source in outer space. While the Earth’s atmosphere and magnetic field
considerably reduce cosmic radiation, some parts of the globe are more
exposed than others. As cosmic radiation is deflected by the magnetic

Annual doses from cosmic radiation*
Space shuttle
Mount Everest~350 km
8.8 km300
mSv

20 mSvJumbo jet
~10 kmMont Blanc
4.8 km
3 mSv

Lhasa
Tibet
3.7 km
1.8 mSv

18 mSv

MexicoCity
2.3 km1 mSv

EmpireState Building
450 m
0.5 mSv

Sea
level
0m
0.36
mSv

* Based on the assumption of exposure at these locations for a year.

28

field to the North and South Poles, they receive more than the equatorial
regions.
Moreover, the level of exposure increases with altitude because thereis less air overhead to act as a shield. Thus, people living at sea level
receive, on average, an effective dose of about 0.3 mSv annually fromcosmic sources of radiation, or roughly 10–15 per cent of their total dosefrom natural sources. Those who live above 2 000 metres receive several
times this dose. Airplane passengers might be exposed to even higher
doses as the radiation exposure from cosmic sources depends not only
on the altitude but also on the length of flights. For instance, at cruising
altitudes, the average effective dose is 0.03–0.08 mSv for a 10 hour flight.
In other words, a New York–Paris round trip flight would expose a person
to about 0.05 mSv. This is approximately equal to the effective dose apatient would receive from a routine chest X-ray examination. Although
the estimated effective doses received by individual passengers during aflight are low, the collective doses may be quite high because of the large
number of passengers and flights worldwide.
EXPOSURE IN WORKPLACES
Doses from cosmic sources are particularly important for people who fly frequently such as pilots and cabin crew, who receive on average about 2–3 mSv
annually. Doses have also been measured for a number of space missions.
The reported doses for short space missions were in the range of 2–27 mSv,
­depending on solar activity. However, an astronaut on a four-month mission to
the International Space Station which orbits the Earth at 350 km receives aneffective dose of about 100 mSv.

Terrestrial sources
Soil
Everything in and on the Earth contains primordial radionuclides. These
extremely long-lived radionuclides found in the ground—such as potassium-40, uranium-238 and thorium-232—together with the radionuclides
into which they decay—such as radium-226 and r­adon-222—have been
emitting radiation since before the Earth took its current shape. UNSCEAR
calculates that every person worldwide receives, on average, an effective
dose of about 0.48 mSv annually as external exposure from terrestrial
sources.
WHERE DOES RADIATION COME FROM?

29

External exposure varies considerably from one location to another.
Studies in France, Germany, Italy, Japan and the United States, for example, suggest that about 95 per cent of their populations live in areas where
the average annual dose outdoors varies from 0.3 to 0.6 mSv. However,in some places in these countries people can receive doses higher than
1 mSv annually. There are other places in the world where radiation exposure from terrestrial sources is higher still. For example, on the southwest
coast of Kerala, India, a densely populated 55-kilometre long strip of land
contains thorium-rich sands, where people receive, on a­ verage, 3.8 mSv
annually. Other regions with high levels of natural terrestrial sources ofradiation are known to exist in Brazil, China, the Islamic Republic of Iran,Madagascar, and Nigeria.
Radon gas
Radon-222 is a radionuclide in the form of a gas that normally emanates from the soil. It is produced from the decay series of uranium-238
present in the rocks and soil of the Earth. When inhaled, some of radon’sshort-lived decay products—mainly polonium-218 and -214—are retainedin the lungs and irradiate cells in the respiratory tract with alpha particles. Radon is, hence, a primary cause of lung cancer in both smokers
and non-smokers; however, smokers are far more vulnerable because ofa strong interaction between smoking and radon exposure.
Radon is present in the atmosphere everywhere, and can seep directly
into buildings through cellars and floors, where its concentration—theamount of activity in terms of decays per time in a volume of air—can build
up. Mainly when homes are heated, warm air rises and escapes at the topof the house through windows or leakages, which creates low pressurein the ground floor and basement. This, in turn, causes active suction ofradon from the subsoil through cracks and leakages (e.g. around service
pipe entries) at the bottom of the house.
The worldwide-average concentration of indoor radon is about
50 Bq/m3. However, this average hides the great variability from place
to place. In general, national average concentrations vary widely, ranging from less than 10 Bq/ m3 in Cyprus, Egypt and Cuba to more than
100 Bq/m3 in the Czech Republic, Finland and Luxembourg. In somecountries such as Canada, Sweden and Switzerland there are houses
with radon concentrations of between 1 000 and 10 000 Bq/m3.
­Nevertheless, the proportion of houses with such high-level concentrations is very small. Some of the factors that cause this variation are the30underlying local geology, the permeability of the soil, the c­ onstruction
material and ventilation of buildings.

Radon entries to buildings
AirpressureRadon
in soilFloor gaps

Plumbing
pipes andfixtures

Gaps and cavity

Groundpores

In particular, ventilation, which depends on the climate, is a key factor.
If buildings are well ventilated, such as in a tropical climate, the accumulation of radon is unlikely to be substantial. However, in temperate orcold climates, where places tend to be less ventilated, the concentrationsof radon can build up considerably. Thus, the effect of restricted ventilation is important when designing energy-efficient buildings. Extensive
measurement programmes have been conducted in many countries andhave formed the basis for implementing measures to reduce indoor radon
concentrations.
The level of radon in water is usually very low but some supplies—
e.g. deep wells in Helsinki, Finland, and Hot Springs, Arkansas, UnitedStates—have very high concentrations. Radon in water can contributeto an increase of the concentration of radon in the air—particularly inthe bathroom when showering. However, UNSCEAR concludes that thedose contribution from radon ingested in drinking water is small in comparison with its inhalation. UNSCEAR estimates that the average annual
effective dose from radon is 1.3 mSv, representing about half of what the
public receives from all natural sources.
WHERE DOES RADIATION COME FROM?

31EXPOSURE IN WORKPLACESFor certain workplaces, inhaling radon gas dominates the radiation exposureof workers. Radon is the main source of radiation exposure in undergroundmines of all types. The annual average effective dose to a coal miner is about
2.4 mSv and for other miners about 3 mSv. In the nuclear industry, the annual
average effective dose to a worker is about 1 mSv, mainly from radon exposurein ­uranium mining.

Sources in food and drink
Food and drink may contain primordial and some other radionuclides,
mainly from natural sources. Radionuclides can be transferred to plants
and then to animals from rocks and minerals present in the soil and water.
Thus, the doses vary depending on the concentrations of radionuclides
in food and water, and on local dietary habits.
For example, fish and shellfish have relatively high levels of lead-210
and polonium-210 and so people eating large amounts of seafood might
receive somewhat higher doses than the general population do. Comparatively higher doses are also received by people in the arctic regions who
consume large amounts of reindeer meat. Reindeer in the arctic containrelatively high concentrations of polonium-210, accumulated in the lichen
they graze on. UNSCEAR estimates that the average effective dose fromnatural sources in food and drink is 0.3 mSv, due mainly to potassium-40
and to the uranium-238 and thorium-232 series radionuclides.
Radionuclides from artificial sources can be present in foodstuffs
in addition to radionuclides from natural sources. However, the dose­contribution from the authorized discharges of these radionuclides tothe environment is usually very small.

3.2. Artificial sources
The uses of radiation have increased significantly over the past
­ ecades as scientists learned to use the energy of the atom for a widedvariety of purposes, from military to medical applications (e.g. cancer
treatment), and from electricity production to domestic applications(e.g. smoke detectors). These and other artificial sources add to theradiation dose from natural sources for both individuals and the global
population.

32

Individual doses from artificial sources of radiation vary greatly. Most
people receive a relatively small dose from such sources but a few receive
many times the average. Artificial sources of radiation are generally wellcontrolled by radiation protection measures.

Medical applications
The use of radiation in medicine to diagnose and treat certain diseases
plays such an important role that it is now by far the main artificial sourceof exposure in the world. On average, it accounts for 98 per cent of theradiation exposure from all artificial sources and, after natural sources,
is the second largest contributor to the population exposure worldwide,
representing approximately 20 per cent of the total. Most of this exposure
occurs in industrialized countries, where more resources for m­ edical care
are available and, therefore, radiology equipment is used much more
extensively. In some countries, this has even resulted in an annual average effective dose from medical use that is similar to the one from natural
sources.

Average effective doses per person in the United States (2007)
All others 0.14 mSv
Interventional radiology
0.40 mSv

m e dicexalNuclear medicine
0.80 mSv

Natural sources
3.1 mSv

Tot
alDiagnostic radiography
0.30 mSv

po

sure

3 mS

v

CT scans 1.5 mSv

There are substantial differences between medical exposure andmost other types of exposure. Medical exposure t­ypically involves only
a portion of the body, whereas other exposure often involves the whole
WHERE DOES RADIATION COME FROM?

33

body. Additionally, the distribution of patients’ ages normally covers anolder age range than that of the general population. Moreover, doses
resulting from medical exposure should be compared with those fromother sources very carefully, considering that patients receive a direct
benefit from their exposure.
Increasing urbanization, together with a gradual improvement in living standards, inevitably means that more people can access healthcare. As a consequence, the population dose due to medical exposure
continues to increase worldwide. UNSCEAR has been regularly ­collecting
information on diagnostic and therapeutic procedures. According to its
survey for the period 1997–2007, about 3.6 billion medical radiation procedures were performed annually worldwide, compared with 2.5 billion
in the previous survey period covering 1991–1996, which is an increaseof almost 50 per cent.
The main general categories of medical practice involving radiation
are radiology (including interventional procedures), nuclear ­medicine
and radiotherapy. Other uses not covered by UNSCEAR’s regular­evaluations include health screening programmes, and voluntary participation in medical, biomedical, diagnostic or therapeutic research
programmes.
Diagnostic radiology is the analysis of images obtained using X-rays,
such as in plain radiography (e.g. chest or dental X-rays), fluoroscopy(e.g. with barium meal or enema) and computer tomography (CT). Imaging modalities which use non-ionizing radiation, such as ultrasoundor magnet resonance tomography, are not addressed by UNSCEAR.
­Interventional radiology uses minimally invasive image-guided procedures to diagnose and treat diseases (e.g. for guiding a catheter in a
blood vessel).
Because of the wider use of CT and the significant dose per examination, the global average effective dose from diagnostic radiologicalprocedures nearly doubled from 0.35 mSv in 1988 to 0.62 mSv in 2007.
According to UNSCEAR’s latest survey, CT scanning now accounts for
43 per cent of the total collective dose due to radiology. These numbers
vary from region to region. About two thirds of all r­adiological procedures are received by the 25 per cent of the world’s population living
in industrialized countries. For the remaining 75 per cent of the world’s
population, the annual frequency of procedures has remained fairly
constant, even for simple dental X-ray examinations.

34

Global exposure from radiology (1988–2008)
COLLECTIVE EFFECTIVE DOSE
(1 000 man Sv)

5 000
4 000

4 000
3 000
2 000

1 800

1 600

1988

1993

2 300

1 000
0
2000

2008

UNSCEAR SURVEY

Nuclear medicine is the introduction of unsealed (i.e. soluble and notencapsulated) radioactive substances into the body, mostly to obtain
images that provide information on either structure or organ function
and less commonly to treat certain diseases, such as hyperthyroidism and thyroid cancer. Generally, a radionuclide is modified to form a

Global exposure from nuclear medicine (1988–2008)
COLLECTIVE EFFECTIVE DOSE
(1 000 man Sv)

250
202

200
160

150

1993

2000

150
100

74

50
0
1988

2008

UNSCEAR SURVEY

WHERE DOES RADIATION COME FROM?

35

r­ adiopharmaceutical that is usually administered intravenously or orally.
It then disperses in the body according to physical or chemical characteristics making a scan possible. Thus, the radiation emitted from theradionuclide within the body is analysed to produce diagnostic images
or is used to treat diseases.
The number of diagnostic nuclear medicine procedures increased
worldwide from about 24 million in 1988 to about 33 million in 2007. This
resulted in a significant increase in the annual collective ­effective dosefrom 74 000 to 202 000 man Sv. Therapeutic applications in ­modern
nuclear medicine are also increasing, reaching about 0.9 million patientseach year worldwide. Again, the use of nuclear medicine is quite uneven,with 90 per cent of examinations occurring in industrialized countries.
Radiation therapy (also called radiotherapy) uses radiation to treat
various diseases, usually cancer, but also benign tumours. External
radiotherapy refers to patient treatment using a radiation source that is
outside the patient’s body and is called teletherapy. This uses a machinecontaining a highly radioactive source (usually cobalt-60) or a high-voltage machine that produces radiation (e.g. a linear accelerator). Treatment
can also be performed by placing metallic or sealed radioactive sources,
either temporarily or permanently, within the patient and this is calledbrachytherapy.
Worldwide, an estimated 5.1 million patients were treated annuallywith radiotherapy during the period 1997–2007, up from an estimated
4.3 million in 1988. About 4.7 million were treated by teletherapy and0.4 million by brachytherapy. The 25 per cent of the population living
in industrialized countries received 70 per cent of the radiotherapy­treatment worldwide and 40 per cent of all brachytherapy procedures.

EXPOSURE IN WORKPLACES
Because the total number of medical radiological procedures has increased­significantly in the past decades, so has the number of health workers involved,
passing 7 million with an average annual effective dose of about 0.5 mSv per
worker. In interventional radiology and nuclear medicine, medical staff might
receive higher than the average dose.

36

Accidents in medical application
Some medical applications of radiation (e.g. radiotherapy, interventional radiology and nuclear medicine) involve the delivery of high doses
to patients. When applied incorrectly, these can cause serious harm oreven death. The people at risk include not only patients, but also physicians and other staff in the vicinity. Human error has been the most common cause of these accidents. Examples include giving a wrong dose
because of treatment planning errors, failure to use equipment properly,
and exposing the wrong organ or, occasionally, even the wrong patient.
While serious radiotherapy accidents are rare, over 100 have beencatalogued. UNSCEAR has reviewed 29 reported accidents since 1967
that caused 45 deaths and 613 injuries. However, it is likely that somedeaths and many injuries have not been reported.
Not only overexposure but underexposure might have serious consequences, when patients receive insufficient radiation dose to treat a lifethreatening disease. Quality assurance programmes help to maintainhigh and consistent standards of practice in order to minimize the riskof such accidents.

Nuclear weapons
In 1945, during the final stage of the Second World War, two atomic
bombs were dropped on Japanese cities—Hiroshima on 6 August andNagasaki on 9 August. The explosions of the two bombs killed nearly
130 000 people. These events remain the only use of nuclear weapons
for warfare in history. However, after 1945, many nuclear weapons were
tested in the atmosphere, mostly in the northern hemisphere. The mostactive testing period was between 1952 and 1962. In all, over 500 tests
were conducted, with a total yield of 430 megatons of trinitrotoluene(TNT) equivalent, the last in 1980. People throughout the world were
exposed to radiation from the fallout from these tests. In response toconcerns about the radiation exposure of humans and the environment,
UNSCEAR was established in 1955.
The estimated annual average effective dose due to global fallout fromatmospheric nuclear weapon testing was highest in 1963, at 0.11 mSv,
and subsequently fell to its present level of about 0.005 mSv. This exposure will decline only very slowly in the future because most of it is now
due to the long-lived radionuclide carbon-14.
WHERE DOES RADIATION COME FROM?

37

ANNUAL EFFECTIVE DOSE (mSv)

World-average dose per person from nuclear test fallout
0.12
0.1
0.08
0.06
0.04
0.02
0

1945

1955

1965

1975

1985

1995

2005

YEAR

As much as 50 per cent of the total fallout produced by surface tests
was deposited locally within about 100 km of the test site. People living near test sites were thus exposed mainly to local fallout. However,
because the tests were conducted in relatively remote areas, the local
populations exposed were small and did not contribute significantly to
the global collective dose. Nevertheless, people living downwind of thetest sites received much higher doses than average.
UNSCEAR’s first report in 1958 laid the scientific grounds on which theTreaty Banning Nuclear Weapon Tests in the Atmosphere, in Outer Spaceand under Water was negotiated. After the signature of this Partial Test
Ban Treaty in 1963, about 50 tests were conducted underground annually until the 1990s; a few tests have also been conducted after that.
Most of these tests had a much lower nuclear yield than the atmospherictests, and any radio­active debris was usually contained unless gases
were vented or leaked into the atmosphere. While the tests generated avery large quantity of radioactive residue, it is not expected to expose thepublic, because it is located deep underground and is essentially fusedwith the host rock.
There is concern regarding the reuse of nuclear test areas (e.g. for animal grazing or crop farming), because some are being reoccupied. The
doses from radioactive residues at some sites, e.g. in localized areas at
the Semipalatinsk test site in today’s Kazakhstan, may be c­ onsiderable,

38

while in others, such as at the Mururoa and Fangataufa Atolls in French
Polynesia, the doses would not contribute more than a fraction of the normal background exposure to a population eventually occupying the site.
For other sites still, such as in the Marshall Islands and Maralinga, where
the United States and the United Kingdom, respectively, ­conducted someof their tests, exposure of the population living there would depend on
diet and lifestyle.

Nuclear reactors
When certain isotopes of uranium or plutonium are hit by neutrons,
the nucleus splits into two smaller nuclei by a process called nuclear fission, releasing energy and two or more neutrons. The neutrons released
may also hit other uranium or plutonium nuclei and cause them to split,
releasing more neutrons, which in turn can split more nuclei. This is calleda chain reaction. These isotopes are normally used as the fuel in nuclear
reactors, where the chain reaction is controlled to stop it going too fast.
The energy released from fission in nuclear reactors can be used to
produce electricity in nuclear power plants. However, there are also
research reactors for testing nuclear fuel and various kinds of material,
for investigations in nuclear physics and biology, and for the productionof radionuclides to be used in medicine and industry. Although differences exist between the two types of reactors, both require industrial
processes such as uranium mining and radioactive waste disposal,
which can give rise to occupational and public exposure.
Nuclear power plants
The world’s first commercial nuclear power station on an industrial
scale, Calder Hall, was built in 1956 in the United Kingdom, and sincethen, the generation of electrical energy by nuclear power plants hasgrown considerably. Despite the increase in the decommissioning of older
reactors, electrical energy production from nuclear sources continues togrow. By the end of 2010, around 440 power reactors were in operation in
29 countries, providing about 10 per cent of global electricity generation,and 240 research reactors were widespread worldwide in 56 countries.
Although the production of electricity by using nuclear power is often
controversial, in normal operation it contributes very little to global radiation exposure. Moreover, the radiation exposure levels vary widely from
one type of facility to another, between different locations and over time.
WHERE DOES RADIATION COME FROM?

39

40

Mexico-2

Argentina-2

United States-104

Canada-18

Brazil-2

Slovenia-1

Switzerland-5

South Africa-2

Armenia-1

Hungary-4

Spain-8

France-58
Bulgaria-2

Romania-2

Ukraine-15

Sweden-10
Finland-4

Slovakia-4
Czech
Republic-6
United Kingdom-19
Netherlands-1
Belgium-7
Germany-17

Nuclear power plants worldwide (2010)

Pakistan-2

India-19

China-19

Russian Federation-32

Japan-54
Republic ofKorea-21

The overall exposure levels due to normal discharges from reactors
have tended to decrease despite the increasing electrical output ofplants. This is partly due to improvements in technology and partly due
to stricter radiation protection measures. In general, discharges from
nuclear facilities give rise to very low radiation doses. The annual collective dose to populations around nuclear power plants is estimatedto be 75 man Sv. Thus, someone living in the vicinity of a power plant is
exposed on average to an annual effective dose of about 0.0001 mSv.
The dominant component for radiation exposure from nuclear energy­operations is mining. Uranium mining and milling produce substantial
quantities of residues in the form of tailings, which contain elevated levels of natural radionuclides. By 2003, the total world production of uranium had reached about two million tonnes while the resultant tailings
totalled over two billion tonnes. Current tailing piles are well maintained,
but many old, abandoned sites exist and only a few have undergone­remediation. UNSCEAR estimated the current annual collective dose topopulation groups around mine and mill sites and tailing piles at about
50–60 man Sv.
Spent fuel from reactors can be reprocessed to recover uranium andplutonium for reuse. Most spent fuel is currently retained in interim storage but about one third of that produced so far has been reprocessed.
The annual collective dose due to reprocessing is estimated to be in therange of 20–30 man Sv.
Low-level and some intermediate-level waste is currently disposedof in near-surface facilities although, in the past, waste was sometimes
dumped at sea. Both the high-level waste from reprocessing and thespent fuel (if not reprocessed) are stored but will eventually need to bedisposed of. Proper disposal of the waste should not give rise to e
­ xposureof people even in the distant future.
EXPOSURE IN WORKPLACESIn the nuclear industry, the release of radon in underground uranium mines
makes a substantial contribution to occupational exposure. The extraction andprocessing of radioactive ores that may contain high levels of radionuclides
is a widespread activity. The average annual effective dose per worker in the
nuclear industry has gradually declined since the 1970s, from 4.4 mSv to 1 mSv
at ­present. This is mainly because of significant reduction in uranium mining
coupled with more advanced mining techniques and ventilation.
WHERE DOES RADIATION COME FROM?

41

42
Deep
geologicalrepositoryis currently held in interim storage pending
final disposal in deep geological sites.

High-level waste including spent fuelspent fuel can be recycled as fuelafter conversion and enrichment.

Reprocessing of uranium and plutonium from

Fuel fabrication produces fuel rods,
generally from uranium in ceramic pellets,
encased in metal tubes.

Natural uranium is extracted mainly by
open pit or underground mining.

The residues become tailings,
containing long-lived radionuclides
in low concentrations.

Milling extracts uranium from ore.

UF6

uranium for use as fuel.

Conversion, enrichment
and refinement prepares

Main processes in the nuclear industry

Radioisotopes

produced in reactors
can be separated out
for use in medicine
and industry.

Surface storage

Shallow andintermediatedepth

is mostly disposed ofin shallow burial sites on land.

Low- and intermediate-level waste

Radioactive by-products makethe fuel less efficient.
After 12-24 months
spent fuel is removed
from the reactor.

where the nuclei of uranium atoms
split (fission) and release energy
used to heat water.

Research and power reactors,

Accidents at nuclear facilities
The exposure levels during the normal operation of civil facilitiesof the nuclear industry are very low. However, there have been some­serious accidents, which received extensive public attention and whose
consequences have been reviewed by UNSCEAR. Examples include theVinca research facility in former Yugoslavia in 1958, the Three Mile
Island nuclear power plant in the United States in 1979, and the fuelconversion facility at Tokai-Mura in Japan in 1999.
Thirty-five severe radiation accidents in nuclear facilities between
1945 and 2007 resulted in deaths or serious injuries of employees, andseven accidents caused off-site releases of radioactive material anddetectable radiation population exposure. There were also severe accidents in facilities related to nuclear weapon programmes. Excluding the1986 Chernobyl and the 2011 Fukushima-Daiichi accidents—which are
discussed below—32 deaths and 61 cases of radiation-related injuries
requiring medical care are known.
The most serious accident at a civilian installation before the one
at Chernobyl was at the Three Mile Island nuclear power station on
28 March 1979. A series of events led to a partial meltdown of the reactor core. This accident released large amounts of fission products and­radionuclides from the failed reactor core into the containment building,but relatively little into the environment and the resulting ­exposure of the
public was very low.
Chernobyl nuclear power plant accident
The accident at the Chernobyl nuclear power plant on 26 April 1986
was not only the most severe in the history of civilian nuclear power,
but also the most serious one in terms of exposure to radiation of the­general population. The collective dose from the accident was manytimes greater than the combined collective dose from all other radiation
accidents.
Two workers died from trauma in the immediate aftermath, and
134 suffered acute radiation syndrome, which proved fatal for 28 ofthem. Skin injuries and radiation-related cataracts were among the main
problems for the survivors. Aside from the emergency ­workers, several
hundred thousand people were subsequently involved in recovery operations. Apart from an apparent increase in ­occurrence of leukaemia and
WHERE DOES RADIATION COME FROM?

43

of cataracts among those who received high doses in 1986 and 1987,
there is no consistent evidence to date of other r­adiation-related healtheffects in this group.
The accident caused the largest uncontrolled radioactive release
into the environment ever recorded for any civilian operation; large
quantities of radioactive substances were released into the atmosphere for about 10 days. The radioactive cloud created by the accident
dispersed over the entire northern hemisphere and deposited substantial amounts of radioactive material over large areas of the former
Soviet Union and other parts of Europe, contaminating land and waterparticularly in today’s Belarus, the Russian Federation and Ukraine,and causing serious social and economic disruption to large segmentsof the population.
The contamination of fresh milk with the short-lived radionuclide
iodine-131 (with a half-life of eight days) and the lack of prompt countermeasures led to very high doses to the thyroid, particularly of children,in parts of the former Soviet Union. Since the early 1990s, the occurrence of thyroid cancer among these persons exposed as children oradolescents in 1986 has increased in Belarus, Ukraine and four of themore affected regions of the Russian Federation. For the period 1991–
2005, more than 6 000 cases had been reported; of these, 15 cases had
proven fatal.
In the longer term, the general population was also exposed to radiation, both externally from radioactive deposits and internally from consuming contaminated foodstuffs, mainly by caesium-137 (with a halflife of 30 years). However, the resulting long-term radiation doses were­relatively low, the average individual effective dose over the period
1986–2005 in contaminated areas of Belarus, the Russian Federationand Ukraine was 9 mSv. This is not likely to lead to substantial healtheffects in the general population. Still, the severe disruption caused by
the accident has resulted in major social and economic impact and great
distress for the affected populations.
UNSCEAR studied the radiological consequences of the accident indetail in several reports. The international community has made unprecedented efforts to assess the magnitude and characteristics of the accident’s consequences in general and in different focus areas in order toimprove understanding of the radiological and other consequences of
the accident and assist in their mitigation.

44

WHERE DOES RADIATION COME FROM?

45

Brest

Rovno

Chernobyl
NPP

Zhytomyr

Kiyev

Gomel

Mogilev

UKRAINE

BELARUS

Minsk

Chernigov

KalugaTula<10 mGy

10–30 mGy

30–150 mGy

150–650 mGy>650 mGy

Orel

RUSSIAN FEDERATION
Bryansk

Average thyroid doses after the Chernobyl nuclear power plant accident

Essentially, studies since 1986 indicate that persons who were
exposed as children to iodine-131 and the emergency and recovery operation workers who received high doses of radiation are at increased riskof radiation-induced effects. However, most area residents were exposed
to low levels of radiation comparable to, or a few times higher than, theannual natural background radiation levels.
Fukushima-Daiichi nuclear power station accident
After the great east-Japan earthquake of magnitude 9.0 and tsunamion the east coast of northern Japan on 11 March 2011, the FukushimaDaiichi nuclear power station was severely damaged and radioactive
material was released to the environment. Nearly 85 000 residents
within 20-km around the nuclear power station site and some nearby
areas were evacuated as a precautionary measure between 11–15 March,while residents living 20–30 km from the station were sheltered in theirhomes. Later, in April 2011, the evacuation of another 10 000 people
living further to the north-west of the station was recommended becauseof the elevated levels of radionuclides on the ground. These evacuations
greatly reduced the levels of exposure that would have been received bythose affected. The consumption of water and certain foodstuffs was
temporarily restricted to limit the radiation exposure of the public. In
managing the emergency situation at the nuclear power station, some
operational staff and emergency response personnel were exposed.
UNSCEAR conducted an assessment of the radiation doses and associated effects on health and the environment. About 25 000 workers had
been involved in mitigation and other activities at the Fukushima-Daiichi
nuclear power station site during the first year and a half after the accident. The average effective dose to these workers for that time was about
12 mSv. However, 6 workers received cumulative total doses of over
250 mSv; the highest reported total dose was 680 mSv for one worker
mainly received from internal exposure (about 90 per cent). Twelve
workers were estimated to have received thyroid doses in the range of
2–12 Gy. No radiation-related deaths or acute diseases were observed
among the workers exposed to radiation from the accident.
The average effective doses for adults in evacuated areas of the Fukushima
Prefecture ranged from 1 mSv up to about 10 mSv in the first year after theaccident. The effective doses for one-year-old infants were estimated to beabout twice as high. For areas of the Fukushima Prefecture that were notevacuated and for neighbouring prefectures, the doses were lower.

46

WHERE DOES RADIATION COME FROM?

47

GUNMA

NIIGATATOCHIGIIBARAKI

FUKUSHIMAYAMAGATAMIYAGI

Fukushima-Daiichi
NPP

Areas assessed
separately

Areas not assessedat district level<10 mGy

10–30 mGy

30–50 mGy

50–70 mGy

Average thyroid doses for infants after the Fukushima-Daiichi nuclear power station accident

Estimates of the average doses to the thyroid, mainly from iodine-131,
among those most exposed ranged up to 35 mGy for adults and up to
80 mGy for one-year-old infants. The annual dose to the thyroid, mainly
from external natural radiation sources, is typically of the order of 1 mGy.
UNSCEAR concluded a theoretical possibility that the risk of thyroid
cancer among the group of children most exposed to radiation could
increase. However, thyroid cancer is a rare disease among young children so that statistically no observable effects in this group are expected.
While comparisons are made with the Chernobyl disaster, theFukushima-Daiichi nuclear accident was certainly different in terms of thetype of reactor, the way the accident happened, the characteristics of theradionuclide releases and their dispersion, and the protective actions taken.
In both cases, large amounts of iodine-131 and caesium-137—the two mostsignificant radionuclides from the perspective of exposure after nuclear
accidents—were released to the environment. The releases of iodine-131
and caesium-137 from the Fukushima-Daiichi accident c­ompared to theChernobyl one were about 10 and 20 per cent, respectively.

Industrial and other applications
Radiation sources are used in a broad spectrum of industrial applications. These include industrial irradiation used for sterilizing medical and pharmaceutical products, preserving foodstuffs or eradicatinginsect infestation; industrial radiography used for examining welded
metal joints for defects; alpha or beta emitters used in luminizing compounds in gun sights and as low-level light sources for exit signs andmap illuminators; radioactive sources or miniature X-ray machines usedin well logging to measure geological characteristics in boreholes drilled
for mineral, oil or gas exploration; radioactive sources used in devices tomeasure thickness, moisture, density and levels of material; and othersealed radioactive sources used in research.
Although widespread, the production of radionuclides for use inindustrial and medical practices causes very low levels of exposure of
the general public. However in the case of accidents, more localized
areas can be contaminated and give rise to high levels of exposure.
EXPOSURE IN WORKPLACESThe number of workers involved in industrial uses of radiation was about one
million in the early 2000s with an annual average effective dose per worker of
0.3 mSv.

48

Thickness measurement device using radiation
Rollers
Radioactive
sourcePaper

Radiation
detector tocontrol rollers

Naturally occurring radioactive material
There are several types of facilities around the world that, while
un­related to the use of nuclear energy, may expose the public to radiation
because of increased concentrations of naturally occurring radioactive
material (NORM) in their industrial products, by-products and waste. The
most important of such facilities involve mining and mineral processing.
Activities related to the extraction and processing of ores can also
lead to increased levels of NORM. These activities include metal m­ iningand smelting; phosphate production; coal mining and power generation from coal burning; oil and gas drilling; rare earth and titanium oxide­industries; zirconium and ceramic industries; and applications using
naturally-occurring radionuclides (typically isotopes of radium and­thorium).
Coal, for example, contains traces of primordial radionuclides. Burning releases these radionuclides into the environment where they can
expose people. This means that for each gigawatt year of electrical energy
produced by the world’s coal-fired power stations, the collective doseto the world population is estimated to increase by about 20 man Sv­annually. In addition, fly ash (a residue generated in combustion) has
been used in landfill and road construction, but using it for building
construction results in radiation exposure from both direct irradiation
WHERE DOES RADIATION COME FROM?

49

and inhalation of radon. Furthermore, dumping fly ash may increase the­radiation exposure levels around the dump site.
Geothermal energy generation is another source of radiation exposure of the general puplic. Underground reservoirs of steam and hot
water are tapped to generate electricity or to heat buildings. Estimatesof the emissions from the use of this technology in Italy and the UnitedStates suggests that it produces about 10 per cent of the collective dose
per gigawatt year of electricity produced by coal-fired power stations.
Geothermal energy currently makes a relatively small contribution to theworld’s energy production and thus to radiation exposure.

Geothermal generation of energy

Electricity
generating
stationCold
water
Steam andhot water

Various other human practices can expose people to NORM, such as
the sludge from water treatment used in agriculture. However, exposurelevels to the public are extremely low, of the order of less than a few
thousandths of a millisievert annually.
A by-product of uranium enrichment is depleted uranium, which is lessradioactive than natural uranium. Depleted uranium has been used for both
civilian and military purposes for many years. Owing to its high density, it
is used in radiation shielding or as counterweights in aircraft. Military useof depleted uranium, especially in armour-piercing munition, has raised
concern about residual contamination. Except for a few specific scenarios,

50such as long-term handling, radiation exposure from depleted uranium isextremely low. In fact, chemical toxicity is its most hazardous property.
Consumer products
A number of products bought for everyday use contain low levels ofradionuclides, deliberately added in order to make use of their chemicalor radioactive properties. Historically, the most significant radionuclide
for use in luminous consumer products was radium-226. This use ended
several decades ago, with radium being replaced by promethium-147
and hydrogen-3 (tritium), which are less radiotoxic. Even so, for clocks
or watches containing tritium compounds, some leakage of tritium may
have occurred, because it is very mobile. However, tritium emits only very
weak beta particles that cannot penetrate the skin, so it exposes people
only if the tritium enters the body.

Smoke detector function using radiation
Ionizing chamber

ScreenMetal plate+

Smoke particles
Metal plate

+

–

α

–

α

α

BATTERY

Alpha particle
Radioactive source (e.g. americium)

Some modern smoke detectors consist of ionizing chambers with small
foils of americium-241, which are emitters of alpha particles and produce
a constant ion current. Ambient air is allowed to freely enter the detectors
and if smoke enters the detector, it disrupts the current triggering an alarm.
The radioactivity of the americium source in a smoke detector is very
low. It decays very slowly with a half-life of about 432 years. This means
WHERE DOES RADIATION COME FROM?

51

that a detector—at the end of 10 years’ use—retains essentially all its original activity. As long as the americium source stays in the detector, exposure would be negligible. Although detectable with sensitive e­ quipment,
the exposure levels received from such products are extremely low. A
person standing two metres away from the detector for eight hours a dayis estimated to receive a dose of less than 0.0001 mSv a year.
Industrial accidents
Accidents involving industrial radioactive sources occur more often
than those at nuclear power plants. Nevertheless, they do not normallyreceive as much attention even though they can cause extensive radiation
exposure to both workers and members of the public.
Between 1945 and 2007, about 80 accidents were reported at i­ ndustrial
facilities using radiation sources, accelerators and X-ray devices. Nine
deaths were reported in these accidents, and 120 workers were injured.
Acute radiation syndrome developed in some injured workers. The hands
were a common site of injury, and often had to be amputated. UNSCEAR
considers it probable that some accidents at industrial facilities ­involving
deaths and injuries have not been reported.
The causes and effects of such accidents are many and varied. Just
two examples are cited here. In 1978, in Louisiana, United States, anindustrial radiographer working on a barge sustained a radiation injury
to the left hand from a 3.7 TBq iridium-192 source, probably because ofdos­imeter malfunction. About three weeks later, his hand was red andswollen, and then skin blisters appeared, healing within 5–8 weeks. Six
months later, however, the index finger had to be partially amputated.
Then, in 1990, in Shanghai, China, because of improper safety measures, seven workers were exposed to radiation from a cobalt-60 source
at an industrial facility. One worker, with a dose estimated at 12 Gy,
died 25 days after exposure. A second, whose dose was estimated at
11 Gy, died 90 days after exposure. The other five workers received doses­estimated to range from 2 to 5 Gy and recovered after medical treatment.
Orphan sources
Between 1966 and 2007, 31 accidents were credited to lost, stolen or
abandoned radioactive sources, also known as orphan sources. These
accidents are known to have resulted in the deaths of 42 members of
the public, including children. In addition, acute radiation syndrome,52serious local injuries, internal contamination or psychological problems
necessitated medical care for hundreds of persons. Six accidents wereassociated with abandoned medical radiotherapy units.
Exactly how many orphan sources there are in the world is not known, but
the numbers are thought to be in the thousands. The United States Nuclear
Regulatory Commission reports that companies within the United States
lost track of nearly 1 500 radioactive sources between 1996 and 2008, withmore than half never recovered. A study by the European Union estimatedthat up to 70 sources are lost annually from regulatory control within its borders. Although the majority of these sources would not pose a significant­radiological hazard, accidents are the major ­concern for orphan sources.

Worldwide estimates of serious radiation accidents*
Type of accident

1945–1965

1966–1986

1987–2007

Accidents at nuclear facilities

19

12

4

Industrial accidents

2

50

28

Orphan source accidents

3

15

16

Accidents in academia/research

2

16

4

Unknown

18

14

Accidents in medicine* Based on accidents which have been reported officially or published. It is ­expected that the
number of unreported accidents, especially in medicine, is much larger.

Sealed sources or their containers can be attractive to people who
scavenge for the scrap metal trade because they appear to be made ofvaluable metal and may not display a radiation warning label. Cases
where unsuspecting workers or even members of the public have tampered with sources have led to serious injury and in some cases death, as
was the case in Goiânia, Brazil in 1987. An abandoned teletherapy device
with a highly radio­active (50.9 TBq) caesium-137 source was stolen andthe source capsule cracked open. Over the next two weeks, soluble caesium chloride powder was spread throughout a scrapyard and surrounding homes. Numerous people developed illnesses and skin lesions and
110 000 people had to be monitored for radioactive contamination, manyof whom were internally contaminated with caesium-137. Because of this
accident four people died, including one child.
WHERE DOES RADIATION COME FROM?

53

3.3. Average radiation exposure to public and workers
Generally, public exposure to radiation from natural sources d­ ominates
the total exposure. UNSCEAR estimated the average annual effective
dose to an individual at about 3 mSv. On average, the annual dose fromnatural sources is 2.4 mSv and two thirds of it comes from radioactive
substances in the air we breathe, the food we eat and the water we drink.
The main source of exposure from artificial sources is radiation used in
medicine, with an individual average annual effective dose of 0.62 mSv.
Medical radiological exposure varies by region, country and health-caresystem. UNSCEAR has estimated the average annual effective dose frommedical applications of radiation in industrialized countries at 1.9 mSv
and in non-industrialized countries at 0.32 mSv. However, these values
might vary considerably (e.g. in the United States with 3 mSv or in Kenyawith only 0.05 mSv).

Average public exposure by radiation sources*
Natural sources | 2.4 mSv

Artificial sources | 0.65 mSv

Food

0.29 mSv

Nuclear power
plants0.0002 mSv

Cosmic0.39 mSv

Chernobyl
accident

0.002 mSv

Soil

0.48 mSv

Weaponfallout

0.005 mSv

Nuclearmedicine

0.03 mSv

Radiology

0.62 mSv

Radon

1.3 mSv* Rounded estimates of the effective dose to a person in a year (world average).

Until the 1990s, attention concerning exposure of workers focused on
artificial sources of radiation. Nowadays, however, it is realized that avery large number of workers are exposed to natural sources of radiation, mainly in the mining industry. For certain occupations in the mining
sector, inhaling radon gas dominates radiation exposure at work. While
the release of radon in underground uranium mines makes a substantial
contribution to occupational exposure on the part of the nuclear industry, the annual average effective dose to a worker in the nuclear industry

54

overall has decreased from 4.4 mSv in the 1970s to about 1 mSv today.
However, the annual average effective dose to a coal miner is still about
2.4 mSv and for other miners about 3 mSv.
The current estimate of the total number of monitored workers isabout 23 million worldwide, of whom about 10 million are exposed toartificial sources. Three out of four workers exposed to artificial sources
work in the medical sector, with an annual effective dose per worker of
0.5 mSv. Evaluation of the trends of the average annual effective dose
per worker shows an increase in exposure from natural sources mainly
due to mining and a decrease in exposure from artificial sources mainly
because of the successful implementation of radiation p­rotection­measures.

Trends in global radiological exposure of workers (mSv)*
Decades

1970s

1980s

1990s

2000s

Aircrew

—

3.0

3.0

3.0

Coal mining

—

0.9

0.7

2.4

Other mining**

—

1.0

2.7

3.0

Miscellaneous

—

6.0

4.8

4.8

Total

—

1.7

1.8

2.9

Medical uses

0.8

0.6

0.3

0.5

Nuclear industry

4.4

3.7

1.8

1.0

Other industries

1.6

1.4

0.5

0.3

Miscellaneous

1.1

0.6

0.2

0.1

Total

1.7

1.4

0.6

0.5

Natural sources

Artificial sources* Estimates of average effective dose per worker in a year.
** Uranium mining is included in nuclear industry.

WHERE DOES RADIATION COME FROM?

55

UNSCEAR PUBLICATIONS
Since its inception, the United Nations Scientific Committee on the
Effects of Atomic Radiation has issued over 25 major reports with over
100 scientific annexes, which are highly regarded as principal sourcesof authoritative evaluations examining radiation exposure from nuclear
weapon tests and nuclear power production, medical usage of radiation,
occupational radiation sources and natural sources. It also evaluatesdetailed studies on radiation-induced cancer and hereditary diseases,
and assesses the radiological consequences of accidents on health andthe environment. UNSCEAR reports and its scientific annexes are issued
as United Nations sales publication (unp.un.org) and as free electronic
downloads (unscear.org) to disseminate the findings for the benefit of
UN Member States, the scientific community and the public.
Feedback and comments on this publication are highly appreciated to:
UNSCEAR secretariat
Vienna International Centre
P.O. Box 500
1400 Vienna, Austria
E-mail: unscear@unscear.org

In 1955, the United Nations General Assembly established theScientific Committee on the Effects of Atomic Radiation (UNSCEAR)
to collect and evaluate information on the levels and effects of­ionizing radiation.

This publication attempts to present objectively the latest­ nowledge on radiation levels and effects in a way that is ­accessiblekto the general reader. It is based on UNSCEAR’s scientific reports,
which are used as the main source of information.

RADIATION EFFECTS and SOURCES

This was in response to concerns about the effects of ionizing
radiation on human health and the environment as at that time
fallout from atmospheric nuclear weapon tests was reaching­people through air, water and food. UNSCEAR’s first report laid the­scientific grounds on which, in 1963, the Partial Test Ban Treaty
prohibiting atmospheric nuclear weapon testing was negotiated.

RADIATION
EFFECTS and SOURCES

What is radiation?
What does radiation do to us?
Where does radiation come from?

›1 000 mSv

100 mSv

Dose used in radiotherapy

Astronaut dose
(4 months)

10 mSv

CT scan of the abdomen

1 mSv

Worker dose in nuclear industry(1 year)

0.1 mSv

Chest X-ray or flight (20 hours)

0.01 mSv

Dental X-ray

0.001 mSv

Brazil nuts (30 g)

United Nations Environment Programme