WHAT IS
RADIOACTIVITY?
1.1

Design: ASN and IRSN Communications Departments - October 2021
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Our bodies are made up of a multitude of tiny bits:
atoms.
They connect with one another to form molecules,
which in turn form the basic structure of matter.
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WHAT ISRADIOACTIVITY?

JOURNEY TO
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There are 2 types of particles in the nucleus:
neutrons and protons. The number of protons
determines the chemical property of the atom.
There can be more or fewer neutrons in the sameelement, thus forming different isotopes.
Some are radioactive. For example, carbon-12 with
6 neutrons is stable, while carbon-14 with 8 neutrons
is unstable and radioactive.

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WHAT ABOUT
MOLECULES?
Atoms connect to one anotherto form molecules.
Molecules also connect with eachother to form all kinds of structures,
cells, objects, and living things.

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ATOMS

in
Potassium-40
89%
19 protons
21 neutronsof casesin Calcium-40
20 protons
89%20 neutronsof casesCalcium-40
20 protons
20 neutrons

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IS IT A HUMAN
INVENTION?

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RADIOACTIVITY:Radioactivity is a natural phenomenon
that occurs everywhere and has existed
since the Earth's origin. Radioactive elements
are found in rocks, water, fruit, and even in
our own bodies.

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An atom itself is made up of a nucleus and asurrounding cloud of electrons. These are thesame electrons that run through our electrical wires.

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WHAT IS 
AN ATOM MADE OF?
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The discovery of radioactivity
led to inventions that produced
artificial radioactive materials.
Some of these are highly radioactive
and could prove dangerous for current
or future generations if they are notcontained and controlled.

In any case, knowing the originof radioactivity allows us to better
understand the phenomena.

1.2

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WHAT ISRADIOACTIVITY?

THREE TYPESO F RADIATION
Some atoms transform over time,emitting invisible radiation.
Materials containing such atoms
are said to be radioactive!

Scientifically, we say that an atom that is transformed by the process of radioactivity decays.
It loses its integrity (disintegrates), releasing particles with varying degrees of energy.
Depending on its nature, an atom can emit three different types of radiation: alpha, beta or gamma.

ALPHA RADIATION
Some heavy atoms are transformed by emitting a massive particle, made up of two protons and twoneutrons; a helium nucleus known as an alpha particle.
Because of their large size, alpha particles are not very penetrating and are stopped by a simple sheetof paper. On the other hand, they release a great deal of energy on impact.

RAY
2 protons, 2 neutrons

URANIUM-238
92 protons, 146 neutrons

THORIUM-234
90 protons, 144 neutrons

BETA RADIATIONIn the nucleus of an atom, a neutron can change into a proton or, conversely, a proton can change
into a neutron. This transformation is accompanied by the emission of an electrified particle called
a beta particle.
These electrified particles, electrons or positrons, can pass through paper but are stopped by aluminium foil.
More penetrating than alpha particles, they also deposit their energy more gradually as they travel.

RAY
Electrons or positrons
POTASSIUM-40
19 protons, 21 neutrons

CALCIUM-40
20 protons, 20 neutrons

GAMMA RADIATION
After emitting an alpha or beta particle, some atoms become unstable.
They then emit gamma radiation to stabilise. Gamma rays are not composed of material particles butof particles of light, or photons.
Gamma rays are highly penetrating and require several centimetres of lead or tens of centimetres ofconcrete to stop them. It is difficult to protect against gamma rays.

RAY
PhotonNICKEL-60 EXCITED STATE
28 protons, 32 neutrons

NICKEL-60 STABLE
28 protons, 32 neutrons

Ray penetration

Alpha

Beta
Neutron
Gamma

Paper

Body

Metal

Water

Concrete

Lead

Some materials are radioactive:
they emit radiation with varying
degrees of energy.
These types of radiation
are all dangerous

and require appropriate
means of protection.

1.3

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WHAT ISRADIOACTIVITY?

HOW LONG
DOES
RADIOACTIVITYLAST?
Radioactivity is not eternal. Radioactive
materials lose particles over time,leaving only stable materials in the end.
Does this happen quickly? To find out,
we need to look at the concept of half-life.

RADIOACTIVITY 
IS NIBBLED AWAYRadioactive materials become less and less radioactive over time.
It's a bit like deciding to nibble on a biscuit every day, biting into
half of what's left. After a day, the biscuit will be half its size. In
three days, only one eighth will remain.Then the piece will get
smaller and smaller, but this can go on for a long time.

Concentration ofradioactive atoms
N

N/2
RADIOACTIVITY
DECREASES OVER TIME
Radioactive atoms decay: there arefewer and fewer of them.
And the fewer radioactive atoms thatremain, the less intense the radioactivity.
Radioactivity decreases according to a
curve which is exponential, becoming
increasingly flat over time.

N/4
N/8
N/16

T0

T1

T2

T3

T4

N/32

N/64

T5

T6

Time scale

THE HALF-LIFE
Physicists refer to the half-life of radioactive material as
the time by which half of the original atoms have decayed.
The half-life gives a good indication of how quickly a radioactive material disappears.
In the case above, scientists would say that the biscuit has a half-life of one day:it is half its size after one day.

EXAMPLESTECHNETIUM-99m
Half-life: 6 hours.
It has a very short half-life. It is used to makemedical diagnoses. It is quickly eliminated.
POTASSIUM-40
Half-life: 1.35 billion years.
Contained in the soil, it is also present
in food and the human body.
URANIUM-238
Half-life: 4.5 billion years.
Like that contained in granite rock, its half-life
is equivalent to the age of the Earth.
The Earth contains half as much uranium-238
as it did at its origin.

1.4

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It will take 300 years for thequantity of caesium-137 released
during the Fukushima accident to be
divided by a thousand.
The same reduction was obtained
after 80 days for radioactive iodine-131,
which disappeared in a few months.

WHAT ISRADIOACTIVITY?

UNITS OFMEASUREMENTOF RADIOACTIVITY

Some materials are radioactive: they emit radiation
with varying degrees of energy.
To measure radioactivity accurately, 3 complementary
units of measurement are used: becquerel, gray andsiervert.

LET'S COMPARE A RADIOACTIVE SOURCE TO AN APPLE TREE

The number of apples fallingfrom the tree is measured
in becquerel (Bq).

The dose of apples fallingon the head of the person under
the tree is measured in gray (Gy).

ACTIVITYOF A SOURCE
The number of becquerels corresponds
to the number of times per second
the source emits radiation.
The greater the number, the greater
the activity of the source.

THE DOSE RECEIVED

THE EFFECTIVE D OSE

The gray is used to measure theenergy resulting from the amountof radiation received.
This is known as the dose received.

The sievert measures dangerousness.
When it comes specifically to the human
body, the effects of different types ofradiation vary according to the organs or
tissues affected. Some are more sensitive
than others.

The dosimeter is designed tomeasure the radioactive doseor dose equivalent received bya person exposed to radioactive
radiation.

The Geiger counteris used to measureradioactivity andeach disintegration
recorded is converted
into sound.

a flight from Paris to
New York, dose due tonatural cosmic rays in
the upper atmosphere.

• 0.7 mSv:

a chest X-ray.

The dose received by an organ is theresult of a calculation that takes various
factors into account. For example,
radiation weighting factors are applied
depending on the organs affected.

WEIGHTING ACCORDING TO ORGANSAFFECTED BY DOSE RECEIVED• Bone marrow 0.12
• Breast 0.12
• Prostate 0.12
• Colon 0.12
• Gonad 0.08
• Lung 0.12
• Bladder 0.04
• Stomach 0.12
• Liver 0.04
• Heart 0.12
• Thyroid 0.04
• Pancreas 0.12
• Brain 0.01
• Small intestine 0.12
• Skin 0.01
• Cervix 0.12
• Muscles 0.12

Key figures•0 .03 mSv:

The effects of the impactof fruit on the person's bodyare measured in sievert (Sv).

• 3 mSv:

one year's exposure
to natural radioactivity
in France.

• 10 mSv:

a CT scan.

• A bove 1 Sv
(1000 mSv)

received in a shortperiod of time,radiation can cause
disorders andmalfunctions, and evendeath in the shortor medium term.

ESTIMATE 
THE DOSE RECEIVED
Estimate your dose foryour next flight by scanningthe following QR Code or visiting
http://www.sievert-system.org/• 100 mSv:

value above which
an increase in the riskof cancer has beenmeasured.

1.5

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WHAT ISRADIOACTIVITY?

WE ARE ALL 

EXPOSEDWe are all constantly exposedto small doses of radioactivity,
whether of natural or artificial origin.

NATURAL RADIOACTIVITY OR
ARTIFICIAL RADIOACTIVITY ?
Radiation comes from the cosmos, the Earth, the air we breathe and the food we eat. Every day we ingest
radioactive atoms that are naturally present in our environment.
Nuclear facilities also generate airborne emissions and waste. In hospital, doctors also use equipment thatemits radiation, such as X-ray and scanner machines, to treat patients.
Two types of exposure need to be taken into account: artificial exposure and natural exposure.

1.5

1.5

RE

XPOSU RERADONRadioactive gas
emanating fromunderground

TOTAL

average exposureof people in France

4.5 mSv/year

U

RA

A

I C I AL E
F
I
T
R
X

PO

S

mSv

U

mSv

LE

MEDICALEXPOSURE

INDUSTRIES
and research, military
nuclear testing, etc.

A

T

0.012

N

mSv

0.63
mSv

0.32
mSv

0.55
mSv

COSMIC RAYSTERRESTRIAL
RADIATION(radioactive
soil minerals)
excluding radon

WATER, FOOD
AND TOBACCOVARIABLE LEVELS OF EXPOSURE 
Our exposure varies according to our lifestyle, where welive and the frequency of medical examinations (X-rays andscans). This leads to a very different annual dose from one
person to another.

ESTIMATE 
YOUR ANNUALEXPOSURE
Estimate your annual exposureby scanning the following QR Codeor visiting https://expop.irsn.fr/

FOR EXAMPLE
Someone who skis a lot(altitude), eats a lot of bananas(naturally radioactive potassium),
lives in Brittany (naturally
radioactive granite) or has a lotof medical check-ups or air travel
will be much more exposed thansomeone who lives in the Paris
region, rarely visits hospitals andrarely stays at altitude.

1.6

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WHAT ISRADIOACTIVITY?

RADIOACTIVITY 
IN FOOD

The food we eat isnaturally radioactive.

NATURALLY RADIOACTIVE
SUBSTANCES
All our food is somewhat radioactive, containing elements such as carbon-14
and potassium-40 in small quantities.
Bananas (130 Bq/kg potassium-40), for example, are sufficiently radioactive
to be detected by security gates in the United States.
The most naturally radioactive foodstuff is Brazil nuts (600 Bq/kg).
160

140

120

100

80

40

20

40

50

40

45

90

100

35

50

90

115

130

150

170

CheeseMilk

Mussels

Eggs

Fish

Beef,
mutton,poultry

Wine

Fruit

Salad

GrainsBananaGreenvegetables

PotatoDAIRY PRODUCTS

MEAT, EGGS, FISHFRUIT, VEGETABLES, PLANTSPRECISELY MEASURE
THE DOSE RECEIVED NATURALLY
Depending on its nature, a radioactive element will bindto one organ or another. The body does not store all theseelements; it evacuates the quantity it does not need oreliminates it little by little.

For example, only a limited quantity of potassium-40
is fixed by the body, the rest is eliminated. Half of the
carbon-14 is eliminated in 40 days. On the other hand,the body can store polonium-210 (very prevalent in fish
and crustaceans) without limit. 0.55 mSv/year is theaverage dose ingested in France.

A table can be used to convert the quantity of becquerels of a radioelement ingested into millisieverts, depending on the
person's age. For example, in crustaceans, there is naturally 18 Bq/kg of polonium-210 and 10 Bq/kg in small fish.
Let's imagine that you ingested 100 Bq of polonium-210 by eating a lot of fish or crustaceans (about 10 kg):
- an adult will receive a dose of 1.2 x 10 -6 x 102 = 0.12 10-3 sieverts, i.e. 0.12 mSv;
- a 5-year-old child will receive a dose of 4.4 x 10-6 x 102 = 0.44 10-3 sieverts, i.e. 0.44 mSv.

RadioelementAge
1 year

5 years

10 years

15 years

Adult

Potassium-40

4.2 10-8

2.1 10-8

1.3 10-8

7.6 10-9

6.2 10-9

Carbon-14

1.6 10-9

9.9 10-10

8.0 10-10

5.7 10-10

5.8 10-10

Polonium-210

2.6 10-5

4.4 10-6

2.6 10-6

1.6 10-6

1.2 10-6

Brazil nuts are naturally
the most radioactive food.
It is made up of

three hundred sextillion atoms(300,000,000,000,000,000,000,000).
Every minute, around twenty of theseatoms emit radiation.

1.7

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0

Activity (Bq/kg potassium-40)

60

WHAT ISRADIOACTIVITY?

MAKINGRADIOACTIVITY
At the end of the 19 century, humans discovered
the natural phenomenon of radioactivity.
This enabled the creation of other radioactive
elements and their use in many fields:
This is artificial radioactivity.
th

THE BEGINNINGS OF ARTIFICIALRADIOACTIVITY"I irradiate this target withalpha rays from my polonium
source; you can hear the Geiger
counter clicking [...] I remove
the source: the clicking shouldstop... but the noisecontinues..."Frédéric Joliot-Curie

In the early part of 1934, Irène and FrédéricJoliot-Curie announced in a note to the Académiedes Sciences (French Academy of Sciences) thatthey had made a radioactive atom that did notexist in nature.
By bombarding a sheet of aluminium with a sourceof alpha rays, they observed the appearance of an
unknown element. This element turned out to be
an isotope of phosphorus, phosphorus-30.

THE APPLICATIONSOF ARTIFICIAL RADIOACTIVITY
Radioactive elements such as uranium and potassium have been naturally present in our environment
since the beginning of the universe, because they are long-lived.
The other shorter-lived elements, which were also present at the origin of the universe,
have since disappeared. However, we now know how to manufacture these elements and create others,
more or less ephemeral, for energy, military, medical and scientific needs.

INDUSTRY

NUCLEAR POWERRESEARCH

MEDICINE
MILITARY

1.8

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WHAT ISRADIOACTIVITY?

RADIOACTIVITY:
A BRIEF HISTORY
Since its discovery at the end of the 19th century,
radioactivity has been used in a variety of fields(research, medical, military, nuclear power, industry)
and the associated risks have been managed.

2027
2026
2025
2024
2023
2022
2021

TIMELINE 
OF RADIOACTIVITY

2020
2019
2018
2017
2016
2015
2014
2013
2012
2011

12 to 15 March 2011

Fukushima nuclear accident (Japan)

2010

1996

Last French nuclear test in French Polynesia andlaunch of the Laser Megajoule programme tosimulate the operation of nuclear weapons

28 March 1979

Three Mile Island nuclear accident (United States)

2009
2008
2007
2006
2005
2004
2003
2002
2001

2000
1999
1998
1997
1996
1995
1994
1993
1992
1991

1990
1976

Creation of the Institute for Nuclear Protection and Safety (IPSN) within the CEA

1972

Invention of the medical scanner by Godfrey N. Hounsfield

1 July 1968

Entry into force of the Treaty on the Non-Proliferation of Nuclear Weapons (NPT)

1989
1988
1987
1986
1985
1984
1983
1982
1981

1980
1979
1978
1977
1976
1975
1974
1973
1972
1971

1970
16 September 1962

Start-up of Chinon A1,
EDF's first nuclear reactor

13 February 1960

Gerboise bleue,France's first nuclear
explosion in the Sahara

1969
1968
1967
1966
1965
1964
1963
1962
1961

1960
26 June 1954

Commissioning of the Obninsk reactor (USSR),
the world's first electricity-generating reactor,
which operated until 29 April 2002

6 December 1953

Speech by President Eisenhower tothe UN General Assembly "Atoms
for Peace," proposing the use of
nuclear technologies fornon-military purposes

1959
1958
1957
1956
1955
1954
1953
1952
1951

1950

20 December 1951

First nuclear power
generation by theBR1 reactor in the
United States

15 December 1948

Divergence of ZOE,
the first French reactor

1949
1948
1947
1946
1945
1944
1943
1942
1941

1940
2 December 1942

First divergence of a nuclear reactor,
Chicago Pile 1, designed by Enrico Fermi

1 May 1939

Frédéric Joliot-Curie filed three secret patents:
two on reactor operation and one on thepossibility of a "nuclear explosive"

1932

Discovery of the neutron by James Chadwick(predicted in 1920 by Ernest Rutherford)

1914

Introduction of the "Petites Curies", vehicles that Marie Curie
equipped with X-ray units to care for the wounded in the field
during the First World War

1939
1938
1937
1936
1935
1934
1933
1932
1931

1930
1929
1928
1927
1926
1925
1924
1923
1922
1921

2006

Creation of the French Nuclear Safety Authority(ASN) and enactment of the law on nuclear
transparency and safety (TSN law)

2001

Creation of the Institut de Radioprotection et de Sûreté Nucléaire (IRSN - Institutefor radiation protection and nuclear safety) from the merger of OPRI and IPSN

26 April 1986

Chernobyl nuclear accident (Ukraine)

1973

Start of mass deployment of nuclear
power in France (Messmer plan)

1957

Windscaleaccident (United
Kingdom), firstmajor nuclear
accident

1973

Creation of the Service central de sûreté des installations
nucléaires (SCSIN - central department for the safety of
nuclear installations) attached to the Ministry of Industry,
which became the Autorité de sûreté nucléaire (ASN French Nuclear Safety Authority) in 2006

1957

Creation of the Service
central de protection
contre les rayonnements
ionisants (SCPRI central department forthe protection against
ionising radiation), whichbecame the Office deprotection contre lesrayonnements ionisants(OPRI - office for theprotection against
ionising radiation)in 1994

1955

Creation of the United Nations
Scientific Committee on the Effectsof Atomic Radiation (UNSCEAR)

16 July 1945

Trinity, the first nuclear
explosion in history in
New Mexico (UnitedStates)25 March 1957

Signature of the Treaty
establishing theEuropean Atomic Energy
Community (EURATOM),
which today remains oneof the three fundamental
treaties of the European
Union

29 July 1957

Creation of theInternational Nuclear
Energy Agency (IAEA)
to promote the safe,
secure and peacefuluse of nuclear
technologies, inparticular bycombatingproliferation

20 January 1955
First sea trip by the Nautilus, the firstnuclear submarine

18 October 1945

6 August 1945

Creation of the French
Atomic Energy Commission(CEA), whose mission is toprovide France with nuclear
energy and nuclear weapons

Hiroshima explosion

9 August 1945

Nagasaki explosion

9 October 1941

Franklin D. Roosevelt approves the launch of the Manhattan
Project, which will lead to the development of nuclear
weapons and the creation of the "nuclear cycle"

1934

Discovery of artificial radioactivity
by Irène and Frédéric Joliot-Curie

1928

Development of theGeiger-Müller counter

1920
1919
1918
1917
1916
1915
1914
1913
1912
1911

1938

Hahn, Strassman and Meitnerdiscover nuclear fission

1928

On the initiative of Rolf Sievert, who gave
his name to the unit measuring received
dose, the "International Committee forRadiological Protection" was set up, later
to become the International Commission
on Radiological Protection (ICRP)

1910

1900

First observation of the physiological effects of ionising radiation(inflammation of the skin after exposure)

1909
1908
1907
1906
1905
1904
1903
1902
1901

1900

2 March 1896

Discovery ofradioactivity by
Henri Becquerel

July 1896

First radiation treatment
carried out in Lyon by
Dr Victor Despeignes totreat a stomach tumour

1899
1898
1897
1896
1895
1894
1893
1892
1891

1901

First results from the use of radium
to treat disease

21 December 1898

Discovery of radium by Marie and Pierre Curie

22 December 1895

First X-ray by Wilhelm Röntgen,
who discovered X-rays

1890

1.9

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