Principles of Radiation
IAEA
International Atomic Energy Agency
Radiation and radioactivity
• The German scientist Wilhelm Roentgen
discovered radiation in 1895
• He observed a mysterious form of invisible
radiation that had the power to fog
photographic film.
• This radiation became known as X-radiation.
• In the following year Henri Becquerel
observed that radiation with similar
properties was being emitted from certain
naturally occurring mineral ores (NORM).
IAEA
2
Module 1: Overview of mining technologies and uranium mining
The structure of matter and elements
Similar atoms group together to form elements, the number of
protons in the nucleus of the atoms determining the particular
element e.g. an atom with one proton only is an atom of the element
hydrogen.
IAEA
3
Module 1: Overview of mining technologies and uranium mining
Isotopes
• By definition, all atoms of a specific element must have the same
•
•
•
•
number of protons in the nucleus (the atomic number).
However they may have differing numbers of neutrons in the
nucleus (mass number). These differing atoms are referred to as
isotopes of a particular element.
Isotopes are therefore atoms with the same number of protons
but different numbers of neutrons.
Stable atoms are required to have the correct ratio of protons and
neutrons within the nucleus.
Atoms that do not satisfy these criteria are unstable, and achieve
stability by the emission of ionising radiation.
IAEA
4
Module 1: Overview of mining technologies and uranium mining
Unstable isotopes
• These unstable atoms are, therefore, “radioactive” and
are referred to as radioisotopes or radionuclides. The
process of emitting radiation is called radioactive
decay.
• For example natural isotopes 238U, 234U and 235U, 232Th
and 228Th, 228Ra and 226Ra
IAEA
5
Module 1: Overview of mining technologies and uranium mining
Radiation and radioactivity
Radioactivity can be defined as the
process by which unstable atoms ‘try’ to
become more stable by emitting ionising
radiation.
There are three principal types of
radiation emitted during radioactive
decay:


• alpha particle radiation
• beta particle radiation
• gamma radiation
Note: Uranium ore emits all three types
of radiation
IAEA

6
Module 1: Overview of mining technologies and uranium mining
Types of radiation
Ionizing Radiation
IAEA
7
Module 1: Overview of mining technologies and uranium mining
Definitions
• Radiation: Energy in the form of particles or
electromagnetic waves
• Ionising radiation: Radiation with sufficient energy to
remove an electron from an atom or molecule.
IAEA
8
Module 1: Overview of mining technologies and uranium mining
Alpha particles
• An alpha particle consists of two protons and two
neutrons tightly bound together and is ejected with a
high velocity from the nucleus of the atom.
• The symbol for alpha particle radiation is α.
• There are many natural alpha emitters e.g. 238U, 232Th,
222Rn
and 226Ra.
IAEA
9
Module 1: Overview of mining technologies and uranium mining
Alpha particles
Cannot penetrate skin
Internal hazard
Stopped by paper
Found in soil, air (radon) and other radioactive
materials
Alpha-radiation is only a hazard when inside your body
(internal hazard)
IAEA
10
Module 1: Overview of mining technologies and uranium mining
Beta particles
• A beta particle decay involves the emission of an
energetic electron from the nucleus of the atom.
• The electron is referred to as the beta particle, with the
symbol β.
• The range of a beta particle is up to several metres in
air and it can also penetrate a short distance into living
tissue.
• Beta particle radiation rarely presents a significant
potential external exposure hazard in mining facilities.
IAEA
11
Module 1: Overview of mining technologies and uranium mining
Beta particles
Skin, eye and internal hazard
Stopped by aluminium, plastic
Found in natural food, air and water
Beta-radiation is a skin, eye and internal hazard
IAEA
12
Module 1: Overview of mining technologies and uranium mining
Gamma radiation
• Gamma radiation is a pulse of high energy,
electromagnetic radiation emitted from the nucleus of
the atom.
• Gamma radiation has the symbol  and often
accompanies alpha or beta radiation.
• Gamma rays may travel considerable distances in air
depending on their energy and may require a
significant thickness of dense material to stop them
(i.e. concrete or lead).
IAEA
13
Module 1: Overview of mining technologies and uranium mining
Gamma radiation
Stopped by lead
Used in medicine (X-rays)
Naturally present in soil and cosmic radiation
Gamma-radiation is a hazard when outside your body
(external, and to a lesser degree, internal hazard)
IAEA
14
Module 1: Overview of mining technologies and uranium mining
Neutrons
Neutrons are very penetrating, but only observed in nuclear industry –
none in mining
IAEA
15
Module 1: Overview of mining technologies and uranium mining
Penetrating power of radiation
Alpha particles travel only a few centimetres in air and are incapable of penetrating
the skin.
Beta particles have a range of more than one meter in air and up to one centimetre
in tissue.
Gamma rays can be very penetrating, they can pass through the walls of plant and
equipment.
IAEA
16
Module 1: Overview of mining technologies and uranium mining
Naturally occurring radioisotopes
Naturally occurring radionuclides include the uranium
series and the thorium series.
• A long-lived isotope is at the head of each series while a
stable isotope of lead ends each one.
• The uranium series originates with
238U
which has a
half-life of 4.5 thousand million years and decays
through a series of radioisotopes involving the emission
of alpha, beta and gamma radiation to stable 206Pb.
IAEA
17
Module 1: Overview of mining technologies and uranium mining
238U
Decay chain
IAEA
18
Module 1: Overview of mining technologies and uranium mining
232Th
Decay chain
IAEA
19
Module 1: Overview of mining technologies and uranium mining
Decay and half-life
• The half-life is the time it takes for half of the original
radioactive material to decay.
• The half-life is a constant for a specific radioisotope.
• Natural radionuclides comprise a wide range of half
lives from a few seconds to billions of years.
IAEA
20
Module 1: Overview of mining technologies and uranium mining
Radiation quantities and units
The quantities and units used in radiation protection and
safety are based on the SI system for scientific units and
are developed by the International Commission on
Radiological Units (ICRU).
The main quantities of interest include:
• Activity e.g. the Becquerel (Bq)
• Dose e.g. the Sievert (Sv)
IAEA
21
Module 1: Overview of mining technologies and uranium mining
Units of radiation : Gray and Sievert
Physical : Absorbed dose is measured in Grays (Gy)
and one Gray is the radiation that is absorbed in
matter producing 1 Joule/ kg
Note: 1 Joule = the energy necessary to raise 9.8 kg to
a height of 1 meter.
Biological : Dose equivalent is measured in Sieverts
(Sv) which has the same definition and units as
absorbed dose (J/kg), but depends on the biological
tissue in which it is absorbed and on the type of
particle (alpha, beta, gamma, neutron).
IAEA
22
Module 1: Overview of mining technologies and uranium mining
Not all radiation has the same biological effect
• Different radiation has different biological effects, mainly
dependent on the density of ionization
• This is reflected in the “Radiation Weighting Factor”, a factor
relative to gamma radiation which shows how much the effect is
multiplied if not gamma
• It is also important to note that different body parts would be
affected differently, and this is presented by special tissue
weighting factors
IAEA
23
Module 1: Overview of mining technologies and uranium mining
Harmful effects of radiation
• The damaging effects of ionizing radiation became
apparent only a few years after the discovery of
radiation (X-ray researchers burns and cancers).
• Extensive research carried out in many countries
around the world has enabled increasingly detailed
estimates of the effects of low doses of radiation to be
made.
IAEA
24
Module 1: Overview of mining technologies and uranium mining
Natural radiation is the greatest source of human exposure
We are all exposed to radiation (average annual dose = 2.0 – 2.4 mSv):
– Cosmic rays from space
– Gamma rays from soil and building materials
– Radon gas emitted from soil and rock (buildings, tunnels, cellars, etc)
– Higher exposure at higher altitudes
– Traces of radioactive materials in food and drink
There are some areas in the world (Brazil, India, China), where the ‘background’ radiation exposure can be much
higher, between 10 and 200 mSv per year
IAEA
25
Module 1: Overview of mining technologies and uranium mining
Some comparisons…
If we take a typical gamma radiation level per hour as 1, the following comparative values can be derived:
1 – typical natural background (may be higher or lower, by a small margin)
3 – typical for an exploration site with U mineralisation of 0.05 – 0.06%
4 – some cement
5 – typical for an exploration site with U mineralisation of 0.10%
5 – certain phosphate fertilisers
6 – some ceramic tiles
7 – typical for an exploration site with U mineralisation of 0.14 – 0.15%
7 – coal burning slag
10 – on board of a local flight
14 – a phosphate mine
16 – titanium minerals
20 – typical for an exploration site with U mineralisation of 0.40%
22 – zirconium minerals
25 – geothermal energy generation waste
30 – water treatment sludge
40 – heavy mineral sands concentrate
60 – on board of an international flight
80 – tin concentrate
120 – uranium mine/processing plant
250 – rare earth processing plant
400 – coal mine (underground water discharge points on the surface)
500 – some areas of titanium dioxide pigment plant
1000 – contaminated equipment from oil and gas industry
2500 – rare earth mineral (monazite)
IAEA
26
Module 1: Overview of mining technologies and uranium mining
Doses comparison
The comparison below demonstrates the levels of radiation exposure in
different industries, in milliSieverts per year
Mineral sands mining: 0.1-0.7 mSv/year
Phosphate ore handling: 0.01-0.8 mSv/year
Operation of nuclear-powered ships, average: 0.8 mSv/year
Ilmenite handling: 0.01-0.9 mSv/year
Zircon handling: 0.5-0.9 mSv/year
Uranium exploration: 0.1-1.5 mSv/year
Rare earth ore mining, expected maximum: 1.0-6.0 mSv/year
Medical uses of radiation (X-ray, dentistry, nuclear medicine, etc), average: 0.5-1.5 mSv/year
Scientific research (radiochemistry, linear accelerators, etc), average: 2.5 mSv/year
Mineral sands processing, average: 2.7 mSv/year (can be up to 10-15 mSv/year)
Industrial uses of radiation (food irradiation, density measurements, X-rays of steel), average: 2.7 mSv/year
Nuclear reactor operation, average: 2.5 mSv/year
Uranium milling, average: 3.3 mSv/year
Air crew on international flights, average: 4.0 mSv/year
Uranium mining, average: 5.0 mSv/year
Monazite processing: 1.5 – 10.0 mSv/year
Removal of scale, titanium dioxide pigment production: 0.01-20.0 mSv/year
Removal of scale, oil and gas exploration/production: 0.01-33.0 mSv/year
IAEA
27
Module 1: Overview of mining technologies and uranium mining
How dangerous is radiation?
And this is the typical radiation dose that a
worker could receive at a uranium mine (5 mSv)
This is the radiation
exposure limit
in one year (20 mSv)
IAEA
*****
**********
****************************************
**********
****************************************
****************************************
****************************************
****************************************
****************************************
****************************************
****************************************
****************************************
****************************************
****************************************
****************************************
****************************************
****************************************
****************************************
****************************************
****************************************
****************************************
****************************************
****************************************
****************************************
****************************************
****************************************
****************************************
****************************************
Module 1: Overview of mining technologies and uranium mining
This amount of radiation
(1000 mSv)
could cause serious harm
28
Annual exposure limits
General Public: 1 mSv / year
Radiation workers: 20 mSv / year
(derived from 100 mSv in five years, provided that the dose does
not exceed 50 mSv in any single year)
29
IAEA
Module 1: Overview of mining technologies and uranium mining
Two ways we can be exposed to radiation
Exposure from a radiation
source outside the body
(external radiation)
Exposure due to inhaling or
ingesting radioactive material
(internal radiation)
IAEA
30
Module 1: Overview of mining technologies and uranium mining
Summary
•
•
•
•
Ionizing radiation was discovered just over 100 years ago.
Radioactive materials are unstable isotopes of elements.
They emit alpha, beta and gamma radiation.
Naturally occurring radioactive materials occur in the
environment.
• Human exposure to radiation involves both internal and external
exposure pathways from both natural and industrial sources.
• The harmful effects of radiation were noted at an early stage.
• Radiation doses require to be limited to reduce the risk of
harmful effects.
IAEA
31
Module 1: Overview of mining technologies and uranium mining