Italian Teachers Programme – September 2016
Radiation and radioactivity
(around us)
Marco Silari
Radiation Protection Group
Occupational Health & Safety and Environmental Protection Unit
marco.silari@cern.ch
M. Silari – Radiation and radioactivity – 6 September 2016
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Why do you have sheep on the CERN site?
M. Silari – Radiation and radioactivity – 6 September 2016
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The wrong answer…
The sheep are there to check radioactivity in the grass…
Of course NOT!
M. Silari – Radiation and radioactivity – 6 September 2016
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CERN has a an extensive environmental monitoring plan
(which does not involve the use of sheep…)
Stray radiation
Air
Water
M. Silari – Radiation and radioactivity – 6 September 2016
Other environmental samples
4
If I say “radiation” or “radioactivity”,
what comes to your mind?
M. Silari – Radiation and radioactivity – 6 September 2016
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I would guess this?
Hiroshima, Japan, 6 August 1945
Chernobyl, Ucraine,
26 April 1986
Fukushima, Japan, 11 March 2011
M. Silari – Radiation and radioactivity – 6 September 2016
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The pacific uses of radiation
M. Silari – Radiation and radioactivity – 6 September 2016
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The pacific uses of ionising radiation
Medicine:
Radiodiagnostics, nuclear medicine
and radiation therapy
Energy production
Scientific research
M. Silari – Radiation and radioactivity – 6 September 2016
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The pacific uses of ionising radiation
Airport security
Industrial radiography
https://uw-food-irradiation.engr.wisc.edu/Process.html
Sterilization of food and medical material
M. Silari – Radiation and radioactivity – 6 September 2016
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The pacific uses of ionising radiation
Non-destructive
measurements in archeometry
THE IRRADIATED MATERIAL DOES
NOT BECOME RADIOACTIVE!
M. Milazzo, University of Milan
M. Silari – Radiation and radioactivity – 6 September 2016
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What is ionizing radiation?
M. Silari – Radiation and radioactivity – 6 September 2016
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Ionising radiation
Gamma radiation
– photons or electromagnetic radiation
– penetrating
– “difficult” to shield
Beta radiation
– “light” charged particles
– limited penetration in matter
– “easy” to shield
Alpha radiation
β¯ (electron)
– “heavy” charged particles
– limited penetration in matter
– “easy” to shield
M. Silari – Radiation and radioactivity – 6 September 2016
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Directly and indirectly ionising radiation
Directly ionizing radiation:
• fast charged particles (e.g., electrons, protons, alpha particles), which
deliver their energy to matter directly, through many small Coulomb-force
interactions along the particle’s track
Indirectly ionizing radiation:
• X- or g-ray photons or neutrons (i.e., uncharged particles), which first
transfer their energy to charged particles in the matter through which
they pass in a relatively few large interactions, or cause nuclear reactions
• The resulting fast charged particles then in turn deliver the energy in
matter
The deposition of energy in matter by indirectly ionising radiation is a twostep process
photon  electron
neutron  proton or recoiling nuclei
M. Silari – Radiation and radioactivity – 6 September 2016
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What is radioactivity?
M. Silari – Radiation and radioactivity – 6 September 2016
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Periodic table of elements
M. Silari – Radiation and radioactivity – 6 September 2016
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The atom
Nucleus:
Electrons
protons + neutrons
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The three isotopes of hydrogen
For example: the simplest chemical element,
hydrogen, exists in three “variants” (ISOTOPES)
Idrogeno
Hydrogen
Deuteron
Tritium
Proton
Electron
Neutron
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Chart of nuclides
protons
Unstable (=radioactive) nuclides ~ 3000
β+ : p+ --> n + e+
α-decay
β- : n --> p+ + e-
α : AX -> A-4Y + 4He2+
Stable nuclides ~250
neutrons
M. Silari – Radiation and radioactivity – 6 September 2016
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Radioactivity and ionising radiation
Radioactivity: the phenomenon whereby atoms undergo spontaneous
random disintegration, usually accompanied by the emission of ionising radiation
The activity of a radioactive source is its rate of decay =
number of disintegrations per second
The unit of activity is the Bequerel
1 Bq = 1 s-1
(the old unit is the Curie: 1 Ci = 3.7 x 1010 Bq)
The half-life T1/2 is the time necessary for half of the nuclei to decay
Radionuclides are either of natural origin or produced by nuclear reactions
(artificial radionuclides)
M. Silari – Radiation and radioactivity – 6 September 2016
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Why does ionizing radiation pose a health risk?
M. Silari – Radiation and radioactivity – 6 September 2016
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Effects of interaction of ionizing radiation with matter
•
Biological systems (humans in particular) are particularly
susceptible to damage by ionizing radiation
•
The expenditure of a trivial amount of energy (~4 J/kg or Gy)
to the whole body is likely to cause death…
•
…even if this amount of energy can only raise the gross
temperature by about 0.001 °C
•
This is because of the ability of ionizing radiation to impart
their energy to individual atoms and molecules
•
The resulting high local concentration of absorbed energy can
kill a cell either directly or through the formation of highly
reactive chemical species such as free radicals (atom or
compound in which there is an unpaired electron, such as H or
CH3) in the water medium that constitutes the bulk of the
biological material
M. Silari – Radiation and radioactivity – 6 September 2016
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Unit
The absorbed dose is the energy deposited by a
given radiation in a unit mass of matter
The unit of absorbed dose is the Gray:
1 Gy = 1 J/Kg
(the old unit is the rad: 1 rad = 10-2 Gy)
Radiation protection uses the operational quantity
“dose equivalent H” in Sievert
H=Q∙D
1 Sv = 1 J/Kg
Q = quality factor of the radiation
M. Silari – Radiation and radioactivity – 6 September 2016
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Effects of radiation at the molecular and cellular level
cell
cromosome
Cromatine fibre
1-10 m
DNA
1 m
nucleosome
30 nm
2 nm
10 nm
Cells have a certain capacity (luckily) to repair damage
M. Silari – Radiation and radioactivity – 6 September 2016
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The biological effects of radiation
Deterministic effects
Example: burn
Probabilistic effects
Example: cellular mutation
M. Silari – Radiation and radioactivity – 6 September 2016
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The biological effects of radiation
Stochastic effects
Deterministic effects
No dose threshold (linear function of
dose)
Dose received in short time interval
dose threshold: > 100 mSv (> 500 mSv)
Increase of probability by 5% per Sv for:
- genetic defects
- cancer
Immediate consequences:
- vomiting
- immun deficiency
- erythema and necrose
Severity of the effect is independent of
the dose received
Health detriments are function of the
dose (and dose rate)
Delayed health detriments
Lethal dose for humans: 5 – 7 Sv
M. Silari – Radiation and radioactivity – 6 September 2016
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The biological actions of radiation
Cell membranes
deterministic
indirect
effects
no-repair
OH
H2O
H
free
radicals
uncontrolled
cell death
(necrosis)
tissue
pathologies
peroxydes,
active substances
Hereditary
effects
mis-repair
non-lethal
mutation
CANCER
programmed cell
death
(apoptosis)
DNA lesions
direct
effects
stochastic
deterministic
IONISATION
excitation
repair
normal cell survival
biomolecule
field
time scale
physics
chemistry
biochemistry
10-16s
10-6s
10-2s
biology, medicine
second,
minute
M. Silari – Radiation and radioactivity – 6 September 2016
day, year, generation
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Lethal dose (LD50/30) for various organisms
Source: Martin Volkmer, Radioaktivität und Strahlenschutz, Informationskreis Kernenergie
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Effects associated with whole-body exposure to radiation
0to0.25grays
No identified pathological symptoms associated with the
exposure to radiation.
0.25to1gray
Some nausea.
Slight fall in
leukocyte count.
1to1.25grays
Vomiting. Noticeable
changes to
the composition
of the blood.
2.25to5grays
Lethal dose for 50%
of the population.
Hospitalisation
essential.
Above5grays
Almost certainly fatal.
Radiation and man, CEA, France
M. Silari – Radiation and radioactivity – 6 September 2016
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Acute whole-body irradiation syndrome
Syndrome
Threshold
Haematopoietic
1 Gy
Time to
appearance
3 weeks
Gastrointestinal
5 Gy
3 to 5 hours
Central nervous
system (CNS)
20 Gy
0,5 to 3
hours
Symptoms
Pathology
Lymphocyte
depletion ,
infections,
bleeding
Diarrhoea,
fever
Depletion of
bone marrow
Lethargy,
convulsions
Destruction
of the
intestinal
mucosa
Inflammation
of CNS,
oedema
Time to
death
2 months
2 weeks
2 days
LD 50 dose by acute whole body irradiation : 5 Gy
M. Silari – Radiation and radioactivity – 6 September 2016
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Relative Biological Effectiveness (RBE)
The spatial distribution of radiation-matter interaction,
and therefore biological damage, depends on type and
energy of radiation (“track structure”)
M. Silari – Radiation and radioactivity – 6 September 2016
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Dose rate dependence
Dose rate = amount of radiation absorbed per unit time
Dose
Dose rate
5 tubes of aspirin
In 50 seconds??
Death
Or in 50 years??
Small risk
In 50 seconds??
Death
Or in 50 years??
Small risk
or
2500 mSv
of radiation
M. Silari – Radiation and radioactivity – 6 September 2016
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What are the natural radiation levels?
To which sources are we all exposed?
(voluntarily or not)
M. Silari – Radiation and radioactivity – 6 September 2016
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Natural radiation exposures
Annual exposure to natural radioactivity in France = 2.5 mSv
(3.3 mSv including medical exposures)
M. Silari – Radiation and radioactivity – 6 September 2016
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Natural radiation exposures
Annual exposure to natural radioactivity in Switzerland = 4.4 mSv
(5.6 mSv including medical exposures)
M. Silari – Radiation and radioactivity – 6 September 2016
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Natural sources of radiation
Cosmic rays
Radioactivity of
terrestrial origin
(radionuclides
present in the
earth crust such
as U, Th, Ra, Rn)
Cosmogenic radionuclides
(14C, 7Be, 3H)
The human body
(radionuclides
present inside
our body, mainly
40K)
+ medical exposures
M. Silari – Radiation and radioactivity – 6 September 2016
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Radiation from space
L. Pinsky, Università di Houston
M. Silari – Radiation and radioactivity – 6 September 2016
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Solar eruption: Coronal Mass Ejections
Coronal Mass Ejections
and planet transit
20 Marzo – 10 Aprile 1999
The Earth
SOHO – Solar and
Heliospheric Observatory
M. Silari – Radiation and radioactivity – 6 September 2016
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Terrestrial radionuclides
During the creation of the Earth, terrestrial nuclides had been
incorporated into the earth crust (T1/2 some millions to billions of years)
Nuclide
Symbol
Half-life
Uranium-235
235U
7.04 x 108 y
0.72% of natural Uranium
Uranium-238
238U
4.47 x 109 y
99.3% of natural Uranium
Thorium-232
232Th
1.41 x 1010 y
Potassium-40
40K
1.28 x 109 y
M. Silari – Radiation and radioactivity – 6 September 2016
Earth: 0.037-1.1 Bq/g
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Cosmogenic radionuclides
Cosmogenic nuclides are produced by nuclear reactions of
cosmic particles with stable nuclei of the atmosphere
Nuclide
Symbol
Half-life
Nuclear Reaction
Carbon-14
14C
5730 y
e.g. 14N(n,p)14C
Tritium-3
3H
12.3 y
Interaction of cosmic radiation with N or O
6Li(n,a)3H
Beryllium-7
7Be
53.28 d
Interaction of cosmic radiation with N or O
Additional cosmogenic radionuclides: 10Be, 26Al, 36Cl, 80Kr, …
M. Silari – Radiation and radioactivity – 6 September 2016
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The radioactivity inside our body
Nuclide
Total activity in human body
(~ 70 kg)
Potassium-40
̴ 5 kBq
Carbon-14
̴ 3 kBq
Tritium
̴ 20 Bq
Polonium-210
̴ 18 Bq
Uranium
̴ 1 Bq
Radium
Thorium
̴ 1 Bq
̴ 0.1 Bq
TOTAL
̴ 8 kBq
M. Silari – Radiation and radioactivity – 6 September 2016
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Radiological exposures
M. Silari – Radiation and radioactivity – 6 September 2016
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Ambient dose equivalent rate versus altitude
Courtesy PTB, Braunschweig
M. Silari – Radiation and radioactivity – 6 September 2016
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Air crew exposure
The average annual effective dose received by
air crew is about 3 mSv
The total dose received in a return flight
Milano - Los Angeles is about 100 μSv
M. Silari – Radiation and radioactivity – 6 September 2016
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The Banana Equivalent Dose (BED)
A general educational example (and should be taken as such!) to indicate the
potential dose due to naturally occurring radioactive isotopes by eating one
average-sized banana
One BED ≈ 0.1 µSv BUT this dose is not cumulative, as the principal radioactive
component is excreted to maintain metabolic equilibrium
Radiation exposure from consuming a banana is approximately 5% of the average
daily exposure to cosmic and terrestrial radiation ≈ 20 BED (2 µSv)
For comparison:
• A flight from London to New York: 400 BED (40 µSv)
• A chest CT scan: 70,000 BED (7 mSv)
WikiPedia
By Evan-Amos - Own work, CC BY-SA 3.0,
https://commons.wikimedia.org/w/index.php?curid=19231740
M. Silari – Radiation and radioactivity – 6 September 2016
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Radon
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Radon and its progeny
Typically ≈ 40 Bq/kg of 226Ra in rocks and soil
222Rn
The effective dose to the
lung is obtained by assuming an
3.82 d
α
equilibrium factor (EF)
between radon and its progeny
218Po
3.05 min
α
Typical indoor EF = 0.4
6.0
MeV
214Pb
26.8 min
β
214Bi
19.7 min
β
214Po
164 μs
α
7.7
MeV
210Pb
22 y
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Propagation of radon from soil into homes
• Radon is emanated from the Uranium rich soil or rocks
• Radon can also be found in water
• Radon escapes easily from the ground into air where it decays into its progeny.
M. Silari – Radiation and radioactivity – 6 September 2016
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Radiation dose to humans
A. M. Mohamed et al., Journal of Physical
Science and Application 2 (2012) 205–215
National Academy of Sciences, NAS-NRC Publication 848
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Radon map of Italy
M. Rossetti, M. Esposito, Radon levels in underground workplaces: a map of the Italian regions, Radiat. Prot. Dosim. (2014) 1–6.
M. Silari – Radiation and radioactivity – 6 September 2016
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Radon map of Switzerland
Source: Swiss Federal Office of Public Health (http://www.bag.admin.ch/org/?lang=en)
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Relative risk of lung cancer
RR = ratio of the probability of a
disease occurring in the exposed group
versus a non-exposed group
According to WHO:
Intervention level: 100 Bq/mc
100 Bq/mc
Relative risk of lung cancer versus
long-term average residential radon
Effective Dose: 5 mSv/y
Lung cancer risk over 40 years:
0.67 – 1.25 %
Darby, S et al. BMJ 330, 223-227 (2005)
M. Silari – Radiation and radioactivity – 6 September 2016
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What are the protective means against the
artificial sources of ionizing radiation?
M. Silari – Radiation and radioactivity – 6 September 2016
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External exposure and contamination
External exposure
Contamination or
internal irradiation
M. Silari – Radiation and radioactivity – 6 September 2016
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Personnel and area classification
• Person occupationally exposed to radiation (> 1 mSv/y)
– Limit < 20 mSv/y
– Category A workers: > 6 mSv/y
– Category B workers: < 6 mSv/y
• Supervised area: area with dose > 1 mSv/y
(accessible to categories A and B workers)
• Controlled area: area with dose > 6 mSv/y
(accessible to categories A workers, and with limited stay
to category B workers)
• Exposure situations:
– risk of external exposure only (sealed radioactive
sources, radiation generators, for example X-ray tube)
– risk of internal and external exposure (use of
unsealed radioactive sources)
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External exposure
Three means to reduce external exposure: distance, time, shielding!
 Distance: the dose rate
decreases with the inverse
squared of the distance
(from a point-like source)
 Time: the dose is proportional
to the time spent close to the
source
D = dD/dt x t
 Shielding: the dose rate approximately
reduces as exp(-d/λ)
λ = shielding properties of the material
M. Silari – Radiation and radioactivity – 6 September 2016
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Shielding ionising radiation
MIRION Technologies - https://www.mirion.com/introduction-to-radiation-safety/types-of-ionizing-radiation/
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Contamination and internal exposure
• Internal exposure: the incorporated radionuclides
irradiate the organs and tissues to which they attach
• Exposure lasts until the complete elimination of the
radionuclides by radioactive decay and biological
metabolism
- ingestion
- inhalation
- skin
M. Silari – Radiation and radioactivity – 6 September 2016
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CERN has a an extensive environmental monitoring plan
(which does not involve the use of sheep…)
Stray radiation
Air
Water
M. Silari – Radiation and radioactivity – 6 September 2016
Other environmental samples
58
Operational radiation protection monitors
CERN detector systems for accelerator radiation protection
REM counter
Air filled ionisation
chamber
Gas filled, high pressure
ionization chamber
Beam-on: to protect workers
in areas adjacent to accelerator tunnels
and experiments against prompt radiation
(mainly neutrons, E < some GeV)
Beam-off: to protect workers during
maintenance and repair against radiation
fields caused by decay of radionuclides
(mainly gammas, E < 2.7 MeV)
Alarm function
M. Silari – Radiation and radioactivity – 6 September 2016
No alarm function
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Site monitors, area identification, work practices
Site Gate Monitor
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Personal dosimetry
People working in radiation areas wear a personal dosimeter (DIS)
and an electronic dosimeter (DMC)
DIS personal dosimeter: "Legal dose”
The DMC gives a signal in the presence of
ionising radiation, and a warning in case a
given threshold is exceeded
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