fundamentals of radiation protection€¦ · fundamentals of radiation protection 6th international...
Post on 05-Oct-2020
1 Views
Preview:
TRANSCRIPT
Kamel ABBAS European Commission, Joint Research Centre
Institute for Transuranium Elements, Nuclear Security Unit Via E. Fermi, 2749, I-21027 Ispra, Italy
tel. +39-0332-785673, e-mail: kamel.abbas@jrc.ec.europa.eu
Fundamentals of radiation protection
6th International Summer School on Operational Issues in Radioactive
Waste Management and Nuclear Decommissioning
Ispra, 8-12 September 2014
Basic radiation physics - Some definitions: element, isotope, uranium
enrichment - Radiation types and sources - Interaction of radiation with matter - Principles of radiation detection (gamma and
neutrons) - Radioactive materials of interest in nuclear
security - Definition of some units used in the nuclear
field
Some definitions
A chemical element is a type of atom that is distinguished by its atomic number (= its number of protons in the nucleus)
protons: positively charged
neutrons: neutral
electrons: negatively charged
orbiting around the nucleus nucleus
atom
An atom is neutral: it has the same number of electrons and protons
An atom which has gained or lost electrons is call an ion
Some definitions
Uranium (U): 92 protons; average mass: 238Uranium (U): 92 protons; average mass: 238Uranium (U): 92 protons; average mass: 238
Some definitions
Some definitions
Isotopes of a chemical element have the same number of protons as it is the same element but have different numbers of neutrons. They have then different atomic masses.
Examples:
U-235: uranium 92 protons; atomic mass 235
Number of neutrons = 235 – 92 = 143 neutrons
U-238: uranium 92 protons; atomic mass 238
Number of neutrons = 238 – 92 = 146 neutrons
Representation: 235U or U-235 - 238U or U-238
The U-235 is fissile, the U-238 is not
Uranium enrichment
The proportion of U-235 defines the enrichment of uranium
• Natural uranium (NU) contains 0.72% U-235 and 99.27% U-238
• Slightly enriched uranium (SEU) contains 0.9% to 2% U-235
• Low enriched uranium (LEU) contains less than 20% U-235
• Highly enriched uranium (HEU) contains more than 20% U-235 and is
qualified “weapon-usable”; if the enrichment is higher than 85%, it is
qualified “weapon-grade”
Typical U enrichments
The enrichment of the fresh fuel used in the Light Water
Reactors is between 3% to 5%
The enrichment of U reprocessed from LWR spent fuel is
around 1% and thus still slightly enriched
Too many or too few neutrons in the nucleus
Seek to become stable by breaking and emitting energy as Radiation. The process is called Radioactivity and the atom is said to be Radioactive
Isotopes of elements
which are radioactive
are called
RADIONUCLIDES
Unstable Atoms
Isotopes Hydrogen Deuterium Tritium
Stable Atom Radioactive Isotope
of hydrogen
Stable Isotope
of hydrogen
Legend: = Electron (- charge)
= Proton (+ charge)
= Neutron (no charge)
Radiation types and sources
What is Radiation?
• Radiation is the flow of energy through space and matter. Some examples of radiation are visible light, radio waves, and radiant heat.
• Radiation can be in the form of particles or waves.
• Ionizing radiation is radiation that produces ions in matter. It is able to disrupt chemical bonds of molecules and cause biologically important changes.
Types of Ionizing Radiations
Two classes of ionizing radiations:
NON-IONISING
Alpha particles
helium nuclei
Beta particles
fast electrons
IONISING
Cosmic rays
Assorted particles
from neutrons and
protons to massive
nuclei
PARTICLES WAVES
Penetration of radiations
Alpha particles can usually be stopped by a very thin barrier like a sheet of paper.
Betas (electrons or positrons) can pass through the skin, but are usually stopped by
a modest barrier such as a few millimeters of aluminum, or even a layer of clothing.
Gammas can be very penetrating and can pass through thick barriers. Several
meters of concrete would be needed to stop (attenuate) some of the more energetic
gammas. A natural gamma source found in the environment (and in the human body)
is K-40, an isotope of potassium.
Neutrons are also very penetrating. Some elements, like hydrogen, “slow down” and
capture neutrons. Water is commonly used as a neutron radiation shield.
Interaction of radiation with matter
1g 241AmO2 for the production of
3 000 000 detectors Alpha particles
• Double positive charge Ionization process.
• The energy with which they are emitted is always distinct
(signature!). For example Am-241 emits alpha-particles of 5.49
MeV (86%) and 5.44 MeV (13%).
• Very easy to shield Very difficult to detect.
Interaction of radiation with matter
• Easy to shield
Beta Particles
• Negative (electron) or positive (positron) electrical charge
Ionization process.
• The energies of the beta-particles from a radioactive source forms a spectrum up to a maximum energy - see figure below. Not a signature.
Direct detection is difficult.
Interaction of radiation with matter
• The energies of gamma-rays emitted from a radioactive
source are always distinct (signature!). For example, 235U
emits gamma-rays, it has a characteristic peak at 185.7 keV
Gamma Rays
Interaction of radiation with matter
Neutrons
• No electrical charge No direct ionization
No direct detection
• Conversion:
Detection
neutrons Charged particles
Radiation detection aspect
As alpha particles can travel only a few cm in air and are readily stopped by a sheet of paper, they are no good candidates to reveal the presence of nuclear/radioactive material.
As beta particles can travel only a few m in air and are readily halted by light material (Al, plastic), they are no good candidates to reveal the presence of nuclear/radioactive material.
detection of nuclear/radioactive material by stand-off equipment is based on the detection of gamma radiations and neutrons.
• Radiological Dispersion Device Any radioactive sources used in industry, medicine,…
These are mostly beta/gamma emitters, few pure beta (T, Sr-90)
Generally high energy gamma (detectable, difficult to mask)
• Nuclear Weapon based on HEU HEU is an alpha/gamma emitter.
Low energy gamma (easily shielded)
• Nuclear Weapon based on Pu Pu is an alpha/beta/gamma/neutron emitter.
Low energy gamma (easy to shield) + neutron
Radiations of interest in nuclear security
Characterisation of a radionuclide
- Type of radioactivity
- Half-life: time taken for half of a radioactive material to decay
For the same quantity of material, the radioactive substance having the shortest half-life will have the highest activity.
0
20
40
60
80
100
0 10 20 30 40 50 60 70 80 90 100
Time (years)
Re
ma
inin
g a
cti
vit
y (
%)
K-40 (1.3E9 y) Cs-137 (30 y) Co-60 (5 y)
After
1 half-life
After
2 half-lives
Some definitions
Activity: number of decays (transformations) per time unit
undergoes by the radioactive source.
The becquerel (symbol: Bq) is the SI derived unit of
radioactivity.
1 Bq is defined as the activity of a quantity of radioactive
material in which one nucleus decays per second.
Analogy: you would say that a source has a
radioactivity of 20 decays per second as you would
say that a machinegun can fire 20 bullets per second.
The curie (Ci) is an older, non-SI unit of radioactivity
1 Ci = 3.7 x 1010 Bq ≈ activity of 1 g 226Ra
Some definitions (radioprotection)
The gray (symbol: Gy) is the SI unit of the absorbed radiation
dose due to ionizing radiation.
Analogy: you would say that some of
the bullets but not all reached the
target and transmitted their energy.
The rad is an older, non-SI unit of the absorbed radiation
dose
1 Gy = 100 rad
1 Gy = 1 joule/kg
The sievert (symbol: Sv) is the SI derived unit of dose equivalent.
To reflect the biological effects of the radiation.
Analogy: you would say that some bullets might “hurt” more
than others and that some parts of the human body are more
sensitive than others (e.g. bone marrow).
The rem is an older, non-SI unit of the dose equivalent
1 Sv = 100 rem
Dose equivalent = absorbed dose x Q (depends on radiation) x N (depends on body part)
Some definitions (radioprotection)
Natural Sources of Radiation
Humans have always been exposed to radiation. The major
components of naturally occurring radiation are illustrated
below. It is important to compare man-made radiation exposure
levels to these natural radiation levels.
Man-Made Sources of Radiation
Humans are exposed to man-made radiation as well. The
major sources are illustrated below. By far, most of the dose
comes from medical x-rays.
Background Radiation
The worldwide average background dose for a human being
is about 2.4 mSv per year
Background Radiation (2)
Every food has some small amount of radioactivity in it. The common
radionuclides in food are potassium 40 (K-40), radium 226 (Ra-226)
and uranium 238 (U-238) and the associated progeny. Here is a table
of some of the common foods and their levels of K-40 and Ra-226.
Food 40K
pCi/kg
226Ra
pCi/kg
Banana 3,520 1
Brazil Nuts 5,600 1,000-7,000
Carrot 3,400 0.6-2
White Potatoes 3,400 1-2.5
Beer 390 ---
Red Meat 3,000 0.5
Lima Bean
raw 4,640 2-5
Drinking water --- 0-0.17
Effects of radiation on human health (1)
• The greater the dose of radiation a cell gets, the greater the chance that the cell will become cancerous. However, very high doses of radiation can kill the cell completely. We use this idea to kill cancer cells, and also harmful bacteria and other microorganisms.
Radiation and living cells
• When radiation ionizes molecules in living cells it can damage them. If the DNA in the nucleus of a cell is damaged, the cell may become cancerous. The cell then goes out of control, divides rapidly and causes serious health problems.
Effects of radiation on human health (2)
The degree to which each different type of radiation is most dangerous to the body depends on whether the source is outside or inside the body. If the radioactive source is inside the body, perhaps after being swallowed or breathed in:
• Alpha radiation is the most dangerous because it is easily absorbed by cells. Local deposition of the whole energy (short range).
• Gamma and neutron radiations are not as dangerous because they are less likely to be absorbed by a cell and will usually just pass right through it. Beta particles can create health problems when inhaled.
If the radioactive source is outside the body:
• Alpha radiation is not as dangerous because it is unlikely to reach living cells inside the body.
• Beta and especially gamma and neutron radiations are the most dangerous sources because they can penetrate the skin and damage the cells inside.
Effects of radiation on human health (3)
There are three ways to minimize the risk of radiation exposure:
Time: reduce the time of the exposure as much as possible.
Distance: the further away from the source of radiation, the better.
Shielding: In an exposed area, choose the appropriate shielding!
Response to a detection event
Nuclear security or safety event
If a radioactive source is discovered, appropriate protection
measures are required to protect individuals from exposure:
1. Protection of the first responders
2. Protection of the public and the environment
Usually, expose to radiation can be reduced to an acceptable
minimum by application of proper shielding.
Health Effects of radiation
Stochastic effects
Associated to exposures to low levels of radiation over a long
time. The effect (usually cancer induction) is uncertain but its
probability to appear is increased. The higher is the (low) dose,
the higher will be the probability of the effect to appear.
e.g. for a dose update of 9 mSv, the probability increase of a
deadly cancer is + 0.5/1000 people.
The “usual” risk of deadly cancer in Germany is 80 / 1000
people in 30 years
Deterministic effects
Associated to exposures to high levels of radiation over a short
time. The effects will not appear under a dose threshold. The
higher is the (high) dose, the higher will be the severity of the
effect.
1 – 2.5 Sv: nausea, persistent fatigue, partial epilation, fatality ≈
10% after 30 days
2.5 – 4 Sv: nausea, vomiting, loss of hair, massive lost of white
blood cells, fatality ≈ 50% after 30 days
6 – 10 Sv: bone marrow destroyed, fatality close to 100% after
14 days 2000 Ci 60Co at 1 m distance unshielded : 25 Sv/h
Health Effects of radiation
Radiation dose uptake: some values
2.4 mSv/year: world average dose due to background
1 mSv/year: maximum dose uptake (in addition to the
background) for the “non-exposed workers” (public, FLO)
20 mSv/year: maximum dose uptake (in addition to the
background) for the “exposed workers”
A week in mountains at 2000 m: 0.03 mSv
Flight Paris – New York: 0.02 mSv
Scanner (whole body): 150 mSv
Is it dangerous or not?
In order to stay below the dose uptake limit it is recommended to fix an intervention threshold:
• If the dose rate at 1 meter from the source is lower than 0.1 mSv/h, it is safe to approach the source for localization and categorization
• Above 0.1 mSv/h at 1 meter do not intervene, but establish a protection boundary such that nowhere the dose rate is >0.02 mSv/h and call expert responders
0.1 mSv/h = 100 µSv/h
Irradiated vs. contaminated
Irradiation: a body exposed to radioactive material is exposed to radiation.
The longer you stay, the closer you get, the higher your
radiation dose.
How to reduce the irradiation?
•reduce time exposure (as for a sunbath, UV
are radiations!)
•stay away from the radiation source
•use the appropriate shielding
Note: irradiation by α, β, γ-ray does NOT cause contamination!
Contamination: if you or an object gets in contact with radioactive material, you/it might become contaminated. Contamination can be external (e.g. skin) or internal the human body (lungs, bones...).
How a contamination could become internal?
•By inhaling radioactive dust
•By ingesting radioactive material
•By contact with an injury (blood circulation)
Note: irradiation by α, β, γ-ray does NOT cause
contamination, contamination causes irradiation!
Irradiated vs. contaminated
Thank you!
Questions?
top related