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?