Radioactivity and radiation
exposure from natural sources
Gerhard Proehl

What is radioactivity?
Radioactivity is the phenomenon of− Disintegration of atomic nuclei and the simultaneous emission
energetic radiation

Elements and isotopes− Atom nuclei comprise of protons and neutrons− An element is defined by the number of protons• The number of neutrons varies, therefore any element has different
isotopes• Non-stable isotopes of an element are called radio-isotopes• Radioactive atoms are called radionuclides− There are 118 elements• Only 80 elements have stable isotopes• In total, there are about 1000 radionuclides

Characterisation of radionuclides
The decay of a radionuclide is specific− Radiation type

• Alpha-radiation: helium-nucleus (2 protons, 2 neutrons)• Beta-radiation: electrons• Gamma-radiation: electro-magnetic radiation− Energy of the radiation emitted• Measured in units of electron-volt [eV, keV, or MeV]
• The emission of alpha- and beta-radiation is usually accompanied by theemission gamma-radiation

Origin of radionuclides− Primordial radionuclides exist since the creation of the Earth− Cosmogenic radionuclides are generated due to interaction of cosmic
radiation with atoms at high altitudes− Man-made radionuclides are generated in nuclear installations as nuclear
power plants, research reactors and accelerators

Every radionuclide is characterised by its physicalhalf-life

Half-lives vary from very small fractions of seconds to billions of years

Types of radiation and characteristics• Alpha radiation− Relatively large particles: He-nucleus (2 protons. 2 neutrons)− Range in air:few cm− Range in water:
Fraction of 1 mm
• Beta radiation− Small particles:
electrons− Range in air:some 10 cm to some meters− Range in water:
few mm• Gamma-radiation− Electro-magnetic radiation− Range in air:some 100 m− Range in water:some 10 cm• X-rays− Similar characteristics as gamma-radiation

Activity and radiation doseRadionuclide

Energy-emission

Unit for activity
1 Bq= 1 decay per second

Radiation type(α, β, γ)

Energy transport

TissueEnergy absorption

Unit for dose
1 mSv

Effects of ionizing radiation• Ionisation of atoms− Formation of free radicals• Interaction of radicals with cells− Damage of the cell nucleus− Damage of DNA• Possible effects− Cell killing− Malignant degeneration => formation of a cancer cell− Mutations⇒ Therefore we need radiation protection

Range of gamma-radiation and of x-rays
Thickness of a layer reducing the radiation by 50 %Photon energy

Material
Air

WaterConcreteLead20 keV

8 mm

0.1 mm

0.005 mm

50 keV

2 cm

2 mm

0.02 mm

4 cm

7 mm

0.1 mm

7 cm

2 cm

0.4 mm100 keV

37 m

200 keV
500 keV

66 m

8 cm

3.4 cm

4 mm

1 MeV

90 m

10 cm4.6 cm

9 mm

2 MeV

130 m

14 cm

6.6 cm

1.3 cm

5 MeV

210 m

23 cm

10 cm

1.4 cmThe relevant gamma-energy for Cs-137 is 662 keV.

Natural radionuclides in the body
Intake via food and drinking water− Natural decay chains− Primordial radionuclides (existing since Earth´s creation)− Cosmogenic radionuclides (generated by cosmic radiation)• Most important radionuclide 40K (potassium-40)− Typical 40K-concentration• Milk50 Bq/kg• Meat50 – 100 Bq/kg• Vegetables 30 – 150 Bq/kg− 40K intake with food: 90 Bq per day• 40K-activity in the body: 4.000 Bq per body
• Effective dose from 40K in foods: 0.15 mSv per year

• Effective dose from all natural radionuclides in the body
− 0.3 mSv/a

Primordial radionuclides
Radionuclide

Half-life(years)

Radionuclide

Half-life(years)

Radionuclide

Half-life(years)

K-40

1.3 × 109

Cd-116

2.6 × 1019

Sm-147

1.1 × 1011

V-50

1.4 × 1017

In-115

4.4 × 1014

Sm-1487.0 × 1015

Ge-76

1.5 ×1021

Te-123

1.2 × 1013

Gd-152

1.1 × 1014

Se-82

1.0 × 1020

Te-1287.2 × 1024

Lu-176

2.6 × 1010

Rb-87

4.8 × 1010

Te-130

2.7 × 1021

Hf-174

2.0 × 1015

Zr-96

3.9 × 1019

La-138

1.1 × 1011

Ta-180

1.2 × 1010

Mo-100

1.2 × 1019

Nd-144

2.3 × 1015

Re-1875.0 × 1010

Cd-1139.0 × 1015

Nd-150

1.7 × 1019

Os-186

2.0 ×⋅ 1015

Pt-190

6.5 × 1011

Cosmogenic radionuclides
Radionuclide

Half-life

Radionuclide

Half-life

Tritium (H-3)

12.3 ySilizium-32 (Si-32)

101 yBeryllium-7 (Be-7)

53.3 dPhosphorus-32 (P32)

14.3 dBeryllium-10 (Be-10)

1.6 × 106 y

Argon-39 (Ar-39)

269 y

Carbon-14 (C-14)5730 yKrypton-81 (Kr-81)

2.1 × 105 y

Sodium-22 (Na-22)

2.6 y

Krypton-85 (Kr-85)

10.7 yNatural exposure
Terrestrial exposure• Radionuclides in rocks, soil, construction material. plants …..
• 0.4 mSv per year

Natural exposure
Inhalation of radon• Radioactive noble gas emanating from soil and construction
materials• Exposure varies widely− 1-10 mSv per yearEffective dose from cosmic radiation (mSv/a)Natural exposure - cosmic radiation

Height above sea level (m)Natural exposure
Internal exposure• Intake with food• Most important: potassium-40 (K-40)• Exposure: 0.3 mSv per year

Natural radiation exposure (UNSCEAR 2008)
SourceIngestion
40K

U- und Th- decay chains
Cosmogenic radionuclides

Annual effective Dose (mSv/a)
Mean
Range
0.3
0.2 - 10,170,120,01

Inhalation
U- Th–decay chain
Radon (222Rn/220Rn and decay chains.)

Total

0.2 - 100.87

0.6 - 2

0,006
1,25

External exposure
Cosmic radiation (at sea level)
Natural radionuclides in soil

1.256

0,3 - 10,3 - 1

0,39
0,48

2.4

1 - 13

Medical radiation exposure
Main source:
Diagnostic applying x-rays and computer tomography
Examples:• Tooth• Extremities• Abdomen• Lumbar spine (in 2 levels)mSv pro per image
up to 0.01
0.01 bis 0.1
0.5 bis 1.0
0.8 bis 1.8• Head – CT
• Spine – CT
• Abdomen – CT

2 bis 4
2 bis 11
10 bis 25

Medical exposure (global average)
Natural exposure
2.4 mSv/a

Medical exposure
0.6 mSv/a

UNSCEAR 2008
United Nations Scientific Committee on the Effects of Atomic Radiation

SummaryNatural exposure varies widely− Global average• Annual dose
• Life-time dose (80 a):

2.4 mSv/a≈ 200 mSv

• Annual dose
• Life-time dose:

1-13 mSv/a≈ 80 - 1000 mSv− Global range:

The level of natural exposure and its variation− One (but not the only one) yardstick to evaluate the relevance ofexposures from other sources