Home | About | Members | Resources |
Comments | Search

Comments | Additions/Updates

Search:

Quick Links

Current
Topics

Introduction

Research
Resources

Organizations
and Societies

Professional
Resources

Educational
Resources

Radioactivity in Nature
Our world is radioactive and has been since it was
created. Over 60 radionuclides can be found in nature, and they can be
placed in three general categories:

Primordial - been around since the creation of the Earth

Cosmogenic - formed as a result of cosmic ray interactions

Human produced - enhanced or formed due to human actions

Radionuclides are found in air, water and
soil, and additionally in us, being that we are products of our
environment. Every day, we ingest/inhale nuclides in the air we breathe,
in the food we eat and the water we drink. Radioactivity is common in the
rocks and soil that makes up our planet, in the water and oceans, and even
in our building materials and homes. It is just everywhere. There is no
where on Earth that you can get away from Natural
Radioactivity.

Note: Many of the units used in
science are broken down into smaller units or expressed as multiples,
using standard metric prefixes. As examples, a kilobecquerel (kBq) in 1000
becquerels, a millirad (mrad) is 10-3 rad, a microrem (�rem) is
10-6 rem, a nanogram is 10-9 grams, and a picocurie
is a 10-12 curies. These are examples of units used frequently
throughout this short paper. To find definitions of terms you're not
familiar with, look on our glossary page.

Common abbreviations used on this page
are: m - meter, m3 - cubic meter, g -
gram, kg - kilogram, Bq - becquerel, Sv - sievert,
Gy - gray, Ci - curie, ppm - parts per million,
yr- year, hr - hour, L - liter

Radioactive elements are often called
radioactive isotopes or radionuclides. There are over 1,500 different
radioactive nuclides. They can be labeled based on the element and on the
atomic weight, as in radioactive hydrogen (tritium) or Hydrogen 3.
Radionuclide names are often abbreviated using the chemical symbol and the
atomic weight, so that Uranium 235 would be shortened to U-235 or
235U.

Much of the information and many of tables
found here are adapted from information found in Environmental
Radioactivity from Natural, Industrial and Military Sources by Merril
Eisenbud and Tom Gesell, Academic Press, Inc. 4th Edition.
Other tables are adapted from the National Council on Radiation Protection
reports 94 and 95. References are listed at the bottom of this page.
Several of the tables below were made from calculation based on available
data.

This page is best viewed with a browser
that is capable of using tables and superscripts.

In the United States, the annual estimated
average effective dose equivalent is 360 mrem per adult. This is broken
down as:

Annual estimated average effective dose equivalent
received by a member of the population of the United States.

Source

Average annual effective
dose equivalent

(�Sv)

(mrem)

Inhaled (Radon and Decay
Products)

2000

200

Other Internally Deposited
Radionuclides

390

39

Terrestrial
Radiation

280

28

Cosmic Radiation

270

27

Cosmogenic
Radioactivity

10

1

Rounded total from natural
source

3000

300

Rounded total from artificial
Sources

600

60

Total

3600

360

Shown in the table above, 82% of the total
average annual effective dose is from natural sources of radiation, and of
that, most is from radon. Of the other 18%, the majority is from medical
diagnosis and treatments, with <1% from nuclear power and
fallout.

This can perhaps be more easily seen with a graph
(6K)

See Radiation and Us for
more info on average U.S. doses of radiation.

United States Geological Survey map of estimated total gamma exposure for the
U.S. (78 k)

Primordial
radionuclides

Primordial radionuclides are left over
from when the world and the universe were created. They are typically long
lived, with half-lives often on the order of hundreds of millions of
years. Radionuclides that exist for more than 30 half-lives are not
measurable. The progeny or decay products of the long lived radionuclides
are also in this heading. Here are few of what we are talking
about:

Primordial nuclides

Nuclide

Symbol

Half-life

Natural
Activity

Uranium 235

235U

7.04 x
108 yr

0.72% of all natural
uranium

Uranium 238

238U

4.47 x
109 yr

99.2745% of all natural uranium;
0.5 to 4.7 ppm total uranium in the common rock types

Thorium 232

232Th

1.41 x
1010 yr

1.6 to 20 ppm in the common rock
types with a crustal average of 10.7 ppm

Radium 226

226Ra

1.60 x
103 yr

0.42 pCi/g (16 Bq/kg) in limestone
and 1.3 pCi/g (48 Bq/kg) in igneous rock

Radon 222

222Rn

3.82
days

Noble Gas; annual average air
concentrations range in the US from 0.016 pCi/L (0.6
Bq/m3) to 0.75 pCi/L (28 Bq/m3)

Potassium 40

40K

1.28 x
109 yr

soil - 1-30 pCi/g (0.037-1.1
Bq/g)

Some nuclides, like 232Th have
several members in their decay chains. You can roughly follow the chain
starting with 232Th

232Th --> 228Ra
--> 228Ac --> 228Th --> 224Ra
-->
220Rn --> 216Po --> 212Pb
--> 212Bi --> 212Po --> 208Pb
(stable)

Some other primordial radionuclides are:
50V, 87Rb, 113Cd, 115In,
123Te, 138La, 142Ce, 144Nd,
147Sm, 152Gd, 174Hf, 176Lu,
187Re, 190Pt, 192Pt,
209Bi.

United States Geological Survey Digital
maps of estimated potassium, equivalent uranium-238,
equivalent thorium-232 concentrations for the U.S.

Cosmogenic

Cosmic radiation permeates all of space,
the source being primarily outside of our solar system. The radiation is
in many forms, from high speed heavy particles to high energy photons and
muons. The upper atmosphere interacts with many of the cosmic radiations,
and produces radioactive nuclides. They can have long half-lives, but the
majority have shorter half-lives than the primordial nuclides. Here is an
table with some common cosmogenic nuclides:

Cosmogenic Nuclides

Nuclide

Symbol

Half-life

Source

Natural
Activity

Carbon 14

14C

5730 yr

Cosmic-ray interactions,
14N(n,p)14C;

6 pCi/g (0.22 Bq/g)

Tritium 3

3T

12.3 yr

Cosmic-ray interactions with N and
O; spallation from cosmic-rays,
6Li(n,alpha)3H

0.032 pCi/kg (1.2 x 10-3
Bq/kg)

Beryllium 7

7Be

53.28 days

Cosmic-ray interactions with N and
O;

0.27 pCi/kg (0.01
Bq/kg)

Some other cosmogenic radionuclides are
10Be, 26Al, 36Cl, 80Kr,
14C, 32Si, 39Ar, 22Na,
35S, 37Ar, 33P, 32P,
38Mg, 24Na, 38S, 31Si,
18F, 39Cl, 38Cl,
34mCl.

Human
Produced

Humans have used radioactivity for one
hundred years, and through its use, added to the natural inventories. The
amounts are small compared to the natural amounts discussed above, and due
to the shorter half-lives of many of the nuclides, have seen a marked
decrease since the halting of above ground testing of nuclear weapons.
Here are a few nuclides:

Human Produced Nuclides

Nuclide

Symbol

Half-life

Source

Tritium

3H

12.3
yr

Produced from weapons testing and
fission reactors; reprocessing facilities, nuclear weapons
manufacturing

Iodine 131

131I

8.04
days

Fission product produced from
weapons testing and fission reactors, used in medical treatment of
thyroid problems

Iodine 129

129I

1.57 x
107 yr

Fission product produced from
weapons testing and fission reactors

Cesium 137

137Cs

30.17
yr

Fission product produced from
weapons testing and fission reactors

Strontium 90

90Sr

28.78
yr

Fission product produced from
weapons testing and fission reactors

Technetium 99m

99mTc

6.03
hr

Decay product of 99Mo,
used in medical diagnosis

Technetium 99

99Tc

2.11 x
105 yr

Decay product of
99mTc

Plutonium 239

239Pu

2.41 x
104 yr

Produced by neutron bombardment of
238U
( 238U + n-->
239U--> 239Np +�-->
239Pu+�)

Other
Interesting Aspects of Natural Radioactivity

Natural
Radioactivity in soil

How much natural radioactivity is found in
an area 1 square mile, by 1 foot deep? The following table is calculated
for this volume (total volume is 7.894 x 105 m3) and
the listed activities. Activity levels vary greatly depending on soil
type, mineral make-up and density (~1.58 g/cm3). This table
represents calculations using typical numbers.

Natural Radioactivity by the Mile

Nuclide

Activity used
in
calculation

Mass of Nuclide

Activity

Uranium

0.7 pCi/gm (25
Bq/kg)

2,200 kg

0.8 curies (31
GBq)

Thorium

1.1 pCi/g (40
Bq/kg)

12,000 kg

1.4 curies (52
GBq)

Potassium 40

11 pCi/g (400
Bq/kg)

2000 kg

13 curies (500
GBq)

Radium

1.3 pCi/g (48
Bq/kg)

1.7 g

1.7 curies (63
GBq)

Radon

0.17 pCi/gm (10
kBq/m3) soil

11 �g

0.2 curies (7.4
GBq)

Natural
Radioactivity in the Ocean

How much natural radioactivity is found in
the world's oceans?

All water on the Earth, including
seawater, contains radionuclides in it. In the following table, the
oceans' volumes were calculated from the 1990 World
Almanac:

Pacific =
6.549 x 1017 m3

Atlantic =
3.095 x 1017 m3

Total = 1.3
x 1018 m3

The activities used in the table below are
from 1971 Radioactivity in the Marine Environment, National Academy
of Sciences:

Natural Radioactivity by the Ocean

Nuclide

Activity used
in
calculation

Ocean

Pacific

Atlantic

All Oceans

Uranium

0.9 pCi/L
(33 mBq/L)

6 x 108 Ci
(22
EBq)

3 x 108 Ci
(11
EBq)

1.1 x 109 Ci
(41
EBq)

Potassium 40

300 pCi/L
(11 Bq/L)

2 x 1011 Ci
(7400
EBq)

9 x 1010 Ci
(3300
EBq)

3.8 x 1011 Ci
(14000
EBq)

Tritium

0.016 pCi/L
(0.6
mBq/L)

1 x 107 Ci
(370
PBq)

5 x 106 Ci
(190
PBq)

2 x 107 Ci
(740
PBq)

Carbon 14

0.135 pCi/L
(5 mBq/L)

8 x 107 Ci
(3
EBq)

4 x 107 Ci
(1.5
EBq)

1.8 x 108 Ci
(6.7
EBq)

Rubidium 87

28 pCi/L
(1.1 Bq/L)

1.9 x 1010 Ci
(700
EBq)

9 x 109 Ci
(330
EBq)

3.6 x 1010 Ci
(1300
EBq)

Human
body

You are made up of chemicals, and it
should be of no surprise that some of them are radionuclides, many of
which you ingest daily in your water and food. Here are the estimated
concentrations of radionuclides calculated for a 70,000 gram adult based
ICRP 30 data:

Natural Radioactivity in your body

Nuclide

Total Mass of Nuclide

Found in the Body

Total Activity of Nuclide

Found in the Body

Daily Intake of
Nuclides

Uranium

90 �g

30 pCi (1.1
Bq)

1.9 �g

Thorium

30 �g

3 pCi (0.11
Bq)

3 �g

Potassium 40

17 mg

120 nCi (4.4
kBq)

0.39 mg

Radium

31 pg

30 pCi (1.1
Bq)

2.3 pg

Carbon 14

95 �g

0.4 �Ci (15
kBq)

1.8 �g

Tritium

0.06 pg

0.6 nCi (23
Bq)

0.003 pg

Polonium

0.2 pg

1 nCi (37
Bq)

~0.6
�g

It would be reasonable to assume that all
of the radionuclides found in your environment would be in you in small
amounts. The average annual dose equivalent from internally deposited
radionuclides is given in the table at the top of this
page.

Natural
Radioactivity in Building Materials

As mentioned before, building materials
have some radioactivity in them. Listed below are a few common building
materials and their estimated levels of uranium, thorium and
potassium.

Estimates of concentrations of uranium, thorium and
potassium in building materials (NCRP 94, 1987, except where noted)

Material

Uranium

Thorium

Potassium

ppm

mBq/g
(pCi/g)

ppm

mBq/g
(pCi/g)

ppm

mBq/g
(pCi/g)

Granite

4.7

63 (1.7)

2

8 (0.22)

4.0

1184 (32)

Sandstone

0.45

6 (0.2)

1.7

7 (0.19)

1.4

414
(11.2)

Cement

3.4

46 (1.2)

5.1

21 (0.57)

0.8

237 (6.4)

Limestone
concrete

2.3

31 (0.8)

2.1

8.5 (0.23)

0.3

89 (2.4)

Sandstone
concrete

0.8

11 (0.3)

2.1

8.5 (0.23)

1.3

385
(10.4)

Dry
wallboard

1.0

14 (0.4)

3

12 (0.32)

0.3

89 (2.4)

By-product
gypsum

13.7

186 (5.0)

16.1

66 (1.78)

0.02

5.9 (0.2)

Natural
gypsum'

1.1

15 (0.4)

1.8

7.4 (0.2)

0.5

148 (4)

Wood'

-

-

-

-

11.3

3330 (90)

Clay Brick"

8.2

111 (3)

10.8

44 (1.2)

2.3

666
(18)

' Chang et al, 1974 " Hamilton,
1970

Oklo
Natural Reactor

Adapted from August 1976 Scientific
American article on Oklo by Cowan.

In 1972, natural nuclear reactor was found
in a Western Africa in the Republic of
Gabon, at Oklo. While the reactor was critical,
approximately 1.7 billion years ago, it released 15,000 megawatt-years of
energy by consuming six tons of uranium. It operated over several hundred
thousand years at low power.

It was discovered by a French mining
geologist while assaying samples for the Oklo Uranium mine. Today, the
fissionable Uranium 235 has an natural abundance of 0.7202%, but the
scientist noticed some samples from Oklo to be 0.7171%. While this
difference was small, it led the scientists to take a look closer at the
Oklo site. Later, samples were found that were even more depleted, down to
0.44%. This difference could only be explained if some of the fuel, the
235U, had been used up in a fission reaction. Upon further
investigation, abnormally high amounts of fission products were found in
six separate reactor zones.

Like present day power reactors, a natural
reactor would require several special conditions, namely fuel, a
moderator, a reflector, lack of neutron absorbing poisons and some way to
remove the heat generated. At Oklo, the area was naturally loaded with
uranium by water transport and deposition. The concentration of Uranium
235 is artificially enriched for most modern reactors, but at the time of
the Oklo reactor it was naturally enriched with an abundance of approximately
3%. This is because when the world was formed, there was a
certain amount of 235U, and it has been decaying ever since.
So, because 235U has a shorter half-life than 238U,
one billion years ago ,235U made up a larger percentage of the
natural uranium. The 3% 235U was enough for a sustained nuclear
reaction. Oklo site was saturated with groundwater, which served as a
moderator, reflector and cooling for the fission reaction. There was a
lack of poisons before the reaction began, and fission products like xenon
and neodymium serve as neutron absorbing poisons, absorbing neutrons,
acting to limit the power.

To confirm that there was a natural
fission reactor, the scientists started looking for other evidence. First
they wanted to look for some element that might have been produced in a
reactor, but would have little natural occurrence else where. They looked
at several, and neodymium gave strong indications that the reactor had
indeed operated. Neodymium has seven stable isotopes, but only six are
fission products. The abundance of the neodymium at Oklo sites was compared to
other areas and to the neodymium found in modern
reactors. Once the samples were compared, the abundance of
neodymium was found to be almost exactly that found in present day
reactors. All in all, the fission products studied matched what would have
been the result of a sustained nuclear reaction. There is even evidence
that the reactor bread its own fuel, bombarding the 238U with
neutrons, making the easily fissionable 239Pu.

Some other interesting information has
come out of this, over half of the thirty fission products found there
were confined to the reactor zones, with all plutonium immobilized. The
strontium was mainly confined to the local zones, with some release to
environment estimated from krypton 85 and cesium 137

One of the greatest works of the
20th century was the building of the first atomic pile (nuclear
reactor) in Chicago in 1941 by Enrico Fermi. It took some of the brightest
minds in modern physics and great engineering efforts to duplicate what
nature did two billion years earlier.

For more information on the Oklo Reactor,
try:

The a-recoil effects of uranium in
the Oklo reactor. Nature 312:535-6 Dec 6 '84

Gabon's natural reactors: nature
shows how to contain radioactive waste.
Nuclear-Engineering-International. vol.39, no.475; Feb. 1994; p.30-1

Organic matter and containment of
uranium and fissiogenic isotopes at the Oklo natural reactors.
Nature. vol.354, no.6353; 12 Dec. 1991; p.472-5

Estimation of burnup in the Oklo
natural nuclear reactor from ruthenium isotopic composition. Journal
of Radioanalytical and Nuclear Chemistry, Letters. vol.155, no.2; 16
Sept. 1991; p.107-13

The origin of the chemical elements
and the Oklo phenomenon. Kuroda, P. K. Berlin ; New York :
Springer-Verlag, 1982.

High
Background Radiation Areas

Background radiation levels result from a
combination of terrestrial (from the 40K, 232Th,
226Ra, etc.) and cosmic radiation (photons, muons, etc.). The
level is fairly constant over the world, being 8-15 �rad/hr. Here is a
radiation detector in Pittsburgh, Penn, USA showing background
radiation levels.

Around the world though, there are some
areas with sizable populations that have high background radiation levels.
The highest are found primarily in Brazil, India and China. The higher
radiation levels are due to high concentrations of radioactive minerals in
soil. One such mineral, Monazite, is a highly insoluble rare earth mineral
that occurs in beach sand together with the mineral ilmenite, which gives
the sands a characteristic black color. The principal radionuclides in
monazite are from the 232Th series, but there is also some
uranium its progeny, 226Ra.

In Brazil, the monazite sand deposits are
found along certain beaches. The external radiation levels on these black
sands range up to 5 mrad/hr (50 �Gy/hr), which is almost 400 times normal
background in the US. Some of the major streets of the surrounding cites
have radiation levels as high as 0.13 mrad/hr (1.3 �Gy/hr), which is more
than 10 times the normal background. Another high background area in
Brazil is the result of large rare earth ore deposits that form a hill
that rises about 250 meters above the surrounding area. An ore body near
the top of the hill is very near the surface, and contains an estimated
30,000 tons of thorium and 100,000 tons of rare earth elements. The
radiation levels near the top of the hill are 1 to 2 mrad/hr (0.01 to 0.02
mGy/hr) over an area of about 30,000 m2. The plants found there
have absorbed so much 228Ra that they will produce a self
"x-ray" if placed on a sheet of photographic paper (an
autoradiograph).

On the Southwest coast of India, the
monazite deposits are larger than those in Brazil. The dose from external
radiation is, on average, similar to the doses reported in Brazil, 500-600
mrad/yr (5 - 6 mGy/yr), but individual doses up to 3260 mrad/yr (32.6
mGy/yr) have been reported.

An area in China has does rates that is
about 300-400 mrad/yr (3-4 mGy/yr). This is also from monazite that
contains thorium, uranium and radium.

From BEIR V, National Research Council
report on Health Effects of Low Levels of Ionizing Radiation:

In areas of high natural background
radiation, an increased frequency of chromosome aberrations has been
noted repeatedly. The increases are consistent with those seen in
radiation workers and in persons exposed at high dose levels, although
the magnitudes of the increases are somewhat higher than predicted. No
increase in the frequency of cancer has documented in populations
residing in areas of high natural background
radiation.

Cosmic
Radiation

Cosmic radiation (as discussed above)
interacts with our atmosphere to produce cosmogenic radionuclides. It also
is responsible for a whole body doses.

Cosmic radiation is really divided into
two types, primary and secondary. Primary cosmic radiation is made up of
extremely high energy particles (up to 1018 eV), and are mostly
protons or sometimes larger particles. A large percentage of it comes from
outside of our solar system and is found throughout space. Some of the
primary cosmic radiation is from our sun, produced during solar
flares.

Little of the primary cosmic radiation
penetrates to the Earth's surface, the vast majority of it interacts with
the atmosphere. When it does interact, it produces the secondary cosmic
radiation, or what we actually see here on Earth. These reactions produce
other lower energy radiations in the form of photons, electrons, neutrons
and muons that make it to the surface.

The atmosphere and the Earth's magnetic
fields also act as shields against cosmic radiation, reducing the amount
that reaches the Earth's surface. With that in mind, it is easy to see
that the annual dose you get from cosmic radiation depends on what
altitude you are at. From cosmic radiation, the average person in the U.S.
will receive a dose of 27 mrem per year and this roughly doubles every
6,000 foot increase in elevation.

Typical Cosmic Radiation Dose
rates:

4 �R/hr in the Northeastern US

20 �R/hr at 15,000 feet

300 �R/hr at 55,000 feet

There is only about a 10% decrease at sea
level in cosmic radiation rates when going from pole to the equator, but
at 55,000 feet the decrease is 75%. This is on account of the effect of
the earth's and the Sun's geomagnetic fields on the primary cosmic
radiations.

Flying can add a few extra mrem to your
annual dose, depending on how often you fly, how high the plane flies, and
how long you are in the air.

Calculated cosmic ray doses to a person flying in
subsonic and supersonic aircraft under normal solar conditions

Route

Subsonic flight at 36,000
ft (11 km)

Supersonic flight at
62,000 (19 km)

Flight
duration
(hrs)

Dose per round
trip

Flight
duration
(hrs)

Dose per round
trip

(mrad)

(�Gy)

(mrad)

(�Gy)

Los
Angeles-Paris

11.1

4.8

48

3.8

3.7

37

Chicago-Paris

8.3

3.6

36

2.8

2.6

26

New
York-Paris

7.4

3.1

31

2.6

2.4

24

New
York-London

7.0

2.9

29

2.4

2.2

22

Los Angeles-New
York

5.2

1.9

19

1.9

1.3

13

Sydney-Acapulco

17.4

4.4

44

6.2

2.1

21

Astronauts are exposed to
cosmic radiation, but they are also exposed to radiation as they pass
through the Van Allen radiation belts that
circle the Earth.

References
and Additional Information Sources

Naturally occurring radioactive
material (NORM I&S,
Inc)

Environmental Radioactivity
from Natural, Industrial and Military Sources
4th Edition by Merril Eisenbud and
Tom Gesell, Academic Press, Inc. (now out!)

Radioactivity in the Environment, Ron
Kathren

Radioactivity in the Marine Environment ,
National Academy of Sciences

NCRP reports 62, 94, 95, 103, 116

BEIR V Report, National Research Council,
NAS

Chart of the Nuclides

Radon Update
, A.B. Brill

Radioactivity from Coal
(ORNL)

Information on Sources of
Radiation

Environmental Radioactivity
Specialty area

Chornobyl and the surrounding
area

Radiation and Us (short essay)

Return to the top of this page

Home | About | Members | Resources |
Comments | Search

©2005 UMSHPS