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Radiation Protection Management Volume 22, No. 1 2005 13

RadiationWhat is Important?

Radiation in the Environment

Mark M. Hart

This is the third article in a series of articles

(collectively titled Radiation-What is Important?)

focusing on the public's understanding of radiation

and radioactivity. Part three of the series highlights

naturally occurring radiation and radioactive

materials and their influence on biological systems. An

abbreviated listing of references follows; if you need a

particular reference, you can get in touch with me viaemail: hart6@llnl. gov, or at the address listed at the

end of this article. Also at the end of this article is a

short list of additional reading resources I could

recommend to anyone interested in further detailed

study.

Presence of Radiation in the Environment

In the environment you will find naturally

occurring radiation, occasions where nature hasconcentrated naturally occurring radioactive

materials, and detect the presence of man-made

radioactive materials.

You may feel that you are aware of naturally

occurring radioactivity in the environment such as

uranium, potassium, and thorium. In fact there are

39 elements that have naturally occurring

radioactive isotopes in the environment. All

isotopes of all elements with atomic numbers

greater than 83 are radioactive. (See Figure 1.)

Some radiation which we are exposed tocomes from outer space (cosmic radiation). Some

otherwise non-radioactive materials in our

environment are made radioactive by this cosmic

radiation (cosmogenic radionuclides), and the

earth contains a number of naturally radioactive

isotopes (terrestrial radioactivity). Radiation

emanating from all of these sources is referred to

collectively as natural background radiation. The

earths atmosphere provides a significant shield,

reducing ionizing radiation coming from outer

space. Someone living in Denver, Colorado,

would receive twice the radiation from outer space

as would someone living in Washington, DC, due

to the higher altitude in Colorado. Fly-ing in high

altitude aircraft, passengers normally receive 1 to2 millirem (0.1 to 0.2 cents)*per hour; they could

receive 10 rem (10 dollars) of radiation in one

hour as the result of giant solar flares impinging

on the earths outer atmo-sphere,[1] which is twice

as much as radiation workers are allowed to

receive in one entire year.

Terrestrial radiation primarily originates from

uranium and thorium and their decay products in

the soil, and from potassium-40 which decays

directly to stable calcium-40. One of the most

commonly mentioned decay products is radon

gas. Building materials such as stone, rock, and

concrete emit ionizing radiation as a result of

naturally occurring radioactive isotopes present

(see Figure 2).

______________

See the Radiation Dose section of Part I by

Mark Hart, which appeared in Volume 21, No. 2ofRPM, for an explanation of the dose-dollar

analogy.


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14 Radiation Protection Management Volume 22, No. 1 2005

Figure 1. There are 39 elements that have naturally occurring radioactive isotopes in the environment.

Figure 2. Autinite uranium ore specimens, Daybreak Mine, Spokane, Washington. Vaseline glass drawer

pull from the 1800s (photographed under natural light). Photo by Jane Hart.


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The stone (granite) used to build Grand Central

Station in New York City has suffi-

cient radio-active material to deliver a dose of

525 millirem (52 cents) in one year.[2] St. Peters

Square in the Vatican in Rome, Italy, will deliver

a dose of 800 millirem (80 cents) in one year.

Yet, because of strict regulations, a nuclear reac-

tor site being decommissioned and returned to

green fields status is only permitted to add

15 millirem (1.5 cents) to the dose from natural

background in one year.

It has been discovered that naturally occurring

nuclear reactors existed in prehistoric times.[3]

These ancient nuclear reactors were discovered by

a European nuclear fuel manufacturer. One of the

final tests during the fabrication of nuclear fuel is

checking for fuel rod activity. The testing of one

batch of fuel rods showed that they were not asactive as they should be. It was thought that there

might have been an error during manufacturing.

The records were checked and no mistakes were

found. The manufacturer went back to the mine

in Gabon, Africa, to the actual locations where the

ore was extracted. An isotopic analysis was

performed and six individual, natural nuclear

reactors were found. The fissile isotope, uranium-

235, was depleted and in its place were fission

product elements.

These six natural nuclear reactors ran for600,000 to 800,000 years each, with the collection

of six reactors running over millions of years.

The reactors were formed 2 billion years ago

when rains washed uranium minerals out of

mountains and down rivers where they settled out

in the river delta. The concentrations were up to

60% uranium, with isotopic concentrations of

fissile uranium-235four times the concentration

that is used in commercial nuclear reactors today.

The river water moderated the neutrons allowing

the uranium silt to go critical. It is suspected that

other natural nuclear reactors have existed.

It is interesting and informative to look around

the world and see what sort of natural background

radiation environments exist. Most of Guangdong

Province in China is not particularly notable in

that its 330-millirem (33 cents) per year environ-

ment is similar to many areas in the United States.

What is interesting, however, is that a large

population of people in one region lives in a

radiation environment of 190 millirem (19 cents)

per year. This population has the same heritage,

living conditions, eating habits, and cultural

traditions. However, the population living in this

reducedradiation environment, with about half

the naturally occurring radiation, experiences a

highermortality rate due to cancer than the people

living in the higher radiation environment of

Guangdong Province.[4,5]

People living in the town of Radon Springs in

France receive a doses of 1.6 rem every year.[6]

This is near the administrative level of 2 rem

(2 dollars) for United States Department of

Energy radiation workers.

People in Kerala, India, receive 3 rem

(3 dollars) per year living on monazite sands

deposited on ocean beaches.[7] The monazite

originates from the natural erosion of thorium

minerals in watershed areas.

Morro Do Ferro in Brazil, with between 7 and

14 rem (7 to 14 dollars) per year, does not have

people living around it. The names English

translation is mountain of iron. This may be so,

but it also is estimated to contain 30,000 tons of

thorium. What is so special about this mountain?

Although there are no human inhabitants in the

area, this small mountain is completely covered

with plant life. As an experiment, a plant growingon the mountain was cut down and placed on a

photographic plate wrapped in black paper. The

radiation from the decay of naturally occurring

radium within the plant was sufficient to image its

stems and leaves on the photographic plate.[8]

People living in Guarapari, Brazil, receive

17.5 rem on a yearly basis.[6] This is over 3 times

the amount of radiation dose that I am allowed as

a radiation worker by U.S. law.


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Ramsari, a small town of 2,000 people in Iran,

holds the record at 48 rem (48 dollars) per

year.[9,10] An astounded plutonium metal-

lographer, upon hearing this, asked how these

people lived in such an environment. The answer

to this question was one that really surprised me

during the special training I received to become a

plutonium handler. I found out that the bodys

cells are able to repair radiation damage. More

information on this is provided below.

Influence of Low Levels of Radiation on

Biological Systems

Cell and DNA repair

I was amazed to learn that there were repairmechanisms on the cellular and DNA level to

repair damage from ionizing radiation. If the

repair was not effective, the body would replace

the cell. (Take into consideration that we evolved

from species that lived on an earth that was ten

times more radioactive than it is today.)

As mentioned in Parts 1 and 2 of this series, I

own a drinking water crock lined with uranium

ore. The Revigator, made by the San Francisco

Revigator Company, has a recorded patent date

of 1912. I like to use the Revigator as an audio

and visual comparison to what is taking place in

the human body. When I hold my geiger probe

inside the crock, it shows 40,000 counts per

minute (cpm) due to radioactive decay. The

sound of the counter is not the characteristic

click, click, click. . .it sizzles.

The sizzling sound of 40,000 counts per

minute (see Figure 3 for a sample meter and

sample display pieces) doesn't even begin to

compare to the natural radioactivity in the human

body. I just about fell out of my chair in the

classroom when I was told that in the humanbody, 500,000 radioactive disintegrations occur

every minute. The human body gives off over

6,000 gamma rays every minute that are more

energetic than the gamma rays given off by

cobalt-60.[11]

It turns out that 200,000 disintegrations per

minute are from the decay of potassium-40 in the

body. They are the source of the hard gamma

emissions. Another 200,000 are due to carbon-14.

This is the same carbon-14 that is used in dating

organic material such as trees. Cosmic rays hit

the upper atmosphere of earth, generating

neutrons that hit nitrogen nuclei, converting the

atom into carbon-14. This carbon-14 enters the

earths carbon cycle, gradually decaying away

with a half-life of 5,700 years. The remaining

100,000 disintegrations are due to the remaining

naturally occurring radioactive isotopes found in

nature.

What if your body were not able to accom-

modate half a million disintegrations each minute?

You would not be reading this article. Cell

damage due to low levels of radiation is repairedon a regular basis by the human body.

If the cell is not properly repaired, it is replaced.

I have been asked about circumstances where

the repair may not be complete and the cell

remains viable. The point I make is that concern

over this aspect is minor when compared to

everything else taking place within the human

body totally unassociated with radiation.

Every hour on the average, every cell in the

human body undergoes approximately 8000

DNA-modifying events, independentofradiation.[12] A dose of 1 rad (1 dollar) of radiation

will cause, on the average in every cell,

approximately 20 DNA-modifying events.[13,14]

This means that a radiation worker receiving

5 rem (5 dollars) in one year will have 100 DNA-

modifying events in each cell due to the influence

of ionizing radiation, compared with 70,000,000

DNA-modifying events due to all other causes.


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Radiation Hormesis

I was introduced to another concept during my

training that was something I had never heard of

and could not believe without supporting

documentation. I was told that mice exposed to

low levels of radiation above background actually

lived longerthan those that were not exposed to

radiation above background. The concept is

called radiation hormesis. There is considerable

literature and lists of experiments that support the

concept that small amounts of radiation (above

background) actually stimulate biologicalsystems, while larger amounts are predictably

harmful.

Currently, discussions continue within the

nuclear community regarding three somewhat

different ways of interpreting the influence of low

levels of radiation on the human body. They are

the linear hypothesis, which assumes that any

amount of radiation puts you at risk; the threshold

model, that says a radiation dose has to reach a

certain level before it becomes harmful; and the

hormesis model, where small amounts of ionizing

radiation greater than background stimulate

biological responses while larger amounts become

harmful.

It is important to recognize that considerable

literature and numerous texts exist on the subjects

of health physics and the biological or health

effects of ionizing radiation. What they say has a

tremendous impact on the economic viability,health, and safety of our society with deleterious

effects occurring at either extreme of lack of

concern or over-concern. For such a technical

subject, it is very interesting in that you will

encounter a range of slants on the part of

authors ranging from any amount of radiation

puts you at risk to the other end of the spectrum

Figure 3. Meter probe on an orange-glazed antique portion plate colored by uranium oxide. The green

glass gets its distinctive color by using dissolved uranium salt. Photo by Jane Hart.


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where numerous experiments indicate stimulation

of and benefit to biological systems at low levels

of ionizing radiation. The point is, do not read

one article, or one text and conclude that you

understand the subject. It is important that you

read a number of authors to develop your own

informed perspective.

References

1. Eisenbud, M.,Environmental Radioactivity

From Natural, Industrial, and Military

Sources, 3rd edition, Academic Press, p. 162.

2. Office of Environmental Management, U.S.

Department of Energy,Radiation in the

Environment, Document Number DOE/EM-0065P, August 1994; internet address

http://www.em.doe. gov/fs/fs1f.html.

3. Cowan, G.A., A Natural Fission Reactor,

Scientific American, July 1976, Vol. 235,

No. 1, pp. 36-47.

4. Luckey, T.D.,Radiation Hormesis, 1991,

CRC Press, Inc., ISBN 0-8493-6159-1,

pp. 107-111.

5. Eisenbud, M.,Environmental Radioactivityfrom Natural, Industrial, and Military

Sources,3rd edition, Academic Press,

pp. 170-171.

6. Mettler, F.A., Moseley, R.D.,Medical Effects

of Ionizing Radiation, 1985, Grune &Stratton,

Inc., ISBN 0-8089-1704-8, p. 39.


CRC Press, Inc., ISBN 0-8493-6159-1, 15.

8. Eisenbud, M.,Environmental Radioactivity

From Natural, Industrial, and Military

Sources, 3rd edition, Academic Press,

pp. 169-170.


CRC Press, Inc., ISBN 0-8493-6159-1, 14.

10.Sohrabi, M., Conference Report: Inter-

national Conference On High Levels of

Natural Radiation, Held at Ramsar, Islamic

Republic of Iran, 3-7 November 1990,Nucl.

Tracks Radiat. Meas., Vol. 18, No.3, 1991,

Int. J. Radiat. Appl. Instrum., Part D,

Pergamon Press plc, pp. 357-361.

11.Luckey, T.D.,Radiation Hormesis, 1991,

CRC Press, Inc., ISBN 0-8493-6159-1,

pp. 19-20.

12.Abelson, P.H.; Science, Vol. 265,

9 September 1994, p. 1507.

13.Ward, J.;Proceedings, 8th International

Congress of Radiation Research, Fielden

et al., Eds., Vol II, 1987, pp. 162-168.

14. Billen, D.; 1990, Radiation Research, 124,

1990, pp. 242-245.

Additional Reading

Medical Effects of Ionizing Radiation, Mettler,

F.A., Moseley, R.D., 1985, Grune & Stratton,

Inc., ISBN 0-8089-1704-8.

Environmental Radioactivity From Natural,

Industrial, and Military Sources, Eisenbud, M.,1987, 3rd edition, Academic Press, ISBN

12-235153-3.

Radiation Hormesis, Luckey, T.D., 1991, CRC

Press, Inc., ISBN 0-8493-6159-1.

Health Effects of Low-level Radiation, Kondo, S.,

1993, Kinki University Press, Osaka, Japan,

Medical Physics Publishing, Madison, WI, ISBN

0-944838-43-X.

Radioactivity and Health, A History, Vol. 1, 2, 3,

Stannard, J.N., 1988, Office of Scientific andTechnical Information, ISBN 0-87079-591-0.


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Radiation & Human Health, Gofman, J.W., 1981,

Sierra Club Books, ISBN 0-87156-275-8.

Hormesis With Ionizing Radiation, Luckey, T.D.,

1980, CRC Press, Inc., ISBN 0-8493-5841-8.

Radiation and Radioactivity On Earth and

Beyond, Draganic, I.G., Draganic, Z.D., Adloff J.,1990, CRC Press, Inc., ISBN 0-8493-0158-0.

The Good News About Radiation, Lenihan, J.,

1993, Cogito Books, Madison, WI, ISBN

0-944838-34-0.

Trashing The Planet, Ray, D.L., 1990, Harper

Perennial, ISBN 0-06-097490-7.

America The Powerless, Waltar, A.E., 1995,

Cogito Books, Madison, WI, ISBN

0-944838-58-8.

The Invisible Passenger, Radiation Risks for

People Who Fly, Barish, R.J., 1996, Advanced

Medical Publishing, Madison, WI, ISBN

1-883526-06-X.

The Author

Mark M. Hart is a multi-disciplined

scientist/engineer with undergraduate degrees in

Physics and Chemical Engineering, and an MS

degree in Electrical Engineering, as well as an

MBA degree. Having earned degrees at Carnegie-Mellon University, Southern Illinois University,

and Washington University in St. Louis, Hart is

currently employed by Lawrence Livermore

National Laboratory (LLNL) and has had the

opportunity to work hands-on with plutonium

over a period of three years. In his work he has

come across interesting, and at times surprising,

information about the subjects of radiation and

radioactivity. He enjoys sharing this information

because there is always something new for

everyone in the audience. Hart has given his

presentation to professional, public, andeducational groups across the country.

Mark M. Hart

Lawrence Livermore

National Laboratory

PO Box 808/L-125

Livermore, CA 94551

phone: 510/423-4770

fax: 510/423-9762

e-mail: [email protected]

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