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A Note on Radiation Damage
"There is no safe level of radiation exposure. So the question is not: What
is a safe level? The question is: How great is the risk?"
Karl Z. Morgan
There have been three major theories as to how radiation damages living
tissue, all set by physicians. All are approximations, and based on broad
assumptions.
(1) The threshold hypothesis: asserts that there exists a safe level of
radiation. The idea behind this thinking is that if the does is low, then
the cell repair rate is of the order of the damage rate. Hence you get
no resultant damage.
(2) The linear hypothesis: under this theory, you would expect 1 malignant
cancer for 1000 person-rems. For example, you would find one cancerous
patient if you exposed 500 people to 2 rems, or 10000 people to 0.1 rems.
(3) The supralinear hypothesis: the main result here is that for low doses
you get more cancers/person-rem than at high doses. Here they not saying you
get more radiation; instead, you get more damaged surviving cells.
Some Facts
There are 4 types of ionising radiation. These are alphas
(fast moving helium nuclei),
betas (electrons), gammas (high energy EM radiation), and neutrons (highly
penetrating).
How does damage occur? In other words, how does radiation cause cancer?
A typical cell is around 0.02mm across, a cell nucleus is about 0.001mm.
When radiation, say a gamma, enters your body, there is a chance it will
intersect with one of your cells. Inside any cell is a nucleus, which
contains chromosomes. These are essentially DNA helixes. DNA looks like
two entwined strings of nucleotides - the amino acids A, T, C, and G. Across
strands they are paired A-T and C-G. A portion of DNA (a series of these
acids) is called a gene. Genes exist along chromosomes, and they contain
the data for proteins.
If the radiation happens to pass into the cell nucleus (which is a relatively
large entity compared to the rest of the cell), one of 4 things can happen.
All exposure subjects cells to risk. In order of decreasing probability:
(1) radiation goes right thru, no interaction.
(2) radiation does irrepairable destruction, and cell dies.
(3) radiation does damage to nucleus. Cell survives in
this damaged state. After it repetitively divides, it
grows into a solid tumour after 30 odd years - cancer.
(4) radiation does repairable damage, and cell returns to
normal state. (Very low probability).
Possibility (3) is the one to watch out for. During division, the DNA
strands stretch out, and it is during this time which your cells are most
susceptible to damage.
It is also possible for the radiation to ionise the water in the cell
cytoplasm, leading to the formation of free radicals, which can travel
some distance. They can react chemically with the DNA in the nucleus,
interfering with the chemical bonding along the helix.
Two types of damaging interaction can occur with the amino acids.
(a) point mutations
- deletion
- substitution
- inversion
- addition
(b) large scale mutations (chromosome aberrations)
- deletion e.g. retinoblastoma
- amplification
- translocation
It is also possible to have compound breaks along the DNA, which is not
easy for the cell to repair, unlike single strand or double strand breaks.
The cell and nuclear membranes are also susceptible to damage. This could
be due to alterations in permeability/osmosis in the membrane due to the
radiation-induced imbalance of ionised particles.
Once a certain threshold is exceeded, you will start saturating the cells.
This lethal threshold serves to define two categories of radiation.
Effects
EFFECT NATURE THRESHOLD? DOSE DEPENDENCE
Stochastic Non-lethal mutations No Probability of
(somatic or affecting single cells effect increases
genetic) with dose
Deterministic Lethal mutations Yes Severity of
affecting large number effect increases
of cells with dose
Cancer
Stem cells are ones which are able to undergo mitosis when the human body
has reached full maturity. Examples are blood cells, and the cells lining
your intestines. During normal functioning of your body, cell replacement
balances cell loss.
In cancer, a stem fails to stop its mitosis. It and its descendants divide
uncontrolled, forming a tumour. A bit like a binary tree in cell
multiplicity.
Oncogenes are genes which interfere with the cell division process. They
are mutations of proto-oncogenes, whose role are to control cell growth
and mitosis. It is thought radiation promotes creation of oncogenes.
There are also cancer-suppressing genes, which inhibit oncogene formation.
The best known example is the Rb gene, which inhibits retinoblastoma.
After all of this, let me add a fourth idea on radiation damage:
(4) probability of hereditary genetic damage or cancer is a function of:
type of radiation (a,b,g,n) x energy of radiation x dose rate
Here you have 4 discrete degrees of freedom, and 2 continuous degrees: rate &
energy. Assume that there is a cut-off energy for a unit of a particular type
of radiation, E_max, such that if E > E_max a cell will die, and E < E_max
the cell will survive (either in damaged or undamaged state). We are worried
about the E < E_max cases. If E > E_max then you get radiation poisoning and
you will definitely die if you get a large enough dose.
The probability of nucleus intersection is a function of radiation type. (The
size of radiation varies considerably.)
The probability of a nucleus being hit twice or more is very low, unless
the number of incident radiation approaches the sample size. In which case
you get radiation poisoning and die anyway.
You get a 6D phase space of statistical mechanics. Supplement this with an
action in path integral form. Plotted, you'd have a 6D graph, unlike your
normal 3D graphs. It's worse than the 4D spacetime of general relativity.
No wonder the physicicans only plot projections! You can trace out a person's
history in this phase space, and then give them a final probability of
cancer/hereditary damage.
============================================================================
Plutonium's Risk to Human Health Depend On Its Form
In a nuclear explosium, plutonium-239 fissions and releases a huge amount of
energy and radiation. But plutonium itself is a highly toxic element that requires
a great deal of care in handling.
Experts agree that the silvery, unstable metal plutonium-239, with a half-life of
24,000 years, is hazardous and sould be isolated from the biosphere. However, the
risks posed to workers and communities by stored plutonium depend on the route of
exposure as well as the particle size, isotope, and chemical form.
Weapons-grade plutonium outside the body presents little risk unless exposures are
frequent and extensive. It emits primarily alpha particles, which cannot penetrate
skin, clothing, or even paper. Nearly all the energy from plutonium is deposited
on the outer, nonliving layer of the skin, where it causes no damage. The neutrons
and the relatively weak gamma photons it emits can penetrate the body, but large
amounts of weapons-grade plutonium would be needed to yield substantial doses.
Workers wearing only lead aprons can handle steel drums containing solid plutonium
metal with no immediate untoward effects. However, as weapons-grade plutonium
ages, it becomes more dangerous because some of the contaminating plutonium-241 is
converted via beta decay to americium-241, which emits far stronger gamma
radiation.
On the other hand, plutonium inside the body is highly toxi. Solid plutonium metal
is neither easily dispersed nor easily inhaled or absorbed into the body. But if
plutonium metal is exposed to air to any degree, it slowly oxidizes to plutonium
oxide (PuO2), which is a powdery, much more dispersable substance. Depending on
the particle size, plutonium-239 oxide may lodge deep in the alveoli of the lung
where it has a biological half-life of 500 days, and alpha particles from the
opxide can cause cancer. Also, fractions of the inhaled plutonium oxide can slowly
dissolve, enter the bloodstream, and end up primarily in bone or liver.
Plutonium oxide is weakly soluble in water. If it is ingested in food or water,
only a small fraction (4 parts per 10,000) is absorbed into the gastrointestinal
tract. However, it may take just a few millionths of a gram to cause cancer over
time. In animals, small doses induce cancer, especially in lung and bone.
In published studies of plutonium's effects on humans, most subjects were exposed
to multiple sources of radiation. Some researchers say the available health data
on plutonium workers have not yet been used to do careful epidemiological studies,
because researchers have been denied access to much of the data on workers and
military personnel exposed to plutonium. In the studies done so far, plutonium
workers do not show major excesses of any type of cancer.
Becuase of the relative lack of human data, the risks of chronic exposure to
plutonium are uncertain. Exposure standards in the U.S. are based partly on
studies of survivors of Hiroshima and Nagasaki and partly on animal experiments. A
1991 White House Office of Science & Technology Policy studye says that
"sufficient human data are not available to provide accurate risk assessment of
exposure."
============================================================================
Nuclear Blast Effects
The first thing bomb victims experience is the intense flux of photons from
the blast, which releases 70-80% of the bomb's energy. See the Hiroshima-
Nagasaki file for first hand accounts. The effects go up to third degree
thermal burns, and are not a pretty sight. Initial deaths are due to this
effect.
Then next phenomenon is the supersonic blast front. You see it before you
hear it. The pressure front has the effect of blowing away anything in its
path. Heavy steel girders were found bent at 90 degree angles after the
Japanese bombings.
After the front comes the overpressure phase. It would feel like being under
water a few hundred metres. At a few thousand metres under the sea, pressurised
hulls implode. The pressure gradually dies off, and there is a negative
overpressure phase, with a reversed blast wind. This reversal is due to
air rushing back to fill the void left by the explosion.
The air gradually returns to room pressure. At this stage, fires caused by
electrical destruction and ignited debris, turn the place into a firestorm.
Just like Dresden in WWII. It is estimated over fifty thousand died in the
first few days of the Hiroshima bombing.
Then come the middle term effects such as keloid formation and retinal
blastoma.
Genetic or hereditary damage can show up up to forty years after initial
irradiation.
The following diagram is of blast zone radii, courtesy of Outlaw Labs.
Note that damage from blast pressure falls off as a function of 1/r^3.
============================================================================
- Breakdown of the Atomic Bomb's Blast Zones -
----------------------------------------------
.
. .
. . .
. .
[5] [4] [5]
.
. . . .
. . . .
. [3] _ [3] .
. . [2] . .
. _._ .
. .~ ~. .
. . [4] . .[2]. [1] .[2]. . [4] . .
. . . .
. ~-.-~ .
. . [2] . .
. [3] - [3] .
. . . .
. ~ ~ .
~
[5] . [4] . [5]
.
. .
. .
.
============================================================================
- Diagram Outline -
---------------------
[1] Vaporization Point
------------------
Everything is vaporized by the atomic blast. 98% fatalities.
Overpress=25 psi. Wind velocity=320 mph.
[2] Total Destruction
-----------------
All structures above ground are destroyed. 90% fatalities.
Overpress=17 psi. Wind velocity=290 mph.
[3] Severe Blast Damage
-------------------
Factories and other large-scale building collapse. Severe damage
to highway bridges. Rivers sometimes flow countercurrent.
65% fatalities, 30% injured.
Overpress=9 psi. Wind velocity=260 mph.
[4] Severe Heat Damage
------------------
Everything flammable burns. People in the area suffocate due to
the fact that most available oxygen is consumed by the fires.
50% fatalities, 45% injured.
Overpress=6 psi. Wind velocity=140 mph.
[5] Severe Fire & Wind Damage
-------------------------
Residency structures are severely damaged. People are blown
around. 2nd and 3rd-degree burns suffered by most survivors.
15% dead. 50% injured.
Overpress=3 psi. Wind velocity=98 mph.
----------------------------------------------------------------------------
- Blast Zone Radii -
----------------------
[3 different bomb types]
____________________________________________________________________________
______________________ ______________________ ______________________
| | | | | |
| -[10 KILOTONS]- | | -[1 MEGATON]- | | -[20 MEGATONS]- |
|----------------------| |----------------------| |----------------------|
| Airburst - 1,980 ft | | Airburst - 8,000 ft | | Airburst - 17,500 ft |
|______________________| |______________________| |______________________|
| | | | | |
| [1] 0.5 miles | | [1] 2.5 miles | | [1] 8.75 miles |
| [2] 1 mile | | [2] 3.75 miles | | [2] 14 miles |
| [3] 1.75 miles | | [3] 6.5 miles | | [3] 27 miles |
| [4] 2.5 miles | | [4] 7.75 miles | | [4] 31 miles |
| [5] 3 miles | | [5] 10 miles | | [5] 35 miles |
| | | | | |
|______________________| |______________________| |______________________|
____________________________________________________________________________
============================================================================
Atmospheric Effects of Blasts
The Mushroom Cloud
The heat from fusion and fission instantaneously raises the surrounding air
to 10 million degrees C. This superheated air plasma gives off so much light
that it looks brighter than the sun, and is visible hundreds of kms away.
The resultant fireball quickly expands. It is made up of hot air, and hence
rises, at a rate of a few hundred metres per second. After a minute or so,
the fireball has risen to a few kilometres, and has cooled off to the extent
that it no longer radiates.
The surrounding cooler air exerts some drag on this rising air, which slows
down the outer edges of the cloud. The unimpeded inner portion rises a bit
more quicker than the outer edges. A vacuum effect occurs when the outer
portion occupies the vacuum left by the higher inner portion. The result is
a smoke ring.
The inner material gradually expands out into a mushroom cloud, due to
convection. If the explosion is on the ground, dirt and radioactive debris
get sucked up the stem, which sits below the fireball.
Collisions and ionisation of the cloud particles result in lightning bolts
flickering to the ground.
Initially, the cloud is orange-red due to nitrous oxide formation (cf car
smog). This reaction happens whenever air is heated.
When the cloud cools to air temperature, the water vapour starts to
condense. The cloud turns from red to white.
In the final stages, the cloud can get about 100km across and 40km high,
for a megaton class explosion.
============================================================================
Electromagnetic Pulse (EMP)
A nuclear explosion gives off radiation at all wavelengths of light. Some
is in the radio/radar portion of the spectrum - the EMP effect. The EMP
effect increases the higher you go into the atmosphere. High altitude
explosions can knock out electronics by inducing a current surge in
closed circuit metallic objects - computers, power lines, phone lines,
TVs, radios, etc. The damage range can be over 1000km.
============================================================================
Here are some good references on radiation damage. See also the main
References file.
AUTHOR: Sumner, David, D. Phil
TITLE: Radiation risks : an evaluation / David Sumner, Tom Wheldon, Walter
Watson. -- 3rd ed.
ISBN/ISSN: 187078104X
IMPRINT: Glasgow [Scotland], Tarragon Press, 1991
PHYS DESC: 236 p., ill., map, 21 cm.
ADD AUTH1: Wheldon, Tom
ADD AUTH2: Watson, Walter
NOTE 1: Includes index Bibliography: p. 227-229
SUBJECT 1: Radiation--Physiological effect
SUBJECT 2: Cells--Effect of radiation on
[Good introductory work.]
CALL NO: Me f 616.989707 LOW
TITLE: Low-level radiation effects: a fact book: prepared by Subcommittee
on Risks of Low-Level Ionizing Radiation: A. Bertrand Brill ... [et
al.]
ISBN/ISSN: 0932004148
IMPRINT: New York, NY: Society of Nuclear Medicine: c1982-
PHYS DESC: 1 v. (loose-leaf): ill: 30 cm.
ADD AUTH1: Brill, A. Bertrand
ADD AUTH2: Society of Nuclear Medicine. Subcommittee on Risks of Low-Level
Ionizing Radiation
NOTE 1: To be kept up to date by inserts
SUBJECT 1: Ionizing radiation--Physiological effect
SUBJECT 2: Ionizing radiation--Toxicology
SUBJECT 3: Radiation injuries
SUBJECT 4: Low-level radiation--Physiological effect
CALL NO: Me 574.1915 BIOL
TITLE: Biological effects of low-level radiation : proceedings of an
international symposium on the effects of low-level radiation with
special regard to stochastic and non-stochastic effects / jointly
organized by the International Atomic Energy Agency and the World
Health Organisation, and held in Venice, Italy, 11-15 April 1983
ISBN/ISSN: 9200101836
IMPRINT: Vienna, International Atomic Energy Agency, 1983
PHYS DESC: 682 p., ill, 24 cm. (Proceedings series)
ADD AUTH1: International Atomic Energy Agency
ADD AUTH2: World Health Organization
SERIES 1: Proceedings series (International Atomic Energy Agency)
NOTE 1: English and French
SUBJECT 1: Radiation--Toxicology--Congresses
SUBJECT 2: Radiation--Physiological effect--Congresses
CALL NO: DS 574.1915 KIEF
AUTHOR: Kiefer, J (Jurgen) , 1936- [Biologische Strahlenwirkung. English]
TITLE: Biological radiation effects / Jurgen Kiefer
ISBN/ISSN: 3540510893
IMPRINT: Berlin, New York, Springer-Verlag, c1990
PHYS DESC: xvii, 444 p., ill, 24 cm.
NOTE 1: Rev. translation of: Biologishce Strahlenwirkung Includes
bibliographical references (p. [415]-435) and indexes
SUBJECT 1: Radiobiology
SUBJECT 2: Radiation--Physiological effect
SUBJECT 4: Radiation protection
To learn more about air explosions, see the Reference by Kinney and Graham,
"Explosive Shocks in Air".
The Red Phoenix, 1994.