NUCLEAR FISSION BOMB
A nuclear bomb detonation is a very difficult subject for
this writer to discuss because of the many deaths and suffering in two Japanese
cities in 1945. Many of the survivors in
suffered from cancer many years
later. This must never happen again.
The treat of a nuclear attack was considered very real
during the Cold War. During the 1950’s,
newspapers carried articles on what would happen if a nuclear bomb were dropped
in the center of the city covered by the newspaper, with damage and radiation
expected at various distances from “ground zero”. Some people built fallout shelters. Schools held drills where children were sent
to the center of the building on a lower floor where radiation would be
expected to be less. The United States
came close to a nuclear war during the Cuban missile crisis in 1963. There was another incident in the early
1980’s when the Soviet military mistook some “ghosts” or “natural phenomena” on
their systems for a U.S.
missile attack and almost launched an all-out counter attack (aired on a TV
Today, the threat seems less real, at least from a
nation-state. But there is still concern
that a nuclear missile site might be taken over by a terrorist group, or a
small nuclear device might be carried in a suitcase by a terrorist.
AristaTek carried an article on nuclear weapons in November
2002. The article can be obtained from
the AristaTek website.
Nuclear weapons may take different forms. We will limit the discussion here to smaller
nuclear fission weapons, which might be carried in a suitcase and detonated at
ground level or near ground level by a terrorist.
Fox News carried a story (see http://www.foxnews.com/story/0,2933,76990,00.html )
that Russian National Security Adviser Alexandr
Lebed in 1997 alleged that up to 100 nuclear 1 KT
potable bombs that looked like suitcases were unaccounted for since the 1991
breakup of the Soviet Union
. Usama Bin Laden
allegedly has purchased a number of suitcase or backpack nuclear bombs from
Chechen organized crime groups. Former
FBI Director Louis Freeh told Congress, “We have not
seen any hard evidence of suitcase-sized nuclear devices unaccounted for or
falling into the hands of terrorists or rogue states”. See also National Fire and Rescue reprint
article (2002), http://www.nfrmag.com/library/HD-Rad.pdf and
What Does A Small Nuclear Fission Bomb Look Like?
The essential starting material is fissionable material such
as uranium 233, uranium 235, plutonium 239, or plutonium 241. Perhaps plutonium 239 produced from nuclear
power plants using uranium 238 as fuel may be the most common fissionable
Detonation of a nuclear device occurs when a critical mass
of fissionable material is achieved. The
amount required to produce a critical mass depends on what the fissionable
material is and the arrangement of material such that enough neutrons are
reflected back to the material to result in detonation.
The detonation of a nuclear device requires a method of
quickly converting a subcritical system to a critical
one. Two methods are generally used:
- One or
more subcritical mass fragments are brought
together very quickly in order to achieve a supercritical mass, for
example, a high explosive device blows one subcritical
mass in some gun-barrel device into another subcritical
mass firmly held at the muzzle end.
method is to rapidly compress a subcritical
quantity such that the density increases and the mass becomes
critical. This is done by using a
spherically-fabricated shape of a high explosive with a subcritical sphere of fissionable material in the
center. When the explosive
detonates, an inwardly-directed implosion wave is produced causing the uranium
or plutonium to be compressed.
Conventional explosives are required to set off a nuclear
Illustrated at the left is
a cut of a possible nuclear fission bomb arrangement using plutonium 239 or
uranium 235. This cut was also used in
an article in the Scientific American for Nov. 2002 (page 78) on weapons of
mass destruction. This illustration is
of interest because it shows an arrangement whereby many subcritical
plutonium pieces are arranged and brought together to form one large critical
mass. A more simple
fission bomb can be created by bringing say two subcritical
pieces together, but the bomb yield (kiloton TNT equivalent) will be less. The subcritical
plutonium 241 is in the shape of inwardly pointing pyramids surrounded by a
shell of high explosives. When the high
explosives detonate, the plutonium pieces are driven together into a sphere
containing a core pellet of beryllium/polonium creating a critical mass. The core pellet controls the neutron flux
from the plutonium allowing a critical mass to be achieved with a smaller
amount of fissionable material (e.g. a few pounds of plutonium 239). Plutonium 239 has a mass density of 19.5
grams/cc; a 5 kg critical mass would be equivalent to a cube 2.5 inches on the
side. The time between the high
explosive detonation to the detonation of the nuclear
device is a small fraction of a second.
The Soviet nuclear backpack system consists of three “coffee
can-sized” aluminum canisters with a 6-inch detonator and powered by a
battery. The canisters are
interconnected as a single unit; the contents are brought together by setting
off an explosive remotely.
More on nuclear weapons design can be found at the website, http://www.fas.org/nuke/intro/nuke/design.htm
Other Nuclear Weapons
weapon. If heavy isotopes of
hydrogen (deuterium or tritium) are heated to very high temperatures (over
one million degrees), they will fuse forming helium and heat energy. This process is called fusion. In order to reach the million plus
temperatures, detonation a fission-type nuclear bomb is required. The combination of the fission and
fusion bomb releases tremendous amounts of energy mostly in the form of
heat. The TNT energy equivalent
usually is in excess of one million tons.
This is sometimes called the “hydrogen bomb”. In one variation, the fusion core of the
bomb is wrapped in a blanket of uranium 238 atoms. The uranium 238 atoms are then split by
the searing energy released from the fusion core initiating a very
powerful secondary fission explosion.
bomb, or Enhanced Radiation Warheads. These are small nuclear devices with
limited blast and heat effects when detonated but are designed to release
a sudden and deadly flux of neutrons which can penetrate tank armor in the
battlefield or disrupt trajectories of an incoming missile attack. They can be a small fission-type bomb
which are constructed of materials (chromium and/or nickel) which allow
for maximum escape of neutrons rather than be absorbed by the bomb
material producing radioactive isotopes.
They can be a fusion type bomb or a thermal nuclear weapon. According to the neutron bomb inventor
[Sam Cohen, see http://www.manuelsweb.com/sam_cohen.htm]
irradiated red mercury can be exploded resulting in temperatures high
enough to trigger a fusion device using hydrogen isotopes without the need
of plutonium or uranium 235. The
neutron bomb could be packaged in a container the size of a baseball. The initial blast and heat effects would
be limited to a few hundred yards, but lethal neutron and gamma radiation
distance would extend much further.
The neutron bomb can be designed to produce minimal residual
radiation. Countries believed to
possess neutron bombs include the U.S.,
China, Russia, Israel,
and France, and
Energy Released From Detonation of a Fission Nuclear Bomb
the instant of detonation of a nuclear device there will be a blinding flash of
light, much brighter than the sun. The
light will be so intense that permanent retinal damage will occur even though
the person is many miles away unless typography or structures block his/her
vision of the fireball. In the worst
case of a detonation of a very large nuclear device at say 10,000 feet
elevation at night, retinal damage can occur even 150 miles away from ground
The maximum light intensity may occur within 0.1 second of
the detonation (a blink of the eye takes about 0.25 seconds). Persons within several miles of ground zero
(depending upon the size of the device) may also receive a lethal dose of gamma
and neutron radiation and fatal third degree burns in the first few seconds,
unless protected by buildings or underground shelters.
the first few seconds or minutes (depending upon the distance from ground zero)
there will be a blast wave and accompanying wind, sufficient to level
The photo to the left is taken of a daytime aerial
detonation taken right after detonation, with the camera lens darkened to blot
out all light except for the flash itself.
Notice the separation between the initial nuclear flash and the debris
from the ground which will form part of the nuclear cloud, and the blast wave
spreading out from ground zero.
Following the events of the first hour, responders may make
decisions whether it is “safe” to enter the stricken area. There will be residual radiation from the
radioactive isotopes formed and dispersed over the area. This residual radiation should decay at a
predictable rate. Complicating this
picture will be radioactive fallout from the sky which may be carried long
distances from the source. There will
also be many secondary fires endangering people.
As a rough rule of thumb, about 200 MeV
of energy is released per atom undergoing fission. Of this 200 MeV, about 185 MeV energy is released
instantaneously in the form of blast and shock waves, heat, and radiation, and
15 MeV in the form of radioactive decay. It is customary to rate the energy released
in terms of TNT equivalents. The
complete fission of one pound of uranium 233 or plutonium 239 releases as much
energy as 8,000 tons of TNT. The atomic
bomb dropped on Japan
in 1945 was rated at 20 kilotons of TNT.
Theoretically a 20-kiloton weapon would require 2.5 pounds of uranium
233 or plutonium 239, but the actual amount used was probably more because the
fission process is not 100% efficient.
In a ground level burst, about 1% of the energy released
would vaporize the ground at the site.
An one-megaton TNT equivalent weapon would vaporize about 4000 tons of
soil material which would be sucked up into the fireball. Large amounts of dirt and water would
be sucked up as the fireball rises.
Neutrons emitted during the first second of the detonation will interact
with the ground producing radioactive isotopes.
The dirt sucked up would be dispersed as radioactive fallout some
distance away from the explosion. In an
air burst, less energy would be absorbed by the ground. More blast and heat energy will affect
locations further away from ground zero.
Less dirt will be sucked up into the fireball, and less fallout overall
might be expected.
Detonation of a nuclear bomb results in the following:
waves and accompanying wind
and blinding light
nuclear radiation (within first minute of blast)
nuclear radiation (after first minute of blast)
PEAC Tool (Version
Information on Nuclear Fission Detonation in the PEAC tool
is accessed at any time by clicking on the red “mushroom” icon at the top
center of the PEAC tool, regardless of anything else that might be displayed,
see figure below.
The Nuclear Detonation Calculator icon
The PEAC tool used information in the public domain from the
fission bomb tests at the Nevada Test Site and other locations and the 1945
detonations at Hiroshima
The information in the PEAC tool is intended for training exercises as
in (1) estimating evacuation distances or shelter in place in case a suspicious
package is located and must be disarmed or (2) a nuclear device has exploded
and rescue operations begin.
When the user opens the “red mushroom” icon, a
descriptor/disclaimer statement is displayed:
“Detonation of a nuclear fission-type device will result in
an initial blinding flash of light, heat, gamma and neutron radiation with the
first second or two of detonation, followed quickly by a blast wave. These calculations consider only initial
damage. The calculations do not consider
radioactive fallout, secondary fires, additional radiation exposure from use of
dirty starting materials, use of enhanced radiation warheads, or detonation of
a thermal nuclear device. Calculations
apply to a ground level fission device on fairly level terrain. An aerial detonation or detonation on a
hilltop may result in greater damage at distances further from ground zero.”
A screen pops up titled “Nuclear Device Yield”. The user must estimate the Yield in units of
kilotons (KT) of TNT energy equivalents.
By convention, the energy released by nuclear bombs is rated in terms of
TNT equivalents, even though no TNT explosives are actually used. If the nuclear device has been detonated, the
KT yield may be estimated by either specifying (1) the mushroom cloud height,
(2) the crater diameter if detonated at ground level, or (3) a blast damage
estimate at some distance away from ground zero. The cloud height can be calculated knowing
the distance from ground zero and the angle from the horizontal (best 10 to 30
minutes after detonation).
The display of the following examples are in metric
units The PEAC user can chose “English
units” if desired.
In the next screen, the user specifies damage
thresholds. Overpressure refers to blast
damage; the number specified is linked to a physical description of the blast
damage, which the PEAC user can display (not shown). There will also be an initial burst of heat
(thermal) energy; the user can specify “second degree burns” or 3rd
degree burns (at different fatality levels).
The user also specifies a radiation dose from the initial pulse of gamma
and neutron radiation, which occurs during the first few minutes of the nuclear
blast. An estimate for the daytime and
nighttime distance for retinal burns is also displayed on the results screen.
The last screen Damage Distance estimates for the kiloton
yield, blast overpressure, thermal heat, and radiation dose specified. The retinal burns distances are not displayed
on the map.
The PEAC Map Tool will automatically display the resulting
distances as polygons on a street map for the specified location. When finished, all of this information is
displayed on one screen, which can be printed or copied or recalled for later
viewing. A portion of a Nuclear
Detonation Results Report is shown in the figure below. Additional information on the distances to
damage of different types infrastructure is provided
in a table (not shown) below the map display of the results.
Example of a Nuclear Detonation Results Report
The calculations apply to someone caught out in the open
when a nuclear detonation occurs. The
retinal burn distances apply for a clear day for a person who happens to be
facing the direction of ground zero at the instant of detonation, and there is
no terrain or structures blocking his/her line of sight. The distances are greater at night because it
is assumed that the pupils are more open.
The retinal damage occurs in the first second of detonation.
In contrast, the blast damage occurs later. The arrival time of the blast front depends
on a number of factors including the height of the nuclear burst. For a 1 kiloton burst at ground level, the
blast front will take 0.5 seconds to travel 1,100 feet, 2 seconds to travel
2,000 feet, and 4.5 seconds to travel 5,850 feet. The actual analysis of the blast is fairly
complicated. The blast wave can undergo
multiple reflections. There is also a
strong wind component moving from the blast.
At 5 psi overpressure, the accompanying wind may be 160 mph.
Neutron radiation exposure occurs within the first second of
detonation. Almost all of the gamma
radiation exposure (excluding gamma radiation from radioactive isotopes and
from fallout) also occurs in the first minute.
The exposure distances are for someone caught out in the open. Because gamma and neutron radiation scatters,
a barricade between a person and the detonation will offer little additional
protection, unless the person is completely surrounded by the barricade. The shielding must be provided in all
directions. The damp earth tenth-value
thickness for gamma rays is 18 inches; for neutrons, it is about 24
inches. Twelve inches of concrete (on
all sides) should reduce gamma radiation intensity by a factor of 10; twenty
four inches by a factor of 100. The
interior lower floors of reinforced buildings may provide a 50 to 300-fold
protection from radiation compared with someone outside. A basement in a one-story house might offer a
15-fold protection factor. The
subbasement of multistory buildings might offer a 1,000 protection factor.
Shielding for neutrons is more complex; the neutrons must
first be slowed down (an elastic scattering material such as one containing
barium or iron best) and then adsorbed (water good for this purpose). Therefore the protection factors for neutrons
offered by a given thickness of shielding are different compared with gamma
Delayed Radiation and Radiation Fallout
The above discussion considers only initial effects. The neutrons emitted during fission will
interact with everything nearby producing radioactive isotopes. The radioactive isotopes will continue to emit
alpha, beta, and gamma radiation over the lifetime of the isotopes which may be
for several decades. The mushroom cloud
formed will carry the radioactive isotopes high into the atmosphere. Some will fall to the ground as radioactive
fallout. Some will be dispersed with the
wind that accompanies the blast. Some of
the radioactive isotopes will be dispersed worldwide and enter the food chain,
resulting in an increased risk of cancer.
The PEAC-WMD application currently doesn’t predict
radioactive fallout patterns because of the many variables involved.
The radiation dose as a function of distance from ground
zero depends how the radioactive isotopes are distributed; they can be absorbed
into or onto the ground or carried by the wind to some distance from the
site. However, if the dose rate
(Roentgens per hour) is known at a location at particular time since
detonation, the dose rate can be estimated for a later time. Fission tests conducted at the Nevada Test
Site and elsewhere roughly 50 years ago have produced a mixture of isotopes
such that the dose rate falls off in a predictable way, for example, if the
dose rate at a particular location is 1,000 Roentgens/hour at one hour after
the detonation, after 1,000 hours, the dose rate is 0.24 Roentgens/hour. About 55% of the “infinity residual radiation
dose” (e.g. the radiation dose if the person remained there for many years) is
received between the first minute and hour since detonation. About 80% of the infinity dosage is received
between the first minute and 24 hours since detonation. This kind of information is of use to
responders who may venture into an area devastated by a nuclear explosion, or
when people in shelters might come out.
The PEAC tool contains a calculator for estimating the radiation dose
rate at a future time if a measurement is taken at an earlier time, providing
that additional fallout has not occurred.
This methodology for radioactive decay should hold true for
ordinary fission-type devices including a fission device used to initiate a
thermonuclear device (the “hydrogen” bomb).
It does not hold true for fission bombs with additional material is
added to produce long-lived radioactive isotopes. An example is where the warhead is incased in
a cobalt shell (the “cobalt bomb”); the radioactive isotope decay will be
enriched in the cobalt 60 radioactive isotope formed during the nuclear
blast. The cobalt 60 radioactive isotope
would decay much slower rate. After
about 20 or so years, the radiation level might decay by a factor of ten or
In a rainy situation, practically all of the radioactive
fallout might occur within the rain location, especially in the case of a lower
yield detonation near or at the ground.
Building structures offer some protection against delayed
radiation including fallout. A one-story
frame house in the center of the house might offer a 2.3 protection factor for
radiation. A basement of a one-story
house might offer a 15 protection factor.
A two-story frame house basement might offer a 37 protection
factor. The protection factor in
subbasements of multistory buildings or in underground shelters (at least 3
feet of dirt on top) could be 1,000.
Certain isotopes from fission explosions are of particular
concern because they get into the food chain.
The two major ones are strontium 90 (half life 27.7 years) and cesium
137 (half life 30.5 years). Moreover
these two isotopes have gaseous precursors as part of the radioactive decay
chain allowing for dispersal over a large area, even worldwide. For every 1,000 atoms undergoing fission,
about 30 to 40 atoms of strontium 90 and 50 to 60 atoms of cesium 137 are
Effect of Radiation on Health
Table 1: Whole Body Radiation Exposure Levels and Resulting Effects for a
to demonstrate a higher incidence in fetal abnormalities or cancer effects
below 10 rem dose. A 10 rem
dose results in a 0.8% lifetime increase in developing cancer.
blood and sperm abnormalities seen
genetic effects demonstrated
decrease in lymphocytes in peripheral blood chemistry profile after 24 hours
indicating some bone marrow depression.
symptoms include nausea, malaise, vomiting, and anorexia. Long term effects
include a 5% cancer increase death risk, 1% genetic risk defects. The onset
of acute symptoms vary with the individual but could be a few days at the low
end of the dose (100 rem) or maybe an hour for
doses above 200 rem. Most patients are without
symptoms below 100 rem.
decreases in sperm count, but recovery of natural fertility usually occurs
after several months or a year
marrow depression symptoms apparent. The onset of symptoms associated with
bone marrow depression can vary with the individual and dose; but can be
several weeks or even months after radiation exposure. These symptoms may
occur weeks after the person has recovered from the initial onset of nausea
and anorexia. Changes in the peripheral blood profile may occur as early as
24 hours after radiation exposure. Lymphocytes will be depressed most rapidly, and other leukocytes and thrombocytes
will be depressed less rapidly. A 50% drop in lymphocytes in 24 hours
indicates significant radiation injury. Symptoms include bleeding
(hemorrhage) and anemia, diarrhea, fluid loss, and decreased resistance to
infection, which become apparent several weeks after radiation exposure.
Minimal treatment includes fluid replacement, antibiotics, and prevention of
infection. More aggressive treatment includes bone marrow resuscitation
of people develop cataracts within several months
Epilation (hair loss)
lethal dose of radiation that will kill 50% of the exposed persons within 60
days without appropriate medical treatment. Mortality is low with aggressive
loss of epithelial cells of the intestinal mucosa results in hemorrhage and
marked fluid loss contributing to shock; these symptoms occur within 1 or 2
weeks after irradiation.
100% fatal within 60 days if untreated. Erythema
occurs. Lymphocyte count decreases from normal level of about 2,000 or 2,500
to about 500 in 24 hours. Cognitive impairment.
incapacitation. Symptoms may occur within an hour after exposure. Diarrhea,
fever, electrolyte imbalance. Mortality rate high even with treatment.
of symptoms within minutes. Neurovascular symptoms occur within several hours
to about 3 days after exposure. These include a steady deteriorating state of
conscience with eventual coma and death.
To convert “rems” to “Sieverts” multiply by 0.01
Individual Protection Against a
The U.S. Center for Disease Control and Prevention has
issued the following advice for individuals and families in case of a nuclear
How can I protect my family and
myself during a nuclear blast?
In the event of a nuclear blast,
a national emergency response plan would be activated and would include
federal, state, and local agencies.
Following are some steps recommended by the World Health Organization if
a nuclear blast occurs:
If you are near the blast
when it occurs:
If you are outside when
the blast occurs:
- Turn away and close and cover your eyes to
prevent damage to your sight.
- Drop to the ground face down and place your
hands under your body.
- Remain flat until the heat and two shock
waves have passed.
If you are already in a
shelter or basement:
- Find something to cover your mouth and nose,
such as a scarf, handkerchief, or other cloth.
- Remove any dust from your clothes by
brushing, shaking, and wiping in a ventilated area—however, cover your
mouth and nose while you do this.
- Move to a shelter, basement, or other
underground area, preferably located away from the direction that the wind
- Remove clothing since it may be contaminated;
if possible, take a shower, wash your hair, and change clothes before you
enter the shelter.
If you are advised to
- Cover your mouth and nose with a face mask or
other material (such as a scarf or handkerchief) until the fallout cloud
- Shut off ventilation systems and seal doors
or windows until the fallout cloud has passed. However, after the fallout
cloud has passed, unseal the doors and windows to allow some air
- Stay inside until authorities say it is safe
to come out.
- Listen to the local radio or television for
information and advice. Authorities may direct you to stay in your shelter
or evacuate to a safer place away from the area.
- If you must go out, cover your mouth and nose
with a damp towel.
- Use stored food and drinking water. Do not
eat local fresh food or drink water from open water supplies.
- Clean and cover any open wounds on your body.
to the radio or television for information about evacuation routes, temporary
shelters, and procedures to follow.
you leave, close and lock windows and doors and turn off air conditioning,
vents, fans, and furnace. Close
disaster supplies with you (such as a flashlight and extra batteries,
battery-operated radio, first aid kit and manual, emergency food and water,
nonelectric can opener, essential medicines, cash and credit cards, and sturdy
your neighbors may require special assistance, especially infants, elderly
people, and people with disabilities.
Treatment for Radiation Exposure
exposure occurs because of radioactive fallout or contact with dust
containing the radioactive isotopes, about 95% of the external radioactive
material can be removed by taking off the victim’s clothing and shoes and
washing with water. Further
decontamination may require the uses of bleaches and/or mild abrasives.
is essential to protect against inhalation of radioactive-contaminated
dust by using appropriate air-purifying respirators or SCBA.
should be treated for hemorrhage and shock. Open wounds are usually irrigated to
cleanse them of any radioactive traces.
radioactive material is ingested, treatment is given to reduce absorption
and enhance excretion and elimination.
This may include stomach pumping, laxatives, and use of aluminum
radioactive isotopes are in the victim’s internal organs and tissues,
treatment may include various blocking and diluting agents. The treatment may include where
appropriate mobilizing agents such as ammonium chloride, diuretics,
expectorants, and inhalants to force tissues to release the
materials. Other treatments may
include chelating agents and use of potassium iodide.
treatments exist (see table 1) to increase survival if a person receives a
radiation dose in the 100 to 600+ Rem
range. The condition where a person
is exposed to high levels of radiation is called Acute Radiation Syndrome
(ARS) and is characterized by damage to the production of major blood
elements in the blood marrow.
Minimal treatment includes fluid replacement, antibiotics, and
prevention of infection. More aggressive treatment includes bone marrow
resuscitation therapy. Hollis-Eden
Pharmaceuticals with the U.S. Armed Forces Radiobiology Research Institute
have developed a drug (NEUMINE, or HE2100) for bone marrow treatment. The drug was demonstrated in non-human
primates to be very effective in treating the bleeding and infections (neutropenia and thrombocytopenia) resulting from
radiation exposure. CBS 60 Minutes
aired a program on this drug on 29 January 2006, acknowledged its success,
but questioned whether it would be available on a mass basis in the event
of a nuclear attack. More details
are at the drug company website, http://www.holliseden.com/content/?page_id=79.