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Effects of nuclear explosions

2007 Schools Wikipedia Selection. Related subjects: Military History and War

   A 23 kiloton tower shot called BADGER, fired on April 18, 1953 at the
   Nevada Test Site, as part of the Operation Upshot-Knothole nuclear test
   series.
   Enlarge
   A 23 kiloton tower shot called BADGER, fired on April 18, 1953 at the
   Nevada Test Site, as part of the Operation Upshot-Knothole nuclear test
   series.

                                                           Nuclear weapons
                                          One of the first nuclear bombs.
                                             History of nuclear weapons
                                                  Nuclear warfare
                                                 Nuclear arms race
                                              Weapon design / testing
                                                 Nuclear explosion
                                                  Delivery systems
                                                 Nuclear espionage
                                                   Proliferation
                                                                    States
                                                  Nuclear weapons states

                                              US · Russia · UK · France
                                                China · India · Pakistan
                                                     Israel · North Korea

   A nuclear explosion occurs as a result of the rapid release of energy
   from an uncontrolled nuclear reaction. The driving reaction may be
   nuclear fission, nuclear fusion or a multistage cascading combination
   of the two.

   Atmospheric nuclear explosions are associated with " mushroom clouds"
   although mushroom clouds can occur with large chemical explosions and
   it is possible to have an air burst nuclear explosion without these
   clouds. Atmospheric nuclear explosions produce large amounts of
   radiation and radioactive debris. In 1963, all nuclear and many
   non-nuclear states signed the Limited Test Ban Treaty, pledging to
   refrain from testing nuclear weapons in the atmosphere, underwater, or
   in outer space. The treaty permitted underground tests.

   The primary application to date has been military (i.e. nuclear
   weapons). However, there are other potential applications, which have
   not yet been explored, or have been considered all but abandoned. They
   include:
     * Nuclear pulse propulsion, including using a nuclear explosion as
       asteroid deflection strategy.
     * An unsafe prototype of fusion power; see PACER
     * Peaceful nuclear explosions

History

   A nuclear explosion (nuclear detonation) has occurred on Earth twice
   using a nuclear weapon during war (during World War II, the atomic
   bombings of Hiroshima and Nagasaki), about 2,000 times during testing
   of nuclear weapons, and about 27 times in the U.S. and 156 in the
   U.S.S.R. in a series of peaceful nuclear explosions; see Operation
   Plowshare; and Nuclear Explosions for the National Economy

Milestone nuclear explosions

   The following list is of milestone nuclear explosions. In addition to
   the atomic bombings of Hiroshima and Nagasaki, the first nuclear test
   of a given weapon type for a country is included, and tests which were
   otherwise notable (such as the largest test ever). All yields
   (explosive power) are given in their estimated energy equivalents in
   kilotons of TNT (see megaton).
   Date Name Yield (kt) Country Significance
   Jul 16 1945 Trinity 19 United States USA First fission weapon test
   Aug 6 1945 Little Boy 15 United States USA Bombing of Hiroshima, Japan
   Aug 9 1945 Fat Man 21 United States USA Bombing of Nagasaki, Japan
   Aug 29 1949 Joe 1 22 Union of Soviet Socialist Republics USSR First
   fission weapon test by the USSR
   Oct 3 1952 Hurricane 25 United Kingdom UK First fission weapon test by
   the UK
   Nov 1 1952 Ivy Mike 10,200 United States USA First "staged"
   thermonuclear weapon test (not deployable)
   Aug 12 1953 Joe 4 400 Union of Soviet Socialist Republics USSR First
   fusion weapon test by the USSR (not "staged", but deployable)
   Mar 1 1954 Castle Bravo 15,000 United States USA First deployable
   "staged" thermonuclear weapon; fallout accident
   Nov 22 1955 RDS-37 1,600 Union of Soviet Socialist Republics USSR First
   "staged" thermonuclear weapon test by the USSR (deployable)
   Nov 8 1957 Grapple X 1,800 United Kingdom UK First (successful)
   "staged" thermonuclear weapon test by the UK
   Feb 13 1960 Gerboise Bleue 60 France France First fission weapon test
   by France
   Oct 31 1961 Tsar Bomba 50,000 Union of Soviet Socialist Republics USSR
   Largest thermonuclear weapon ever tested
   Oct 16 1964 596 22 People's Republic of China China First fission
   weapon test by China
   Jun 17 1967 Test No. 6 3,300 People's Republic of China China First
   "staged" thermonuclear weapon test by China
   Aug 24 1968 Canopus 2,600 France France First "staged" thermonuclear
   test by France
   May 18 1974 Smiling Buddha 12 India India First fission nuclear
   explosive test by India
   May 11 1998 Shakti I 43 India India First potential fusion/boosted
   weapon test by India
   (exact yields disputed, between 25kt and 45kt)
   May 13 1998 Shakti II 12 India India First fission "weapon" test by
   India
   May 28 1998 Chagai-I ~9 Pakistan Pakistan First fission weapon test by
   Pakistan
   Oct 9 2006 Hwadae-ri <1 North Korea North Korea First fission device
   tested by North Korea

   "Deployable" refers to whether the device tested could be
   hypothetically used in actual combat (in contrast with a
   proof-of-concept device). "Staging" refers to whether it was a "true"
   hydrogen bomb of the so-called Teller-Ulam configuration or simply a
   form of a boosted fission weapon. For a more complete list of nuclear
   test series, see List of nuclear tests. Some exact yield estimates,
   such as that of the Tsar Bomba and the tests by India and Pakistan in
   1998, are somewhat contested among specialists.

Effects of a nuclear explosion

   The energy released from a nuclear weapon comes in four primary
   categories:
     * Blast—40-60% of total energy
     * Thermal radiation—30-50% of total energy
     * Ionizing radiation—5% of total energy
     * Residual radiation ( Nuclear fallout)—5-10% of total energy

   An American nuclear test.
   Enlarge
   An American nuclear test.

   However, the above values vary depending on the design of the weapon,
   and the environment in which it is detonated. The interaction of the
   X-rays and debris with the surroundings determines how much energy is
   produced as blast and how much as light. In general, the denser the
   medium around the bomb, the more it will absorb, and the more powerful
   the shockwave will be. Thermal radiation drops off the slowest with
   distance, so the larger the weapon the more important this effect
   becomes. Ionizing radiation is strongly absorbed by air, so it is only
   dangerous by itself for smaller weapons. Blast damage falls off more
   quickly than thermal radiation but more slowly than ionizing radiation.

   The dominant effects of a nuclear weapon (the blast and thermal
   radiation) are the same physical damage mechanisms as conventional
   explosives, but the energy produced by a nuclear explosive is millions
   of times more per gram and the temperatures reached are in the tens of
   millions of degrees.

   The energy of a nuclear explosive is initially released in the form of
   gamma rays and neutrons. When there is a surrounding material such as
   air, rock, or water, this radiation interacts with the material,
   rapidly heating it to an equilibrium temperature in about a
   microsecond. The hot material emits thermal radiation, mostly soft
   X-rays, which accounts for 75% of the energy of the explosion. In
   addition, the heating and vaporization of the surrounding material
   causes it to rapidly expand and the kinetic energy of this expansion
   accounts for almost all of the remaining energy.

   When a nuclear detonation occurs in air near sea level, most of the
   soft X-rays in the primary thermal radiation are absorbed within a few
   feet. Some energy is reradiated in the ultraviolet, visible light and
   infrared spectrum, but most of the energy heats a spherical volume of
   air. This forms a fireball and its associated effects.

   In a burst at high altitudes, where the air density is low, the soft
   X-rays travel long distances before they are absorbed. The energy is so
   diluted that the blast wave may be half as strong or less. The rest of
   the energy is dissipated as a more powerful thermal pulse.

   In 1945 there was some initial speculation among the scientists
   developing the first nuclear weapons that there might be a possibility
   of igniting the Earth's atmosphere with a large enough nuclear
   explosion. This would concern a nuclear reaction of two nitrogen atoms
   forming a carbon and an oxygen atom, with release of energy. This
   energy would heat up the remaining nitrogen enough to keep the reaction
   going until all nitrogen atoms were consumed. This was, however,
   quickly shown to be unlikely enough to be considered impossible .
   Nevertheless, the notion has persisted as a rumour for many years.

Direct effects

Blast damage

   Overpressure ranges from 1 to 50 psi of a 1 kiloton of TNT air burst as
   a function of burst height. The thin black curve indicates the optimum
   burst height for a given ground range.
   Enlarge
   Overpressure ranges from 1 to 50 psi of a 1 kiloton of TNT air burst as
   a function of burst height. The thin black curve indicates the optimum
   burst height for a given ground range.

   The high temperatures and pressures cause gas to move outward radially
   in a thin, dense shell called "the hydrodynamic front." The front acts
   like a piston that pushes against and compresses the surrounding medium
   to make a spherically expanding shock wave. At first, this shock wave
   is inside the surface of the developing fireball, which is created in a
   volume of air by the X-rays. However, within a fraction of a second the
   dense shock front obscures the fireball, making the characteristic
   double pulse of light seen from a nuclear detonation. For air bursts at
   or near sea-level between 50-60% of the explosion's energy goes into
   the blast wave, depending on the size and the yield-to-weight ratio of
   the bomb. As a general rule, the blast fraction is higher for low yield
   and/or high bomb mass. Furthermore, it decreases at high altitudes
   because there is less air mass to absorb radiation energy and convert
   it into blast. This effect is most important for altitudes above 30 km,
   corresponding to <1 per cent of sea-level air density.

   Much of the destruction caused by a nuclear explosion is due to blast
   effects. Most buildings, except reinforced or blast-resistant
   structures, will suffer moderate to severe damage when subjected to
   overpressures of only 35.5 kilopascals (kPa) (5.15 pounds-force per
   square inch or 0.35 atm).

   The blast wind may exceed several hundred km/h. The range for blast
   effects increases with the explosive yield of the weapon and also
   depends on the burst altitude. Contrary to what one might expect from
   geometry the blast range is not maximal for surface or low altitude
   blasts but increases with altitude up to an "optimum burst altitude"
   and then decreases rapidly for higher altitudes. This is due to the
   nonlinear behaviour of shock waves. If the blast wave reaches the
   ground it is reflected. Below a certain reflection angle the reflected
   wave and the direct wave merge and form a reinforced horizontal wave,
   the so-called Mach stem (named after Ernst Mach). For each goal
   overpressure there is a certain optimum burst height at which the blast
   range is maximized. In a typical air burst, where the blast range is
   maximized for 5 to 20 psi (35 to 140 kPa), these values of overpressure
   and wind velocity noted above will prevail at a range of 0.7 km for 1
   kiloton (kt) of TNT yield; 3.2 km for 100 kt; and 15.0 km for 10
   megatons (Mt) of TNT.

   Two distinct, simultaneous phenomena are associated with the blast wave
   in air:
     * Static overpressure, i.e., the sharp increase in pressure exerted
       by the shock wave. The overpressure at any given point is directly
       proportional to the density of the air in the wave.
     * Dynamic pressures, i.e., drag exerted by the blast winds required
       to form the blast wave. These winds push, tumble and tear objects.

   Most of the material damage caused by a nuclear air burst is caused by
   a combination of the high static overpressures and the blast winds. The
   long compression of the blast wave weakens structures, which are then
   torn apart by the blast winds. The compression, vacuum and drag phases
   together may last several seconds or longer, and exert forces many
   times greater than the strongest hurricane.

   Acting on the human body, the shock waves cause pressure waves through
   the tissues. These waves mostly damage junctions between tissues of
   different densities ( bone and muscle) or the interface between tissue
   and air. Lungs and the abdominal cavity, which contain air, are
   particularly injured. The damage causes severe haemorrhaging or air
   embolisms, either of which can be rapidly fatal. The overpressure
   estimated to damage lungs is about 70 kPa. Some eardrums would probably
   rupture around 22 kPa (0.2 atm) and half would rupture between 90 and
   130 kPa (0.9 to 1.2 atm).

   Blast Winds: The drag energies of the blast winds are proportional to
   the cubes of their velocities multiplied by the durations. These winds
   may reach several hundred kilometers per hour.

Thermal radiation

   At the atomic bombing of Hiroshima, "shadows" were burnt into the walls
   by the flash burn of the thermal radiation from the bomb.
   Enlarge
   At the atomic bombing of Hiroshima, "shadows" were burnt into the walls
   by the flash burn of the thermal radiation from the bomb.

   Nuclear weapons emit large amounts of electromagnetic radiation as
   visible, infrared, and ultraviolet light. The chief hazards are burns
   and eye injuries. On clear days, these injuries can occur well beyond
   blast ranges. The light is so powerful that it can start fires that
   spread rapidly in the debris left by a blast. The range of thermal
   effects increases markedly with weapon yield. Thermal radiation
   accounts for between 35-45% of the energy released in the explosion,
   depending on the yield of the device.

   There are two types of eye injuries from the thermal radiation of a
   weapon:

   Flash blindness is caused by the initial brilliant flash of light
   produced by the nuclear detonation. More light energy is received on
   the retina than can be tolerated, but less than is required for
   irreversible injury. The retina is particularity susceptible to visible
   and short wavelength infrared light, since this part of the
   electromagnetic spectrum is focused by the lens on the retina. The
   result is bleaching of the visual pigments and temporary blindness for
   up to 40 minutes.
   On this victim of the atomic bombing of Hiroshima, the pattern of the
   kimono is clearly visible as burns on the skin.
   Enlarge
   On this victim of the atomic bombing of Hiroshima, the pattern of the
   kimono is clearly visible as burns on the skin.

   A retinal burn resulting in permanent damage from scarring is also
   caused by the concentration of direct thermal energy on the retina by
   the lens. It will occur only when the fireball is actually in the
   individual's field of vision and would be a relatively uncommon injury.
   Retinal burns, however, may be sustained at considerable distances from
   the explosion. The apparent size of the fireball, a function of yield
   and range will determine the degree and extent of retinal scarring. A
   scar in the central visual field would be more debilitating. Generally,
   a limited visual field defect, which will be barely noticeable, is all
   that is likely to occur.

   Since thermal radiation travels in straight lines from the fireball
   (unless scattered) any opaque object will produce a protective shadow.
   If fog or haze scatters the light, it will heat things from all
   directions and shielding will be less effective. Massive spread of
   radiation would also occur, which would be at the mercy of the wind.

   When thermal radiation strikes an object, part will be reflected, part
   transmitted, and the rest absorbed. The fraction that is absorbed
   depends on the nature and colour of the material. A thin material may
   transmit a lot. A light colored object may reflect much of the incident
   radiation and thus escape damage. The absorbed thermal radiation raises
   the temperature of the surface and results in scorching, charring, and
   burning of wood, paper, fabrics, etc. If the material is a poor thermal
   conductor, the heat is confined to the surface of the material.

   Actual ignition of materials depends on how long the thermal pulse
   lasts and the thickness and moisture content of the target. Near ground
   zero where the light exceeds 125 J/ cm², what can burn, will. Farther
   away, only the most easily ignited materials will flame. Incendiary
   effects are compounded by secondary fires started by the blast wave
   effects such as from upset stoves and furnaces.

   In Hiroshima, a tremendous fire storm developed within 20 minutes after
   detonation and destroyed many more buildings and homes. A fire storm
   has gale force winds blowing in towards the centre of the fire from all
   points of the compass. It is not, however, a phenomenon peculiar to
   nuclear explosions, having been observed frequently in large forest
   fires and following incendiary raids during World War II.

Indirect effects

Electromagnetic pulse

   Gamma rays from a nuclear explosion produce high energy electrons
   through Compton scattering. These electrons are captured in the earth's
   magnetic field, at altitudes between twenty and forty kilometers, where
   they resonate. The oscillating electric current produces a coherent
   electromagnetic pulse (EMP) which lasts about one millisecond.
   Secondary effects may last for more than a second.

   The pulse is powerful enough to cause long metal objects (such as
   cables) to act as antennae and generate high voltages when the pulse
   passes. These voltages, and the associated high currents, can destroy
   unshielded electronics and even many wires. There are no known
   biological effects of EMP. The ionized air also disrupts radio traffic
   that would normally bounce off the ionosphere.

   One can shield electronics by wrapping them completely in conductive
   mesh, or any other form of Faraday cage. Of course radios cannot
   operate when shielded, because broadcast radio waves can't reach them.

   The largest-yield nuclear devices are designed for this use. An air
   burst at the right altitude could produce continent-wide effects.

Ionizing radiation

   About 5% of the energy released in a nuclear air burst is in the form
   of ionizing radiation: neutrons, gamma rays, alpha particles, and
   electrons moving at incredible speeds, but with different speeds that
   can be still far away from the speed of light (alpha particles). The
   neutrons result almost exclusively from the fission and fusion
   reactions, while the initial gamma radiation includes that arising from
   these reactions as well as that resulting from the decay of short-lived
   fission products.

   The intensity of initial nuclear radiation decreases rapidly with
   distance from the point of burst because the radiation spreads over a
   larger area as it travels away from the explosion. It is also reduced
   by atmospheric absorption and scattering.

   The character of the radiation received at a given location also varies
   with distance from the explosion. Near the point of the explosion, the
   neutron intensity is greater than the gamma intensity, but with
   increasing distance the neutron-gamma ratio decreases. Ultimately, the
   neutron component of initial radiation becomes negligible in comparison
   with the gamma component. The range for significant levels of initial
   radiation does not increase markedly with weapon yield and, as a
   result, the initial radiation becomes less of a hazard with increasing
   yield. With larger weapons, above fifty kt (200 TJ), blast and thermal
   effects are so much greater in importance that prompt radiation effects
   can be ignored.

   The neutron radiation serves to transmute the surrounding matter, often
   rendering it radioactive. When added to the dust of radioactive
   material released by the bomb itself, a large amount of radioactive
   material is released into the environment. This form of radioactive
   contamination is known as nuclear fallout and poses the primary risk of
   exposure to ionizing radiation for a large nuclear weapon.

Earthquake

   The pressure wave from an underground explosion will propagate through
   the ground and cause a minor earthquake. Theory suggests that a nuclear
   explosion could trigger fault rupture and cause a major quake at
   distances within a few tens of kilometers from the shot point.

Summary of the effects

   The following table summarizes the most important effects of nuclear
   explosions under certain conditions.

                                   Effects

                      Explosive yield / Height of Burst

                                1 kT / 200 m

                                20 kT / 540 m

                                1 MT / 2.0 km

                               20 MT / 5.4 km

                   Blast—effective ground range GR / km

               Urban areas almost completely levelled (20 PSI)

                                     0.2

                                     0.6

                                     2.4

                                     6.4

                 Destruction of most civil buildings (5 PSI)

                                     0.6

                                     1.7

                                     6.2

                                     17

                 Moderate damage to civil buildings (1 PSI)

                                     1.7

                                     4.7

                                     17

                                     47

             Thermal radiation—effective ground range GR / km

                                Conflagration

                                     0.5

                                     2.0

                                     10

                                     30

                             Third degree burns

                                     0.6

                                     2.5

                                     12

                                     38

                             Second degree burns

                                     0.8

                                     3.2

                                     15

                                     44

                             First degree burns

                                     1.1

                                     4.2

                                     19

                                     53

   Effects of instant nuclear radiation—effective slant range^1 SR / km

                Lethal^2 total dose (neutrons and gamma rays)

                                     0.8

                                     1.4

                                     2.3

                                     4.7

                  Total dose for acute radiation syndrome^2

                                     1.2

                                     1.8

                                     2.9

                                     5.4

   ^1) For the direct radiation effects the slant range instead of the
   ground range is shown here, because some effects are not given even at
   ground zero for some burst heights. If the effect occurs at ground zero
   the ground range can simply be derived from slant range and burst
   altitude (Pythagorean theorem).

   ^2) "Acute radiation syndrome" corresponds here to a total dose of one
   gray, "lethal" to ten grays. Note that this is only a rough estimate
   since biological conditions are neglected here.

Other phenomena

   As the fireball rises through still air, it takes on the flow pattern
   of a vortex ring with incandescent material in the vortex core as seen
   in certain photographs. At the explosion of nuclear bombs sometimes
   lightning discharges occur. Not related to the explosion itself, often
   there are smoke trails seen in photographs of nuclear explosions. These
   are formed from rockets emitting smoke launched before detonation. The
   smoke trails are used to determine the position of the shockwave, which
   is invisible, in the milliseconds after detonation through the
   refraction of light, which causes an optical break in the smoke trails
   as the shockwave passes. A fizzle occurs if the nuclear chain reaction
   is not sustained long enough to cause an explosion. This can happen if,
   for example, the yield of the fissile material used is too low, the
   compression explosives around fissile material misfire or the neutron
   initiator fails.

Survivability

   This is highly dependent on factors such as proximity to the blast and
   the direction of the wind carrying fallout.

   There has also been controversy as to whether cockroaches would survive
   a nuclear blast. The answer is that they have a high degree of
   survivability, since they are resistant to radiation and can burrow
   underground for extended periods of time and avoid fallout. However,
   cockroaches would be instantly incinerated by the initial blast.

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