ExplosionsA Presentation by Paige Bennett and Dillon O’Connor

Explosion

An explosion is a sudden, violent change of potential

energy to work

Exothermic

All the stored energy within a substance provides force

across a distance

Basics of Explosions

Contain an oxidizer and a fuel (if it burns)

Form gases

Release intense heat

React rapidly

Require initiation

Explosive Material

Chemically or energetically unstable

When initiated:

Produces a sudden expansion of the material

Large changes in pressure (explosion)

Classifications of Explosives

Low explosives Burn through deflagration

Initiated by heat and require confinement to explode

High explosives Explode without confinement

Initiated by shock or heat

High Brisance (shattering effect)

Classified by rate of decomposition

Low Explosives

Auto-combustion at various rates ranging from a few

cm/s to 400 m/s.

Usually serve as propellant

Example: Gasoline

High Explosive

Detonate at rates ranging from 1,000 m/s to 8,500 m/s

Two classes based upon sensitivity

Primary: Extremely sensitive; burn rapidly or detonate if

ignited

Secondary: Relatively insensitive; may burn when ignited,

require detonation

Example: Warheads

Physical Properties

There are several key physical properties that define explosives Sensitivity Stability Power Brisance Density Volatility Hygroscopicity Toxicity

Sensitivity

Inclination of an explosive to ignite or detonate

Several kinds of sensitivity Impact, Friction, and Heat

Testing sensitivity Impact: distance through which a standard weight must be

dropped to cause the material to explode.

Friction: what occurs when a weighted pendulum scrapes across the material

Heat: temperature at which explosion of the material occurs

Stability

Molecular stability

Integrity of the compounds structure. If unstable, decomposition can take place at room temperature.

Temperature of storage

Rate of decomposition increases at higher temperatures. Highly stable between -10 and 35 degrees Celsius

Resilience to sunlight

Ultraviolet rays from the sun can cause explosive compounds to rapidly decompose

Power

Ability to perform work Various tests to evaluate

Cylinder expansion test Cylinder fragmentation test Detonation Pressure (Chapman-Jouget) Determination of critical Diameter Infinite diameter detonation velocity Pressure versus scaled distance Impulse verses scaled distance Relative bubble energy (RBE)

Cylinder Expansion and Air-Blast Tests are common

Measuring a Chemical Explosive Reaction

Thermochemistry deals with changes in internal energy (as heat) in chemical reactions.

Information can be learned based upon chemical laws or by analysis of products.

Characteristics that can be theoretically computed Oxygen balance

Heat of reaction

Volume of products

Potential energy

Nuclear Explosions

Chemical explosions are relatively simple

They consist of a series or multiple series of chemical

reactions for their energy

Nuclear explosions follow a more complex process

They rely upon fission or fusion to cause powerful chain

reactions at an atomic level for their energy

Fission

o Materials used to produce nuclear explosions by fission are certain isotopes of the elements uranium and plutonium.

o In nature, uranium consists mainly of two isotopes uranium-235 (about 0.7%) and uranium-238 (about 99.3%)

o The less abundant, uranium-235 is the readily fissionable species that is commonly used in nuclear weapons.

o Since plutonium is only found naturally in insignificant amounts, plutonium-239, which is the fissionable isotope used, is made artificially from uranium-238.

Fission Processo A neutron is accelerated towards the

uranium-235 nucleus making the nucleus unstable and it splits parts into two fissionproducts (Barium & Krypton), along with 2-3neutrons.

o The neutrons produced by the fission reaction cause other large atoms to fission, and their neutron production causes still other atoms to fission…leading to a chain reaction

o This entire process is very rapid and only takes a few millionths of a second.

o The resulting energy production heats the surrounding air and causes it to expand in the form of a blast wave.

Fission

Fusion Reactions *Much more powerful than fission*

• 2 main stages:• PRIMARY STAGE:

Regular fission chain reaction & the radiation produced from this reaction is used to heat the interior of the bomb to temperatures where fusion can happen.

• SECONDARY:Composed of lithium deteuride which splits apart under intense heat into 6 Li atoms and deuterium ions.1 neutron from fission reaction reacts with the 6Li to produce 4 He and 3 H

Stars = or < sunStars > sun

Damage

o 4 categories:1.Blast, (40 – 50%)2. Thermal Radiation, (30 – 50%)

3. Ionizing Radiation, (5%)4. Residual Radiation (5-10%)

However, depending on the design of the weapon and the environment in which it is detonated the energy distributed to these categories can be increased or decreased.

http://www.youtube.com/watch?v=WwlNPhn64TA&feature=related

BLAST EFFECTS

o The air immediately behind the shock front is accelerated to high velocities and creates a powerful wind.

o These winds in turn create dynamic pressure against the objects facing the blast. Shock waves cause a virtually instantaneous jump in pressure at the shock front.

o The combination of the pressure jump (called the overpressure) and the dynamic pressure causes blast damage. Both the overpressure and the dynamic pressure reach to their maximum values upon the arrival of the shock wave.

o They then decay over a period ranging from a few tenths of a second to several seconds, depending on the blast's strength and the yield.

THERMAL RADIATION

o A primary form of energy from a nuclear explosion is thermal radiation. Initially, most of this energy goes into heating the bomb materials and the air in the vicinity of the blast. Temperatures of a nuclear explosion reach those in the interior of the sun, about 100,000,000° Celsius, and produce a brilliant fireball.

o Two pulses of thermal radiation emerge from the fireball. The first pulse, which lasts about a tenth of a second, consists of radiation in the ultraviolet region. The second pulse which may last for several seconds, carries about 99 percent of the total thermal radiation energy.

o It is this radiation that is the main cause of skin burns and eye injuries suffered by exposed individuals and causes combustible materials to break into flames.

o Thermal radiation damage depends very strongly on weather conditions. Clouds or smoke in the air can considerably reduce effective damage ranges versus clear air conditions.

http://www.youtube.com/watch?v=gz3F-02FwZc&feature=related

Nuclear Radiation

1. Ionizing Radiation:• High energy particles and rays are created.• They have enough energy to “ionize” neutral atoms• Some of this ionized radiation is absorbed by the air, but neutrons

and gamma and X-rays (extremely high energy forms of light) do reach the ground, and create damage.

• Close to ground zero of both explosions, dosages were high enough to be immediately lethal for persons not already killed by the blast or fire.

Nuclear Radiation (cont.)

2. Residual Radiation, the hazards in the “Fallout”• This radiation comes from the weapon debris, fission products, and, in the

case of a ground burst, radiated soil.• There are over 300 different fission products that may result from a fission

reaction. This radiation hazard comes from radioactive fission fragments with half-lives of seconds to a few months, and from soil and other materials in the vicinity of the burst that were made radioactive.

• Their principal mode of decay is by the emission of beta particles and gamma radiation. Most of the radiation hazard from nuclear bursts comes from short-lived radionuclides external to the body; these are generally confined to the locality downwind of the weapon burst point.

Particles found in Fallout

o Many fallout particles are especially hazardous biologically. Some of the principal radioactive elements are as follows:

Strontium 90

Iodine 131

Tritium

Cesium 137

Plutonium