My Explosives Report

I wrote this report a few years ago in 8th grade for my "8th Grade Project", the project every 8th grader does at my old school. I did a lot of research on it, and tried to cover as much of the explosives spectrum as possible. Most of the information is still rather basic, but it covers a lot. I don't know anyone who knows much about explosives, so I was the most knowledgeable person to proofread it. There may be errors here, if you catch any, it would be nice for you to tell me about them!

Forgive the crappy diagrams, I made them in paint, and am too lazy to redo them with Freehand.

Explosives

Table of Contents

Introduction
The First Explosive
Chemical Explosives
Low Explosives
LE Uses: Fireworks
LE Uses: Guns
LE Uses: Other
High Explosives
HE Uses: Military
HE Uses: Industrial
HE Uses: Commercial
HE Uses: Agricultural
Mechanical Explosives
Nuclear Explosives
Nuclear Weapons: Types
Nuclear Weapons: History
Nuclear Weapons: Delivery Systems
Antimatter
Conclusion
Bibliography

Introduction

An explosive is any device or material that can be made to produce a large amount of rapidly expanding gas in a short period of time. There are three basic types of explosives. They are chemical, mechanical, and nuclear.

The first explosive was black powder, commonly known as gunpowder. It is a chemical low explosive. Black powder is a mixture of potassium nitrate, charcoal, and sulfur. It is a powder with a black color, hence the name black powder. Nobody knows for sure when or where black powder originated, but it was probably in China. Estimates as to when it was invented range from the 6th to the 10th century. According to one story, Chinese chemists were trying to make people immortal. Sulfur was used for lowering fevers. The potassium nitrate and charcoal may have been believed to have special properties, or just a result of random experimentation. Another story says it was invented by alchemists trying to make gold. Somehow, potassium nitrate, charcoal, and sulfur were mixed, and black powder was invented.

The most common modern black powder contains 75% potassium nitrate, 15% charcoal, and 10% sulfur. Potassium nitrate is the oxidizer. This means it contains chemically bound oxygen and supplies it for the chemical reaction. Sulfur and charcoal are both fuels, meaning they burn creating heat, light, and gases. Sulfur is also an ignition promoter, meaning it makes the mixture easier to ignite.

The First Explosive

The first use of black powder was probably in fireworks as early as the 7th century. Fireworks were used in religious ceremonies to scare away evil spirits. Later, they were uses for signaling and warfare. In wars, bamboo tubes were filled with black powder to make simple bombs. Simple rockets were also made around the 12th century. Neither was very powerful, so they were mostly used to scare horses.

The Arabs learned of black powder from the Chinese some time between the 7th and 12th centuries. The first firearms were probably made by the Arabs in the 12th or 13th century. The first guns shot flaming materials, and later ones used stones, metals, and arrows of different shapes, sizes, and types. The guns were made with bamboo tubes reinforced with iron. They were very dangerous and exploded accidentally quite often.

Chemical Explosives

Of the three types of explosives, chemical is the most common. Chemical explosives use extremely rapid chemical reactions to produce gases, heat, and light. They are divided into two categories, high explosives, and low explosives.

Low Explosives

Low explosives (LE) are different from high explosives in several ways. The biggest difference is power. High explosives are much more powerful. Low explosives do not detonate, except in a few exceptions. They work by extremely rapid burning, called deflagration, instead of rearrangement of molecules. Because of this, LE's usually need to be contained to explode. The casing is to briefly contain the rapidly expanding gases for a fraction of a second. Once sufficient pressure has built up (a few thousandths of a second) it is released all at once from the container. Many LE's will explode without containment if there is a large enough amount in a pile. For example, black powder will explode unconfined if there is 500 pounds or more in a pile. If it is spread out, it will just flare up. One exception is flash powder. It can explode unconfined with only 30 grams. It is most commonly made with 70% potassium perchlorate, and 30% finely powdered aluminum. It is very powerful for a low explosive.

LE Uses: Fireworks

Black powder, the first explosive, is a low explosive (LE). Its fist use was in fireworks in China. Later uses were in guns and mining. Except for fireworks and a few other applications, LE's were almost entirely replaced by HE's by the mid 1800's.

The first fireworks were black powder filled tubes. After that came fountains, rats, wheels, rockets, aerial shells, comets, and mines. Later fireworks included cakes, candles, tourbillions, and spinners.

Firecracker-type fireworks are called salutes. A salute is a device that explodes on the ground and is primarily for sound. They have cylindrical casings and a fuse coming out the end or side. The casing is made of cardboard. They can be filled with many different types of explosives, but flash powder is most commonly used. Although there are many flash powder formulas, the most common is a 70/30 mix of potassium perchlorate and fine aluminum powder. The ends of the tube are sealed with glue, clay, or glued paper discs.

Fountains are either cylindrical or conical; either way, they do the same thing. A fountain is filled with packed powder and has a nozzle pointing up. They shoot colored flames and sparks out the nozzle. The height can be anywhere from 6" to 100', as is the case with Clarks Giant Steel Fountain. Fountains are like upside-down rocket engines with a low thrust. Different chemicals are added for different colors, metals can be added for sparks, they can whistle, and they can crackle.

Rats are small fountains with more thrust. When ignited, they zoom around on the ground or along a guide wire. They can have all the same effects of a fountain.

Wheels are fireworks that spin around a central axis with a shower of sparks. They have two or more drivers (the fireworks that spin the wheel) and are pretty much rats that spin in a circle.

Pyrotechnic rockets fly through the air and usually have an aerial shell or salute type payload. These kinds of rockets were the first step towards more advanced kinds like guided missiles and space ships. Pyrotechnic rockets usually use strongly compressed black powder as a propellant. The powder needs to be compressed or the rocket will explode. This is because of something called surface area. For example, small, thin sticks will ignite easier and burn much faster than a log. With black powder, it is pressed into a single chunk, called a grain, to control the burn rate.

Aerial shells are some of the most beautiful and complex fireworks. There are two types, spherical and cylindrical; but they do the same thing. They have a main casing with the break powder, stars, and any inserts that may be in it. A second section contains the lift charge. The two sections are joined by a length of time fuse. The lift charge is black powder, and is ignited by quick match or an electric match. Quick match is a very fast burning fuse used to connect multiple devices so they ignite simultaneously. In aerial shells it runs from the lift to the end of the launch tube. When the lift charge is lit, it shoots the shell out of the tube and at the same time lights the time fuse. The time fuse is used to determine the delay between when the shell is fired and when it explodes. The time fuse ignites the burst charge, also called break powder, which makes the shell explode. Along with bursting the shell, it creates enough heat to ignite the stars in the shell. Stars are hard balls of chemical mixes called star compositions. They burn brightly with different colors. Stars can also have effects like glitter, flitter, strobe, willow, smoke, and split comet.

There are two kinds of shells, spherical and cylindrical. Spherical shells are also called oriental shells because they are the type first made in China and the most common type used there. Cylindrical shells are also called Italian shells because they are the type Italy focused on when fireworks came to Europe. Besides China, Italy was one of the biggest contributors to pyrotechnic development.

Besides differences in construction, there are differences in style. The Chinese, who invented spherical shells and use it most, focus on color and symmetry. Spherical shells produce much better round breaks then cylindrical shells. Cylindrical shells were probably invented in China, but once in Europe, were used and developed by several counties, especially Italy. The main focus of cylindrical shells is usually multiple effects. These effects include multiple breaks (such as the one shown in the diagram), rocket or salute inserts, crackle, and combined effects.

Comets and mines are both similar to aerial shells because they are launched into the air from tubes. The biggest difference is they do not have casings and are burning when they leave the tube. Mines shoot many stars into the air at once, like a shotgun. Comets are basically one large star.

Cakes are multiple small shells fused together to fire in a sequence. They can have tubes of multiple sizes on the same device. They can have any number of shells, but it is usually between 25 and 75.

Roman candles, often called just candles, are tubes that fire stars one at a time in succession. They usually have five or ten shots. The stars can have almost all the effects of aerial shells. There are several design methods. The most common two are shown in the diagrams.

The candle in the first diagram uses a packed chemical delay composition. The second has a fuse running the length of the tube of the candle for delay.

Tourbillions, also called helicopters or spinners, are cylindrical tubes with wings. The tube is similar to a rocket engine, except that the nozzle is on the side. The wings are perpendicular to the tube and have a twist so they spin and lift off the ground. They can also be without wings to spin on the ground.

LE Uses: Guns

Although nearly all modern firearms use double-base smokeless powder, black powder was used for centuries. Single-base smokeless powder is also used in guns, and is a low explosive. Neither one is actually a powder, but they are in grains. Single-base powder is nitrated cellulose called nitrocellulose. Double-base powder is nitrocellulose mixed with 20-40% nitroglycerin. Neither one is completely smokeless, but they produce much less smoke than black powder. Smokeless powders have several other advantages over black powder. They are more powerful, leave much less residue in the barrel, have less flash, are less sensitive, are more water resistant, more reliable, and have more consistent burn rates.

LE Uses: Other

Low explosives have several uses other than fireworks and guns. They are used in road flares to warn of an accident, flares dropped from planes for illumination during emergency landings, and in parachute flares used to illuminate battlefields at night. Other uses of flares are in flare guns for emergency signaling or communication. Pyrotechnic smoke screens are used by the military to obscure views and in rockets to mark targets.

High Explosives

High Explosives (HE) are different from low explosives (LE) because they detonate. Under some conditions a HE can burn without detonation if it is thinly spread and ignited without a shock wave. Some examples of high explosives are trinitrotoluene (TNT), pentaerythritoltetranitrate (PETN), and cyclotrimethylenetrinitramine (RDX). High explosives are divided in many different ways, but the most important is primary and secondary. Primary explosives detonate from sources such as sparks, flame, and impact. Some examples of primary explosives are mercury fulminate, lead azide, and diazodinitrophenel (DDNP). In most cases, secondary explosives require a shock wave to detonate. Examples of secondary explosives are dynamite, ammonium picrate (Explosive D), and trinitrophenylmethlnitramine (tetryl). Some explosives can be both a primary and a secondary. For example, tetryl is a primary explosive in its normal form, but is a secondary explosive when compressed. Usually, the shock wave used to detonate a secondary explosive comes from a primary explosive.

High explosives detonate, meaning they decompose extremely quickly, releasing large amounts of heat and gas. They work either by the rupture and rearrangement of molecules or in a way similar to extremely rapid burning. This process happens in a few millionths of a second. The sensitivity of an explosive is determined by the strength of the molecular bonds. For example, the bonds on nitroglycerin (NG) are much weaker than ANFO; so it is easier to set off.

TNT, a common HE, works by rupture and rearrangement of molecules. A TNT molecule consists of carbon, hydrogen, oxygen, and nitrogen. When hit by a shock wave of sufficient force, the molecules collapse. The oxygen atoms combine with the carbon and hydrogen atoms forming carbon dioxide and water vapor. The freed nitrogen atoms become nitrogen gas. Besides creating a rapidly expanding gas cloud, it is very hot.

TNT is a very common explosive used for many different things. While it is not very powerful compared to other common explosives like PETN, RDX (which is 140% more brisant than TNT), and cyclotetramethylenetetranitramine (HMX, the most powerful explosive used on a significant scale), it is important as a desensitizer mixed with other explosives. It is also valuable because it is castable, meaning it can be melted easily to fill containers. Many explosives are not castable and are mixed with TNT so they can fill casings easier. There are many explosive mixtures of TNT and another HE. The most common are listed below. They are mixed in different percentages to get the desired properties.

TNT + HMX = octol
TNT + RDX = cyclotol
TNT + PETN = pentolite
TNT + tetyl = tetrytol
TNT + ammonium nitrate (AN) = amatol
TNT + ammonium picrate = picratol

There are several factors that determine which explosives are used for what. These are sensitivity, the amount of force it takes to detonate; the volume and kind of gases produced; brisance, the speed with which an explosive reaches its maximum pressure; and hgroscocipity, its tendency to absorb water.

HE Uses: Military

High explosives are the most commonly used explosives and are the basis of modern warfare. Without explosives, we would probably still use swords, bows, and catapults.

The first explosive weapons were black powder-filled bamboo tubes. Later, cast iron was used making them more powerful and producing more shrapnel. Other early explosive weapons included rockets and early guns. Modern explosive weapons include guided missiles, cluster bombs, and torpedoes.

Nearly all guns use an explosive propellant. There are guns that use compressed air or nitrogen, but their use is very limited. All artillery shells use explosive propellants and can have many different kinds of warheads. There are basic HE shells, shrapnel shells, shells that disperse mines or cluster bombs, and nuclear shells.

Airplanes revolutionized warfare and allowed explosive weapons to be dropped from the air. There are many kinds of air-dropped bombs. There are bombs that explode on impact, bombs with proximity fuses to explode in the air above a target and release shrapnel, and bombs with reinforced casing and delayed impact fuses. These bombs fall through several floors of a building or through reinforced ceilings to explode inside the building. One example of this kind of bomb is the Tallboy used in WWII. It was used for destroying underground German U-boat pens. There are bombs designed to destroy dams that are released at high speed while flying over the water. These bombs skip across the water until they hit the dam, sink and explode underwater. Other bombs include leaflet bombs that disperse printed messages and incendiary bombs.

Glide bombs are like normal, air-dropped bombs except they have wings and are guided by remote control. They can glide up to five miles to a target.

Cluster bombs are delivered by planes, missiles, or artillery. They can carry between 100 and 300 clusters called bombletts, depending on their size. The clusters are released in the air and cover a large area. They are particularly useful against troops, parked aircraft, and light vehicles.

Smart bombs are guided to their targets by lasers and are very accurate. This allows smaller bombs to be used so more can be carried by each plane and less explosives to be used, reducing collateral damage.

Missiles are very common weapons that serve many different purposes. There are anti-aircraft (AA), anti-ship (AS), anti-tank (AT), and missiles for use against buildings. AA missiles can be either radar guided (such as the AIM-120 AMRAAM) or infrared guided (such as the AIM-9). They have proximity fuses to detonate when they are a certain distance from the target. They can be launched from aircraft, boats, or from the ground. AA missiles can also be used to intercept other missiles. AS missiles (such as the Harpoon missile) are launched from planes, shore sites, submarines, or other boats. AT missiles (such as the LAWS) are launched from aircraft, ground vehicles, or small launchers that can be carried by a single person. They have either shaped charge warheads, or less common, squash warheads. Shaped charge explosives are specially shaped so most of the force is directed in one direction and can pierce thick armor. Squash warheads are different because they are not shaped charges. They have a very short delay between hitting the target and detonation that allows the semi-plastic explosive to spread out over the target surface so more of it is directly on the target.

There are two kinds of military mines, underwater and land mines. Underwater mines are for destroying boats and submarines. They can be delivered by boat, plane, or submarine. They usually have about 500 pounds of explosives. The most commonly used explosive for torpedoes and underwater mines in US weapons is torpex. Torpex is a mixture of TNT, RDX, and aluminum. Old mines had contact fuses, but newer ones explode when they detect the acoustic signature or magnetic field of a target.

There are two kinds of land mines, anti-tank (AT) and anti-personnel (AP). Both use pressure fuses to explode when the target is directly above the mine. Land mines are usually buried, but AP mines can be dropped from planes, artillery, and missiles.

Torpedoes are fired from submarines, boats, and aircraft and are used to sink boats and submarines. They travel underwater at speeds of 50-60 knots. The warheads are torpex and weight 400-500 pounds. Because they hit targets below the waterline, sometimes a single hit can sink a boat.

Fuel-Air Explosives (FAE's) are some of the most powerful non-nuclear explosives. They work by spraying fuel oil into the air and igniting it. The fuel oil is sprayed by a canister on a parachute. Once all the fuel is sprayed, the cloud is ignited by several HE initiators. FAE's were originally designed for clearing large minefields, but they are also very effective against troops, buildings, and light vehicles.

Reactive armor is used on vehicles to defend against missiles. The sides of some vehicles have a layer of explosives that cover the sides. When a missile is detected, the explosives detonate an instant before the missile would hit. They are directed outward to do little damage to the vehicle, but can often destroy the missile or significantly reduce the damage.

HE Uses: Industrial

High explosives have several industrial uses; the most common is to bond metal. Some metals, like aluminum and steel, do not bond with conventional means. Explosive bonding can bond incompatible metals like aluminum and steel, titanium and steel, and stainless steel and normal steel. The two sheets of metal are placed about a quarter inch apart. An explosive called a plate charge is detonated on the top plate and the metals are pressed together with so much force they become bonded.

Explosives are also used to compress carbon to make diamond powder for grinding and cutting tools.

HE Uses: Commercial

The most common non-military uses of explosives are mining and quarrying. Other commercial uses of explosives include helping make roads, railways, and tunnels. Explosives help build canals and dams, widen and deepen harbors, and find oil. They can also be used to demolish buildings and other structures and put out fires.

A phone uses 42 different minerals and a color TV uses 35. All the minerals are mined with explosives. Even toothpaste, talcum powder, and many medicines contain minerals mined with explosives.

Limestone, concrete, and cement are all products of explosive quarrying. They allowed people to stop using cobblestones and bricks.

Explosives are used in mining and quarrying to blast rock into smaller pieces so that it can be moved and its resources removed. The earliest records of explosive mining are 1627 when black powder was used for mining in France.

The explosives used must be carefully selected. In underground mining, it is very important that the explosive does not make much smoke or hazardous fumes. One danger in underground mining is hitting a gas pocket or having a dust explosion. A dust explosion happens in a way similar to a FAE except that instead of a liquid fuel, it is dust. This is most common with coal dust and can be very dangerous. Rock can have pockets of methane or other flammable gases that could make an explosion more powerful than normal. To reduce these risks, a short, cool explosive is used. Short means that the duration of the flame is short and cool means that it is a lower temperature than most explosives. For example, TNT has a relatively hot detonation temperature, but if it is mixed with ammonium nitrate (AN) to form amatol, it will be cooler. The AN will also add more oxygen; so there will be less smoke from the explosion.

There are several requirements for explosives that are the same for mining and quarrying. The explosive needs to be insensitive to reduce the risk of accidents, it needs to be water resistant (in many cases, but not always) because boreholes are often wet, and it needs to have an appropriate amount of brisance. For military or demolition, a high brisance explosive is best because of its shattering force. For mining and quarrying, however, a low brisance explosive is best. This is because the purpose of mining and quarrying is to remove and recover ore, not blast it into a dust cloud.

One commonly used explosive, especially in quarrying, is ammonium nitrate/fuel oil (ANFO). It is cheap, very insensitive, and has a fairly low detonation velocity and brisance. For a comparison of detonation velocities, standard ANFO is 4,300 meters per second, and PETN is 8,400 m/s. High quality black powder explodes at only 500 m/s, with significant variation depending on confinement, showing the difference in power between high and low explosives. ANFO has countless variations, but the standard formula is 94% AN prills and 6% fuel oil. Many fuels can be used, such as diesel, kerosene, and white gas. Because ANFO is insensitive enough that it will not detonate with a commercial #8 detonator (the most powerful commercial detonator), it is considered a blasting agent rather than a blasting explosive. To set off standard ANFO, a detonator and booster are used. #8 commercial detonators have a 0.3 gram primary charge of tetryl and a 0.8 gram secondary charge of PETN. Military detonators often use lead azide, but it is being phased out by DDNP for health reasons. Boosters to detonate insensitive explosives like ANFO are usually made of PETN or a similar explosive. They are cylindrical to fit in boreholes and have a hole in them for the detonator. The detonator can be set off either by primacord or an electrical charge. Primacord is a core of PETN wrapped in a textile and plastic coating. It is very much like rope and can be tied in knots to connect lengths of cord.

Diagram 1 shows a detonator with an electric igniter. Diagram 2 is a side view of a borehole. Diagram 3 shows the firing sequence in a quarry. Quarry blasts are fired sequentially to reduce the shock wave.

Explosives are also used to clear paths for roads and railways. The biggest thing they do for that is help clear boulders. A powerful explosive such as dynamite is most often used.

Tunnels are important to transportation and many are built with the help of explosives. The earliest record of explosives I civil engineering is the construction of the Malpas Tunnel in France in 1679. Explosive tunneling is like mining, but a little safer. There is still the risk of a cave in, but there is not any risk of a gas or dust explosion. ANFO type explosives are usually used.

Gas and oil deposits can be located with seismic testing. Explosives are used to make shock waves. The waves are recorded by seismographs and compared. Large deposits partially absorb shock waves and the difference can be seen in seismographs.

Explosives can be used to demolish buildings quicker and safer than normal methods. Holes are drilled in the support columns of the building and they are filled with explosives. Dynamite is commonly used for concrete, RDX for metal, and the charges are connected with primacord. If done right, the main supports are shattered and the building collapses on itself or to one side. The direction it falls is very important and is a difficult part of the setup. It can be controlled by making the explosives on one side or area of the building detonate before the others. Underwater concrete piers are often removed with explosives also.

Some other uses of high explosives are putting out large fires, such as big coal and oil fires, and avalanche control.

HE Uses: Agricultural

Explosives have also found many uses in agriculture. They can be used to remove stumps and trees, break up boulders, split logs, plant trees, loosen soil, and dig post holes and ditches.

Stumps can be removed easily with explosives. They are very useful when a tractor is not available or the stump is particularly large or difficult to remove. One or more holes are dug on the sides of the stump, depending on its size. The placement depends on the type of root. If it is a bushy, fibrous root, the explosive is put near the central rot mass below the stump. If it is a long tap root, the explosive is placed farther down on one side. The most commonly used explosive used for stumps is ANFO. It is usually detonated by a #8 detonator and a quarter stick of dynamite as a booster. The amount of explosives used depends on the size of the stump. For stumps with a diameter of 2-3 feet, about a pound of ANFO is used. For larger stumps, multiple charges are often used.

Boulders often need to be removed from fields or other places. This is usually impossible to do by hand and often very difficult, if not impossible, to do with a tractor. In these cases, explosives are an extremely valuable tool. They break the rocks into smaller, more manageable pieces. Dynamite is often used because the rocks need to be broken into small chunks. The placement depends on how much of the rock is buried. If most of the rock is above ground, the explosive is placed under the rock. If it is mostly underground, the explosive is placed near the center of the exposed area on an indentation or crack, sometimes with tamping material like mud on top of the explosive.

Holes to plant trees can be dug quickly with explosives. A small hole is dug and the explosive is placed in it. Almost any explosive can be used, but the amount needs to be adjusted to the size of the tree roots and the compactness of the soil. Besides just making a hole, it also loosens the soil.

Sub-soiling, loosening soil, can be done with explosives. Sub-soiling is good because it helps to have loose soil for planting. ANFO is commonly used because the dirt should stay in the area, not blown away. Explosives are placed the same way as in quarrying, in a grid pattern, and are detonated sequentially.

Mechanical Explosives

Mechanical explosives work by overloading a container with air. The explosion is not a direct result of a chemical reaction. A simple analogy is a balloon. If you inflate it enough, it will pop. These explosives are not used very much because they are not very powerful and require more equipment. One benefit is there is no heat produced. This is good for underground mining where there is a high risk of gas pockets or dust explosions.

Nuclear Explosives

Nuclear explosives are the most powerful explosives except antimatter (discussed later). Nuclear weapons work by either fission or fission and fusion. Fission is the splitting of heavy nuclei and fusion is the joining of light nuclei. In fission, the heavy elements U235, a uranium isotope, and Pu239, plutonium are used. The center of a molecule is called the nucleus. It is made of protons and neutrons. When the nucleus of a U235 or Pu239 atom is hit by a free neutron it splits in a process called fission. This releases large amount of heat and energy. The core temperature is millions of degrees. The nucleus breaks into two smaller pieces and releases two or three free neutrons. These free neutrons run into other nuclei, creating a self-sustaining chain reaction. Dangerous radiation is also released.

Fusion is the opposite of fission, light atoms are joined. The elements usually used are the hydrogen isotopes tritium and deuterium. These combine to form helium and release energy. The reaction is thermonuclear (heat-induced). The more heat, the more atoms fuse; creating more energy. Because of the extremely high temperatures needed to initiate a thermonuclear reaction, a fission bomb is used as the trigger. Unlike fission, fusion does not produce radiation.

The power of nuclear weapons is measured in kilotons (kt) and megatons (mt). One kiloton is equivalent to one thousand tons of TNT. One megaton is equivalent to one million tons of TNT.

Nuclear Weapons: Types

There are two types of fission bombs; gun-type and implosion-type. Gun-type fission bombs work by forcing a smaller chunk of U235, called a plug, into a larger mass, called the target. About 40% of the fissile mass is in the plug. When the plug hits the target, the amount exceeds critical mass. This starts a uncontrolled chain reaction that makes the explosion.

Implosion-type fission bombs work by compressing a hollow sphere of fissile material around a fissile core. There is already enough fissile material for critical mass, but it does not explode until compressed because it is not all together. To compress the U235 or Pu239 (which is more common) it is surrounded in a shell of high explosives. These explosives are called lenses and are carefully shaped and fitted together so even pressure is applied to the fission sphere. There are two types of high explosive lenses in the HE sphere. The U235 or Pu239 must be held together for a couple millionths of a second. This is done most effectively by using explosives of different speeds. This means that after the first explosive detonates and compresses the fission sphere, the second explosive goes off an instant later. This creates more pressure, holding it together longer so that the fission of the Pu239 is more efficient. The explosive lenses must be very hard so they don't lose shape over long periods of storage. While many different mixtures are used, the first fast lenses were made of TNT, RDX, and wax. The slow lenses were made with TNT, nitrocellulose, barium nitrate, and aluminum powder.

Implosion-type bombs are much more efficient than gun-type bombs because they are compressed so more of the material fissions. They also use less fissile material. Four "Fat Man" implosion bombs could be made from the large amount of U235 in one "Little Boy" gun-type bomb.

Nuclear Weapons: History

The idea that splitting heavy atoms could create energy came around the early 1900's. In 1903, a scientist named Ernest Rutherford discovered that many heavy elements like uranium, radium, and polonium spontaneously split, releasing radiation. While his partner Frederick Soddy, at their laboratory at the Mcgill University in Canada, was looking at uranium as a source of electrical energy, Rutherford was looking at its use in weapons. He said, "Could a proper detonator be found, it was just conceivable that a wave of atomic disintegration might be started through matter, which would indeed make this old world vanish in smoke." Scientists continued experiments on splitting atoms and did a lot of theoretical work. When WWII began on September 3, 1939, many scientists increased their efforts to discover how a nuclear bomb could be made. The American and British governments said research on the weapons should proceed with the highest priority.

The essential part of a nuclear bomb is achieving a self-sustaining chain reaction. This means that enough nuclei are splitting and releasing secondary neutrons that the reaction will continue by itself. The first self-sustaining occurred in an experiment on December 2, 1942. The test was called Chicago Pile 1 (CP-1)and proved it was possible that if U235 of good purity was used, it could be a powerful weapon. U235 is an isotope of natural uranium, U238. U238 does not normally fission and absorbs neutrons. The U238 must be separated from the U235 for the fission sphere or it will absorb too many neutrons. U235 is very rare and occurs in less than 1% of uranium. Plutonium was discovered after the CP-1 experiment. Pu239 does not occur naturally. It is formed when U238 absorbs an extra neutron.

The Manhattan Project was started in 1942 and headed by General Leslie Groves. The program was devoted to making nuclear weapons. The head scientist was Robert J. Oppenheimer. Other scientists who played a part in the program were Albert Einstein and Enrico Fermi.

Through the Manhattan Project, the gun-type and implosion-type bombs were developed. The first one designed was the gun-type It used U235. Pu239 would not work in a gun-type bomb because the pieces could not be fired together fast enough to efficiently fission. To solve this problem, the implosion-type bomb was made to use Pu239. The implosion-type was much more complicated than the gun-type; so a full-scale test was done. The gun-type was not tested for two reasons. It was simpler and they did not have enough U235 to make a second bomb.

The Trinity Test at Alamogordo, New Mexico occurred on July 16, 1945. The bomb was on the top of a 100' tower and weighed about 9,000 pounds. The bomb, called "Gadget," exploded with a yield (the power of the explosion) somewhere between 18kt and 23kt. This was much more powerful than the 8kt to 10kt predicted yield.

On August 1, 1945, the Enola Gay, a B-29 bomber, dropped "Little Boy" on the Japanese city of Hiroshima. It was the first nuclear weapon used in war and the first ever gun-type bomb used. The bomb exploded at an altitude of about 1900' and had a yield of about 15kt. About 70,000 people died within 24 hours.

When Japan did not surrender, a second bomb was used. The bomb was an implosion-type named "Fat Man." It was carried by "Bock's Car," a B-29 bomber. The initial target was Kokura, but heavy clouds, enemy fighters and anti-aircraft fire forced them away. The plane was running low on fuel and the only other target in range was Nagasaki. Because they were very low on fuel, only one pass could be made. The bomb hit several miles from the intended target. It exploded at an altitude of about 1650' with a yield of about 21kt. About 40, 000 were killed initially, but nobody really knows the eventual death toll from either bomb.

In 1942, Oppenheimer's theoretical study group was primarily focused on fission bombs, but fusion was also considered. In 1946, Edward Teller suggested that lithium-6 could be used as a fusion fuel to boost the power of fission weapons. Work was still concentrated on fission, so progress on fusion weapons was slow. On January 31, 1950, President Truman announced that the US should start focusing on the development of fusion bombs. From there, development increased greatly.

The first fusion bomb test was "Ivy Mike," on November 1, 1952. The bomb had a yield of 10.4mt, by far the most powerful explosion up to that time. It was the first bomb to use the Teller-Ulam staged design. The design uses a large fission bomb at one end and a tank of fission fuel at the other end. Between these were a plutonium rod called a spark plug. The fusion fuel was liquid deuterium and was surrounded by a large U238 tamper. The tamper absorbed neutrons and added to the bomb's power from a process called fast fission. While U238 will not ordinarily fission, if it is hit by high speed neutrons released from fusion, it can fission. The first stage of Ivy Mike, a TX-5 fission bomb, had a yield of 50kt. The deuterium fusion produced 2.4mt of the yield. The 465 kg U238 tamper was the largest contributor to the large yield, it produced 7.9mt as a result of fast fission by fusion neutrons. The diagram below shows the Teller-Ulam configuration.

A later test named "Bravo" had a yield of 15mt, the largest US test. The largest nuclear test in history was on October 31, 1961, by the USSR. It was tested in Siberia and had a yield of 58mt.

Nuclear Weapons: Delivery Systems

For any weapon to be practical, it needs a way to get to the target reliably. Driving up to the target with a bomb on the truck is not usually an option. The first method of deliver for nuclear weapons was dropping unguided bombs from planes. The first bombs such as Little Boy were just like regular HE bombs with a different explosive. Newer bombs have parachutes for more getaway time, although air-dropped nuclear bombs are not very common.

Glide Bomb Units (GBU's) have wings and can glide up to 5 miles to a target. Another way to get longer range from a plane-dropped bomb is to use a method called a toss delivery. This is where gravity bombs are released from a plane while near the peak of a steep climb or while upside down and diving. With this technique, a standard gravity bomb travels in a arc and can travel about two miles to the target. Until GBU's and improved missiles were available, this was the best delivery system.

The next advancement came with the development of missiles with large payload capability. Early nuclear weapons were very heavy. Little Boy weighed 10,300 pounds. The first missiles were still launched from planes, but had much longer range. For example, the Blue Steel missile made in the 60's had a range of 220 miles.

Missiles are the most common delivery system for nuclear warheads. They can be launched from planes, mobile trucks, submarines, boats, silos, trains, anti-ship or aircraft missiles, tiny warheads that can be launched from bazooka type weapons, and even from space.

Mobile trucks and trains have the advantage of moving easily. A mobile target in much more difficult to locate, track, and attack than a stationary one.

Silo launched missiles are for hitting targets very far away. The missiles are called Intercontinental Ballistic Missiles (ICBM's) The longest range ICBM's can hit targets anywhere in the world. The advantage of these is they can be any size. This means they can carry more fuel and larger or more warheads. The more advanced missiles are MIRV capable. MIRV stands for Multiple Independently targeted Reentry Vehicle. MIRV capable missiles can hold up to ten separate warheads. Ballistic missile submarines nicknamed "boomers" also carry ICBM's.

Boats and smaller attack submarines can carry nuclear weapons in cruise missiles such as the subsonic Tomahawk. Larger boats can carry longer range supersonic missiles.

Anti-ship and anti-aircraft missiles can carry nuclear payloads. AS missile can be launched from shore emplacements, boats, planes, or submarines. Although uncommon, there are also nuclear torpedoes. Nuclear AS missiles and torpedoes are primarily for use against aircraft carriers that can withstand many hits before being destroyed. AA missiles are launched either from ground sites or planes. They are for destroying large enemy plane formations.

The smallest nuclear weapons, such as the MK-54, are so small they can be carried by a single person and fired from a portable launcher. The MK-54 weighs about 50 pounds, is the size of a basketball, and has a yield of 10 to 20 tons (not kilotons). They are not very common because of their short range and low power.

The newest delivery system is from space. While arming orbiting satellites violates the Space Armament Treaty, there is one system that sneaks around the treaty. The Fractional Orbit Bombardment System (FOBS) is similar to a satellite. It is launched from a normal satellite launch system and gets by the space weapons treaty because it does not make a complete orbit. Once in the right spot in orbit, retrorockets steer it so that it de-orbits and hits its ground target before making a full orbit. The reentry vehicles travel at extremely high speeds making them very difficult to intercept.

Nuclear artillery is another delivery system that is not commonly used. They do not have enough range to be very practical. The first nuclear artillery shell was a 15kt shell with a diameter of 280mm. Most artillery fired nuke warheads are between 10kt and 30kt.

Nuclear depth charges, while uncommon, could be very effective against submarine. Submarine hunting can take hours if it is found at all. The advantage of nuclear depth charges is that it does not need to be close to the sub to destroy it. This would save a lot of very important time, especially when facing multiple nuclear armed subs.

Antimatter

Antimatter is the opposite of matter. It is made of antiparticles; anti-electrons (also called positrons), anti-protons, and anti-neutrons. They have electrical charges opposite to their corresponding matter. Anti-electrons have a positive charge and anti-protons have a negative charge. The magnetic movement of antimatter is also opposite.

When antimatter meets normal matter, both are annihilated. It releases more energy than any other known kind of reaction. One kilogram of antimatter would have the power of 22,500,000 megatons. This is 387,931 times more powerful than the largest nuclear bomb ever exploded (58mt).

Antimatter was first made in 1996 by a team of international scientists. Several molecules of anti-hydrogen were made. Because antimatter explodes on contact with normal matter, it lasted only 40 billionths of a second before it exploded.

Conclusion

Explosives are some of the most useful tools ever invented. While most people consider them only as weapons of destruction, they are extremely important to our current standard of living. Most people don't know how important mining and quarrying are and don't know how much explosives are relied upon for both. Without explosives, the efficiency of mines and quarries would be reduced to one one-hundredth of what they are at now. While explosives are somewhat dangerous, so is life, and the benefits far outweigh the risks.

Bibliography

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Watkius, T.F. (1968) Chemical Warfare, Pyrotechnics, and the Fireworks Industry. Oxford, New York.: Permagon Press.

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