You* have pr*obably read in history books about the atomic bombs used in World War II. You may also have seen fictional movies where nuclear weapons were launched or detonated .
We have seen that these devices have incredible destructive power, but how do they work?
*Nuclear bombs involve the forces, strong and weak, that hold the nucleus of an atom together, especially atoms with unstable nuclei. There are two basic ways that nuclear energy can be released from an atom:
Nuclear fission - You can split the nucleus of an atom into two smaller fragments with a neutron. This method usually involves isotopes of uranium (uranium-235, uranium-233) or plutonium-239.
Nuclear fusion -You can bring two smaller atoms, usually hydrogen or hydrogen isotopes (deuterium, tritium), together to form a larger one (helium or helium isotopes); this is how the sun produces energy
Up Next
How Nuclear Power Works
In either process, fission or fusion, large amounts of heat energy and radiation are given off.
To build an atomic bomb, you need:
A source of fissionable or fusionable fuel
A triggering device
A way to allow the majority of fuel to fission or fuse before the explosion occurs (otherwise the bomb will fizzle out)
We'll take a look at atomic structure on the
Before we talk about the physics of atomic bombs, it's a good idea to go over the basic properties of atoms.
Atoms are incredibly small -- the smallest is about 10-8* cm in diameter. For an idea of how small this really is, think of a baseball. The diameter of a baseball is about 7 cm. If an atom were the size of a baseball, an actual baseball would be about 3044 miles high.
An atom is made up of three subatomic particles -- protons, neutrons and electrons. The center of an atom, called the nucleus, is composed of protons and neutrons. Protons are positively charged, neutrons have no charge at all and electrons are negatively charged. The proton-to-electron ratio is always on*e to one, so the atom as a whole has a neutral charge. For example, a carbon atom has six protons and six electrons.
An atom's properties can change considerably based on how many of each particle it has:
The number of protons in an atom determines the type of element. Elements are classified by their atomic number, which is simply the number of protons in an atom's nucleus. Some common elements on Earth are oxygen, carbon and hydrogen. You can see the elements on the periodic table here.*
There are different types of atoms called isotopes. These isotopes look and act the same in nature -- the only difference is the number of neutrons in the nucleus.
You can calculate the “mass” of an atom by counting the number of protons and neutrons inside the nucleus. This number is called the *atomic mass. Carbon has three isotopes, for example -- carbon-12 (six protons + six neutrons), carbon-13 (six protons + seven neutrons) and carbon-14 (six protons + eight neutrons).
If atoms are so small, then how can they release the kind of energy that creates an atomic bomb?
Two important concepts in physics explain how massive amounts of energy can come from very small particles -- Einstein's famous equation E = MC2 and nuclear radiation.
E = mc2
An atom's nucleus and the structure of certain isotopes make it possible to release incredible amounts of energy when the atom splits. You can understand how much energy this process releases by looking at Einstein's equation E = mc2, where E is energy, m is mass and c is the speed of light (approximately 300,000 kilometers per second). Although you may have heard of this equation without knowing what it really means, the concept behind it is pretty simple. Matter and energy are essentially interchangeable -- matter can be converted into energy, and energy can be converted into matter, and the numbers involved are enormous. The speed of light is a huge number -- if you multiply a large amount of mass by the speed of light, you get an extreme amount of energy. And even though atoms are small -- they don't have a lot of mass -- it takes a vast number of them to make a substance.
Substances like uranium, which are commonly used in nuclear bombs, have a very high atomic number -- the atoms themselves are larger and contain more particles than the atoms of other naturally-occurring substances. Because of this additional nuclear material, uranium has the power to release a lot of energy. If you multiplied 7 kilograms of uranium by the speed of light squared, you would get about 2.1 billion Joules of energy. By comparison, a 60-watt light bulb uses 60 joules of energy per second. The energy found in a pound of highly enriched uranium is equal to something on the order of a million gallons of gasoline. When you consider that a pound of uranium is smaller than a baseball and a million gallons of gasoline would fill a cube that is 50 feet per side (50 feet is as tall as a five-story building), you can get an idea of the amount of energy available in just a little bit of U-235.
We have seen that these devices have incredible destructive power, but how do they work?
*Nuclear bombs involve the forces, strong and weak, that hold the nucleus of an atom together, especially atoms with unstable nuclei. There are two basic ways that nuclear energy can be released from an atom:
Nuclear fission - You can split the nucleus of an atom into two smaller fragments with a neutron. This method usually involves isotopes of uranium (uranium-235, uranium-233) or plutonium-239.
Nuclear fusion -You can bring two smaller atoms, usually hydrogen or hydrogen isotopes (deuterium, tritium), together to form a larger one (helium or helium isotopes); this is how the sun produces energy
Up Next
How Nuclear Power Works
In either process, fission or fusion, large amounts of heat energy and radiation are given off.
To build an atomic bomb, you need:
A source of fissionable or fusionable fuel
A triggering device
A way to allow the majority of fuel to fission or fuse before the explosion occurs (otherwise the bomb will fizzle out)
We'll take a look at atomic structure on the
Before we talk about the physics of atomic bombs, it's a good idea to go over the basic properties of atoms.
Atoms are incredibly small -- the smallest is about 10-8* cm in diameter. For an idea of how small this really is, think of a baseball. The diameter of a baseball is about 7 cm. If an atom were the size of a baseball, an actual baseball would be about 3044 miles high.
An atom is made up of three subatomic particles -- protons, neutrons and electrons. The center of an atom, called the nucleus, is composed of protons and neutrons. Protons are positively charged, neutrons have no charge at all and electrons are negatively charged. The proton-to-electron ratio is always on*e to one, so the atom as a whole has a neutral charge. For example, a carbon atom has six protons and six electrons.
An atom's properties can change considerably based on how many of each particle it has:
The number of protons in an atom determines the type of element. Elements are classified by their atomic number, which is simply the number of protons in an atom's nucleus. Some common elements on Earth are oxygen, carbon and hydrogen. You can see the elements on the periodic table here.*
There are different types of atoms called isotopes. These isotopes look and act the same in nature -- the only difference is the number of neutrons in the nucleus.
You can calculate the “mass” of an atom by counting the number of protons and neutrons inside the nucleus. This number is called the *atomic mass. Carbon has three isotopes, for example -- carbon-12 (six protons + six neutrons), carbon-13 (six protons + seven neutrons) and carbon-14 (six protons + eight neutrons).
If atoms are so small, then how can they release the kind of energy that creates an atomic bomb?
Two important concepts in physics explain how massive amounts of energy can come from very small particles -- Einstein's famous equation E = MC2 and nuclear radiation.
E = mc2
An atom's nucleus and the structure of certain isotopes make it possible to release incredible amounts of energy when the atom splits. You can understand how much energy this process releases by looking at Einstein's equation E = mc2, where E is energy, m is mass and c is the speed of light (approximately 300,000 kilometers per second). Although you may have heard of this equation without knowing what it really means, the concept behind it is pretty simple. Matter and energy are essentially interchangeable -- matter can be converted into energy, and energy can be converted into matter, and the numbers involved are enormous. The speed of light is a huge number -- if you multiply a large amount of mass by the speed of light, you get an extreme amount of energy. And even though atoms are small -- they don't have a lot of mass -- it takes a vast number of them to make a substance.
Substances like uranium, which are commonly used in nuclear bombs, have a very high atomic number -- the atoms themselves are larger and contain more particles than the atoms of other naturally-occurring substances. Because of this additional nuclear material, uranium has the power to release a lot of energy. If you multiplied 7 kilograms of uranium by the speed of light squared, you would get about 2.1 billion Joules of energy. By comparison, a 60-watt light bulb uses 60 joules of energy per second. The energy found in a pound of highly enriched uranium is equal to something on the order of a million gallons of gasoline. When you consider that a pound of uranium is smaller than a baseball and a million gallons of gasoline would fill a cube that is 50 feet per side (50 feet is as tall as a five-story building), you can get an idea of the amount of energy available in just a little bit of U-235.
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