How Do Atomic Bombs Work? A Simple Overview
During the Cold War era fear of nuclear warfare blanketed the entire globe, and even in the 21st century it isn't uncommon for people to build shelters and stockpile supplies in case of a sudden nuclear attack. The atomic bomb, the most powerful weapon ever built by human kind, has captivated the population for nearly a century now. But how do atomic bombs work? What's the science behind the most dangerous weapons ever built? What exactly is nuclear fission, what does Uranium have to do with it, and how worried do we really need to be about nuclear war breaking out?
Some Background Knowledge:
To understand how nuclear bombs work a little bit of background chemistry knowledge is needed:
- Atoms, which are the building blocks that make up life as we know it, consist of a positively charged nucleus surrounded by a cloud of negatively charged electrons.
- The nucleus itself consists of protons, which have a positive charge, and neutrons, which have a neutral charge.
- Because particles with the same charge repel each other the nucleus needs something to hold it together. This force is called the strong force, and without it the nucleus would break apart as the protons repelled away from each-other.
- The process of the nucleus of an atom splitting apart is known as nuclear fission.
What is Nuclear Fission?
Now that we have the basics down we can move on to the good stuff; what nuclear fission actually is. As I mentioned previously, the basic explanation is that it's the splitting of the nucleus in an atom. When the nucleus splits a massive amount of energy is released. There are two different types of nuclear fission; spontaneous and induced. Spontaneous fission, as the name suggests, occurs spontaneously and without a catalyst. Induced fission, unlike spontaneous fission, must be triggered purposefully. We'll explore how this occurs a little later. Nuclear fission is generally possible in elements with an atomic number of 90 or higher (that is, anything beyond thorium in the periodic table).
How can Fission be Induced?
At the core of a nuclear weapon is a device called a neutron generator. This is usually a small pellet of the elements Beryllium-9 and Polonium, which are kept separated by a piece of foil. When the foil is broken and the two elements come together the Polonium emits something called alpha particles. The alpha particles collide with the Beryllium-9 and cause it to release a neutron. The neutrons fly off and collide with the Uranium or Plutonium fuel. The nuclei of the fuel atoms break up, releasing yet more neutrons which break up more nuclei, and so on. This kind of reaction is called a chain reaction. Nuclear weapons are designed so that the reaction doesn't stop until all of the fuel has been detonated and all of the energy in the atom has been released.
The most common fuel for atomic bombs is the element Uranium. Discovered in 1789 by Martin Heinrich Klaproth, Uranium is highly radioactive and is heavy enough to make it susceptible to nuclear fission. However, it's not actually the normal form of Uranium that’s used in atomic bombs. Instead, a sample of the isotope Uranium-235 is used, which has three less neutrons than the common form of the element. This isotope is used in favour to others because of its ability to readily absorb an extra neutron and the speed at which is undergoes fission after the extra neutron is taken into the nucleus. Samples of uranium that are used in atomic bombs must be 'enriched,' which means that the content of Uranium-235 needs to be at least 3.5% of the weight of the total sample. The enriching process is conducted using a centrifuge. Samples of uranium are spun at high speeds in tubes and the lighter Uranium-235 migrates into the middle of the tubes.
What About Plutonium?
Nuclear weapons can also be made out of Plutonium-239. It has to be produced in nuclear reactors as there isn't enough of the raw material in nature, but it has similar fission properties to Uranium so it can be used as an alternative fuel source. The atomic bomb that was dropped on Nagasaki during world war II contained Plutonium instead of Uranium.
How Powerful are Atomic Bombs?
The first taste that the world got of the power of nuclear weapons was in August of 1954, when the United States dropped two atomic bombs onto the Japanese cities of Hiroshima and Nagasaki. The effect was devastating, with an estimated 146,000 people killed in Hiroshima alone and the cities almost completely destroyed. That was over sixty years ago, though. The most powerful modern atomic bomb ever detonated, the Tsar Bomba, was 3,000 times as explosive as the one dropped over Hiroshima. Suffice it to say that nuclear weapons are really, really powerful.
Which Countries Have Nuclear Weapons?
Number of warheads
Atomic bombs are the most powerful weapon invented by mankind. They work due to a chain reaction called induced nuclear fission, whereby a sample of a heavy element (Uranium-235 or Plutonium-239) is struck by neutrons from a neutron generator. The nuclei of the fuel atoms split, releasing massive amounts of energy and more neutrons, which perpetuate the reaction. There are currently 9 countries that have nuclear weapons caches and many more than are suspected to have secret stocks or nuclear programs in the works. Even though the principle of mutually assured destruction protects us from the threat of nuclear warfare to some degree, there will always be reason to fear when such potentially destructive weapons still exist.
Sources and further reading:
Questions & Answers
© 2018 K S Lane