How does an Atomic Bomb Work?

Michael Anissimov
Michael Anissimov

An atom bomb works by initiating a nuclear chain reaction, which releases a huge amount of energy relative to conventional explosives. Per unit volume, an atom bomb may be millions or billions of times more powerful than TNT. The first atomic explosion occurred on 16 July 1945 at the Alamogordo Test Range in New Mexico, during a test called Trinity. It was developed during the top secret Manhattan Project, which was directed by General Leslie R. Groves of the US Army.

Replica of the "Fat Man" atom bomb in a museum.
Replica of the "Fat Man" atom bomb in a museum.

Nuclear reactions occur when neutrons are fired at closely packed atoms with heavy nuclei (uranium or plutonium isotopes). These heavy nuclei break apart into lighter nuclei when hit by a neutron, in turn generating more neutrons which bombard other nuclei, creating a chain reaction. This process is known as fission. (Another process known as fusion releases energy by fusing together nuclei rather than breaking them apart.) By breaking down the nuclei themselves rather than releasing energy through a conventional chemical reaction, atom bombs can release more than 80 terajoules of energy per kilogram (TJ/kg).

The People's Republic of China has nuclear weapons.
The People's Republic of China has nuclear weapons.

In the earliest bombs, the chain reaction was initiated simply by firing two half-spheres of high purity uranium isotope at one another in a small chamber. In updated designs, a uranium or plutonium bomb core is surrounded by high-explosive lenses designed to compress the core upon detonation. The compressed core goes critical, initiating a chain reaction that persists until many of the heavy nuclei have been broken apart.

Nuclear weapons typically produce mushroom clouds that rise into the upper atmosphere when they detonate.
Nuclear weapons typically produce mushroom clouds that rise into the upper atmosphere when they detonate.

The atom bomb and its cousin the hydrogen bomb have probably been the most powerful weapons in the world since their creation many decades ago. Large bombs can destroy entire cities. Thousands of atom bombs have been detonated, though only two have been used in warfare - both used by the US against Japan during World War II. There are seven countries that openly declare possessing nuclear weapons; the United States, Russia, the United Kingdom, France, the People's Republic of China, India and Pakistan. The world currently possesses enough nuclear capability to make the human race go extinct many times over.

Pakistan is one of seven countries that openly admits to posessing nuclear weapons.
Pakistan is one of seven countries that openly admits to posessing nuclear weapons.
Japan had two atomic bombs used against it during World War II.
Japan had two atomic bombs used against it during World War II.
India is one of the seven countries that has acknowledged that it possesses nuclear weapons.
India is one of the seven countries that has acknowledged that it possesses nuclear weapons.
Michael Anissimov
Michael Anissimov

Michael is a longtime wiseGEEK contributor who specializes in topics relating to paleontology, physics, biology, astronomy, chemistry, and futurism. In addition to being an avid blogger, Michael is particularly passionate about stem cell research, regenerative medicine, and life extension therapies. He has also worked for the Methuselah Foundation, the Singularity Institute for Artificial Intelligence, and the Lifeboat Foundation.

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Discussion Comments


What is the word reaction for an atomic bomb?


Now if any countries try to attack with nuclear or atomic bombs. There are literally enough nuclear and atomic bombs to destroy the world.


@irontoenail - Always remembering, of course, that they have been used. Japan can testament to that. So, yes, there are definitely individual heroes, but for the most part I think they haven't been used because everyone has them now. Dropping the atomic bomb isn't a way to win a war now. It means everyone dies.


@pleonasm - You know, for a while I was quite depressed whenever I thought about the fact that there are so many nuclear weapons stockpiled around the world.

But eventually I came to see that the fact that they haven't been used by now is fairly hopeful. I've even read stories about people during the cold war who were essentially told by (mistaken) co-workers that World War Three had started and that they had to push the button.

These people refused to do it. I know that not everyone would, but you know, there are people out there who wouldn't do it. And that's something that makes me hopeful about humanity.


@anon124662 - I don't think there's a definitive answer to that. It would depend on what size the bombs were, how people were protected and so forth. There are places in the mountains where people have essentially burrowed under the mountain and can live in vaults. I don't know how many bombs it would take to penetrate that kind of protection. Then you have people on little islands and so forth.

Or, possibly, the human race could become extinct from just a couple of bombs, if they set off a nuclear winter (which is when the bombs create such a large dust cloud, it won't let the sun through). If that happened and it was bad enough, all life would potentially go extinct.

I've also heard theories that a big enough atomic bomb drop in the wrong place could push the Earth out of orbit, again potentially changing the seasons enough so that everything dies.

I'm sure there is a government calculation somewhere about how many it would potentially take, but it is a complicated question.


At least it helped me. I'm kind of satisfied. It needs a lot of pictures for better knowledge and sure bombs are okay for projects but dangerous for practice.


this is probably not the best thing in the world.


I agree it does need pictures but the information is very well thought out.


If we could be extinct several times over, exactly how many do you think would be possible? I'm just asking cause "several" is pretty vague to me. Is it two? Six? Two-hundred-sixty-seven? Just my curiosity wanting to know!


Enough to kill us all? How wonderfully reassuring.


thanks. I'm doing a big project on Niels Borh (he created the atomic bomb).


Great info. Especially the fact that the people have enough of these bombs to the destroy the world over and over again.


this has helped me a lot.


thanks a lot.


I've been wondering about this for a while, thanks.


this site is so good! i needed extra credit in science and this totally helped.


thank you so much. i really needed this info. i'm doing weapons and strategy in World War II


Great, thanks. saved me on my project and came up in my marks!


Nice. thanks a lot


cool beans. thanks a lot.


thanks. now i know how it works. =)


This saved my life. I have a big project and the a bomb is the subject.


This saved my life. I have a big project and the a bomb is the subject.


what chemicals react together to make the bomb explode?


what excactly is able to split the atom?


I really thought the atomic bomb was just from a simple atom being split.


you really need pictures.


a simple cartoon type video would help as well as the plain info which helps understand the process easily


why do people attempt these vile destruction projects anyway? i am no hippy. why have something that could kill everyone?


How is the reaction started? Is it due to the impact or is there an electronic trigger?


Thank you so much I have always wondered about this. It's crazy to think that something so terrifying can be so fundamentally simple. thanks again


I think this article is great and very informative. please explain how the fission process is started.


wow. this is exactly what i need for my project! this answers everything. thanks a lot! this website is soooooooooo handy!


if water exists on mars, can we use this technology by exploding nuclear bombs around mars with the intentions of creating "atmosphere"?


why haven't you said that berylium and polonium is the trigger that gives the neutrons needed to start the fission process?


But why are atomic weapons so destructive?


This answered a lot of my questions.


Wonderful info.....Need pictures!!!!!!!!

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