# How much energy does the nuclear fission in one uranium atom give?

1. Jun 16, 2012

### Karimspencer

Does it give a lot or is nuclear fission only powerful when you have a large quantity?

2. Jun 16, 2012

### Staff: Mentor

~200 MeV, or ~3*10^(-11)J. To power a 100W light bulb for one second, you need ~3*10^12 (3 trillion) fission processes.

The energy is large for an atom, but as atoms are really small it is small compared to all everyday scales.

3. Jun 17, 2012

### Karimspencer

I see... That means if you get about 1 kg of uranium235, you could make a huge explosion....

When making nuclear bombs , how much uranium do you need to release such energy?

4. Jun 17, 2012

### Staff: Mentor

Google and wikipedia will answer this one for you... Much depends on the detailed design of the evil thing.

A primitive U-235 bomb such as the one that destroyed the medium-sized city of Hiroshima and killed about 100,000 people requires more than 50 kilograms; but most of the uranium doesn't fission because the bomb blows itself apart before fission is complete. That bomb released about 10^14 joules, which means (thanks to mfb for the MeV to joules conversion) about 3*10^24 uranium atoms actually fissioned. That's about 1 kg.

5. Jun 17, 2012

### Karimspencer

That's pretty huge and viscous... Isn't it easy to make a huge explosion. I mean there are people that sneak some uranium with them and i am guessing they can take in about 1 kg of uranium, can't they?

6. Jun 17, 2012

### Drakkith

Staff Emeritus
No it isn't that easy. The process either requires enough material to have critical mass without compression, which is much more than 1 kg, or it requires compression by explosives, which is extremely challenging in itself due to the required timing accuracy of the explosions. Even if you did have enough material, simply throwing it together in a big lump would be dangerous, but would not result in a nuclear explosion of any significant magnitude. The short story is that making a nuclear weapon is not simple and easy.

7. Jun 17, 2012

### krd

Not as challenging as it was in the 1940s.

It's a lot easier than it was in comparison to the 1940s. All the maths could be done on a laptop. And many of the engineering problems could be solved with off the shelf components.The centrifuges the Iranians are using are commercially available - I'm pretty sure they're off the shelf isotope splitters.

It would not be easy or next to impossible for a bunch of guys in a cave, or in the badlands of Pakistan to knock up a nuclear weapon, but for a government of any mediumly developed country, it wouldn't.

I believe the Iranians already have the bomb.

8. Jun 17, 2012

### Karimspencer

Yes i believe that the iranians do have a bomb .. They have some of the greatest scientist and most brilliant scientist that have been studying nuclear energy and physics for years.

9. Jun 17, 2012

### ZapperZ

Staff Emeritus
This is not a politics forum. If participants cannot stick to the physics, this thread is done.

Zz.