# How large is the primer for an H bomb

**URL:** <https://boards.straightdope.com/t/how-large-is-the-primer-for-an-h-bomb/643934>\
**Category:** Factual Questions\
**Created:** [December 13, 2012, 5:09pm UTC](https://boards.straightdope.com/t/how-large-is-the-primer-for-an-h-bomb/643934 "2012-12-13T17:09:03Z")\
**Posts on this page:** 2\
**Page:** 2

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**Author:** ![Hail\_Ants](https://avatars.discourse-cdn.com/v4/letter/h/dc4da7/32.png) [@Hail\_Ants](https://boards.straightdope.com/u/Hail_Ants)\
**Post date:** [December 16, 2012, 2:37pm UTC](https://boards.straightdope.com/t/how-large-is-the-primer-for-an-h-bomb/643934/21 "2012-12-16T14:37:11Z")

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> [@DesertDog](#):
>
> [Little Boy](http://en.wikipedia.org/wiki/Little_Boy) was the first and only uranium bomb made and the makers were confident enough that it would work, it was dropped on Hiroshima without testing the design first. With the implosion plutonium bomb [Fat Man](http://en.wikipedia.org/wiki/Fat_Man), on the other hand, there were enough doubts (as well as enough plutonium) that they proofed the concept with the Trinity test.

It was the only uranium ‘gun-type’ weapon made and deployed _by the US_, but other countries have made them. South Africa had a small stockpile of about a dozen uranium, gun-type weapons. And I wouldn’t doubt that Israel may have slapped together a few gun-types before they fully perfected an implosion weapon.

Not only are uranium gun-type A-bombs inefficient and less powerful, their less complex design makes them much more difficult to reliably ‘safe’ (i.e. prevent an accidental, full-nuclear detonation).

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**Author:** ![handsomeharry](https://avatars.discourse-cdn.com/v4/letter/h/e9c0ed/32.png) [@handsomeharry](https://boards.straightdope.com/u/handsomeharry)\
**Post date:** [December 16, 2012, 5:29pm UTC](https://boards.straightdope.com/t/how-large-is-the-primer-for-an-h-bomb/643934/22 "2012-12-16T17:29:42Z")

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> [@Chefguy](#):
>
> An H-bomb is just a large black ball with a fuse sticking out of it. It’s usually lit by some cartoonish character like a coyote, who then sticks his fingers in his ears.

I think the design has been improved since then.  
They have a fail-safe device, so that if it is necessary to abort the explosion, one can either blow on, or pull out, the fuse. I can’t explain the physics of it here. It would require a new thread.

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