# I need a radioactive McGuffin

**URL:** <https://boards.straightdope.com/t/i-need-a-radioactive-mcguffin/517280>\
**Category:** In My Humble Opinion\
**Created:** [November 12, 2009, 4:50am UTC](https://boards.straightdope.com/t/i-need-a-radioactive-mcguffin/517280 "2009-11-12T04:50:18Z")\
**Posts on this page:** 2\
**Page:** 2

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**Author:** ![matt](https://avatars.discourse-cdn.com/v4/letter/m/a6a055/32.png) [@matt](https://boards.straightdope.com/u/matt)\
**Post date:** [November 13, 2009, 6:26am UTC](https://boards.straightdope.com/t/i-need-a-radioactive-mcguffin/517280/21 "2009-11-13T06:26:29Z")

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> [@History\_Monk](#):
>
> I know enough Pu-239 to reach critical mass with all that lead shielding weighs upwards of a thousand pounds, so that won’t work. So how much scary can you fit into a backpack?
> 
> (And mods: if this is the wrong forum, sorry about that…)

No it doesn’t. Plutonium is an alpha emitter - you don’t need any shielding at all. What you DO need is a fair amount of conventional explosives arranged with rather precise geometry to implode your 5-10 kg plutonium core into a supercritical mass, and a whole lot of precision initiators and a neutron generator to light them off, respectively. Which in an old “Fat Man” type device did come to about a thousand pounds but today we can do rather better and you can indeed fit a fission bomb in your backpack.

If you want something else for a nasty plot device, google “gamma kolos” - lots to play with there!

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**Author:** ![mswas](https://avatars.discourse-cdn.com/v4/letter/m/e99b99/32.png) [@mswas](https://boards.straightdope.com/u/mswas)\
**Post date:** [November 13, 2009, 6:36am UTC](https://boards.straightdope.com/t/i-need-a-radioactive-mcguffin/517280/22 "2009-11-13T06:36:46Z")

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Umm, it’s a McGuffin, you don’t need to specify what it is.

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