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From: greg@mit-eddie.UUCP (Greg McMullan)
Newsgroups: net.bizarre
Subject: Re: Re: plutonium
Message-ID: <4882@mit-eddie.UUCP>
Date: Tue, 6-Aug-85 16:05:19 EDT
Article-I.D.: mit-eddi.4882
Posted: Tue Aug  6 16:05:19 1985
Date-Received: Fri, 9-Aug-85 02:20:47 EDT
References: <541@bentley.UUCP> <499@mit-vax.UUCP> <217@kitty.UUCP> <544@mit-vax.UUCP>
Reply-To: greg@mit-eddie.UUCP (Greg McMullan)
Organization: MIT, Cambridge, MA
Lines: 106

FLAME ON!!!!!!!!!!!!!!!!!!!!!!!
>
>>> Nothing, probably. Plutonium is VERY VERY VERY poisonous, but not
>>> particularly explosive (the amount needed to make a bomb is not easily
>>> transported).
>>
>>This is pure bull.
>
> One atom of plutonium can cause cancer. A hundreth of a mole (6.02 x
> 10^20) atoms is about a gram. That could be carried by anybody --
> safely.

One atom of plutonium can cause cancer, but the probability is
infinitesimal. If you want to cause cancer with small numbers of
radioactive atoms, I would think that you could do much better than
plutonium by choosing a more common isotope and/or one that concentrates
by chemical processes in critical parts of the body. Some examples:

 - Strontium 90, which is made in nuclear explosions and some in
   reactors, and which concentrates in the bones, being chemically
   similar to calcium. 

 - Iodine 131 (I think, my references aren't here now), which is a
   decay product of uranium 235, and thus is made in reactors. This one
   concentrates in the thyroid, which is why it is used to diagnose
   thyroid problems by doctors. (It has a short half life, so not much
   harm is done.)

 - Carbon 14, which is made by natural processes (I believe cosmic rays,
   mostly, but I'm not sure), and is a major ingredient in DNA and RNA,
   and so is a very good candidate for causing cancer, anyway.

>> And to make a bomb all you need is a couple times critical mass.
>
> THIS is pure bull. If you have ONE times critical mass it will blow up,
> you lunkhead! That's what critical mass MEANS! Bombs contain LESS than
> critical mass so that they're stable. The activation energy is supplied
> by a conventional bomb set off as to compress the matter an "fool" it
> into thinking it's critical mass. Take a high school physics course. I
> did, and look where it got me!

This is a common misconception. What critical mass REALLY means is that
on average, one neutron in the assembly will cause exactly one fission
neutron to be created. Specifing a certain mass as "critical mass"
without giving other relevant factors (what shape your material is, how
dense it is, what chemical form it is in, what other materials are
around it, how isotopically pure it is, etc) is meaningless.

A nuclear reactor is a large assembly of material, some radioactive,
that is kept exactly critical, within very close tolerances, except when
changing power level, and it categorically CANNOT explode atomically.
Bombs are assemblies of material which are not critical until the
chemical explosives around the radioactives are set off, when the
materials rearrange themselves into a configuration which is more than
critical (supercritical) for a short time. The explosoves do not provide
any significant amount of energy in terms of activation, and the bomb is
not "fooled" into anything. It contains a small number greater than one
times the criticsl mass of radioactives (when in the intermediate state
- after the high explosives go off, but before the chain reaction has
really gotten going). Try taking a nuclear engineering survey course
(22.001 at MIT is a good one), or even an introductory reactor design
class. 

>>That can
>>be carried in a briefcase. The whole bomb can be fit into a backpack. In
>>fact the army has a low-weild backpack bomb.
>
>Fine, why don't I just fill your briefcase with plutonium and see how
>long you can carry it around before you drop dead. 8 grams of plutonium
>will boil a liter of water in about a minute. I don't think you want to
>carry around a breifcaseful.

I'm not sure where your 8 minute figure came from, and I don't have the
time to check it right now, but the dangerous form of the energy to
humans (as long as it isn't released to quickly, which would not be the
case for a usable suitcase bomb before detonation) is neutrons, which
can be significantly attenuated by relatively small amount of many
plastics, which aren't very dense, so your suitcase bomb would probably
contain maybe 8 or 10 kg of Pu, 1 or 2 kg of high explosive, 8 kg of
polyethelyene, and some other structural materials. If we allow 5 kg for
the structural materials and suitcase, we have a 25 kg bomb that might
yield something on the order of a kiloton, (probably between .1 and 5
kT), and would not be extremely radioactive from the outside. See _The
Curve Of Binding Energy_ by John McPhee, I think, for more information,
and better details.

FLAME OFF
Sorry about the length of this factual posting to net.bizarre, but this
exchange hit a sensitive spot, and I haven't slept enough recently.

>Charles Forsythe
>CSDF@MIT-VAX

					Greg McMullan
    		 (Soon to receive a bachelor's in nuclear engineering
		      from MIT, so I know what I'm talking about.)

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