🚀 go-pugleaf

In article <1992Jul29.130825.19399@icf.hrb.com> trb@icf.hrb.com (Terry Bower) writes:
>
>	  In a discussion the other day with some co-workers, the topic of
>     nuclear detonations came up  ...

Sounds like a fun group to have lunch with!

First, the best reference on all this is "Effects of Nuclear Weapons" 
from the USGov printing office, also available in any depository library. 
Ask the librarian at a large state university near you, it may be one. 
If so, it is in the D (for defense) section not too far away from the 
civil defense and bomb test reports.

>     1) What causes the characteristic mushroom cloud associated with open
>     air nuclear detonations and what is it composed of?
>     (My guess was that the cloud is made up of matter that was vaporized
>     due to the heat generated by the nuclear reaction; The form of the
>     cloud related to aero/thermodynamics... hot matter rising then
>     cooling, shape due to jet/vortex kinds of airflow.)

All bombs mushroom to some extent.  Only the size of nuclear explosions 
makes them really interesting to look at.  Your conclusion is correct -- 
it is the result of superheated air rising and cooling with the vapor 
condensing into a cloud.  Its appearance differs depending on where the 
explosion occurs: air burst photos show something almost like a smoke 
ring while water bursts make really nice clouds; I suppose vaporized 
water works better than vaporized dirt.

>     2) What matter is contained in "fallout"?
>     (My guess is the material that was vaporized in the blast.)

Not quite.  It is that stuff, but usually "fallout" refers to the 
radioactive part -- which is not the original stuff but rather the 
original stuff transmuted by fast nuclear reactions (mostly neutron 
capture, like in a supernova) during the explosion. 

>     3) What is the mechanism that makes fallout radioactive?
>     (The reaction must affect the matter "sucked up" into the cloud in
>     some way that makes it radioactive... since the actual amount of
>     fissionable material in the bomb must be very small compared to the
>     fallout that is generated.)

Neutrons from the reaction in the bomb get captured by whatever gets in 
the way and/or cause other reactions to occur.  The cloud forms later. 
(If you like, the nuclear reactions are inside the atom while the 
vaporization etc is a result of materials physics of the atoms.) 
The nature of the fallout is then a function of what was in the bomb 
and what is around it when it goes off.

--
J. A. Carr                                    |  "The New Frontier of which I  
jac@gw.scri.fsu.edu                           |  speak is not a set of promises
Florida State University  B-186               |  -- it is a set of challenges."
Supercomputer Computations Research Institute |   John F. Kennedy (15 July 60)