On 27/6/19 12:24 pm, Kurt Feltenberger wrote:
> I'm trying to wrap my mind around how fallout radiation effects flora
> and structures/contents.  First, I understand the 7:10 and 7/7/7
> rules, but what I haven't been able to find is just how radioactive is
> the fallout.  A lot of examples are used, and that's cool, but that
> doesn't help trying to build some reasonable numbers for what the
> players might face.
>
> So...in no real order, here are some questions for the following
> scenario:
>
> The world is relatively similar to Earth in size, composition,
> gravity, water percentages, atmosphere percentages, etc; for all
> intents and purposes, other than the specific shape and such of land
> features, it could be Earth.  The enemy shows up and from orbit
> thoroughly bombards it with nuclear weapons (both "enhanced radiation"
> as well as thermonuclear weapons - sub/surface/air bursts as the
> target requires) striking population, military, government, and key
> infrastructure centers.  The attack happens over several hours, no
> more than six or eight.  (Essentially, the characters are going to be
> either on or having to visit a planet that was attacked in much the
> same way that BSG showed Caprica and the other colonies being attacked
> for visual reference.)
>
> 1.  Is the atmospheric disruption and increased particulates in the
> air likely to cause increased rainfall?
>
> 2.  What is good estimate on the output of the fallout after an hour?
>
> 3.  Items that are in a house, say canned goods, dry foods, and meats
> in hermetically sealed packets, a danger to the person eating the
> contents if the packet has been washed off (decontaminated)?
>
> 4.  How much insulating material will be needed to protect someone
> from the fallout provided that they are in a shelter that is sealed
> and has a way of effectively filtering the air?
>
> Thanks!
>
> Kurt
>

Well, Kurt, I'll try to help you where I can.

1 - If there's enough humidity, then yes - a (large) extension of the
principle behind pyrocumulus clouds, (IF I understand correctly).  Of
course, as those rain outs concentrate the airborne fallout, they'll be
a lot nastier than the average square metre of contaminated ground.

2 - I don't have a reference off the top of my head, but 1,000 rads/hr
one hour after a megatonne fission groundburst comes to mind.
Keep in mind that larger device yields (which are, IIRC, less efficient
militarily, which raises the cost of Operation Proper Shoeing) inject
more of their fallout into the unfortunate planet's stratosphere, where
it would stay (and be distributed about that particular hemisphere's
stratosphere) for a fair while before descending back to the troposphere.
Smaller yields (I don't remember the rough dividing line, off hand)
inject their fallout into the troposphere only, resulting in faster
deposition of more radioactive fallout.

2a - By contrast, airbursts (where the fireball doesn't reach the
ground) produce comparatively little fallout, and subject roughly twice
the area to a given overpressure (5 psi will do a number on most
buildings today) than the same device groundbursted (where the fireball
reaches the ground, vapourising and irradiating large amounts of dirt,
rock, water, etc etc).

3 - If the items in question were otherwise safe, fine, no hazard to
health, etc before the Great Day Of Near-Universal Bereavement, there
would be no additional danger after decontaminating them.

4 - Assuming that no one's moving around with creatively-modified
nuclear dampers (such as to accelerate radioactive decay to speed
decontaminating an area, or to suppress decay to allow you to leg it),
the best way to stop the gamma radiation that is fallout's primary
radiohazard, while sheltering in place, is sheer, brute, mass.

"Nuclear War Survival Skills" (http://www.oism.org/nwss/) recommended
approx 90 cm of ordinary dirt as sufficient to reduce gamma dose by
1000x.  56 cm of concrete would do the same.
People in such a shelter would take (using the 7/10 rule) ~4 rads during
the first 6 hours after the single groundburst mentioned in 2, while the
unshielded dose decays from 1000 R/hr to 100 R/hr, then less than 4 rads
over the next 42 hours as the unshielded dose decays to 10 R/hr, then
about 2 rads during the next 294 hours (reaching 2 weeks - actually 343
hours - after initiation) as the unshielded dose decays to 1 R/hr.

Receiving roughly 10 rads over 2 weeks is not a major concern in
post-attack conditions.
It looks like whole-body doses above 1,000 rads are almost invariably
fatal, especially in post-attack conditions.

Alex

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