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Old 04-17-2008, 01:31 AM
Jinx Jinx is offline
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How Many Rads Equate to Hiroshima?

I don't even know enough about how to ask this, but Mythbusters did a poor job explaining how they busted a myth of whether cockroaches would survive (the nuclear fallout from) an atomic blast. While the bugs were irradiated at 1000 rads, 10,000 rads, and 100,000 rads...they never once bothered to say how this equates to what kind of bomb and/or at what distance from the epicenter one would be to experience an equivalent dose.

So, how does this compare to ground zero? Or, 50 miles from ground zero? Like I said, I don't even know enough about what I'm trying to ask. But, hopefully some ex-military or warbuff SDopers will come along to help quantify things on an apples to apples basis. - Jinx
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Old 04-17-2008, 02:42 AM
sleestak sleestak is offline
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Quote:
Originally Posted by Jinx
I don't even know enough about how to ask this, but Mythbusters did a poor job explaining how they busted a myth of whether cockroaches would survive (the nuclear fallout from) an atomic blast. While the bugs were irradiated at 1000 rads, 10,000 rads, and 100,000 rads...they never once bothered to say how this equates to what kind of bomb and/or at what distance from the epicenter one would be to experience an equivalent dose.

So, how does this compare to ground zero? Or, 50 miles from ground zero? Like I said, I don't even know enough about what I'm trying to ask. But, hopefully some ex-military or warbuff SDopers will come along to help quantify things on an apples to apples basis. - Jinx

According to the Atomic Bomb Museum:

Quote:
*Estimated air dose of gamma rays: Hiroshima: 10,300 rads; Nagasaki: 25,100 rads.
*Estimated neutron dosages: Hiroshima, 14,100 rads; Nagasaki: 3,900 rads.
From here.

Note, they don't really give a distance for that dosage.

The Rad has gone through a couple different definitions. The one I remember is 100 ergs of energy absorbed per kilogram. I could be wrong about that though....

Slee
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Old 04-17-2008, 08:32 AM
MarcusF MarcusF is offline
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I have a reference book that gives a table of initial radiation yield for different weapons yields - unfortunately it doesn't give a source and the table itself is in Roentgens.

For what its worth, this tables gives:

---------- 1 mile------2 miles-----3 miles
10kT----- --80R -------100mR-------0.3mR
20kT------160R--------200mR-------0.6mR
100kT---1000R--------- 1.25R------3.7mR
1MT----16800R------------21R-----63mR

(Apologies for this - no idea how to do a table in a post.)

To convert from Roentgen to Rads divide by 1.072

Given the yield of the Hiroshima and Nagasaki bombs was about 15 and 21kT respectively the figures from the Atomic Bomb Museum (total of ~25krad and 29krad) appear to be very close to ground zero (if my table is anything like correct).

The table looks not unreasonable with the figures given for survival rates at different distances also on the Atomic Bomb Museum site. This gives about a 30% mortality rate at 1 mile.

160R is about 150 rad and - for gamma radiation - this is equivalent to 150rem (the rem takes acount of the biological effects of different types of radiation).

Ignoring for the moment that a proportion of the radiation was neutrons - that are much more destructive - this looks consistent with the normal figure given of 300rem giving a 50% mortality rate.

Please don't take this analysis as gospel - the data is suspect and it is long time since I was directly involved in radiological protection! (It's also a long time since I used rads and rems - grays and sieverts are the unit of choice.)
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Old 04-17-2008, 09:39 AM
bump bump is offline
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IIRC, with most reasonably sized nuclear weapons (10 kt or larger), if you're close enough to get irradiated, you're probably done for due to blast and heat.

From the Nuclear Weapons Archive FAQ, Section 5: Effects of Nuclear Weapons (http://nuclearweaponarchive.org/Nwfaq/Nfaq5.html)

Quote:
5.1 Overview of Immediate Effects
The three categories of immediate effects are: blast, thermal radiation (heat), and prompt ionizing or nuclear radiation. Their relative importance varies with the yield of the bomb. At low yields, all three can be significant sources of injury. With an explosive yield of about 2.5 kt, the three effects are roughly equal. All are capable of inflicting fatal injuries at a range of 1 km.
The equations below provide approximate scaling laws for relating the destructive radius of each effect with yield:


r_thermal = Y^0.41 * constant_th
r_blast = Y^0.33 * constant_bl
r_radiation = Y^0.19 * constant_rad

If Y is in multiples (or fractions) of 2.5 kt, then the result is in km (and all the constants equal one). This is based on thermal radiation just sufficient to cause 3rd degree burns (8 calories/cm^2); a 4.6 psi blast overpressure (and optimum burst height); and a 500 rem radiation dose.

The underlying principles behind these scaling laws are easy to explain. The fraction of a bomb's yield emitted as thermal radiation, blast, and ionizing radiation are essentially constant for all yields, but the way the different forms of energy interact with air and targets vary dramatically.

So, with that in mind, a Hiroshima sized weapon (15 kt) will give a 500 rem dose at about 1.41 kilometers.
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Old 04-17-2008, 10:54 AM
mlees mlees is offline
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Those dosages are for the initial detonation of the weapon, right?

I assume roaches (and people) are going to be subjected to radiation poisoning from ingesting (either by breathing, eating, or drinking contaminated substances) for a some amount of time after "zero hour".

Shouldn't continued exposure to "fall out" be considered in the equation (of roaches surviving)?

Did the Myth Busters consider that?

An insect doesn't seem to breathe in a large volume of air (or injest much by way of the other injesting methods mentioned above) compared to a human. So I assume a human will injest more radiation poisoning faster. The roach has a smaller body, and may suffer system failure with less total amount of contaminated material injested. I assume that this is not a wash, however...

Are my assumptions (trying to consider body sizes) correct?

How does the difference in body sizes (and possibly the methodology of breathing) affect the rate at which a subject is contaminated in a given contaminated zone?
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