Mushroom Cloud

Ok, this may be a stupid question and it probably has been discussed before, so if that's the case I apologize.
What I am wondering is what is it about an Atomic blast that creates the distinctive mushroom cloud?
Correct me if I'm wrong but the cloud isnt exclusive to a nuclear blast, it can also be created by a conventional blast as long as its big enough.
Didnt the test of the MOAB bomb in Florida a few years ago creat a small mushroom cloud of dust?
Whether its exclusive to nuclear blasts or not, I wonder what causes this shape at all?
I dont know what made me think to even ask this, I wasnt even looking at anything nuclear related at all, the question just popped into my head and I figured if anybody knew the answer it would be some of you guys here.

edit: forgot to add an image of a mushroom



[edit on 26-1-2007 by Kr0n0s]

Here's a concise explanationL

www.hindu.com...

The fireball expands rapidly engulfing the surrounding air. The ball of hot air is less dense than the surrounding air. It rises swiftly like a hot air balloon.

This rising column pulls up debris of the weapon, dust and moisture along with it forming a cloud. As it moves up, it cools gradually and reaches about 10 km where the atmosphere is extremely stable.

The ball of air mass moving up does not have enough energy to penetrate this stable layer. It flattens out. As the relatively warmer layers at the bottom push up, the top layers spread laterally and equally in all directions, and the cooler denser layers descend at the edges, giving a distinct mushroom shape.

Atmospheric layers:



And a further explanation

www.hindu.com...
as the hot cloud meets the colder air at higher altitudes, it slowly cools. Eventually the cloud reaches the temperature of the surrounding air and ceases to rise, but spreads horizontally along air levels at the same altitude, which are at the same temperature. This forms the cap of the mushroom.

The smoke, dust and debris gushing into the central column cause toroidal eddy currents in the horizontally spreading hot cloud. This introduces curling under the cap of the mushroom.

Very cool, I knew there had to be a specific scientific explanation for this to occur. Thanks a bunch for the reply

Kr0n0s, your question is not stupid at all.

When I was an NBC Instructor a few years ago, I had many students ask me the same question. My answer however, was not as long winded as the replies in the links Nygdan gave you

The two Hindu links are ever so slightly innaccurate in the case of 'H' Hour + [whatever] Yield and Height, Width and Shape.

A nuclear weapon detonated on the ground [Ground Burst] will produce the characteristic mushroom cloud - from the beginning.

An airburst however [where the fireball does not touch the ground] will produce a doughnut shaped cloud. Immediately below this, at Ground Zero, a stem of radioactive dust and debris forms and starts to rise.

This stem will meet and pass through the doughnut shaped cloud and may form a mushroom shaped cloud, as it starts to cool or meets much colder air.

Where a nuclear device is detonated on or above water, then a massive cauliflower shaped cloud will form.

An Exo-Atmospheric detonation will not produce a cloud of any kind, as it is beyond the earth's atmosphere.

With regards to the paragraph in the link that states:

Within an extremely short time after the explosion, the fire ball from a high yield nuclear weapon will be about 130 metres across increasing to about 1700 metres in ten seconds.

This statement is factually incorrect.

You can measure the height and width of a cloud at any time after 'H' Hour. This will give you a rough size or 'yield' of the weapon or device detonated.

You can only do this, provided you know the EXACT time that 'H' Hour [detonation] occured and then only by using special instruments, usually issued to Warning, Reporting & Monitoring Cells or here in the UK, the UKWMO - The United Kingdom Warning & Monitoring Organisation.

It may be of further interest to you Kr0n0s, but even though a nuclear explosion produces temperatures well in excess of billions of degrees Centigrade, strangely, ice is also formed at the instant of detonation and this caps any rising cloud or stem.

Wierd or what?

thanks for posting this question Kronos,
and thanks to fritz for the simple answer, can you poss elaborate on the ice you mentioned please?

thanks

snoopyuk

Hey Fritz thanks a lot for the detailed reply. It is very strange about the ice forming at the insntant of detonation, im assuming it doesnt last very long at all lol..
On a side note, I wonder how much water is thrown into the air during an underwater blast. I am aware that a lot of it will be instantly turned to vapor but I bet millions of tons of it are thrown up into the atmosphere as well.
Thanks guys, and thanks to the mod that gave me the applause

Originally posted by snoopyuk
thanks for posting this question Kronos,
and thanks to fritz for the simple answer, can you poss elaborate on the ice you mentioned please?

thanks

snoopyuk

Simply put Snoopy - no. I'm afraid that I can't.

When I was on my NBC Instructor's course at Winterborne Gunner way back in the Neolithic Age, I also asked the same question. The Officer in charge of course was also the Senior Instructor. Imagine the Nuclear Course work.

Scene 1: Welcoming address.

Officer addresses course intake, welcoming students to Nuclear Week. Behind him, film of various nuclear detonations rolls on; to his right is an overhead projector screen with various slides going on; to his left, is another OHP screen with more slides and across the room on the extreme right, is another short film about radiation.

Scene 2: Characteriostics of a Nuclear Explosion.

Officer presses hidden button. 12 x 500 watt bulbs are switched on and off.
After image lasts 20 to 30 minutes - about the duration of our tea break.

Scene 3: Questions.

Q. Why does ice form at the instant of detonation and why doesn't the fireball melt it, as it rises?

A. Because it can, and then because it can't. Have I made myself clear?

So you see my friend, I can only give you the answer my course officer gave me. Sorry.

Really though, the only thing I can think of, is the two phases of a nuclear explosion - the Positive and the Negative Phases.

During the Positive Phase, the rapidly expanding Fireball rushes out in all directions but pushing superheated air and a Thermal Pulse out in front of it. [This is also known as a 'push' phase.]

Behind the Fireball, at Ground Zero, there is nothing except a vacuum. Inside a vacuum, it is so cold [I think] that tiny particles of ice start to form.

As the energy of the Fireball, the Blast (Land) or Shock Wave [Water or Sea] and Thermal Pulse reaches the end of the Positive Phase, the vacuum collapses and everything rushes back towards Ground Zero. This is called the Negative or 'drag back' Phase.

As the dust and debris particles form the stem below the Fireball which by now is rapidly rising, the ice particles are trapped above the upper layer of the dust/debris cloud.

More and more water vapour in the air is attracted to the cloud and, as the cloud reaches higher and higher, ice continually forms, melts and reforms - much like an undersea volcano errupting - the lava spills out, rapidly cools, then spills out again. It never stops.

Kr0n0s, I really don't have a clue about water displacement during a detonation.

Again I can only reiterate that if you can see the detonation on film [try UTube etc] you will see the Fireball is in fact the Shock Wave, rapidly expanding.

I suppose water displacement is in direct proportion to the size of the weapon detonated. The 'Yield' would have nothing to do with this.

I'll see if I can get some info for u.

Originally posted by fritz

I suppose water displacement is in direct proportion to the size of the weapon detonated. The 'Yield' would have nothing to do with this.

Do you reckon you could explain the difference between the 'yield' and the 'size' of the weapon a bit more? I never thought there was a difference?

Unless you are talking about the physical size of the weapon case, i.e. width and length, and how much water that displaces, in which case just ignore me.

First, many thanks to Nygdan who, for some obscure and unknown reason, has voted me 'top something or other' and enabled me to get another 500 points. Many thanx my friend - although I'm not sure I deserve them.

Size and Yield:

I'm not too sure about this and having scoured all my old notes and talked to 2 current NBC instructors, it all boils down to how a weapon is detonated and the size the explosives and type of radiological element used - ish.

Roger so far......................................................?

OKay........... now for the science bit

On 7th May, 1945, during the so called 'Trinity test', scientists conducted a pre-nuclear detonation of 108 tons of TNT in order to calibrate machines and instruments that would be used later, to measure the effects of a nuclear detonation which were of course, unknown. This is why 'Yield' is now measured as being equivalent to tons of TNT.

In the actual event, a sphere of plutonium was compressed by 500 tons of TNT - producing 19 Kilotons of energy. The Nuclear Bomb was reality.

There are 4 types of nuclear detonation:

1. Gun-triggered Fission Bomb;
2. Implosion-Triggered Fission Bomb;
3. Modern Implosion-Triggered Design and
4. The Fusion Bomb.

1. Gun-triggered Fission Bomb;

The 'Little Boy' Atom Bomb was a uranium gun-type device and used a relatively small sphere [600 milligrams] of U235 with an even smaller
'bullet' of U235 as a triggering device - the bullet being fired into the sphere. The size of 'Little Boy's TNT was 9,700 lbs and produced a 'Yield' of 14.5 Kilotons;

2. Implosion-Triggered Fission Bomb;

'Fat Man', on the other hand, was a device measuring 5 feet in diameter, weighed in at 10,200 lbs and used a sphere of subcritical plutonium surrounded by an inner and outer sphere of both high and low explosives that are detonated simultaneously to compress the plutonium, producing the required chain reaction. 'Fat Man' produced a 'Yield' of 23 Kilotons.

While both these devices worked well for the technology of the time, both weapons were really heavy and required big and cumbersome aircraft to carry them.

To overcome this problem, scientists came up with the

3. Modern Implosion-Triggered Design Bomb:

This consisted of a sphere of Beryllium and Polonium in the core, surrounded by an outer sphere of Plutonium segments mixed with high and low explosives.

When the device detonates, the explosives drive the Plutonium segments together to produce a very rapidly shrinking sphere which strikes the
sphere of Beryllium and Polonium, the fission reaction is completed and the weapon explodes.

I am not too sure about the size of the explosives used but given the examples of 'Little Boy' and 'Fat Man', I have little doubt that the Modern Implosion Triggered design Bomb would produce a 'Yield' of several Megatons.

The Fission Bomb was vastly expensive, used hundreds of tons of explosives badly needed elsewhere and were again, large and heavy.

They were also very, very inefficient. At least a third of the energy produced went towards the nuclear initiation [detonation] itself.

Scientists such as Ulam and Teller wondered what would happen if you brought together, both implosion and a bullet triggered device in a single bomb. The result came to be known as the Thermonuclear or Fusion Bomb.

4. The Thermonuclear/Fusion Bomb.

Basically this is a Fission Bomb which, when detonated, is fired into a cylinder casing of uranium-238 that acts as a 'tamper'. Within the tamper is the lithium deuteride (fuel) and a hollow rod of plutonium-239 in the center of the cylinder. Separating the cylinder from the implosion bomb is a shield of uranium-238 and plastic foam [filler].

Basically as the Fission bomb detonates, it smashes into the U238, vapourising it and this energy smashes into the lithium deuteride and the U239 rod which collapses producing even more radiation, heat and energy and the bomb explodes.

A Thermonuclear or Fusion device weighing just a few thousands pounds can produce a 'Yield' of several Megaton.

So I think that the 'Size' of the explosive charge relates directly to the 'Yield' given off as a nuclear device detonates.

I do so hope that this explains the subtle differences between size and yield because to be honest, this has taken me 5 hours to read up my notes, drag a couple of mates away from their warm English beer and now all I want to do is watch 'Cross of Iron' on ITV 4.

There are loads of links - far too many to list, but sod it! Here are a goodly few:

en.wikipedia.org...

en.wikipedia.org...

en.wikipedia.org...

www.howstuffworks.com...

www.atomicmuseum.com...

Wow, thanks fritz. I kinda knew all that about the different bombs, but I always thought there were three: gun-type fission, implosion-type fission, and thermonuclear fusion, which is a two stage design. Your 'Modern Implosion-Triggered Design Bomb' really threw me off. Research time!

btw, you've got a WATS from me for the help.

I always thought there was the yield, and that was that. I mean, I think that talking about a nuclear/atomic weapons' 'size,' i.e. the amount of high/low explosive within the casing that is to compress the fissile material, would not help at all. A nuclear bomb from the 50's, take the Ivy Mike bomb for example, is going to be using a helluva lot more explosive than one from today, simply because they couldn't finely hone the design like they do today with computers.

So you could only really consider 'size' with modern (ish) weapons that do not have old-fashioned innards. In which case, I've heard the upper limit of the going rate is about 6 megatons of explosive power per metric ton the weapon weighs?

I cam across this "instruction manual" for building an atomic bomb a couple of years ago and was very surprised that this information was so easily found on the internet.. I googled it again so that i could post it hear, i hope my query didnt trigger eschelon lmao.
I hope its ok to post this, also didnt mean to hijack my own thread but i just thought this was interesting.
Also curious as to how true this is, so if theres any nuclear physicists on board here feel free to chime in

Source Page


BTW, good idea to give fritz a WATS vote. i did as well, he deserves it for the time hes put in and for the quality of his answers..
Thanks fritz

[edit on 29-1-2007 by Kr0n0s]

Kr0n0s thanx. Again, I'm not sure that I deserve any recognition or whatever because of my background but Hey Ho. Thanx.

Regarding Size and Yield. I have now spoken to a long time friend who works at DNBCC Winterborne Gunner who not only called me a pratt for forgetting the basics of nuclear technology, but also gave me the low down.

As previously stated, the Size of a given device [weapon] is proportionate to the Yield.

To be as simple as possible, if you take a 1 pound [size] lump of plastic explosive and mould this round a pellet of say, U238 or U239 and then detonate it, the amount of energy [yield] released can be measured in equivalent tons of TNT if it were detonated simultaneously.

So basically, size = energy released = yield.

Got it?..........................................I hope so.

Ahh, so size and yield are the same thing.

No watch_the_rocks, it does not.

'Size' relates to the pound for pound weight of the explosive used to trigger a nuclear device.

'Yield' relates to the amount of energy and radiation released at the moment of detonation.

'Dial-a-yield' refers to the ability of some thermonuclear devices to have their effects multiplied [or lessened] by using different quantites of fissionable or fusionable meteriels in said device.

I am sorry if I confused you. I confuse myself sometimes. This is a very complicated subject and we had this sort of lectures and radiological problems for a week. Imagine how my head must have felt. It was almost a physical relief to pass the nuclear phase test.