[Steve]

Steve asked the Naked Scientists:

We know how much energy and damage a hydrogen bomb inflicts, but if a helium bomb was possible how much energy and damage would it inflict?  More or less? my calculations say less since less mas is converted to energy. Am I right?


What do you think?

[DoctorBeaver]

The only effect of a Helium bomb would be to make everyone in a 5-mile radius talk funny!  []

I'm not sure of the actual science involved, but a helium bomb would be less powerful per given weight than a hydrogen bomb. It would therefore be a pointless exercise.

As Helium is the lightest element, it would have to be a fusion weapon. Fuse 2 Helium nuclei together & you get Hydrogen (I think), so you may as well start with Hydrogen which, as far as I know, gives the greatest yield per weight.

[JP]

You've confused Helium and Hydrogen, DoctorBeaver.  Hydrogen is the lighest element (atomic number 1) and you can fuse four hydrogens together to form helium (atomic number 2), which gives off a lot of energy.  This is the basis of the hydrogen bomb.  (See http://en.wikipedia.org/wiki/Proton-proton_chain)

If you fuse two helium nuclei together, you would get beryllium (atomic number 4).  Apparently this isn't stable and decays back quickly: http://en.wikipedia.org/wiki/Helium_fusion 
If you get 3 or 4 heliums to fuse together (extremely unlikely on earth) you'd get carbon or oxygen as a product.  I have no idea how much energy this gives off, and the odds of making a bomb out of it seem pretty small since you need temperatures and pressures higher than you get in our sun in order to start fusing 3-4 heliums together.

[Bored chemist]

He is cheaper than tritium- if it worked they would use it.

[syhprum]

If Helium could be coaxed into fusing which seem very unlikely you would have the technical problem of storing it as even to get it to a liquid form requires that it is cooled to 4°K and as yet it has not been forced into forming any compounds (such as Tritium will do) being the most inert of gasses.

[chris]

The above is not quite right in relation to hydrogen fusion. The Sun actually fuses 4 hydrogen atoms together to make one helium atom, a free neutron and some energy.

Chris

[JP]

Ah yes--I'll fix my post.  Thanks, chris.

[Bored chemist]

"The above is not quite right in relation to hydrogen fusion. The Sun actually fuses 4 hydrogen atoms together to make one helium atom, a free neutron and some energy."
I doubt that. The products would be roughly 20% heavier than the ingredients unless you are talking about rare isotopes.

[turnipsock]

You've confused Helium and Hydrogen, DoctorBeaver.  Hydrogen is the lighest element (atomic number 1)

I wondered who would spot that first, well done.

[JP]

"The above is not quite right in relation to hydrogen fusion. The Sun actually fuses 4 hydrogen atoms together to make one helium atom, a free neutron and some energy."
I doubt that. The products would be roughly 20% heavier than the ingredients unless you are talking about rare isotopes.

If Wikipedia is to be believed (and if I did the math right), the total fusion reaction that dominates in the sun is

2 electrons + 6 Hydrogen -> 1 Helium + 2 Hydrogen + 2 electron neutrinos + 6 photons + Energy

You need all 6 hydrogen to begin with, but if you subtract off the two that remain at the end, your net reaction is turning 4 hydrogen into 1 helium, neutrinos, photons and energy.  Of course it's totally possible I added wrong...

[chris]

Apologies; I got excited and wrote "neutron". I meant to write "neutrino".

Sorry, and thanks for picking up my pick up!

Chris

[lyner]

The fusion of H into He is a multistage process. The probability of two protons coming together, then another one and then another to make a He nucleus is very small and requires a long time, as well as extreme conditions like you find in the Sun. You get Deuterium and Tritium formed along the way to the final product.
The way that any viable fusion reactor works is, first, to separate the tiny amounts of Deuterium occurring naturally and /or to obtain Tritium (from Lithium?). It's quite a cheat, really and makes a nonsense of the worry about all the Hydrogen in the Oceans going up with a bang due to some 'chain reaction'.

[DoctorBeaver]

You've confused Helium and Hydrogen, DoctorBeaver.  Hydrogen is the lighest element (atomic number 1) and you can fuse four hydrogens together to form helium (atomic number 2), which gives off a lot of energy.  This is the basis of the hydrogen bomb.  (See http://en.wikipedia.org/wiki/Proton-proton_chain)

 [:I]

What on Earth was I thinking! I can't even blame the tequila this time.

[Dr. Dan]

The He fusion reaction is what makes a star go nova, so yes, there is the potential for a very big explosion there.

Someone above said the Sun did not have high enough temperatures to support the He fusion reaction(s).  This is incorrect.  The secret is the pressure.  In an old star where the hydrogen is about burned up, the core collapses on itself and suddenly you can have the start of the 'helium flash' explosion.  The star explodes like one huge bomb.  (Also includes the outer shell of unburned hydrogen which is triggered to fuse as well, adding to the explosion.)

It takes around 100 million kelvins to start the He reaction, which is within the capability of a hydrogen thermonuclear device. Why haven't we perfected the He reaction into a weapon yet?  I am sure some deranged person will eventually want to blow up the planet and perfect it, but luckily, they have not yet done so.

However, the theoretical work is interesting.

Someone stated the hydrogen reaction incorrectly above.  It is the D-T reaction that gives off an extra neutron.
one Deuterium (wt.=2) plus one Tritium (wt.=3) yields one Helium(wt.=4) plus one neutron (wt.=1)     D + T → 4He + n

Tritium being unstable it has to be created within the reaction chamber. This can be done using lithium in either of the following reactions.
n + 6Li → T + 4He      (exothermic)
n + 7Li → T + 4He + n   (endothermic)

It is also possible to react Deuterium with itself in either of the following ways
D + D → T + p
D + D → 3He + n

For those who don't know, deuterium is the name for hydrogen with an extra neutron, and tritium is the name given hydrogen with two neutrons (which is highly unstable).  To produce the above, a special type of lithium hydride called lithium deuteride is used. This will create the proper atomic components for the hydrogen reaction.

Oh, and to the person that thought the energy product released would be too low to make it worthwhile, that is true of the hydrogen devices too.  The reaction energy is much lower than the energy from a plutonium or uranium fission, and yet in practice, the results are over a thousand times greater.  Plutonium fission device ↑ 50 kilotons   Hydrogen fusion devices (built and tested) ↑ 50 Megatons.

[Soul Surfer]

The helium flash in stars causes violent brightening and the shedding of outer layers and probably nova processes but it is not the runaway process  that causes a supernova. 

the energy released by the thermonuclear processes is much less that that when hydrogen atoms are fused to helium it is only the gravitational energy of the collapse of large quantities of mass that makes the explosion violent.

Weapons processes use explosives and not gravitation to cause the collapse and compression so the synthesis of elements higher than helium cannot produce the violent explosion of the hydrogen bomb  without putting in significantly larger amounts of explosive energy to create the conditions in the absence of a gravitational field to do the job for you.

so helium bombs would have to be be a very big bang followed by a substantial fizzle!

[Dr. Dan]

I posted an answer, if you caught it already, great,
but I will send email and delete this post.

Instead, I will just say, yes, you are right.