Nuclear detonation inside the sun

What would happen if you detonated a nuclear bomb inside the sun?

I realize that getting any bomb to the sun would take an amazing
delta-V, and that surviving the thermal and pressure environment long
enough to get to any significant depth is... maybe not in the realm of
possibility.

But I'm curious about the effects of detonating a bomb in a dense
hydrogen medium. I would imagine the neutron and radiation burst
would stimulate fusion reactions in the surrounding hydrogen. Is
there a critical hydrogen density at which the reaction becomes
self-sustaining?

And, does anyone have an idea what the pressure/density gradient in
the sun might be? The average density is about 1.4 g/cc, but I
imagine you have to get in a long way before it gets that soupy.

In article ,
Iain McClatchie wrote:
But I'm curious about the effects of detonating a bomb in a dense
hydrogen medium. I would imagine the neutron and radiation burst
would stimulate fusion reactions in the surrounding hydrogen.

Not significant ones, or people wouldn't bother doing isotope separation
for building hydrogen bombs.

The easiest fusion reaction burning ordinary hydrogen is the proton-proton
chain, which starts with two hydrogens fusing into deuterium plus some
odds and ends. Even in star-core conditions -- much hotter and denser
than anything you will get at a reachable depth -- that reaction is so
slow that burning a mass of hydrogen that way takes billions of years.
(The time taken for the average pair of protons to undergo that reaction,
in star-core conditions, is estimated at seven billion years. Theoretical
estimates are all we have -- the reaction is far too slow to be measured
in the laboratory.)

The only reason the Sun can stay lit at all, with such a slow reaction
powering it, is that it has such a tremendous volume for that reaction to
take place in, and -- comparatively speaking -- such a very small surface
area for heat to be lost through.

(Imagine a hypothetical big fusion reactor, a sphere 150 meters across --
the supporting cradle for the sphere is roughly the size and shape of a
football stadium. Assume that its outer shell is a magical perfect
reflector, except for one tiny hole, a barely-visible pinhole 0.1mm
across, so that all the energy generated within that reactor has to come
out through that hole. That's about the same ratio of surface area to
volume as the Sun.)

Is there a critical hydrogen density at which the reaction becomes
self-sustaining?

Nothing short of a supernova reaches conditions severe enough to burn
ordinary hydrogen quickly. Hydrogen bombs aren't even in the same league.
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

you don't think that the sun is currently a self-sustaining fusion reaction?
fascinating.

"Iain McClatchie" wrote in message
om...
What would happen if you detonated a nuclear bomb inside the sun?

I realize that getting any bomb to the sun would take an amazing
delta-V, and that surviving the thermal and pressure environment long
enough to get to any significant depth is... maybe not in the realm of
possibility.

But I'm curious about the effects of detonating a bomb in a dense
hydrogen medium. I would imagine the neutron and radiation burst
would stimulate fusion reactions in the surrounding hydrogen. Is
there a critical hydrogen density at which the reaction becomes
self-sustaining?

And, does anyone have an idea what the pressure/density gradient in
the sun might be? The average density is about 1.4 g/cc, but I
imagine you have to get in a long way before it gets that soupy.

"Iain McClatchie" wrote ...
What would happen if you detonated a nuclear bomb inside the sun?

Sod all.

The Sun is Big. If I was to use the term 'drop in the ocean' I would be
vastly over-stating the significance of the 'drop'.

(Iain McClatchie) writes:

What would happen if you detonated a nuclear bomb inside the sun?

It would not even notice it.


I realize that getting any bomb to the sun would take an amazing
delta-V, and that surviving the thermal and pressure environment long
enough to get to any significant depth is... maybe not in the realm of
possibility.

But I'm curious about the effects of detonating a bomb in a dense
hydrogen medium. I would imagine the neutron and radiation burst
would stimulate fusion reactions in the surrounding hydrogen.

Nope. The energy-release would be negligible compared to the energy density
that already exists at the core of the sun. Moreover, "ordinary" hydrogen
cannot fuse without a weak interaction simultaneous with the collision
(and the probability of both of those simultaneously happening is so
absurdly small that it cannot be measured in the lab, but only calculated
theoretically). Furthermore, the concentration of deuterium in the core
of the Sun is FAR too small to sustain a "burn," since it is already being
consumed almost as fast as it is generated. Hence, there is no fuel that
could support a "runaway chain reaction" --- and if there _were_, the Sun
would have _already_ detonated itself !!!

Finally, the small fraction of the neutrons that manage to get captured by
protons before they decay would only produce a small amount of deuterium
(which would again be consumed almost immediately!), and said amount
would be no where near enough to make a significant difference.


Is there a critical hydrogen density at which the reaction becomes
self-sustaining?

Yes, but one only sees that sort of hydrogen density on the surface of
white dwarf or neutron stars accreating hydrogen from their companions
--- which is many, MANY, =MANY= times larger than the core of the Sun,
and far beyond the density that any current human-created process could
possibly achieve.


And, does anyone have an idea what the pressure/density gradient in
the sun might be? The average density is about 1.4 g/cc, but I
imagine you have to get in a long way before it gets that soupy.

The core of the Sun has roughly ten times the density of lead.


-- Gordon D. Pusch

perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;'

Henry, Gordon,

once again you provide fascinating info. Thanks.

It sounds like fusion in the Sun is rate limited by the production of
deuterium. So it sounds like exploding a nuclear bomb in the sun
is very similar to simply releasing the equivalent mass of deuterium
at sufficient depth. The local fusion rate goes up, consumes all the
deuterium, and then drops right back down again.

But I wonder about deuterium production being sped up by the local
pressure and temperature around the bomb's fireball.

Gordon says the hydrogen density in the star core is around 100 g/cc.
A quick google says the core temp might be 1.5e7 K. Henry says the
mean time for a H+H-D is 7 billion years in those conditions.

To speed up deuterium reactions to the point that the explosion would
be self-sustaining, the mean time for H+H-D would have to be
measured in ns, or 1e26 times faster. This does seem like a pretty
good safety factor.

Suppose you detonated a 100 MT bomb closer to the surface of the Sun,
where the hydrogen was at about 1 g/cc. It doesn't seem out of the
realm of possibility that for a few ns, the surrounding plasma would
be compressed to 100 g/cc. According to Carey Sublette's FAQ, the
temperature of the early nuclear fireball is 6e7 to 10e7 K. That's
quite a bit hotter than the Sun's core.

I suppose we don't know much about the rate vs (temperature, density)
curve for the H+H-D reaction if it's so slow. Assuming that it's
exponential in temperature, the rate would have to double for every
million degrees K in order to keep up with the rate at which the
fireball would otherwise cool down.

Is there any information on the temperature or pressure sensitivity
of the H+H-D reaction?

Nothing short of a supernova reaches conditions severe enough to burn
ordinary hydrogen quickly. Hydrogen bombs aren't even in the same league.

I suppose this gets back to your original quip, Henry. If H+H-D was
fast enough at 100M K, then three-stage bombs probably wouldn't bother
with deuterium since plain hydrogen would work fine.

Iain McClatchie wrote:
Henry, Gordon,

once again you provide fascinating info. Thanks.

It sounds like fusion in the Sun is rate limited by the production of
deuterium. So it sounds like exploding a nuclear bomb in the sun
is very similar to simply releasing the equivalent mass of deuterium
at sufficient depth. The local fusion rate goes up, consumes all the
deuterium, and then drops right back down again.

But I wonder about deuterium production being sped up by the local
pressure and temperature around the bomb's fireball.

The p+p reaction is very slow, so it's doubtful much would happen.

Now, if the Sun were a really old red dwarf ( current age of the universe),
it would have accumulated a lot of 3He in its core. It might be possible
to get *that* to explode.

Paul

(Iain McClatchie) writes:

It sounds like fusion in the Sun is rate limited by the production of
deuterium.

That is correct.


So it sounds like exploding a nuclear bomb in the sun is very similar
to simply releasing the equivalent mass of deuterium at sufficient
depth. The local fusion rate goes up, consumes all the deuterium, and
then drops right back down again.

Crudely but approximately correct.


But I wonder about deuterium production being sped up by the local
pressure and temperature around the bomb's fireball.

As already stated, the energy released by the bomb is negligible compared
to the energy density that already exists at the core of the sun ---
it's be light tossing a match into a blast furnace !!!


Gordon says the hydrogen density in the star core is around 100 g/cc.
A quick google says the core temp might be 1.5e7 K. Henry says the
mean time for a H+H-D is 7 billion years in those conditions.

To speed up deuterium reactions to the point that the explosion would
be self-sustaining, the mean time for H+H-D would have to be
measured in ns, or 1e26 times faster. This does seem like a pretty
good safety factor.

Suppose you detonated a 100 MT bomb closer to the surface of the Sun,
where the hydrogen was at about 1 g/cc. It doesn't seem out of the
realm of possibility that for a few ns, the surrounding plasma would
be compressed to 100 g/cc.

A few nanoseconds is insufficient. One needs to maintain those temperatures
for _BILLIONS_ of years, as henry has already noted.


According to Carey Sublette's FAQ, the temperature of the early nuclear
fireball is 6e7 to 10e7 K. That's quite a bit hotter than the Sun's core.

....But still not hot enough to make the p+p -- d + e^+ + \bar\nu reaction
go significantly faster: 10e7 kelvin is only a mere 10 keV, whereas typical
nuclear reactions require energies two orders of magnitude higher, on the
order of several MeV, and weak interactions are characterized by energies
on the order of many tens of GeV, almost seven orders of magnitude higher.
(The only reason fusion can occur in the core of the Sun at all is that
two protons can quantum mechanically "tunnel" through the coulomb energy
barrier that separates them to (briefly!) get close enough to fuse, if one
of them _also_ happens to coincidentally inverse-beta decay to a neutron
withing the time limitations imposed by the Heisenberg Uncertainty Principle
for energy.)

Furthermore, "hotter" is not "better:" Deuterium is a very fragile nucleus;
it is just _barely_ bound by the nuclear force (1.1 MeV/nucleon), so heat it
up past 12 billion kelvin or so, and you start breaking it apart into protons
and neutrons instead of fusing protons together...


I suppose we don't know much about the rate vs (temperature, density)
curve for the H+H-D reaction if it's so slow.

"Abysmally slow" would be a good term for it. (Essentially all of
the _minuscule_ amount of deuterium in the universe was created by
the Big Bang, and stellar and brown-dwarf fusion have been steadily
consuming it ever since...)


Assuming that it's exponential in temperature, the rate would have to
double for every million degrees K in order to keep up with the rate at
which the fireball would otherwise cool down.

....Which in fact it does not. The characteristic energies are MUCH higher,
corresponding to temperatures of _BILLIONS_ of degrees, not millions!


Is there any information on the temperature or pressure sensitivity
of the H+H-D reaction?

Sure --- check any textbook on stellar physics. You'll find that the
reaction-rate sucks under even "Big Bang" conditions, and that if you
get it _too_ hot, the breakup reaction d -- p + n overwhelms the
p + p -- d + e^+ + \bar\nu reaction.


Nothing short of a supernova reaches conditions severe enough to burn
ordinary hydrogen quickly. Hydrogen bombs aren't even in the same league.

I suppose this gets back to your original quip, Henry. If H+H-D was
fast enough at 100M K, then three-stage bombs probably wouldn't bother
with deuterium since plain hydrogen would work fine.

A-yup...


-- Gordon D. Pusch

perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;'

In article ,
Iain McClatchie wrote:
It sounds like fusion in the Sun is rate limited by the production of
deuterium...

Quite so. The other reactions in the proton-proton chain are not exactly
speed demons either -- if memory serves, the average time to add a proton
to deuterium to make He3 is seconds, and then the time for two He3's to
fuse to make He4 and two protons is thousands of years -- but production
of deuterium is definitely the rate-limiting step.

I suppose we don't know much about the rate vs (temperature, density)
curve for the H+H-D reaction if it's so slow.

My understanding is that we have no experimental data at all, but the
theoreticians could probably venture a guess. I don't know what it would
be, though.
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

"Henry Spencer" wrote in message
...
In article ,
Iain McClatchie wrote:
It sounds like fusion in the Sun is rate limited by the production of
deuterium...

Quite so. The other reactions in the proton-proton chain are not exactly
speed demons either -- if memory serves, the average time to add a proton
to deuterium to make He3 is seconds, and then the time for two He3's to
fuse to make He4 and two protons is thousands of years -- but production
of deuterium is definitely the rate-limiting step.

I suppose we don't know much about the rate vs (temperature, density)
curve for the H+H-D reaction if it's so slow.

My understanding is that we have no experimental data at all, but the
theoreticians could probably venture a guess. I don't know what it would
be, though.

For the best overview of this subject, to the man himself - Bethe's Nobel
lectu
http://www.nobel.se/physics/laureate...e-lecture.html

You will see (pg. 11 of the PDF) that the H+H-D reaction is very
insenstive to temperature, and the rate of increase flattens out as the
temperature rises, and is nearly flat above 30 million K. Thus no amount of
heating will increase the rate markedly, the limiting increase is about a
factor of 10 over the sun's energy production rate in the core - this is 70
erg/g-sec (Sun's core rate is 7 erg/g-sec, its average rate is 2 erg/g-sec).
If you do the math, you find that 70 erg/g-sec is 0.5% of the average
metabolic rate of a human. That is to say - average human tissue produces
heat 7000 times faster than the Sun's average.

The theoreticians estimates on this are very, very good. Models based on
theory accurately describe the observable behavior of stars.

Carey Sublette