[meteorite-list] Neutron production in hyper-velocity impacts

[Göran Axelsson]

Rob Matson wrote:

... snip ...
> I still have a big problem coming up with the mechanism by which
> E.P.'s large impact is supposed to generate these neutrons.  Since
> the temperature is too low to achieve a nuclear reaction thermally,
> and the impact velocity is far too low to do it kinetically, the
> only thing left I can think of is some sort of fusor-like plasma
> reaction -- alas, without the benefit of deuterium.   --Rob
>
>   

As the temperature that is required to get kinetic fusion between atoms 
is way too high to be reached in an impact that way to generate neutrons 
is closed. The only remaining way that I see is by photo spallation of 
atoms by high energy photons.
Typically photons begin to produce neutrons on interaction with normal 
matter at energies of about 7 to 40 MeV

For you who don't feel at home with electron volts as energy unit, MeV 
is huge, visible light lies in 1.5-3 eV, x-rays between 124 eV to 124 
keV, and gamma rays above that.

What needs to be calculated is the number of photons that is emitted by 
the plasma surrounding the impactor during it's ascent. A good 
approximation should be black body radiation and with the knowledge of 
area and typical plasma temperature a number of high energetic photons 
could be calculated.

Basically I see the "possible" process to be...
 1. An impactor enters the atmosphere and creates a plasma.
 2. The plasma acts as a black body, radiating energy in a continuous 
spectra from IR, visible, UV, x-rays and up to gamma rays.
3. Photons with a sufficient energy has the possibility to eject 
neutrons from ordinary atoms.
4. After cooling down by repeated impacts with atoms the neutrons are 
finally absorbed by nitrogen atoms creating carbon 14.

To get a number we need to
 1. Get the plasma temperature (literature sources, maybe measurements 
from Shoemaker-Levy 9?)
 2. Calculate the amount of photons, this is just a matter of using 
Stefan-Boltzmann law or Plancks law. We also have to get an 
approximation of the size of the fireball.... or is it a plasma ball?
3. Divide the number above by half. Half of the neutrons will hit the 
impactor and be absorbed in other atoms.
4. Find the elusive constant that describes how many photons actually 
creates a neutron and not nuclear fission. This one is for a nuclear 
physicist to calculate.
5. Compare the number of atoms created with the amount of C14 already in 
the atmosphere.

Am I totally wrong or not? Anyone wants to try to do all or part of the 
calculation needed to finally let this assertion die?

My gut feeling is that there is at best a minute amount of C14 created 
by a hyper velocity impact. My best argument against it is if a large 
impact would create nuclear reactions then every meteor striking the 
atmosphere would also create C14 and with all the incoming material in 
form of micrometeorites it would add a large portion to the C14 in the 
atmosphere. I'm sure that some scientists would have noticed the 
difference between C14 produced by cosmic radiation and the amount added 
to the atmosphere each year.

Göran