[meteorite-list] Neutron and Proton production in hyper-velovity impacts

From: E.P. Grondine <epgrondine_at_meteoritecentral.com>
Date: Sun, 30 Dec 2007 14:41:02 -0800 (PST)
Message-ID: <190657.36753.qm_at_web36904.mail.mud.yahoo.com>

Hi Gran, all -
Nice reply. Thanks much for the information on photon
energy levels. But you're analyzing two different
cases...

>My gut feeling is that there is at best a minute
>amount of C14 created by a hyper velocity impact.

That's why the spikes in the data in the INTCAL98 C14
chart are so important. Those spikes APPEAR to
correlate with large hyper-velocity impacts.

What you've described is normal meteors, where you
have a pea size grain being stopped by the atmosphere
- large surface area/mass ratio. Meteors also have a
regular flux, which does not very that much year per
year, and any C14 would be quickly dispersed and lost
in the general noise of regular production.

One big question is x-ray production by meteors - that
would give a better idea of the energy states of the
photons produced by a normal meteor. Electrophorenic
sound has been discussed many times here on the list,
and that may also have a bearing.

Of course, there's the intermediate case of bollides,
where you have limited releases of binding energies.

For large impactors, the atmospheric entry process can
be ignored.

For large impactors, we know that the binding forces
on a molecular level have been released, as we can see
 the spherules, but binding forces on the atomic
level...

I don't know whether any data on neutron or proton
production was gathered for the Shoemaker Levy 9 comet
fragment impacts. I think even the measurements of the
photon releases went off the sensors' scales - they
went white. I suppose one could extend the observed
visible, x-ray and gamma ray production to estimate
photon production at the 7-40 MeV level.

E.P. Grondine
Man and Impact in the Americas

>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 [descent}. 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.

G?ran


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Received on Sun 30 Dec 2007 05:41:02 PM PST