[meteorite-list] Neutron freeing in large hypervelocity impacts

From: E.P. Grondine <epgrondine_at_meteoritecentral.com>
Date: Thu, 29 Oct 2009 20:42:54 -0700 (PDT)
Message-ID: <561849.73059.qm_at_web36902.mail.mud.yahoo.com>

Hi Rob -

Yes, I have read through all that before, but the spike that gets to me is that huge spike in the INTCAL98 data right around the time of the Barringer impact.

I don't think the neutron release is related to what hits, or what is hit, but rather just the total impact energy. I wonder what the big ones like Chicxulub or Shiva or Zamanshin will show. If part of the impact energy in the form of infra-red is concentrated in a small enough region, then releases could occur.

Take the IR measured from Tunguska for example, then scale massively and localize to points. Do we hit freeing energies?

Speaking of Beryllium, the protons released at the same time as the neutrons should be causing spikes in 10Be as well.

In closing, I have been wrong before, and reserve the right to be wrong both now and in the future.

E.P. Grondine
Man and Impact in the Americas
( a damn fine book, really, despite all its flaws)

"Matson, Robert D." <ROBERT.D.MATSON at saic.com>
Subject: Re: [meteorite-list] Odessa

E.P. wrote:

> Take a look at the INTCAL98 14C calibration chart. Major spikes appear
> to map to impacts.

"Spikes" in the C14 calibration chart can be caused by a number of
factors (including measurement uncertainty/error). But the main cause of
variability in the production rate of atmospheric C14 is simply variation in the flux of cosmic rays. Cosmic ray intensity is modulated by both the strength of the earth's magnetosphere and the sun's solar wind, neither of which is constant.

"From the other side of the equation, atmospheric C12 is ALSO modulated
by earthly processes (e.g. volcanic eruptions, ocean temperature
changes)which can produce regional anomalies in the samples used to build the radiocarbon calibration curves.

"There is no evidence that large impacts can cause nuclear reactions that
release neutrons. There isn't sufficient energy or fissionable material,
so I have difficulty coming up with a mechanism which could cause a
large spike in neutrons. I suppose if an impactor had an anomolously
high beryllium content and it happened to hit an earth location with rich
uranium deposits, then you could get a small neutron hiccup. But
siderites are very low in berrylium (< 10 parts per billion), so that's a no-go on Odessa. Even chondrites typically have only a few hundred parts per billion.

--Rob




      
Received on Thu 29 Oct 2009 11:42:54 PM PDT