[meteorite-list] Question

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Mon, 31 Dec 2007 03:33:23 -0600
Message-ID: <0be901c84b90$310f28b0$b64fe146_at_ATARIENGINE>

Hi,

    All elements have a minimum threshold for photoneutron
production. The maximum photoneutron production occurs
at often higher energies. The lowest photoneutron threshold
is for poor old deuterium which has only one neutron to cough
up, of course, and it's 2.32 MeV. Photoneutron production
peaks at about ten times that value. Denser materials like metals
have higher thresholds and peak closer to the threshold, like
lead, whose threshold is around 7 MeV. (People frequently have
quite unreasonable notions about trusting lead shielding; true, it
will stop 10 MeV photons... by effectively translating them into
neutrons!) 25 MeV will pretty much kick plentiful neutrons out
of most elements.

    The x-rays produced by electrons striking a metallic target
is a mechanism for producing energetic photons and it is the
original "discovery" means of producing so-called "Roentgen Rays,"
what today we call x-rays, technically any photon with a wave
length of 10 nm down 0.01nm. "Soft" x-rays (like from the TV
tube), the longer wavengths, are actually an overlap with what
we would call extreme ultraviolet today. "Hard" x-rays, the shorter
wave lengths, shade up into gamma rays.

    You don't even need the 25 kV of an old TV to generate "soft"
x-rays; a few kV's will produce feeble (but still damaging!) x-rays.
Oddly enough, and largely forgotten today, is the fact that the
human eye can directly "see" x-rays. Roentgen himself observed
a "pale blue diffuse" glow from one of his more powerful first
x-ray tubes -- through a wooden door! He dismissed it as unreal
until the phenomenon was called to his attention by other early
experimenters. It requires that the eye be completely dark-adapted,
as if you were using an astronomical telescope. It is not known
whether the x-radiation stimulates the visual pigment directly or
the optical nerves, but however it does it, we're pretty sure that
it ain't good for you! Git out of there!

    More powerful x-rays can also stimulate air to produce "full
spectrum" airglow, a bright white light where the x-ray beam is,
making it appear that the x-ray beam is a "shaft of very bright light."
This has only rarely been observed, as it is an even more dangerous
phenomenon than the directly stimulated blue glow -- if you ever
see it, run, don't walk...

    While there is much to be learned from stream meteor meteoroids
my intuition tells me that attempting to scale between the phenomena
associated with an impactor of a 1-3 millimeters and an impactor that
is one kilometer is a waste of time, as one has a million trillion times
the size (mass) of the other. Very few events scale well over a range
of 10^18!

    Mention has been made of the "electrophonic" sounds of fireballs,
mechanism unknown, that produces low frequency radio waves (10
to 10,000 hertz) strong enough to cause natural oscillators to convert
them into audio (acoustic) waves. They are a great source of argument:
http://www.geocities.com/CapeCanaveral/Cockpit/3240/electro1.htm
Again, arguments about energy and sources and unknown mechanisms.
(Lot of that going around.)

    The only other phenomenon on this planet with the energy to produce
similar waves are the more powerful lightnings, with plasma temperatures
of 30,000 Kelvin or more. As for their electric potential, the dialectric
breakdown of air is about three million volts per meter, so a "small"
1000 foot bolt has a potential of a GigaVolt, or one billion volts,
sufficient to accelerate particles substantially (and a TeraJoule of
energy, too). As for the electrophonic radio waves of lightning, they
are easy to observe, but hard to account for.

    In 1992, it was hypothesized that lightning was triggered by cosmic
ray shower events (frequent enough to do it) which generated ionized
pathways long enough for the bolt to begin (what triggers lightning is
a mystery). In 1994, NASA released reports of TGF's (Terrestrial
Gamma-Ray Flashes) accidentally observed by the Compton Gamma
Ray Observatory. Further studies show that there are at least 50 short
intense gamma ray bursts in the earth's atmosphere each day and that
their energies average 20 MeV or higher.

    After many years, one TGF was coordinated with (within 1500
meters of and simultaneous with) a large lightning strike, so it is now
assumed that lightning is capable of generating gamma ray bursts,
unless something else generates the gamma ray burst and it triggers
the lightning by ionization, of course. How even the high electric
potential of a lightning bolt would generate a substantial burst of
gamma rays is a complete and utter mystery.

    Jumping back momentarily to electrophonic sound and meteors,
it is noteworthy that while both lighning and fireballs generate similar
strong low frequency radio waves, the electrophonic sounds produced
by lightning (they have been observed) can be heard by sympathic
oscillation in the audio range only a very short distance from the "bolt"
itself, while the electrophonic sounds of meteor fireballs apparently
have a range of at least 80 miles (or more). Since we have no idea of
how these radio waves are generated (another complete and utter
mystery), this may say nothing more than that exotic mechanisms
at work in meteoritic entry are not inferior in strength to those of
lightning.

    I think all the urgings to do basic "black body" calculations for
impacts is admirable... and wasted. As an approach, it's both far too
theoretical AND too unsophisticated. I sit in a room well-lit by tiny
devices (called light bulbs) a small portion of which has a black body
temperature of over 4,000 degrees; I didn't need to heat the entire
room to 4000 degrees to illuminate it properly, only about 1 gram
of it -- the filament.

    Analysis: a mechanism existed to channel a small energy (for a
big light bulb, less than the heat radiated by my own slow chemical
engine, the body), mechanisms channeled that little energy into a tiny
area and amped a few atoms up enough to light 100 cubic meters. The
mechanism is the key. How does lightning generate gamma rays intense
enough to be picked up (off-axis) by space observatories in orbit?
Obviously, there is a mechanism, since "on paper" or by black body
calculation of lightning, it is utterly impossible.

    Einstein said God was "subtle." He also said God was "devious but
not malicious." Although I greatly respect Albert's opinion, I'm more
cynical. Would you settle for "tricky"? It is likely more fruitful to look
for evidence of a phenomenon than to theoretically decide whether it
can or can not exist and act on that basis alone. I'm always impressed
by how much we don't know.

    He's tricky, you know.



Sterling K. Webb
------------------------------------------------------------------------
----- Original Message -----
From: "Chris Peterson" <clp at alumni.caltech.edu>
To: "LIST" <meteorite-list at meteoritecentral.com>
Sent: Sunday, December 30, 2007 8:35 PM
Subject: Re: [meteorite-list] Question


The problem with X-rays from TVs wasn't with B&W, but happened when
color TVs made the scene. An X-ray tube works by bombarding a metal
target with energetic electrons. Color TV tubes have a metal screen just
before the phosphor that acts as a mask to make sure the correct gun
sees only the corresponding colored phosphor dots. It is the electrons
hitting this metal mask that produces X-rays. These are soft X-rays,
with energies on the order of 10 keV. Meteors may well produce some
X-rays, but at meteor temperatures these would also be soft X-rays. Even
very hard X-rays, up as high as 1 MeV, don't have enough energy to
liberate neutrons (typically). For that you need several MeV, what would
be considered gamma rays.

Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com


----- Original Message -----
From: "Peter A Shugar" <pshugar at clearwire.net>
To: "LIST" <meteorite-list at meteoritecentral.com>
Sent: Sunday, December 30, 2007 7:03 PM
Subject: [meteorite-list] Question


> Hello List,
> I have a question.
> Years ago when tv's were "young" one of the problems was that the
> acceleration of electrons from the cathode to the plate " the screen"
> was that when the electron collided with the screen, Xrays were
> generated.
> Granted that the level was not near as large as what would be
> generated if
> you got a chest Xray, or a mamogram, It was never made clear what
> caused the Xrays. I do remember that the ultra high voltage was on the
> order of 25 to 35KV.and if this was enough to cause Xrays, then the
> energy needed to creat Xrays is not very large. The ionization trail
> of the atmosphere as the meteorite plows through it will cause plenty
> of electrons to help create the Xrays.
> If the Xrays knock particles around that can cause the Nitrogen to
> convert to C14 then maybe there may be more Xrays than what we
> thought there was.
> I would venture to say that this might also bear investigation.
> Pete

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Received on Mon 31 Dec 2007 04:33:23 AM PST