[meteorite-list] Meteorites That Glow (Was: Ultraviolet Space Rocks?)

From: bernd.pauli at paulinet.de <bernd.pauli_at_meteoritecentral.com>
Date: 02 Oct 2010 13:39:28 UT
Message-ID: <DIIE.000000390000511B_at_paulinet.de>

S.W.S. McKEEVER and D.W. SEARS (1980) Meteorites
That Glow (Sky and Telescope, July 1980, pp. 14-16, excerpts):

In 1802, Edward C. Howard exposed a sample of the Benares meteorite
to an electrical discharge and it glowed in the dark.

A. Herschel discovered that some grains from the Middlesbrough meteorite
glowed distinctly when sprinkled onto a hot plate in the dark (= thermo-
luminescence [TL] a result of heat stimulation).

Thermoluminescence

Ordinary chondrites luminesce brightly with a maximum at about 200?C;
a second peak occurs at 350?C, and the color at both peaks is blue green.

Aubrites are a small class of meteorites with an entirely different glow
curve, with several peaks and colors ranging from blue to red.

In ordinary chondrites the mineral feldspar produces the TL

In aubrites, enstatite is primarily responsible.

Cathodoluminescence

Samples irradiated by an electron beam can glow with what is called cathodo-
luminescence (CL). The electron gun and an optical microscope each point to
a spot on the specimen's surface, and the result is observed directly.

Most thermoluminescent minerals also turn out to be cathodoluminescent.
CL is bright, so luminescent grains in the slice of a meteorite are easy
to locate, and they can be photographed through the microscope.

As in TL, feldspar produces most of the light, a distinctive blue green.
Feldspar is an important component of ordinary chondrites and the chondrules
in them. Their intricate, often beautiful structures are strikingly revealed
by CL.

Applications

Determining the cosmic age of meteorites by spotting the red CL of chlorapatite
against the blue background of feldspar and examining the nuclear fission tracks
of now-extinct isotopes like plutonium 244.

Determining the terrestrial age of meteorites: decrease in TL
provides a means to estimate how long ago a meteorite fell.

TL levels can help detect heating processes of meteoroids
in space, for example: a close passage to the sun.

Detecting meteorites that suffered a violent event (shock and heating attending
the parent body breakup). This caused them to blacken and lose their TL and CL.
Such shock-darkened meteorites seem to be much younger.

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Best wishes,

Bernd
Received on Sat 02 Oct 2010 09:39:28 AM PDT