October 17, 1997
Contact Ron Brown LSU News Service 504 388-3867 e-mail: [email protected]
BATON ROUGE -- Astronomers at two Louisiana universities investigating an old cosmological mystery have produced some very down-to-earth results.
They have developed a sensor that will be able to do such things as detect very small tumors in mammograms or determine whether the paint on your wall has lead in it.
Greg Stacy, an astronomer working at both LSU and Southern University, and LSU gamma-ray astronomers Mike Cherry and Greg Guzik, along with Brad Ellison, head of the LSU physics department's electronics lab, recently received a patent on the sensor, which was originally developed to help pinpoint the mysterious cosmological phenomena of "gamma-ray bursts."
Showers of gamma-rays -- high-energy x-rays -- reach earth about once a day from random points in the sky. Astonomers have been aware of these bursts for about 30 years, but until recently, no one had ever been able to find a visible counterpart to them, Stacy said, because each one comes from a portion of the sky too large to search before the burst dies out.
But in February, astronomers using several spacecraft and the Hubble Space Telescope detected a fireball associated with a gamma-ray burst. The fireball grew in intensity and then diminished over the course of five days.
"For the first time it was possible to determine the position (of one of these events) accurately enough to focus with an optical telescope and identify the object," Cherry said.
The visible light from the event permitted astronomers to make a spectrographic analysis of the object and determine its redshift -- the amount by which light is shifted from its normal place on the spectrum toward the red end of the spectrum. The redshift enables astronomers determine how far away an object is.
"We are looking at something that happened several billion years ago, when the universe was about 40 percent of its present age," Cherry said.
The characteristics of light from the fireball indicated it may have come from two neutron stars spiraling into each other, Stacy said.
Gamma-ray bursts are highly energetic events. According to NASA, if they are as distant as the new observations suggest, they are the most violent explosions known, emitting in one second as much energy as the sun will release in its lifetime.
To more accurately pinpoint where these events originate, Cherry and his colleagues have developed a device that is the high-tech equivalent of the old pinhole camera. If you draw a line from a pinhole in a piece of paper to the spot of light the pinhole casts, you can project that line backward all the way to its source. That is the principle on which the device works.
But rather than using a single pinhole, the detector will use a tungsten plate perforated with many holes to cast an x-ray "shadow pattern." And rather than casting this pattern on a photographic plate, it will cast it onto a charge-coupled device, or CCD.
CCDs are light-detecting silicon wafers commonly found in video cameras. They can be designed to detect either visible light or x-rays.
Unlike the CCD in a video camera, the CCD the LSU group has developed is extremely sensitive and so fast it can register a single photon falling on its surface.
It is these qualities that make their CCD a potentially valuable tool for other uses. "Suppose you want to take a picture from a fast-moving airplane, or take a picture through a microscope of a transient biological process," Cherry said. His CCD will register it.
The improved CCD will do other things as well.
"Different elements emit photons at characteristic wavelengths. Imagine you want to do a survey to find out whether any of the paint on your wall has lead in it. Spectroscopic analysis of the photon can determine what element it came from,"Cherry said.
Another potential application is x-ray mammography. Very small tumors, especially in younger women with dense breast tissue, are difficult to distinguish from the surrounding tissue. "One way of enhancing the contrast is by measuring the energy of the x-rays,"Cherry said. Conversely, physicians would be able to get the same contrast they get now with a lower x-ray exposure, he said.
The first prototypes of the chip are now being tested. "The next step is to build up the electronic circuitry to read the signals," Cherry said. "It should be completed by fall."
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