"In these tunnels, sodium ions are very loosely held," explains Clearfield. "Because cesium ions are bigger than sodium ions, when a cesium ion goes in and replaces a sodium ion, it cannot move around like the sodium ion. Instead it gets trapped."
In other inorganic ion exchangers, the ingoing and outgoing ions can each have different charges or the channels have different sizes. To study the exchangers' properties, Clearfield and his collaborators study their crystal structure by X-ray diffraction before and after the exchange of different types of ions.
"We try to make compounds in which either a sodium or a potassium ion is exchanged, and then we do the crystal structure," says Clearfield. "We try to exchange a given ion species with these crystals and then we do the crystal structure again, and we see what has happened to the ingoing and outgoing species. It can take from a few weeks to many months before we understand what happened."
Inorganic ion exchangers can also be used in nuclear medicine. Radioactive elements with short half-lives currently are used to determine blood flow or to locate a tumor. With the ion exchanger, it might be possible to better target the tumor by sparing surrounding healthy cells.
"If you could target a radioactive species directly into the tumor," says Clearfield, "and the health physicist would calculate, from the size of the tumor, how much radioactivity to inject, you would not damage the healthy tissue around."
Work is in progress and part of a project with Lynntech, Inc., a technology development
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Contact: Patrice Pages
patrice-pages@tamu.edu
979-845-4618
Texas A&M University
18-Jun-2001