ITHACA, N.Y. -- Like a physician examining X-rays, Leslie Allee lends an expert eye to the film hanging on the light screen.
No broken bones here. Allee, a Cornell University doctoral student in entomology, is looking at film that shows a thin white line branching off in different directions. Around it are three or four tiny white marks, maybe 1/4-inch long -- the objects of her attention. These are living corn rootworms in soil, caught in the act of searching for the plant root.
"Here you can see where they were when we started. In this picture you can see where they were 24 hours later. The dark lines show the path of the rootworm," she says.
No ordinary pictures, these. Allee is making use of a Cornell resource to study, along with Paula Davis, assistant professor of entomology, the behavior of this major corn pest in the hope of developing a natural way to control it.
By using the 500-kilowatt nuclear reactor on campus, the entomologists can get sharp pictures on film of their corn roots and the rootworms in soil around it. The technique is called neutron radiography, and professors from art historians and agronomists to zoologists can use it to get detailed pictures that X-rays cannot produce. It is the first time neutron radiography has been used to study insects.
"X-rays pass through the rootworms without attenuation. Neutrons, however, are attenuated by the hydrogen in the rootworms," Davis said. "With a neutron beam, we can also see the corn roots and see the behavior of the insects as they are growing. And it's all totally non-invasive."
Here is how it works: The TRIGA Mark II nuclear reactor at Ward Laboratory produces a
beam of neutrons that is focused to a plate holding a sample. Behind the sample is film.
The neutrons pass through the film (unlike X-rays, without activating the emulsion) and
land on a conversion screen (made of the rare-earth metal gadolinium) that absorbs them. The metal screen emi
Contact: Larry Bernard
Cornell University News Service