seal  Purdue News

February 1997

Dangerous UV light snakes its way into the shade

NOTE TO JOURNALISTS: A fish-eye-view color photo of the sky with a leafy canopy is available. It's called Grant/UVlight

WEST LAFAYETTE, Ind. -- You're at a softball game on a hot, sunny summer day. You left the sunscreen in the car, so you put the baby down under a tree, figuring the shade will protect her.


Cancer-causing ultraviolet-B (UVB) light can snake its way around the shade, according to research by Purdue University agronomist Richard Grant and the U.S. Forest Service's Gordon Heisler. Their research was reported in December in the International Journal of Biometeorology.

Because you can't actually see UVB, Grant says, you can't easily gauge how much is hitting you. People commonly -- and mistakenly -- equate the amount of UVB exposure to the amount of visible light they see, according to Grant.

"When people in the shade estimate UVB exposure based on an eyeball assessment, they're getting about twice as much UVB as they think," Grant says. UVB, unlike visible light, doesn't shine down in a straight line from the sun. It bounces around in the atmosphere.

"How much UVB you're getting more closely correlates with how much sky you can see," Grant says. "If lots of the sky is obstructed, you're getting a lot less UVB."

In other words, if you're in a grove of trees or surrounded by tall brick walls with direct light hitting you, you're probably better off than you would be in the dense shade of a lone tree in a field.

What about winter exposure? Snow reflects between 30 percent and 95 percent of the UV reaching it, while green summer grass reflects only about 5 percent, Grant says.

However, UVB exposure generally is less on a snowy day than on a sunny summer day, because the amount of UV reaching earth at a snow-producing latitude of 40 degrees is about three to five times higher in summer than winter, according to Craig Long, a meteorologist for the National Weather Service. There are exceptions. People skiing in the mountains of Colorado face greater exposure risks because the thinner air layer absorbs less UVB.

Two types of ultraviolet light hit the surface of the earth: UVA and UVB. UVA gives people a tan, but causes little harm to plants and animals. The shorter-wavelength UVB, on the other hand, can damage plant tissue. It also causes skin cancer in humans and can impair immune systems.

Grant and Heisler noticed that articles in the popular press urged people to duck into the shade to avoid unwanted ultraviolet exposure. That advice ran counter to what Heisler and Grant knew about the way UVB travels, but they couldn't find any studies that proved the point. So they decided to do their own.

With combined funding from Purdue and the U.S. Forest Service, Heisler and Grant took measurements of UVB along tree-lined streets, in farm fields and in grassy areas away from streets. At each test point they also took a fish-eye view photo, which gave them a complete picture of the sky and allowed them to measure how much sky-view was obstructed.

CONTACT: Richard Grant, (765) 494-8048; e-mail,

Purdue lab helps solve mysteries, aids scientific studies

WEST LAFAYETTE, Ind. -- Purdue University researchers have combined chlorine, cosmic rays and a particle accelerator to help solve a mystery about the earth's ancient climate.

Scientists at the Purdue Rare Isotope Measurement Laboratory, or PRIME Lab, recently conducted experiments that helped scientists from New Mexico determine that 20,000 years ago, temperature fluctuations in the North Atlantic were part of global-scale climate variations.

That's just one example of how researchers across the country rely on PRIME Lab in a wide variety of investigations, from studying soil erosion and weather patterns to tracking aluminum absorption in humans to dating ancient glaciers, archaeological artifacts and meteorite falls.

PRIME Lab scientists specialize in accelerator mass spectrometry, a technique that uses a particle accelerator to "count" the number of rare atoms, called radioisotopes, of a given substance in a sample.

Researchers have used the technique and the Purdue facility to date geologic events such as ancient glacial activity in Wisconsin and California. Such investigations aid in the study of the past climate, and may shed light on future climatic patterns. Studies also are under way to trace how calcium, aluminum and cholesterol are absorbed in the body.

The lab also is used to date and determine the origin of meteorites that have fallen to earth, and to track the flow of pollutants in samples of air and ground water.

Radioisotopes have been used for many years to obtain information, but before accelerator mass spectrometry, accurate results were hard to achieve unless large quantities of the sample material were available. For accelerator mass spectrometry, scientists need a much smaller sample, as small as a milligram in some cases.

PRIME Lab was established in 1992 as one of three National Science Foundation research facilities for accelerator mass spectrometry. The lab also receives funding from the W.M. Keck Foundation of Los Angeles. The Web page for the lab is

Here's an example of a project the lab was recently involved with. Details of this study were published in November in the journal Science:

Researchers at the New Mexico Institute of Mining and Technology set out to determine whether cycles of extreme temperature fluctuations in Greenland late in the last ice age were part of global-scale climate variability or were restricted to the North Atlantic.

The New Mexico scientists gave researchers at PRIME Lab rock samples from four sites in the Sierra Nevada mountains in east-central California. The rocks had been gouged out of the mountains by advancing glaciers during the last ice age, and when the glaciers melted, the rocks were left behind in piles called moraines.

Rocks that previously had been buried in the mountain were left on top of the moraines, where they were exposed to the sky for the first time. They also were exposed to cosmic rays, high-energy, fast-moving nuclear particles from outer space.

"When cosmic rays hit the rock, they produced chlorine-36," says David Elmore, director of PRIME Lab and a professor of physics who analyzed the rocks. Chlorine-36 is a radioactive isotope of the element chlorine, which normally contains 18 or 20 neutrons. Chlorine-36 contains 19 neutrons, giving the isotope a slightly different mass.

"There was negligible chlorine-36 in this rock before it was exposed to the sky, but it accumulates over time as the rock is bombarded with cosmic rays," Elmore explains. "By counting how many chlorine-36 atoms were in a given mass of the sample, we could tell how long the rock had been exposed, and hence the approximate date when the glacier melted."

Elmore and colleague Pankaj Sharma determined that the rocks were exposed about 20,000 years ago, near the time of the North Atlantic temperature fluctuations, supporting the hypothesis that temperature fluctuations during the last ice age were part of global-scale climate variations.

CONTACTS: Elmore, (765) 494-6516; e-mail,

Fred M. Phillips, New Mexico Institute of Mining and Technology, (505) 835-5540; e-mail,

Rube Goldberg contest not for the technologically challenged

NOTE TO JOURNALISTS: Video and photographs of past contests are available. Journalists will not be allowed on the stage with the machines during the competition, but they are welcome on stage before and after the contest. Purdue will provide video and photo pool coverage and direct audio and video feeds. Video b-roll, photos and a news release will be available the afternoon of the event. Satellite assistance is available. If you have questions, call Amanda Siegfried, Purdue News Service, (765) 494-4709; e-mail,

WEST LAFAYETTE, Ind. -- It's a technophobe's worst nightmare -- a machine that actually makes a computer MORE difficult to operate.

But that's what college students are building -- on purpose! -- for the 10th annual National Rube Goldberg Machine Contest, to be held at 11:30 a.m. April 5 in Purdue University's Elliott Hall of Music. (NOTE: The date has been changed from March 29.)

The challenge of the contest is to build a machine that takes at least 20 steps to load a CD into a computer and run a program, or into a CD player and play music. The machines often incorporate objects scavenged from attics, toy chests and trash bins, including bowling balls, marbles, rubber tubing, old bicycle parts, hair dryers and electric drills.

The event honors the late cartoonist Rube Goldberg, who specialized in drawing whimsical machines with complex mechanisms to perform simple tasks.

Purdue's entry in the contest will be chosen this month in an all-Purdue contest. Additional entries will be chosen from regional contests held this month at other universities.

The national contest is organized by student members of the Purdue chapter of Theta Tau, a professional engineering fraternity, with support from Rube Goldberg Inc.

Each machine in the competition must run, be reset and run again in nine minutes. Machines also will be judged on the creative use of materials and use of related themes. Points will be deducted if human intervention is need for the machine to complete the task.

Student organizers of the contest maintain a World Wide Web page at

CONTACT: Daniel Colpi, contest chairman, (765) 743-2461; e-mail,

Expert advocates behavior modification to control ADHD

WEST LAFAYETTE, Ind. -- Only 10 percent of children with attention deficit hyperactivity disorder (ADHD) receive any kind of therapy to help them modify their behavior. A Purdue University expert on ADHD says that figure should be near 100 percent.

"Ninety percent of children with ADHD are treated with stimulant medication at some time in their lives, but taking a pill is only a three-hour solution to the problem," says Betsy Hoza, assistant professor of psychological sciences. "Teaching children to control their behavior might be expected to make more of an impact on their lives."

Hoza is a faculty supervisor for Purdue's Child and Adolescent Clinic, which provides behavior modification therapy for youths with a variety of problems.

"Medication should not be the first choice for treating ADHD," she says. Hoza advocates trying behavior management techniques first, and then adding medication if the child's behavior remains unacceptable. She maintains that medication dosages often could be cut in half if they were coupled with behavioral treatment.

When behavior modification methods are put into practice, it's the adults who get most of the formal training. In the Purdue clinic, parents of ADHD children attend 10 sessions to learn simple skills for managing their child's behavior. The children's teachers also are asked to fill out daily report cards on the student's conduct. Parents then provide home-based rewards when children exhibit proper school behavior.

Among the topics covered is how to give commands in a way that will bring about compliance by the child. "For example, telling a child to be good is not specific enough," Hoza says. "If you want them to sit in a chair with their feet on the floor, tell them that." Parents also receive information on how to use time-outs and how to tackle difficult times such as getting ready for school or bedtime.

"It's not that these parents have bad parenting skills," Hoza says. "We assure them and remind them that they probably have other children at home who are doing just fine. Even excellent parents need to learn how to structure the environment differently for a child with ADHD."

Hoza says one reason more children may not be receiving behavior modification is because of the commitment it requires of parents. "It's a lot easier to give a child a pill than to teach them how to manage their behavior," she says. "Also, many parents may not know where to go to get help."

Hoza says parents need to ask their local clinics and counselors if they provide behavior modification training. "In some areas there are many people who are doing it, but that's not the case everywhere, so you just have to look for it," she says.

Hoza is part of a national multi-site research project comparing various treatments for ADHD, including behavior management. Results of the long-term study are about two years away.

CONTACT: Hoza, (765) 494-6996; e-mail,

Compiled by: Susan Gaidos, (765) 494-2081; e-mail,

Purdue News Service: (765) 494-2096; e-mail,

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