But Dr. Stephen M. Shafroth, professor of physics and astronomy emeritus at the University of North Carolina at Chapel Hill, isn't one of them. Although he no longer teaches formally or gets paid by the University, he still goes in to work in the laboratory every day to pursue his passion for science.
While working at the Triangle Universities Nuclear Laboratory, an accelerator laboratory jointly operated and used by UNC, N.C. State and Duke University physics faculty, Shafroth and his group were among the first to study an atomic process he named "resonant transfer excitation" or RTE.
"This process was an important energy loss mechanism for nuclear fusion power reactors, and it was important to know just how big the effect would be," he said. "Hundreds of papers have been written on this subject since then."
Now, at age 77 -- nine years after retiring and six years after starting on the project -- Shafroth and a New York colleague have developed the world's smallest portable X-ray emission device.
"The miniature X-ray generator has proven useful for analyzing elements in complex materials like tree leaves, rocks and air filters," Shafroth said. "It could used to look for lead in blood or for other medical purposes. Among the applications we see are for calibrating instruments, helping to teach undergraduates and conducting various kinds of research in the field such as environmental pollution studies."
About twice the size of a small box of matches, the unique device runs on a standard nine-volt battery, he said. Its chief component is a pyroelectric crystal which, when heated, generates energetic electrons that produce X-rays when they hit any kind of matter. It is a self-contained, solid-state system that contains no radioactive material and does not produce a constant and potentially hazardous stream of X-rays.
"That's one of its big advantages," Shafroth said. "It is completely safe for students to use."
Amptek Inc. of Bedford, Mass., has begun manufacturing the portable X-ray generator, along with a companion X-ray detector. The company has named the former "COOL-X."
The UNC professor helped James D. Brownridge, a radiation safety officer at the State University of New York at Binghamton, make the device work better. Shafroth describes his colleague as "a really remarkable man, a workaholic who was not able to pursue a doctorate earlier in life but who has become not only obsessed with science and discovery, but also is highly productive.
"I was looking for something to get involved in after I retired and heard about James' work with crystals," he said. "It just seemed like a good fit, and it has turned out to be a fruitful collaboration."
Brownridge said he met the UNC professor at a scientific conference in the early 1990s after presenting some of his early work on crystal X-ray generators.
"After we began collaborating, that led to many new findings, and we worked so closely and so well, I truly can't say what was his and what was mine," Brownridge said. "Our ideas and conversations merged almost immediately, and the origins of particular ideas got lost. He is a unique person, and his interest and insights continue to inspire me."
It has been known for many years that the crystals they work with have unique properties, but no one knew they could be used to produce high-energy focused electron and ion beams until he and Shafroth discovered and developed that concept, Brownridge said. The idea of using crystals to produce X-rays was proposed in 1972.
"My lab created the first X-ray generator with crystals, and I published a report about it in Nature in 1992," the SUNY-Binghamton staff member said. "Then together Steve and I produced the first focused beams, including the first high-energy electron beam and the first high-energy ion beam."
Shafroth said his colleague is "undoubtedly one of the most creative and innovative radiation safety officers in the world."
"He has exceptional scientific curiosity," the UNC physicist said. "For example, he discovered that super-cooled water produces an electrical signal just before freezing. He also has studied elements on tree leaves using a pyroelectric crystal electron accelerator to produce characteristic X-ray signals arising from the underside of leaves which are different from the X-ray signals arising from the top side."
The leaf observations are interesting because they show at what point in the growth cycle a leaf takes up particular elements and how the undersides of leaves differ from the tops in element uptake, Shafroth said.
The American Physical Society and Physics Update, a leading scientific news publication, cited the friends' combined work as being among the highlights of physics research in 2002. Applied Physics Letters, a top journal, will soon publish a new paper they wrote about how to boost the energy of electron beams significantly by optimizing the surrounding gas pressure.
"This is a lot of fun, in part because we are ahead of the field," Shafroth said. "In fact, we believe that we know more about the behavior of these crystals in dilute gases than anyone in the world, and yet we know that there are many more surprises waiting to be found and understood.
"I will keep on doing this work as long as I can," the UNC physicist said. "One of my other interests that has been on the back burner for a while is storage of spent fuel rods at nuclear plants. I have concerns about that and want to help make it safer."
By DAVID WILLIAMSON
UNC News Services
Note: Shafroth is best reached via e-mail: shafroth@physics.unc.edu.
Brownridge: 607-777-4370.