April 1999

Filling the gaps

Sheldon Datz has explored the niches in ‘little and middle-sized’ physics

Sheldon Datz
“A growing atmosphere of ‘get relevant or get out’ works against the long-term informal system of opportunities interacting with serendipity.”
In the scheme of physics research, size matters. There is “big physics,” or research performed at large science facilities. Examples are strewn about the globe: Switzerland’s CERN, Brookhaven National Laboratory’s Relativistic Heavy-Ion Collider, and the Heavy-Ion Institute (GSI) in Germany.

And then there is middle-sized physics and even little physics, performed at more modest facilities nestled away in universities, national laboratories, or even industries. Researchers use these more specialized machines to fill the basic-research gaps in what is known and understood about atomic and molecular physics.

Sheldon Datz last year received the American Physical Society’s Davisson-Germer Prize for his research into atomic interactions with ions, electrons and photons. Datz, who heads the Atomic and Molecular Physics section in ORNL’s Physics Division, has also recently received an honorary doctorate from Stockholm University and another honor from the Japanese government.

“I’m kind of peculiar in that I have moved from one area to another,” Datz says. “I started out in chemistry, but as I’ve seen holes in science, I’ve tried to fill them, and maybe in not the same way as I filled the last one.”

In the early 1950s Datz and then Chemistry Division Director Ellison Taylor were the first to explore molecular-beam techniques for studying chemical reactions. That research laid important groundwork in the field of chemical dynamics. Two researchers who followed after the ORNL work won Nobel prizes.

Datz says it was a gap in knowledge of the mechanism of radiation damage in reactor materials that led to the discovery of ion channeling. “The Solid State Division, at the time, was very interested in radiation damage that results from atomic collision interactions. The channeling phenomenon was discovered on a computer—the only time, to my knowledge, that’s happened. Mark Robinson and Dean Oen were studying why neutron irradiation caused swelling in reactor components.

“In 1962, computers were rather limited, but they set up a Monte Carlo model of a copper lattice. They sent off an energetic copper atom to see how far it would go, and this thing kept coming out of the other end of the lattice. They later discovered that the ion was traveling between the atomic rows. Hence, channeling. It explained a lot of phenomena, and it has proven highly useful in many areas of particle-solid interactions.”

The Atomic and Molecular Physics section’s work is funded mainly by DOE’s Basic Energy Sciences and Fusion programs. Datz’s particular link to fusion began years ago when John Clark, who led the Fusion Energy Division, suggested to Datz, “You atomic physics guys should do stuff related to fusion.” Datz heeded the advice and recognized another gap: the total lack of information on an important process called “dielectronic recombination.”

“Dielectronic recombination results in radiation and hence energy loss from the stored plasma in tokamak reactors, and no one had done any real research on the matter,” he says. “We were the first to make measurements in that area. These have since been highly refined by people working with storage rings.”

Datz and his colleagues have also expanded the base of knowledge in accelerator science. Huge colliders are now being constructed, and the atomic physics aspects of ultrarelativistic collisions have a bearing on their design and operation.

“Here was another gap. Their poison is our meat,” Datz says. “That is, good new basic atomic collision physics had to be investigated to meet the needs of the accelerator folks. We then set out to investigate this new area. We have been going to CERN to do this work, and we have probably done our last of experiments with their Super Proton Synchrotron.

“We have two or three days to accomplish five experiments. We have done it in the past very well, thanks to people like Randy Vane and Herb Krause, but you have to do a lot of planning. You don’t have time to stop and fix things.”

Using the magnetic storage ring in Stockholm, Datz initiated studies of the interaction of electrons with molecular ions, a process called dissociative recombination. The results are of direct interest to astrophysics and cosmology.

Even more recently, his interests have turned to the effect of high-energy, heavy-ion bombardment on DNA using the ORNL Holifield and a Japanese synchrotron.

The well-traveled physicist

Increasingly, using even the mid-range facilities requires packing a bag. Medium-sized facilities—ORNL’s Holifield Radioactive Ion Beam Facility could be considered in that class—are increasingly found overseas.

“In the early eighties, I worked for several years to get a heavy-ion magnetic storage ring built at ORNL. It was about a $15 to $20 million project—not huge, but not peanuts,” Datz says. “We didn’t get it. That’s one reason that we have to pack a suitcase and get on airplanes.”

In a career like Datz’s, what you discover over the years may seem arcane at first glance, but it adds up. Sometimes it adds up to billion-dollar industries.

“For example, we began studying particle-solid interactions many years ago. This had to do with what happened to recoiling energetic fission products. The results, aside from an enormous amount of basic physics, include analytic methods and materials modification typified by ORNL’s SMAC (Surface Modification and Characterization) facility, which was initiated by Bill Appleton and the multi-billion-dollar ion implantation industry.”

Datz says a “growing atmosphere of ‘get relevant or get out’ works against this long-term informal system of opportunities interacting with serendipity.” He worries that research that is too focused on particular results will close off important avenues to discovery. “I was a student at Columbia University when the laser was invented there. They were seeking a means of doing better atomic spectroscopy. No one said, ‘go out and invent a laser so that we can use a scanner at the supermarket checkout counter.’ ”

Datz apparently hadn’t perfected his knack for finding the knowledge gaps in those early days.

“They were on the tenth floor,” he says. Unfortunately, I was on the seventh.”—B.C.