The device is being installed on Civic Center Boulevard in a vast, mostly underground chamber with concrete walls six to eight feet thick. The electric bill when the machine is up and running will be about $10,000 a day.

It also generates jobs and business: The University of Pennsylvania's cyclotron is scheduled to open for business late in 2009; it will be the sixth of its kind in the nation.

Hahn expects patients from across the East Coast to come for the potentially lifesaving treatment, which lasts six to eight weeks. "They're going to rent apartments. They're going to rent hotel rooms," he said.

The Roberts Proton Therapy Center (named to honor a $15 million grant from cable titans Ralph J. and Brian L.) will be able to treat as many as 200 patients a day and is expected to create 50 to 100 jobs.

The greater good: Theoretically - the science is too new to be sure - proton beams should kill tumors with less collateral damage to patients than when standard radiation is used.

Cancer patients from Children's Hospital of Philadelphia, a proton center partner, will be among those receiving care, as will soldiers and sailors from the Walter Reed and Bethesda national Army and Navy hospitals. The Department of Defense is chipping in $30 million to $50 million for PET scanners and other amenities.

A dreamer in spreadsheet land: Hahn is an unapologetic physics geek and can wax poetic about subatomic particles. He keeps a scale model in his office of a 90-ton contraption called a gantry that is used to aim proton beams. "Docs love new stuff," he said.

He and colleagues at Penn have pined for proton "stuff" for a decade. Just one detail stood between the oncologists and their dreams - a $144 million price tag.

Getting to "yes" on a nine-digit medical expense: As a first step, Hahn and other proton cheerleaders positioned the project as being in line with one of the Penn health system's strategic objectives: to advance cancer care. Of course, he allows, "there are many, many worthwhile projects for patients."

Step two: The dog-at-a-bone technique. "I'm going to brag," Hahn said. "We've got really good people who are very forward-thinking and who are driven - driven like mad men and women - to do the best thing for the patient. To think out of the box, you need that sort of relentless approach."

They got the OK in November 2005 and took delivery of the behemoth this winter.

If you build it, they will come: As a recruiting tool, Penn's cyclotron is already attracting hot prospects in radiation oncology from top medical schools nationwide.

Once Penn powers it up, technicians from the Belgian company that makes it will relocate to Philly to keep the machine humming.

Been there, done that, came back: Hahn grew up in Norristown and crisscrossed the country to train in oncology (at the National Cancer Institute, among other facilities) before boomeranging back home. He, his wife and their four children live in Glen Mills, Delaware County.

Nonsubatomic idea he wishes he'd had: The Internet. Also, texting. "When I was in college, I called my family once or twice a month. You had to pay for it, and we didn't have a lot of money," he said. "Now, I communicate with my son at college on a daily basis.

"My wife and I text each other. Believe it or not - and I know this sounds nerdy - we pass articles around."