Dr. Demos (left) with a 17-million-electrons volt machine.
Dr. Demos (left) with a 17-million-electrons volt machine.

With an endless supply of patience and a devotion to being a mentor, Peter T. Demos explained physics problems to each of his students at MIT for hours until they grasped the material.

“It’s very rare . . . for a university professor to be able to spend that much time, day or night, with one student, just to make sure that the student understands,” said his friend and MIT colleague Ray Pariser. “He cared enormously for his students.”

Dr. Demos, who helped bring one of the first linear accelerators to the Massachusetts Institute of Technology, died Sept. 18 in his Belmont home of ischemic cardiomyopathy. He was 94.

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“His excellent scientific taste, his unquestioned integrity, and his determination to support every user of the laboratory were critical in establishing a style of operation that was a model for laboratories around the world,” Robert Redwine, a physics professor and director of the Bates Linear Accelerator Center at MIT, said in a statement.

Pariser said Dr. Demos connected so well with others that it was as if he had “X-ray vision” and could read thoughts.

Dr. Demos also “was full of life and full of stories and jokes,” Pariser said.

In the early 1950s, Dr. Demos helped lead design and construction of the first linear accelerators, according to the institute. With the linear accelerator, Dr. Demos and his colleagues were able to study atomic nuclei.

About a decade later, he worked with others to found the Bates Linear Accelerator Center, which “opened up a huge new area of research in nuclear physics,” Stanley Kowalski, a former student of Dr. Demos’s and later an MIT colleague, said in a statement.

A team of MIT physicists that included Kowalski and Dr. Demos created the Bates Center. Dr. Demos also worked with Fred Eppling, the lab’s associate director for nuclear science, to get federal funding for the center. They garnered support from William Bates, the late US representative from Massachusetts for whom the accelerator is named.

Eppling said Dr. Demos was an outstanding director, as well as an ideal teacher who possessed great courage and leadership skills.

“He was easygoing at times, he could be tough at times, and he could negotiate well,” Eppling said.

Dr. Demos was director of the Bates Center from 1973 until he retired in 1983. During retirement, he assisted in modifications that increased the energy of the accelerator.

Born in Toronto to Greek immigrant parents, Dr. Demos and his family frequently moved because his mother suffered from asthma, which at the time was difficult to treat.

As a child, Dr. Demos cleaned hats and shined shoes in his father’s shop, and worked for his uncle in a Greek restaurant. He attended high school in Peterborough, Ontario, and graduated in 1941 from Queen’s University in Kingston, Ontario, with a degree in physics and English.

His family said he was awarded a provincial scholarship, which paid three years of his college tuition. During World War II, Dr. Demos tested armaments for the Canadian government. Because the research was highly secretive, his family often did not know where he was working.

While in high school, Mr. Demos met Elizabeth Laverty-Jack, and they married in June 1941. She died in 2003. “They were so in love, and he was so devoted,” said their son John of South Berwick, Maine.

In 1946, Dr. Demos and his family moved to the United States so he could attend graduate school at MIT. He received a doctorate in physics in 1951 and began working as assistant director of the MIT Laboratory for Nuclear Science.

MIT said Dr. Demos was a member of the American Physical Society, the American Academy of Arts and Sciences, and that the Peter T. Demos Award was created for graduate students who demonstrate his “spirit, persistence, and intellectual qualities.”

“I looked to him as an idol, I really did,” said his sister, Georgia Davies of Calgary, who added that Dr. Demos was a loving brother and always modest about his accomplishments.

John said he valued the brilliance of his father, from whom he received a great scientific education. “I’d get a free lecture on string theory or black holes, or stuff that borders on mystical,” he said. “And that’s something I came to really, really appreciate as an adult.”

Dr. Demos had very strong opinions, John said, but never let his differences get in the way of friendships.

In his spare time, Dr. Demos played violin and piano, and listened to classical music. He also liked to fish and to sail on Lake Conway in New Hampshire.

In addition to his son and sister, Dr. Demos leaves another son, Theodore of Venice, Calif.; a daughter, Ellen of Dublin; six grandchildren; and three great-grandchildren. A service is being planned for the spring.

“Peter was one of the select group of men who have been giving to their fellow men and never asking for anything in return,” his sister said. “And he was so gracious and kind in everything that he did that he became an inspiration to all who knew him.”