John M. “Jack” Carpenter, an American nuclear engineer who pioneered using accelerator-based pulsed neutrons for scientific research, died on March 10. He was 84.

Jack is perhaps best known for his development of the short-pulsed spallation neutron source concept. It was prototyped, fully realized with the Intense Pulsed Neutron Source (IPNS) at Argonne National Laboratory and culminated in the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL) and the Japanese Spallation Neutron Source (JSNS) at the Japan Research Accelerator Complex (J-PARC).

He is known as “the Father of Spallation” to the international community, although he would gently emphasize that he did not name the phenomenon—he turned it into an efficient way to generate beams of useful slow neutrons.

He enjoyed a prolific scientific career, with his home base at Argonne, in addition to numerous appointments at other national labs and international institutions, including ORNL’s SNS, Rutherford Appleton Laboratory’s ISIS spallation facility, Los Alamos National Laboratory’s (LANL’s) Neutron Science Center, and the Japanese High Energy Accelerator Research Organization (KEK). He earned his BS in engineering at Pennsylvania State University and his MS and PhD in nuclear engineering at the University of Michigan.

He instituted two long-standing international collaborations, the International Collaboration on Advanced Neutron Sources (ICANS) and the Union of Compact Accelerator Neutron Sources (UCANS).

Throughout his career, Jack not only developed neutron technologies, but is also credited for developing a cadre of scientists—many of them are working in the field today and, in turn, are mentoring the next generation of neutron scattering researchers.

He was a tremendous advocate for neutron scattering research, and is featured in outreach projects including “Advancing Materials Science using Neutrons at Oak Ridge National Laboratory” and “The Flight from Wonder – The Shull & Wollan story,” the documentary of the neutron scattering pioneers Clifford Shull and Ernest Wollan.

He is a fellow of the American Nuclear Society, the Neutron Scattering Society of America, the American Physical Society, and the American Association for the Advancement of Science. and Sigma Xi. He received the Ilya Frank Prize from the Joint Institute for Neutron Studies in Dubna, Russia, and the Clifford Shull Prize from the Neutron Scattering Society of America. He authored more than 180 publications and technical reports, and co-authored two books: “Living with Nuclei: 50 years in the Nuclear Age, Memoirs of a Japanese Physicist” (with Motoharu Kimura, 1993), and “Elements of Slow-Neutron Scattering: Basics, Techniques, and Applications” (with Chun-Keung Loong, 2015).

Jack loved cooking and sharing meals with friends, traveling, music, and the beauty of numbers in everyday life.

He is survived by his wife Rhonda; children John M. Carpenter, Jr., and his wife Julia Heberle, Kathryn Carpenter, Susan Carpenter, Janet Carpenter, Catherine Norden, Amy Norden and her husband Scott Osborne, Adam Norden and his wife Dana Norden; and eight grandchildren.

A memorial service and celebration of life is planned for June at Jack and Rhonda’s home in suburban Chicago.

Here’s what friends and colleagues had to say (Jack saw no difference between the two):

“Jack was one of the main driving forces behind the development of spallation neutron sources. His presence, intellect, sense of humor, and his willingness to collaborate and share his ideas will be greatly missed at Oak Ridge by many of us.” —Paul Langan, ORNL

“Jack always had time for everybody and would tackle any problem. He found the beauty in elegant complexity as well as simplicity. He took as much delight in his students’ success as in his own. He is a constant inspiration and example for a life well lived.” —Erik Iverson, Argonne/ORNL

“Jack was visionary with a talent for tackling complex problems in a methodical way that he applied to a wide range of topics from understanding ‘porches’ and ‘tails’ in neutron pulse shapes to ‘burping’ of a solid methane moderator. His contributions to neutron sciences have been many and foundational to the success not only of the Spallation Neutron Source at ORNL but at similar sources worldwide. His friends and colleagues will miss his ready wit and inspirational leadership.” —Ken Herwig, ORNL

“Condolences to Rhonda and Jack’s family. I remember him always enjoying life to its fullest. Jack was a great mentor to the neutron community and will be sorely missed. He always encouraged new ideas and was willing to discuss them at length. I always remember and often repeat his quote, ‘Simulation is no replacement for thinking.’” —Garrett Granroth, ORNL

“Jack has been a source of inspiration to me, not only for neutron scattering but also about classical music. God rest his soul.” —Wei-Ren Chen, ORNL

“For many years, Jack lectured at the National School on Neutron and X-ray Scattering, and it truly was a remarkable experience to the students and to me to hear from the father of the spallation source method for neutron scattering.” —Bryan Chakoumakos, ORNL

“As a fresh postdoc at SNS, I found myself in a conversation with a nice older gentleman in the hallway who was asking me about my work. It wasn’t until later, when I was asked where I knew Jack Carpenter from, did I realize his fundamental contribution to all neutron spallation sources and that I was talking to an actual science celebrity. Jack had a wonderful dry humor and I always enjoyed a nice short talk with him … nothing fundamental, most often just an anecdote or a story.” —Matthias Frontzek, ORNL

“Jack was a mentor to me and a curator of neutron scattering knowledge, filled with the most amazing curiosities. He shared his experiences with encouragement and humor. His knowledge and capacity to recall a paper or a discussion of a subject closely related to the topic in question was remarkable. When I started thinking about a ‘next-generation neutron diffractometer,’ he provided many ‘hints’ and pieces of guidance that lead to thriving instruments in a thriving science community. I think of him as the ‘Grande Father’ of time-of-flight neutron scattering and am thankful to have had the pleasure of learning from him. Jack will be missed greatly.” —Christina Hoffmann, ORNL

“He has been both a friend and mentor to me since I first met him at IPNS. I loved our scientific discussions and listening to his stories, and really treasured his willingness to listen to me.” —Ken Littrell, Argonne/ORNL

“I am eternally grateful for Dr. John (Jack) Carpenter’s patience and enthusiasm, taking his valuable time to share his knowledge and wisdom when I first started working for the SNS project at Argonne, and for the lesson of equally respecting everyone that came along that experience. He will always be greatly admired by all who had the honor of meeting him.” —André Parizzi, Argonne/ORNL

“Jack was a respected colleague and beloved friend to many of us. I am deeply saddened by his passing and so sorry for your loss. May his memory be for a blessing.” —Stephen Nagler, ORNL

“Jack was one of the first friends I made when I moved to Illinois. He was a good man and a good friend. I will miss him.” —Rick Goyette, Argonne/ORNL

“It was always a pleasure to see Jack. I was his admin for five years at SNS. Jack had such a kind heart and sweet disposition. He never just stopped by my office. He always sat down and would chat about his latest vacation or trip and always had to brag about his family. As an admin, so many people come through my office visiting people I support. Jack was one of a kind. He will be sorely missed. He loved visiting the lab and I feel like everyone considered him part of our SNS family.” —Talia Holder, ORNL

“As a raw recruit to the Spallation Neutron Source project with no time-of-flight neutron scattering experience, I depended on Jack’s help to understand technical issues and the science that one can do. He was always generous with his time and provided just the right amount of guidance while letting me figure things out on my own. His IPNS notes series helped get me oriented to the technical issues. He is an inspiring scientist, collaborator, and teacher.” —Doug Abernathy, ORNL

“Jack challenged you to do your best, and because of him the IPNS lasted longer than the experts thought. I feel strongly that knowing Jack had made me work harder in my effort to become better in my profession.” —Don (Boh) Bohringer, Argonne

“He has been always inspiring to all of us and we will miss him.” —Thomas Gutberlet, Jülich Centre for Neutron Science (FZJ)

“He was a great friend to us all and a great teacher.” —John Hammonds, Argonne

“Jack was a great friend and mentor since the early days of IPNS. I always looked forward to our meetings over the years and he will be greatly missed but always in our thoughts.” —Paul Sokol, Argonne/Penn State/Indiana University

“Here I promise to step forward following his genius, kind and positive suggestions. May he rest in peace and hopefully keep watching us.” ­—­Hirohiko Shimizu, Nagoya University

“He was a truly great scientist. I’m proud that I could work together with him. Those days are my treasure.” —­Susumu Ikeda, KEK

“...For me he will always be in the front row of any meeting, smiling around, making remarks that will help us to think a bit harder, a bit deeper. It was a privilege of colleagues around the world to enjoy his friendship and warmth, his genius and his understanding.” —­Rolando Granada, CNEA-Bariloche

“Jack was one of the most wonderful people that one could ever know. So kind, funny and a complete genius – a wonderful scientist and engineer, and a friend to all – special and unique. It was such a pleasure and privilege to have known and worked with Jack, and played with him too.” ­—­Rob Robinson, LANL/CSIRO

“I first met Jack when I visited Argonne in 1985 and was very fortunate to be a colleague for many years. He is a wonderful person, and I cannot thank him enough for his patient mentoring during such an important time in my life. Truly a remarkable scientist and individual.” —Frans Trouw, Argonne/LANL

“His creativity and imagination were always amazing to me and were the key elements for our success.” ­­—Bruce Brown, Argonne

“Jack was a major part of my scientific career at Argonne and after, as he was for so many of our colleagues and friends.” ­—Mike Rowe, National Institute of Standards and Technology

“Jack was a wonderful scientist and an even more wonderful person. We will all be poorer following his departure.” ­—Ray Teller, Argonne

"Jack’s good humor and inquisitiveness always impressed me. He clearly enjoyed interacting with people, include the graduate students he taught for many years during his lecture “Neutron Generation and Detection” as part of the Annual National School on Neutron and X-ray Scattering, hosted by Argonne and Oak Ridge National Laboratories.” —Suzanne G.E. Velthuis, Argonne

“Jack was a great source of inspiration to many of us. I particularly enjoyed the many enlightening conversations we had over lunch, ranging from detailed scientific issues all the way to the joys of keeping a House in the woods.” —Stephen Rosenkranz, Argonne

“Thanks for the many happy years you enabled me to spend as your colleague at IPNS.” ­—Kent Crawford, Argonne

Hey Jack, keep it rolling.
Is it a ball or a wave?
Tame it, bounce it as you may
but not for your keeping.
No, not even you, for soon it will decay.
Only to remember, what a fantastic ride along its way.

Hey Jack, keep it rolling.
Is it firewood or a tree?
Standing it brings shelter, tapping it makes sweet.
But why it falls, sprawling with fungi covered?
No, not even you, for this is what to be.
Only to remember, the growth of your planted seedlings.

Hey Jack, keep it rolling.
Is it a script or a journal?
It sweats over a decade and traverses continents.
But in print it darts a course hither and thither.
No, not even you, for it frees up new endeavors.
Only to remember, within it the words blessed by a guardian angel.

Hey Jack, keep it rolling...
—by Chun-Keung Loong, Argonne

Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation’s first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America’s scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science.

SNS is a Department of Energy Office of Science User Facility. UT-Battelle LLC manages ORNL for the DOE Office of Science. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit—by Jeremy Rumsey (ORNL) and Christopher Garland (Argonne)