nuclear physics

Nuclear physicist Paul Quin has passed away

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Paul Quin

Emerit professor of physics Paul Quin passed away on October 9, 2025. He was 84.

Born in Brooklyn, NY in 1941, Quin received his doctorate in physics from the University of Notre Dame, where his thesis work centered on the spectroscopy of the SD-shell nuclei. He joined the nuclear physics group at UW–Madison as a postdoc in 1969, playing a central role in the construction and installation of the new Lamb-Shift polarized ion source. He was also one of three survivors of the 1970 Sterling Hall bombing.

Quin joined the faculty in 1971. His research focused on the use of polarized beams as a tool for nuclear spectroscopy and his group made numerous important contributions in this field. In addition, Quin was an important player in the many instrumentation development projects that took place in the nuclear physics lab during the 1970s and the early 80s. In particular, he was the leader of the first experiment to test storage-cell technology for targets of polarized hydrogen atoms, a technology which has gone on to become important for polarization experiments at storage ring machines throughout the world.

Around 1980, Quin began expanding his research focus, moving into the field of weak interactions. In the years that followed, he carried out a variety of interesting and important experiments on β decay of polarized nuclei. These experiments typically involved tests of the conserved-vector-current hypothesis or searches for right-handed currents. In 1986, he and T. Girard published an important paper which described a new and potentially very sensitive technique for detecting right-handed currents in β decay. This new concept, which involves measuring the polarized-nucleus beta asymmetry correlation, became the basis for a number of experiments performed over the subsequent decade in both the U.S. and Europe, with Quin playing a central role in many cases.

Later in his career, Quin continued to work in the area of weak interactions, helping to define the role of various nuclear physics experiments that place constraints on extensions of the standard model. Quin retired in 2001.

Quin also made many contributions to the teaching mission of the department. His great enthusiasm for teaching was always evident, and he frequently introduced new and innovative ideas in the classes he taught. In the ‘80s, he took responsibility for developing new experiments for the Physics 321 lab and upgraded a number of the existing experiments. Towards the end of his teaching career, he was a tireless instructor in the large introductory courses, contributing in a number of important ways to the implementation of computer-based laboratories. In addition, Quin was a staunch supporter of the department’s then-new Peer Mentor Tutor Program. He also supervised nine students who received doctorates under his guidance.

This post was derived from department archives

Entangled neutrinos may lead to heavier element formation

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Elements are the building blocks of every chemical in the universe, but how and where the different elements formed is not entirely understood. A new paper in The Astrophysical Journal by University of Wisconsin–Madison physics professor Baha Balantekin and colleagues with the Network for Neutrinos, Nuclear Astrophysics, and Symmetries (N3AS) Physics Frontier Center, shows how entangled neutrinos could be required for the formation of elements above approximately atomic number 140 via neutron capture in an intermediate-rate process, or i-process.

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Baha Balantekin

Why it’s important

“Where the chemical elements are made is not clear, and we do not know all the possible ways they can be made,” Balantekin says. “We believe that some are made in supernovae explosions or neutron star mergers, and many of these objects are governed by the laws of quantum mechanics, so then you can use the stars to explore aspects of quantum mechanics.”

What is already known?

  • Immediately after the Big Bang, lighter elements like hydrogen and helium were abundant. Heavier elements, up to iron (atomic number 26) continued to form through nuclear fusion in the centers of hot stars.
  • Above iron, fusion is no longer energetically favorable, and nuclear synthesis occurs via neutron capture, where neutrons glom onto atomic nuclei. At high enough concentrations, neutrons can convert into protons, increasing the atomic number of the element by one.
  • This conversion is dependent on neutrinos and antineutrinos. Neutron capture has been found to occur slowly (s-process, over years) and rapidly (r-process, within minutes); an intermediate timescale, or i-process has been proposed but little evidence exists to support it. Rapid or intermediate neutron capture can only take place in catastrophic events where a huge amount of energy is released, such as supernova collapse.
  • “When a supernova collapse occurs, you start with a big star, which is gravitationally bound, and that binding has energy,” Balantekin says. “When it collapses, that energy has to be released, and it turns out that energy is released in neutrinos.”
  • The laws of quantum mechanics state that those neutrinos can become entangled because they interact in the collapsing supernova. Entanglement is when any two or more particles interacted and then “remember” the others, no matter how far apart they might be.

A quick summary of the research

  • “One question we can ask is if these neutrinos are entangled with each other or not,” Balantekin says. “This paper shows that if the neutrinos are entangled, then there is an enhanced new process of element production, the i-process.”
a plot of mass number A (atomic number) on the x-axis and abundance as a log scale on the y-axis. a purple line shows the i-process abundance, black line shows r-process, and grey line shows s-process. Above atomic number 140 or so, there is a visible enhancement of the purple line over the other two lines (below 140 the black and grey lines are much higher abundance values than the purple line)
The abundance pattern based on calculations in this paper (ν i-process pattern; purple line), compared with the solar system s-process (gray line) and r-process (black line) abundance data (Sneden et al. 2008). The ν i abundance for A = 143 is scaled to the solar r-process data for pattern comparison. | Source: The Astrophysical Journal

The experimental and simulated evidence

  • The researchers used two known facts to set up their calculations: well-established rates of neutron capture, and catalogs of the atomic spectra of stars, which astronomers have collected over decades to identify the abundance of different elements. They also knew that a supernova collapse produces on the order of 10^58 neutrinos, a number that is far too large to use in any standard calculations.
  • Instead, they made simulations of up to eight neutrinos and calculated the abundance of elements that would be created via neutron capture if the neutrinos were entangled, or were not entangled.
  • “We have a system of, say, three neutrinos and three antineutrinos together in a region where there are protons and neutrons and see if that changes anything about element formation,” Balantekin says. “We calculate the abundances of elements that are produced in the star, and you see that the entangled or not entangled cases give you different abundances.”
  • The simulations showed that elements with atomic number greater than 140 are likely to be enhanced by i-process neutron capture — but only if the neutrinos are entangled.

Caveats and future work

  • Balantekin points out that these simulations are just “hints” based on astronomical observations. Astrophysics research requires using the cosmos as a lab, and it is difficult to conduct true experimental tests on earth.
  • “There’s something called the standard model of particle physics, which determines the interaction of particles. The neutrino-neutrino interaction is one aspect of the standard model which has not been tested in the lab, it can only be tested in astrophysical extremes,” Balantekin says. “But other aspects of the standard model have been tested in the lab, so one believes that it should all work.”
  • The researchers are currently using more astrophysical data of element abundance in extreme environments to see if those abundances continue to be explained by entangled neutrinos.

This research is supported in part by the National Science Foundation grants Nos. PHY-1630782 and PHY-2020275 (Network for Neutrinos, Nuclear Astrophysics and Symmetries). Balantekin is supported in part by the U.S. Department of Energy, Office of Science, Office of High Energy Physics, under Award No. DE-SC0019465 and in part by the National Science Foundation Grant PHY-2108339 at the University of Wisconsin-Madison. 

The paper’s co-authors include Michael Cervia, Amol Patwardhan, Rebecca Surman, and Xilu Wang, all current or former members of N3AS.

Willy Haeberli remembered as physicist, teacher, and museum supporter

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Willy Haeberli in 2013 | Credit: Pupa Gilbert

University of Wisconsin–Madison Professor Emeritus Willy Haeberli passed away October 4, 2021. He was 96.

Born in Zurich, Switzerland on June 17, 1925, Haeberli received his PhD from the University of Basel (Switzerland) in 1952. He joined the faculty of UW–Madison in 1956, retiring in 2005.

Haeberli was a world-class experimental nuclear physicist. His research focused on studying spin effects in nuclear processes and in fundamental interactions. He and his collaborators developed spin-polarized gas targets of atomic hydrogen and deuterium. These “Haeberli cells” were used in many experiments worldwide including the Indiana University Cyclotron Facility, Brookhaven National Laboratory, and DESY Laboratory in Germany, and they were crucial for the success of those experiments.

Haeberli was the Raymond G. Herb Professor of Physics and a Hilldale Professor. He was elected to the American Academy of Arts and Sciences and the National Academy of Sciences, and he won the American Physical Society’s Bonner Prize in nuclear physics in 1979.

In addition to his scientific achievements, Haeberli was an accomplished teacher. He taught physics courses at UW–Madison for 49 years and developed the popular course Physics 109: Physics in the Arts, with Prof. Ugo Camerini. Physics in the Arts has been offered successfully and continuously since 1969, and has been emulated by tens of universities across the country. In the last five years before retiring, he co-taught the course with Prof. Pupa Gilbert. After he retired, Gilbert convinced him to co-write a textbook for Physics in the Arts, published by Academic Press-Elsevier in 2008, and 2011, translated into Chinese and published by Tsinghua University Press in 2011.

“Willy is a giant in my life. He was career changing, life changing, teaching changing, everything. Just the most amazing person I could have ever met,” Gilbert says. “He was, until the last day, my best friend ever, and the closest thing to a father figure I have ever had.”

Gilbert says that Haeberli’s interest in Physics in the Arts may have stemmed from his musician days — he played the flute in a quartet in college — and his wife’s passion for the figurative arts. She continues:

He always loved a lot more the physics of sound compared to the physics of light and color. He and I had feisty disagreements about the physics of light, and I enjoyed every one of them. Very often before classes I would come up with questions, and he could always, always answer them and pacify me. The last one was last spring, when I was teaching sound, and started wondering: Okay, we know that the speed of sound changes dramatically with temperature, but does the frequency change too? In other words, does a tuning fork sound different indoors or outdoors in Madison’s winters? I looked into this seemingly trivial question and could not find any answer I could trust to be right. Until I asked Willy, who (of course!) knew the answer right away, and charmingly explained that the wavelength and the speed of sound vary with temperature for a guitar string or a tuning fork, but the frequency does not. I will miss these elegant answers tremendously!

Haeberli recently made a significant donation to the Ingersoll Physics Museum, which allows for new exhibits to be developed, allows for current exhibits to be improved, and helps fund the docents program which provides tours for visiting school groups. He and his late wife, Dr. Gabriele Haberland, also supported the Madison Museum of Contemporary Art, UW­–Madison’s Chazen Museum, and Tandem Press with generous gifts.

Several current and emeritus department members shared their memories of Willy. Please visit the Willy Haeberli tribute page to read those stories. The Wisconsin State Journal also ran an obituary.

Many thanks to Profs. Pupa Gilbert and Baha Balantekin for helping with this obituary