Nav: Home

Physicists use supercomputers to solve 50-year-old beta decay puzzle

March 11, 2019

Beta decay plays an indispensable role in the universe. It drives the stellar explosions that synthesize elements--every piece of gold or platinum jewelry owes its beginnings to beta decay. It gives scientists a glimpse of physics beyond the Standard Model--the framework of particles and forces that gives a sense of order to the physical world. And for 50 years it has held onto a secret that puzzled nuclear physicists. With ever-advancing computing power at Oak Ridge National Laboratory, a team of researchers has solved that mystery, with the results appearing in Nature Physics.

When a nucleus has too many protons or neutrons, a neutron will transform into a proton, or a proton will transform into a neutron. The process--beta decay--brings the nucleus closer to a region of stability. For half a century, nuclear physicists have been dogged by something of a problem of scale: why was it they could calculate the beta decay rate of a single neutron, but using that information for an atomic nucleus resulted in a too-fast decay?

Thomas Papenbrock, professor of theoretical nuclear physics at the University of Tennessee, Knoxville, and co-author on the Nature Physics paper, explained that the adjustment for this discrepancy came in the form of "quenching"--reducing a fundamental coupling constant between decay rates for a free neutron and the decay rate scientists observed in an atomic nucleus. The puzzle was that there was no first-principles theoretical understanding for why quenching worked.

"Our work shows that the beta decay of a nucleus is more complicated," Papenbrock said. "Even if we think of it as a decay of a neutron to a proton inside the nucleus, this decay is influenced by processes where two neutrons interact and transition into a proton and a neutron. Taking these effects into account, and using state-of-the art nuclear models and supercomputers, we were able to solve the puzzle of 'quenched' beta decays."

Availing themselves of the Cray XK7 Titan Supercomputer at ORNL, the researchers simulated the decay of tin-100 into indium-100. Tin-100 is known as a "doubly-magic" nucleus: it has 50 protons and 50 neutrons in complete shells, making it strongly-bound. The relative simplicity of its structure makes tin-100 an ideal candidate for the sort of large-scale calculations where scientists need to understand the forces between the protons and neutrons in an atomic nucleus.

The results of this study are consistent with experimental data and could also inform predictions for the matrix element that governs neutrino-less double beta decay. This is a hypothetical process where two neutrons decay into protons at the same time, but without emitting neutrinos. Neutrino-less double beta decay, as the Nature Physics paper points out, has its own puzzle in terms of understanding the scale of mass in neutrinos, which up until 1998 were thought to have no mass at all.
The Nature Physics paper includes two authors with UT Physics ties: Papenbrock and Gaute Hagen (adjunct assistant professor). Please see the Oak Ridge National Laboratory press release (link) for more detailed information about this research.


Catherine Longmire (865-974-8950,

Andrea Schneibel (865-974-3993,

University of Tennessee at Knoxville

Related Neutrinos Articles:

Borexino sheds light on solar neutrinos
For more than ten years, the Borexino Detector located 1,400 meters below surface of the Italian Gran Sasso massif has been exploring the interior of our Sun.
A first 'snapshot' of the complete spectrum of neutrinos emitted by the sun
About 99 percent of the sun's energy emitted as neutrinos is produced through nuclear reaction sequences initiated by proton-proton (pp) fusion in which hydrogen is converted into helium, say scientists including physicist Andrea Pocar at the University of Massachusetts Amherst.
Study of high-energy neutrinos again proves Einstein right
A new study by MIT and others proves Einstein is right again.
A blazar is a source of high-energy neutrinos
A celestial object known as a blazar is a source of high-energy neutrinos, report two new studies.
Blazar accelerates cosmic neutrinos to highest energies
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos.
Origin of neutrinos proved by Drexel University astrophysicist, IceCube colleagues
With nine-and-a-half years of data and a South Pole observatory, a Drexel University professor and her colleagues has shown the origin of at least some of the high-energy particles known as 'neutrinos.'
IceCube neutrinos point to long-sought cosmic ray accelerator
An international team of scientists, with key contributions from researchers at the University of Maryland, has found the first evidence of a source of high-energy cosmic neutrinos, ghostly subatomic particles that travel to Earth unhindered for billions of light years from the most extreme environments in the universe.
University of Alabama professors help in discovery of potential cosmic ray source
Three professors at The University of Alabama are part of an international team of scientists who found evidence of the source of tiny cosmic particles, known as neutrinos, a discovery that opens the door to using these particles to observe the universe.
NOvA experiment sees strong evidence for antineutrino oscillation
The NOvA collaboration has announced its first results using antineutrinos, and has seen strong evidence of muon antineutrinos oscillating into electron antineutrinos over long distances, a phenomenon that has never been unambiguously observed.
Matter-antimatter asymmetry may interfere with the detection of neutrinos
From the data collected by the LHCb detector at the Large Hadron Collider, it appears that the particles known as charm mesons and their antimatter counterparts are not produced in perfectly equal proportions.
More Neutrinos News and Neutrinos Current Events

Top Science Podcasts

We have hand picked the top science podcasts of 2019.
Now Playing: TED Radio Hour

Why do we revere risk-takers, even when their actions terrify us? Why are some better at taking risks than others? This hour, TED speakers explore the alluring, dangerous, and calculated sides of risk. Guests include professional rock climber Alex Honnold, economist Mariana Mazzucato, psychology researcher Kashfia Rahman, structural engineer and bridge designer Ian Firth, and risk intelligence expert Dylan Evans.
Now Playing: Science for the People

#541 Wayfinding
These days when we want to know where we are or how to get where we want to go, most of us will pull out a smart phone with a built-in GPS and map app. Some of us old timers might still use an old school paper map from time to time. But we didn't always used to lean so heavily on maps and technology, and in some remote places of the world some people still navigate and wayfind their way without the aid of these tools... and in some cases do better without them. This week, host Rachelle Saunders...
Now Playing: Radiolab

Dolly Parton's America: Neon Moss
Today on Radiolab, we're bringing you the fourth episode of Jad's special series, Dolly Parton's America. In this episode, Jad goes back up the mountain to visit Dolly's actual Tennessee mountain home, where she tells stories about her first trips out of the holler. Back on the mountaintop, standing under the rain by the Little Pigeon River, the trip triggers memories of Jad's first visit to his father's childhood home, and opens the gateway to dizzying stories of music and migration. Support Radiolab today at