Big Ideas Lab - Neutrinos

Episode Date: December 30, 2025

Neutrinos are particles that defy expectations. They slip through matter effortlessly, changing identities and traveling vast cosmic distances. In this episode, we explore the surprising ways they connect the tiniest scales of physics to the grandest structures in the universe. From deep underground detectors to experiments designed to observe the unobservable, scientists at Lawrence Livermore are working to uncover secrets that could reshape our understanding of matter, energy, and the origins of everything around us.Guests featured (in order of appearance):Mike Heffner, Staff Scientist, LLNLNathaniel Bowden, Physicist, LLNL--Big Ideas Lab is a Mission.org original series. Executive Produced by Levi Hanusch.Script by Caroline Kidd.Sound Design, Music Edit and Mix by Matthew Powell. Story Editing by Levi Hanusch. Audio Engineering and Editing by Matthew Powell. Narrated by Matthew Powell. Video Production by Levi Hanusch.Brought to you in partnership with Lawrence Livermore National Laboratory.  Hosted by Simplecast, an AdsWizz company. See pcm.adswizz.com for information about our collection and use of personal data for advertising.

If I had an orange, and I threw an orange, and you caught it, and it was an apple when you caught it, that is a quantum mechanical effect that happens with these things. We measure it all the time. There are particles in our universe so unique and so strange, they can change what they are while moving. They can shift form mid-flight. They're as old as time. They come from the beginning of the universe. as well as from stars, nuclear reactors, the Earth, they're everywhere.

Even passing through you at this very second. It's called the neutrino, and over the past century, each scientific discovery has raised more questions that need to be answered. Studying this mysterious particle may unlock answers to some of humanity's most pressing questions about matter. Questions about why anything exists. at all. And scientists at Lawrence Livermore National Laboratory are determined to uncover its secrets. Welcome to the Big Ideas Lab, your exploration inside Lawrence Livermore National Laboratory. Hear untold stories, meet boundary-pushing pioneers, and get unparalleled access inside the gates.

From national security challenges to computing revolutions, discover the innovations that are shaping tomorrow today. When we think about what the universe is made of, most of us imagine atoms. Matter we can touch, see, or feel. But peel back the layers of reality, and the truth is far simpler. and far stranger. Neutrinos are one of the fundamental particles that make up everything. There are only 17 particles in what we call the standard model of particle physics.

Only 17 building blocks construct everything in existence. Every star, every planet, every human. And three of those are neutrinos. It's kind of amazing that we can know that, and that's what nature tells us. That's how the world is constructed. Meet Mike Hefner, a particle physicist at Lawrence Livermore National Laboratory. He studies neutrinos, exploring the mysteries of their weekly interacting and abundant nature. The sun, it's some 90 million miles away or something like this, it's emitting so many neutrinos right now that there's a trillion per second going straight through you.

And you don't sense them because they just go straight through, they go through the earth and come out the other side. The neutrino seldom interacts with anything, slipping through our unit. universe without a trace. That's one of the most distinguishing features of a neutrino compared to the other particles. If you were to try to shield yourself from a neutrino, it would take one light year of lead to stop it. So that's how weakly interacting they are. They just basically pass through everything.

It passes straight through rock, metal, and the instruments built to catch it, forcing us to wait for the brief, rare flash that says a neutrino finally brushed against. something. So how do we know neutrinos are there? The neutrino was first theorized in the 1930s during studies of a process called beta decay. During beta decay, when certain atoms broke apart, scientists expected the emitted electron to always carry a specific, fixed amount of energy. But something wasn't right. The electrons came out with a whole spread of energies, as as if some of the energy had gone missing. And in physics, that's not supposed to happen.

Energy can't just disappear. So if the electron wasn't carrying all of it, then something unseen had to be carrying that energy away. That mystery lingered for years until... Another crazy idea came out, which is there's a particle that's so weakly interacting that we can't see it and it's actually carrying away that energy. The search felt unending. Finding particles that react so weakly to anything was like trying to catch a ghost. Finally, after 20 years of searching, researchers detected the first

neutrino, confirming the existence of a particle that had haunted physics for generations. But even after confirmation of their existence, the properties of neutrinos remain obscure. Studying them isn't just an academic exercise. Neutrinos could reveal fundamental truths of the universe. When we look at the evolution of the universe, it starts off as this ball of energy with equal amounts of matter and antimatter. And that had to evolve into a universe now, which is dominated by matter. And we know this because we look out in the universe and we can see that it's made of matter. There's very little antimatter remaining. We don't understand how that occurred, we have theories. And it turns out the neutrino might be the key to that mystery

of how the universe evolved from a bunch of energy into a matter-dominated universe. If we didn't have that happen, we wouldn't be here. The universe would just be a bunch of photons flying around. There'd be no structure, no matter. We wouldn't exist. Neutrinos baffle us, not only in the role they may play in the makeup of the cosmos, but also in the way they work. Daniel Bowden is a physicist at Lawrence Livermore National Laboratory, who has been at the helm of some of the most cutting-edge neutrino experiments in the country. They're one of the hardest ones to study. In the starting point, they were thought to be massless.

But further study of this enigmatic element revealed something different. The most significant advance is the observation that neutrinos can oscillate. They can oscillate between the so-called different flavors, the electron, the muon, and the tau. And because we observe this oscillation phenomena, we know that neutrinos have mass, which was not obvious. And the fact that they have mass opens up all kinds of possibilities about using neutrinos to study other aspects of physics. Lawrence Livermore is probing neutrinos on two fronts, uncovering their quantum nature and searching for heavy versions that may reshape our understanding of particle physics. The true quantum identity of the neutrino remains unanswered. A neutrino might be similar to the familiar particles that build everyday matter,

but there's a more profound possibility that they may behave much differently. One tied directly to why the universe exists at all. Some people actually frame this question is, why do we exist? We're studying neutrinos to understand that. Fundamentally, we care because we're here because the physics of the universe works the way it does. You change the physics a little bit, we're probably not even here as the chemistry changes, the biology changes, we're just not here. It's theorized that the neutrino might be its own antiparticle.

In the first moments of the universe, matter and antimatter should have balanced each other out. They should have destroyed each other, but somehow an excess of matter survived. And we don't know how. Neutrinos might carry the answer, and scientists are chasing their trails in massive experiments to uncover why we exist at all. There's only one established way to explore the quantum nature of the neutrino. Scientists must capture evidence of an extraordinarily rare nuclear process

called neutrinoless double beta decay. In nearly a hundred years of investigation, No one has ever seen it. That decay has never been measured. Lawrence Livermore has been working on technology for detecting neutrino-less double beta decay since 2014, and enabling technologies years before that. Neutrinos are hard to work with because they're hard to measure. They don't interact with things.

In this case, we're not actually measuring the neutrinos. We're actually trying to measure the decay and from the decay infer something about the neutrinos. And that's easier. At Lawrence Livermore National Laboratory, researchers are leading the technology to detect this rare phenomenon. Their approach relies on tons of enriched xenon, a noble gas cooled into liquid form and placed underground to shield it from natural radiation. In this quiet environment, the xenon acts as both the material where the decay can happen

and the medium that records the activity. The xenon is placed into a time projection chamber that operates on a scale 100 times larger than previous attempts, making it more possible than ever to observe neutrinalist double beta decay. The way that they typically work is when the decay occurs, this electron comes out, and the electron is charged, and when the electron comes out with a significant amount of energy and it's charged and it goes through material, it tends to knock electrons off of its neighbors as it's going through the material. And we can actually see those. If neutrinoless double beta decay occurs, it produces electrons with a very specific energy.

Photo detectors and charge sensors inside the time projection chamber pick up that signature. I think the best analogy is if you look up in the sky when the conditions are just right, you can see a jet airplane flying overhead. You can't see the jet airplane itself, but you can see the contrail that came from it. And so you can see where that airplane went. And I think these particles coming out in the material is very similar to that. We don't see the electron itself, but we see its contrail effectively. These TPCs, or time projection chambers, allow us to see those contrails,

and from that we can see, okay, there's a decay. And it's kind of like a three-dimensional camera for nuclear reactions, because you would never be able to see these with your eye or anything like that. But the time projection chamber isn't the only way to study neutrinos. Another theory points to a different kind of neutrino, a heavy or sterile neutrino. heavy in that it carries more mass, but only interacts gravitationally, sterile because it ignores other forces, and it may be the answer to why dark matter exists at all.

Dark matter is a form of matter that does not emit, absorb, or reflect light, which means we can't see it. But we know it exists because of the gravitational effects it has on the universe. Candidates for dark matter that people have focused on for the last couple of days. weekly interacting massive particles or wimps. There are things called axions, and then there are sterile neutrinos. That explains why so much effort goes into searching for those three categories. That's where the prospect and beast experiments come in. They're both trying to bring more sensitive tools to specific regimes where the sterile neutrinos could exist.

And both are designed to search for sterile neutrinos in different ways. The prospect experiment ran in the year 2018 at the high-flux isotope reactor at the Oak Ridge National Laboratory. We were very fortunate to be able to work at that unique facility. It's a small research reactor. The reactor core is about a half-meter dimension, and it runs at a really high power. It has a really high neutron flux, and they say it's the highest energy density system that's not exploding, that's under control. So it was a really perfect place to do the study because it gives off a lot of neutrino, The goal of prospect was to measure the number of neutrinos the reactor produced.

And it measures that as a function of energy and as a function of position within the detector. However, to observe the neutrino, you have to be very close. For this experiment, they were able to get as close as 8 or 9 meters from the reactor core. That was the first time that was done at scale and done with enough fidelity, enough precision to do neutrino physics measurements in that really adverse environment. Working only steps from the reactor core was like holding a magnifying glass to a moving stream, revealing fine structure in the neutrino flow that distant measurements simply couldn't show. Its proximity and precision was a major milestone in the search for the heavy neutrino.

Lawrence Livermore also participates in the beryllium electron capture in superconducting tunnel junctions, or Beast Experiment, which hunts for heavy neutrinos. There's a really interesting contrast between Prospect and Beast. They work in completely different ways, but they're both really pushing the limits of their respective technologies. The Beast experiment uses a superconducting tunnel junction. It's a complicated name for basically a superconducting detector that has really, really good energy resolution. These instruments can measure tiny variations in the energy released during decay, allowing scientists to infer whether an additional type of neutrino exists beyond the three already known.

They've been looking for a while now and they haven't found anything, but it was still a really cool idea. It was a relatively small project. We have the world expert in STJs here, which is Stefan Friedrich, and Kyle, who's a really smart guy and Colorado School Mines, came together and said, hey, well, we can use these detectors to look for this, and that caused quite a bit of buzz. By searching for heavy neutrinos, experts like Stefan Friedrich and Kempel Kyle Leach are working to uncover the hidden components of matter that make up much of the cosmos, potentially solving the puzzle of dark matter. Studying neutrinos also extends beyond topics like

the origin of dark matter and the genesis of the universe. For researchers at Lawrence Livermore National Laboratory, it also has national security implications, especially for nuclear reactors. The neutrinos could tell us is the reactor operating. is vision occurring, they could tell us what is the power level of that reactor? That's essentially how many neutrinos are coming out. And by studying more subtle variations about the number that are coming out and how that number is changing in time or what their distribution of energies is, we can say something about what the nuclear fuel in a reactor is.

For nuclear reactors, neutrinos can act as invisible auditors, tallying the reactor's output without ever being noticed. These measurements allow scientists to monitor and verify how a reactor is operating without needing to enter the facility. Because they pass through matter effortlessly, measurements can be made from outside. If scientists can detect and characterize radiation accurately, it helps prevent the illicit use or diversion of nuclear materials, which supports non-proliferation efforts and promotes global safety. Elusive, almost intangible, and unlike anything else we know, the neutrino might be more than a silent traveler through the universe. They act as cosmic messengers, carrying information from the hearts of stars, while also revealing the inner workings of nuclear reactors here on Earth.

At Lawrence Livermore National Laboratory, scientists are tracing these elusive signals, using cutting-edge detectors to capture their rare interoperable. actions and decode the secrets they carry. It's amazing that we can know what we know about the universe and the particles, the very few out there. I just find that unbelievably fascinating, and it's something that I want to see how far we can go with this. What can we know? Neutrinos remind us that the universe is built from the invisible, from forces and

particles we never feel, and they're not alone. Ahead, another hidden frontier waits. One woven from something even more mysterious. Dark matter. Thank you for tuning in to Big Ideas Lab. If you loved what you heard, please let us know by leaving a rating and review. And if you haven't already, don't forget to hear. hit the follow or subscribe button in your podcast app to keep up with our latest episode.

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