Dean Lee is a professor of physics at MSU's Facility for Rare Isotope Beams. At the Lee Research Group he asks: How do we connect fundamental physics to forefront experiments? With new science waiting to be discovered at FRIB and the dawning of the era of exascale supercomputing, this question is a profound challenge and opportunity for nuclear theory. Lee works to understand the nature and origins of matter by crafting new approaches that link quantum chromodynamics and electroweak theory to precise predictions for nuclear structure and reactions relevant to the FRIB science mission.
White: So, tell us a little bit about your research; what do you do?
Lee: Sure. Let me start off by telling you some of the science questions that FRIB is involved in. So, take a look for example at your hand. If you're driving, don't be distracted by that. So, your hand is composed of all these different elements you may remember from the periodic table. And if you were to rank the elements in your hand according to how much weight or how much mass it has, at the top of the list would be oxygen. After that would be carbon, then you have hydrogen and nitrogen.
And, you may wonder where these elements come from. And these light elements, most of the ones I just mentioned come from stars. Hydrogen is special because it's very basic. It's just a proton and an electron, and that comes from the very beginning, the big bang.
But then if you look at your hand again, if you're married you have a ring, maybe you have a platinum or a gold ring, and those are elements that are not made in stars, but are rather made in more exotic events in the universe. For example, there was an observation of two what are called neutron stars, and neutron stars are these funny stars that are small in shape but big in mass and made of neutrons. So, neutrons are different from protons in that they don't have this electric charge.
It was actually an event in August 2017 where they saw or they detected the merger of two neutron stars, and the signal that they saw it with gravity waves, they looked with telescopes in various different frequencies of light that there were elements being produced that were consistent with these heavy elements like platinum and gold.
So, FRIB's involved in trying to understand exactly how this works. We're looking at exotic, rather heavy elements, ones that are rich in these particles that are called neutrons. And so my research is on the theoretical end of this. I'm trying to explain and understand from first principles, from the basic building blocks, how I can have interactions between protons and neutrons, these particles inside the atomic nucleus. And, how I can take these pieces of a jigsaw puzzle and then develop the whole puzzle itself. How does it put together; how do things hang together?
That's basically what I'm doing with computers, with super computers and techniques like that.
White: So Dean, how mature is the research and what might it lead to that we could all understand?
Lee: So, the field of nuclear theory is quite a mature field. However, there are many subtle questions that we don't understand. For example, there was a recent discovery involving some scientists here at MSU, experimentalists, where they found that calcium, this is an atomic element that we know quite well, it's in our bones, but they found that calcium which has 20 protons can actually glob on to a whole bunch of neutrons. And the surprise is they could actually form a nucleus with 40 neutrons stuck to these 20 protons, which is kind of a surprise. We didn't know that. So, this was new.
So, we knew that there are all these different elements, but we don't know the limits of stability. And so, this is the frontier and this is what I'm working on and what a lot of my colleagues are working on. The approach we take is by starting from the basic building blocks as I said. And the actual method we use is a little bit, it sounds like science fiction, we imagine the universe as being built in terms of points on a grid, a three dimensional grid. And then our protons and neutrons can be on the grid, and then, these protons and neutrons have interactions. We code this into a computer code and then we let the computer do the calculations using a technique that involves something called Monte Carlo Methods, which is kind of an exotic sounding thing. But, I can explain what Monte Carlo Methods are.
They're basically using random numbers to calculate something that's incredibly complicated. For example, if you wanted to determine the area of a circle, right? One way to calculate the area of a circle is to put a square just around the edges of the circle so that they touch. And hopefully you know how to calculate the area of a square. And what you can now do is take random points in the square, even distributed, and then figure out what percentage of the points are inside the circle versus the number of points inside the square. And that gives you a ratio of the areas of the circle to the square.
We use this sort of technique of random numbers, what's called the Monte Carlo Method, to do simulations of a lot of protons and neutrons and how they stick together.
White: Now as you move forward then, what's next? What are some of the challenges and opportunities and goals you have?
Lee: So, a lot of the challenges are really understanding the subtle things that happen. So, a lot of the questions we ask are not what happens in nature, but we actually ask the other question: what could happen in nature and why doesn't it happen? So if you can answer both of the questions what happens in nature and what doesn't happen in nature, we get the full spread of possibilities and how things really work, right?
And so one of the questions we're trying to understand, I'll give you an example of a recent paper we've written. We played around with the interactions of the protons and neutrons, a change to the interactions that really didn't show up at the level of when you have two particles or three particles or four particles. But once you got to the level of 16 particles or 20 particles, it was completely different from nature. We found that these atomic nuclei actually didn't hold their glue together, they actually fell apart into smaller nuclei, which are the helium nuclei. And, this was sort of exciting to us, but it showed that nature was very subtle. So, we're now going deeper into this question trying to understand what other subtle things are going on at this level.
White: What's new at FRIB as things progress towards the official opening?
Lee: Well, actually I got a tour yesterday from the Director, from Thomas Glasmacher, it was very exciting. Lots of things going on. They're building the accelerator that will accelerate these ions to about 40 percent of the speed of light. There is a lot of progress going on there. They're ahead of schedule so the target date is June 2022, but it's on track to be open hopefully by 2021.
So, lots of excitement on the experimental side and on the theoretical side. Everybody's eager and there are a lot of meetings going on to figure out what is the first day science that we can do at FRIB.
White: And, Dean Lee, you recently presented on your research that we've been discussing to the MSU Board of Trustees meeting. Are there a couple of messages you hope the Board and the rest of the attendees took away about your work?
Lee: Well, one of the things I wanted to emphasize was that there are really interesting questions that are just sitting in front of your face that you may not have realized. Look at your hand. What are you made of and where did it come from? And these are deep philosophical questions that could be answered by science. And what's very exciting is that Michigan State is at the forefront of this. We have this three quarters of a billion dollars facility called FRIB that will explore the limits of stability of atomic nuclei.
We will try to go even beyond today's headlines, we're going to try to figure out what are tomorrow's headlines? What are the new questions? For example, you may know if you're interested in electronics how electrons flow through metal. And there was in the 19th century an understanding of how this works. And it worked very well. However, if you dig a little bit deeper, and with the discovery of superconductivity, there was something subtle going on there that we hadn't noticed.
And I think the same thing could happen in nuclear physics. There are subtle things. When FRIB turns on and we look carefully at experiments and theory, hopefully we'll see that they agree pretty well. But there will be small differences there. And in the differences there could be new things that we will discover that will then propel science into the future.
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