NSCL/JINA Outreach Coordinator (almost) 14 BILLION YEARS OF NUCLEI Dr. Zach Constan NSCL/JINA Outreach Coordinator With thanks to Hendrik Schatz, Chris Wrede, Dan Coupland, and Rebecca Shane

What do we know, and how? The Scientific Perspective In science, “theory” means a single explanation that fits many observations. A “law” describes a set of observations, but does not explain them. A “hypothesis” is an educated guess that you can test with experiment. Scientists strive to understand our universe from observable, testable and repeatable facts. While theories come and go, the best theories: make predictions that are tested and proven correct (usually many times). Are supported by multiple lines of inquiry. Dominant theories become dominant because they are the most reliably-accurate explanations of how our universe works. Scientists don’t believe in a theory, they accept the evidence that supports the theory.

JINA-CEE & That Great Nuclear Science Laboratory in the Sky THEORY EXPERIMENT OBSERVATION

BIG QUESTIONS in Nuclear Astrophysics Statement of fact: Our solar system (including ourselves) is made of matter. SO WHERE DID IT COME FROM? Also… How do stars shine? Why/how do stars explode? How is matter in the universe changing? What is a neutron star? Etc., etc.

Let’s start small: everything is made of atoms "National Superconducting Cyclotron Laboratory: MSU's Premier Research Lab for Nuclear Science" Let’s start small: everything is made of atoms Example: A Helium Atom “Physicists are made of atoms. A physicist is an attempt by an atom to understand itself.” – Michio Kaku Electron Neutron Proton NSCL scientists study the atomic nucleus (Have audience identify parts of the atom) At NSCL, we study the nucleus of the atom. Specifically, we study nuclei that are rare, unstable.

Atoms can be one of many elements Human-made Of course, we also do research because we’re curious. One big mystery we’re trying to solve is where all the different elements came from. H and He were created in the beginning of our universe, after the Big Bang, these were mostly created when stars fused hydrogen into heavier elements for fuel, these are man-made… but the vast majority of elements were made in a lot of strange and complicated ways! One of which: supernovas (exploding stars) form unstable nuclei that later become these elements, so we study the unstable nuclei to understand how. Not naturally-occurring

Amounts of each element in our solar system One of the great unsolved mysteries: Nucleosynthesis Where did the elements come from? Why do we have more of some than others?

The Entire History of the Universe Fireball 7 protons for every neutron 2 min after BB – deuterium starts to stick together 20 min after BB, gets too cold What is it called when two nuclei join The first nuclei

Big Bang Nucleosynthesis (first 2-20 min) Big Bang theory prediction: 1 neutron for every 7 protons Should lead to 75% H, 25% He (by mass) by 5 minutes after BB Matches observations of oldest (undisturbed) gases

WMAP hears the echoes of the Big Bang The first atoms Fireball 7 protons for every neutron 2 min after BB – deuterium starts to stick together 20 min after BB, gets too cold What is it called when two nuclei join Wilkinson Microwave Anisotropy Probe

Big Bang made about 75% H, 25% He — plus a little Li and Be Human-made Of course, we also do research because we’re curious. One big mystery we’re trying to solve is where all the different elements came from. H and He were created in the beginning of our universe, after the Big Bang, these were mostly created when stars fused hydrogen into heavier elements for fuel, these are man-made… but the vast majority of elements were made in a lot of strange and complicated ways! One of which: supernovas (exploding stars) form unstable nuclei that later become these elements, so we study the unstable nuclei to understand how. Not naturally-occurring

Chemical composition of the universe is evolving– why? Mass fraction [%] There are more “metals” now! Where are the rest of the elements being created since the Big Bang? (i.e. where can nuclear reactions take place?) Doesn’t vary much after BB, but still need all the heavy elements. Don’t just form by themselves. Why do we need stars, etc. Interesting note – most of deuterium in universe formed now – another good test of BB theory

The Entire History of the Universe Fireball 7 protons for every neutron 2 min after BB – deuterium starts to stick together 20 min after BB, gets too cold What is it called when two nuclei join Stellar nucleosynthesis

The Sun: how does it shine? Its age is a clue. Time Luminosity = Energy radiated Luminosity Lifetime = Energy available

E = mc2 —Einstein, 1905 The Sun: how does it shine? Luminosity ~ 10,000 years Chemical Energy Content Is it on FIRE? … NO! E = mc2 —Einstein, 1905 It is powered by NUCLEAR ENERGY! Luminosity ~ 10 billion years Nuclear Potential Energy (core)

Why does fusion make stars shine? INPUT 4 protons OUTPUT 4He 2 positrons 2 neutrinos Energy out! AND 2 gamma rays (mass is 0.7% lower)

Why can fusion happen in stars? Protons (hydrogen nuclei) are positively charged, and repel each other In a star, high temperatures mean that protons are moving very fast They can get close enough that the nuclear strong force binds them together

Fusing hydrogen to helium: how do we know? The Sun releases energy by fusing four hydrogen nuclei into one helium nucleus. Neutrinos created during fusion fly directly out of the Sun (while light can take one million years to escape). Observations of these solar neutrinos can tell us what’s happening in the core.

Running out of fuel

Multiple Shell Burning Each time fuel runs out, collapse starts new fusion Multiple Shell Burning In the red giant phase, advanced nuclear burning proceeds in a series of nested “onion-like” shells. Low-mass stars will stop after forming helium or carbon. High-mass stars can produce high enough temperature and pressure to fuse nuclei from helium all the way up to iron.

Iron: a dead end Nuclear reactions can convert matter into energy. This is how fusing light elements into heavier ones powers a star! However, once the star fuses up to iron (Fe), any nuclear reactions with that will actually lose energy, so fusion stops.

Stellar fusion (in massive stars) can produce many elements… Big Bang Stellar fusion Human-made Of course, we also do research because we’re curious. One big mystery we’re trying to solve is where all the different elements came from. H and He were created in the beginning of our universe, after the Big Bang, these were mostly created when stars fused hydrogen into heavier elements for fuel, these are man-made… but the vast majority of elements were made in a lot of strange and complicated ways! One of which: supernovas (exploding stars) form unstable nuclei that later become these elements, so we study the unstable nuclei to understand how. Not naturally-occurring

… And yet many elements are still unmade!

Red giants and supergiants Of course, we also do research because we’re curious. One big mystery we’re trying to solve is where all the different elements came from. H and He were created in the beginning of our universe, after the Big Bang, these were mostly created when stars fused hydrogen into heavier elements for fuel, these are man-made… but the vast majority of elements were made in a lot of strange and complicated ways! One of which: supernovas (exploding stars) form unstable nuclei that later become these elements, so we study the unstable nuclei to understand how.

The slow neutron capture “s-process” Free neutrons are created by reactions (e.g. 13C + 4He -> 16O + n) in a red giant A stable nucleus (Fe-58) absorbs a neutron New nucleus (Fe-59) is neutron-rich and unstable (radioactive) Unstable nucleus becomes stable by beta decay, turning a neutron into a proton Final nucleus (Co-59) has more protons/is a heavier element than original nucleus New stable nucleus absorbs a neutron…

How can we know this is going on? “Spectroscopy”: every element absorbs/emits specific colors Analyze light from a red giant, and you find: This star contains Technetium (Tc) !!! (heavy element Z = 43, T1/2 = 4 million years, Merrill 1952)

S-process can produce many elements – but not all! Big Bang Stellar fusion s-process Human-made Of course, we also do research because we’re curious. One big mystery we’re trying to solve is where all the different elements came from. H and He were created in the beginning of our universe, after the Big Bang, these were mostly created when stars fused hydrogen into heavier elements for fuel, these are man-made… but the vast majority of elements were made in a lot of strange and complicated ways! One of which: supernovas (exploding stars) form unstable nuclei that later become these elements, so we study the unstable nuclei to understand how. Not naturally-occurring

When fusion stops, gravity kills the star … at the end of its “life”, a massive star collapses, then explodes in a supernova, resulting in a neutron star or black hole

Where are the rest of the elements made? How can you add neutrons to the nucleus even faster? In a very hot environment with tons of neutrons… a neutron star merger!

The rapid neutron capture “r-process” Like the s-process, but much faster! With high neutron density and high temperature/pressure, it can make many kinds of nuclei that are far more unstable.

Amounts of each element in our solar system Neutron-capture processes help explain this chart!

The r-process can fill in the chart – sort of. Big Bang Cosmic rays Stellar fusion s-process r-process Human-made Of course, we also do research because we’re curious. One big mystery we’re trying to solve is where all the different elements came from. H and He were created in the beginning of our universe, after the Big Bang, these were mostly created when stars fused hydrogen into heavier elements for fuel, these are man-made… but the vast majority of elements were made in a lot of strange and complicated ways! One of which: supernovas (exploding stars) form unstable nuclei that later become these elements, so we study the unstable nuclei to understand how. Not naturally-occurring … and more capture processes? i-process, p-process, rp-process …

How did we come to be? The stellar “life cycle” continually enriches the universe with more of the elements necessary for life!

FRIB will help us to understand stellar nucleosynthesis in detail! Problem: MOST of the nuclei involved ONLY exist in stars FRIB will help us to understand stellar nucleosynthesis in detail! Isotopes created and studied at current NSCL

National Superconducting Cyclotron Laboratory at MSU Learn more about our Lab and outreach programs SPARTAN YOUTH PROGRAMS Get our just-published history Up From Nothing from MSU Press msupress.org or on Amazon Find camps and programs at MSU for pre-college students: spartanyouth.msu.edu Get the Android/ iPhone/iPad game Isotopolis for free! Visit our “Gift Shop” on shop.msu.edu (click on “NSCL/FRIB” under “Specialty Shops”) GIFT SHOP contact visits@nscl.msu.edu or go to nscl.msu.edu @nscl

April 2018 sciencefestival.msu.edu sciencefestival.msu.edu

What’s holding it up? Nuclear energy Gravitational equilibrium: Gravity pulling in balances pressure pushing out. Energy balance: Thermal energy released by fusion in core balances radiative energy lost from surface.

Helium fusion -> the origin of life Helium fusion does not begin right away because it requires higher temperatures than hydrogen fusion—larger charge leads to greater repulsion. The fusion of two helium nuclei doesn’t work, so helium fusion must combine three He nuclei to make carbon.

Massive stars can fuse heavier elements How do high-mass stars make the elements necessary for life? High core temperatures allow helium to fuse with heavier elements.

Amounts of each element in solar system 40Ca 56Fe 138Ba 196Pt 208Pb Atomic Mass Number A Amounts of each element in solar system 130Te One of the great unsolved mysteries: Nucleosynthesis (i.e. where did all this come from? Why does it have such a funny looking pattern? Can we explain it? Let’s start at the beginning