An introduction to Nuclear Physics Jorge Pereira pereira@nscl.msu.edu National Superconducting Cyclotron Laboratory Joint Institute for Nuclear Astrophysics
The Origin of Everything
Layout The Nucleus. Some concepts What holds nucleons together? Walking to the Valley of Stability: Radioactivity Modern Alchemy: Nuclear Reactions Fusion reactors in the Cosmos: Stars Current Research
The Nucleus Some concepts
The nucleus u d u
The family portrait Number of neutrons N Nuclei with the same number of protons Z: ISOTOPES Nuclei with the same number of neutrons N: ISOTONES Nuclei with the same number of nucleons A: ISOBARS
What holds nucleons together?
The four interactions
The Gravitational potential Energy E G (r) that a subject of mass m (climber) acquires at a distance r from the object of mass M (Earth) E (r ) mv(r ) m G G M G r F(r ) G d dr E (r ) G m M G 2 r V G (r) V G (r) E G (r) (r ) F G r The climber has E G (r) Kinetic energy!!! r 2 E G(r ) 2 (v r ) m G r M
The Electromagnetic potential Potential energy E E (r) that a subject of charge q 1 (proton) acquires at a distance r from an object of charge q 2 (proton) E(r ) q V(r ) q E 1 E 1 K q r 2 F(r ) E d dr q V(r ) K 1 E q r 2 2 E K =0 E E (r) E K E E =0 1 2 m v p 2 Coulomb Barrier
The Weak potential Interaction of quarks and leptons Change quarks flavors Protons can transform into Neutrons and vice versa e n p e e p n e n p
The potential: Strong Potential energy E N (r) that a quark-made subject (proton) acquires at a distance r from a quark-made object (neutron) E *
The Binding energy of a nucleus B N B Z Neutrons Protons B/A B/ A a A a A a A 2 / 3 c v s 1/ 3 a s N Z A
Walking to the Valley of Stability Radioactivity
Radioactivity: Unstable nuclei E=M.c 2 (Energy=Mass) ds/dt >0 de/dt<0 M=Z.m p + N.m n - B A nucleus will do whatever it takes to maximize its binding energy (minimize energy)!!! How does a nucleus evolve to maximize the binding energy? Valley of stability
Releasing packets of protons and neutrons (2p+2n) radioactivity 4 He I can increase my binding energy!!! decay: 4 ( Z,N) (Z 2,N 2) 2He2 Q
Mass excess Transforming protons into neutrons (and vice versa) radioactivity A=100 - decay: ( Z,N) (Z 1,N 1) e e + decay: ( Z,N) (Z 1,N 1)e e Q Q
Releasing energy (de-exciting) radioactivity E * decay: (Z,N) (Z,N) E
Spontaneous Fission B 2 252 98Cf 154 B 1 126 126 49In77 77 Fission 49In There is a net gain in energy!!! Q fiss =B 2 +B 2 -B 1
Modern Alchemy: Nuclear Reactions
Nuclear Reactions How to convert a nucleus into a different one Light projectile (e.g. deuterium) collides with a target nucleus (Z initial, N initial ) at a given energy E initial Intermediate nuclei (Z, N, E * ) Final nuclei: Z final, N final, E final The reaction absorbs energy: Endoenergetic The reaction releases energy: Exoenergetic
Nuclear Reactions Example: neutron-induced reactions
Two types of exoenergetic reactions 56 26Fe 30 Fusion Fission
Nuclear Fission Reactions Deuterium-induced fission Projectile: light nucleus Target nucleus: Z, N Two nuclei + Energy + Free protons and neutrons
Fission Chain 1. Many nuclei (e.g. 235 U) 2. Each fission releases energy Q fiss and produces neutrons 3. Each neutron, will favor the fission of more 235 U Q fiss Q fiss Q fiss Q fiss
Use of Fission Reactions There is a huge release of energy in a short time interval!!! N( 235 U) x Q fiss Uncontrolled chain: Supercritical regime Increasing flow of neutrons Atomic bomb!!! Controlled chain: Critical or subcritical regime Steady/decreasing flow of neutrons Nuclear Reactor
Fission Reactor Control rods: neutron absorbers Steam Nuclear Fuel Clean energy (generated from steam) If neutron absorber fails Accidents!!! Long-live radioactive residues (some of them used in bombs)
Nuclear Fusion Reactions 24 12Mg 12 12 12 6C6 6 Fusion 6C
Use of Fusion Reactions A lot of energy could be generated More than in fission reactions Fusion reactors! It is necessary a lot of energy to compress the fusion nuclei (deuterium: 2 H, tritium: 3 H) to overcome Coulomb repulsion Uncontrolled compression: (e.g. fission-induced) Thermonuclear bomb!!! Controlled compression: (not yet found) Fusion reactor
Fusion Reactors 1. Keep nuclear fuel confined in a VESSEL 2. Increase the temperature (pressure) in the VESSEL 3. Hot nuclei (PLASMA) undergoes Fusion The BIG problem (not yet solved): How to create a VESSEL to confine and compress PLASMA Magnetic confinement (Tokamak) Inertial confinement (Laser compression)
Examples of Fusion Reactors ITER (In progress) Our Sun
Fusion reactors in the Cosmos Stars
The best fusion reactors As the cloud grows (heavier) Gravitational compression increases Star Formation Gravitation force forms a cloud of galactic dust: p, n, d, t, When compression is large enough: Fusion of protons (hydrogen burning) Gravitation confines the fusion nuclei: No Thermonuclear Explosion!!! 4 4p He 2e 2 e Q fus A new Star Gravitation vs. Fusion of hydrogen
When the hydrogen (proton) fuel is exhausted the star collapses until the compressed residual 4 He undergoes fusion (helium burning) 4 12 6 He C 6 Star Formation 4 4 He He 4 He 18 8 O 8 12 6 C Q 6 2 Q 1 When helium is exhausted Carbon burning sets in 12 12 12 C C C 12 12 12 C C C 20 10 23 11 23 12 Ne Na Mg 10 10 11 4 He p n Q Q Q 2 3 1 Then oxygen burning Then neon burning Then silicon burning Then IRON!!!
Star Formation Gravitation wins! Violent collapse SUPERNOVA The fusion-burning reactions stop with IRON E0102-72.2 Cassiopeia A The death of the star: Neutron Star / Black Hole
Nuclear Research (The Origin of Matter)
How to Study Nuclei We smash them! As a result: new excited nuclei are created Their decay will tell us a lot about them!!!
Nuclear Research at the National Superconducting Cyclotron Laboratory 1. Acceleration of nuclei 2. Smashing process 3. Selection of reaction products
Nuclear Research at the National Superconducting Cyclotron Laboratory 4. Study of decaying nuclei ( decay emission + neutron emission)
There is a lot to learn A journey of a thousand miles starts with one step (Lao Tse) it can be yours