Why study nuclei Basic facts about Nuclei Nuclear structure and nuclear reactions

1. Part I: An introduction to basic nuclear science Why study nuclei Basic facts about Nuclei Nuclear structure and nuclear reactions Basic facts about collisions and reactions Where we do our experiments How we do the experiments What one can learn from debris Nuclear Chemistry at Indiana: http://nuchem.iucf.indiana.edu Romualdo T. de Souza

2. 1) Why study nuclei? • Nuclei are at the heart of every atom; What is their structure, properties? What is the nature of the force that hold them together? • Necessary to understand the formation of the elements – nucleosynthesis • Important in understanding the properties of astrophysical objects such as neutron stars ( a giant nucleus with a radius of ~ 0.6 km)  nuclear equation-of-state. • Important in understanding the thermodynamic properties of small, finite systems (ties to the study of atomic clusters). • Important in understanding nuclear fission and nuclear fusion (energy source/ weapons) Stable Nuclei Known Nuclei Terra Incognita Protons Neutrons Romualdo de Souza

3. 1) Why study nuclei? Only elements Z=1-4 produced in the Big Bang  Fundamentals of supernova explosions are not understood!  Synthesis of the heavy elements is not understood  Limits of nuclear stability (superheavy elements, N/Z exotic) poorly known

4. 2) Basic facts about nuclei: • Nuclei behave like microscopic drops of liquid (fairly incompressible yet deformable). • Nuclei are small (R= 1-10 x 10-15 m);104-105 times smaller than an atom; requires measuring instruments of a comparable size to measure them e.g. other nuclei • Nuclei are positively charged so one has to overcome the mutual repulsion between two nuclei (Coulomb repulsion) i.e. Particle accelerators are required.

5. 2) Basic facts about nuclei: Binding energy TBE= Total Binding Energy Analogous to the heat of vaporization TBE/A = “average bond strength” Binding energy curve for nuclei How can one understand this binding energy curve?

6. 2) Basic facts about nuclei: The liquid drop model Charge denisty,  Radial distance (r) TBE = C1A C2A2/3 C3Z2/A1/3 C4(N-Z)2/A2 + C6/A1/2 volume surface Coulomb symmetry pairing <BE> = TBE/A <BE> = C1 C2A1/3 C3Z2/A4/3 C4(N-Z)2/A3+ C6/A3/2

7. 2) Basic facts about nuclei: The liquid drop model The first three terms in the liquid drop model (Volume, surface, and Coulomb) already explain the shape and magnitude of the Binding energy curve for nuclei.

8. 2) Basic facts about nuclei: The shell model Nuclei are not “formless blobs”. They have an internal structure in which protons and neutrons occupy orbitals much as in the atom (though with differences). Proton number Z (Mmeasured – Mliquid drop)c2 Neutron number N Red arrows indicate nuclei of additional stability. They occur at the MAGIC NUMBERS: 2,8,20,50,82, and 126

9. 3) Nuclear structure and nuclear reactions Nuclear structure involves studying the internal levels in a nucleus. Since the transition between levels involves the emission of gamma rays, nuclear structure involves gamma ray spectroscopy 110 Ge detectors on a 10 inch radius sphere The next generation: Segmented Gamma ray detectors (GRETINA)

10. 3) Nuclear structure and nuclear reactions • total number of protons is conserved • total number of neutrons is conserved • Q (energy release) can be either positive (exothermic) or negative (endothermic) • to get the nuclei to react one must get into the range of the short range nuclear force (projectile and target nuclei must touch) • The reaction products are quite likely excited (their protons and neutrons are not in the ground state) and they will de-excite by emission of gamma rays, neutrons, protons, alpha particles and other clusters.

11. 4) Basic facts about collisions and reactions? camera Classical drops: Collisions of mercury drops Deposit of a fraction of initial kinetic energy into heat and stretching the drops. How strong is the inter-atomic interaction? Role of surface tension. We want to study the same type of processes but with nuclear drops to learn about the forces holding nuclei together! Impact parameter selection: direct inspection t=0 ms 30 ms 60 ms 90 ms 120 ms 150 ms Fusion-like event Strongly Damped/Deeply inelastic event Deep inelastic + neck emissions event

12. Antisymmetrized Molecular Dynamics Supercomputer simulations of 114Cd + 92Mo at E/A = 50 MeV; b=7.37 fm

13. http://www.iucf.indiana.edu IU Cyclotron Facility The Indiana University Cyclotron Facility (IUCF) is a multidisciplinary laboratory performing research and development in the areas of accelerator physics, nuclear physics, materials science, life science and biomedical applications of accelerators. Accelerator PhysicsDefining the physics of producing and handling beams of sub-atomic particles Biomedical and Life SciencesHarnessing the power of radiation for research in biology and medicine Materials ResearchImaging, modeling and manipulating macromolecules Neutron PhysicsUsing neutrons to explore the molecular structure of proteins, crystals, surfaces, and much more Nuclear Physics and ChemistryProbing matter and forces at the sub-atomic scale

14. 5) Where we do our experiments (the accelerator side)

15. 5) Where we do our experiments (the accelerator side ) Ion sources • Up to C at 96MeV/A or U at 24MeV/A • CSS1, CSS2 K=380 • SISSI - fragmentation beams • SPIRAL - re-acceleration of radioactive beams with CIME

16. Principle of acceleration of a cyclotron • 4 dipole magnets act to bend the moving charged particle in a circular orbit • a voltage applied at radiofrequency as the particle moves between the dipoles causes the particle to accelerate, therefore spiraling outward • When the particle reaches the maximum radius of the cyclotron it is at the maximum energy and is extracted by a small electrostatic deflection

17. A sense of scale : A K=200 cyclotron (IUCF) • Remember that GANIL has two K=380 cyclotrons coupled sequentially • Michigan State has two coupled superconducting cyclotrons (K=500 and K=1200)

18. 6) How we do our experiments (the detector side) Interaction of radiation with matter! Charged particles: protons, deuterons, tritons, alpha particles, intermediate mass fragments (IMF: 3≤Z≤20), fission fragments Gas detectors (incident particles cause ionization) Solid state detectors: Si, Ge (incident particles cause electron-hole pairs) • Neutral particles: • gamma rays • neutrons Scintillators: liquid, plastic (incident particles cause scintillation)

19. 6) How we do our experiments (the detector side) E detector dE  Z2A Incident particle with (Z,A,E) dx E dx Interaction of radiation with matter! E detector Different “bands” represent different isotopes.

20. 6) How we do our experiments (the detector side) Backed by CsI(Tl) with photodiode readout … Are stacked to make a telescope… Segmented Si detectors 4x CsI(Tl) 4cm Si-E 1.5 mm Si-DE 65mm pixel 16 strips v (front) 16 strips h. (back) Target 16 strips v. (front) Beam And electronics…

21. 6) How we do our experiments (the detector side) Many telescopes are combined together to give as complete a measurement as possible.

22. 7) What one can learn from debris Collision of a nucleus with a light-ion (Z<3) or a heavy-ion (Z>2) converts kinetic energy of relative motion into intrinsic excitation i.e. heats the nucleus. From the debris – the fragmentation pattern we need to determine what happened • identity of all the particles • number of clusters (Z>2) • number of light particles Z=1,2 • energy of all the particles • angles of all the particles

23. 4 measurements ISiS: Indiana Silicion Sphere We measure all information collision-by-collision (event-by-event). • 162 individual telescopes covering 74% of 4 • Gas Ionization chamber/500 µm Si(IP)/CsI(Tl(PD) • Each telescope measures Z,A, E, and  • Identification of Z for 0.6≤E/A≤96 MeV • Identification of A for E/A ≥ 8 MeV for Z≤4

24. Thermometers Kinetic equilibrium: motion of all particles reflects a common temperature H2 gas P(v) v (m/s) Physical Chemistry, R. Chang, 2000 • Maxwell Boltzmann distribution • Coulomb Barrier for α-particles Helium Isotopes Kinetic energy spectra fit  Maxwell-Boltzman distribution  TSlope Charity, et.al., PRC (2001)

25. Angular distribution: comparing emission time to rotation time When the rotation time is short compared to the emission time, a uniform emission pattern is observed. Emission from a hot nucleus Circular ridge  PLF* emission “Isotropic” component Other emission (mid-rapidity, ...) Projectile velocity

26. Another Thermometer: Excited state populations Chemical equilibrium: different partitions are populated according to their statistical weights. Relative energy spectrum of daughters reflects internal quantum levels of parent 6Li Emitting system F. Zhu et al., PRC52, 784 (1995) 10B  Pm = (2Jm+1)e-(E*-Em/T) Pm/Pn = (2Jm+1)/(2Jn+1)e-(En-Em)/T Extract temperature T

27. Phase transitions for small, finite, open systems Constant P Infinite matter Closed system  Transition from one phase to an other at constant T “Caloric curve” for nuclear matter J. Pochodzalla et al., PRL 75, 1040 (1995) Gas phase Liquid phase Liquid-gas coexistenceBOILING ?