What have we learned last time? Q value Binding energy Semiempirical binding energy formula Stability

Nuclear Reactions

Scattering Reactions Elastic scattering A(a,a)A Inelastic scattering A(a,a’)A*

Other reactions

Energetics of nuclear reactions Energy, mass number, momentum conservation Q-value : positive exoergic; negative endoergic Example of endoergic 14 N + 4 He  1 H + 17 O + Q Q = MeV Is it enough to start the reaction?

Momentum correction

Coulomb barrier correction 14 N + 4 He  1 H + 17 O + Q Threshold energy in SL: 3.6 MeV [(4+14)/14] = 4.6 MeV

Cross section Symbol σ Geometrical cross section σ = π (R target ) cm 2 Barn, 1 b = cm 2 = 100 fm 2 1 mb = cm 2 1 μm = cm 2

Measurements of cross sections Thin targets Thick targets

Compound Nucleus Reactions yrast line – lowest energy for a given angular momentum 3-4 MeV/A

Discovery of Fission 1938 average number of 2.4 neutrons. statistical phenomenon, Gaussian distribution, independent of the fissioning nucleus. Otto Hahn and Lise Meitner, 1913, at the KWI for Chemistry in Berlin 1944 Nobel Prize in Chemistry for Otto Hahn "for his discovery of the fission of heavy atomic nuclei” Until 1938 all scientists believed that the elements with Z > 92 (transuranium elements) arise when uranium atoms are bombarded with neutrons.

Radioactive Decay Processes These radioactive products are the waste products of nuclear reactors.

The fragments in the vicinity of A = 95 and A = 140 share 92 protons. Prompt neutrons are emitted in s. Delayed neutrons intensity 1 in 100 fissions or 0.02 neutrons per fission (from neutron emission). Delayed neutrons are essential for controlling the reactors. Mass Distribution of Fission symmetric Source: University of Waterloo

Neutron Cross Sections for fission of U and Pu 1 b = m 2 ; 1 MeV = 1.6 x J 1/v - dependence Source: World Nuclear Association

Binding energy per nucleon

Q-value Energy released in a nuclear reaction (> 0 if energy is released, < 0 if energy is used) Example: The sun is powered by the fusion of hydrogen into helium: 4p  4 He + 2 e e Mass difference dM released as energy dE = dM x c 2

Fusion Reaction

How Do We Produce Exotic Nuclei?

58 Zn and the rp-process Astrophysics rp-process: hot and explosive hydrogen burning environments (X-ray burst) stops at 56 Ni? beyond 56 Ni: 56 Ni(p, γ ) 57 Cu(p,γ) 58 Zn rates 56 Ni(p,γ) 57 Cu; spectroscopy of 57 Cu rates 56 Ni(d,p); spectroscopy of 57 Cu 57 Cu(p,γ) 58 Zn – no information calculations based on 58 Ni- 58 Zn mirror symmetry Spectroscopic Information 58 Zn (Z=30, N=28) no excited states, spin and parity predicted from 58 Ni Cu Ni Zn N=Z ? no excited states in Z > N mirror symmetry – 59 Zn- 59 Cu – 58 Zn- 58 Cu rp-process

58 Zn Ar + 24 Mg → 60 Zn*→ 58 Zn + 2n  n  μb (20 x m 2 ) Spokespersons: C. Andreoiu and P.E. Garrett, University of Argonne National Laboratory, Chicago, 2006

Gammasphere + Ancillary Detectors Gammasphere (100 Ge detectors) MICROBALL (95 CsI) 20 neutron detectors

Particle Detectors - MICROBALL 95 CsI detectors average efficiency 80% alphas 70% protons D.G. Sarantites et al. Nucl. Instrum. Meth. A 400, 87 (1997)