Sophia Heinz

1. Synthesis of Elements Sophia Heinz GSI Helmholtzzentrum Darmstadt, Germany and Justus-Liebig-University Giessen

2. The Origin of Matter in the Universe Big Bang 14 · 109 y Today 5 · 108 y The first galaxies are formed 10–32 s End of inflationary expansion 10–5 s Nucleons are formed 100 s Synthesis of light nuclei with Z ≤ 3 109 y First stars; formation of nuclei with Z > 3

3. Evolution of the Early Universe ▪ A description of the universe in frame of our familiar laws of nature is only possible for the period starting after the Planck time: G: Gravitational Constant Planck length: ▪ for t < tPlanck the laws loose their validity → in this regime, the quantisation of space and time is required ▪ The evolution of the universe can already be well described for the time t > 10–10 s after the Big Bang; this time corresponds to a temperature of T ≈ 1015 K and energy E = kBT ≈ 100 GeV → energy region is accessible experimentally with particle accelerators (e.g. LHC at CERN)

4. The first 10 μs: Neutrons and Protons are formed t ≈ (10–43 - 10–5) s; T ≈ (1032 - 1013) K ▪ plasma-like state composed of elementary particles and radiation (quark-gluon plasma, electrons, neutrinos and photons) → all constituents are in thermal equilibrium; the universe Is dominated by electromagnetic radiation; distinction bet- ween matter and radiation is hardly possible (E = mc2) t ≈ 10–5 s (10 μs); T ≈ 1013 K ▪ formation of the first nucleons („Baryogenesis“) ▪ thermal energy: Etherm ≈ 1 GeV ≈ mp, mn ▪ for T < 1 GeV, the created nucleons can no longer be destroyed by photons

5. t ≈ 1 s: Beginning of Nucleosynthesis t ≈ 1 s: T ≈ 1010 K; E ≈ 1 MeV ▪ The first deuterons are synthesized in fusion reactions: n + p → d + γ (Eγ = EB = 2.23 MeV) → the break-up of deuterons can be induced by photons with E ≥ 2.23 MeV t ≈ (1 – 400) s; T ~ 109 K; E ~ 0.1 MeV ▪ due to expansion and cooling of the universe, the number of photons with E > 2 MeV is now sufficiently small to stop the break-up of deuterons → the expansion rate of the early universe is a very critical parameter for the first nucleosynthesis processes („primordial nucleosynthesis“) ▪ When the number of high-energy photons is small enough, the synthesis of nuclei heavier than A = 2 can proceed in fusion reactions

6. t ≈ 5 minutes: End of Primordial Nucleosynthesis Z Result of primordial nucleosynthesis: ▪ composition of matter: ~ 25% He-4, ~ 75% protons; heavier elements only in traces ▪ endpoint nucleus of all reaction paths: He-4 (→ high binding energy) N

7. t > ~109 years: Synthesis of Heavier Elements Natural nucleosynthesis reactions ▪ Fusion ▪ n-capture, p-capture s – Process (end point at 209Bi) • slow neutron capture • time scale: years • in red giant stars Sp=0 Sn=0 rp – Process rapid proton capture r – Process • rapid neutron capture • time scale: milliseconds to seconds • in supernova explosions • > 1020 neutrons/(cm2s) Fusion → end point unknown (A ≈ 270 ?) ▪ up to Z ~ 26 (Fe) (largest binding energy per nucleon)

8. Nucleosynthesis in the Laboratory 1) Fragmentation, spallation und fission → at relativistic energies: vprojektile ≈ 0.9 c, E ≈ (300 – 1000) MeV/n figure: CERN

9. Nucleosynthesis in the Laboratory 2) Fusion reactions → beam energies at the Coulombbarriere: vbeam ≈ 0.1 c, E ≈ 5 MeV / nucleon Excited compound nuclus Evaporation residue → presently the only and most effective way to produce nuclei heavier than uranium (Z > 92) → The elements with Z > 100 were synthesized in fusion reactions

10. The Fusion Process in Heavy Systems Nuclear Molecule FUSION Compound Nucleus (CN) TRANSFER, QUASI-FISSION FUSION-FISSION Fission Fragments Evaporation Residue (ER) Evaporation residue cross-section:

11. Nucleosynthesis in the Laboratory Fusion, Fragmentation and Fission Fusion Projektil-Fragmentation Projektil-Spaltung

12. 1935 114 114 1958 184 184 82 82 Proton number 126 126 50 50 2015 82 82 28 28 50 20 20 50 8 8 28 20 2 2 28 20 8 8 2 2 Giorgio Fea, 1935 Karlsruher Nuklidkarte Neutron number

13. Physics at the boarders of the Chart of Nuclides Superheavy Nuclei 118 known elements ca. 3000 known isotopes ca. 4000 still unknown isotopes new decay modes: proton emission Astrophysical nucleosynthesis very exotic nuclear structure Halo nuclei

14. V fission barrier Bf ES EC deformation What is a „Superheavy“ Nucleus? Binding energy of a nucleus in the liquid drop model (Weizsäcker formula): Coulomb- energy EC Surface energy ES Condensation energy Asymmetry energy Superheavy nuclei: Bf = 0 for Z2 / A > 50 → Z > 100

15. Fission Barriers of Superheavy Nuclei Shell corrections and pairing LD 25098152 Microscopic corrections to the binding energy LD + shell 268106162 Potential energy / MeV The fission barriers of superheavy nuclei are determined by the shell correction energy and the pairing term: 298114184 Bf = B(N,Z)micro = Eshell + Epair Quadrupole deformation β2

16. Fission Barriers of Superheavy Nuclei Model calculations of shell correction energies of superheavy nuclei N = 184 Z = 114 A. Sobiczewski et al., 1995 Enhanced stability is expected for nuclei in the following regions: ► Z = 108, N = 162 (deformed nuclei) → experimentally confirmed ► Z = 114, 120 or 126, N = 184 (spherical nuclei) → exp. confirmation still missing

17. The Search for New Elements ● 1932: Discovery of the neutron by J. Chadwick ● 1940 - 1952: Synthesis of the elements Z = 93 - 100 by irradiation of uranium nuclei with neutrons (Berkeley) → application of chemical identification methods 1951: Nobel prize for Chemistry for G.T. Seaborg and E.M. McMillan for their „discovery in the chemistry of the transuranium elements“ ● 1958 - 1974: Synthesis of the elements Z = 101 – 106 in Berkeley and Dubna in fusion reactions ● since 1980: Investigation of nucleontransfer reactions (e.g. in collisions of U+U or Ca+U) for the synthesis of new elements → successful up to Z = 101 ● since 1980: Investigation of fusion reactions → turned out to be the more successful method − Synthesis of the elements Z = 107 – 112 at GSI (SHIP) in fusion reactions with Pb and Bi- targets at energies below the Coulomb barrier (P. Armbruster, S. Hofmann, G. Münzenberg et al., 1981 - 1996); 2004: Synthesis of Z = 113 at RIKEN, Japan (K. Morita et al.) → Identification of the nuclei via their alpha decay chains − Synthesis of the elements Z = 113 – 118 in Dubna in fusion reactions with actinide targets (U, Pu, Cm, ...)

18. „Cold“ and „Hot“ Fusion Reactions Cold Fusion → doubly magic target nuclei: Pb, Bi; E*(CN) = 10 – 20 MeV; evaporation of 1 – 2 neutrons; up to now successful for Z ≤ 113 Hot Fusion → actinide targets (U, Cm, …) and 48Ca projectiles; E*(CN) = 30 – 40 MeV; evaporation of 3 – 4 neutrons; up to now successful for Z ≤ 118

19. Excitation Functions Characteristics: • Maxima of cold fusion excitation functions are located below the Coulomb barrier • Location of the maxima corresponds to an internuclear distance of d > R1 + R2 → σcapture increases with beam energy but PCN and Psurvival decrease Cold Fusion σER = σcapture x PCN x Psurvival Compound nucleus excitation energy: Hot Fusion E* = Ecm + Q (Q ≈ −200 MeV)

20. Production Cross-sections and Rates kalte Fusion (X + Pb, Bi) HeißeFusion (48Ca + X) 1 pb; corresponds to 1 nucleus / week → requires very sensitive separation and detection techniques !

21. Decay Channels and Half-lives figure: A. Sobiczewski, S. Hofmann → Nuclei on and around the island of stability have long fission half-lives and decay predominantly via alpha decay

22. vacuum H or He gas (A/q)1 (A/Z1/3)1 (A/q)2 (A/Z1/3)2 (A/q)3 q ≈ vion/vo Z1/3 Experimental Techniques: Separators 1) Separation according to magnetic rigidity Bρ Magnetic dipole field Gas-filled dipole magnet

23. Experimental Techniques: Separators Example:: The Dubna gas-filled recoil separator (DGFRS)

24. Experimental Techniques: Separators 2) Separation according to velocity Principle of a velocity filter (Wien filter): crossed electric und magnetic fields Fel particle can pass the aperture if: Fel = FL → qE = qvoB + vo = E / B + velocity filter aperture FL

25. 1 E, T1/2 2 E, T1/2 3 E, T1/2 sf Separation and Detection Ge Detectors Si Detectors Example: the velocity filter SHIP (Separator for Heavy Ion reaction Products) at GSI ToF Detectors 7.5° Magnet Ndetector ≈ 100 / s Target wheel Beam stop Magnets Electric field Quadrupoles Isotope identification via alpha decay chains Ion beam v ~ E/B Nbeam ≈ 5·1012 / s

26. 293116 89 ms α 10.54 289114 3.9 s α 9.81 285112 300 μm 66 s α 9.11 281110 35 mm 16.5 s sf α-particle 80 mm ER Particle Identification via Alpha Decays focal plane detector (silicon „stop detector“) → recording of the decays during beam-off periods for background suppression

27. Present State of SHE Research N = 184 ? Z = 120, 126 ? Z = 114 ? ▪ Island of spherical shell closures is not yet reached ▪ bottleneck: available projectile / target combinations have not enough neutrons to reach N = 184

28. RIKEN GANIL 54Cr 248Cm 302120* Heavy Element Research Worldwide Physics and Chemistry with Single Ions Mass measurements Dubna Berkeley GSI Lanzhou Spectroscopy Search for Z = 119 and 120

29. Summary ▪ The first „natural elements“ were synthesized in fusion reactions in the first 5 min. after the Big Bang („primordial nucleosynthesis“) → mainly He-4 ▪ After a „break“ of ~1 Billion years, nucleosynthesis continued, also to elements with Z > 2 with the upcoming of the first stars ▪ Nature uses fusion reactions and n or p – capture reactions for nucleosynthesis ▪ Laboratory nucleosynthesis applies mainly fusion, fragmentation and fission ▪ The synthesis of new elements with Z > 100 is performed in fusion reactions ▪ For synthesis and detection of new elements highly senstiive exp. techniques are required (small production rates) → efficient separation techniques and single event identification ▪ Present main focus: attempt to produce Z=119 and 120; at Z=120 a possible spherical shell closre is expected