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
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
5 · 108 y
The first galaxies
are formed
14 · 109 y
Today

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– –5) s; T ≈ ( ) 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
▪ 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
t ≈ (1 – 400) s; T ~ 109 K; E ~ 0.1 MeV

6. t ≈ 5 minutes: End of Primordial NucleosynthesisZ
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
• slow neutron capture
• time scale: years
• in red giant stars
(end point at 209Bi)
Sp=0
Sn=0
rp – Process
rapid proton capture
r – Process
• rapid neutron capture
• time scale: milliseconds to seconds
• in supernova explosions
• > neutrons/(cm2s)
→ end point unknown (A ≈ 270 ?)
Fusion
▪ 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 1958 2015 Proton number Giorgio Fea, 1935 Karlsruher Nuklidkarte
126 2 8 20 28 50 82
114
184
1958
Proton number
126 2 8 20 28 50 82
114
184
2015
Giorgio Fea, 1935
Karlsruher Nuklidkarte
Neutron number

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

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

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

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
● : Synthesis of the elements Z = 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“
● : Synthesis of the elements Z = 101 – 106 in Berkeley and Dubna
in fusion reactions
● since 1980: Investigation of nucleon transfer 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., );
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: σER = σcapture x PCN x Psurvival
• 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)
Heiße Fusion
(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. Experimental Techniques: Separators
1) Separation according to magnetic rigidity Bρ
Magnetic dipole field
Gas-filled dipole magnet
vacuum
(A/q)3
(A/q)2
(A/q)1
(A/Z1/3)1
(A/Z1/3)2
H or He gas
q ≈ vion/vo Z1/3

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

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

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

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