W. Nazarewicz

Limit of stability for heavy nuclei Meitner & Frisch (1939): Nucleus is like liquid drop For Z>100: repulsive Coulomb force stronger than attractive nuclear force Shell Model explains stability of MAGIC NUCLEI due to large binding of closed shells Strutinsky combined liquid drop model and shell model Superheavy nuclei are stabilized only by shell effects

Exact position of magic proton shell gap is in question N=184 neutron shell gap is predicted by all theoretical models Position of proton shell gap very sensitive on details of the theory (Z=114, 120, 126 ?)  structure of superheavy elements provides sensitive test for models Z N

Heavy-ion fusion reactions to produce new elements Hot fusion light beam on actinide target (traditional approach) (also due to limits of accelerators)  large asymmetry predicted to lead to larger cross section  relatively high excitation energy of Compound Nucleus Cold fusion heavy beam on double magic 208 Pb or 209 Bi (most successful for Z > 108) (possible with modern accelerators)  low excitation energy of Compound Nucleus  higher survival probability

The challenge of detecting and identifying superheavy elements expected count rate N =  N t N p  production cross section  = 1 pbarn ( cm 2 ) projectiles per secondN p = 5 ·10 12 s -1 target nucleiN t = cm -2 efficiency of detection system  = 50 % detection rate :N = 2.5 ·10 -6 s -1 ( 1 atom per 5 days) competition by fission  = 100 mbarn ( > times stronger) scattered beam particles or transfer products can have the same kinematics need good separation of produced elements up to Z=104 : standard chemical separation up to Z=106 : fast chemistry, atom by atom Z > 106: separation in flight unique identification necessary alpha - alpha parent-daughter correlation

Separation in flight Filters (Vacuum) SHIPVelocity filterGSI Darmstadt, Germany VASILISSAEnergy filterJINR Dubna, Russia Gas-filled separators GNSJINR Dubna, Russia GARISRIKEN Tokyo, Japan HECKGSI Darmstadt, Germany BGSLBNL Berkeley, USA Filters (Vacuum) SHIPVelocity filterGSI Darmstadt, Germany VASILISSAEnergy filterJINR Dubna, Russia Gas-filled separators GNSJINR Dubna, Russia GARISRIKEN Tokyo, Japan HECKGSI Darmstadt, Germany BGSLBNL Berkeley, USA Separation between beam particles superheavy element transfer products fission fragments target Separator beamdetector beam stop new element

The SHIP Velocity Filter at GSI, Darmstadt, Germany Electric dipole Magnetic dipole Beam stop Magnetic quadrupole Target wheel Position sensitive focal plane detector Time of flight detectors

Gas-filled separator magnet filled with ~ 1 Torr He gas heavy ions leave target with charge distribution scattering of heavy ions with gas  combination of charge states into narrow distribution  larger acceptance than vacuum system since vacuum system can only accept few charge states magnetic rigidity B  is velocity independent since average charge state depends on velocity B  = A v/v 0 q -1 q = v/v 0 Z 1/3  - effective radius of trajectory q - average charge state large acceptance BUT reduced resolution reduced suppression

The Berkeley Gas-filled Separator V. Ninov, K. Gregorich, et al. Phys. Rev. Lett.

 -  mother daughter correlation technique detection of  -decay chain at one position energies time correlation correlation with known daughter decays uniquely identifies mother nucleus

Discovery of Z=114 in Dubna The problem: no daughter product known no link to known nuclei short decay chain correlation not very strong identification not clear

Discovery of Z=118 at the BGS in Berkeley The problem: no daughter product known  no link to known nuclei BUT: strong correlation No clear identification not yet confirmed by GSI, RIKEN confirmation experiment at BGS in March The problem: no daughter product known  no link to known nuclei BUT: strong correlation No clear identification not yet confirmed by GSI, RIKEN confirmation experiment at BGS in March Three consistent chains observed! Three consistent chains observed!

Perspectives with radioactive beams 92 Sr would allow Z=120 production with ~1nb Yields predicted for Munich accelerator for fission fragments (MAFF)

Structure study of heavy nuclei ( 254 No) Gamma-rays at target position in coincidence with recoils detected at the focal plane of the separator Unique identification by use of  -  correlations Test of deformation, fission barrier Odd-A Nuclei will reveal single-particle strucutre Gamma-rays at target position in coincidence with recoils detected at the focal plane of the separator Unique identification by use of  -  correlations Test of deformation, fission barrier Odd-A Nuclei will reveal single-particle strucutre RITU + Jurosphere & Gammasphere + FMA P. Reiter et al. R Julin et al.

SASSYER (Small Angle Separator System at Yale for Evaporation Residues) Combine SASSY 2 with YRAST Ball  powerful system for channel selection, fission suppression  recoil decay tagging (RDT) capabilities Combine SASSY 2 with YRAST Ball  powerful system for channel selection, fission suppression  recoil decay tagging (RDT) capabilities SASSY 2 from LBNL comes to Yale in March gas-filled separator large acceptance high transmission efficiency SASSY 2 from LBNL comes to Yale in March gas-filled separator large acceptance high transmission efficiency Only two other labs worldwide: Berkeley (BGS) and Jyvaskyla (RITU) Physics program: - exotic nuclei proton emitters heavy elements neutron-rich nuclei - reactions studies relevant to production of superheavy elements Only two other labs worldwide: Berkeley (BGS) and Jyvaskyla (RITU) Physics program: - exotic nuclei proton emitters heavy elements neutron-rich nuclei - reactions studies relevant to production of superheavy elements

SASSYER - Physics Projects Light actinide nuclei near A = 204 Magnetic Rotation Superdeformation High-spin structure Actinides around A = 224 Octupole deformation Collective excitations Structure of heavy nuclei Spectroscopy of transactinides Alpha spectroscopy  -spectroscopy at focal plane Reaction studies relevant for production of superheavy elements Structure of nuclei near the proton dripline Shape coexistence Onset of deformation High-K isomers N=Z nuclei Mass measurements of r-process nuclei  -decay to T=0 and T=1 states Study of fission fragments Nuclear Astrophysics