Heavy Element Research at Dubna (current status and future trends) Yuri Oganessian Flerov Laboratory of Nuclear Reactions Joint Institute for Nuclear Research Dubna, Moscow region, Russian Federation Talk at the CCAST Workshop on "Isospin Physics and Nuclear Liquid-Gas Phase Transtion" August 18-21, 2005, Beijing, China

Cyclotron k=550 Cyclotron k=600 Microtron E e =25 MeV Low energy RIB-line 4π-array FOBOS Fragment separator COMBAS Mass-separator MASHA High resolution RIB-line Gas-filled recoil separator Energy selector of the recoiling nuclei + electron & γ-array Also radiochemical Lab. and applied research Lab’s Flerov Laboratory of Nuclear Reactions of the Joint Institute for Nuclear Research Flerov Laboratory of Nuclear Reactions of the Joint Institute for Nuclear Research

How many chemical elements can exist?

nucleus electrons Z E. Rutherford (1932) According to QED such an atomic structure is valid for very heavy atoms with Z~170 or even more …but the limit of existence of elements is reached much earlier because of instability of the nucleus itself

β - -decay electron capture or β + -decay α -decay spontaneous fission Yu. Oganessian.. CCAST Workshop. August 19-21, 2005, Beijing, China CCAST Workshop

G. Flerov and K. Petrjzak Leningrad 1940 N. Bohr and J.A. Wheeler (1939)

108

Shell corrections to the Liquid Drop

Microscopic theory

Yu. Oganessian.. CCAST Workshop. August 19-21, 2005, Beijing, China

After all this is a theoretical hypothesis - reactions of the SHE synthesis key problem - what are we expecting to see in the experiment properties of SHE - what we have already observed decay modes of SHE - setting the experiments synthesis of elements 113 and Chemistry of SHE identification of atomic numbers of SHE - overall picture of SHE nuclear shells and stability of the SHE - the search for surviving SHE. Prospects We shall try finding the answer to this question talking about:

Reactions of Synthesis of the Heaviest Nuclei SHE 248 Cm + 48 Ca → 116

Here there are two questions: What is the fusion probability for 48 Ca and actinide nuclei? What is the survival probability of the compound nucleus with Z= at the excitation energy E * 30 MeV?

fusion probability Let us consider the fusion of the 48 Са and 248 Cm occurred and resulted in the formation of the compound nucleus with an excitation energy of about 40 MeV Evidently, the dominant decay mode of such a nucleus would be fission into two fragments Accordingly, one could attempt investigating the probability of formation of the compound nucleus by measuring its fission characteristics.

Target 238 U, 244 Pu 248 Cm F1F1 F2F2 48 Ca solid angle – 0.3 sr angular resolution – TOF-start detector beam position sensitive stop detector x, y, E mass resolution – 2 a.m.u CORSET setup TOF-start detector Yu. Oganessian.. CCAST Workshop. August 19-21, 2005, Beijing, China

M. Itkis, Yu. Oganessian, et al., (2002) Fragment Energy and Mass Distributions in Cold and Hot Fusion Reactions target-like beam-like CN

cold fusion 0 Potential energy surface Z=116

Fusion probability

hot fusion

Fusion probability Yu. Oganessian.. CCAST Workshop. August 19-21, 2005, Beijing, China

BfBf E x = 40 МeV E x = 0 neutrons γ-rays fission σ xn = (Γ n / Γ f ) x ; х – number of neutrons (Γ n / Γ f ) ~ exp [(B f – B n ) / T] ~ 1/100 B f = B f LD + ΔE Shell 0 Survival probability SHE 100 1

Survival probability the limit of the exp. sensitivity Superheavy nuclei

The survivability of the compound nucleus is an independent evidence for the stabilizing effect of the N=184 shell in the domain of SHE

Natural occurrence of Ca isotopes (in %): 40 Ca – Ca – Ca – Ca – Ca – Ca – x 400 → Ca 5+ isotope production high flux reactors (Oak Ridge, Dimitrovgrad) isotope enrichment 98-99% S-2 separator (Sarov) technology of the target preparation – 0.3 mg/cm 2 Separation of super heavy nuclei and detection of their radioactive decays now: DGFRS

208 Pb+ 64 Ni cold fusion 248 Cm+ 48 Ca Decay properties Yu. Oganessian.. CCAST Workshop. August 19-21, 2005, Beijing, China

Spectra of alpha particles in the decay chains of isotopes with Z = 116 even-odd even-even

CL ≥ 99.9%

Isotope charge (Z) and mass (A) identifications obtained by the measurements of neutron evaporation cross sections vs. excitation energy of compound nucleus

Number of observed decays Z = % 10% Mass variation of the target-nuclei Excitation functions Decay properties For Z-odd nuclei hindrance factor: for SF- decay ≥ 1000 for α – decay ≤ 10 Z variation of the target-nuclei Z-even nuclei

Synthesis of Element 115 in the Reaction: 243 Am Ca 20 → 291-x 115 Yu. Oganessian.. CCAST Workshop. August 19-21, 2005, Beijing, China

v ( A=48 ) = 0.11 c q = v ( A=288 ) = c q = 6.2+

 =87% from 4  For  -particles For SF-fragments  =100% Front detector: sensitive area – 50 cm 2

Energy spectra of all “  -like” signals from the focal plane detector in the 243 Am + 48 Ca reaction July 14 – July 29 beam time – 270 h beam dose – 4.3∙10 18 July 29 – Aug.10 beam time – 250 h beam dose – 4.3∙10 18

odd-odd  Yu. Oganessian.. CCAST Workshop. August 19-21, 2005, Beijing, China

Chemical isolation of 268 Db ~20 s June 2004 Actinides Z ≤ 103 Transactinides Z ≥ 104 Nb / Ta / Db - fraction

SF of Z=105 from the Nb/Ta chemical fraction

Spontaneous fission half-life of 268 Db (N=163) T 1/2 = 30h 15 events 252 Cf 268 Db Q F ~ 280 MeV

5 Yu. Oganessian.. CCAST Workshop. August 19-21, 2005, Beijing, China

Synthesis of Element 118 in 249 Cf + 48 Ca Reaction Cm+ 48 Ca 242 Pu+ 48 Ca 238 U+ 48 Ca

10 8 y 10 5 y 1 y1 y 1 d1 d the search for SHE in Cosmic rays Yu. Oganessian.. CCAST Workshop. August 19-21, 2005, Beijing, China

Search for SF of natural Eka Os (common extractive metallurgy) by detection of fission neutrons 1 SF-event per year (T 1/2 =10 9 y) corresponds to the concentration: EkaOs/Os = g/g (or g/g in the terrestrial matter, or of U) Fréjus peak Modane Entrance to the road tunnel France Italy

Developments and Prospects On-line Separator MASHA Upgrade of heavy ion accelerators PHYSICS GOAL

Nuclear Exotica in Superheavy Nuclei a limit caused by Coulomb forces LD + shell effect

Search in Nature Chemical properties (relativistic effect) Astrophysics (search for SHE in cosmic rays) Nucleosynthesis (test of the r-s process) Atomic physics (structure of SH-atoms) Elements with Z ≥ 120 Yu. Oganessian.. CCAST Workshop. August 19-21, 2005, Beijing, China

Flerov Laboratory of Nuclear Reactions of JINR …in February Thanks for your attention