1. 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

2. 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

3. How many chemical elements can exist?

4. 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

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

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

7. 108

8. Shell corrections to the Liquid Drop

9. Microscopic theory

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

11. 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 115 - 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:

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

13. 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=114-118 at the excitation energy E * 30 MeV?

14. fusion probability Let us consider the fusion of the 48 Са and 248 Cm occurred and resulted in the formation of the compound nucleus 296 116 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.

15. Target 238 U, 244 Pu 248 Cm F1F1 F2F2 48 Ca solid angle – 0.3 sr angular resolution – 0.3 0 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

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

17. cold fusion 0 Potential energy surface Z=116

18. Fusion probability

19. hot fusion

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

21. 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

22. Survival probability the limit of the exp. sensitivity Superheavy nuclei

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

24. Natural occurrence of Ca isotopes (in %): 40 Ca – 96.94 42 Ca – 0.647 43 Ca – 0.135 44 Ca – 2.086 46 Ca – 0.004 48 Ca – 0.187 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

25. 208 Pb+ 64 Ni cold fusion 248 Cm+ 48 Ca Decay properties Yu. Oganessian.. CCAST Workshop. August 19-21, 2005, Beijing, China

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

27. 116 114 112 110 CL ≥ 99.9%

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

29. Number of observed decays Z = 118 3 116 19 114 45 112 52 50% 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

30. Synthesis of Element 115 in the Reaction: 243 Am 95 + 48 Ca 20 → 291-x 115 Yu. Oganessian.. CCAST Workshop. August 19-21, 2005, Beijing, China

31. v ( A=48 ) = 0.11 c q = 16.5+ v ( A=288 ) = 0.017 c q = 6.2+

32.  =87% from 4  For  -particles For SF-fragments  =100% Front detector: sensitive area – 50 cm 2

34. 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

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

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

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

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

40. 5 Yu. Oganessian.. CCAST Workshop. August 19-21, 2005, Beijing, China

41. Synthesis of Element 118 in 249 Cf + 48 Ca Reaction 2002 2005 116 29 2002 - 2004 245 Cm+ 48 Ca 242 Pu+ 48 Ca 238 U+ 48 Ca

43. 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

44. 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 = 5.10 -15 g/g (or 10 -22 g/g in the terrestrial matter, or 10 -16 of U) Fréjus peak Modane Entrance to the road tunnel France Italy

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

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

48. 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

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