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Heavy Element Research at Dubna (current status and future trends)

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

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Heavy Element Research at Dubna (current status and future trends)

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

  3. How many chemical elements can exist?

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

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

  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 We shall try finding the answer to this question talking about: • - reactions of the SHE synthesis key problem • what are we expecting to see in the experimentproperties 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

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

  13. Here there are two questions: What is the fusion probability for 48Ca 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 48Са and 248Cmoccurred and resulted in the formation of the compound nucleus 296116 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. CORSET setup position sensitive stop detector x, y, E F1 TOF-start detector TOF-start detector mass resolution – 2 a.m.u beam Target 238U,244Pu 248Cm F2 48Ca angular resolution – 0.30 solid angle – 0.3 sr Yu. Oganessian.. CCAST Workshop. August 19-21, 2005, Beijing, China

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

  17. Z=116 Potential energy surface cold fusion 0

  18. Fusion probability

  19. hot fusion

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

  21. Ex= 40 МeV fission fission neutrons 100 1 Bf SHE γ-rays Ex= 0 σxn= (Γn / Γf)x;х – number of neutrons (Γn / Γf) ~ exp [(Bf – Bn) / T]~ 1/100 Bf= BfLD + ΔEShell 0 Survival probability

  22. the limit of the exp. sensitivity Survival probability 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. x 400 → Ca5+ technology of the target preparation – 0.3 mg/cm2 Separation of super heavy nuclei and detection of their radioactive decays now: DGFRS isotope enrichment 98-99% S-2 separator (Sarov) isotope production high flux reactors (Oak Ridge, Dimitrovgrad) Natural occurrence of Ca isotopes (in %): 40Ca – 96.94 42Ca – 0.647 43Ca – 0.135 44Ca – 2.086 46Ca – 0.004 48Ca – 0.187

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

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

  27. 110 CL ≥ 99.9% 116 114 112

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

  29. Z variation of the target-nuclei Excitation functions Mass variation of the target-nuclei Decay properties Z-even nuclei For Z-odd nuclei hindrance factor: for SF- decay ≥ 1000 for α – decay ≤ 10 10% Number of observed decays Z = 118 3 116 19 114 45 112 52 50%

  30. Synthesis of Element 115 in the Reaction: 243Am95 + 48Ca20→ 291-x115 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. Front detector: sensitive area – 50 cm2 For a-particles e=87% from 4p For SF-fragments e=100%

  33. Energy spectra of all “a-like” signals from the focal plane detector in the 243Am + 48Ca reaction July 14 – July 29 beam time – 270 h beam dose – 4.3∙1018 July 29 – Aug.10 beam time – 250 h beam dose – 4.3∙1018

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

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

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

  37. 15 events Spontaneous fission half-life of 268Db (N=163) T1/2 = 30h 268Db 252Cf QF ~ 280 MeV

  38. 5 Yu. Oganessian.. CCAST Workshop. August 19-21, 2005, Beijing, China

  39. 2002 2002 - 2004 245Cm+48Ca 242Pu+48Ca 238U+48Ca Synthesis of Element 118 in 249Cf + 48Ca Reaction 2005 29 116

  40. the search for SHE in Cosmic rays 108 y 105 y 1y 1d Yu. Oganessian.. CCAST Workshop. August 19-21, 2005, Beijing, China

  41. Fréjus peak Entrance to the road tunnel Modane France Search for SF of natural Eka Os (common extractive metallurgy) by detection of fission neutrons Italy 1 SF-event per year (T1/2=109y) corresponds to the concentration: EkaOs/Os = 5.10-15g/g (or 10-22g/g in the terrestrial matter, or 10-16 of U)

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

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

  44. 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

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

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