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Kazimierz 2011 T. Cap, M. Kowal, K. Siwek-Wilczyńska, A. Sobiczewski, J. Wilczyński Predictions of the FBD model for the synthesis cross sections of Z.

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Presentation on theme: "Kazimierz 2011 T. Cap, M. Kowal, K. Siwek-Wilczyńska, A. Sobiczewski, J. Wilczyński Predictions of the FBD model for the synthesis cross sections of Z."— Presentation transcript:

1 Kazimierz 2011 T. Cap, M. Kowal, K. Siwek-Wilczyńska, A. Sobiczewski, J. Wilczyński Predictions of the FBD model for the synthesis cross sections of Z = 114-120 elements based on macroscopic-microscopic fission barriers

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3 Nuclear Elongation Existence of super–heavy nuclei due to shell effects

4 Yu. Ts. Oganessian et al. PRL 104, 142502 (2010) 249 Bk( 48 Ca,xn) 297-xn 117; x = 3, 4 X + 208 Pb, 209 Bi 48 Ca + X

5  = 2.5 (+1.8,-1.1) pb GSI 279 Ds 9.520  0.015 /232  15 MeV T ½ = 6.9 s b sf = 0.5 210 MeV T ½ = 0.18 s CN  6.9 – 2.3  30 – 15  0.32 –0.07 283 Cn  = 0.72 (+0.58,–0.35) pb 3 chains 4 chains S. Hofmann et al., Eur. Phys. J. A32,251 (2007) 260 MeV TKE T ½ = 1.3 h b sf = 1.0 279 Ds 275 Hs 267 Rf 9.54±0.06 MeV T ½ = 3.8 s b sf = 0.10 9.70 / 228 MeV T ½ = 0.20 s b  = 0.10 9.29±0.08 MeV T ½ = 0.19 s b  = 1.0 8.54 / 248 MeV T ½ = 1.9 min b  = 0.70 283 Cn CN 271 Sg FLNR 48 Ca + 238 U  286 Cn + 3n Confirmation of Dubna results at GSI

6 Yu.Ts. Oganessian, Phys. Rev. C 70, 064609 (2004) Yu.Ts. Oganessian, J. Phys. G 34 (2007) R165 8 events,  = 48 Ca + 244 Pu  288 114 + 4n FLNRGSI 284 Cn 9.94  0.06 T ½ = 0.8 s 216 MeV T ½ = 97 ms CN  0.27 – 0.16  30 – 15  31 –19 288 114 284 Cn 9.94  0.04 T ½ = 0.47 s T ½ = 101 ms CN  0.24 – 0.12  50 –25 288 114 Ch. Düllmann et al., PRL 104, 252701 (2010) J.M. Gates et al. PRC 83, 054618 (2010) 12 events,  =

7 GSI 281 Ds 9.85  0.04 T ½ = 0.97 s T ½ = 20 s CN  0.97 – 0.32 289 114 285 Cn 9.19  0.04 T ½ = 30 s  20 – 7  30 – 10  18 – 2 277 Hs T sf = 3 s (8.67 MeV) (T  = 5.7 s) Yu.Ts. Oganessian, Phys. Rev. C 70, 064609 (2004) Yu.Ts. Oganessian, J. Phys. G 34 (2007) R165 2 chains, 48 Ca + 244 Pu  289 114+3n FLNR 281 Ds 9.82  0.05 T ½ = 2.6 s 212 MeV T ½ = 11.1 s CN  1.2 – 0.7  5.0 –2.7 289 114 285 Cn 9.15  0.05 T ½ = 29 s  13 – 7 Ch. Düllmann et al. PRL 104, 252701 (2010) J.M. Gates et al. PRC 83, 054618 (2011) 5 chains,  = ==

8 48 Ca + 248 Cm  296-xn 116 248 Cm 296 116 S. Hofmann et al., GSI Scientific Report 2010, 197 4 chains 6 chains 4 chains 1 chains 3.4 pb 0.9 pb E* = 41.0 MeV GSI-SHIP 6 chains 2 chains 3.3 pb 1.2 pb E* = 39.0 MeV FLNR

9 242 48 Ca + 242 Pu  290-xn 114 +xn x = 3, 4, 5 L. Stavstera et al., Phys. Rev. Lett. 103, 132502 (2009) P. A. Ellison et al., Phys. Rev. Lett. 105, 182701 (2010) Yu.Ts. Oganessian, Phys. Rev. C 70, 064609 (2004) Yu.Ts. Oganessian, J. Phys. G 34 (2007) R165 2n - 1 event,  =0.5 (+1.0, -0.5) pb 3n - 15 events,  =3.6 (+2.4, -1.6 ) pb 4n - 9 events,  =4.5 (+2.5, -1.5) pb 3n - 1 event,  =3.1 (+4.9, -2.6) pb 4n - 1 event,  =3.1 (+4.9, -2.6) pb 5n - 1 event,  =0.6 (+0.9, -0.5) pb FLNR, DUBNA LBNL, Berkeley Confirmation of Dubna results in LBNL

10 How to produce elements with Z > 118? Essential experimental difficulties: The use of 48 Ca beams will require heavier targets of Z > 98. Possibilities: Z=99, 252 Es, 254 Es T 1/2 = 472 d, 275.7 d Z=100 257 Fm T 1/2 = 100.5 d Alternative: Heavier beams → much smaller cross section Multi-nucleon transfer reactions.

11 Experiments 2007/2008 GSI Dubna Number of irradiation days : 120 days --- Excitation energy of the CN : 36.0 MeV45.5 MeV Total number of beam particles : ≈ 2 x 10 19 7.1 x 10 18 Number of detected events : 0 0 Cross section limits : < 0.1 pb< 0.4 pb First experiments to produce element of Z = 120 GSIDubna 58 Fe 244 Pu Yu. Ts. Oganessian et al. Phys. Rev. C 79, 024603 (2009)

12 capture fusion survive evaporation residue symetric fission fast fission  (synthesis) =  (capture) × P(fusion) × P(survive) Nucleus-nucleus collision which may lead to the formation of super-heavy nuclei T. Cap, K. Siwek-Wilczyńska, J. Wilczyński, IJMP E 20, 308 (2011) T. Cap, K. Siwek-Wilczyńska, J. Wilczyński, PR C 83, 054602 (2011)

13 W. Świątecki, K. Siwek-Wilczyńska, J. Wilczyński Phys. Rev. C 71 (2005) 014602, Acta Phys. Pol. B34(2003) 2049 3 parameters: B 0, w, R  obtained from  2 fit to 48 experimental near- barrier fusion excitation functions for 40 < Z CN < 98 (K. Siwek-Wilczyńska, J. Wilczyński Phys. Rev. C 69 (2004) 024611) l max – calculated from the capture cross section. semiempirical formula Gaussian error function This formula derived assuming: Gaussian shape of the fusion barrier distribution Classical expression for σ fus (E,B)=πR 2 (1-B/E) FBD

14 λ= (d 1 + d 2 )/(R 1 + R 2 ) - neck parameter ρ = r/(R 1 + R 2 ) – relative distance Δ = (R 1 - R 2 )/(R 1 + R 2 ) – asymmetry parameter R1R1 R2R2 r d2d2 d1d1 P l (fusion) J. Błocki, W. J. Świątecki, Nuclear Deformation Energies, Report LBL 12811 (1982) CN Smoluchowski Diffusion equation for the parabolic potential P l (fusion) = ½(1-erf√H(l )/T) H - the barrier opposing fusion T - the temperature of the fusing system

15 Partial widths for neutron emission – Weisskopf formula where: The fission width (transition state method), E*< 40 MeV Upper limit of the final-state excitation energy after emission of a particle i Upper limit of the thermal excitation energy at the saddle  i – cross section for the production of the compound nucleus in the inverse process m i, s i, ε i - mass, spin and kinetic energy of the emitted particle ρ, ρ i – level densities of the parent and daughter nuclei P xn l (survive) for xn reaction

16 The level density is calculated using the Fermi-gas-model formula included as proposed by Ignatyuk (A.V. Ignatyuk et al., Sov. J. Nucl. Phys. 29 (1975) 255) Shell effects where: U - excitation energy, Ed - damping parameter – shell correction energy, δ shell (g.s.),δ shell (saddle) B s, B k ( W.D. Myers and W.J. Świątecki, Ann. Phys. 84 (1974) 186), (W. Reisdorf, Z. Phys. A. – Atoms and Nuclei 300 (1981) 227)

17 P <1n -probability that after emission of the first neutron the excitation energy is smaller than the threshold for second chance fission or 2n emission. threshold Neutron energy spectrum 1n reaction channel 2n reaction channel xn reaction channel  P<P< (1 - P < )

18 To calculate the survival probability we need to know (for all nuclei in the xn deexcitation cascade): ground state masses, fission barriers, shell correction energies and deformations (in the ground state and saddle). Those values were calculated using the Warsaw macroscopic- microscopic model including the nonaxial shapes. M. Kowal, Jachimowicz, A. Sobiczewski, Phys. Rev. C82 (2010) 014303 M. Kowal (unpublished) A. Sobiczewski (unpublished).

19 R1R1 R2R2 r d2d2 d1d1 s inj Systematics of the s inj parameter from the fit to the maximum values of the experimental cross sections for 2n, 3n, 4n and 5n channels in 48 Ca + X reactions (complete set of existing data)

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21 The systematics of the s inj used to predict cross sections for Z = 119 The reaction 48 Ca + 252 Es predicted to have measurable cross section

22 These values of the evaporation residue cross sections are much smaller (at least one order of magnitude) than previously published predictions. V.Zagrebaev and W. Greiner, Phys. Rev. C78 (2008) 034610 K. Siwek-Wilczynska, T. Cap, J. Wilczynsk i, IJMP E19 (2010) 500 Z = 120

23 The largest cross section for producing the element 120 is expected for the reaction Ti + Cf. Maximum value, of several femtobarns, is however below possibilities of present experiments. V.Zagrebaev and W. Greiner, Phys. Rev. C78 (2008) 034610 Z. H. Liu, Jing-Dong Bao, Phys. Rev C80 (2009) 054608 K. Siwek-Wilczynska, T. Cap, J. Wilczynski, IJMP E19 (2010) 500 A. Nasirov et al. IJMP E20 (2011) 406

24 SUMMARY A modified, l-dependent version of the Fusion by Diffusion model was applied to calculate synthesis cross sections of superheavy nuclei of Z =114 – 120 in hot fusion reactions. Fission barriers and ground state masses calculated with the Warsaw macroscopic-microscopic model (including nonaxial shapes) were applied. Good agreement with experimental cross sections was obtained. This allowed us to use the same theoretical input to predict cross sections for synthesis of elements Z = 119 and 120.

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28 M. Kowal, P. Jachimowicz, A. Sobiczewski, PRC 82,014303 (2010) P. Möller et al., PRC 79, 064304 (2009)


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