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Octupole excitations at high spins in A~160 nuclei

Octupole excitations at high spins in A~160 nuclei. J. Kvasil,R. G. Nazmitdinov, A. S. Sitdikov, P. Vesel ý. High spin physics. Fast rotating nuclei. The most interesting phenomena:.

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Octupole excitations at high spins in A~160 nuclei

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  1. Octupole excitations at high spins in A~160 nuclei J. Kvasil,R. G. Nazmitdinov, A. S. Sitdikov, P. Veselý

  2. High spin physics

  3. Fast rotating nuclei The most interesting phenomena: • Dependence of moment of inertia (the kinematical and the dynamical) on the rotational frequency W – backbending • Shape evolution with increasing W – e.g.phase transition from axial def. to triaxiality • Parity breaking octupole bands – the field of our interest !!

  4. Theoretical approaches to fast rotation • Semiphenomenological: cranking Nilsson + monopole pairing + multipole-multipole and spin-multipole spin-multipole residual interaction e.g. T.Nakatsukasa, K.Matuyanagi, S.Mizutori, Y.R.Shimizu, Phys. Rev. C53, 2213 (1996) (no self-consistency of deformation and res. int.) or J.Kvasil, R.G.Nazmitdinov, Phys. Rev. C73, 014312 (2006) (elements of selfconsistency of def. and res. int.) RPA + response function method :

  5. Octupole correlations • Past two decades: a lot of experimental data on low-lying states of negative parity for Ra-Th (Z~88,N~134) and Ba-Sm (Z~56,N~88) large octupole correlations in the lowest states near Fermi level (in some nuclei like Th possible octupole deformation of the mean field in the ground state) • Essential features of the presence of the nonzero octupole def. on the yrast (ground) states can be described with reflection symmetric mean field with octupole correl. involved in the res. int. • Our contribution: Nilsson+quasipart.RPA Yb, Hf calc. - observed merging of negative parity bands with the positive parity yrast band for Yb, Hf (octupole deformation on the yrast) 162 164,166

  6. Used theoretical approach Cranked Nilsson field Residual interaction (with pairing) in the separable multipole-multipole form RPA phonons + RPA equation :

  7. Extracting of the routhians & other nuc. characteristics from the experimental data Experimental data In the high spin region of the R-symmetric nucl. is characterized by the parity and signature – different notations a=0 for r=+1 a=1 for r=-1 Experimental data ( Yb, Hf) from Brookhaven data archive www.nndc.bnl.gov/nudat2/

  8. Results Equillibrium deformations in b-g plane as a function of the angular momentum I~<I1> (equillibrium points correspond to <Q’’2m>=0)

  9. Results SCNM – calculated as , RPA – calculated as mass parameter of the spurious mode connected with I1 See J.Kvasil, S.Cwiok, N.Choriev, Zeit.f.Phys. A303, 313 (1981)

  10. Results

  11. Results

  12. Results Reduced transition probabilities B(M1), B(E2), B(E1),B(E3) of the transitions going from the lowest one-phonon band to the yrast band. Left panels – transitions without sign. change Right panels – trans. with sign. change

  13. Conclusion • Strong increase of the octupole correlations for hW>0.4 MeV • The backbending phenomenon described • Good description of the lowest Routhians

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