Structural Evolution in the (N,Z,I  ) Coordinate Frame for A~100 Paddy Regan* Dept. of Physics University of Surrey,UK * partially supported by WNSL-Yale Flint and Science Development Fund

Sr-Mo region ‘famous’ for dramatic collapse in I  =2 + energy going from N=58 to N=60

Explanation by Federman & Pittel in terms of quadrupole deformation ‘driving’ T=0 (pn) interaction. Particularly noticeable for protons and neutron orbitals with large spatial overlaps (e.g., Spin Orbit Partners such as  g 9/2 and  g 7/2 in A~100)

Other aspects ? Correlation between deformation & population of ‘deformation aligned’, low-  h 11/2 neutron intruder orbitals. Classic ‘chicken and egg’. Does population of orbital ‘cause’ deformation or is deformation there from the core and thus h 11/2 orbital lies closer to the Fermi Surface ? How does this situation evolve with spin ?

Alignment (rotational picture at least) driven by Coriolis interaction on high-j, low-  orbitals (ie. ones with large j x on collective rotation axis. V cor = -j x.  eg. h 11/2 [550]1/2 ‘intruder’ FS for N~57,  2 ~0.15->0.2 jxjx [550]1/2 - 1h 11/2 1g 9/2 [541]3/2 -

= 101 Mo, new data, see later

Alignments and rotational motion in ‘vibrational’ 106 Cd (Z=48, N=58), PHR et al. Nucl. Phys. A586 (1995) p351

Detailed spectroscopy allowed by investigating gamma-decay sequences from high-spin states. YRASTBALL allows triples to show band-like structures in 101 Ru. see A.D.Yamamoto et al., Phys. Rev. C66 (2002)

TRS calculations for 101 Ru by F.R. Xu (Bejing) for different parity (and signature) configs. 22   =0.2MeV  =0.4MeV  =0.3MeV  =0.6MeV A.D.Yamamoto et al. Phys. Rev. C66 (2002)

Crossing and alignments well reproduced by CSM, although AHVs see PHR et al., Phys. Rev. C68 (2003)

PHR, Beausang, Zamfir, Casten, Zhang et al., Phys. Rev. Lett. 90 (2003)

Vibrator-Rotator phase change is a feature of near stable (green) A~100. ‘Rotational alignment’ can be a crossing between quasi- vibrational GSB & deformed rotational sequence. (stiffening of potential by population of high-j, equatorial (h 11/2 ) orbitals). PHR, Beausang, Zamfir, Casten, Zhang et al., Phys. Rev. Lett. 90 (2003)

Simon et al., Nucl. Inst. Meth. A452, 205 (2000) BLF TLF beam  tlf  tlf  blf  blf Ge TOF ~5-10 ns. ns-  s isomers can de-excite in be stopped by CHICO position detector. Delayed  s can still be viewed by GAMMASPHERE. Rochester Group

z x y    

Use ‘isomer gating’ to identify h 11/2 band in N=59, 101 Mo. {180}{429,616,772,891} total, DIC prompts delayed delayed coincs with prompt 429, 616, 772 & 891 keV

See PHR, Yamamoto, Beausang, Zamfir, Casten, Zhang et al., AIP Conf. Proc. 656 (2002) p422 ‘Weak Coupling’ E  /(I-j) E-GOS extension for odd-A Suggests 11/2 - band is an anharmonic vibrator or  -soft rotor? seems to work ok for +ve parity bands though

Wheldon suggested extension of E-GOS by ‘renormalising’ the rotational energies at the bandhead. If the band-head spin of a sequence is given by j then substituting I  j in place of I, one obtains,

 seems to work ok, h 11/2 bands now look like rotors, Even-Even yrast sequences and odd-A +ve parity only show rotational behaviour after ( h 11/2 ) 2 crossing….

Even simpler to just take E  (I->!-2) / I for odd-A e.g., R = [ E  (15/2 - ->11/2 - ) / (11/2) ]

Other signatures of (perfect) vibrators and rotors State lifetimes, i.e., B(E2) values and selection rules (eg.  n=1).

Need to measure lifetimes B(E2) values of yrast stretched E2 decays in N=58 isotones (best cases) + h 11/2 bands in N=57 isotones. RDM measurements in 103,4 Pd, 105,6 Cd due Aug at Yale to ‘prove’ vibrator-to-rotor picture. ( Frauendorf’s ‘tidal wave’ picture is similar).

From Dudek et al., Phys. Rev. Lett. 59 (1987) p1405 Single particle spectra (for minimised LDM energy at spin 60 hbar) shows distinct gaps for  2 ~0.4 at Z=42, N=58 ( 100 Mo). Note these are the homologs of A~80 SD (N=42) and A~130 SD (Z=58)

SD (  2 =0.4) minimum predicted in 100 Mo to become yrast around spins h. ‘Doubly-Magic’ SD shell gaps at (Z=42, N=58) = 100 Mo. J. Skalski et al.,Nucl. Phys. A617 (1997) p282 DIC Pb + Mo proposal to Be submitted to upcoming GAMMASPHERE PAC (deadline 26 th April!)

P.H. Regan 1,2, C. Wheldon 1,3, A.D. Yamamoto 1,2, S. Ashley 1, P. Mumby-Croft 1, D. Seaborne 1, C.Y. Wu 4, A.O. Macchiavelli 5, D. Cline 4, J.F. Smith 6, R.S. Chakrawarthy 6, M. Cromaz 5, P. Fallon 5, S.J. Freeman 6, W. Gelletly 1, A. Görgen 5, A. Hayes 4, H. Hua 4, S.D. Langdown 1,2, I.Y. Lee 5, C.J. Pearson 1, Zs. Podolyák 1, R. Teng 4, J.J. Valiente-Dobón 1, 1 University of Surrey, UK 2 Wright Nuclear Structure Laboratory, Yale University, USA 3 HMI, Berlin, Germany 4 Nuclear Structure Research Laboratory, University of Rochester, USA 5 Nuclear Science Division, Lawrence Berkeley National Laboratory, USA 6 Department of Physics and Astronomy,The University of Manchester, UK E-GOS story, PHR, Con Beausang, Victor Zamfir, Rick Casten, Jing-Ye Zhang Money from…EPSRC (UK), DOE (USA), NSF (USA), Yale Flint-Science Development Funds Acknowledgments

International Conference On NUclear STructure, Astrophysics & Reactions University of Surrey, Guildford, UK 5-8 January