Nuclear moment measurements in projectilefragmentation reactions complementarity to the ISOL techniq

1
Nuclear moment measurements in projectile-fragmen
tation reactions complementarity to the ISOL
techniques

• G. Georgiev
• for the E384 collaboration

2
N 40 far from beta-stability

• NO effect in the d2n (H.Seifert et al., ZPA
  349(94) 25) ? explained by quadrupole shape
  correlations (P.G. Reinhard et al., RIKEN Review
  26 (2000) 23)

• B(E2) in 68Ni ? shell closure washed-out by
  pair scattering (O. Sorlin et al., PRL 88(01)
  92501)
• main strength above 4 MeV
• (K.H. Langanke et al. PRC 67 (03) 44314)

? collectivity in the Zn (S. Leenhardt et al.,
EPJ A14 (02) 1) and Fe isotopes (M. Hannawald et
al., PRL 82(99) 1391)
3
ng9/2 in 61Fe
a g-factor measurement can fix the spin/parity
assignment and shed lighton the single-particle
properties of the isomeric state
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Production of neutron-rich isomeric states
Intermediate energy projectile-fragmentation

• neutron-rich nuclear states in very pure
  conditions

• very short separation time ( 200 ns)

• chemical independence

• spin-oriented ensemble of nuclear states!

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Experimental method
Time Dependent Perturbed Angular Distributions
(TDPAD)
orientation
perturbation
measure the anisotropy

• well established method for fusion-evaporation
  reactions
• alignment of isomeric states in high-energy (500
  MeV/u) projectile - fragmentation was observed
  for the first time by Schmidt-Ott et al. (ZP A350
  (94) 215) for the case of 43mSc

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Experimental setup

• 55 MeV/u 64Ni bean on 9Be target ? 61mFe and
  54mFe

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Experimental results
gexp. (61mFe) - 0.229(5)
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Comparison with theoretical calculations
Large-basis SM calculations using 48Ca core and
allowing up to 4 p-h excitations? good agreement
with the exp. value
? the quadrupole moment (and its sign!) of 61mFe
has to be measured
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Conclusions and perspectives

• the gyromagnetic factor of the isomeric state in
  61Fe has been measured. This clearly fixes the
  neutron g9/2 character of the isomeric state
• TDPAD after projectile-fragmentation reactions
  is a working technique to study isomeric states
  in the time range between 200 ns up to more
  than 10 ms as well as the nuclear orientation
  obtained in the reaction
• one has to measure the quadrupole moment 61mFe
  in order to shed more light on its deformation

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The E384 collaboration
GANIL, Caen, France - I. Matea, F. de Oliveira
Santos, M. Lewitowicz The Weizmann Institute,
Israel - M. Hass, L.T. Baby, G. Goldring The CE
Bruyères le Châtel, France - J.M. Daugas, G.
Belier, M. Girod, H. Goutte, V. Meot, O.
Roig IKS, Leuven, Belgium - D. Borremans,P.
Himpe, G. Neyens Univ. Sofia/Univ. Camerino -
D.L. Balabanski FLNR-JINR, Dubna, Russia - R.
Astabatyan, S. Lukyanov, Yu.E.
Penionzhkevich Warsaw University, Poland - M.
Sawicka
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Alignment
Assuming pure M2(654 keV) and M1(207 keV)
transitions we get the radiation
parametersA2(654) - 0.433A2(207) 0.374

• From GEANT simulations of the realistic setup
• Amp.(654/207)GEANT 1.30(6) vs.
  Amp.(654/207)exp 1.3(1) - consistent with pure
  character of the transitions
• geometrical factor (decrease if the measured
  amplitude due to the finite size of source/det.)
  is 0.81(3)