Technical solutions for NZ Physics

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Technical solutions for NZ Physics

• David Jenkins

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Outline of talk

• Physics
• ISOL Beam development
• Recoil separator
• Coulomb excitation
• Long-lived isomers
• New techniques

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Defining the Physics

• Oblate/prolate shape coexistence
• Proton-neutron pairing
• T0 vs T1 states
• Alignment differences in isobaric multiplets in
  fp shell
• Isospin mixing e.g. E1 transition matrix
  elements, B(E2) in isobaric multiplets
• Most Physics is near the ground state not high
  spin!

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Region of interest
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RIB issues

• Can be produced in thick target approach -
  replacing UCx
• Light Kr easily produced and re-accelerated. Need
  104 pps for Coulomb excitation of e.g. 72Kr.
  Continuation of work of Saclay group
• Electronegative elements impossible? - e.g. Br,
  Se
• Zr and heavier (Nb, Mo) do not come out easily in
  ISOL technique - refractory elements
• Ti-Co has similar problems

ISOLDE target yield information
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Molecular beam techniquesCoulomb Excitation of
70Se
Se is very electronegative element Positive ions
needed for reacceleration Se extracted as SeCO
molecule and broken up in EBIS to form Se ion
555 keV 104Pd 2
945 keV 70Se 2
70Se on 104Pd target 104 pps June 2005 -
REX-ISOLDE
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RIB composition

• Issue of isobaric contamination
• Kill it at source or live with it?
• Techniques for selection
• Ion chamber
• Bragg spectrometer

Preliminary design of Bragg spectrometer for
REX-ISOLDE
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Case for a separator
Issues Residues too slow Problem with Z
separation in a transmission ion chamber e.g.
40Ca(40Ca,2n)78Zr Residues too fast FMA-type
separator has insufficient rigidity to bend
residues from very inverse reactions e.g. 40Ca12C
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Solutions

• Build a more rigid separator
• Needs higher electric fields - physically larger
  plates
• Problems with conditioning
• Reaccelerate residues to 2 MeV/u for good Z
  separation
• Wide range in residue energy
• Beam needs focussing/rebunching

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Transmission ion chamber

• 12C(40Ca,3n)49Fe test with FMA at Argonne
• 230 MeV beam energy
• Residue energy too high for FMA so degrader foils
  were used - not satisfactory introduces
  scattering and energy spreading
• Can clean up by gating on Et2 (dimensions of mass)

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Reacceleration - pipe dream?
1 MeV/u
2 MeV/u
Recoil separator
RF cavity
Wien Filter
Ion Chamber
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Separator Physics

• In-beam spectroscopy
• Reactions with unstable beams
• Start closer to dripline - fewer residues and
  exotica more abundant
• Lower gamma counting rates from reactions - but
  rate from potentially gamma emitting beam
• Reactions with stable beams
• High beam currents - rotating targets
• High counting rates in target ge array
• Exotic channels needle-in-haystack
• Coulomb excitation at the focal plane

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Reactions with RIBS

• 34Ar 40Ca (105-120 MeV)
• 69Br ?p 1 mb
• 71Kr 2pn 5 mb
• 68Br ?pn 0.2 mb
• 72Rb pn 0.1 mb
• How do we study the proton unbound cases e.g.
  69Br?
• 58Cu 28Si (200 MeV)
• 81Nb ?n 0.1 mb
• 56Ni 28Si (200MeV)
• 79Zr ?n 0.2 mb

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Stable beam reactions

• Examples
• Classic
• 58Ni24Mg - 80Zr 2n
• Would benefit from more rigid separator
• Could improve in-beam spectroscopy or produce
  intense beam for focal plane Coulomb excitation
• How fast can ge array run?
• New
• 40Ca40Ca - 78Zr 2n
• 36Ar40Ca - 74Sr 2n
• These would need reacceleration to work well with
  the ion chamber
• Calcium is poor target -oxidation

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Coulomb excitation at focal plane

• Jasmin Schwartz thesis work on 78Rb at the back
  of the FMA
• Beam energy low (2 MeV/u) but currents in
  principle enough e.g. 104 pps
• Ideas
• Coulex of 80Zr - very deformed nucleus
• Coulex of 68Se and 72Kr - deduce B(E2) and sign
  of quadrupole moment. Locate unknown non-yrast 2
  states

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Coulex of isobaric chains

• Determine extent of isospin mixing into B(E2)
  rates - most pronounced for odd-odd NZ nucleus
• Perform Coulomb excitation of isobaric chains
  e.g.
• 30S,30P,30Si - not easy from ISOL
• 46Ti,46V, 46Cr - ditto
• Need high stats (1-2 effects) - but systematic
  errors constrained through simultaneous
  measurements of B(E2)s

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Long-lived isomers in odd-odd NZ nuclei
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Total absorption measurements

• 70Br produced in 36Ar(40Ca,apn) at 145 MeV
• Recoils into gaseous discharge ion source
• Produced 55 keV beam of 70Br suitable for TAS
  measurement - Karny et al, Phys. Rev. C 70,
  014310 (2004)
• Showed that 9 isomer is at 2293 keV in 70Br
• Where is 5.6 s (5) isomer in 78Y?
• High current 40Ca40Ca??

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New technique IRecoil beta tagging

• Test experiment at JYFL 40Ca(36Ar,pn)74Rb _at_ 95
  MeV
• Implant residues in focal plane
• Thick DSSD and planar germanium serve as DE-E
  combination to discriminate high energy betas
  e.g. from Fermi superallowed decays
• Would benefit from mass separation
• How competitive is this with charged
  particle/neutron detection?

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New technique IIBeta-delayed proton tagging

• Route to study Tz-3/2 nuclei e.g. 69Kr, 65Se,
  57Zn
• Cleaner tag than betas - use characteristic
  proton energy
• Programme initiated by Dave Joss, Liverpool

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New technique 3 Radiative capture

• 90Zr(90Zr,0n)180Hg studied by Kondev et al.,
  Phys. Rev. C 62, 044305 (2000)
• 0n cross-section is 30 ?b due to cold-fusion
  reaction
• Potential for 40Ca40Ca??

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Conversion electrons

• Well-known E0 0 -0 in 72Kr
• Shape coexistence suggests missing 0 states in
  68Se,70Se, 70Br
• Locating such states would constrain shape mixing
  etc.
• Electron detection is important (in conjunction
  with gamma detection)