Technical solutions for N=Z Physics David Jenkins

Outline of talk  Physics  ISOL Beam development  Recoil separator  Coulomb excitation  Long-lived isomers  New techniques  Physics  ISOL Beam development  Recoil separator  Coulomb excitation  Long-lived isomers  New techniques

Defining the Physics  Oblate/prolate shape coexistence  Proton-neutron pairing  T=0 vs T=1 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!  Oblate/prolate shape coexistence  Proton-neutron pairing  T=0 vs T=1 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!

Region of interest

RIB issues  Can be produced in thick target approach - replacing UC x  Light Kr easily produced and re-accelerated. Need 10 4 pps for Coulomb excitation of e.g. 72 Kr. 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

Molecular beam techniques Coulomb Excitation of 70 Se 945 keV 70 Se keV 104 Pd Se on 104 Pd target 10 4 pps June REX-ISOLDE Se is very electronegative element Positive ions needed for reacceleration Se extracted as SeCO + molecule and broken up in EBIS to form Se + ion

RIB composition  Issue of isobaric contamination  Kill it at source or live with it?  Techniques for selection:  Ion chamber  Bragg spectrometer  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

Case for a separator Issues: Residues too slow: Problem with Z separation in a transmission ion chamber e.g. 40 Ca( 40 Ca,2n) 78 Zr Residues too fast: FMA-type separator has insufficient rigidity to bend residues from very inverse reactions e.g. 40 Ca+ 12 C

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  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

Transmission ion chamber  12 C( 40 Ca,3n) 49 Fe 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 Et 2 (dimensions of mass)  12 C( 40 Ca,3n) 49 Fe 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 Et 2 (dimensions of mass)

Reacceleration - pipe dream? Recoil separator RF cavityWien FilterIon Chamber Secondary target 1 MeV/u2 MeV/u

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  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

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

Stable beam reactions  Examples:  Classic:  58 Ni+ 24 Mg -> 80 Zr + 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:  40 Ca+ 40 Ca -> 78 Zr + 2n  36 Ar+ 40 Ca -> 74 Sr + 2n  These would need reacceleration to work well with the ion chamber  Calcium is poor target -oxidation  Examples:  Classic:  58 Ni+ 24 Mg -> 80 Zr + 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:  40 Ca+ 40 Ca -> 78 Zr + 2n  36 Ar+ 40 Ca -> 74 Sr + 2n  These would need reacceleration to work well with the ion chamber  Calcium is poor target -oxidation

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

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

Long-lived isomers in odd-odd N=Z nuclei

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

New technique I: Recoil beta tagging  Test experiment at JYFL: 40 Ca( 36 Ar,pn) 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?  Test experiment at JYFL: 40 Ca( 36 Ar,pn) 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?

New technique II: Beta-delayed proton tagging  Route to study T z =-3/2 nuclei e.g. 69 Kr, 65 Se, 57 Zn  Cleaner tag than betas - use characteristic proton energy  Programme initiated by Dave Joss, Liverpool  Route to study T z =-3/2 nuclei e.g. 69 Kr, 65 Se, 57 Zn  Cleaner tag than betas - use characteristic proton energy  Programme initiated by Dave Joss, Liverpool

New technique 3: Radiative capture  90 Zr( 90 Zr,0n) 180 Hg studied by Kondev et al., Phys. Rev. C 62, (2000)  0n cross-section is 30  b due to cold- fusion reaction  Potential for 40Ca+40Ca??  90 Zr( 90 Zr,0n) 180 Hg studied by Kondev et al., Phys. Rev. C 62, (2000)  0n cross-section is 30  b due to cold- fusion reaction  Potential for 40Ca+40Ca??

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