Production of Exotic Nuclear Isomers in Fragmentation and Deep-Inelastic Reactions

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Production of Exotic Nuclear Isomers in
Fragmentation and Deep-Inelastic Reactions

• Paddy Regan
• Dept. of Physics, University of Surrey,
• Guildford, GU2 7XH, UK
• e-mail p.regan_at_surrey.ac.uk

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• Outline of Talk
• Where do you find (long-lived) isomers ?
• Restrictions ?
• Isomer predictions.
• Towards the neutron rich.
• Deep-inelastic reactions and results
• Projectile Fragmentation, effects of atomic
  stripping

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What is an isomer ? Metastable (long-lived)
nuclear excited state. Long-lived could mean
10-19 seconds, shape isomers in alpha-clusters
or 1015 years 180Ta 9--gt1 decay. Why/when do
you get isomers? If there is (i) large change in
spin (spin-trap) (ii) small
energy change (iii) dramatic
change in structure (shape, K-value) What do
isomers tell you ? Isomers occur due to single
particle structure.

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From Walker and Dracoulis, Nature 399, p35 (1999)
Ex gt 1 MeV, T1/2 gt 1 ms (red), T1/2 gt 1 hour
(black)
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Bohr and Mottelson, Phys. Rev. 90, 717 (1953)
NB. wrong spin for isomer !!! Ipgt11 shown
later to be Kp8-, Korner et al. Phys. Rev.
Letts. 27 , 1593 (1971) K-value and detailed
spectroscopy very imporant in understanding
isomers.
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Search for long (gt100ms) K-isomers in
neutron-rich(ish) A180 nuclei.
Walker and Dracoulis Hyp. Int. 135 83 (2001)
(Stable beam) fusion limit makes high-K in
neutron rich hard to synthesise
Alaga, Alder, Bohr and Mottelson, Mat. Fys.
Medd. 29 no 9 (1955)
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Forbiddenness in K isomers
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Classic 31 yr 16 isomer in 178Hf , spin-trap
K-forbidden (NB. Idaho invention!)
Smith,Walker et al., in press Phys. Rev. C
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Smith, Walker et al., in press Phys. Rev. C
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170Dy, double mid-shell, best case yet for
pure K-isomer ? (see PHR, Oi et al. Phys.
Rev. C65 (2002) 037302)
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Ways to make 178Hf 31 yr isomer ?

• Neutron capture
• 176Yb(a,2n)178Hf
• 176Yb(9Be,a3n)178Hf (see Dracoulis talk)
• Coulomb excitation (Hayes et al., PRL (2002))
• Deep-inelastic heavy-ion binary reactions
• Projectile Fragmentation

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Astrophysical Consequences of Isomers
180Ta is stable in its isomeric state, but its
ground state decays in hours! Longstanding
problem as to how the isomeric state is created
in nature (via eg. S-process). Possible mechanism
via heavier nuclei spallation or K-mixing of
higher states in 180Ta.
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(from Wiescher, Regan and Aprahamian Physics
World, Feb 2002).
K9- isomer might be de-excited to 1 ground
state through intermediate path with states of
Kp5 (see Walker, Dracoulis and Carroll Phys.
Rev. C64 061302(R) (2001))
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Towards the Neutron-Rich ?
Fusion-evap. great for high-spins, BUT.stable
beams/targets create predominantly
neutron-deficient nuclei.
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Projectile Fragmentation Reactions
Energy (velocity) of beam gt Fermi velocity inside
nucleus 30 MeV/u Can shear off different
combinations of protons and neutrons. Large
variety of exotic nuclear species created, all at
forward angles with beam velocity. Some of
these final fragments can get trapped in isomeric
states.
Problem 1 Isotopic identification. Problem 2
Isomeric identification.
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In-Flight Technique Using Projectile Fragmentation
Production target
Central focus, S2
Final focus, S4
primary beam Pb _at_ 1GeV/u
dipole, Br
degrader
degrader
MWx,y
scint
catcher
scint
DE(Z2)
scint (veto)
Use FRS_at_GSI or LISE3_at_GANIL to ID nuclei.
Transport some in isomeric states (TOF
x00ns). Stop and correlate isomeric decays with
nuclei id.
eg. R. Grzywacz et al. Phys. Rev. C55 (1997)
p1126 -gt LISE C.Chandler et al. Phys. Rev.
C61 (2000) 044309 -gt LISE M. Pfutzner et
al. Phys. Lett. B444 (1998) p32 -gt FRS Zs.
Podolyak et al. Phys. Lett. B491 (2000) p225 -gt
FRS M. Pfutzner et al. Phys Rev. C65
(2002) 064604 -gt FRS
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undressing (to fiddle the decay probability)
Fully stripping the nucleus of its atomic
electrons (in-flight) switches off the
electron conversion decay branches. Result is
that the bare nuclear isomeric lifetime is
increased compared to atomic value. (important
in explosive stellar scenarios).
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from Bouchez et al., Phys. Rev. Lett. 90 082502
(2003)
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208Pb beam at 1 GeV/u allows production of
(a) neutron-rich heavy (Agt160) and (b)
high-spin isomers, Schlegel et al.Physica
Scripta T88 (2000) p72
High spins (gt35/2) populated
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Gamma-gamma analysis on 200Pt isomer (21 ns!), M.
Caamano et al. Nucl. Phys. A682 (2001) p223c
Acta Phys. Pol. B32 (2001) p763 stripping effect
again (a la 74Kr).
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M. Pfutzner, PHR et al. Phys Rev. C65, 064604
(2002)
Higher spins for greater DA.
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Can not use fusion-evaporation reactions to study
high-spin states in beta-stable and neutron-rich
systems. Use deep-inelastic reactions.
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z
x
q1
q2
f1
f2
y
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Simon et al., Nucl. Inst. Meth. A452, 205 (2000)
Rochester Group
TOF 5-10 ns. ns-ms isomers can de-excite in
be stopped by CHICO position detector.
Delayed gs can still be viewed by GAMMASPHERE.
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198Pt 136Xe _at_ 850 MeV, Dobon, Wheldon, PHR et
al.,
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First id of doubly mid-shell nucleus, 170Dy
(N104, Z66). K6 isomers predicted for well
deformed N104 nuclei. TRS calcs (F.Xu) predict
a very stiff, highly deformed prolate nucleus.
Could be the best K-isomer?
Data from M.Caamano et al.
33 ns isomer in 195Os (last stable 192Os), useful
test of structure in prolate/oblate shape
coexistence region. 194Os Wheldon et al. Phys.
Rev. C63 (2001) 011304(R)
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Target-like fragment isomers from 136Xe198Pt
DIC, Valiente-Dobon et al., (Surrey/Rochester/Berk
eley/Manchester/bPaisley/Daresbury collaboration)
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Target-like fragment isomers from 136Xe198Pt
DIC, Valiente-Dobon et al., (Surrey/Rochester/Ber
keley/Manchester/bPaisley/Daresbury collaboration)
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• Isomers in Nature, nuclear astrophysics aspects
• 26Al in r-p processed path, inversion of states
• 180Ta, natures only stable isomer (nuclear
  battery ?)
• 176Lu, cosmic chronometer and thermometer
• r-process path and structure of odd-odd nuclei
• Production and identification of isomers ?
• Fusion-evap, projectile frag. Deep-inelastics,
  spallation, neutron capture
• electronic timing, proj. frag.
• Mass separation for long-lived isomers
• Cheating with isomer half-lives.undressing!
• 74Kr (GANIL) bare, 201,200Pt (GSI) H-like

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• Summary of some special, exotic cases!
• 178Hf K-isomer with many branches.e.g., E5
  decays.
• 176Lu, cosmothermoter for two phases in
  s-process.
• 26Al decay seen from space as example of
  nucleosynthesis, rp-process by-pass.
• Nuclear batteries/gamma-ray lasers, can we
  de-excite the isomers ? (180Ta paper by PMW, GDD,
  JJC 178Hf 31 yrs state?).
• Lengthing the half-lifestripping of 74Kr, 201Pt
  etc.

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Thanks!

• Bertram Blank (Bordeaux) et al., GANIL
• Zsolt Podolyak (Surrey) et al. GSI
• Carl Wheldon (Surrey/GSI) Berkeley expts.
• Surrey PhD students, Katie Chandler, Jose Javier
  Valiente-Dobon, Monica Camaano, Arata Yamamoto,
  Sareh Al-Garni for hours and hours of analysis
  etc.
• Physics comments/help from Phil Walker, Bill
  Gelletly (Surrey), Dave Warner (Daresbury) many
  others!
• Money from EPSRC (UK)

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100Mo 136Xe _at_ 750 MeV
GAMMASPHERE CHICO, PHR et al. Submitted to
Phys. Rev. C. (Surrey, Rochester, Berkeley,
Manchester)
BLFs
TLFs
elastics
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Kinematics and angular mom. input calcs (assumes
rolling mode) for 136Xe beam on 100Mo
target. Estimate 25hbar in TLF for 25 above
Coul. barrier. For Eb(136Xe)750 MeV, in lab
qblf30o and qtlf50o.
100Mo 136Xe (beam) DIC calcs.
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Identification of new isomeric state in 136Ba,
N80 isotone.
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N80 isotonic chain, 10 isomers (nh11/2)-2I10
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Structure of 8 final state changes from 134Xe -gt
136Ba ?
Isomer decay also depends on structure of final
state
N80, (nh11/2)-210 isomers
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M. Mineva et al. Eur. Phys. J. A11 (2001) p9-13
Use FRS to select projectile fission products
(forward boosted ones). Note transmission a few
. T1/2565(50) ns state in 136Sb (Z51, N85)
135Te
136Sb
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Online-Mass Separation Technique
Select by mass
Select by decay times
Surrey/GSI/Liverpool, 136XeTanat
Lifetimes from grow-in curve
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S. Al Garni, PhD thesis, Surrey (2002)
Surrey/GSI/Liv./Goettingen/Milano
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Use grow-in curve technique RAo(1-exp(t/t))
Gate on electron (b or ec) at implantation point
of tape drive, gives clean trigger. Use
add-back
Select cycle length for specific t, add together
multiple tape cycles.
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Basic Technical Requirements for Studies with
Isomers

• Beam pulsing, good t0 reference for short (ns)
  lifetimes.
• In-flight separator (eg. FMA, LISE, FRS...) for
  microsecond-ms decays.
• Tape drive/helium jet system for 10ms-gthours
  lifetimes
• Traps, cyclotrons etc. for longer lived species

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e.g., Diehl et al., Atron. Astrophys 97, 181
(1993) Publications of the Astr. Society of
the Pacific 110637 (1999)
Full-sky Comptel map of 1.8 MeV gammas in 26Mg
following 26Al GS b-decay.
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26Al isomer and the rp-process
Tlt4x108K not in equilibrium, must be modelled as
separate isotopes in rp-process path. Jose et
al., Astr. J. 520, 347(1999)
rp-process can bypass 26Al ground state,
decays via isomer
Yield of 1.8 MeV gs from 26Algs decay (e.g.,
relative to 22Na decay) gives insight into T and
r where rp-process forming 26Al occurs.
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How do you produce and measure (high-energy)
isomers ?

• Produce via nuclear reaction e.g.,
  fusion-evaporation, deep-inelastic, projectile
  fragmentation..
• Isomeric targets ? (see A.Tonchev NIM paper).
• Isomeric beams
• Measure, depending on lifetime using
• ns Use in-beam electronic techniques (eg.
  start-stop)
• ns -gt ms In-flight technique, projectile
  fragmentation.
• 100 ms -gt hours On-line mass-separator (eg. GSI
  set-up).
• gt hours Measure mass differences from ground
  state using e.g. ion traps, coupled cyclotrons
  etc.

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In-beam, electronic technique (g-g-t)
eg, PHR, G.D. Dracoulis et al. Nucl. Phys. A586
(1995) p351
Fusion-evaporation reaction with pulsed beam
(1ns), separated by fixed period (500ns). Using
coincidence gamma-rays to see across isomer
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Proton drip line isomer physics from 208Pb
fragmentation. N74 chain of Kp8- isomers. Next
in chain would be 140Dy, proton decay daughter
of (deformed) 141Tb. (See Filip Kondevs talk)
136Sm, 138Gd Isomers orginally seen in
fusion-evap (ANU data) A.M.Bruce et al.
Phys. Rev. C50 (1994) p480 and C55 (1997) p620
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Heaviest odd-odd,NZ gammas, isobaric analog
states ? NZ43 86Tc, C. Chandler et al. Phys.
Rev. C61 (2000) 044309
500 86Tc in 1 week
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8 isomer in 78Zn, real evidence of 78Ni shell
closure. J.M.Daugas et al. Phys. Lett. B476
(2000) p213
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Isomeric Ratio Calculations
M. Pfutzner et al. Phys Rev. C65, 064604 (2002)
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M. de Jong et al. Nucl. Phys. A613 (1997) p435
M. Pfutzner et al. Phys Rev. C65, 064604 (2002)
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Bock et al., Nukleonika 22 (1977) 529