Kisomers in the astrophysical sprocess: 176Lu, 180Ta, 186Re - PowerPoint PPT Presentation

Title: Kisomers in the astrophysical sprocess: 176Lu, 180Ta, 186Re


1
K-isomers in the astrophysical s-process 176Lu,
180Ta, 186Re

• Peter MohrDiakonie-Klinikum Schwäbisch
  HallD-74523 Schwäbisch Hall, Germany

ECT Trento - June 15, 2009
RaBoe/Wikipedia
2
K-isomers in odd-odd nuclei on the s-process
path 176Lu, 180Ta, 186Re

• Properties of isomers K quantum number and
  selection rules thermal coupling between low-K
  and high-K states
• Reaction rates in a stellar thermal photon bath
  example 16O(a,g)20Ne, 20Ne(g,a)16O
• Nucleosynthesis of 180Ta s-process, r-process,
  p(g)-process, n-process ?
• Nucleosynthesis of 176Lu thermometer for the
  s-process
• Branching points in the s-process 186Re and
  the Re/Os chronometer

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K-isomers in odd-odd nuclei on the s-process
path 176Lu, 180Ta, 186Re
Properties of isomers
K quantum number- projection on symmetry
axis- approximately conserved

• Selection rules allowed DK multipolarity
  El, Ml
• Suppression factorFW t(exp) / t(W.u.)
• FW 100 per K-suppression
• Ex. (180Ta) E2, Ki 9, Kf 1DK 8 ?
  K-suppression 6 FW 1012 DE 100 keV ? t
  106 s!
• Similar for b-decay

coupling j1(p) ? j2(n)
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K-isomers in odd-odd nuclei on the s-process
path 176Lu, 180Ta, 186Re
16O(a,g)20Ne and 20Ne(g,a)16O ER 1058 keV, Jp
1-

• Breit-Wigner resonances w Ga Gg / (E-ER)2
  G2/4
• Partial widthsG GaGg Gg Gg0Gg1
• Branching ratiosb0 Gg0/Gg 18 b1 82
• Resonance strength (wg) w GaGg/G
• Stellar (a,g) reaction rateltsvgt (wg)
  exp(-ER/kT)

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K-isomers in odd-odd nuclei on the s-process
path 176Lu, 180Ta, 186Re
16O(a,g)20Ne and 20Ne(g,a)16O ER 1058 keV, Jp
1-

• (g,a) in the lab (kT 0)20Ne in 0 ground
  state!
• from time reversal ? s(Eg) s(Eg) GaGg0 /
  (Eg-Eg0)2 G2/4
• Reaction rate llab for (g,a) in the lab from
  folding with black body radiationng(Eg,T) Eg2
  exp(-Eg/kT)
• (g,a)-reaction rate in the labllab b0 (wg)
  exp-(ERQ)/kT)

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K-isomers in odd-odd nuclei on the s-process
path 176Lu, 180Ta, 186Re
16O(a,g)20Ne and 20Ne(g,a)16O ER 1058 keV, Jp
1-
independent of Jp and Ex of the 2 state in 20Ne!

• (g,a) at stellar kT gt 0n(2)exp(-Ex/kT)
  compensated by lower photon energy ER-Ex
• Stellar reaction rate l for (g,a)l b0 (wg)
  exp-(ERQ)/kT) b1 (wg) exp-(ER-ExExQ)/kT
  ) (wg) exp-(ERQ)/kT)
• Detailed balance between stellar forward (a,g)
  and backward (g,a) rates l / ltsvgt exp(-Q/kT)

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K-isomers in odd-odd nuclei on the s-process
path 176Lu, 180Ta, 186Re
16O(a,g)20Ne and 20Ne(g,a)16O ER 1058 keV, Jp
1-

• Summary
• Detailed balance for stellar reaction rates l
  / ltsvgt exp(-Q/kT)
• Stellar enhancement for l(g,X) because stellar
  reaction rates proportional to Gg (not Gg0)
  l(g,X) Gg
• Experiments in the lab will find only
  contribution prop. b0!
• Review P. Mohr et al., EPJA 32, 357 (2007)
• Formalism P. Mohr et al., EPJA 27, 75 (2006)

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K-isomers in odd-odd nuclei on the s-process
path 176Lu, 180Ta, 186Re
Nucleosynthesis of 180Ta
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K-isomers in odd-odd nuclei on the s-process
path 176Lu, 180Ta, 186Re
Nucleosynthesis of 180Ta Properties

• Isotopic abundance0.01201(8)(deLaeter et al.
  2005)
• Absolute abundance2.5x10-6 rel. to Si106
  (Anders et al. 1989)
• The only quasi-stable isomer in natureJp 9-
  (Bissell et al. 2006)
• Half-life (lower limit)T1/2(9-) gt 7.1x1015 yr
  (Hult et al. 2006)

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K-isomers in odd-odd nuclei on the s-process
path 176Lu, 180Ta, 186Re
Nucleosynthesis of 180Ta
n-process

• s-process

r-process
p-process
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K-isomers in odd-odd nuclei on the s-process
path 176Lu, 180Ta, 186Re
Nucleosynthesis of 180Ta experiment

• Photoactivation using bremsstrahlungE0 1 3
  MeV
• Targets- metallic Ta- 180Ta2O5 (150 mg, 5
  high enrichment)
• 180Tag.s.clearly detected- T1/2(1) 8.1 h-
  X-ray and g-energies
• Yield as f(E0)

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K-isomers in odd-odd nuclei on the s-process
path 176Lu, 180Ta, 186Re
Nucleosynthesis of 180Ta results

• Kink in yield curve f(E0) signature of IMSBelic
  et al., NIMA 463, 26 (2001)

Schematic example IMS at 1.2 and 1.9 MeV
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K-isomers in odd-odd nuclei on the s-process
path 176Lu, 180Ta, 186Re
Nucleosynthesis of 180Ta results

• Kink in yield curve f(E0) signature of IMS
• Detected IMSEx - Ex(9-) 1.01, 1.22, 1.43,
  1.55, 1.85, 2.16, 2.40, 2.64, 2.80 MeV
• Interpretation as (8), (9), (10) of Kp 5
  band Ex(5) 594 keV(Walker et al. 2001)

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K-isomers in odd-odd nuclei on the s-process
path 176Lu, 180Ta, 186Re
Nucleosynthesis of 180Ta results

• Stellar half-life T1/2 changes dramatically by
  up to 20 orders of magnitude!
• s-process13C(a,n)16O 8 keV22Ne(a,n)25Mg 26
  keV
• At 26 keV T1/2 1 yr
• Convection within a few days

BUT llab ? lstellar (thermal excitations)
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K-isomers in odd-odd nuclei on the s-process
path 176Lu, 180Ta, 186Re
Nucleosynthesis of 180Ta thermal excitations

• Lab (case A) yield prop.- population nMB(T)-
  photon density ng(E,T)- partial width Gg,i?IMS
• Branching to Ex (case B)nMB(T)
  exp-Ex/kTng(E,T) exp-(E-Ex)/kT
• Stellar reaction rate l for each IMS prop.
  toGg?IMS Si Gg,i?IMS
• New IMS 2 (case C) Jp 5, 594 keV

New IMS2 without direct branch to 9- not visible
in photoactivation experiment!
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K-isomers in odd-odd nuclei on the s-process
path 176Lu, 180Ta, 186Re
Nucleosynthesis of 180Ta thermal excitations

• Results for the s-process
• 180Ta is thermalized
• T1/2 10 h at kT 26 keV
• convection defines abundance of 180Ta
• 180Ta as mixometer
• Future experiments
• decay properties of the new IMS at 594 keV
• 179Ta(n,g)180m,gTa

(new IMS2)
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K-isomers in odd-odd nuclei on the s-process
path 176Lu, 180Ta, 186Re
Nucleosynthesis of 180Ta reaction rates

• Reaction rate from isomer (9-) to ground state
  (1)
• l(9- ? IS ? 1)
• (2JIS1)/(2Jm1) x
• Gg(IS?9-) Gg(IS?1) / Gg(IS) x
• h-1 exp-(EIS Em)/kT)
• Detailed Balance for 180m,gTa
• l(9- ? 1) / l(1 ? 9-)
• (2Jg1)/(2Jm1) exp(Em/kT)

N.B. G(T) 1 for isomer and ground state
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K-isomers in odd-odd nuclei on the s-process
path 176Lu, 180Ta, 186Re
Nucleosynthesis of 180Ta reaction rates

• Result for the p- or n-process
• reaction rate l exceeds 106/s at kT gt 100
  keV(experimentally confirmed!)
• production of 180Ta inthermal equilibrium
• freeze-out at l 1/s corres-ponds to kT 40
  keV
• 354 180Ta survive as 9-
• independent of details of the production (g,n),
  (n,e)

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K-isomers in odd-odd nuclei on the s-process
path 176Lu, 180Ta, 186Re
Nucleosynthesis of 180Ta thermal equilibrium

• Boltzmann factors at temperature Tlevel 1 Ex1,
  Jp1level 2 Ex2, Jp2n2/n1 (2J21)/(2J11)
  exp-(Ex2-Ex1)/kT
• All levels have to be taken into account!
• For 180Ta at kT 40 keV (freeze-out in
  p-process) g.s. (1) isomer (9-, 77
  keV)2-level system 52.0 48.0 all
  levels 65.5 34.5 (0, 40, 77, 108, 111,
  131, 171, 178, 185, 235, 258, 280, )

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K-isomers in odd-odd nuclei on the s-process
path 176Lu, 180Ta, 186Re
176Lu chronometer or thermometer?

• Without isomerN(176Lu)/N(176Hf)
  f(t)chronometer

• Thermal coupling between ground state and isomer
  in 176Luthermometer

• s-process paths-only nuclei 176Lu, 176HfM.
  Heil et al., ApJ 673, 434 (2008)P. Mohr et al.,
  PRC 79, 045804 (2009)V. Gintautas et al.,
  arXiv0804.0223 (2008)

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K-isomers in odd-odd nuclei on the s-process
path 176Lu, 180Ta, 186Re
176Lu level scheme and decay properties

• Ground stateJp 7- , Kp 7-T1/2 36.8 Gyr
• IsomerJp 1- , Kp 0- Ex 123 keV T1/2
  3.64 h
• Ground state and isomer decay with 100 to 176Hf

S. Walter et al., Phys. Rev. C 75, 034301 (2007)
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K-isomers in odd-odd nuclei on the s-process
path 176Lu, 180Ta, 186Re
176Lu level scheme and thermal coupling

• Lowest IS known (?)Jp 5-, Kp 4-,Ex 838.6
  keV
• Decay branchings to 1- measured0.022 lt Vglt
  0.055(Klay 1991, Lesko 1991)
• Lower and upper limits for lifetime t gt 10 ps
  (Doll 1999)t lt 433 ps (Klay 1991)

conversion-e-
Transition 5- ? 7- (gs) dominates! Experimental
determination of stellar reaction rate possible!
(photoactivation)
But Laboratory(!) enhancement by internal
conversion Vg ? VgCE nK-shell(e-) 2 in the
lab, 0.4 at 25 keV Laboratory enhancement
factor of 2
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K-isomers in odd-odd nuclei on the s-process
path 176Lu, 180Ta, 186Re
176Lu reaction rates und detailed balance

• Detailed balance for 176Lu
• l(1- ? 7-) / l(7- ? 1-)
• (2Jg1)/(2Jm1) exp(Em/kT)
• at kT 23 keV
• l(1-?7-) / l(7-?1-) 3000
• l(7-?1-) 2x10-7/s 6/yr
• l(1-?7-) 6x10-4/s 2/h
• 1- isomer is depopulated much faster than it is
  populated!

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K-isomers in odd-odd nuclei on the s-process
path 176Lu, 180Ta, 186Re
176Lu Branching fn between (n,g) and b decay

• IR isomer ratio in 175Lu(n,g)176Lu prod.
• nn neutron density
• (n,g) cross section
• IMS propertiest lifetimeV decay branching
• Energy-integrated cross sectionIs ? s(E) dE
  V(1-V)/t

1- isomer b-decay 7- ground state (n,g)
depopulation of the isomer (kT lt 25 keV)fn
increases
repopulation (kT gt 25 keV) fn decreases
M. Heil et al., ApJ 673, 434 (2008)
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K-isomers in odd-odd nuclei on the s-process
path 176Lu, 180Ta, 186Re
176Lu new photoactivation experiment

• IS (from kinks)880(30) keV,1060(30) keV,
  1330(30) keV, 1630(30) keV
• Distance of 180(15) keV between lowest and second
  IS!
• U. Kneissl, BgNS Trans. 10, 55 (2005)
• P. Mohr et al., PRC 79, 045804 (2009)

• Exp. yield proportional toIs ? s(E) dE Vgs
  (1-V)GVgs Vhigh-K for 5-, 838.6 keV

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K-isomers in odd-odd nuclei on the s-process
path 176Lu, 180Ta, 186Re
176Lu integrated cross section Is (combined data)

• Stellar rate l and exp. yield proportional to Is
  Is ? s(E) dE V (1-V)G.
• Vgs V for 5-,838.6 keVand 921.5, 1032.4 keV
  (?)
• Lowest IMS at 838.6 keVwith 0.1 W.u.lt G lt 3 W.u.
• Coulomb excitationVgs (1-V)G 7.9 x 10-6 eV-
  uncertainty of factor 2- IMS not identified

Consistent solution for IsIs(838.6) upper
limitIs(921.5) lower limit Experimental
confirmation by photoactivation?
Experimentally consistent solutionstellar
Is(838.6) 1.2 eV fm2 in disagreement with
stellar s-process analysis (Heil et al.)stellar
Is(838.6) 0.07 eV fm2
N. Klay et al., PRC 44, 2801 (1991) C. Doll et
al., PRC 59, 492 (1999) J. Vanhorenbeeck et al.,
PRC 62, 015801 (2000) M. Heil et al., ApJ 673,
434 (2008) U. Kneissl, BgNS Trans. 10, 55
(2005) P. Mohr et al., PRC 79, 045804 (2009)
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K-isomers in odd-odd nuclei on the s-process
path 176Lu, 180Ta, 186Re
176Lu reaction rates

• Intermediate states 176Lu
• 839 keV Is from com-bined experimental data
  factor 17 larger than Heil et al.
• Further IS at higher and lower energiesnot
  relevant for l(437, 723, 788, 922, 963, 1032
  keV)

• Huge uncertainty for suggested K-mixing of two
  almost degenerate 7- states at 725 keVV.
  Gintautas, A. Champagne, F. G. Kondev, R.
  Longland, arXiv0804.0223 (2008)

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K-isomers in odd-odd nuclei on the s-process
path 176Lu, 180Ta, 186Re
s-process branching at 185W and 186Re

• Branchings at 185W and 186Re (without
  isomer)s-process kT 30 keV, nn 4 x
  108/cm3fn(185W) 33 more important than
  fn(186Re) 6
• But (8) isomer in 186Re

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K-isomers in odd-odd nuclei on the s-process
path 176Lu, 180Ta, 186Re
s-process branching at 185W and 186Re

• Branching at 186Re depends on
• IR isomeric ratio in production
  185Re(n,g)186Re 1.30.8Hayakawa et al., ApJ
  628, 533 (2005)
• nn neutron density
• (n,g) cross section
• Potential IMS (6)-, Ex 186 keVdecay
  properties unknown
• n(8)/n(1-)2x10-3 at kT23 keV
• Isomer contribution negligible!

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K-isomers in odd-odd nuclei on the s-process
path 176Lu, 180Ta, 186Re
Summary

• Transition rates l in a stellar thermal photon
  bathproportional to total radiation width Gg
  (not g.s.-Gg0)
• Nucleosynthesis of 180Tanew intermediate states
  ? thermalizations-process 180Ta as
  mixometerp(g)-process, n-process 354 180Ta
  survive as 9- independent of details of the
  production (g,n), (n,e)
• 176Lu as s-process thermometerdominating IMS
  Is(839) 1.2 eV fm2 (before 0.07)additional
  K-mixing of 725 keV states?
• 186Re (8) isomer does not affect the branching

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Isomere in der Nukleosynthese- 180Ta und andere
Beispiele -

• Vielen Dank für Ihre Aufmerksamkeit!

Mainz, 11.02.2008
32
K-isomers in the astrophysical s-process 176Lu,
180Ta, 186Re

• Thank you very much for your attention!

ECT - June 2009
33
K-isomers in odd-odd nuclei on the s-process
path 176Lu, 180Ta, 186Re
16O(a,g)20Ne and 20Ne(g,a)16O ER 1058 keV, Jp
1-
independent of Jp and Ex of the 2 state in 20Ne!

• (g,a) at stellar kT gt 0n(2)exp(-Ex/kT)
  compensated by lower photon energy ER-Ex
• Stellar reaction rate l for (g,a)l b0 (wg)
  exp-(ERQ)/kT) b1 (wg) exp-(ER-ExExQ)/kT
  ) (wg) exp-(ERQ)/kT)
• Detailed balance between stellar forward (a,g)
  and backward (g,a) rates l / ltsvgt exp(-Q/kT)

Why can 3- (6130) and 0 (6049) in 16O be
neglected in the (a,g) rate?
Ex gtgt kT wrong!!!
Correct answer Coulomb barrier is the same for
16Og.s.-a and 16O-a ! No compensation for
Boltzmann factor exp(-Ex/kT) for (a,g)