1. Nuclear-Physics far from Stability r-Process Nucleosynthesis
and
r-Process Nucleosynthesis
Karl-Ludwig Kratz
- Institut für Kernchemie, Univ. Mainz, Germany
- HGF VISTARS, Germany
- Department Of Physics, Univ. of Notre Dame, USA
Hirschegg XXXIV ‘06

2. r-process observables
Historically,
nuclear astrophysics has always been
concerned with
interpretation of the
origin of the chemical elements
from astrophysical and cosmochemical
observations,
description in terms of specific
nucleosynthesis processes
(already B²FH, 1957).
Solar system isotopic abundances, Nr,
T9=1.35; nn=
, Bi
r-process observables
CS abundances
scaled solar r-process
ALLENDE INCLUSION
EK-1-4-1
isotopic
composition
Ca, Ti, Cr,
Zr, Mo, Ru,
Nd, Sm, Dy ↷
r-enhanced
scaled theoretical solar r-process Zr Pt Ru Cd Ba Os Pb Sr Sn Nd
d [‰] Ga Mo Pd Dy Ge Gd Ce Sm Er Yb Ir Y Rh Hf Nb Ag La Eu Ho Pr Tb Au Lu Tm Th U
Mass number
Elemental abundances in UMP halo stars
Hirschegg XXXIV ‘06
“FUN-anomalies” in meteoritic samples

3. Nuclear-data needs for the classical r-process
nuclear masses
Sn-values ↷ r-process path
Qb, Sn-values ↷ theoretical b-decay properties, n-capture rates
b-decay properties
T1/2 ↷ r-process progenitor abundances, Nr,prog
Pn ↷ smoothing Nr,prog Nr,final (Nr,)
b-decay
freeze-out
n-capture rates
sRC + sDC ↷ smoothing Nr,prog during freeze-out
nuclear structure development
extrapolation into unknown regions
fission modes
SF, bdf, n- and n-induced fission ↷ “fission (re-) cycling”; r-chronometers
Hirschegg XXXIV ‘06

4. History and progress in measuring r-process nuclei
Definition: r-process isotopes lying in the process path at freeze-out
↷ when r-process falls out of (n,g)-(g,n) equilibrium
even-neutron isotopes ↷ “waiting points”
important nuclear-physics property T1/2
odd-neutron isotopes ↷ connecting the waiting points
important nuclear-physics property Sn  sn.g
In 1986 a new r-process astrophysics era started:
at the ISOL facilities OSIRIS, TRISTAN and SC-ISOLDE
T1/2 of N=50 “waiting-point” isotope 80Zn50 (top of A80 Nr, peak)
T1/2 of N=82 “waiting-point” isotope 130Cd82 (top of A130 Nr, peak)
In 2006, altogether more than 50 r-process nuclei have been measured
(at least) via their T1/2, which lie in the process path at freeze-out.
These r-process isotopes range from 68Fe to 139Sb.
The large majority of these exotic nuclei was identified at CERN/ISOLDE
via the decay mode of
b–delayed neutron emission.
(see talk O. Arndt)
Hirschegg XXXIV ‘06

5. Snapshots: r-process paths for different neutron densities Ba Cs Xe
heaviest isotopes with measured T1/2 I Te Sb Sn In Cd Ag Pd
g9/2 Rh Ru Tc Mo Nb Zr
p1/2 Y Sr Rb
p3/2 Kr Br Se As
f5/2 Ge Ga Zn Cu Ni Co
f7/2 Fe Z
g9/2
d5/2
s1/2
g7/2
d3/2
h11/2 N
Hirschegg XXXIV ‘06

6. r-Process path for nn=1020 nn=1020 Ba Cs Xe I Te Sb Sn In Cd Ag Pd Rh Ru Tc Mo Nb Zr Y Sr Rb Kr Br Se As Ge Ga Zn Cu Ni Co Fe Z
„waiting-point“ isotopes at nn=1020 freeze-out N
Hirschegg XXXIV ‘06

7. r-Process paths for nn=1020 and 1023 Ba Cs Xe I Te Sb Sn In Cd Ag Pd Rh Ru Tc Mo
nn=1023 Nb Zr Y Sr Rb Kr Br Se As Ge Ga Zn Cu Ni Co Fe Z
„waiting-point“ isotopes at nn=1023 freeze-out N
(T1/2 exp. : 28Ni – 31Ga, 36Kr, 37Rb,47Ag – 51Sb)
Hirschegg XXXIV ‘06

8. r-Process paths for nn=1020, 1023 and 1026 Ba Cs Xe I Te Sb Sn In Cd Ag Pd Rh Ru Tc Mo
nn=1023 Nb Zr Y Sr Rb Kr Br
nn=1026 Se As Ge Ga Zn Cu Ni Co Fe Z
„waiting-point“ isotopes at nn=1026 freeze-out N
(T1/2 exp. : 28Ni, 29Cu, 47Ag – 50Sn)
Hirschegg XXXIV ‘06

9. b-Decay properties
T1/2, Pn gross b-strength properties from theoretical models, e.g. QRPA
in comparison with experiments.
Requests: (I) prediction / reproduction of correct experimental “number”
(II) detailed nuclear-structure understanding
↷ full spectroscopy of “key” isotopes, like 80Zn50 , 130Cd82.
Total Error = 3.73
Total Error = 5.54
Half-lives
Pn-Values
QRPA (GT)
QRPA (GT)
QRPA (GT+ff)
QRPA (GT+ff)
(P. Möller et al.,
PR C67, (2003))
Total Error = 3.08
Total Error = 3.52
Hirschegg XXXIV ‘06

10. Effects of T1/2 on r-process matter flow
T1/2 (GT + ff)
Mass model: ETFSI-Q
all astro-parameters kept constant
r-process model:
“waiting-point approximation“
T1/2 x 3
T1/2 : 3
r-matter flow too slow
r-matter flow too fast
Hirschegg XXXIV ‘06

11. Nuclear masses Over the years, development of
various types of mass models / formulas:
Weizsäcker formula
Local mass formulas
(e.g. Garvey-Kelson; NpNn)
Global approaches
(e.g. Duflo-Zuker; KUTY)
Macroscopic-microscopic models
(e.g. FRDM, ETFSI)
Microscopic models
(e.g. RMF; HFB)
Comparison to NUBASE (2001) // (2003)
FRDM (1992) srms = // [MeV]
ETF-Q (1996) srms = // [MeV]
HFB-2 (2002) srms = [MeV]
HFB-3 (2003) srms = [MeV]
HFB-4 (2003) srms = [MeV]
HFB-8 (2004) srms = [MeV]
HFB-9 (2005) srms = [MeV]
HFB-12 (2005) srms = ?
No improvement of srms
J. Rikovska Stone, J. Phys. G: Nucl. Part. Phys. 31 (2005)
Main deficiencies at Nmagic !
D. Lunney et al., Rev. Mod. Phys. 75, No. 3 (2003)
Hirschegg XXXIV ‘06

12. The N=82 shell gap as a function of Z (1)
The N=82 shell closure dominates the matter flow of the „main“ r-process (nn≥1023).
Definition „shell gap“: S2n(82) – S2n(84) ↷ paired neutrons.
Therefore request:
experimental masses and reliable model predictions for the respective
N=82 waiting-point nuclei 125Tc to 131In
FRDM DZ
Groote
EFTSI-Q
HFB-2
HFB-8
HFB-9
Exp
A≈130 Nr, peak
RESERVE
Achtung farbe—kommt gruen gut raus bei der praesentation
Etfsi-q schwarz ganze linie; DZ schwarz gestrichelt ebesno HFB-9 and HFB2
Abbildung aus cgs 12 proceedings;; kombination aus folie 11 and 12 mit gleichen modellen
Hirschegg XXXIV ‘06

13. The N=82 shell gap as a function of Z (2)
Definition „shell gap“: S2n(81) – S2n(83) ↷ unpaired neutrons.
Large odd-even Z staggering for „microscopic“ HFB models ‼
HFB-9
FRDM
FRDM
EFTSI-Q DZ
Groote
RESERVE
Auch hier hellblau und gruen ersetzen durch schrze ganz/gestrichelt
Exp
Exp
HFB-8
HFB-2
Hirschegg XXXIV ‘06

14. Effects of nuclear masses on Nr, fits
T1/2+Pn and all astro-parameters kept constant !
Bei hfb 8 im massembereich 180 einfaerben, bei allen gelb durch giftgruen ersezten siehe folie zuvor…
Hirschegg XXXIV ‘06

15. From classical to high-entropy wind model
SO FAR, site-independent parameter study
within classical Waiting-Point Model
understand effects of nuclear-physics input on Nr,calc
NOW, more realistic r-process model
High-Entropy Wind of SN II
“best” nuclear-physics input
full dynamical network
start with a-process
charged-particle freeze-out 
n-rich seed beyond N=50 (94Kr, 100Sr,…)
for subsequent r-process
avoids N=50 “bottle neck” in classical model !
Three main parameters:
electron abundance Ye = Yp = 1 – Yn
radiation entropy S ~ T³·r
expansion speed vexp  process durations ta and tr
Hirschegg XXXIV ‘06

16. Main results of dynamical r-process calculations
Conditions for successful r-process
(even for Ye=0.49!)
 „strength“ formula
Due to improved nuclear-physics input
 max. S=280 (for Ye=0.45)
Total process duration up to Th, U
 tr=465 ms
leaves time for fission recycling
Freeze-out effects (late non-equilibrium phase)
 negligible up to A=130 peak
important for REE „pygmy“ peak and A=195 peak
Separate fits of Nr, peaks
Fit of total Nr, abundance pattern
Application to Th, U r-chronometers
Hirschegg XXXIV ‘06

17. Synthesizing selected mass region
Superposition of individual S-components Pb Th U
Hirschegg XXXIV ‘06

18. Basis for detailed astrophysical parameter studies
Superposition of 5 S-sequences to reproduce the Nr, pattern (100<A<240)
N=50
N=82
N=126
Th, U
r-process
chronometers
„weak“
r-process
(Thesis K. Farouqi, 2005 )
Basis for detailed astrophysical parameter studies
Hirschegg XXXIV ‘06

19. Calculated r-process abundances as function of neutron densities
(K.-L. Kratz, B. Pfeiffer, 2005)
Hirschegg XXXIV ‘06

20. Abundance predictions as function of nn
“weak”
“main”
“weak”
“main”
r-process computations
for selected elements
r-process computations
for selected isotopes
Hirschegg XXXIV ‘06

21. r-Process elemental abundances
“weak” r-process
(see talk F. Montes)
“main” r-process
Solar system Simmerer et al., 2004
CS Sneden et al., 2003
Hirschegg XXXIV ‘06

22. Conclusion Nuclear-physics data for r-process calculations
still unsatisfactory !
better global models
for all nuclear shapes
(spherical, prolate, oblate, triaxial, tetrahedral,…)
and all nuclear types
(even-even, even-odd, odd-even , odd-odd)
more measurements
masses !
gross b-decay properties
fission properties
full spectroscopy of selected
“key“ waiting-point isotopes
Hirschegg XXXIV ‘06

23. ≈ ≈ ≈ ≈ Example “future“ GSI experiment 78Ni50 78Ni50 28 28 78Cu49 29
Full understanding of shell structure of “key isotope“ 78Ni
Mass measurement ↷ Qb, Sn T1/2 + Pn, sng
g-spectroscopy ↷ Eℓ and log(ft) of np1/2pp3/ T1/2
Eℓ and log(ft) of ng9/2pg9/ Pn
pn interaction ms ms
Folded - Yukawa
Woods - Saxon
78Ni50
Q = ± 1.17 MeV
(Audi ´03)
78Ni50 28
Lipkin - Nogami 28
Lipkin - Nogami ≈
9.6% 3.5
1+ nf5/2  pf7/2
6.93
12.8%
1+ nf5/2  pf5/2
6.34 ≈
45.7%
1+ ng9/2  pg9/2
5.46
1+ ng9/2  pg9/2
51.1%
4.97
6.6%
1+ nf5/2  pf7/2
Sn=
4.24±0.57 MeV
1+ ng9/2  pg9/2
4.23
3.6%
4.35
5.4%
1+ nf5/2  pf7/2
3.95
0.5%
1+ nf5/2  pf7/2
3.65
1+ nf5/2  pf7/2
3.4%
1+ np1/2  pp3/2
3.00
32.3%
2.76
1+ np1/2  pp3/2
27.9% ≈
2.48 ≈
ng9/2  pp3/2
ng9/2  pp3/2
78Cu49 29
78Cu49 29
Hirschegg XXXIV ‘06

24. … as an example for long “diffusion time”
from KCh Mainz → GSI Darmstadt
from experimentalist → theoretician
Hirschegg XXXIV ‘06

25. … How were the heavy elements
Among the
… Eleven Greatest Unanswered Questions of Physics (Discover Magazine, 2002)
“After the discovery of “antimatter” and “dark matter”, we have recently found the existence of “doesn’t matter”, which seems to have no effect on the Universe whatsoever.”
… How were the heavy elements
from Fe to U made?
Hirschegg XXXIV ‘06

26. Nuclear physics in the r-process
Fission rates and distributions:
n-induced
spontaneous
b-delayed
b-delayed n-emission branchings (final abundances)
b-decay half-lives (progenitor abundances, process speed)
Neutron-capture rates
for A> in slow freeze-out
for A<130 maybe in a “weak” r-process ?
Note: how far down one needs T12/masses on n-rich nuclei depends on seed
this is experimental and theoretical challenge !!
n-physics ?
Seed production rates (aaa,aan, a2n, ..)
Masses (Sn) (location of the path)
Hirschegg XXXIV ‘06

27. Motivation: N/Z R - abundances Nuclear structureg
9/2 i
13/2 p
1/2 f
5/2
3/2
7/2 h
11/2 d s ;f
N/Z
112 70 40 50 82
126 ) w h of
7.0
Units (
6.5
Energies
6.0
5.5
Single – Neutron
5.0
FK²L (Ap.J. 403 ; 1993)
“..the calculated r-abundance ‘hole‘ in the A  120 region reflects ... the weakening of the shell strength ... below “
100%
70%
40%
10%
132Sn
Strength of ℓ 2
-Term
B. Pfeiffer et al.,
Acta Phys. Polon. B27 (1996)
Hirschegg XXXIV ‘06

28. Nuclear-Physics Input
from “internally consistent“ models, with local improvements.
Waiting-point approximation requires
Sn  defines r-process path (Saha equ.)
T½  determines progenitor abundances (Nr,prog)
Pxn  smoothens Nr,prog  Nr,
Start with
input for
Nuclear-Mass Model
FRDM, ETFSI-Q, HFB-2,...
macroscopic microscopic
finite-range folded Yukawa
droplet single particle
Q, Sn, 2, s.p. wave fcts.
Shell Model
QRPA(global), OXBASH, ANTOINE,...
Gamow-Teller strength functions
T½, Pxn, EQP, JQP, QP 
In addition
experimental data (up to Dec. 2003)
short-range model extrapolation
due to known nuclear-structure developments
inclusion of ff-strength (Gr.Th.)
Hirschegg XXXIV ‘06

29. R-abundance peaks and neutron-shell numbers
already B²FH (Revs. Mod. Phys. 29; 1957)
C.D. Coryell (J. Chem. Educ. 38; 1961)
...still today important r-process
properties to be studied experimentally
and theoretically.
132Sn 50
131In82 49
133In84
129Ag82 47
128Pd82 46
127Rh82 45
126
127
128
129
130
131
132
133
Pn~85%
165ms
278ms
46ms(g)
r-process
path
(n,)
135
136
137
134
158ms(m)
130Cd82 48
162ms b
“climb up the staircase“ at N=82;
major waiting point nuclei;
“break-through pair“ 131In, 133In;
K.-L. Kratz (Revs. Mod. Astr. 1; 1988)
climb up the N= 82 ladder ...
A  130 “bottle neck“
 total r-process duration r
“association with the rising side of major
peaks in the abundance curve“
Hirschegg XXXIV ‘06

30. What we knew already in 1986 ... Request: SELECTIVITY !
Shell-model (QRPA; Nilsson/BCS) prediction 1+
1.0
Q = 8.0 MeV
T1/2 = 230 ms 1+
6.0
IKMz – 155R(1986) 1+
T1/2 = (195 ± 35) ms 1+
5.0 1+ 1+
4.0 1+
K.-L. Kratz et al (Z. Physik A325; 1986)
3.0
g7/2, g9/2
Exp. at old SC-ISOLDE
with plasma ion-source
and dn counting 1+
4.1
2.0
streichkandidat
Problems:
high background from
-surface ionized 130In, 130Cs
-molecular ions [40Ca90Br]+
T1/2(GT) = 0.3 s
1.0 1-
Request: SELECTIVITY !
Hirschegg XXXIV ‘06

31. Request: Selectivity ! Why ? How? at an ISOL facility Fast UCx targetAg Cd In Cs Sn Sb Te I Xe
the Ag “needle” in the Cs “haystack”
How?
at an ISOL facility
Fast UCx target
Neutron converter
Laser ion-source
Hyperfine splitting
Isobar separation
Repeller
Chemical separation
Multi-coincidence setup
streichkandidat 50
800
>105
Hirschegg XXXIV ‘06

32. Request: Selectivity ! g-singles spectrum Laser ion-source (RILIS)
Laser ON
Comparison of
Laser ON to
Laser OFF
spectra
Laser OFF
g-singles spectrum
130Cd
1669 keV
1732 keV
Laser ON
Laser OFF
130Sb
1749 keV
Energy [keV]
Chemically selective,
three-step laser ionization
of Ag into continuum
streichkandida
Properties of the laser system:
Efficiency ≈ 10%
Selectivity ≈ 103
Hirschegg XXXIV ‘06

33. The N=82 shell gap as a function of Z
The N=82 shell closure dominates the matter flow of the „main“ r-process (nn≥1023).
S2n(82) – S2n(84) ↷ paired neutrons
S2n(81) – S2n(83) ↷ unpaired neutrons.
Therefore request:
experimental masses and more reliable model predictions
A≈130 Nr, peak
FRDM
FRDM
HFB 9
HFB 9
Groote
EFTSI-Q
Groote
EFTSI-Q
Hirschegg XXXIV ‘06

34. Hirschegg XXXIV ‘06

35. The -process 3<T9<6
NSE: All nuclear reactions via strong and electro-magnetic interactions are very fast when compared with dynamical time scales.
At T9 ~6, -particles become the dominant constituent of the hot bubble!
Recombination of the -particles is possible via:
3→ 12C and
++n → 9Be, followed by 9Be(,n) 12C
Charged-particle freeze-out at T9 ~ 3 with:
Dominant part of -particles ~ 80%
Some heavy nuclei beyond iron (80 <A< 110)
Probably a little bit of free neutrons
 Seed composition for a subsequent r-process.
Hirschegg XXXIV ‘06

36. define three parameters: Electron abundance: Ye=Yp=1-Yn
For a given blob of matter behind the shock front above the proto-neutron star :
define three parameters:
Electron abundance: Ye=Yp=1-Yn
Example: Ye=0.45  55% neutrons & 45% protons
Radiation entropy: Srad ~ T3/r
Expansion speed Vexp
determines process durations  and r :
Example: Vexp= 7500 km/s, R0= 130 km   = 35 ms, r= 280 ms
Hirschegg XXXIV ‘06

37. Seed nuclei after an -rich freeze-out S=200, Vexp=7500 km/s
Neutron-rich seed beyond N=50
difference to „classical“ r-process with 56Fe seed
avoids N=50 r-process bottle-neck
 seed nuclei: 94Kr, 100Sr (87Se, 103Y, 89Br, 84Ge, 95Kr, 76Ni, 95Rb below 5%)
Hirschegg XXXIV ‘06

38. This means: (n,γ) <  (γ,n) No need of neutron capture rates!
Definition of the r-process freeze-out
Classical r-process: nn, T9= const up to break-out of (nγγn) equilibrium!
This means: (n,γ) <  (γ,n)
 instantaneous freeze-out!
No need of neutron capture rates!
Dynamical r-process: nn = f(t,T9), T9= f(t)
This means: (nn) <  (n,γ) and  (nn) < (γ,n)
 no instantaneous freeze-out!
Neutron capture rates are needed!
Hirschegg XXXIV ‘06

39. Freeze-out is fast  no significant effect on A=130 peak
Effect of neutron-capture rates on the A=130 peak
Freeze-out is fast  no significant effect on A=130 peak
Hirschegg XXXIV ‘06

40. Freeze-out is slow  significant effect on A=195 peak
Effect of neutron-capture rates on the A=195 peak
Freeze-out is slow  significant effect on A=195 peak
Hirschegg XXXIV ‘06

41. Synthesizing the A=130 peak
Process duration: 146 ms
reserve Ye
Entropy S
r-process duration
t [ms]
nn [cm-3] at freeze out
T9 [109 K] at freeze out
0,49
230
234
1,9 x1020
0,53
0,45
190
146
8,1 x1021
0,79
0,41
160
109
9,0 x1021
0,77
Hirschegg XXXIV ‘06

42. Synthesizing the A=195 peak
Process duration: 327 ms
not yet enough Pb Th U
reserve Ye
Entropy S
r-process duration
t [ms]
nn [cm-3] at freeze out
T9 [109 K] at freeze out
0,49
290
412
2,0 x1021
0,33
0,45
260
327
1,5 x1022
0,41
235
213
2,9 x1022
0,42
Hirschegg XXXIV ‘06

43. Present status r-process-rich Galactic halo stars
(C. Sneden, J.J. Cowan, et al.)
Hirschegg XXXIV ‘06

44. Reproduce isotopic Nr, distribution (lsq-fits; A > 80, 120)
CS abundances
scaled solar r-process
scaled theoretical solar r-process Zr Pt Ru Cd Os Pb Ga Sr Ba Mo Pd Sn Nd Dy Ge Gd Ce Sm Er Yb Ir Y Rh Hf Nb Ag La Pr Eu Ho Tb Au Lu Tm Th U
Hirschegg XXXIV ‘06

45. Cosmo chronology with Thorium  U  
Hirschegg XXXIV ‘06

46. GSI-Experiment E040 (2000) • 238U beam @ 750MeV/u on Pb-Target
Projectile fission produces neutron-rich nuclei
• Separation and identification of fission products with the FRS
• Measuring T1/2 and Pn after implantation of nuclei in Si-stack
T1/2 = 296 (35)ms
T1/2 = 334 (14)ms
J. Pereira, NSCL and R. Kessler, Uni Mainz
Hirschegg XXXIV ‘06

47. Example: recent experiment
110 40 Zr 70
... a new double-magic „waiting-point“ nucleus?
Beta-decay
Normal shell strength
strongly deformed (2=0.31)
Shell strength quenched
spherical
B. Pfeiffer et al.,
Acta Phys. Polon. B27 (1996)
T½ = 88 ms
Pn = 8 %
T½ = 14 ms
Pn = 0.7 %
73%
10% 0+
110Zr GT
1+ Levels
110Nb 2- …
Q  9.27 MeV
Sn  3.73 MeV 3- 0+
110Zr 1+
1.13
5.22
6.44
7.04
7.64
Q  9.27 MeV GT
Sn  3.21 MeV
[g9/2g7/2]
99%
1.67
0.85
110Nb
Exp at NSCL/MSU; Nov. 2005; to be continued at GSI ?
Hirschegg XXXIV ‘06