Tuning the ReOs clock: neutron cross sections

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Tuning the Re/Os clock neutron cross sections

• Re/Os
• Measurements at CERN n_TOF at FZK
• Stellar rates
• Uncertainties

a.mengoni_at_iaea.org
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Re/Os clock()
BANG!
Now
4.5 Ga
?
s-only
Os
Os 184 0.02
Os 185 94 d
Os 186 1.58
Os 187 1.6
Os 188 13.3
Os 189 16.1
Os 190 26.4
Os 191 15.4 d
Os 192 41.0
Re
Re 183 71 d
Re 184 38 d
Re 185 37.4
Re 186 90.64 h
Re 187 62.6
Re 188 16.98 h
Re 189 24.3 h
Re 190 3.1 m
42.3x109 a
W
W 182 26.3
W 183 14.3
W 184 30.67
W 185 75.1 d
W 186 28.6
W 187 23.8 h
W 188 69 d
s-process
r-process
r-only
() DD Clayton, ApJ 139 (1964) 637 gtgt
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Key quantity cross sections
BANG!
Now
4.5 Ga
t0
s-process condition s(186)N(186) s(187)N(187)
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The n_TOF facility at CERN
www.cern.ch/n_TOF
The n_TOF Collaboration
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The n_TOF facility

• commissioned in 2001-2002

www.cern.ch/n_TOF
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Os measurements setup
?-ray detection C6D6 scintillators
Sample changer
C6D6
C6D6
Pulse height weighting technique Correction of
the ?-response by weighting function to make the
detector efficiency proportional to ?-ray
energy Neutron flux monitor Silicon detectors
viewing a thin 6LiF foil
Neutron beam
The n_TOF Collaboration
www.cern.ch/n_TOF
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Samples capture yields

• 186Os (2 g, 79 )
• 187Os (2 g, 70 )
• 188Os (2 g, 95 )
• Al can
• environmental background
• 197Au (1.2g)
• flux normalization
• (using Ratynski and Macklin
• high accuracy cross section data)
• natPb (2 g)
• in-beam gamma background
• natC (0.5 g)
• neutron scattering background

M Mosconi, FZK
www.cern.ch/n_TOF
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n_TOF-04 186Os capture x-section
NB the calculation is normalized NOT fitted to
experimental data
www.cern.ch/n_TOF
The n_TOF Collaboration
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n_TOF-04 186Os capture x-section
Hauser-Feschbach theory (statistical model)

• Neutron transmission coefficients, Tn
• from OMP calculations
• g-ray transmission coefficients, Tg
• from GDR (experimental parameters)
• Nuclear level densities
• fixed at the neutron binding from ltDgtexp

www.cern.ch/n_TOF
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n_TOF-04 187Os capture x-section
NB the calculation is normalized NOT fitted to
experimental data
The n_TOF Collaboration
www.cern.ch/n_TOF
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Key quantity cross sections
BANG!
Now
4.5 Ga
t0
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The clock from x-sections to age
BANG!
Now
4.5 Gyr
t0

• s-process synthesis of 186,187Os

• e-Lt r-process enrichment of 187Re

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Laboratory cross sections the clock
BANG!
Now
4.5 Ga
t0
Rs 0.43 0.02 t0 8.7 0.4 Ga age 8.7
4.6 13.3 Ga
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Stellar 187Os(n,g) rate
187Os at kT 30 keV P(gs)
33 P(1st) 47 P(all others) 20

• Include thermal population
• Include super-elastic scattering channels
• Nuclear structure effects (deformation)

ltsn,ggt SEF ltsn,ggt
SE Woosley and WA Fowler, ApJ 233 (1979) 411
a.mengoni_at_iaea.org
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(n,n)
A neutron (inelastic) scattering experiment
performed at FZK-Karlsruhe
alberto.mengoni_at_cern.ch
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(n,n) theory
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(n,n) theory
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n_TOF-04 186Os capture x-section
CC calculations including ground-state collective
band in a deformed OMP
a.mengoni_at_iaea.org
www.cern.ch/n_TOF
19
n_TOF-04 187Os capture x-section
CC calculations including ground-state collective
band in a deformed OMP
a.mengoni_at_iaea.org
www.cern.ch/n_TOF
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Stellar enhancement factor
ltsn,ggt SEF ltsn,ggt
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Laboratory cross sections the clock
BANG!
Now
4.5 Ga
t0
Rs 0.43 0.02 t0 8.7 0.4 Ga age 8.7
4.6 13.3 Ga
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Stellar cross sections the clock
BANG!
Now
4.5 Ga
t0
Rs 0.34 0.02 t0 10.7 0.5 Ga age 10.7
4.6 15.3 Ga
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Uncertainties
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Nuclear Data Abundances
Abundances 0.49 Ga x-section
ratio 0.47 Ga Re-187 b-decay
half-life 0.29 Ga Total uncertainty lt 1 Ga
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Summary

• Cosmological way (WMAP observation)
• Astronomical way (globular clusters)
• Nuclear way Re/Os clock U/Th
  clock

13.7 ? 0.2 Ga
CL Bennett et al., ApJS, 148 (2003) 1
14 ? 1 Ga
G Imbriani et al., AA 420 (2004) 625
15.3 ? 0.8 2 Ga()
gt13.4 ? 0.9 2.2 Ga
A Frebel et al. ApJ 660 (2007) L117
() 2 Ga uncertainty assigned to GCE modeling
astration(?)
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U/Th and Re/Os clockscomplementary
BANG!
Now
4.5 Ga
GCE independent Primordial yields
model-dependent
GCE dependent Yields well determined
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n_TOF-04 ExperimentM Mosconi, FZK KarlsruheK
Fujii, INFN TriesteA Mengoni, IAEA Vienna/CERN
Geneva (sp)F Käppeler, FZK KarlsruhePM Milazzo,
INFN TriesteC Domingo Pardo, GSI DarmstadtR
Gallino, Universita di Torinoand The n_TOF
Collaboration
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End
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Slides annex
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Lets assume the age from WMAP is correct
13.7 ? 0.2 Gyr
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Reverse argument
BANG!
Now
4.5 Ga
t0
assuming Age 13.7 Ga or t0 9.2 Ga
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Playing with the 187Re production rate
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Ages

• Cosmological way based on the Hubble time
  definition (expansion age)
• Astronomical way based on observations of
  globular clusters
• Nuclear way based on abundances decay
  properties of long-lived radioactive species

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Age from Hubble time
The most recent estimate of the Hubble constant
based on observations provides() H0 72 ? 8
km/sec/Mpc and implies an age of
13.9 ? 1.5 Ga
() HST Key Project see WL Friedman et al.,
ApJ 553, (2001) 47
NB if WWm1, then age2/31/H0 9.3?1.0 Ga
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Cosmological problems with age
http//map.gsfc.nasa.gov/
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Age from WMAP observations
The detailed structure of the cosmic microwave
background fluctuations will depend on the
current density of the universe, the composition
of the universe and its expansion rate. WMAP has
been able to determine these parameters with an
accuracy of better than 5. Thus, we can estimate
the expansion age of the universe to better than
5. When we combine the WMAP data with
complimentary observations from other CMB
experiments (ACBAR and CBI), we are able to
determine an age for the universe closer to an
accuracy of 1.
13.7 ? 0.2 Ga
Source CL Bennett et al., ApJS, 148 (2003) 1
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Age from globular clusters
The age derived from observationof the
luminosity-color relation of stars in globular
clusters
from gt 11.2 Ga () to 14 ? 2.0 Ga() LM
Krauss and B Chaboyer, Science 299 (2003) 65
Source DN Spergel et al.Proc. Natl. Acad. Sci.
USA 94 (1997) 6579
alberto.mengoni_at_cern.ch
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The nuclear way

• Traditional nuclear clocks are those based on
• 235U/238U
• 232Th/238U
• 187Os/187Re
• Th/Eu, Th/X or U/Th abundances in low-Z stars

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187Re(b-) decay
The b-decay half-life of 187Re is tb 43.2 ? 1.3
Gyr. Under stellar conditions, the 187Os and
187Re atoms can be partly or fully ionized. The
b-decay rate can then proceed through a
transition to bound-electronic states in 187Os.
The rate for this process can be orders of
magnitude faster than the neutral-atom decay.
The bound-state b-decay half-life of
fully-ionized 187Re has been measured _at_ GSI.
The half-life of fully-ionized 187Re turns out to
be tb 32.9 ? 2.0 yr. (F. Bosch, et al., PRL 77
(1996) 5190)
Impact on the age 1 Gyr(?)
alberto.mengoni_at_cern.ch
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Brancing(s)
BANG!
Now
4.5 Gyr
Os
Os 184 0.02
Os 185 94 d
Os 186 1.58
Os 187 1.6
Os 188 13.3
Os 189 16.1
Os 190 26.4
Os 191 15.4 d
Os 192 41.0
Re
Re 183 71 d
Re 184 38 d
Re 185 37.4
Re 186 90.64 h
Re 187 62.6
Re 188 16.98 h
Re 189 24.3 h
Re 190 3.1 m
42.3x109 a
W
W 182 26.3
W 183 14.3
W 184 30.67
W 185 75.1 d
W 186 28.6
W 187 23.8 h
W 188 69 d
The 185W(n,g)186W rate is needed
The inverse 186W(g,n)185W cross section has been
measured K. Sonnabend et al. ApJ 583 (2003),
506-513.
Impact on the age negligible
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Nuclear Astro issues
In addition to the particular conditions which
allows to use the Re/Os abundance pair as a clock
there are a number of complications

• The b-decay half-life of 187Re is strongly
  dependent on
• temperature
• The stellar neutron capture cross section of
  187Os is influenced
• by the population of low-lying excited levels
• (the 1st excited states is at 9.8 keV)
• Branching(s) at 185W and/or at 186Re

• The chemical evolution of the galaxy
  influences the history of the nucleosynthesis
• Re and Os abundances

alberto.mengoni_at_cern.ch
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More on stellar rates
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Thermal population
For example, in 187Os at kT 30 keV it
is P(gs) 33 P(1st)
47 P(all others) 20
alberto.mengoni_at_cern.ch
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More on stellar rates
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WMAP observation and the age
sourceThe Cosmic Neutrino Background and the Age
of the Universe Authors Francesco de Bernardis
(Rome), Alessandro Melchiorri (Rome), Licia Verde
(ICE Princeton), Raul Jimenez (ICE
Princeton) http//arxiv.org/abs/0707.4170v2
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WMAP observation and the age
wrel wg Neff wn
sourceThe Cosmic Neutrino Background and the Age
of the Universe Authors Francesco de Bernardis
(Rome), Alessandro Melchiorri (Rome), Licia Verde
(ICE Princeton), Raul Jimenez (ICE
Princeton) http//arxiv.org/abs/0707.4170v2
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Playing with the 187Re production rate
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Ages
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Nuclei in the Cosmos IX CERN, Geneva, June 2006