Neutron induced reactions: Experiments and Theory 1.BANG! Stuff with light nuclei (BBN, Coul_diss exp, C x-sections) 2.The Metals & the s-process (canonical s-process, Fe-60) 3.Heavy (Sm, Nd, etc.) 4.Specials: The Re/Os clock

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

The most recent estimate of the Hubble constant based on observations provides( *) : H 0 = 72  8 km/sec/Mpc and implies an age of: Age from Hubble time 13.9  1.5 Gyr (*) HST Key Project see: WL Friedman et al., ApJ 553, (2001) 47 NB: if  =  m ~1, then age=2/3×1/H 0 = 9.3  1.0 Gyr

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%. Age from WMAP observations Source: CL Bennett et al., ApJS, 148 (2003)  0.2 Gyr

Cosmological “problems” with age

Cosmological “problems” with age

Age from globular clusters The age derived from observation of the luminosity-color relation of stars in globular clusters

Age from globular clusters from > 11.2 Gyr (*) to 14  2.0 Gyr (*) LM Krauss and B Chaboyer, Science 299 (2003) 65 The age derived from observation of the luminosity-color relation of stars in globular clusters Source: DN Spergel et al. Proc. Natl. Acad. Sci. USA 94 (1997) 6579

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

Tuning the Re/Os clock: neutron cross sections Re/Os Measurements at CERN n_TOF & at FZK Stellar rates Uncertainties

Time Now4.5 Gyr ? Solar-system formation Galaxy formation BANG!

Re/Os clock W W Re Os Re d Os W W W d W W h W d Re d Re Re h Re x10 9 a Re h Re h Re m Os d Os Os Os Os Os Os d Os Now4.5 Gyr BANG! The  -decay half-life of 187 Re is 42.3 Gy ? Effect on the abundance of the decay daugther 187 Os

Re/Os clock(*) W W Re Os Re d Os W W W d W W h W d Re d Re Re h Re x10 9 a Re h Re h Re m Os d Os Os Os Os Os Os d Os s-only r-processr-only s-process Now4.5 Ga BANG! ? (*) DD Clayton, ApJ 139 (1964) 637 >>>>

Key quantity: cross sections Now4.5 Ga BANG! t0t0 s-process condition:  (186)N(186) ≈  (187)N(187)

Enhanchement of [ 187 Os] by 187 Re(  - ) The s-process condition  A N A = const. implies that:  186 [ 186 Os] =  187 [ 187 Os] From (n,  ) systematics 0.5  186 /  187 ~ 0.5 On the other hand, from solar-system abundances: ± [ 187 Os] / [ 186 Os] = ±

The n_TOF facility at CERN n_TOF Collaboration

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 6 LiF foil -ray detection: C 6 D 6 scintillators C6D6C6D6 C6D6C6D6 Neutron beam Sample changer Os measurements setup The n_TOF Collaborationwww.cern.ch/n_TOF

186 Os 186 Os (2 g, 79 %) 187 Os 187 Os (2 g, 70 %) 188 Os 188 Os (2 g, 95 %) Al can Al can environmental background 197 Au 197 Au (1.2g) flux normalization (using Ratynski and Macklin high accuracy cross section data) nat Pb nat Pb (2 g) in-beam gamma background nat C nat C (0.5 g) neutron scattering background Samples & capture yields M Mosconi, FZK

The n_TOF Collaboration n_TOF-04: 186 Os capture x-section MACS-30 BrB81438 ± 30 mb WiM82418 ± 16 mb n_TOF 414 ± 17 mb NB: the calculation is normalized NOT fitted to experimental data

Hauser-Feschbach theory: (statistical model) Neutron transmission coefficients, T n : from OMP calculations  -ray transmission coefficients, T   : from GDR (experimental parameters) Nuclear level densities: fixed at the neutron binding from exp n_TOF-04: 186 Os capture x-section

The n_TOF Collaborationwww.cern.ch/n_TOF n_TOF-04: 187 Os capture x-section MACS-30 BrB81919 ± 43 mb WiM82874 ± 28 mb n_TOF 969 ± 32 mb NB: the calculation is normalized NOT fitted to experimental data

Key quantity: cross sections Now4.5 Ga BANG! t0t0

The clock: from x-sections to age Now4.5 Gyr BANG! t0t0 e -  t r-process enrichment of 187 Re s-process synthesis of 186,187 Os

Laboratory cross sections & the clock Now4.5 Ga BANG! t0t0 R  = 0.43 ± 0.02 t 0 = 8.7 ± 0.4 Ga age: = 13.3 Ga

Stellar 187 Os(n  ) rate 187 Os at kT = 30 keV: P(gs) = 33% P(1st) = 47% P(all others) = 20% SE Woosley and WA Fowler, ApJ 233 (1979) 411 A.Include thermal population B.Include super-elastic scattering channels C.Nuclear structure effects (deformation)  n   * = SEF ∙ <  n,  

(n,n’) A neutron (inelastic) scattering experiment performed at FZK-Karlsruhe

(n,n’) + theory

MACS-30 BrB81438 ± 30 mb WiM82418 ± 16 mb n_TOF 414 ± 17 mb CC calculations including ground-state collective band in a deformed OMP n_TOF-04: 186 Os capture x-section

n_TOF-04: 187 Os capture x-section MACS-30 BrB81919 ± 43 mb WiM82874 ± 28 mb n_TOF 969 ± 32 mb CC calculations including ground-state collective band in a deformed OMP

Stellar enhancement factor  n   * = SEF ∙ <  n,  

Laboratory cross sections & the clock Now4.5 Ga BANG! t0t0 R  = 0.43 ± 0.02 t 0 = 8.7 ± 0.4 Ga age: = 13.3 Ga

Stellar cross sections & the clock Now4.5 Ga BANG! t0t0 R*  = 0.34 ± 0.02 t 0 = 10.7 ± 0.5 Ga age: = 15.3 Ga

Uncertainties

Abundances: 0.49 Ga x-section ratio*: 0.47 Ga Re-187 b-decay half-life: 0.29 Ga Total uncertainty : < 1 Ga Nuclear Data & Abundances

Summary Cosmological way (WMAP observation) Cosmological way (WMAP observation) Astronomical way (globular clusters) Nuclear way: Re/Os clock U/Th clock 13.7  0.2 Ga 14  1 Ga 15.3  0.8 ± 2 Ga(*) (*) 2 Ga uncertainty assigned to GCE modeling + astration(?) >13.4  0.9 ± 2.2 Ga A Frebel et al. ApJ 660 (2007) L117 CL Bennett et al., ApJS, 148 (2003) 1 G Imbriani et al., A&A 420 (2004) 625

Now4.5 Ga BANG! U/Th and Re/Os clocks: complementary GCE: independent Primordial yields: model-dependent GCE: dependent Yields: well determined

Let’s assume the age from WMAP is correct 13.7  0.2 Gyr

Reverse argument Now4.5 Gyr BANG! t0t0 assuming Age = 13.7 Gyr or t 0 = 9.2 Gyr

Cosmo-Chronology from others sources Day 1: 8 Gyr Day 2: 4 Gyr Day 3: 2 Gyr Day 4: 1 Gyr Day 5: 1/2 Gyr Day 6: 1/4 Gyr 15.8 Total: 15 ¾ = 15.8 Gyr

The End

Slides annex

Brancing(s) W W Re Os Re d Os W W W d W W h W d Re d Re Re h Re x10 9 a Re h Re h Re m Os d Os Os Os Os Os Os d Os Now4.5 Gyr BANG! The 185 W(n,  ) 186 W rate is needed The inverse 186 W(  n) 185 W cross section has been measured K. Sonnabend et al. ApJ 583 (2003), Impact on the age: negligible

Re/Os clock W W Re Os Re d Os W W W d W W h W d Re d Re Re h Re x10 9 a Re h Re h Re m Os d Os Os Os Os Os Os d Os s-only r-processr-only s-process Now4.5 Gyr BANG! ?

Nuclear & Astro issues The chemical evolution of the galaxy influences the history of the nucleosynthesis Re and Os abundances own uncertainties 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  -decay half-life of 187 Re is strongly dependent on temperature The stellar neutron capture cross section of 187 Os is influenced by the population of low-lying excited levels (the 1st excited states is at 9.8 keV) Branching(s) at 185 W and/or at 186 Re

Issue 1: 187 Re(  - ) decay 43.2  1.3 Gyr The  -decay half-life of 187 Re is   = 43.2  1.3 Gyr. Under stellar conditions, the 187 Os and 187 Re atoms can be partly or fully ionized. The  -decay rate can then proceed through a transition to bound-electronic states in 187 Os. The rate for this process can be orders of magnitude faster than the neutral-atom decay. The bound-state  -decay half-life of fully-ionized 187 Re has been GSI  2.0 yr The half-life of fully-ionized 187 Re turns out to be:   = 32.9  2.0 yr. (F. Bosch, et al., PRL 77 (1996) 5190) ≈1 Gyr Impact on the age: ≈ 1 Gyr

Stellar 187 Os(n  ) rate For example, in 187 Os at kT = 30 keV it is: P(gs) = 33% P(1st) = 47% P(all others) = 20%

The 186 Os(n,  ) cross section: theory Hauser-Feschbach theory: (statistical model) Neutron transmission coefficients, T n : from OMP calculations  -ray transmission coefficients, T   : from GDR (experimental parameters) Nuclear level densities: fixed at the neutron binding from exp All these parameters can be derived and fixed from the analysis of the experimental data at low-energy in the resolved resonance region

More on stellar rates