Neutron induced reactions & nuclear cosmo-chronology. chronology. A Mengoni IAEA Vienna/CERN, Geneva

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1 Neutron induced reactions & nuclear cosmo-chronology chronology A Mengoni IAEA Vienna/CERN, Geneva

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

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

4 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% ± 0.2 Gyr Source: CL Bennett et al., ApJS, 148 (2003) 1

5 Cosmological problems with time

6 Cosmological problems with time

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

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

9 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

10 Time? 4.5 Gyr Now Solar-system formation Galaxy formation BANG!

11 Re/Os clock BANG!? 4.5 Gyr Now Os Os Os d Os Os Os Os Os Os d Os Re Re d Re d Re Re h Re Re h Re h Re m 42.3x10 9 a W W W W W d W W h W d The β-decay half-life of 187 Re is 42.3 Gy Effect on the abundance of the decay daugther 187 Os

12 Nucleosynthesis Mixing (abundance distribution) ejection, explosion interstellar gas & dust condensation neutrons Nuclear reactions: energy generation nucleosynthesis

13 Re/Os clock BANG!? 4.5 Gyr Now s-only Os Os Os d Os Os Os Os Os Os d Os Re Re d Re d Re Re h Re Re h Re h Re m 42.3x10 9 a W W W W W d W W h W d s-process r-only r-process

14 The clock: from x-sections x to age BANG! t Gyr Now s-process synthesis of 186,187 Os Os Re c 187 = 187 Os Os c = Os 187 Os 187 σ (186) σ (187) Re Re 187 Os σ (186) σ (187) Os Os Re 186 e -Λt r-process enrichment of 187 Re Os Re c Λ λ 1 e λt Λ e e Λt = Λ t 1 λ = ln(2) τ β ( 187 Re)

15 The clock BANG! t Gyr Now Λ=0 Λ= assuming R σ = 0.5 age: = 13 Gyr key quantity : R σ σ (186) σ (187)

16 The n_tof facility at CERN somewhere around here The n_tof Collaboration

17 CERN accelerator Complex n_tof Linac(s): up to 50 MeV PSB: up to 1 GeV PS: up to 24 GeV The n_tof Collaboration

18 The n_tof facility at CERN The n_tof Collaboration

19 The n_tof facility at CERN Design: the n_tof tunnel & target+moderator assembly movie by V Vlachoudis (CERN) alberto.mengoni@cern.ch

20 The real world n_tof commissioned in sample

21 n_tof basic parameters proton beam momentum intensity (dedicated mode) repetition frequency pulse width 20 GeV/c 7 x protons/pulse 1 pulse/2.4s 6 ns (rms) n/p 300 lead target dimensions 80x80x60 cm 3 cooling & moderation material moderator thickness in the exit face neutron beam dimension in EAR-1 (capture mode) H 2 O 5 cm 2 cm (FWHM) The n_tof Collaboration

22 The real world n_tof beam characteristics: Neutron intensity and resolution in the full energy range 2 nd collimator φ=1.8 cm

23 The real world n_tof beam characteristics: energy resolution TAC 237 TAC 237 Np(n,γ) ) 2004 measurement

24 Capture 151 Sm 204,206,207,208 Pb, 209 Bi 232 Th 24,25,26 Mg 90,91,92,94,96 Zr, 93 Zr 139 La 186,187,188 Os 233,234 U 237 Np, 240 Pu, 243 Am n_tof experiments Measurements of neutron cross sections relevant for Nuclear Waste Transmutation and related Nuclear Technologies Cross sections relevant for Nuclear Astrophysics Fission 233,234,235,236,238 U Neutrons as probes for fundamental Nuclear Physics 232 Th 209 Bi 237 Np 241,243 Am, 245 Cm The n_tof Collaboration

25 The n_tof Collaboration Os measurements setup γ-ray detection: C 6 D 6 scintillators Sample changer Pulse height weighting technique Correction of the γ-response by weighting function to make the detector efficiency proportional to γ-ray energy Neutron flux monitor Silicon detectors viewing a thin 6 LiF foil Neutron beam C 6 D 6 C 6 D 6

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

27 n_tof-04: : preliminary results BrB81 MACS ± 30 mb WiM82 n_tof 418 ± 16 mb 384 ± 17 mb The n_tof Collaboration

28 n_tof-04: : preliminary results BrB81 MACS ± 28 mb WiM82 n_tof 874 ± 28 mb 940 ± 18 mb The n_tof Collaboration

29 Laboratory cross sections & the clock BANG! t Gyr Now R σ = 0.41±0.02 age: = 15 Gyr

30 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 β-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 The chemical evolution of the galaxy influences the history of the nucleosynthesis Re and Os abundances own uncertainties alberto.mengoni@cern.ch

31 187 Re( Issue 1: 187 Re(β - ) decay The β-decay half-life of 187 Re is τ β = 43.2 ± 1.3 Gyr. Under stellar conditions, the 187 Os and 187 Re atoms can be partly or fully ionized. The β-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 β-decay half-life of fully-ionized 187 Re has been GSI. The half-life of fully-ionized 187 Re turns out to be: τ β = 32.9 ± 2.00 yr. (F. Bosch, et al., PRL 77 (1996) 5190) Impact on the age: 1 Gyr alberto.mengoni@cern.ch

32 Stellar 187 Os(n,γ,γ)) rate For example, in 187 Os at kt = 30 kev it is: P(gs) = 33% P(1st) = 47% P(all others) = 20%

33 Thermal population (2J + 1) e Ek / kt k P ( Ek ) = Em / kt (2J m + 1) e m For example, in 187 Os at kt = 30 kev it is: P(gs) = 33% P(1st) = 47% P(all others) = 20% alberto.mengoni@cern.ch

34 The he Os(n,γ) ) cross section: theory Hauser-Feschbach theory: (statistical model) σ Neutron transmission coefficients, T n : from OMP calculations γ-ray transmission coefficients, T γ : from GDR (experimental parameters) π Nuclear level densities: fixed at the neutron binding from <D> exp n, ls γ, J ls n, γ ( En) = g J W 2 J k γ, n Jπ Tn, ls + Tn ', ls + Tγ, J ls ls T T All these parameters can be derived and fixed from the analysis of the experimental data at low-energy in the resolved resonance region

35 Stellar 187 Os(n,γ,γ)) rate

36 More on stellar rates

37 (n,n ) A neutron (inelastic) scattering experiment performed at FZK-Karlsruhe Karlsruhe alberto.mengoni@cern.ch

38 (n,n )) + theory needed alberto.mengoni@cern.ch

39 Brancing(s) BANG! 4.5 Gyr Now Os Os Os d Os Os Os Os Os Os d Os Re Re d Re d Re Re h Re Re h Re h Re m 42.3x10 9 a W W W W W d W W h W d The 185 W(n,γ) 186 W rate is needed The inverse 186 W(γ,n) 185 W cross section has been measured K. Sonnabend et al. ApJ 583 (2003), Impact on the age: negligible

40 Laboratory cross sections & the clock BANG! t Gyr Now R σ = 0.41±0.02 age: = 15 Gyr

41 Stellar cross sections & the clock BANG! t Gyr Now R * σ = 0.35±0.02 age: =16.5 Gyr

42 Let s s assume the age from WMAP is correct 13.7 ± 0.2 Gyr

43 Reverse argument BANG! t Gyr Now assuming Age = 13.7 Gyr or t 0 = 9.2 Gyr

44 Nucleosynthesis: the s-process s & the r-process r residuals N r = N solar - -N N s

45 The Th/U clock 14.5 ± Gyr Source: Dauphas, Nature 435 (2005) 1203

46 Th/U and Re/Os clocks: complementary BANG! 4.5 Gyr Now GCE : independent Primordial yields : model-dependent GCE Yield production : dependent : well determined

47 Summary Cosmological way Astronomical way 13.9 ± 1.5 Gyr or 13.7 ± 0.2 Gyr > 11.2 Gyr or 14 ± 2 Gyr Nuclear way: Re/Os clock Th/U clock 16.5 ± 2Gyr(*) 14.5 ± 2.5 Gyr (*) preliminary

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

49 The End