1 / 28

N eutron reactions & nuclear cosmo-chronology

N eutron reactions & nuclear cosmo-chronology. Re/Os clock how does it work? recent experimental improvements preliminary results. M. Mosconi, A. Mengoni, M. Heil, F. K. and the n _TOF collaboration. Cosmic A ges.

quentin-christensen
Download Presentation

N eutron reactions & nuclear cosmo-chronology

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Neutron reactions & nuclear cosmo-chronology • Re/Os clock • how does it work? • recent experimental improvements • preliminary results M. Mosconi, A. Mengoni, M. Heil, F. K. and the n_TOF collaboration

  2. Cosmic Ages • Cosmological way based on the Hubble time (“expansion age”) • Astronomical way based on observations of globular clusters • Nuclear way based on abundances of long-lived radioactive species

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

  4. Re/Os clock BANG! ? 4.5 Gyr Now solar system galaxies 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 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 W The b-decay half-life of 187Re is 42.3 Gy Effect on the abundance of the decay daugther 187Os

  5. Re/Os production σNs(186Os) =σNs(187Os) 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 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 W s-process r-only r-process

  6. BANG! t0 4.5 Gyr Now The clock: from x-sections to age • 187Os: s-process and • radiogenic component • e-Lt : r-process • enrichment of 187Re uniform synthesis: L →0 sudden synthesis: L→ ∞

  7. -ray detection: C6D6 scintillators Sample changer C6D6 C6D6 Neutron beam Os (n, g) cross sections measured at n_TOF/CERN • 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 The n_TOF Collaboration

  8. (n,g) cross sections

  9. clocks need adjustment corrections due to nuclear & stellar effects

  10. Nuclear & Astro issues the use of the Re/Os abundance pair as a clock has to address several complications: • The b-decay half-life of 187Re is strongly dependent on • temperature • The stellar (n, γ) cross section of 187Os is influenced by low-lying • excited levels (strong population of1st state at 9.8 keV, • competition by inelastic channels) • Branching(s) at 185W and/or at 186Re • Destruction of 187Re in later stars (Astration) • The chemical evolution of the galaxy was not uniform • Re and Os abundance uncertainties

  11. Issue 1: 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 @ 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 (by astration): ≈1 Gyr alberto.mengoni@cern.ch

  12. Issue 2: Thermal population in 187Os at kT = 30 keV: P(gs) = 33% P(1st) = 47% P(all others) = 20% alberto.mengoni@cern.ch

  13. Stellar186Os(n,g) cross section: theory Hauser-Feshbach 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 <D>exp Stellar correction factor Fσ = f186 / f187 All these parameters can be derived and fixed from the analysis of the experimental data at low-energy

  14. More stellar rates: competition by inelastic channels

  15. inelastic scattering on 187Os • samples: • 187Os • 188Os (pure elastic) • empty can

  16. scattering yields

  17. CROSS SECTION (barn) NEUTRON ENERGY (MeV) alberto.mengoni@cern.ch inelastic scattering on 187Os

  18. Issue 3: Branching(s) 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 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 W 185W(n,g)186W rate is needed inverse 186W(g,n)185W cross section measured K. Sonnabend et al. ApJ 583 (2003), 506-513. Impact on the age: negligible

  19. BANG! t0 4.5 Gyr Now Stellar cross sections & the clock Age: 14.9 Gyr 8.5 10.4

  20. Th/U and Re/Os clocks: complementary GCE : independent primordial yields : model-dependent GCE : dependent production yields : well determined

  21. Summary • Cosmological way • Astronomical way • Nuclear way 13.9  1.5 Gyr or 13.7  0.2 Gyr > 11.2 Gyr or 14  2 Gyr 15  2 Gyr or 14.5  2.5 Gyr

  22. The End Uppsala, Sept. 2002

  23. 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 Gyr (*) HST Key Project see: WL Friedman et al., ApJ 553, (2001) 47

  24. Age from WMAP observations fluctuations of the cosmic microwave background depend on the current density of the universe, the composition of the universe, and its expansion rate. WMAP has determined these parameters with an accuracy of better than 5%. Thus, the WMAP data yield the expansion age of the universe to better than 5%. When combined with complimentary observations from other CMB experiments (ACBAR and CBI), the age of the universe can be derived with an accuracy close to 1%. 13.7  0.2 Gyr Source: CL Bennett et al., ApJS 148 (2003) 1

  25. Age from globular clusters The age derived from observationof the luminosity-color relation of stars in globular clusters

  26. Age from globular clusters The age derived from observationof 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

  27. Cosmological “problems” with time

  28. n_TOF basic parameters The n_TOF Collaboration

More Related