Nucleosintesi oltre il picco del Fe. Misure di ca3ura neutronica di interesse Astrofisico

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1 Nucleosintesi oltre il picco del Fe. Misure di ca3ura neutronica di interesse Astrofisico

2 Introduc,on: Nuclear Astrophysics the majority of the chemical elements in the universe is produced through nuclear reac6ons in the hot interiors of the stars

3 Introduc,on: Nuclear Astrophysics SCIENCE volume 225 (1984) 922

Abundances beyond Fe ashes of stellar burning n um b e r fra c tio n 10 0 10-1 10-2 10-3 10-4 10-5 10-6 10-7 10-8 10-9 10-10 10-11 10-12 10-13 Gap B,Be,Li α-nuclei 12 C, 16 O, 20 Ne, 24 Mg,.

4 Abundances beyond Fe ashes of stellar burning n um b e r fra c tio n Gap B,Be,Li α-nuclei 12 C, 16 O, 20 Ne, 24 Mg,. 40 Ca Fe peak Elements heavier than Fe are the result of neutron capture processes NEUTRONS r-process peaks (nuclear shell closures) s-process peaks (nuclear shell closures) Au Pb H C 10 Fe 1 Au Th, U mass number

Nucleosynthesis s-process lifehme 10 4 years n n 10 8 neutron/cm 3 r-process lifehme µs n n 10 22 neutron/cm 3 β-decay lifehme: few hours to some months The canonical s-process Cu 62 Cu 9.

5 Nucleosynthesis s-process lifehme 10 4 years n n 10 8 neutron/cm 3 r-process lifehme µs n n neutron/cm 3 β-decay lifehme: few hours to some months The canonical s-process Cu 62 Cu 9.74 m 63 Cu Cu 12.7 h neutrons Ni 60 Ni Ni Ni Ni 100 a Co 58 Co d 59 Co Co a 61 Co 1.65 h Fe 56 Fe Fe Fe Fe d 60 Fe a 61 Fe 6 m

7 processo-p La maggiore parte degli elemenh più pesanh del Fe vengono sintehzzah tramite ca3ura neutronica. Ci sono, comunque, 35 elemenh in cui il numero di protoni è maggiore del numero di neutroni

8 processo-p Le abbondanze degli p-isotopi è molto bassa rispe3o agli altri isotopi (1-0.1%) ecce3o per gli isotopi 92,94 Mo e 96 Ru. Si ipohzza lche gli isotopi s e r sono uhlizzah come nuclei seme per il processi-p. Molto probabilmente il processo-p ha luogo negli strah O/Ne delle supernove di Hpo II, durante la fase esplosiva

9 s-only & r-only istopes

10 Stellar Models: local equilibrium approximation σ A N A = cost

11 Stellar Models: Standard stellar model f the frachon of 56 Fe seed nuclei that are subjected to an exposure of neutron τ neutron exposure proporhonal to the Hmeintegrated neutron flux Main component: A = f 0,06% τ 0 0,3 mb -1 à n c = 10 Weak component: A < 90 f 1,6% τ 0 0,07 mb -1 à n c = 3

12 Stellar Models: Standard stellar model f the frachon of 56 Fe seed nuclei that are subjected to an exposure of neutron τ neutron exposure proporhonal to the Hmeintegrated neutron flux Main component: A = f 0,06% τ 0 0,3 mb -1 à n c = 10 Weak component: A < 90 f 1,6% τ 0 0,07 mb -1 à n c = 3

13 Stellar Models: Standard stellar model

s-process stellar sites Low mass Asympotic Giant Branch (AGB) M 1.

14 s-process stellar sites Low mass Asympotic Giant Branch (AGB) M M 13 C(α,n) 16 O T ~ 8 kev N n < 10 7 n/cm 3 22 Ne(α,n) 25 Mg T ~ 23 kev N n ~ n/cm 3 Massive stars M M 22 Ne(α,n) 25 Mg In core He-burning T ~ 26 kev N n ~ 10 6 n/cm 3 In core C-burnig T ~ 90 kev N n ~10 11 n/cm 3

15 Asympotic Giant Branch (AGB) False-color picture of CO molecules tracing material around the AGB star TT-Cygni

16 Asympotic Giant Branch (AGB)

17 The TP Stellar Model SchemaHc out-of-scale picture of the structure of AGB stars.

18 neutron density Hme neutron density 10-4 Hme - C proton diffusion 13 C(α,n) 16 O 22 Ne(α,n) 25 Mg

20 Neutron in laboratory Thermal reactors almost monoenergehc neutron, very high flux MonoenergeHc neutron Based on reachon (p,n) or (d,n) d(d,n), t(p,n), 7 Li(p,n), 9 Be(p,n) 7 Li(p,n) 7 Be Time of Flight facilihes wide neutron energy spectrum High energy resoluhon

21 Time of Flight facilities Photoproduc,on (γ,n): Heavy metal targets are bombarded by electron beams of typical MeV. The resulhng neutron spectra contains all energies from thermal to near the inihal γ energy. ORELA, GELINA and RPI

22 Time of Flight facilities Spalla,on: neutron are are ejected from a heavy target due to the impact of charged parhcles as protons. It provides the most prolific source of fast neutrons. n_tof, LANCSE, ISIS

23 Time of Flight Technique SpallaHon target γ-ray detector Proton beam sample t start (neutron produchon) flight path length L tof = t stop t star t stop (γ-ray detechon) E n = 72,2977 L tof 2 E School on Nuclear Data Measurements for Science and ApplicaHons, Trieste 19/06/2015 giuseppe.tagliente@ba.infn.it n 2 1 = m c 1 n 2 L tof c

24 ToF Technique (Flux & Energy resolution) School on Nuclear Data Measurements for Science and ApplicaHons, Trieste 19/06/2015

25 The n_tof facility at at CERN CERN somewhere around here

The CERN n_tof Facility n_tof features broad neutron energy

Spallation Target n-beam excellent Neutron energy Beam

angle low neutron sensitivity low backgrounds Proton Beam

astrophysics neutron capture cross sections for intensity

protons/pulse 1 MeV) small capture cross sections repetition

4s small pulse sample width quantities (isotopically 6 ns (rms)

4 samples GeV (low intrinsic background) lead target dimensions

26 The CERN n_tof Facility n_tof features broad neutron energy range n_tof 200m Tunnel high instantaneous flux Sample Pb Spallation Target n-beam excellent Neutron energy Beam resolution 10 o prod. angle low neutron sensitivity low backgrounds Proton Beam 20GeV/c 7x10 12 ppp proton beam momentum 20 GeV/c Use in astrophysics neutron capture cross sections for intensity (dedicated 7 x 10 s-process 12 mode) studies (1 ev protons/pulse 1 MeV) small capture cross sections repetition frequency 1 pulse/2.4s small pulse sample width quantities (isotopically 6 ns (rms) enriched n/p samples) 300 Booster radioactive 1.4 samples GeV (low intrinsic background) lead target dimensions 80x80x60 cm 3 cooling & moderation H 2 O material resonance dominated cross sections moderator thickness in 5 cm accurate the exit Linac cross face section measurements PS 20GeV even for 50 large MeV σ el /σ capture

27 GELINA Facility

28 GELINA Facility

29 Flux Integrated neutron flux Istantaneous neutron fllux

30 Resolution

31 n_tof GELINA Resolution

32 Neutron Capture E n E * = S n + A A +1 E n n + A X E n D =10 ev σ E * = γ E j j S n =10 MeV D =100 kev A+1 X

33 Neutron Capture: Cross Section E * = S n + A A +1 E n σ c * ( E n ) = g π 2 k n Γ n Γ ( E n E ) 2 + # Γ 0 % $ 2 2 & ( ' g spin factor k n neutron wave number Γ = Γ Γ total n + Γ width g + Γ f + Γ n neutron sca3ering width Total radiahve area:

34 Neutron Capture: Resonances Resonance Region: Γ < D Resolved Resonance Region (RRR): DetecHon resoluhon < D Unresolved Resonance Region (URR): DetecHon resoluhon > D

35 Neutron Capture Gamma-Ray Detection E x Activation - cross sections integrated over known neutron spectrum - applicable to some nuclei only - no time of flight Level population spectroscopy - applicable to some nuclei only - feasible with HPGe detectors, Total energy detection - ε c E x, requires weighting function - neutron insensitive detector C 6 D 6 detector used at GELINA and n_tof A+1 X radioactive Total absorption detection - requires Ω = 4π, efficiency 100% - capture/fission discrimination possible BaF 2 detector used at n_tof

36 (n,γ) Total energy detec,on Improvements in the Experimental Setup & Data Analysis Lowest neutron sensihvity No neutron background correchons! (n,γ) Impossibile visualizzare l'immagine. La memoria del computer potrebbe essere insufficiente per aprire l'immagine oppure l'immagine potrebbe essere danneggiata. Riavviare il computer e aprire di nuovo il file. Se viene visualizzata di nuovo la x rossa, potrebbe essere necessario eliminare l'immagine e inserirla di nuovo.

(n,n) (n,γ) Impossibile visualizzare l'immagine.

oppure l'immagine potrebbe essere danneggiata.

37 (n,γ) Total energy detec,on Improvements in the Experimental Setup & Data Analysis Lowest neutron sensihvity No neutron background correchons! (n,n) (n,γ) Impossibile visualizzare l'immagine. La memoria del computer potrebbe essere insufficiente per aprire l'immagine oppure l'immagine potrebbe essere danneggiata. Riavviare il computer e aprire di nuovo il file. Se viene visualizzata di nuovo la x rossa, potrebbe essere necessario eliminare l'immagine e inserirla di nuovo.

38 Experimental details: Yield Yield: The fraction of incident neutrons undergoing a (n,γ) reaction in the sample n γ The relahon between capture Yield and cross sechon is given by: A+1 X

39 Experimental details: PHWT Accuracy of the Pulse Height WeighHng Technique? (used to count properly capture cascades) Use of detailed MC simulahons of detector response with the full setup W irij = i E j 56 Fe + Use of the nuclear stahshcal model to make systemahc correchons accuracy < 2%

40 Experimental details: Sample

41 Experimental details: Area analysis Due to the instrumental limitahons and Doppler effect the effechve observable is: The area of a resonance. The area below a resonance is independent of the experimental resoluhon and Doppler effect

42 Experimental details: Area analysis

43 Experimental details: Normalization 197 Au

44 Maxwellian Averaged Cross Sections:MACS Neutrons produced in the stars are quickly thermalised M-B distribu,on 13 C(α,n) 16 O 22 Ne(α,n) 25 Mg

45 Maxwellian Averaged Cross Sections:MACS Neutrons produced in the stars are quickly thermalised M-B distribu,on 13 C(α,n) 16 O

46 Data analysis: Main steps Energy CalibraHon ( 137 Cs, 60 Co,Pu/C) Noise rejechon by suitable choice of cuts and threshold Efficiency correchon à PHWT Background eshmahon Flux normalizahon

47 The Zr case

48 Nucleus N ʘ Normalized to N(Si)=10 6 atoms N s / N ʘ % 90 Zr Zr Zr Zr Zr

49 Zr in SiC grains

50 MACS: Experimental energy ranges 92 Zr Energy range investigated(kev) n_tof Yield 90 Zr Zr Zr Zr E n (ev) 94 Zr Zr Yield The n_tof data have to be complemented with the library Jendl 3.3 and ENDF IV E n (ev)

51 30 kev MACS in mbarn Isotope KaDoNiS N_TOF MOST 90 Zr 21 ± 2 91 Zr 60 ± 8 92 Zr 34 ± 6 93 Zr 95 ± Zr 26 ± 1 95 Zr Zr 10.7 ± ± ± 4 38 ± 3 95.± ± ± ±

52 Astrophysical implication: Abundances Nucleus N ʘ N s / N ʘ % N s / N ʘ % Normalized to Old MACS MACS from this N(Si)=10 6 atoms work 90 Zr Zr Zr Zr Zr

53 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

54 The nuclear way TradiHonal 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

55 Os measurements Long β-decay half-life of 187 Re s-only 186 Os and 187 Os

56 Os: results BrB81 MACS ± 30 mb WiM82 n_tof 418 ± 16 mb 384 ± 17 mb M. Mosconi et al.,phys. Rev. C

57 Os: results BrB81 MACS ± 28 mb WiM82 n_tof 874 ± 28 mb 940 ± 18 mb K. Fujii et al.,phys. Rev. C The n_tof Collaboration

58 Os: implications Cosmological way Astronomical way 13.7 ± 0.2 Gyr 14 ± 2 Gyr Nuclear way: Re/Os clock 14.9 ± 2 Gyr(*) Th/U clock 14.5 ± 2.5 Gyr (*) 0.4 Gyr uncertainty due to x-sechons

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

Neutron induced reactions & nuclear cosmo-chronology chronology A Mengoni IAEA Vienna/CERN, Geneva Ages Cosmological way based on the Hubble time definition ( expansion age ) Astronomical way based on