Ne(alpha,n) revisited

Transcription

1 22 Ne(alpha,n) revisited Joachim Görres University of Notre Dame & JINA Ph.D. Thesis of Rashi Talwar

2 Neutron sources for the s-process Main Component A>100 Weak Component A< 100 low mass AGB stars T= 0.1 GK N n ~ 10 7 /cm -3 s-process at kt=8 kev Time scale: a few 10,000 years 13 C(α,n) & 22 Ne(α,n) core He burning in massive stars T=0.3 GK N n ~ 10 6 /cm -3 s-process at kt=25 KeV Time scale: Last few 10,000 years 22 Ne(α,n) Shell C burning in massive stars T=1 GK N n ~ up to /cm -3 s-process at kt=90 KeV Time scale: 1 year (not the typical s-process) 22 Ne(α,n)

3 Core Helium Burning weak component of s-process A<100 Hubble Space Telescope Betelgeuse

4 Simple 1-Zone Model 12.6 million years

5 Shell Carbon Burning burns on the ashes of He-Burning 12 C, 16 O, 20,22 Ne and 25,26 Mg main energy source: 12 C+ 12 C 12 C+ 12 C 20 Ne+α 23 Na+p! p/α-ratio main neutron source: 22 Ne(α,n) possible neutron source at end of burning: 25,26 Mg(α,n) well known at 1GK residual from He burning how much is left at end of He burning? Small production branch: 20 Ne(p,γ) 21 Na(β + ) 21 Ne(p,γ) 22 Na(β + ) 22 Ne poison: 22 Ne(p,γ) Most abundant isotopes at end of burning: 16 O, 20 Ne, 23 Na and 24 Mg

6 s-process (Main Component A>100) TP-AGB Stars Large Mass Loss Chemical Evolution meteorite inclusions Fluorine Lines Observed On Surface of AGB Star 29,30 Si isotope ratios

7 Reaction Rates non-resonant reaction S(E) constant resonant reaction S(E) Breit-Wigner Resonance Strength:! Gamow Peak Γ p (E<<E C ) ~ exp(-k E R -1/2 )!

8 Indirect approach ωγ = need to know: Spin and parity (natural J π? ω) excitation energy (see above) Γ α or S α from transfer reaction Γ n /Γ γ if both channels are open Γ α Γ n ω Γ α +Γ γ +Γ n ω Γ α = ω S α Γ sp α assuming Γ α,γ γ/n << Γ n/γ alpha-transfer reaction e.g. ( 6 Li,d) S α S α and Γ α sp are model dependent if Γ α is known, only relative value are needed! (see example later on)

9 22 Ne(α,n) neutron source competition between (α,n) & (α,γ) reaction channels NO (α,γ) below 832 kev resonance!! Q(α,n) = MeV 630 kev J π =1 - resonance?? Jaeger et al., PRL 87, (2001) present upper limit: < 60 nev

10 25 Mg+n: new n-tof data 20 kev average spacing of states Γ n /Γ γ : from 1000 to 1/ Below n-threshold: no widths and nearly no spins are known 234±2 kev = last known resonance at 831 kev Massimi et al 2012

11 Experiments at RCNP Osaka aims: 1) unique spin assignments 2) alpha spectroscopic factors Cyclotrons and spectrometer Total mass of 3500 tons iron Power consumption of 2 MW Grand Raiden Spectrometer High resolving power p/δp = Focal plane detectors: 2 Multi Wire Drift Chambers: x,y (0.25mm) 2 Plastic Scintillators: TOF, PID Last quadrupole triplet of beam line

12 First step: 26 Mg(α,α 206 MeV Going to 206 MeV to learn about 206 kev 18 out of known 92 states α- unbound n-unbound (α,α ) populates preferentially natural parity states no unnatural parity state observed below α-threshold

13 Second step: 22 Ne( 6 80 MeV n-unbound α- unbound

14 Result: n-threshold lowest known resonance calculated from Γ α calculated from ωγ experimental resonance strengths

15 Result: n-threshold ωγ αγ = 0.5 μev! within experimental reach adopted Γ n / Γ 0.1 upper limit from Jaeger

16 Reaction Rates: 22 Ne(α,γ) ABG temperature 22 Ne(α,n) (α,n)/(α,γ) General Impact: reduction of s-process synthesis but significant uncertainties remain

17 ABG Nucleosynthesis: Massive Stars (25 solar mass) Thanks to: S. Bisterzo M. Pignatari

18 Low Energy Alpha Capture Notre Dame St. George Recoil Separator experiments are time consuming ECR in terminal knowledge from indirect search are very helpful single ended 5 MV vertical accelerator

19 Osaka Minoh Waterfall R. Talwar, 1, T. Adachi, 2 G. P. A. Berg, 1 L. Bin, 3 S. Bisterzo, 4, 5 M. Couder, 1 R. J. deboer, 1 X. Fang, 1 H. Fujita, 2, 3 Y. Fujita, 2, 3 J. Görres, 1 K. Hatanaka, 2 T. Itoh, 3 T. Kadoya, 6 A. Long, 1 K. Miki, 2 D. Patel, 1 M. Pignatari, 7 Y. Shimbara, 8 A. Tamii, 2 M. Wiescher, 1 T. Yamamoto, 2 and M. Yosoi 2 1 Department of Physics, University of Notre Dame, Notre Dame, Indiana USA 2 Research Center for Nuclear Physics, Osaka University, Ibaraki, Osaka Japan 3 Department of Physics, Osaka University, Toyonaka, Osaka Japan 4 Department of Physics, University of Turin, Italy 5 INAF - Astrophysical Observatory of Turin, Italy 6 Department of Physics, Kyoto University, Sakyo-ku, Kyoto Japan 7 Konkoly Observatory, Research Center for Astronomy and Earth Sciences, Hungarian Academy of Sciences 8 CYRIC, Tohoku University, Aramaki, Aoba, Sendai, Japan

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