Doppler Shift Attenuation Method: The experimental setup at the MLL and the lifetime measurement of the 1 st excited state in 31 S

Transcription

1 Doppler Shift Attenuation Method: The experimental setup at the MLL and the lifetime measurement of the 1 st excited state in 31 S Clemens Herlitzius TU München (E12) Prof. Shawn Bishop Clemens Herlitzius, TU München

2 Doppler Shift Attenuation Method: The experimental setup at the MLL and the lifetime measurement of the 1 st excited state in 31 S 1. Motivation 2. Method, setup and experiment 3. Analysis: simulation and line shape calculation 4. Results and conclusion Clemens Herlitzius, TU München

3 1. Motivation H-rich material accumulates on surface of white dwarf (C/O or O/Ne core) energy production via pp-chain (e~t 4 ) (Credit: NASA/CXC/M.Weiss) classical nova illustration CNO sets in (e~t 17 ) pressure overcomes degeneracy ejection of the envelope proton capture up to A=40 competition: p-capture / b decay Clemens Herlitzius, TU München

4 1. Motivation (p,g) vs. b decay reaction rates

5 1. Thermonuclear Resonant Reaction Rate σv σv 1/ 2 8 = σ πµ = ωγi = 3/ π µ kt E kt 3/ 2 ( kt ) E ( E)exp de resonance strength ( 2 + 1)( 2 + 1) J p 2J i = g(1 Bp ) Bp τi = g(1 Bγ ) Bγ τi i + 1 J X 0 E ωγ i exp kt ΓpΓγ Γp + Γγ i life time µ - reduced mass J i,j p,j X Spins of: resonance state/ projectile/ target T temperature E i relative energy of state (to Q) Γ p, Γ γ partial width of p- / γ- decay B p = Γ p / Γ branching ratio

6 2. Lifetime measurements 10 fs <τ < 1ps 1 ps <τ < 100ps 100ps <τ population of the state t = 0s Doppler Shift Attenuation Method Recoil-Distance Doppler Shift Method Fast electronic timing: Start-stop measurements Counting measurements time

7 2. Doppler Shift Attenuation Method Setup: thick target ion beam HPGe at 0 β ( t) v = ion c ( t) E obs γ = E 0 γ 2 β v 1 β cosα 1 << c E 0 γ ( 1+ β cosα )

8 2. Doppler Shift Attenuation Method Setup: thick target ion beam HPGe at 0 β ( t) v = ion c ( t) E obs γ = E 0 γ 2 β v 1 β cosα 1 << c E 0 γ ( 1+ β cosα )

9 2. DSAM setup at the MLL Setup: ion beam thick target HPGe at 0 Reaction: Beam: Target: 32 S( 3 He, 4 He) 31 S* 32 S at 85 MeV 3 He implanted Au (stops 31 S) HPGe at 90 detector Recoils: 31 S with E ex = 1.25 MeV 4 He for PID & coinc.

10 2. Commissioning experiment: 32 S( 3 He, 4 He) 31 S* 3 rd Reaction: Beam: 32 S( 3 He, 4 He) 31 S* 32 S at 85 MeV 2 nd Low trans. strength: 2 nd 1 st, 3 rd 1 st 1 st 31 S (Nudat, Dec. 2012) High trans. strength: 4 th 1 st, 5 th 1 st levels nicely separated Detector response function known known lifetime no feeding

11 2. DSAM setup at the MLL Condensation tube Cooled target ladder rotated by θ=54 beam Si detectors at θ=39 HPGe

12 2. DSAM setup at the MLL

13 2. DSAM setup at the MLL Features: beam diagnostic mini cup with suppressing voltage optional collimator in Cu tube CsI crystal for visual diagnostic

14 2. DSAM setup at the MLL Features: target ladder 5+2 positions linear translator rotation angle 54 coolable to T = -100 C

15 2. DSAM setup at the MLL Features: Silicon telescopes E/E (50μm/1mm) for PID polar angles: 25 < < 60 distance: 32 mm mm 2 position sensitive

16 2. DSAM setup at the MLL

17 Technische Universität München

18 3. Analysis: Simulation and lineshape calculation Three major analysis steps: 3.1 Proceeding the acquired data of the experiment calibration background reduction in the E g spectra 3.2 Simulation of the Stopping process: Geant4 3.3 Line shape analysis: Fitting with APCAD

19 3.1 Proceeding the experimental data Three major analysis steps: 3.1 Proceeding the acquired data of the experiment calibration background reduction in the E g spectra 3.2 Simulation of the Stopping process: Geant4 3.3 Line shape analysis: Fitting with APCAD

20 3.1 Proceeding the experimental data Raw data: 90 ~90 hours (with 2.3 pna) 32 S 3 He + Au target ~30 hours (with 6.3 pna) 32 S Au-only target global trigger on charged particles in the Si telescopes

21 3.1 Proceeding the experimental data Proceeding: 90 Particle identification in the de/e Si telescopes Background subtraction

22 3.1 E γ background subtraction

23 3.1 E γ spectra for lineshape analysis HPGe 110 HPGe 90 HPGe 0

24 3.2 Simulation of the stopping process: Geant4 Three major analysis steps: 3.1 Proceeding the acquired data of the experiment calibration background reduction in the E g spectra 3.2 Simulation of the Stopping process: Geant4 3.3 Line shape analysis: Fitting with APCAD

25 3.2 Simulation of the stopping process: Geant4 Monte Carlo simulation: beam: - energy - elliptical spot target: - 1 st layer: 3 He in gold - 2 nd layer: Au only - rotation transfer reaction

26 3.2 Simulation of the stopping process: Geant4 Output file: if transfer reaction occurs: - save 31 S vector - save 4 He vector for each time step

27 3.1 Proceeding the experimental data Three major analysis steps: 3.1 Proceeding the acquired data of the experiment calibration background reduction in the E g spectra 3.2 Simulation of the Stopping process: Geant4 3.3 Line shape analysis: Fitting with APCAD

28 3.3 Line shape analysis: APCAD Analysis Program for Continuous Angle DSAM Christian Stahl, TU Darmstadt, AG Pietralla Idea: 1. Simulate stopping process v ion (t) 2. Determine observed Doppler Shift distribution m det (t) 3. Assume lifetime and covolve it with m det (t) 4. Fit experimental line shape by varying assumed lifetime

29 3.3 Fitting the experimental data HPGe detector at = 110

30 3.3 Fitting the experimental data HPGe detector at = 90

31 3.3 Fitting the experimental data HPGe detector at = 0

32 3.3 Fitting the experimental data = 110 = 90 = 0 simultaneous fit of all angles τ = ( ± 19 Error )fs 964 stat ± syst preliminary

33 4. Results and error discussion 16% 2.4% geometry of the setup preliminary stopping power

34 4. Conclusion and outlook Successful commissioning of the new DSAM setup at the MLL 1 st excited state in 31 S: τ = 964 ± 19 stat 311 ± 89 syst fs The error is dominated by systematic uncertainties of the stopping power Outlook: Neutron detector for access to additional reaction channels DAQ: digitizer Ice target (hydrogen target) MLL GSI

35 5. Additional slides

36 5.1 previous measurements: Engmann et al τ 720fs Δτ 180fs Δτ stat Δτ syst 20% 32 S( 3 He, 4 He) 31 S, 7MeV, direct kinematic Doornenbal et al A Doornenbal et al B 1.2ps 3.2 ps 0.7ps 4.8ps +1.3 ps -0.9 ps 5.2ps 2-step fragmentation, 40 Ca+ 9 Be-> 37 Ca 37 Ca+ 9 Be-> 31 S Miniball, Tonev et al fs 24fs 10% Fusion evaporation, 20 Ne+ 12 C-> 31 S+n

37 5.2 feeding High trans strength: 4 th 1 st, 5 th 1 st γγ coincidences

38 5.2 Energy of 4 He particles

39 5.3 Fusion evaporation 32 S + 12 C X + 4 He 39 K 36 Ar

40 5.3 Fusion evaporation E γ

41 2. Recoil-Distance Doppler Shift Method Setup: thin target stopper ion beam HPGe at 0 β = 0 v flight /c, t < t, t > t flight flight d t flight d = β c flight E obs γ = E 0 γ 2 β v 1 β cosα 1 << c E 0 γ ( 1+ β cosα ) N shifted t flight = t= 0 N all t exp τ

42 2. Recoil-Distance Doppler Shift Method Setup: thin target stopper ion beam HPGe at 0 β = 0 v flight /c, t < t, t > t flight flight d t flight d = β c flight E obs γ = E 0 γ 2 β v 1 β cosα 1 << c E 0 γ ( 1+ β cosα ) N shifted t flight = t= 0 N all t exp τ

43 3.1 TDC gate TDC data 90 common start: trigger Si telescopes individual stop: - delayed Si telescopes

44 3.1 charged particle identification PID gate with E/E Si telescopes two groups: protons 3 He, 4 He 3 He and 4 He can not be separated

45 3.1 charged particle identification PID gate with E/E Si telescopes effective thickness d eff of E depends on (θ,φ) d eff = d p n norm

46 3.1 charged particle identification

47 3.1 PID α gate on E γ spectra TDC gated TDC & α- PID gated

48 3.3 Projection on a HPGe detector Observed Doppler shift is determined by the ion s velocity component in the direction of observation E obs γ = E E 0 γ 0 γ E m = E 2 1 β 1 β cosα ( 1+ β cosα ) 0 γ obs γ ( m) E obs = E 0 1+ γ γ 2 1 β 1= 1 1 β cosα

49 3.3 Projection on a HPGe detector 0

50 3.3 Doppler Shift distribution: projection 0

51 3.3 Line shape modeling Technische Universität München

52 3.3 Line shape modeling Technische Universität München

53 Technische Universität München 3.3 Line shape modeling

54 3.3 Physical energy in the HPGe ( m) E obs = E 0 1+ γ γ 1 st state in 31 S: 0 =1248.9keV E γ

55 3.3 HPGe detector response Detector response function: Gaussian

56 3.3 Fitting the experimental data Optimize 2 free parameters: lifetime transition energy number of events background offset 0 E γ τ = 500fs Fixed parameters: HPGe detector response background slope