Structure of 8 B through 7 Be p diffusing - PowerPoint PPT Presentation

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Structure of 8 B through 7 Be p diffusing

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  1. Structure of 8B through 7Be+p scattering 1Jake Livesay, 2DW Bardayan, 2JC Blackmon, 3KY Chae, 4AE Champagne, 5C Deibel, 4RP Fitzgerald, 1U Greife, 6KL Jones, 6MS Johnson, 7RL Kozub, 3Z Ma, 7CD Nesaraja, 6SD Pain, 1F Sarazin, 7JF Shriner Jr., 4DW Stracener, 2MS Smith, 6JS Thomas, 4DW Visser, 5C Wrede 1Colorado School of Mines 2Oak Ridge National Laboratory 3University of Tennessee at Knoxville 4University of North Carolina 5Yale University 6Rutgers University 7Tennessee Tech University 3/10/2014 ORNL Workshop

  2. Outline of Talk • Motivation • Previous Measurements • Making 7Be (TUNL) • Experimental Setup (HRIBF) • Normalization • Preliminary Results • Future Work

  3. Predicted Positive Parity States Positive Parity States come from coupling of proton and neutron in p shells There are other predicted levels which have yet to be observed 3/2- + 3/2- → 0+,1+,2+,3+

  4. Basic shell Model Prediction 7Be ground state is 3/2- due to the unpaired 3/2- neutron – a very proton rich nucleus p 1/2 7Be+ (l=0) p 3/2 proton is an elastic scattering reaction with expected positive parity states: 0+ ,1+ ,2+ ,3+ p 3/2 7Be+ (l=1) p 1/2 proton is an inelastic scattering reaction with expected positive parity states: 0+ ,1+ ,2+ s 1/2 proton neutron

  5. 7Be(p,p)7Be CRC-Louvain-le-Neuve C. Angulo et al., NPA 716 (2003) 7Be(p,)8B extrapolation Junghans et al. (2003) P. Descouvemont, PRC 70 (2004) 7Be+p: a01= 25  9 fm, a02 = -7  3 fm 7Li+n: a01= 0.87  0.07 fm, a02 = -3.63  0.05 fm • Uncertainty in shape of d/d and 7Be(p,) extrapolation to solar energies dominated by s-wave scattering lengths ~ 5% uncertainty in S17(0)

  6. Previous Measurements of 7Be(p,p) 3+ at 2.32 MeV • Agrees with literature value for 3+ • Doesn’t locate other positive parity states in region • Two measurements nearly overlap in energy 2- at 3.5 MeV 1+ at 1.3 MeV – ruled out Rogachev et al, PRC 2002

  7. Li metal 12 MeV protons ~ 10 mA 7Li(p,n)7Be 7Be beam production 0.2 Ci 2*1077Be/s 0.12 Ci

  8. 7Be(p,p)7Be Setup 7Be and protons 7Be Thin Target • 17 bombarding energies • 100 g/cm2 CH2 target • Ecm = 0.4 to 3.3 MeV • θ 1cm=80-128, θ2cm=118-152, θtotal=80 - 152 • Normalization to 7Be+Au scattering and to 7Be+12C Thick Target • 14 MeV beam of 7Be • 4.3 mg/cm2 CH2

  9. Silicon Detector Array • 16 Strips per detector • 40 keV energy resolution • 128 channels of electronics 5804.77keV 5762.64keV

  10. 15 12C(7Be,7Be)12C Ecm = 2.5 MeV 10 Livesay et al. SIDAR strip d/d (mb/sr) Rutherford 5 1 cm (degrees) E (MeV) 0 4 8 12 16 20 7Be+Au & 7Be+12C Scattering 7Be+p beam current determined by fitting 7Be +12C cross section 12C(7Be,7Be)12C Ecm = 9.5 MeV Livesay et al. (d/dRutherford DWUCK5 lab (degrees)

  11. 7Be scattered from 12C 50.08 48.94 47.76 46.52 45.22 43.85 42.42 40.92 39.35 37.71 35.99 34.19 32.31 30.35 28.31 26.19 7Be+12C Protons elastically scattered from 7Be 7Be+p 2.903 6.154 Spectra without Inelastic Peak (7 MeV)

  12. Spectra with Inelastic Scattering Elastic 7Be+p Elastic 7Be+12C Inelastic 7Be+p α Some background is due to knocked-out C from the target

  13. Thick Target Method p 7Be • Energy loss in thin target is much less than excited state energy Ep = Ebeam –ΔEbeam-ΔEp p’ 7Be Ep’ = Ebeam –ΔEbeam’-ΔEp’-Eexcited state Many positions in target can produce equal elastic and inelastic energies ΔEbeam’- ΔE p’ - Eexc = ΔEbeam - ΔEp

  14. Thick-target excitation function Thick target good for comparison to previous measurement – but difficult to analyze and not as informative as thin target 1+ Background 7Be+12C Front of target protons above this energy forbidden by beam energy Counts/channel  Counts/channel Ecm (keV)

  15. ΔE Inelastic Scattering • Inelastic locus behaves kinematically like protons – Shape • Inelastic locus is of correct energy (elastic proton energy less 7Be FES energy) - Separation

  16. Inelastic Prediction General behavior of inelastic prediction consistent with data

  17. Simultaneous Fit of Elastic and Inelastic • Fitting must be done simultaneously for many dimensions • This requires a single set of resonance parameters for whole data set • Consequence is that total χ2 must be considered

  18. Thin-target data • Example of p and p` at one angle • Possible positive parity resonance observed in inelastic channel • Not the known 3+ • 3+ f-wave in inelastic • Ecm~ 2.3 MeV • Possible: J=0+, 1+, 2+ • Accurate absolute normalization should allow accurate determination of scattering lengths • Resonance is too high in energy to significantly affect S(0), but may explain some of the higher energy behavior 150 Elastic cm=128 100 50 d/d (mb/sr) 20 Inelastic cm=124 15 10 5 0 Ecm (MeV)

  19. Minimization versus Grid Search Minimization versus Grid Search χ2 χ2 parameteri parameteri • Grid Search • +Allows for arbitrarily precise parameter search • -Eats up computer time • Minimization • -Favors nearest minima (would be plus for well-known landscape) • +Converges quickly based on local curvature parameterj parameterj Minimization tends toward broad minima – not necessarily the deepest. This is a well known weakness of purely minimizing routines. Combined Grid-Powell Technique may lift this weakness – but add considerable CPU time

  20. Current Analysis Grid search gets quickly out of hand x11 x12 x13 . . x1n • Multi Calculations being performed with large parameter space – grid search • Search requires iteration over assignments of Jπ, energies and widths #calculations = #steps(#parameters) 5steps(12 parameters) ≈ 2.4 106 Calculations x11 x12 . . . x2n x11 . . . . . . . . xn1 xn2 xn3 . . . xnn

  21. Future Work • Determine Resonance Parameters of states in the region of 1 to 4 MeV and sensitivity to each parameter • Another 7Be(p,p) experiment would help to flesh out the cross section above 3.5 MeV • Determine scattering lengths from low energy data.

  22. SIDAR Lampshade Configuration • Increased solid-angle coverage • Can be configured for ΔE-E telescopes • Extends angular coverage to more ‘backward’ angles