Structure of 8B through 7Be p scattering

1
Structure of 8B through 7Bep 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
9/12/2015
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 (l0) p 3/2 proton is an elastic scattering
reaction with expected positive parity states 0
,1 ,2 ,3
p 3/2
7Be (l1) p 1/2 proton is an inelastic
scattering reaction with expected positive parity
states 0 ,1 ,2
s 1/2
proton
neutron
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7Be(p,?)8B extrapolation
Junghans et al. (2003)
P. Descouvemont, PRC 70 (2004)
7Bep a01 25 ? 9 fm, a02 -7 ? 3 fm
7Lin 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)
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Previous Measurements of 7Be(p,p)
3 at 2.32 MeV

• Agrees with literature value for 3
• Doesnt 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
7Be beam production
0.2 Ci
2107 7Be/s
0.12 Ci
8
7Be(p,p)7Be Setup
7Be and protons
7Be

• Thick Target
• 14 MeV beam of 7Be
• 4.3 mg/cm2 CH2

• Thin Target
• 17 bombarding energies
• 100 ?g/cm2 CH2 target
• Ecm 0.4 to 3.3 MeV
• ? 1cm80-128, ?2cm118-152, ?total80 - 152
• Normalization to 7BeAu scattering and to
  7Be12C

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Silicon Detector Array

• 16 Strips per detector
• 40 keV energy resolution
• 128 channels of electronics

5804.77keV
5762.64keV
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7BeAu 7Be12C Scattering
7Bep 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)
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Spectra without Inelastic Peak (7 MeV)
12
Spectra with Inelastic Scattering
Elastic 7Bep
Elastic 7Be12C
Inelastic 7Bep
a
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 ?Ebeam-?Ep
p
7Be
Ep Ebeam ?Ebeam-?Ep-Eexcited state
Many positions in target can produce equal
elastic and inelastic energies
?Ebeam- ?E p - Eexc ?Ebeam - ?Ep
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 7Be12C
Front of target protons above this energy
forbidden by beam energy
Counts/channel
?
Counts/channel
Ecm (keV)
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Inelastic Scattering

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

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Inelastic Prediction
General behavior of inelastic prediction
consistent with data
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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 ?2 must be considered

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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 ?cm128?
100
50
d?/d? (mb/sr)
20
Inelastic ?cm124?
15
10
5
0
Ecm (MeV)
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Minimization versus Grid Search
Minimization versus Grid Search
?2
?2
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
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Current Analysis
Grid search gets quickly out of hand
x11 x12 x13 . .
x1n
calculations steps(parameters) 5steps(12
parameters) 2.4 106 Calculations
x11 x12 . . .
x2n
x11 . . .
.
.
.

.
.

xn1 xn2 xn3 . . . xnn

• Multi Calculations being performed with large
  parameter space grid search
• Search requires iteration over assignments of Jp,
  energies and widths

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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.

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SIDAR Lampshade Configuration

• Increased solid-angle coverage
• Can be configured for ?E-E telescopes
• Extends angular coverage to more backward angles