d,p γ as surrogate for neutron capture in inverse kinematics
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William A. Peters August 8, 2009 ANL 1
description
William A. Peters. d,p γ as surrogate for neutron capture in inverse kinematics. d. B*. C. Surrogate method. Compound nucleus. b. A. D. a. “Surrogate” reaction. “Desired” reaction. c. different decay modes. Surrogate candidates. Fission vs. neutron capture - PowerPoint PPT Presentation
Transcript of d,p γ as surrogate for neutron capture in inverse kinematics
William A. Peters
August 8, 2009ANL 1
D“Surrogate”reaction
db
B*
Aa
“Desired” reaction
Cc
Compound nucleus
different decay modes
August 8, 2009ANL 2
Fission vs. neutron captureRecent capture/fission ratio work shows promise. J. M. Allmond et al., Phys. Rev. C 79, 054610
(2009). Short-lived isotopes
Important for stewardship and basic science. Astro-physical reactions Nuclear reactors and device modeling Stockpile and waste storage
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xp
xpx
CN
EN
ENEG
Compound nucleus decay becomes independent of spin and parity.
WE(E) =
CN(E) . G(E)
No sum over J,π!
(Ex ) CN
J , (Ex , J, )G
CN (Ex , J, )
First factor can be calculated. Second factor is difficult.
Requires W-E limit of H-F. Measure one reaction relative to
another. Reduces systematic uncertainties. No need to measure singles rate.
August 8, 2009ANL 5
)(
)(
)()()(
)()()(
)(
)()2(
)1(
)1()2()2(
)2()1()1(
)2(
)1(
xp
xp
xpxpxCNn
xpxpxCNn
xn
xn
EN
EN
ENENE
ENENE
E
E
Assumes Np1/Np2 cancel
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18.5 MeV deuteron beamfrom cyclotron
• Targets: two isotopically enriched metallic foils of 171Yb (0.981 mg/cm2) and 173Yb (0.502 mg/cm2)
• 3 Si detectors for particle detection (STARS):
dE: 500 m, 48 rings, 16 sectors
E1: 1000 m, 24 rings, 8 sectors
E2: 1000 m, 16 rings, 16 sectors
angular range covered: 44° to 73°
• 6 Ge clover detectors to detect coincident -rays (LiBerACE)
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Not in W-E limit Resolution not as good as n,γ Try to selectively match neutron capture
spin distribution Singles rate might not cancel Ratio seems consistent above 100 keV
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Needed for short lived isotopes (<100 days).
A reliable method and analysis could start an exciting new campaign of capture measurements.
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View of (d,pγ) components
8 Silicon(ORRUBA) detectors
4 Germanium clovers
Target manipulator
Cubic chamber
Beam direction
High-ratediamond detector
-J. CizewskiAugust 8, 2009 10ANL
ORRUBA + Gammasphere – chamber conceptORRUBA + Gammasphere – chamber concept
28°
175mm
214mm
145mm
Feed-throughs
BGO
-S. Pain
Original design by Charles Reed, first used by Micah Johnson
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73As/74As = 1/2 σ74(n,2n) Фn (D.Vieira)
Isotope ratios measured after event (n,2n) reactions most important (n,γ) reactions can effect results
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Deuterated plastic target 400 μg/cm2
75As at 530 MeV Tandem voltage near 24 MV Beam rate was 10^7 pps 1 week of beam time Trigger on ORRUBA (proton) singles
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Gamma Spectrum (keV)
Spectrum not Doppler corrected
165 511
Partial level scheme (from ENDSF) of 76As used to identify successful (d,pγ) events. Quoted branching are from (n,γ) experiments.
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Doppler corrected6 keV FWHM
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Carbon target CD2 target
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Sn=7.33 MeV
Fusion on carbon dominates background Resolution poor Still need to gate on γ-rays Will G(E) match n,γ?
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Can n,γ CN be mimicked by surrogates? Can d,pγ work in inverse kin? Will another reaction work for rare isotopes? Must we give up on ratio method if W-E not met? Can we calculate spin mismatch of d,pγ-n,γ? How to deal with deformed nuclei?
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Use n-rich beams. Tag on d,p recoils.
Timing Recoil separator Pure target
Increase resolution and acceptance.
Improved signal to noise for gammas.
Improved resolution with more space for ORRUBA.
Beam energy range better for d,pg. More n-rich beams available. Might work with less beam.
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Rutgers University. J. Cizewski, R. Hatarik, P. O’Malley
University of Tennessee K. L. Jones, K. Schmitt, R. Kapler, B. Moazen, A. Chae, S.
Pittman Louisiana State University
J.C. Blackmon Tennessee Technological University
R.L. Kozub LANL
D. Vieira, M Jandel, J.B. Wilhelmy ORAU
C. Matei LLNL
A. Becker, C. Y. Wu, J. Escher, F. Dietrich ORNL
D.W. Bardayan, S.D. Pain, M.S. Smith, D. Stracener
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Measure 75As d,pγ for benchmark. Develop 73,74As beams at HRIBF. Use benchmark for ratio measurements
to radioactive As isotopes.
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Measured (n,γ) cross section (from NNDC) to compare to surrogate (d,pγ).
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Proton energy (a.u.)
PRELIMIN
ARY
PRELIMIN
ARY
165 keV
511 keV
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-J. Escher
a
bc
dJ distributions
considered
PRELIMIN
ARY
PRELIMIN
ARY
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75As+12C 530 MeV
0.00
2.00
4.00
6.00
8.00
10.00
12.00
14.00
16.00
80.00 100.00 120.00 140.00 160.00 180.00
Lab Angle (deg)
Pro
ton
En
erg
y (
MeV
)
EvapOR calculations show high energy protons come out at back angles from C-fusion. –J. Cizewski
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Diamond beam-rate detector was tested for activation. Beta-gamma analysis confirmed 82Sr, 85Sr, and 83Rb.
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Multi-crystal350 um thickGold plated1.0” diameter0.1 ns timing10^8 pps limit
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Preceded by large-bore quadNo need to tune past first set of slitsInstall Silicon stack for id (need rate less than 10 kHz).Will have more trouble with unreacted beam than C-fusion
150
650
1150
1650
2150
2650
3150
3650
4150
3 53 103 153 203
Cro
ss s
ecti
on
(m
b)
Neutron energy (keV)
171Yb 173Yb
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Using 4-2 transition
Known neutron capture cross sections for 171Yb and 173Yb from K. Wisshak et al., Phys Rev C 61, (2000) 065801.
0+2+4+
6+
J
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Intensity ratios of the 4+ 2+ and 6+ 4+ different for 171Yb (1/2-) and 173Yb (5/2-)
Calculated by DICEBOX
R. Hatarik
Subtract 6+ feeding of 4+ to get spin distribution closer to (n,)
