The 3Hea,7Be at LUNA

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The 3He(a,?)7Be at LUNA

• Federica Confortola
• INFN ed Università di Genova

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Astrophysical Motivations
?B ?B (SSM) s33-0.43 s34 0.84 s17 se7-1
spp-2.7 com1.4 opa2.6 dif 0.34 lum7.2
Observed flux from SK (PRD 73 (2006) 112001)
The production of 7Li in BBN is very sensitive
to 3He(?,?)7Be cross section.
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3He(?,?)7Be

• Eg 1586 keV Ecm (DC?0)
• Eg 1157 keV Ecm (DC?429)
• Eg 429 keV

Eg 478 keV
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Previous Measurements
S34(0) (keV b)
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LUNA setup
3He gas target
Si monitor

• 3He recirculating gas target
• HPGe detector in close geometry for online ?
  detection
• Removable beam stopper for offline 7Be counting
• Si-monitor for target purity and density
  measurements

Removable calorimeter cap
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Background
Suppression factor 105
0.7 counts/(day keV) ROI 1230 - 1765
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Target characterization
Density (1015 atm/cm3)
Distance from the entrance collimator (cm)
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Target characterization
Beam Heating Effect (?real/?0)
Dissipated power per unit length (mW/cm)
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Activation Measurement
Irradiation Ebeam 300, 350 and 400 keV Charge
63 215 C Target pressure 0.7
mbar Collection efficiency 97.4 7Be
backscattered 1.3 - 2.2
7Bee?7Li(?)?e
Offline measurement Two HPGe 120 relative
efficiency lead shielded in close
geometry Branching adopted 10.44
E? 350 keV T 2 days
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Systematic uncertainties
Systematic uncertainty on S-factors 3
Statistical uncertainty on S-factors 2
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Results
S34(0) 0.547 0.017 keV b
Activation data internal scatter reduced to 5.5,
much lower than prompt-? data (9.8)
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Activation Prompt ? 400 keV run
400 keV run T 4.79 d C 112.68 C
429 ? 0 Cts 2584
DC ? 429 E? 1329 keV Cts 3332
DC ? 0 E? 1757 keV Cts 6773
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Activation prompt ? measurements
Online ? data analysis is still in progress!
The goal is understand the discrepancy between
data obtained with the two methods