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The 2-Body Photodisintegration Reaction 4He(g,n)3He below 30 MeV
John Kelley, R. Raut, G. Rusev, S.C. Stave, A.P. Tonchev, W. Tornow Triangle Universities Nuclear Laboratory North Carolina State University Duke University
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“Equality” vs Inequality of 4He(g,n/p)3He/3H s What are the Implications?
Charge Symmetry Isospin Mixing
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Present State
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4He(g,3He)n below 30 MeV at the High Intensity g-ray Source (HIGS)
Compton backscatter FEL photons from electrons in a storage ring FEL.
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Photon Flux from Plastic Scintillator Paddle
Efficiency measured by comparison with NaI Pb 10” x 12” NaI detector Well understood efficiency g-ray beam Plastic scintillator paddle / PMT Pb 10 mm Collimator
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Experimental Setup PMT 3He-Xe gas Pb scintillator Plastic
g-ray beam Plastic Scintillator paddle/PMT Pb 10 mm Collimator
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Active 4He/Xe 5 cm diameter scintillation cell
Eg (MeV) Pressure PSI. Xe/He E3He 3He range mm 27 (710 4He/40 Xe) 0.056 1.6 0.8 27.5 750 1.73 0.9 28 1.85 1.0 max 50 mm diameter
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4He/Xe scintillation cell vs Xe scintillation cell “target out”
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Photon-induced reaction thresholds (in MeV)
Isotope Nat. Abundance (%) (g,p) (g,a) (g,n) (g,2n) (g,na) xenon isotopes magnesium isotopes oxygen isotopes He isotopes Atomic effects “charged” kinetic energy Edge effects ignored Lt 1 MeV 1-3 MeV (1.6) 5-10 MeV 10-20 MeV Eg=27 MeV 4He+g -> 3He(1.6 MeV) & n (4.8 MeV)
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High Rate/ High Threshold Anti-Pileup Circuit
High Threshold – minimize multi-pulse pileup in the CFD Linear Gate Dt~100 ns – (with inhibit Dt~10 us) minimize pileup in Spectroscopic Amplifier Scaler PULSER FIFO AMP AMP FIFO FIFO Linear Gate AMP inhibit 3He Cell CFD Scaler GDG Busy Inhibit Paddle AMP Logic Scaler Computer Busy
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Results Proof of principle Beamtime expected in the next quarter
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