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

“Equality” vs Inequality of 4He(g,n/p)3He/3H s What are the Implications? Charge Symmetry Isospin Mixing

Present State

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.

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

Experimental Setup PMT 3He-Xe gas Pb scintillator Plastic g-ray beam Plastic Scintillator paddle/PMT Pb 10 mm Collimator

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

4He/Xe scintillation cell vs Xe scintillation cell “target out”

Photon-induced reaction thresholds (in MeV) Isotope Nat. Abundance (%) (g,p) (g,a) (g,n) (g,2n) (g,na) xenon isotopes 128 1.92 8.17 1.77 9.61 16.84 11.19 131 21.18 8.82 2.55 6.61 15.87 8.85 136 8.87 9.93 3.66 7.99 14.44 11.73 magnesium isotopes 24 78.99 11.69 9.31 16.53 26 11.01 14.15 10.61 11.09 oxygen isotopes 16 99.762 12.13 7.16 15.67 18 0.200 15.94 6.23 8.05 He isotopes 4 99.762 19.81 - 20.58 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)

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

Results Proof of principle Beamtime expected in the next quarter