Low-Energy Photonuclear Reactions A Review

Transcription

1 Low-Energy Photonuclear Reactions A Review B.L. Berman Department of Physics The George Washington University Washington, DC 20052, USA International Topical Meeting on Nuclear Research Applications and Utilization of Accelerators Vienna, Austria May 5, 2009 Berman--AccApp--May 5,

2 Monoenergetic Photon Beams Positron Annihilation in Flight Livermore, Saclay Tagged Photons Illinois, Saskatchewan, MAX-lab at Lund [High-Energy: MAMI, Jefferson Lab] Compton Back-Scattering LEGS at BNL, HIγS at TUNL [High-Energy: GRAAL, SPRing-8] Berman--AccApp--May 5,

3 Polarized Photon Beams Positron Annihilation in Flight Unpolarized Tagged Photons Polarized at High-Energy Facilities Only Compton Back-Scattering Polarized Berman--AccApp--May 5,

4 Thanks to Kevin Fissum Berman--AccApp--May 5,

5 Research program Berman--AccApp--May 5,

6 O Rielly et al. (SAL, 2004)

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8 3 He(γ,d) see arxiv: Berman--AccApp--May 5,

9 Motivation Elastic Compton Scattering on D sum of proton and neutron polarizabilities σ D (ω) r 02 2 r 0 (α p + α n ) ω 2 Requirements must separate elastic from breakup! Data monoenergetic (tagged) photons high-resolution photon detector ( E/E < 2% at 100 MeV) Lucas Illinois (1994) Hornidge SAL (2000) Lundin Lund (2003) Theory diagrammatic approach (Levchuk/L vov) E γ = 49, 69 MeV E γ = MeV E γ = 55, 66 MeV Berman--AccApp--May 5, EFT (Hildebrandt, Griesshammer, Hemmert, Phillips, )

10 Experiment at Lund energies: E γ = MeV using tagged photons two tagger settings: and MeV bin data in 5 MeV energy bins (with 5% statistics) angles: θ γ = 60,, 120,, 150 with 3 NaI detectors simultaneously detectors: 3 large-volume (50 cm 50 cm) NaI s excellent photon energy resolution ( E γ /E γ ~ 2%) 120 o BUNI UK BUNI: Boston Univ. CATS: Mainz Univ. CATS Berman--AccApp--May 5, 2009 UK: Univ. of Kentucky 10

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12 25 Elastic Compton Scattering on the Deuteron World Data Set Lucas Illinois (1994) E γ = 49, 69 MeV Hornidge SAL (2000) E γ = MeV Differential Cross Section (nb/sr) Illinois 49 MeV Lund 55 MeV Illinois 69 MeV Lund 66 MeV Lundin Lund (2003) E γ = 55, 66 MeV Thanks to Jerry Feldman SAL 95 MeV 5 Berman--AccApp--May 5, Angle (deg)

13 Carbon missing energy (MeV) time rel. to tagger Deuterium Berman--AccApp--May 5,

14 Upgraded ΗΙγS Facility 1.2-GeV Booster Injector RF System with HOM Damping Thanks to Henry Weller Berman--AccApp--May 5,

15 HIγS Nearly Mono-energetic γ-rays from 2 to 160 MeV Tunable Energies Energy resolution selected by collimator size Linearly and Circularly Polarized γ-rays High Beam Intensities Pulsed Beam TOF Techniques to reduce non-beam related backgrounds Berman--AccApp--May 5,

16 Berman--AccApp--May 5,

17 Experimental Setup γ-ray beam direction into the screen BC-501A Liquid scintillators 1 meter flightpath Target at θ=45,φ=45 to make the out-going path Using 1 collimator material length similar for Approximate flux: 1x10 7 γ/s all θ=90 detectors Thanks to Sean Stave Berman--AccApp--May 5,

18 Preliminary Berman--AccApp--May 5,

19 Preliminary Berman--AccApp--May 5,

20 Preliminary Berman--AccApp--May 5,

21 Preliminary Berman--AccApp--May 5,

22 Preliminary Berman--AccApp--May 5,

23 Preliminary Berman--AccApp--May 5,

24 Elemental Identification Preliminary

25 Summary and Prospects for the Future Although the main efforts in photonuclear physics have shifted to higher energies (notably at Jefferson Lab) in the past 25 years, the new facilities at MAX-lab and HIγS are now beginning to produce significant low-energy photonuclear data. At both MAX-lab and HIγS, important experiments on few-body nuclei have been done or are under way. At MAX-lab, the Compton-scattering experiments that are underway promise to help us to understand and quantify the hitherto elusive nucleon polarizabilities. At HIγS, Compton-scattering experiments with polarized photons will enable us to quantify their spin polarizabilities as well. At HIγS, new data on photoneutron spectra from heavy nuclei enable one to distinguish fissionable nuclei from others. Most exciting, the fact that we now have polarized monoenergetic photon beams with intensities comparable to or greater than the unpolarized beams of the past means that virtually the entire field of low-energy photonuclear reactions can be redone, with the expectation of uncovering a wholly new generation of both basic and applied physics results. Berman--AccApp--May 5,

26 To be continued Berman--AccApp--May 5,