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Low-energy neutron detector for charge-exchange reactions (EXL and R3B collaborations)

Low-energy neutron detector for charge-exchange reactions (EXL and R3B collaborations). A. Krasznahorkay, R. Reifarth (GSI), A. Algora, M. Csatlós, Z. Gácsi, J. Gulyás, M. Hunyadi, A. Vitéz MTA, ATOMKI, Debrecen Hungary.

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Low-energy neutron detector for charge-exchange reactions (EXL and R3B collaborations)

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  1. Low-energy neutron detector for charge-exchange reactions(EXL and R3B collaborations) A. Krasznahorkay, R. Reifarth (GSI), A. Algora, M. Csatlós, Z. Gácsi, J. Gulyás, M. Hunyadi, A. Vitéz MTA, ATOMKI, Debrecen Hungary

  2. Isovector GR’s in unstable nuclei (spin-flip and isospin-flip giant resonances) -The physics case • Macroscopic & microscopic info • Neutron skin • SDR sum-rule • Ex(GTR)-Ex(IAS) • nuclear astrophysics (R. Reifarth) • Experimental considerations ((p,n) in inverse kinematics) • High cross sections (~10mb/sr) • Complete kinematics (use FRS) • low-En, no energy loss in target

  3. Sum rule for the SDR strength neutrons protons Neutron-skin thickness A. Krasznahorkay et al., Phys. Rev. Lett. 82 (1999) 3216.

  4. Requirements on kinematical parameters 35 30 25 20 15 Ex: Relativistic calculation of inverse kinematics cm 132Sn 3.5° • Ebeam=400 MeV·A • 122-132Sn • Ex(SDR)=18-24 MeV • cm=2°-3° (L=1) 3.0° 2.5° 2.0° 1.0° 55°<lab<70°

  5. Reaction kinematics Direct Inverse • Special technical conditions - long flight path for fast neutrons - difficulties around angular distributions • Large background • Bulky detectors • Simple and safe construction - short flight path for slow neutrons - large laboratory angles • Complete kinematic measurement: suppression background • Relatively thin detectors still can provide sufficient efficiency for low-energy neutrons

  6. Technical requirements • To avoid n-scattering less material in holder structures and environment • Positioning of detector frames (40°<<80°) • Flight path of neutrons  EXL chamber • Sharp TOF-start signal • Cross-scattering of neutrons  MC-simulation

  7. Elastic neutron scattering Ep= Encos(Θ)2

  8. The response of plastic scintillators to low-energy protons Birks relation:

  9. VM2000 multilayer reflector

  10. Test with 60Co-source • Time- and position resolution: 1ns, 10cm • Light attenuation: <10%

  11. Time resolution(50 ps/channel) FWHM ~ 0.8 ns Time difference (channels) Energy (channels) Time difference

  12. Plastic ring detectors for TOF measurements (L = 1 m, 27 rings) 108 2” PMT’s

  13. Monte-Carlo simulation • Efficiency, cross- and out-scattering, threshold effects GEANT3 (J.L. Tain, Valencia, Spain) GEANT4 (A. Algora, M. Csatlós, Debrecen, Hungary):  =4°

  14. Plan of geometric arrangement

  15. Ranges of acceptance

  16. Ranges of acceptance

  17. Resolution in Ex

  18. Resolution in Ex

  19. New geometry

  20. Kinematical coverage

  21. Neutron scattering between the detectors

  22. Block diagram of the electronics

  23. Neutron spectrum expected from a 252Cf source

  24. Neutron TOF spectrum

  25. Efficiency for neutrons

  26. Efficiency calibrationplanned at PTB Braunschweig

  27. R. Beyer, E. Grosse et al., Rossendorf, NIM

  28. Conclusions • GR studies in RIB’s • Challenges for the detectors • Future plans

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