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Status of SAMURAI Neutron Array (NEBULA)

Status of SAMURAI Neutron Array (NEBULA). Yosuke Kondo Tokyo Institute of Technology. Invariant-mass spectroscopy of neutron-rich nuclei. Physics subjects Coulomb breakup as a spectroscopic tool Giant resonance soft dipole resonance pigmy resonance

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Status of SAMURAI Neutron Array (NEBULA)

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  1. Status of SAMURAI Neutron Array(NEBULA) Yosuke Kondo Tokyo Institute of Technology

  2. Invariant-mass spectroscopy of neutron-rich nuclei • Physics subjects • Coulomb breakup • as a spectroscopic tool • Giant resonance • soft dipole resonance • pigmy resonance • Low-lying unbound states of neutron-rich nuclei near the dripline • Unbound exotic systems beyond the dripline • 10He, 4n, 28O • etc… Ex Erel AZ* AZ core n AZ* core n core neutron decay target n excitation measure  Ex (Erel) can be reconstructed neutron decay threshold Sn A-1Z+n AZ

  3. Typical setup (Coulomb breakup) neutron Pb target RI beam from BigRIPS charged fragment NEBULA

  4. NEBULA(Neutron-detection system for Breakup of Unstable-Nuclei with Large Acceptance) • 240 Neutron counters (60 modules x 4 stacks) • 48 VETO counters

  5. NEBULA(Neutron-detection system for Breakup of Unstable-Nuclei with Large Acceptance) • Neutron counter • scintillator • BC408 • 12cm x 12cm x 180cm • PMT • R7724ASSY (both ends) • vertical position is determined by time difference • VETO counter • 1cm-thick scintillator • used to identify the charged particles

  6. NEBULA(Neutron-detection system for Breakup of Unstable-Nuclei with Large Acceptance) • 240 Neutron counters (60 modules x 4 stacks) • 48 VETO counters • High efficiency • ~70% for 1n detection • Large acceptance • effective area : 3.6m (H) x 1.8m (V) -10o<qH<10o, -5o<qV<5o • Multi-neutron detection • aiming at 4n detection

  7. Multi-neutron detection(example:2n case) Same Wall event • crosstalk … more than 2 hits caused by 1n • should be eliminated for multi-neutron detection kinematical condition is used to reject the crosstalk • Same wall event  position information • 2 hits are clustered and are regarded as 1hit if positions are close • lose efficiency for small Erel • Different wall event  velocity information • the event is true if b12 >b1 • because crosstalk neutron must be slow • can measure up to Erel~0 Stack-1 Stack-2 Different Wall event Stack-1 Stack-2 hit detector

  8. Photo 4.2m neutron counter 3.6m VETO counter (1cm thickness) after mounting the VETO counters before mounting the VETO counters

  9. Status • Half of neutron counters are purchased • the other half are not funded • Efficiency  ~40% • Mounting – finished • It was very hard… • Test 1 stack using cosmic ray • This summer • we are now connecting many many cables … not yet

  10. Summary • NEBULA is designed for neutron measurements in SAMURAI project • half of volume will be ready in 2011 • Test will be done soon

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