status of samurai neutron array (nebula)
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
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Status of SAMURAI Neutron Array(NEBULA)
Yosuke KondoTokyo Institute of Technology
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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…
np
n
corecp
coren
AZ*
target
n
AZcore
iiirel MpEE 22 AZ
A-1Z+nSn
Ex Erel
neutron decaythreshold
excitation
neutrondecay
AZ*
measureEx (Erel) can be reconstructed
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neutron
charged fragment
Pb targetRI beamfrom BigRIPS
Typical setup (Coulomb breakup)
NEBULA
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NEBULA(Neutron-detection system for Breakup of Unstable-Nuclei with Large
Acceptance)
• 240 Neutron counters (60 modules x 4 stacks)• 48 VETO counters
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• 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
NEBULA(Neutron-detection system for Breakup of Unstable-Nuclei with Large Acceptance)
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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
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Multi-neutron detection(example:2n case)
• crosstalk … more than 2 hits caused by 1n– should be eliminated for multi-neutron detectionkinematical 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
Same Wall event
Stack-2Stack-1
12b1b
Stack-2Stack-1
Different Wall event
hit detector
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neutron counter
before mounting the VETO counters
Photo
VETO counter(1cm thickness)
after mounting the VETO counters
4.2m
3.6m
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not yet
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 …
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Summary
• NEBULA is designed for neutron measurements in SAMURAI project– half of volume will be ready in 2011– Test will be done soon