Status of SAMURAI Neutron Array (NEBULA) Yosuke Kondo Tokyo Institute of Technology
Feb 24, 2016
Status of SAMURAI Neutron Array(NEBULA)
Yosuke KondoTokyo 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
– 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
neutron
charged fragment
Pb targetRI beamfrom BigRIPS
Typical setup (Coulomb breakup)
NEBULA
NEBULA(Neutron-detection system for Breakup of Unstable-Nuclei with Large
Acceptance)
• 240 Neutron counters (60 modules x 4 stacks)• 48 VETO counters
• 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)
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
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
neutron counter
before mounting the VETO counters
Photo
VETO counter(1cm thickness)
after mounting the VETO counters
4.2m
3.6m
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 …
Summary
• NEBULA is designed for neutron measurements in SAMURAI project– half of volume will be ready in 2011– Test will be done soon