Event time-stamping is becoming common in thefield of nuclear
physics with radioactive isotope (RI) beams[1]. A time-stamp provides
absolute timing information to event data, and allows the use of
individual triggers for separate data acquisition (DAQ) systems. After
the measurements are complete, a variety of physics events can be
identified by analyzing the time-stamps. This approach is suitable for
β-decay experiments because the trigger rates for beam and β-ray
detectors are very different like about 100 and 500 events/s respectively. To maintain a consistent time frame, clock synchronization
between separate DAQ systems is necessary. Such time-stamping
systems have already been implemented in theγ-ray detector arrays
of EXOGAM[2],RAISING[3],AGATA[4] and SeGA[5].IntheRIKEN
Radioactive Isotope Beam Factory (RIBF), a new time-stamping system
has been developed for nuclear physics experiments. One of the
remarkable features is that it can attach the time-stamp information to
an existing CAMAC/VME based DAQ system. In this system, timestamp information is equivalent to the absolute time of the trigger.
Since developed time-stamping system is compliant with the CAMAC
and VME specifications, time-stamp information can be taken together
with other CAMAC/VME read-out modules. The timing resolution of
the time-stamping system is 10 ns and this is enough tofind the event
correlation between separated DAQ systems. This specification enables
us to merge separately taken data on an event-by-event basis, after the
measurement.
RIBF produces intense RI-beams and a variety of nuclear physics
experiments are performed. The length of the beam line is over 100
meters. Since detectors are placed at distant places, a networkdistributed DAQ system (RIBF DAQ) has been introduced[6].RIbeams are measured by a beam line detector set on an event-byevent basis. The beam line detector set consists of plastic scintillators, parallel plate avalanche counters and ionization chambers.
These detectors measure information of time-of-flight, position
and energy. There are about 500 signals in the beam line detector
set. These signals are acquired by about 50 read-out modules
distributed in 10 CAMAC/VME front-end systems. However, these
CAMAC/VME front-end systems run in parallel, the same trigger
signal is applied to all. Because all beam line detectors arefired by
incoming beams at the almost the same timing. This trigger timing
is also recorded as a time-stamp datum. The RIBF DAQ system
merges data from multiple CAMAC/VME front-end systems in
online. CAMAC/VME front-end systems have different transaction
times, i.e. the dead time. Each front-end system generates a busy
signal which corresponds to the dead time for one event. In the RIBF
DAQ system, the longest busy signal from multiple CAMAC/VME
front-end systems is adopted as the veto signal to the trigger. This
insures that each CAMAC/VME front-end system can accept all
Event time-stamping is becoming common in thefield of nuclear
physics with radioactive isotope (RI) beams[1]. A time-stamp provides
absolute timing information to event data, and allows the use of
individual triggers for separate data acquisition (DAQ) systems. After
the measurements are complete, a variety of physics events can be
identified by analyzing the time-stamps. This approach is suitable for
β-decay experiments because the trigger rates for beam and β-ray
detectors are very different like about 100 and 500 events/s respectively. To maintain a consistent time frame, clock synchronization
between separate DAQ systems is necessary. Such time-stamping
systems have already been implemented in theγ-ray detector arrays
of EXOGAM[2],RAISING[3],AGATA[4] and SeGA[5].IntheRIKEN
Radioactive Isotope Beam Factory (RIBF), a new time-stamping system
has been developed for nuclear physics experiments. One of the
remarkable features is that it can attach the time-stamp information to
an existing CAMAC/VME based DAQ system. In this system, timestamp information is equivalent to the absolute time of the trigger.
Since developed time-stamping system is compliant with the CAMAC
and VME specifications, time-stamp information can be taken together
with other CAMAC/VME read-out modules. The timing resolution of
the time-stamping system is 10 ns and this is enough tofind the event
correlation between separated DAQ systems. This specification enables
us to merge separately taken data on an event-by-event basis, after the
measurement.
RIBF produces intense RI-beams and a variety of nuclear physics
experiments are performed. The length of the beam line is over 100
meters. Since detectors are placed at distant places, a networkdistributed DAQ system (RIBF DAQ) has been introduced[6].RIbeams are measured by a beam line detector set on an event-byevent basis. The beam line detector set consists of plastic scintillators, parallel plate avalanche counters and ionization chambers.
These detectors measure information of time-of-flight, position
and energy. There are about 500 signals in the beam line detector
set. These signals are acquired by about 50 read-out modules
distributed in 10 CAMAC/VME front-end systems. However, these
CAMAC/VME front-end systems run in parallel, the same trigger
signal is applied to all. Because all beam line detectors arefired by
incoming beams at the almost the same timing. This trigger timing
is also recorded as a time-stamp datum. The RIBF DAQ system
merges data from multiple CAMAC/VME front-end systems in
online. CAMAC/VME front-end systems have different transaction
times, i.e. the dead time. Each front-end system generates a busy
signal which corresponds to the dead time for one event. In the RIBF
DAQ system, the longest busy signal from multiple CAMAC/VME
front-end systems is adopted as the veto signal to the trigger. This
insures that each CAMAC/VME front-end system can accept all
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