JAEA-Conf 2011-002 - 日本原子力研究開発機構

the air and stopped at a beam dump placed 7 m downstream from the target.
Emitted neutrons were detected with NE213 liquid organic scintillators, which dimension
was 12.7 cm in diameter and 12.7 cm thick. The NE213 detectors were placed to
measure angular distributions at 15 ◦ ,30 ◦ ,45 ◦ ,60 ◦ ,75 ◦ and 90 ◦ . Scintillation lights from
the NE213 liquid organic scintillators are originated from as well as γ-rays and charged
particles. Since the synchrotron was operated in a pulse mode (0.3 Hz repetition cycle) and
incident oxygen beam intensity was very weak in level of 104∼105 particles/3.3 s, the number
of incident oxygens can be individually counted. A veto detector, 150 × 150 × 2mm3 ,
made of NE102A plastic scintillator, was set in front of each NE213 scintillator to eliminate
charged particle events.
In order to reduce neutrons from the beam dump, a couple of an iron of 63 cm thick
and a concrete of 50 cm thick shields was placed between the detectors and beam dump.
For measurement of background neutrons, the measurement with an iron shadow bar of
110 cm thick set between a target and detector were carried out.
3. Data analysis
In this measurement, the beam pick up detecter detects not only the single incident
oxygen events but also the plural incident oxygen events. As clearly shown in Fig. 2, when
two or three projectiles pass through the beam pick up detecter coincidentally, the pulse
heights appear twice or three times higher than that of single projectile. The ratio of
events obtained by single projectile to the all events was employed to correct the number
of projectiles.
Count [-]
3
10
2
10
10
Single Incident Particle Events
200 400 600 800 1000 1200 1400 1600 1800 2000 2200
ADC [ch]
JAEA-Conf 2011-002
Fig. 2: spectrum of the beam pick up detector
Count [-]
3
10
2
10
10
1
Foreground
Background (Shadow Bar)
Flash γ-Ray
500 1000 1500 2000 2500 3000
TDC [ch]
Fig. 3: An example of TOF spectra
Typical measured TOF spectra are shown in Fig. 3. Both foreground and background
spectra contain neutron and γ-ray events. The flash γ-rays were generated from the target