JAEA-Conf 2011-002 - 日本原子力研究開発機構

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10
3
10
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Charged-Particle Events
100 200 300 400 500 600 700 800 900 1000
ADC with Total Gate [ch]
Fig. 4: spectrum of the veto detector
JAEA-Conf 2011-002
ADC with Slow Gate [ch]
400
350
300
250
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50
Neutron
γ-ray
0
0 100 200 300 400 500 600 700 800 900 1000
ADC with Total Gate [ch]
Fig. 5: Two dimensional plots of two ADC
outputs, total and slow, for neutron-γ-ray
discriminaton
nuclei excited by incident oxygens and shown as a sharp peak in this figure. This peak
was utilized as the base time for the neutron TOF.
The charged particle events were excluded using the data from the veto detectors
as shown in Fig. 4. To discriminate neutron and γ-ray events, the two-gates charge
integration method was adopted. Figure 5 presents an example of two-dimensional scatter
plot for total- and slow-gated electric charges of NE213 signals. The total gate width was
300 ns and that of the slow gate was 250 ns after delay of 50 ns from the start point of the
total gate. One can see neutron and γ-ray events were separated well. The flash γ-ray
events were not included in this figure because they were already excluded by the TOF.
Neutron spectra were obtained by subtracting the results of the background measurement
from those of the foreground, after normalization with the number of incident
oxygens.
The number of neutron-detection events were converted into the double-differential
cross sections using neutron detection efficiencies. The efficiencies were obtained by calculations
with a Monte Carlo simulation code SCINFUL-QMD [7]. This code is capable
of calculating the detection efficiency for various sizes of organic scintillators for incident
neutron energies up to 3 GeV. The neutron detection efficeincies were calculated with
60Co bias.
4. Results and discussion
The neutron-production double-differential cross sections are indicated in Fig. 6 for
incident oxygen energies of 290 MeV/u on C. The vertical error bars consist of statistical
errors and the horizontal ones are composed of FWHM of flash γ-ray peak. The experi-