JAEA-Conf 2011-002 - 日本原子力研究開発機構

φ = φbm · ρtof · ρmulti
(2)
Efficiency
0.18
where φbm is the count of coincidence among
the BMs, ρtof is the ratio of events that con- 0.16
sist of single proton count during neutron flight
to all events, and ρmulti is the ratio of events
0.14
4.2 MeVee Bias
this work
that consist of single proton in a beam bunch
to events of single proton count during neutron
0.12
SCINFUL-QMD
flight. The former and later could be deter-
0.1
mined using data of ”scalar in flight” and ADC
BM1 shown in Fig.2. The numerical values of
0.08
ρtof and ρmulti were 0.82 and 0.46, respectively.
0.06
The neutron detection efficiency, ε(E),
was determined experimentally based on the
238U(n, f) cross sections [8] at Los Alamos
0 100 200 300 400
Incident Neutron Energy [MeV]
500
Neutron Science Center (LANSCE). The detail
of the experiment
in elsewhere. Figure
will be discussed
3 shows the de-
Fig. 3 Experimental and calculated neutron detection
efficiencies of the NE213 scintillator at 4.2 MeVee bias.
tection efficiency determined from the experiment
as well as calculations by SCINFUL-QMD code [9]. The difference between experimental
and calculation data was less than 15 % except for energy region from 80 to
150 MeV. Therefore, the uncertainty of the detection efficiency was determined as 10 %.
4 Results and discussions
Figure 4 shows TTNY as well as one
for target-out measurement. The experimental
data cover the energy region between 16
and 1600 MeV. The threshold energy was attributed
to the lower limit of detection efficiency.
The upper energy was determined with
considering the energy resolution for time-offlight.
Enough statistics were obtained since
the uncertainty from statistics was 3 % for 1600
MeV at maximum. The uncertainty of experimental
results was dominated by that of the
detection efficiencies. Therefore, the detection
efficiency of NE213 scintillator should be studied
further for high energy neutrons to improve
accuracy of TTNY.
As shown in Fig. 4, the target-out result
shows markedly increase at 80 MeV. The fact
indicates the target-in result includes contribution
of background neutron from the beam
dump. As well as the dump, certain amount of
JAEA-Conf 2011-002
TTNY [1/MeV/sr]
-1
10
10
-2
10
2
10
Neutron energy [MeV]
target in
target out
3
10
Fig. 4 Double differential neutron yield for 120 GeV proton
incidence on 60 cm copper target. The results are
compared with results of target out measurement, and
include neutrons from floor and dump below 200 MeV.