JAEA-Conf 2011-002 - 日本原子力研究開発機構

JAEA-Conf 2011-002
remote-controlled target holder together with a beam viewer and a blank target in the vacuum
chamber. The target holder was insulated from the ground and served as a Faraday cup to read
the beam current. The beam spot and current was also checked with the beam viewer and
blank target, which protons passed through, by reading the beam current at a beam stop.
Neutrons and -rays emitted from the target were detected with organic liquid scintillators
(5.08-cm-diameter 5.08-cm-thick NE213) equipped with an electric circuit for pulse-shape
discriminations (PSD) and time-of-flight (TOF) measurements 4) . The beam current was
measured using a current integrator connected to the target. These digital data were collected
with the CAMAC system event by event using the Kakuken on-line data acquisition system
(KODAQ) for off-line analysis 6) .
Neutron TOF spectra were obtained by gating the events with the two light output data
(total component and slow component) on the two-dimensional graphical plots after removing
random background events. The pulse height distribution of the light output was calibrated
with -rays from a 241 Am-Be, 60 Co, and 137 Cs source with energies of 4.43 MeV, 1.173 and
1.333 MeV, and 0.662 MeV, respectively. The detector bias was set at 1.3 MeV for neutrons.
The TOF spectra were converted into neutron energy spectra, according to the Lorentz
conversion 5) . The energy spectrum data were normalized by dividing with the detector solid
angle, an integrated charge of the incident beam. The detection efficiency was calculated using
the Monte Carlo code SCINFUL-R 7) .
Experimental uncertainties were estimated on the basis of systematic error propagation.
Statistical uncertainties were generally below 10% but increased to above 10% at the highest
energy. The uncertainty of detector efficiency with the SCINFUL-R code was estimated to be
5% 8) . The uncertainties of beam current measurements were estimated to be 5%.
The energy spectrum of prompt -rays was measured with the same NE213 scintillator of
5.08 cm thickness and diameter. After discriminating the -ray events from those of neutrons
by the PSD method, the energy spectrum of -rays emitted within 50 ns around the prompt
-ray peak was obtained with the unfolding technique using the FERDOU code 8) . The
response functions of -rays for the incident energies up to 20 MeV were calculated by
applying the EGS4 code 9) .
The TTYs of neutrons obtained from various targets for each emission angle are
shown in Figs.2, 3, 4, 5, 6, and 7 with the corresponding calculation results obtained with
MCNPX ver. 2.5. The energy spectra covered from 1.5 MeV up to 16 MeV. The highest energy
was consistent with each reaction Q-value, e.g. (-2.44 MeV) of the 18 O(p,n) 18 F reaction. The