Neutron-Production Double-Differential Cross Sections for 150 MeV
Neutron-Incidence on Fe
Hiroyuki Arakawa1 , Tsuyoshi Kajimoto1 , Shusaku Noda1 , Takehito Watanabe1 ,Nobuhiro Shigyo1 , Kenji Ishibashi1 , Satoshi Kunieda2 , Robert C. Haight3 ,1

Kyushu University, 744, Motooka, Nishi-ku, Fukuoka 819-0395 Japan

2Japan Atomic Energy Agency, Tokai, Naka, Ibaraki 319-1195 Japan
3Los Alamos National Laboratory, Los Alamos, NM 87545 USA

The neutron-production double-differential cross sections for the neutron-induced reaction were measured onFe at 140 – 160 MeV. Neutrons produced by a 800 MeV proton-bombarded spallation target were used as incident
particles. The results are compared with calclated data.

1Introduction

High-energy neutron production double-differential cross sections are important for realization of accelerator
driven systems (ADS) and radiotherapy. Proton-induced neutron-production double-differential cross sections
have been measured up to 3 GeV. However, data of neutron-induced neutron-production double-differential
cross sections above 100 MeV are insufficient because of neutron measurement difficulties and a few quasimonochromatic neutron sources. Utilization of a continuous energy neutron source by spallation reaction enables
us to measure cross section for various incident energies at a time.
The purpose of this study is to measure the neutron-production double-differential cross sections at 150 MeV
on Fe using a continuous energy neutron source.

2

Experiments

Experiments were performed at the Weapons Neutron Research (WNR) facility in Los Alamos Neutron ScienceCenter (LANSCE)1) which has an 800 MeV proton linear accelerator. Neutrons generated at a tungsten spallation
target (Target-4) were used as incident particles. The neutron energies cover a wide energy range up to 750 MeV.
The distance between the spallation target and the experimental room is about 90 m. The geometry of the WNR
facility is illusrated in Fig. 1.
Experiments consist of 2 parts. One part was the measurement of response functions of neutron detectors.
The energy spectra of emitted neutrons were derived from unfolding their deposition-energy spectra with theresponses of the detectors. These response functions were measured by using the spallation neutrons which werecollimated to 2 mm in diameter. The alignent of the experiment is in Fig. 2. The response function of each
NE213 liquid organic scintillator 12.7 cm thick and 12.7 cm in diameter was measured by irradiating neutrons
from the Target-4. The time-of-flight (TOF) between the spallation target and a neutron detector and the charge
spectrum from the photomultiplier connected with the NE213 scintillator were measured.

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(2.

Fig. 1. Schematic view of the beam line at the WNR facility2)

Fig. 2. Arrangement of the measurement for response function

Another part of the experiment was the measuremnt of double-differential cross sections. Setup of the measurement are shown in Fig. 3.
Six NE213 scintillators were employed to detect neutrons emitted from an Fe sample (10 mm thick, φ50 mm)
and placed at 15◦ , 30◦ , 60◦ , 90◦ , 120◦ and 150◦ . The distance between the sample and the detectors were about
0.7 m. A fission ionization chamber3) was set to know the incident-neutron flux. A 10 mm thick NE102A plastic

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Fig. 3. Set up of the measurement for deposition-energy spectra

scintillator as a veto detector was set in front of each NE213 scintillator. The beam size was adjusted to 36 mmin diameter.

3Analysis

3.1

Elimination of charged particles and gamma rays

Charged particle events were eliminated by discrimination of signals from an NE102A scintillator plastic scintillators because charged particles gave larger energy in an NE213 scintillator than neutrons and gamma-rays.
An example of ADC spectra by an NE102A plastic scintillator is shown in Fig. 4.

Fig. 4. An example of ADC spectrum of a veto detector

Gamma-ray events were discriminated using the two gate integration method 4) since NE213 liquid organic
scintillators were sensitive to not only neutrons but also gamma rays. Fig. 5 stands for schematic view of the gate2006 Symposium on Nuclear Data

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integration method. Comparison between ADC spectrum with the prompt-gate and that with the delayed-gate
enables to discriminate between neutron events and gamma ray ones. Fig. 6 illustrates an example of the 2D-plotof the ADC spectra with the prompt gate and the delayed one.
TimePulse hight(log scale)γ -rayAnalogue signals
Neutron  

Prompt gate  

Delayed gate

Fig. 5. Schematic view of gate integration method

Fig. 6. Discrimination of neutrons and gamma rays

3.2

Incident neutron energy

Incident neutron energies were obtained by neutron flight times between Target-4 and NE213 scintillators.
Because the distance between Target-4 and the sample were much longer than those between the sample and thedetectors, the flight time of the latter was negligible. Fig. 7 shows a schematic view of the TOF measurementalignment. The timing of flash gamma-rays from the spallation target was used as the time base of TOF analysis.
Fig . 8 shows one of TOF spectra.

3.3Incident neutron flux

The number of incident neutrons was possible to be gotten by the equation
φµp (En )∆En =nf (En )∆En
1×σ(En ) × ef f × ρfnµp × Sbeam(1)

where φµp (En ), nf (En ), and σ(En ) are the number of incident neutron flux, the number of fission events detectedby the fission chamber, and the fission cross sections of 238 U for corresponding neutron energy En 5) , respectively.

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Fig. 7. Schematic view of the TOF measurement alignment

Fig. 8. TOF spectrum between the spallation target and a neutron detector

ef f is the detection efficiency of the fission chamber, and ρf is the arial density of the number of atoms of fissile
material on the foil in chamber. Sbeam is the cross section of the beam.

3.4

Calibration

Charge-integration spectra were calibrated to get corresponding electron-equivalent light-output for all neutrondetectos. The gamma-ray Compton edges of 60 Co and Pu-Be sealed sources were converted into light-unit withthe semi-empirical formula by Dietze et al.6) for low-energy (a few MeV) parts. For the calibrations of higherenergy, neutron energies were identified by the TOF between the spallation target and neutron detectors and wereconverted into light-unit by the empirical equation by Cecil et al.7)
Te = 0.83Tp − 2.82[1.0 − exp(−0.25Tp0.93)](2)

where Tp , Te are proton and electron energy in an NE213 scintillator, respectively. The maximum channel of theADC spectrum was used as corresponding charge-integration values. The relationship between charge-integrations
and electron-equivalent light-outputs for the NE213 scintillator used at 90◦ is shown in Fig. 93.5

Response functions and Deposition-energy spectra

Response functions normalized by the number of incident-neutrons were shown in Fig. 10. In this experiment,
the SCINFUL-QMD8) calculations adjusted to reproduce experimental data with light attenuation were used as2006 Symposium on Nuclear Data

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120

Spollation Neutrons
Checking SourceFit

Light Output [MeVee]1008060402000100200300400500600700

ADC [Channel]

Fig. 9. Relationship between integrated charge and light output for 60◦ detector

response matrix elements below 30 MeV incident energy for all neutron detectors since there are no experimental
data below 30 MeV incident energies.

SHINFUL-QMD
Measured values

Response [1/MeVee]

10-2
10-3
10-4
10-5

10-6204060
Light Output [MeVee] 80
10012020406080

100120140160

Neutron energy [MeV]Fig. 10. Response functions of the NE213 scintillator at 60◦Deposition-energy spectra at 140 – 160 MeV normalized by the number of incident-neutrons and subtracted

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background (sample-out) spectra are shown in Fig. 11.
10-3

10-3

10-4

10-5

10-6

10-7

10-8

10-5

10-6

10-7

11010-8

100

110-8

100

110-6

10-7

10-4

120 deg

10-5

10-6

10-7

100

Light Output [MeVee]

10-8

10100

Light Output [MeVee]

Counts [1/sr/MeVee]

10-5

1010-610-3

10-4

90 degCounts [1/sr/MeVee]

Counts [1/sr/MeVee]

1010-3110-5Light Output [MeVee]

10-3

10-460 deg

10-7

Light Output [MeVee]

10-8

10-430 deg
Counts [1/sr/MeVee]

15 degCounts [1/sr/MeVee]

Counts [1/sr/MeVee]

10-4

10-3

150 deg

10-5

10-6

10-7

110100

10-8

1Light Output [MeVee]

10100

Light Output [MeVee]

Fig. 11. Deposition energy spectra at 140 – 160 MeV neutron incident energy

3.6Unfolding

The energy spectra of emitted neutrons were derived by unfolding their deposition-energy spectra with theresponses of the detectors. In this experiment, elastic scattering component was considered separatly from theother reaction ones. The determinant of this experiment was  
 .  .
 . ..
..
..
..
..
..
.
. .
   ..      ..
·k+·yξ  =  . aξ,E
ax.   Eξ,Ein  · xel · k  


..
..
..
..
..
..
.
.
.
.
.
.

(3)

where yξ , aξ , E, and xE were deposition-energy spectra, response function, outgoing energy spectra (unfoldingresults), respectively. xel was elastic scattering factor. k was matting factor for absolute value of response
functions with deposition-energy spectra. xE (=x(E, θ)) was assumed to conform following equation.
(!)
 23d σx(E, θ) XE + m − pβi cos θ
p==pAi exp −−mdEdΩρ∆E
1 − βi2i=1(4)where E and p is the kinetic energy (MeV) and the momentum (MeV/c) of an emitted neutron in the laboratory
frame and m the neutron mass (MeV), respectively. The quantities of A, β, and T are called amplitude, velocity

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and temperature parameters, respectively. Three components of i =1 to 3 correspond to individual processes of
the cascade, the preequilibrium and the evaporation. In the process of unfolding these deposition-energy spectra,
neutron-induced neutron-production double-differential cross sections were parameterized with moving source
model by SALS code9) as a least mean square approximation program.

4Results

The provisional parameterized double-differential cross sections by the moving source model with it’s elements
as experimental results for 140 – 160 MeV neutron incident energy are shown in Fig. 12. These results werecompared with the PHITS10) calculation data, the evaluated value of LA15011) (GNASH12) + Kalbach and Mann’ssystematics13) ) and JENDL-HE14) . The experimental results show that under 50 MeV neutron emission energy
are approximately good agreement with calculated data except for 15 ◦ and 30◦ results. 15◦ and 30◦ experimental
results overestimate calclation data from 5 MeV to 100 MeV neutron emission energy and underestimated above
that. For backward angles of experimental results over 50 MeV neutron emission energy have some discrepancies
with calclation data.
10210210215 deg

30 deg

10-1101
DDX [mb/sr/MeV]

100

10-2

100

10-1

110-210100
Neutron emission energy [MeV]1021120 deg

10100
Neutron emission energy [MeV]1

DDX [mb/sr/MeV]

100

10-2

100

1010-1110150 deg

110-1

1

Neutron emission energy [MeV]

10DDX [mb/sr/MeV]

DDX [mb/sr/MeV]

10-2

10100
Neutron emission energy [MeV]10290 deg
1100

100

10-1

102

1010-260 deg

101
DDX [mb/sr/MeV]

DDX [mb/sr/MeV]

10110010-1110100
Neutron emission energy [MeV]

10-2110100
Neutron emission energy [MeV]Fig. 12. Double-Differential Cross Sections for 140 – 160 MeV neutron incident energy with calclated data

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5Conclusion

The neutron-production double-differential cross sections at 150 MeV on Fe are measured using a continuous
energy neutron source. The double-differential cross sections were parametalized by moving source model. The
experimental results have some discrepancies with calculated data. To understanding these discrepancies, formore detailed analysis are needed.
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