Forschungszentrum Karlsruhe
in der Helmholtz-Gemeinschaft
Nuclear Physics Institute
Řež
Simulation of quasi-monoenergetic
Li(p,n) neutron source up to 50 MeV proton energy
S.P. Simakov1, P. Bém2, V. Burjan2, U. Fischer1, M. Götz2,
M. Honusek2, V. Kroha2, J. Novák2, E. Šimečková2
1) Association Euratom-FZK, Institut für Reaktorsicherheit,
Forschungszentrum Karlsruhe GmbH, Germany
2) Association Euratom-IPP/NPI.CR, Nuclear Physics Institute,
Řež , Czech Republic
Workshop on Activation Data EAF 2007,
Prague, 2 - 4 October 2006
Computational Tools and Data for Li neutron Simulations up to 50 MeV
Neutron production and transport calculation:
-
Charge particle transport code – MCNPX (version 2.5)
Cross sections files and models for (p,xn) reactions on light nuclei:
Lithium-7 as a neutron source:
Eth = 1.88 MeV for 7Li(p,n0)7Be(g.s.)
= 2.38 MeV for 7Li(p,n1)7Be(1st excited state = 0.43 MeV)
= 3.70 MeV for 3-body breakup 7Li(p,n3He)4He
= 7.70 MeV for 7Li(p,n2)7Be(2nd excited state = 4.55 MeV)
LA-150h proton cross sections library (S.G. Mashnik et al.,
Report LA-UR_00-1067, Los Alamos 2000)
Carbon as a proton beam stopper and parasitic neutron source:
12C
abundance 98.9%
12C(p,n), E = 19.6 MeV
th
LA-150h library
2-4 October 2006, Prague
13C
abundance 1.1%
13C(p,n), E = 3.2 MeV
th
MCNPX in-build model
Workshop on Activation Data EAF 2007
2
Double Differential Cross Sections (DDX) for 7Li(p,xn) reaction at Ep= 20-40 MeV
2. J.W. Wachter, NIM 113(1973)185
Ep = 40.6, 63.8 MeV, Θ = 0 deg
(data looks strange)
3. J. Jungerman, NIM 94(1971)421
Ep = 39.3 MeV, Θ = 0 deg
4. M. Österlund, NIM B241(2005)419
Ep = 21.8, 46.5 MeV, Θ = 0 deg
(DDX not available in EXFOR yet)
7
o
Li(p,xn), Ep = 39.3 MeV, Θn = 0
1
10
MCNPX/LA-150h
o
1. M. McNaughton, NIM 130(1975)555
Ep = 15, 20 ,30 MeV, Θ = 0 deg
(DDX not available in EXFOR)
dσ/dEdΩ (θ = 0 ), mb/sr/MeV
Known Measurements:
Wachter'73
0
10
Jungerman'71
-1
10
0
5
10
15
20 25 30 35 40
Neutron Energy, MeV
45
The measured DDX for Li(p,xn) are scarce, only at 0 deg. …;
LA-150 evaluation reasonable reproduces available (in EXFOR) experimental data;
The high energy peak shares ≈ 40% of the whole neutron spectra at 0 deg!
2-4 October 2006, Prague
Workshop on Activation Data EAF 2007
3
Monoenergetic Neutron Sources employing Li(p,n) reaction
Laboratory
Neutron
Li
Proton
Reference
Energy,
thickness,
current,
MeV
mm
μA
With proton beam deflection magnet
25 – 70
3
10
NIM A421 (1999) 284
Louvain Univ.,
Belgium
TIARA,
41 – 85
3.6 – 6.75
1-3
NIM A428 (1998) 454
Japan
Uppsala Univ.
22 – 142
2 – 24
1 - 12
NIM B241 (2005) 419
Sweden
Without deflection magnet, ≈ 2 cm thick C proton beam stopper behind Li target
CYRIC,
20 – 40
2
?
NIM A389 (1997) 463
Japan
NPI/Řež,
< 35
2
10
P. Bĕm, this workshop
Czech
For activation measurements the thin Li plate and thick C stopper looks more
preferable than deflecting magnet, since the activation foil could be located
closer to the neutron source, but the contribution of the C(p,xn) neutrons
should be assessed.
2-4 October 2006, Prague
Workshop on Activation Data EAF 2007
4
Example of the
Li Neutron Source
with deflecting magnet
at TSL, Uppsala
/M. Österlund et al.,
NIM B241(2005)419/
Look as drawbacks for neutron
activation experiments:
- Activation foil being located
close to the Li target will be
irradiated by the protons
(or use a ring shape with
a hole for p-beam ?),
otherwise has to be positioned
at ≈1 m from the Li target,
where n-Flux is much lower !
- Deflecting magnet causes
additional expenses
2-4 October 2006, Prague
Workshop on Activation Data EAF 2007
5
Li/C Neutron Source at CYRIC, Tohoku University
/Y. Uwamino et al., NIM A389(1997)463/
Target set-up:
- 2 mm thick 7Li
- 12 mm thick carbon stopper
Neutron Spectra measurement:
- TOF technique
- NE 213 scintillator at 12 m
- Proton Energies = 20 - 45 MeV
2-4 October 2006, Prague
Workshop on Activation Data EAF 2007
6
o
Neutron Flux (θ = 0 ), n/MeV/sr/μC
Validation of MCNPX calculations against CYRIC data
Energy Differential Neutron Yield
7
o
Li/C + protons (Ep= 40 MeV), Θn = 0
9
10
7
Li/C+p(40MeV)
7
Li+p(40MeV)
8
10
thick C +
p(39.2MeV)
7
10
nat
C+p(39.2 MeV)
12
C(p,xn)
6
10
0
5
10
13
C(p,xn)
15 20 25 30 35
Neutron Energy, MeV
40
MCNPX/LA-150h reasonable reproduces CYRIC neutron source spectrum
and thick carbon neutron yield
2-4 October 2006, Prague
Workshop on Activation Data EAF 2007
7
Li/C neutron source set-up at NPI/Řež
/P. Bem et al., this Workshop/
7 cm
18 cm
CH2 Radiator
45o
42
cm
Foil to be
activated
DΔE2
DΔE1
Following details of the set-up were simulated in MCNPX:
Li-plate, C-stopper, Cooling media, Al-flange,
Activation foil, CH2 radiator, ∆E-E proton detector
2-4 October 2006, Prague
Workshop on Activation Data EAF 2007
8
Energy Neutron Fluxes in Activation Foil and CH2 Radiator
as predicted by MCNPX/LA-150h
Energy differential Fluxes
NPI/Řež: Flux for 10 μA proton current
Neutron Flux, n/MeV/sr/μC
7
Position
Li/C Target, Ep = 30 MeV
7
10
Foil dia. 1.4 cm at 7 cm
7
Li+C(p,xn)
C(p,xn)
6
10
Total
>25MeV
Activation Foil
at 7 cm, Li+C
0.9 10+9
0.3 10+9
(36%)
Only C stopper
0.02 10+9
(3%)
CH2 Radiator
at 18 cm
0.1 10+9
5
10
CH2 radiator
dia 1.6 cm at 18 cm
4
10
0
5
10
15
20
25
Neutron Energy, MeV
30
- the high energy peak of Li/C source
at NPI/Rez facility amounts 40%, ΔE = 1.7 MeV
- neutrons from Carbon stopper contributes
only 3% and mainly below 5 MeV
2-4 October 2006, Prague
Flux, n/cm2/s
Workshop on Activation Data EAF 2007
0.05 109
(41%)
Comparison with 14 MeV sources:
1. TU/Dresden: 1.9 10+9 n/cm2/s
/K. Seidel et al. this Workshop/
2. SNEG-13/Sergiev Posad:
10. 10+9 n/cm2/s
/V.D. Kovalchuk et al. IAE-5589/8 (1992)/
9
Proton Recoil Spectrum from CH2 Radiator
Proton Flux, p/MeV/sr/μC
16000
Details of calculations:
7
Li/C + p (30 MeV)
o
H(n,p)n, Θp = 45
14000
12000
10000
Calculations
without
with energy resolution
8000
6000
1. no counts in the
MCNPX proton tally (?)
2. for transformation
neutron => proton spectra
we used:
Experiment
Ep = En * cos2(Θp)
protons or noise ?
4000
dσ(Ep)/dΩ = σnp(En)*cos(Θp)
2000
0
0
2
4
6
8 10 12 14 16
Proton Energy, MeV
18
- good prediction of the main proton group ;
- the reason of the underestimation below 10 MeV
could be the Si detector noises or Li target neutrons (?)
2-4 October 2006, Prague
Workshop on Activation Data EAF 2007
10
Conclusions
•
The MCNPX code and Los Alamos evaluation for the 7Li(p,n) and
12C(p,n) reactions cross sections was shown reasonably reproduce
available spectral data for neutron source consisting of the thin lithium
foil and thick carbon beam stopper and driven by the proton beam
•
Such a source at, e.g., 30 MeV incident proton energy and 10 μA current
will produce ≈10+9 neutrons/cm2/s in the small foil located at the distance
of a few cm:
-
•
40% of the neutrons being a monoenergetic group with energy 28 MeV and
width 1.7 MeV
the neutrons born in the Carbon beam stopper contribute around 3% of Li(p,n)
ones and have the energy distribution with a maximum below 5MeV
The main energy group in the proton spectra of the recoil telescope has
been successfully reproduced by employing n-p scattering classical
formula, whereas the low energy part needs further analyses
2-4 October 2006, Prague
Workshop on Activation Data EAF 2007
11