Transcript hp.ujf.cas.cz

M&C 2005 Avignon
September 12-15, 2005
MCNPX STUDIES OF SPALLATION NEUTRON
PRODUCTION ON A THICK LEAD TARGET
Mitja Majerle
NPI CAS
Řež, The Czech Republic
Introduction
 Generally :
 Experiments with high-energy protons on heavy targets
(~ADS), spallation neutrons, direct beam
 We measure transmutation possibilities, neutron fields,
we compare data with model simulations
 Focus – The PHASOTRON experiment :
Protons, neutron field (threshold detectors)
... and the simulations
What and how we calculate
Comparison with the experiment
The influence of the setup parts
M&C 2005, Avignon, September 12-15, 2005
•Neutrons and protons react with detectors: (n,g), (n,2n), (n,xn), (n,a), (p,n), (p,a), ...
•Yields of produced elements are detectable in g-detectors
M&C 2005, Avignon, September 12-15, 2005
Experimental results
B=Number of produced nuclei in 1 g of material per one incident proton
27
Al(n,a )24Na
B [g-1 proton-1]
1E-05
1E-06
1E-07
1E-08
0
5
10
15
20
25
30
35
40
207
45
Bi(n,xn)Bi
Distance along the target [cm]
1E-05
Bi-206
Au(n,x)Au
1E-05
Au-194
1E-06
Au-196
-1
-1
B [g proton ]
1E-04
Au-198
B [g-1 proton-1]
196
Bi-205
1E-06
Bi-204
Bi-203
1E-07
Bi-202
Bi-201
1E-08
0
1E-07
10
20
30
40
Distance along the target [cm]
1E-08
0
5
10
15
20
25
30
35
40
45
Distance along the target [cm]
M&C 2005, Avignon, September 12-15, 2005
50
Simulations, how/what
we calculate
 MCNPX code v. 2.4.0 (on
Linux, parallel computing)
 Input :
 setup geometry
 starting conditions
 Output 1:
 neutron distribution
 Cross-section libraries
(Au, Al - ENDF; Bi experimental; Iodine - ?)
 Output 2:
 masses of produced
elements or B-values
M&C 2005, Avignon, September 12-15, 2005
Neutron spectra + cross-sections
• We can convolute the calculated neutron
spectrum with the cross-section for a given
reaction (SSW+HTAPE3X+convolution).
197Au(n,2n)196Au
Neutrons per incident proton
Calculated neutron spectrum
1E+1
1E+0
1E-1
27Al(n,a)24Na
1E-2
1E-3
Spectrum information
only for regions
1E-4
1E-5
1E-7
1E-5
1E-3
1E-1
1E+1
1E+3
Energy [MeV]
197Au(n,g)198Au
• Computer can convolute the spectrum with
cross-sections and outputs B (F4+FM tally).
M&C 2005, Avignon, September 12-15, 2005
Calculations vs. experiment
27
Al(n,a )24Na
1,5
1,4
1,3
Ratio
Calculated values in comparison with
the experiment for 27Al(n,a)24Na
1,2
1,1
1
0,9
27
Al(n,a )24Na
0,8
0,7
0
5
10
1E-5
20
25
30
35
40
45
197
Au(n,2n)196Au
1E-6
experimental
1,6
1,4
simulation
1,2
Ratio
1E-7
1E-8
1
0,8
0,6
0,4
0
5
10
15
20
25
30
35
40
0,2
45
0
Distance along the target [cm]
0
5
10
15
20
25
30
35
40
45
35
40
45
Distance along the target [cm]
197
Au(n,4n)194Au
1,6
1,5
1,4
Ratios between calculated and
experimental values for 24Na, 196Au, 194Au
Ratio
B [g-1 proton-1]
15
Distance along the target [cm]
1,3
1,2
1,1
1
0,9
0,8
0,7
0
5
10
15
20
25
30
Distance along the target [cm]
M&C 2005, Avignon, September 12-15, 2005
Influence of the setup parts
 Concrete walls :
Neutrons are
moderated and
reflected back
197
Au(n,g)198Au
B [g-1 proton-1]
1E-4
1E-5
experimental
no walls
HTAPE3X
FM
1E-6
1E-7
1E-8
0
5
10
15
20
25
30
35
40
45
Distance along the target [cm]
M&C 2005, Avignon, September 12-15, 2005
Influence of other simplifications
 Extensive calculation tests on PHASOTRON and EPT setup
revealed that :
 HTAPE3X and F4 methods results do not always agree.
 Beam profile and displacement influence the neutron field (3 mm ~
5%).
 The use of different models (BERTINI, CEM, ISABEL) ~ 10%.
 Detectors minimally influence the neutron field.
 Metal holders, tables, ... have minimal influence.
 ...
M&C 2005, Avignon, September 12-15, 2005
Parallel processing
90
Histories simulated in 1 s
 The use of parallel
processing (PVM)
speeds up our
calculations significantly.
80
8000
6000
70
60
50
4000
nps=2000k
nps=50k
40
30
2000
20
10
0
0
2000
4000
6000
8000
10000
Accumulated processor power [MHz]
M&C 2005, Avignon, September 12-15, 2005
Conclusion
We try to imitate an ADS systems with the
setup
We can describe new, similar systems
with the computer with the accuracy (50%)
Thank you.
M&C 2005, Avignon, September 12-15, 2005