Transcript Neutron Effective Dose calculation behind Concrete

Neutron Effective Dose calculation behind
Concrete Shielding of Charge Particle
Accelerators with Energy up to 100 MeV
V. E Aleinikov, L. G. Beskrovnaja, A. R. Krylov
Joint Institute for Nuclear Research, Dubna,
Russia
1
Introduction
All accelerators of the charged particles
with energy up to 100 MeV represent a
complex geometrical design with set of
sources of radiation. The most penetrating
component of radiation at the working
accelerator is the neutrons of a wide energy
spectrum.
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Introduction
Calculations of shielding and the doses of neutrons
behind shield are used various methods and, created on
their basis, algorithms:
•
Method Monte-Carlo allows carrying out direct
modeling of radiation transport through substance in real
geometry. The codes, created on its basis, require essential
expenses of computer time at account of a dose behind
rather thick shields.
•
Much more practicable method is phenomenological
approach based on existent experimental and calculated
data of dose attenuation by shielding.
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The purpose is comparison of results
of calculations of neutron doses
behind concrete shielding by
method Monte-Carlo and
phenomenological method.
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Methods used
The calculation by a method of MonteCarlo was carried out with the program
MCNP4B (package of libraries DLC189). The
statistical error of the calculated data did not
exceed 5%.
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The phenomenological method based on following expression
was used :
f
E ef  d , E   2  h  E   B  E   exp   d /   E 
R
This equation applies to a source of monoenergetic neutrons of
energy E with symbols having the following meanings:
Еef (d,Е) is the effective dose behind shield with thickness of d;
f is the neutron yield per steradian;
R is the distance from the source to the point of interest outside
the shield;
h(E) is the conversion coefficient that relate neutron fluence to the
effective dose;
B(E) is the build-up factor of neutrons;
(Е) is the attenuation length for effective dose through the shield.
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The geometry of calculation
d
10 m
Cell for Monte Carlo
calculation: cylinder
h = 50cm, r = 75 cm
Neutron
Source
30O

нейтронов

Location of dose
calculation
for
phenomenological
method
5m
Geometry
of
barrier
shielding
was
chosen
for
comparison
of
calculation methods. The thickness of the shield varied from 25 сm up
to 300 сm with a step 25 cm. The calculations have been performed by
Monte Carlo and phenomenological methods for
monoenergetic
neutrons with energy from 5 MeV to 100 MeV as well as for neutron
spectra produced by protons with energies of 30 MeV and 72 MeV in
thick targets.
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A tten u a tio n fa kto r o f n eu tro n effectiv e d o se
10
0
10
-1
10
-2
10
-3
10
-4
10
-5
10
-6
10
-7
10
-8
10
-9
10
-1 0
10
-1 1
100 M eV
50 M eV
20 M eV
5 M eV
C a lc u la tio n b y M o n te -C a rlo m e th o d
fo r e n e rg y n e u tro n
Е = 5 М эВ
Е = 2 0 М эВ
Е = 5 0 М эВ
Е = 1 0 0 М эВ
0
50
100
150
200
250
300
S h ie ld in g th ic kn e ss(d ), c m
Comparison between Monte Carlo and phenomenological methods calculated
data of neutron effective dose attenuation by concrete. Isotropic point neutron
source with energy 5, 20, 50 and 100 MeV at 5 m from shield.
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1E-3
1E-4
1m
Effective dose, pSv
1E-5
1E-6
1E-7
2m
1E-8
1E-9
1E-10
3m
1E-11
1E-12
1E-13
20
30
40
50
60
70
80 90 100
Neutron energy, MeV
The neutron effective dose as a function of incident neutron energy
calculated for concrete shield of the thickness indicated.
Phenomenological method, Monte-Carlo
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1E-6
###
10
2
8
Y Axis Title
Effective dose, pSv
1E-5
1E-7
6
4
2
1
0
1E-8
0
2
4
6
8
10
X Axis Title
1,0
1,5
2,0
2,5
3,0
Shielding thickness, m
Comparison of effective dose calculations as a function of a concrete
shield thickness when the shield irradiated by neutrons produced in a
copper thick target by protons with energies of 72 MeV at an angle of 90
with an axis of proton beam :
1 – phenomenological method, 2 - Monte-Carlo
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Effective dose, pSv
1E-5
1E-6
2
1E-7
1
1E-8
1,0
1,5
2,0
2,5
3,0
Shielding thickness, m
Comparison of effective dose calculations as a function of a concrete
shield thickness when the shield irradiated by neutrons produced in a
copper thick target by protons with energies of 72 MeV at an angle of 900
with an axis of proton beam :
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1 – phenomenological method, 2 - Monte-Carlo
1E-6
Effective dose, pSv
1E-7
1E-8
1E-9
1
1E-10
1E-11
1E-12
2
1E-13
1,0
1,5
2,0
2,5
3,0
Shielding thickness, m
Comparison of effective dose calculations as a function of a concrete
shield thickness when the shield irradiated by neutrons produced in a
copper thick target by protons with energies of 30 MeV at an angle of 00 with
an axis of proton beam :
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1 – phenomenological method, 2 - Monte-Carlo
.
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Attenuation length, cm
35
30
1
25
20
15
10
2
10
100
Neutron energy, MeV
The variation of the attenuation length of effective dose for monoenergetic
neutrons in concrete as a function of neutron energy.
1 – phenomenological method, 2 - Monte-Carlo
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Build-up factor
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
2
20
30
40
50
60
70 80 90100
Neutron energy, MeV
.
Build-up factor for effective dose of neutrons:
1 – phenomenological method, 2 - Monte-Carlo
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Conclusions.
Data obtained by these two methods agree
within factor 2 over considered range of neutron
energies and shielding thickness. Comparison of
the results shows that difference in shield’s
thickness between calculated by Monte Carlo and
phenomenological method is not exceeded halfvalue layer for neutron effective dose, that is from
10 cm to 30 cm for considered energies and
thickness of shields.
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