1 neutron effective dose calculation behind concrete shielding of charge particle accelerators with...
DESCRIPTION
3 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.TRANSCRIPT
1
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. KrylovJoint Institute for Nuclear Research, Dubna,
Russia
2
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.
3
IntroductionCalculations 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.
4
The purpose is comparison of results of calculations of neutron doses behind concrete shielding by method Monte-Carlo and phenomenological method.
5
Methods used
The calculation by a method of Monte-Carlo was carried out with the program MCNP4B (package of libraries DLC189). The statistical error of the calculated data did not exceed 5%.
6
The phenomenological method based on following expression was used :
EdEBEhRfEdEef /exp, 2
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.
7
The geometry of calculation
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.
Neutron Source нейтронов
d
30O
Location of dose calculation for phenomenological method
Cell for Monte Carlo calculation: cylinder h = 50cm, r = 75 cm
5 m
10 m
8
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.
0 50 100 150 200 250 30010-11
10-10
10-9
10-8
10-7
10-6
10-5
10-4
10-3
10-2
10-1
100
5 MeV
20 MeV
50 MeV
100 MeV
Att
enua
tion
fakt
or o
f neu
tron
eff
ecti
ve d
ose
Shielding thickness(d), cm
Calculation by Monte-Carlo method for energy neutron Е=5 МэВ Е=20 МэВ Е=50 МэВ Е=100 МэВ
9
20 30 40 50 60 70 80 90 1001E-13
1E-12
1E-11
1E-10
1E-9
1E-8
1E-7
1E-6
1E-5
1E-4
1E-3
3m
2m
1m
Effe
ctiv
e do
se, p
Sv
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
10
0 2 4 6 8 100
2
4
6
8
10
Y A
xis
Title
X Axis Title
###
1,0 1,5 2,0 2,5 3,0
1E-8
1E-7
1E-6
1E-5
1
2
Effe
ctiv
e do
se, p
Sv
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
11
1,0 1,5 2,0 2,5 3,0
1E-8
1E-7
1E-6
1E-5
1
2
Effe
ctiv
e do
se, p
Sv
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 :
1 – phenomenological method, 2 - Monte-Carlo
12
1,0 1,5 2,0 2,5 3,0
1E-13
1E-12
1E-11
1E-10
1E-9
1E-8
1E-7
1E-6
2
1
Effe
ctiv
e do
se, p
Sv
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 :1 – phenomenological method, 2 - Monte-Carlo
13
10 10010
15
20
25
30
35
40
2
1
Atte
nuat
ion
leng
th, c
m
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
14
20 30 40 50 60 70 80 9010023456789
101112131415161718
2
1
Build
-up
fact
or
Neutron energy, MeV
. Build-up factor for effective dose of neutrons:1 – phenomenological method, 2 - Monte-Carlo
15
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 half-value layer for neutron effective dose, that is from 10 cm to 30 cm for considered energies and thickness of shields.