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. Krylov
Joint 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
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
.
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 calculat
ed data
did
not
exceed 5%.
6
The phenomenological method
based on following expression
was used :
E
d
E
B
E
h
R
f
E
d
E
ef
/
exp
,
2
This
equation
applies
to
a
source
of
monoenergetic
neutrons
of
energy
E
with
symbols
having
the
following
meanings
:
Е
ef
(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
с
m up
to 300
с
m 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
30
O
Location of dose
calculation for
phenomenological
method
Cell for M
onte 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
p
oint
neutron
source
with energy
5, 20, 50
and
100
MeV at
5
m
from shield.
0
50
100
150
200
250
300
10
11
10
10
10
9
10
8
10
7
10
6
10
5
10
4
10
3
10
2
10
1
10
0
5 MeV
20 MeV
50 MeV
100 MeV
Attenuation faktor of neutron effective dose
Shielding thickness(d), cm
Calculation by MonteCarlo 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
100
1E13
1E12
1E11
1E10
1E9
1E8
1E7
1E6
1E5
1E4
1E3
3m
2m
1m
Effective dose, pSv
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
10
0
2
4
6
8
10
Y Axis Title
X Axis Title
###
1,0
1,5
2,0
2,5
3,0
1E8
1E7
1E6
1E5
1
2
Effective dose, pSv
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
9
0
with
an
axis
of
proton
beam
:
1
–
phenomenological
method
,
2

Monte

Carlo
11
1,0
1,5
2,0
2,5
3,0
1E8
1E7
1E6
1E5
1
2
Effective dose, pSv
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
9
0
0
with
an
axis
of
proton
beam
:
1
–
phenomenological
method
,
2

Monte

Carlo
12
1,0
1,5
2,0
2,5
3,0
1E13
1E12
1E11
1E10
1E9
1E8
1E7
1E6
2
1
Effective dose, pSv
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
0
0
with
an
axis
of
proton
beam
:
1
–
phenomenological
method
,
2

Monte

Carlo
13
10
100
10
15
20
25
30
35
40
2
1
Attenuation length, cm
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
90
100
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
2
1
Buildup factor
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
.
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