Neutron Effective Dose calculation behind Concrete Shielding of Charge Particle Accelerators with Energy up to 100 MeV

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 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
100
1E-13
1E-12
1E-11
1E-10
1E-9
1E-8
1E-7
1E-6
1E-5
1E-4
1E-3
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
1E-8
1E-7
1E-6
1E-5
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
1E-8
1E-7
1E-6
1E-5
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
1E-13
1E-12
1E-11
1E-10
1E-9
1E-8
1E-7
1E-6
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


Build-up 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
.