Progress
report
ACTIVATION
STUDY OF ATLAS DETECTOR
Here is presented some result of the
first phase of ATLAS activation study which is under way in the Moscow
Engineering Physics Institute (MEPhI).
The aim of the first phase is to collect
data necessary for a comprehensive estimation of both activation and gamma dose
rate due to operation of LHC after shout down. Both activation induced by low
energy neutrons and high energy hadrons is taken into consideration.
As a result of implementation of the
first phase, the major factors relevant to activation of ATLAS will be
determined for a further detail research, namely: distribution of specific
induced activity for commonly used materials (steel, cooper, aluminum, and so
on); areas (systems/subsystems of the detector) where the materials will be
highly radioactive, radioactive, and slightly radioactive; list of
systems/materials most sensitive for activation and, hence, required for some
kind of "optimization" or limited use of those materials; data sets
and codes necessary for further calculation of gamma-dose rate in various
scenarios of maintenance.
Input
data and assumptions
In
order to calculate specific induced activity one should know:
·
flux of incident particles;
·
concentration of target nuclei;
·
cross-section of nuclear reactions
producing radioactive nuclei;
·
operation scenario: time of operation
(hereafter T) and time of cooling (t).
|
Status
of input data
|
|
1) Fluxes
|
Ok
|
|
2) Concentration of target nuclei;
|
for high energy activation – almost Ok – bulky items, such as shielding,
are represented rather well in geometry files;
for thermal neutron activation - incomplete-
concentration of impurities taken conservative
|
|
3) Cross-section of nuclear reactions
producing radioactive nuclei
|
for thermal neutrons - Ok
for high energy hadrons - incomplete-
proton cross-sections are used
|
|
4) Operation scenario
|
General
assumptions are made; more details on maintenance
procedure and operation history are needed for further study of doses
|
1) Fluxes
in the region 0<R<12 m, 0<Z<24 m were produced by Mike Shupe
together with a readback procedure. The following data available:
·
Fluxes on 10cm x 10cm grid
1 High energy neutrons above 20 MeV;
2 Fast neutrons - 2.19 MeV to 20 MeV;
3 Intermediate neutrons - 3.78 keV to 2.19 MeV;
4 Moderated neutrons - 0.414 eV to 3.78 keV;
5 Thermal neutrons - 10E-5 to 0.414 eV;
6 Protons above 20 MeV;
7 Pi minus above 20 MeV;
8 Pi plus above 20 MeV;
9 Stars, threshold 50 MeV.
·
Neutron spectra on 100cm x 100cm grid, 61
energy group.
·
Charged hadron spectra on 50cm x 50cm
grid, 21 energy group:
1 protons,
2 p-
pions,
3 p+
pions.
As an example, fig 1-2 shows flux against
R, at Z=0.
|
|
|
Fig. 1. Flux of
thermal, moderated and fast neutrons against R,
at
Z=0
(thermal 1.10-5 eV - 0.14 eV; moderated 0.14 eV- 3.78 keV; fast 2.19
MeV- 20 MeV).
|
|
|
|
Fig. 2. Flux of hadrons with energy above 20 MeV against R, at Z=0.
|
1) Concentration
of target nuclei were taken from various sources. Most informative are results
of neutron activation analysis, though available only for a restricted number
of materials. Other possible sources can be either real specifications of
materials or industrial specifications like ASTM, and so on.
It
is very often, that impurities at level of 1-100 ppm may produce major
contribution to activation induced by thermal and moderated neutrons. For
example, the most sensitive impurity in steel is cobalt. Its content ranges
from 30 ppm to 150 ppm in carbon steel, and from 150 ppm to 2000 ppm in
stainless steel. It is Co-60 (reaction Co-59(n,g)Co-60)
that will determine radiation environment after few years of operation.
Concentration
of elements in some materials used for the study are given in the Tab.1.
Table
1
Concentrations
of elements in materials, ppm (mg/g)
|
Element
|
Stainless
steel1
|
Polyethylene1
|
Tungsten1
|
Copper2
|
Aluminum
alloy2
|
|
Na
|
<40
|
6.0(3)
|
<50
|
|
|
|
Mg
|
<2000
|
390(50)
|
<4E+3
|
13
|
<4.9E+4
|
|
Al
|
80(30)
|
<30
|
<200
|
420
|
|
|
S
|
<2000
|
<4E+3
|
<3E+4
|
|
|
|
Cl
|
<400
|
43(3)
|
<400
|
|
|
|
K
|
<3000
|
<7
|
<1E3
|
|
|
|
Ca
|
<500
|
<30
|
<500
|
18
|
|
|
Sc
|
<0.2
|
3(1)E-3
|
<0.02
|
|
|
|
Ti
|
<600
|
<50
|
<1E4
|
30
|
<1.5E+3
|
|
V
|
30(4)
|
<0.3
|
<8
|
|
|
|
Cr
|
15(1)E+4
|
5.7(3)
|
6(2)
|
100
|
<2.5E+3
|
|
Mn
|
250(20)
|
5.5(3)
|
<3
|
28
|
<1E+4
|
|
Fe
|
41(2)E+4
|
93(10)
|
120(40)
|
240
|
<4E+3
|
|
Co
|
0.17(2)E3
|
0.04
|
0.05(3)
|
104
|
1
|
|
Ni
|
32(5)E+4
|
<50
|
<5E+3
|
100
|
|
|
Cu
|
<150
|
<5
|
<500
|
99.2E+4
|
<1E+3
|
|
Zn
|
<70
|
3(1)
|
<10
|
<0.25
|
|
|
Ga
|
<150
|
<0.2
|
<100
|
|
|
|
As
|
80(40)
|
0.012(7)
|
<200
|
|
|
|
Se
|
<20
|
<0.06
|
<3
|
|
|
|
Br
|
<100
|
0.29(5)
|
<300
|
|
|
|
Rb
|
<70
|
<0.3
|
<3
|
|
|
|
Sr
|
<700
|
<5
|
<150
|
|
|
|
Zr
|
<800
|
<5
|
<50
|
70
|
|
|
Mo
|
<500
|
1.0(3)
|
<700
|
|
|
|
Ag
|
<7
|
<0.04
|
<0.7
|
|
|
|
Cd
|
<800
|
<0.1
|
<1E+3
|
|
|
|
In
|
<0.15
|
<2E-3
|
<0.5
|
|
|
|
Sn
|
<2000
|
<10
|
<2E+4
|
|
|
|
Sb
|
1,3(8)
|
<0.05
|
<0.15
|
200
|
|
|
I
|
<20
|
<0.08
|
<150
|
|
|
|
Cs
|
<3
|
<0.01
|
<0.1
|
|
|
|
Ba
|
<3
|
<1
|
<70
|
|
|
|
La
|
6(2)
|
0.09(1)
|
<1
|
|
|
|
Ce
|
<20
|
0.014(4)
|
<3
|
|
|
|
Sm
|
<4
|
0.037(3)
|
<5
|
|
|
|
Eu
|
<0.4
|
<0.004
|
<0.05
|
|
|
|
Dy
|
<1.5
|
0.011(6)
|
<8
|
|
|
|
Yb
|
<6
|
5(3)E-3
|
<1
|
|
|
|
Lu
|
<0.8
|
3(2)E-3
|
<0.15
|
|
|
|
Hf
|
<1.5
|
0.025(8)
|
<0.8
|
|
|
|
Ta
|
3(1)
|
<0.01
|
<0.1
|
|
|
|
W
|
110(10)
|
0.11(2)
|
98(3)E+4
|
|
|
|
Au
|
<1
|
12(6)E-4
|
<1
|
|
|
|
Hg
|
<7
|
<0.02
|
<0.7
|
|
|
|
Bi
|
|
|
|
70
|
|
|
Pb
|
|
|
|
24
|
|
|
1 Results of neutron activation analysis at MEPhI research
reactor, not published.
|
|
2 Specifications of copper proposed for manufacturing of
JT, E-mail from Werner Witzeling, December 1, 2000.
|
|
3 ASTM, specifications for aluminum based structural alloy
5083.
|
|
4 Conservative assumption.
|
3) Cross-section of nuclear reactions
producing radioactive nuclei are usually available in form of data libraries.
Historically, neutron cross-sections,
ranging from thermal energies up to 20 MeV, are studied rather well, because
they are extensively used in fission reactor applications. There a number
sources available, e.g ENDF, JANDL, IRDF, and others.
Calculated neutron cross-sections for
threshold reactions are available up to energy 100 MeV (MENDL-2 data library
for nuclear activation and transmutation).
Proton reaction data up to energy 10 GeV
are available in form of experimental or calculation data compilations for a
limited list of materials (Be, C, Al, Ti, Mn, Fe, Ni, Cu).
There were no pions reaction data found
so far. For the purpose of this study,
proton cross-sections are used for all hadrons. It is rather a coarse
estimation, but it will allow to detect most important reactions and then to
calculate necessary cross-sections using special codes, which implement nuclear
interaction models.
4)
Operation scenario.
For the purpose of this study there is no
need in detail specifying LHC operation history. It is assumed that LHC is
operated at high luminosity during T and then is shut down. Set of used time
parameters is presented in Tab.2.
Table
2
|
T
|
t
|
|
30 d
|
1 h, 3 h, 10 h,
1 d, 3 d, 10 d
|
|
200 d
|
1 h, 3 h, 10 h,
1 d, 3 d, 10 d, 30 d, 100 d
|
|
10 y
|
1 d, 3 d, 10 d,
30 d, 100 d, 1 y, 3 y
|
|
h-hour; d-day, y-year
|
For further study it is necessary to compose maintenance scenarios,
including probable LHC operation history, access locations and time after shut
down for dose calculation, sequence of dismantling operation, and so on.
Results
Activation of stainless steel and copper
have been already studied.
1) Specific Ke, kerma-equivalent, of
steel and copper averaged over volume 0<R<100cm by 0<Z<100cm (Inner
Detector) are given in the table 3. Kerma-equivalent is absorbed dose rate in
standard layout – dose from a pointwise source at distance 1 m without shielding.
So, if one need to estimate dose rate D, Gray per second, from an item of
mass M,
gram, at distance R, meter, he can use a simple formula D=M Ke/R2.
2) Contributions
of separate radionuclides induced by hadrons (20 MeV <E) to kerma-equivalent
of steel are given in table 4.
3) Contributions
of separate radionuclides induced by neutrons (E<20 MeV) to kerma-equivalent
of steel are given in table 4.
4) 2-d
activity fields of are given in Annex (see the zip file). The fields outlines
areas, where a steel item will be highly radioactive (above 100 mSy/h
in terms of surface dose rate), radioactive (from 100 mSy/h
to 10 mSy/h),
and slightly radioactive (from 10 mSy/h
to 0.1 mSy/h),
as well as areas were low energy neutrons will make high contribution to total
activation.
Table
3
Specific
kerma-equivalent, Gy.m2/(s. g)
|
|
stainless
steel
|
copper
|
|
t
|
neutrons
(E<20
MeV)
|
hadrons
(20MeV<E)
|
neutrons
(E<20
MeV)
|
hadrons
(20MeV<E)
|
|
|
T=30 day
|
|
1
hr
|
6.3.10-14
|
2.9.10-13
|
1.3.10-12
|
1.6.10-13
|
|
3
h
|
5.6.10-14
|
2.8.10-13
|
1.2.10-12
|
1.4.10-13
|
|
10
h
|
4.5.10-14
|
2.5.10-13
|
8.0.10-13
|
1.2.10-13
|
|
1
d
|
4.3.10-14
|
2.3.10-13
|
3.8.10-13
|
9.7.10-14
|
|
3
d
|
4.2.10-14
|
1.8.10-13
|
2.8.10-14
|
7.2.10-14
|
|
10
d
|
3.8.10-14
|
9.3.10-14
|
7.8.10-16
|
4.4.10-14
|
|
|
T=200 day
|
|
1
h
|
2.4.10-13
|
3.5.10-13
|
1.3.10-12
|
2.3.10-13
|
|
3
h
|
2.2.10-13
|
3.4.10-13
|
1.2.10-12
|
1.2.10-13
|
|
10
h
|
2.2.10-13
|
3.2.10-13
|
8.1.10-13
|
1.9.10-13
|
|
1
d
|
2.2.10-13
|
2.9.10-13
|
3.8.10-13
|
1.7.10-13
|
|
3
d
|
2.0.10-13
|
1.5.10-13
|
3.0.10-14
|
1.4.10-13
|
|
10
d
|
2.0.10-13
|
7.2.10-13
|
2.8.10-15
|
1.1.10-13
|
|
30
d
|
1.8.10-13
|
5.8.10-14
|
2.4.10-15
|
7.5.10-14
|
|
100
d
|
1.7.10-14
|
2.9.10-14
|
1.6.10-15
|
3.9.10-14
|
|
|
T=10 year
|
|
1
d
|
1.8.10-12
|
3.4.10-13
|
3.8.10-13
|
2.2.10-13
|
|
3
d
|
1.8.10-12
|
2.9.10-13
|
3.4.10-14
|
1.9.10-13
|
|
10
d
|
1.8.10-12
|
2.0.10-13
|
6.2.10-15
|
1.6.10-13
|
|
30
d
|
1.8.10-12
|
1.2.10-13
|
5.7.10-15
|
1.2.10-13
|
|
100
d
|
1.7.10-12
|
7.0.10-14
|
4.5.10-15
|
7.9.10-14
|
|
1
y
|
1.5.10-12
|
3.1.10-14
|
2.7.10-15
|
3.6.10-14
|
|
3
y
|
1.1.10-12
|
7.9.10-15
|
1.4.10-15
|
1.9.10-14
|
|
|
|
|
|
|
Table 4
Contribution of separate radionuclides to activity induced by
hadrons (E<20 MeV) to kerma-equivalent of steel
|
T=30 d
|
|
t
|
1 h
|
3 h
|
10 h
|
1 d
|
3 d
|
10 d
|
|
Na-24
|
3.99E+0
|
3.77E+0
|
2.98E+0
|
1.72E+0
|
|
|
|
Sc-44
|
2.60E+0
|
1.89E+0
|
|
|
|
|
|
Sc-44m + Sc-44
|
5.81E+0
|
5.92E+0
|
6.05E+0
|
5.65E+0
|
4.13E+0
|
|
|
Sc-46
|
1.21E+0
|
1.25E+0
|
1.36E+0
|
1.48E+0
|
1.88E+0
|
3.36E+0
|
|
V-48
|
1.35E+1
|
1.40E+1
|
1.51E+1
|
1.61E+1
|
1.90E+1
|
2.66E+1
|
|
Mn-52
|
5.93E+1
|
6.07E+1
|
6.40E+1
|
6.53E+1
|
6.56E+1
|
5.22E+1
|
|
Mn-54
|
1.36E+0
|
1.40E+0
|
1.53E+0
|
1.68E+0
|
2.15E+0
|
4.01E+0
|
|
Co-55
|
4.89E+0
|
4.68E+0
|
3.88E+0
|
2.44E+0
|
|
|
|
Co-56
|
4.61E+0
|
4.77E+0
|
5.20E+0
|
5.67E+0
|
7.18E+0
|
1.28E+1
|
|
T=200 d
|
|
t
|
1 h
|
3 h
|
10 h
|
1 d
|
3 d
|
10 d
|
30 d
|
100 d
|
|
Na-22
|
|
|
|
|
|
4.26E-1
|
7.98E-1
|
1.50E+0
|
|
Na-24
|
3.13E+0
|
2.95E+0
|
2.28E+0
|
1.28E+0
|
|
|
|
|
|
Sc-44
|
2.03E+0
|
1.48E+0
|
|
|
|
|
|
|
|
Sc-44m +Sc-44
|
4.55E+0
|
4.63E+0
|
4.62E+0
|
4.23E+0
|
2.92E+0
|
|
|
|
|
Sc-46
|
3.48E+0
|
3.59E+0
|
3.82E+0
|
4.09E+0
|
4.88E+0
|
7.19E+0
|
1.16E+1
|
1.29E+1
|
|
V-48
|
1.46E+1
|
1.50E+1
|
1.58E+1
|
1.65E+1
|
1.84E+1
|
2.12E+1
|
1.69E+1
|
1.61E+0
|
|
Mn-52
|
4.76E+1
|
4.87E+1
|
5.00E+1
|
5.01E+1
|
4.75E+1
|
3.11E+1
|
4.95E+0
|
|
|
Mn-54
|
5.91E+0
|
6.11E+0
|
6.51E+0
|
6.99E+0
|
8.45E+0
|
1.30E+1
|
2.36E+1
|
4.00E+1
|
|
Co-55
|
3.83E+0
|
3.66E+0
|
2.96E+0
|
1.83E+0
|
|
|
|
|
|
Co-56
|
1.28E+1
|
1.32E+1
|
1.40E+1
|
1.50E+1
|
1.79E+1
|
2.62E+1
|
4.16E+1
|
4.40E+1
|
|
T=
10 y
|
|
t
|
1 d
|
3 d
|
10 d
|
30 d
|
100 d
|
1 y
|
3 y
|
|
|
Na-22
|
1.32E+0
|
1.55E+0
|
2.21E+0
|
3.47E+0
|
5.37E+0
|
1.10E+1
|
2.90E+1
|
|
|
Na-24
|
1.09E+0
|
|
|
|
|
|
|
|
|
Sc-44m
|
1.74E+0
|
1.16E+0
|
|
|
|
|
|
|
|
Sc-44
|
1.84E+0
|
1.23E+0
|
|
|
|
|
|
|
|
Sc-46
|
4.28E+0
|
4.96E+0
|
6.72E+0
|
9.06E+0
|
8.28E+0
|
2.31E+0
|
|
|
|
V-48
|
1.40E+1
|
1.51E+1
|
1.60E+1
|
1.07E+1
|
8.37E-1
|
|
|
|
|
Mn-52
|
4.24E+1
|
3.90E+1
|
2.35E+1
|
3.13E+0
|
|
|
|
|
|
Mn-54
|
1.65E+1
|
1.94E+1
|
2.73E+1
|
4.16E+1
|
5.81E+1
|
8.03E+1
|
7.10E+1
|
|
|
Co-55
|
1.55E+0
|
|
|
|
|
|
|
|
|
Co-56
|
1.52E+1
|
1.76E+1
|
2.38E+1
|
3.16E+1
|
2.75E+1
|
6.35E+0
|
|
|