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Reduction of cosmogenic activation of Ge by means of movable iron shielding. Outline Entry conditions for simulations The method Principal results Analysis Prospects and open questions Conclusions. - PowerPoint PPT Presentation
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I. Barabanov, S. Belogurov et al. INR/ITEP, Moscow Dubna GERDA meeting 27-29.06.05
Reduction of cosmogenic activation of Ge by means of movable iron shielding
I. Barabanov, S. Belogurov, L. Bezrukov, A. Denisov, V. Kornoukhov, and N. Sobolevsky
Outline
• Entry conditions for simulations• The method• Principal results• Analysis• Prospects and open questions• Conclusions
I. Barabanov, S. Belogurov et al. INR/ITEP, Moscow Dubna GERDA meeting 27-29.06.05
Entry conditions for simulations
Nuclear disintegrations at the sea level are mostly due to N-component of CR (98%) and induced fast nucleons (~2%), [Cocconi, 1951].
Our goal is to suppress N-component.
Flux density of nucleons at the sea level,[Ziegler, 1981]
Angular distribution: ~cos3.5(θ)
Compare to February, inconsistence in spectra is found and corrected.
neutrons
protons
I. Barabanov, S. Belogurov et al. INR/ITEP, Moscow Dubna GERDA meeting 27-29.06.05
The method
Our tool for hadron transport simulations is the SHIELD code, - why?
• There is a lot of criticism about hadron transport simulation in GEANT 3,4
• We have an expert in nuclear interactions models and their software realizations – Prof. Sobolevsky, the head of the SHIELD team, so we do not deal with a “black box”
Details of the SHIELD simulations will be reported by Andrey Denisov to TG10.
I. Barabanov, S. Belogurov et al. INR/ITEP, Moscow Dubna GERDA meeting 27-29.06.05
Ground (5),Depth=4 m
Container Fe (1)
Air gap (6) Normalizing sphere (4),R=150 cm
Air (7)
OUT (8)
Cavity (2)
Ge(3)
120 cm
Container: R1=70 cm, H1=126.5 cm Bottom depth 15 cmCavity: R2=27 cm, H2=40 cmGe-shipment: R3=21 cm, H3=27 cm
Ground (5)Depth= 4m
Simulation geometry
I. Barabanov, S. Belogurov et al. INR/ITEP, Moscow Dubna GERDA meeting 27-29.06.05
Principal results
Simulation of a complete configuration
– Absolute isotope production rates
– Reduction coefficients
Step by step analysis for comparison with literature and optimization of shielding
– Spectra of nucleons inside the cavity
– Excitation functions (cross section) for isotope production
I. Barabanov, S. Belogurov et al. INR/ITEP, Moscow Dubna GERDA meeting 27-29.06.05
Production rates of 60Co and 68Ge
Target Total By sea level protons
No shield Shield No shield Shield
70Ge 281.4 (0.5%) 33.0 (2%) 17.17 (1.1%) 4.90 (1.5%)
72Ge 55.34 (1.4%) 6.20 (4%) 4.78 (2%) 0.96 (3%)
73Ge 28.0 (1.3%) 2.94 (7%) 2.54 (3%) 0.45 (6%)
74Ge 14.53 (2%) 1.46 (8%) 1.48 (4%) 0.24 (6%)
76Ge 4.22 (4%) 0.4 (8%) 0.54 (6%) 0.06 (12%)
68Ge production rates (per day, per 1 kg )
I. Barabanov, S. Belogurov et al. INR/ITEP, Moscow Dubna GERDA meeting 27-29.06.05
Production rates of 60Co and 68Ge
Inside the container, sea level protons produce 15% of 68Ge and 20% of 60Co , while their initial flux is only 3-4% of all the nucleons.It is due to hardness of proton spectrum.
Target Total By sea level protons
No shield Shield No shield Shield
70Ge 1.73 (7%) 0.118 (33%) 0.170 (11%) 0.028 (19%)
72Ge 2.88 (6%) 0.256 (19%) 0.285 (9%) 0.046 (14%)
73Ge 3.14 (4.0%) 0.265 (24%) 0.335 (8%) 0.035 (21%)
74Ge 3.35 (4%) 0.23 (21%) 0.380 (8%) 0.050 (14%)
76Ge 3.31 (4%) 0.156 (13%) 0.455 (7.0%) 0.036 (15%)
Table 3: 60Co production rates (per day, per 1 kg)
I. Barabanov, S. Belogurov et al. INR/ITEP, Moscow Dubna GERDA meeting 27-29.06.05
Attenuation factors
For 68Ge production by N-component 10
For 60Co production by N-component 15-20
Taking into account contribution from
For 68Ge 8
For 60Co 12-15
I. Barabanov, S. Belogurov et al. INR/ITEP, Moscow Dubna GERDA meeting 27-29.06.05
Analysis and comparison with literatureAttenuation of neutron flux in Iron (through the upper plane of the cavity with and without
container) - published attenuation length ~200 g/cm2
* -neutrons in the cavity
-Sea level neutrons-Sea level protons
- protons in the cavity
Spectra are not in equilibrium
max ~ 240 g/cm2 (for neutrons)
I. Barabanov, S. Belogurov et al. INR/ITEP, Moscow Dubna GERDA meeting 27-29.06.05
Neutron fluxes from different surfaces
Container Fe
Cavity
I. Barabanov, S. Belogurov et al. INR/ITEP, Moscow Dubna GERDA meeting 27-29.06.05
Neutron fluxes from different surfaces
Container Fe
Cavity
Container Fe
Cavity
20% improvement of shielding
I. Barabanov, S. Belogurov et al. INR/ITEP, Moscow Dubna GERDA meeting 27-29.06.05
Nucleon flux density inside the cavity- total neutrons
- total protons
-protons from Sea level neutrons only
* - neutrons from sea
level neutrons only
Rate =
pnpnpn dEnVEEJ
, 0
,, )()(
I. Barabanov, S. Belogurov et al. INR/ITEP, Moscow Dubna GERDA meeting 27-29.06.05
Excitation functions (cross sections) for isotope production
10 100 10000,1
1
10
100
Target: Ge70 Ge72 Ge73 Ge74 Ge76
Cro
ss s
ect
ion
, mb
Energy, MeV
Excitation Functions of Production of the Ge68 at Interactionof Protons with Nuclei-Targets
100 1000
0,1
1
10
100
Targets: Ge70 Ge72 Ge73 Ge74 Ge76
ISABEL code: Ge76
Excitation Functions of Production of the Ge68 at Interactionof Neutrons with Nuclei-Targets
Cro
ss s
ect
ion
, mb
Energy, MeV
I. Barabanov, S. Belogurov et al. INR/ITEP, Moscow Dubna GERDA meeting 27-29.06.05
Excitation functions (cross sections) for isotope production
100 1000 10000
0,01
0,1
1
Excitation Functions of Production of the Co60 at Interactionof Neutrons with Nuclei-Targets
Targets: Ge70 Ge72 Ge73 Ge74 Ge76
Cro
ss s
ectio
n, m
b
Energy, MeV
100 10001E-3
0,01
0,1
1
Excitation Functions of Production of the Co60 at Interactionof Protons with Nuclei-Targets
Targets: Ge70 Ge72 Ge73 Ge74 Ge76
Exp. points: Ge70 Ge76
Cro
ss s
ectio
n, m
b
Energy, MeV
60Co production cross section increaseswith increase of Ge mass number !
I. Barabanov, S. Belogurov et al. INR/ITEP, Moscow Dubna GERDA meeting 27-29.06.05
Prospects and open questions Applied task: Shape optimization within fixed mass
0 20 40 60 80 100 1200,0
0,1
0,2
0,3
0,4
0,5
0,6
Number of particlesentered the Germanium from specified zone of the container
Pa
rtic
les,
1/c
m2
Height, cm
Side Distribution of Effective Penetration Points for Neutrons of Cosmic Rays over the Surface of Containerwithout Bottom (Statistics 10 mln initial neutrons)
0 10 20 30 40 50 60 700,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
1,8Distribution of Effective Penetration Pointsfor Neutrons of Cosmic Rays over the Top Surface of Container
Number of particlesentered the Germanium from specified zone of the container
Par
ticle
s, 1
/cm
2
Radius, cm
Container Fe
Cavity
I. Barabanov, S. Belogurov et al. INR/ITEP, Moscow Dubna GERDA meeting 27-29.06.05
Prospects and open questions Applied task: Shape optimization within fixed mass
0 20 40 60 80 100 1200,0
0,1
0,2
0,3
0,4
0,5
0,6
Number of particlesentered the Germanium from specified zone of the container
Pa
rtic
les,
1/c
m2
Height, cm
Side Distribution of Effective Penetration Points for Neutrons of Cosmic Rays over the Surface of Containerwithout Bottom (Statistics 10 mln initial neutrons)
0 10 20 30 40 50 60 700,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
1,8Distribution of Effective Penetration Pointsfor Neutrons of Cosmic Rays over the Top Surface of Container
Number of particlesentered the Germanium from specified zone of the container
Par
ticle
s, 1
/cm
2
Radius, cm
Container Fe
Cavity
I. Barabanov, S. Belogurov et al. INR/ITEP, Moscow Dubna GERDA meeting 27-29.06.05
Prospects and open questions
Methodical task:Validation of a method by
simulating the classical work
of Cocconi
I. Barabanov, S. Belogurov et al. INR/ITEP, Moscow Dubna GERDA meeting 27-29.06.05
Prospects and open questions
Scientific tasks:
To take into account muon induced fast nucleons a lot of data for less energetic neutrons, a lot of doubts
subject for discussion at TG10 and common work with Tuebingen
a review paper “muon-nuiclear interactions: theory, experiment, simulations”
is wanted
How to measure contents of 60Co in the detector?76Ge detector is not a low background one – 22 decay smears the 60Co
spectrum. Measurements with natural, or better depleted detector with known activation history may help, however RELATIVE production
cross sections should be checked – it is a new task for accelerator activation experiment.
I. Barabanov, S. Belogurov et al. INR/ITEP, Moscow Dubna GERDA meeting 27-29.06.05
Conclusions• The container provides activation reduction factor about one order of
magnitude
• Absolute rates are known within factor 2-3
• Shape optimization within fixed mass is possible
• 60Co production rate increases with increase of Ge mass number
• 68Ge production rate decreases with increase of Ge mass number
• Contribution of muon induced fast nucleons should be studied better
• Transportation is not a bottle neck any more. Next step? 0.5-1 m iron shielding above technological equipment at every stage of detector manufacturing seems feasible.
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