Reduction of cosmogenic activation of Ge by means of movable iron shielding
description
Transcript of Reduction of cosmogenic activation of Ge by means of movable iron shielding
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.