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Reduction of cosmogenic activation of Ge by means of movable iron shielding

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.

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Reduction of cosmogenic activation of Ge by means of movable iron shielding

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  1. 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 I. Barabanov, S. Belogurov, L. Bezrukov, A. Denisov, V. Kornoukhov, and N. Sobolevsky I. Barabanov, S. Belogurov et al. INR/ITEP, Moscow Dubna GERDA meeting 27-29.06.05

  2. Entry conditions for simulations Nuclear disintegrations at the sea level are mostly due to N-component of CR (98%) and m induced fast nucleons (~2%), [Cocconi, 1951]. Our goal is to suppress N-component. neutrons 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. protons I. Barabanov, S. Belogurov et al. INR/ITEP, Moscow Dubna GERDA meeting 27-29.06.05

  3. 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

  4. Simulation geometry Container: R1=70 cm, H1=126.5 cm Bottom depth 15 cm Cavity: R2=27 cm, H2=40 cm Ge-shipment: R3=21 cm, H3=27 cm OUT (8) Air (7) Container Fe (1) Cavity (2) Ge (3) Normalizing sphere (4), R=150 cm Air gap (6) 120 cm Ground (5) Depth= 4m Ground (5), Depth=4 m I. Barabanov, S. Belogurov et al. INR/ITEP, Moscow Dubna GERDA meeting 27-29.06.05

  5. 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

  6. Production rates of 60Co and 68Ge 68Ge production rates (per day, per 1 kg ) I. Barabanov, S. Belogurov et al. INR/ITEP, Moscow Dubna GERDA meeting 27-29.06.05

  7. Production rates of 60Co and 68Ge Table 3: 60Co production rates (per day, per 1 kg) 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. I. Barabanov, S. Belogurov et al. INR/ITEP, Moscow Dubna GERDA meeting 27-29.06.05

  8. Attenuation factors For 68Ge production by N-component 10 For 60Co production by N-component 15-20 Taking into account contribution from m For 68Ge 8 For 60Co 12-15 I. Barabanov, S. Belogurov et al. INR/ITEP, Moscow Dubna GERDA meeting 27-29.06.05

  9. Analysis and comparison with literature -Sea level neutrons -Sea level protons * -neutrons in the cavity Attenuation of neutron flux in Iron (through the upper plane of the cavity with and without container) - published attenuation length l ~200 g/cm2 - protons in the cavity Spectra are not in equilibrium l max ~ 240 g/cm2 (for neutrons) I. Barabanov, S. Belogurov et al. INR/ITEP, Moscow Dubna GERDA meeting 27-29.06.05

  10. Neutron fluxes from different surfaces Container Fe Cavity I. Barabanov, S. Belogurov et al. INR/ITEP, Moscow Dubna GERDA meeting 27-29.06.05

  11. 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

  12. Nucleon flux density inside the cavity - total neutrons *- neutrons from sea level neutrons only - total protons Rate = • protons from Sea level neutrons only I. Barabanov, S. Belogurov et al. INR/ITEP, Moscow Dubna GERDA meeting 27-29.06.05

  13. Excitation functions (cross sections) for isotope production I. Barabanov, S. Belogurov et al. INR/ITEP, Moscow Dubna GERDA meeting 27-29.06.05

  14. Excitation functions (cross sections) for isotope production 60Co production cross section increases with increase of Ge mass number ! I. Barabanov, S. Belogurov et al. INR/ITEP, Moscow Dubna GERDA meeting 27-29.06.05

  15. Prospects and open questions Applied task: Shape optimization within fixed mass Container Fe Cavity I. Barabanov, S. Belogurov et al. INR/ITEP, Moscow Dubna GERDA meeting 27-29.06.05

  16. Prospects and open questions Applied task: Shape optimization within fixed mass Container Fe Cavity I. Barabanov, S. Belogurov et al. INR/ITEP, Moscow Dubna GERDA meeting 27-29.06.05

  17. 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

  18. 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 – 2b2n 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

  19. 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. I. Barabanov, S. Belogurov et al. INR/ITEP, Moscow Dubna GERDA meeting 27-29.06.05

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