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O ptical T ime P rojection C hamber for radon and thoron detection

O ptical T ime P rojection C hamber for radon and thoron detection. Wojciech Dominik Zenon Janas Krzysztof Miernik Marek Pf ü tzner. Institute of Experimental Physics Warsaw University. PMT CCD. visible light. 1 m s/cm. Gate. O ptical T ime P rojection C hamber.

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O ptical T ime P rojection C hamber for radon and thoron detection

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  1. Optical Time Projection Chamber for radon and thoron detection Wojciech Dominik Zenon Janas Krzysztof Miernik Marek Pfützner Institute of Experimental Physics Warsaw University

  2. PMT CCD visiblelight 1 ms/cm Gate Optical Time Projection Chamber 1 atm. gas: 49% He 49% Ar 1% N2 1% CH4 M. Ćwiok et al., IEEE TNS, 52 (2005) 2895

  3. OTPC at Warsaw Chamber active volume: 20 x 20 x 15 cm3 Materials used: Stesalit fibreglass PCB plates Pyrex optical window

  4. Registration of a particle CCD PMT

  5. Principle of 3D track reconstruction z a vdt1 vdt2 Lxy Total track length: Inclination angle: vd– electron drift velocity  10 mm/ms

  6. What one can measure with OTPC ? • length and position on XY plane (from camera picture) • length of projection on Z axis (from the length of the PMT signal) • no Z coordinate • energy (from the total track length) • charge of the particle (from the energy loss) • time and position correlation between succesive a-decays • - no sensitivity for electrons

  7. Example: 214Po a-decay CCD Dt= 5 ms PMT Lxy=115 mm

  8. Example: energy loss along the particle track projection of CCD picture fit of Bethe-Bloch formula

  9. T= 0 min T= 3 min a218Po a222Rn Example: correlation between succesive a-decays - tracks originate from the same XY position- track lengths compatible with the 222Rn and 218Po a energies

  10. OTPC background measurement -5hours measurement - circles mark the beginning of the tracks Total of 260 tracks - most of them start from the walls 14 tracks starting from the center Y - position X - position

  11. Tracks starting from the central region (16 x 16 x 15 cm3 gas volume ?) Background activity estimate

  12. 2161 5 ms Search for 220Rn - a -216Po - a decay - two triggers within 300 ms gate 155 ms 216Po 9 cm 220Rn

  13. Range ofa particles in Ar(50%) + He (50%) gas 1 atm 216Po 220Rn

  14. Decays in the center (thoron gate)

  15. Decays from the walls (thoron gate)

  16. Time correlation between two a particles

  17. Background thoron activity estimate

  18. 16x16 mm2 Super-Kamiokande radon detector S = 2(counts/day)/(1 mBq/m3) Background – 2.4± 1.3 counts/day Y. Takeuchi et al.. NIM A 421 (1999) 334

  19. 100 cm 15 cm 50 cm 20 cm 50 cm OTPC for radon detection 20 cm V = 6·10-3 m3 S = 6·10-3 m3 1 mBq/m3  24 h = 0.5 (counts/day) / (1 mBq/m3) V = 0.25 m3 S = 0.25m3 1 mBq/m3  24 h = 21.6 (counts/day) / (1 mBq/m3) Background: 200 mBq/m3 radon 20 mBq/m3 thoron

  20. 220Rn56 s 6.29 212Po300 ns 216Po145 ms 212Bi61 m 6.78 8.78 212Pb10.6 h 208Pbstable 6.1 208Tl3 m 220Rn decay products

  21. 5.49 222Rn3.8 d 210Po138 d 214Po164 ms 218Po3.1 m 214Bi20 m 6.00 7.69 5.30 210Bi5 d 210Pb22.3 y 206Pbstable 5.45 4.65 214Pb27 m 210Tl1.3 m 206Tl4.2 m 222Rn decay products

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