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Fission setup based on PPACs using a coincidence technique L. Audouin, S. Isaev, L. Tassan-Got, C. Stephan IPN dOrsay I. Durán, C. Paradela, D. Tarrío.

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Presentation on theme: "Fission setup based on PPACs using a coincidence technique L. Audouin, S. Isaev, L. Tassan-Got, C. Stephan IPN dOrsay I. Durán, C. Paradela, D. Tarrío."— Presentation transcript:

1 Fission setup based on PPACs using a coincidence technique L. Audouin, S. Isaev, L. Tassan-Got, C. Stephan IPN dOrsay I. Durán, C. Paradela, D. Tarrío Univ. Santiago de Compostela (on behalf of the n_TOF Collaboration)

2 C. Paradela ANIMMA June 6-9, 2011 ICC-Ghent Motivation Fast reactors and ADS have renewed the interest on nuclear data, in particular those beyond 20 MeV. A new generation of facilities allows studying nuclear reactions at high neutron energies. For measuring fission, new devices are needed for discriminating fission from competing reactions ( spallation, multifragmentation,…)

3 C. Paradela ANIMMA June 6-9, 2011 ICC-Ghent Parallel Plate Avalanche Counter (PPAC) Very thin detectors. High detection efficiency for heavy ions (FF) Fast timing with anode signal (0.5 ns resolution). Fragment position from cathode signals.

4 C. Paradela ANIMMA June 6-9, 2011 ICC-Ghent Detection setup 10 PPACs and 9 targets ( 235 U and 238 U as references). Gas flow inside a reaction chamber Thin targets (300 µg/cm 2 ) and backings (550 µg/cm 2 ) Both fragments detected by the closest PPACs. Trajectory reconstruction.

5 C. Paradela ANIMMA June 6-9, 2011 ICC-Ghent Coincidence technique U-234: singles U-234: coincidences Coincidence condition between anode signals rejects most of the background Coincidence technique

6 C. Paradela ANIMMA June 6-9, 2011 ICC-Ghent Fission target identification Correlation between PPAC time differences allows the unambigous target identification T0T1T2 T1T2T0T1T2T0T1T2

7 C. Paradela ANIMMA June 6-9, 2011 ICC-Ghent Cathode positioning Diagonal condition: (Tch1-Tanode)+(Tch2-Tanode)=DLT DLT: Total delay line length (~320 ns) The time difference between both cathode ends provides the position of the signal.

8 C. Paradela ANIMMA June 6-9, 2011 ICC-Ghent Cross Section: Energy Resolution Very low background: lower yield between resonances than expected from evaluations

9 C. Paradela ANIMMA June 6-9, 2011 ICC-Ghent Cross Section: Energy Range Fission measured for neutron energies up to 1 GeV. Cross sections have been measured for different isotopes: 234,233 U, 237 Np, 232 Th, nat Pb, 209 Bi. [1] C. Paradela et al. Phys. Rev. C 82, (2010) [2] L. Audouin et al. Proc. of ND2007, p. 421 [3] D. Tarrío et al. Phys. Rev. C 82, (2011)

10 C. Paradela ANIMMA June 6-9, 2011 ICC-Ghent U-234 cosine distribution for neutron energies near the fission threshold Fission Fragment Angular Distribution Cos ( ) Log E =5.6 Log E =5.4 Log E =5.8 Log E =5.5 Log E =6.0 Log E =5.9

11 C. Paradela ANIMMA June 6-9, 2011 ICC-Ghent Anisotropy extrapolation B (Anisotropy parameter) Angular Distribution of fission fragments is described by W( ) 1+Bcos 2 Results obtained fitting in our reduced angular range Despite the constraints, present results are quite in agreement with previous data from Leachman ( Phys. Rev. 137, B814 (1965) ) and Tutin et al. ( Nucl. Instrum. Meth. A 457 (2001) ) Neutron energy (MeV) This work Leachman Tutin

12 C. Paradela ANIMMA June 6-9, 2011 ICC-Ghent Conclusions A fission detection setup based on PPACs has been implemented for the CERN n_TOF facility. Both fission fragments are detected in coincidence and their trajectory is reconstructed. Cross sections and angular distributions can be measured up to 1 GeV at the CERN n_TOF facility.


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