Fission Properties of Neutron-Rich Nuclei

Transcription

1 Fission Properties of Neutron-Rich Nuclei Walter F. Henning (RIKEN, ANL, TU Munich) 3/21 22/2013 1

2 Fission Properties of Neutron-Rich Nuclei Motivation Predictions from recent theory Experimental fission barriers Proposed approach to n-rich isotopes Summary and outlook 3/21 22/2013 2

3 SHE: the limits of heavy nuclei -4 Cold fusion -6-5 Neutron capture -3-2 U -4-2 Th -5 Hot fusion Act.+ 48 Ca Pb Bi U Fission termination and recycling of the r process r process production of 232 Th and 238 U 3/21 22/2013 3

4 Fission in the simple liquid-drop picture Fissility ~ Z 2 /A A = constant N=126 B f However: P. Mӧller et al: Pb Isotopes N 3/21 22/2013 4

5 Predictions from recent theory 3/21 22/2013 5

6 Fisson Barrier [MeV] Mass Number A 3/21 22/2013 Radium Isotopes Microscopic features: Cross sections for reflectionsymmetric and asymmetric fission depend on relative level densities at saddles as well as barrier heights and widths. Calculation of microscopic level densities based on single particle levels and many-particle-many-hole excitations Pairing individually for all configurations within BCS formalism. Fission barrier (MeV) N=126 Lead Isotopes 10 N A

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8 SHE: the limits of heavy nuclei -4 Cold fusion -6-5 Neutron capture -3-2 U -4-2 Th -5 Hot fusion Act.+ 48 Ca Pb Bi U Theory of Nuclear Fission: Understanding the structure and dynamics ofthe prototypical many-body process of the nucleus Fission termination and recycling of the r-process r-process yield for 232 Th and 238 U 3/21 22/2013 8

9 Experimental determination(s) of fission barriers 3/21 22/2013 9

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11 Earlier fission barrier studies at low energies employing direct nucleon-transfer reactions B.B. Back et al.; Nucl. Phys. A165 (1971) 449 E. Konecny et al.; Phys. Lett. B 45 (1073) 329 C O (d,p) Ϭ f /ϭ p (d,pf) Ϭ f /ϭ p 3/21 22/

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13 Entry Distribution, Fission Barrier, and Formation Mechanism of 254 No P. Reiter,1,2 T. L. Khoo,1 T. Lauritsen,1 C. J. Lister,1 D. Seweryniak,1 A. A. Sonzogni,1 I. Ahmad,1 N. Amzal,3 P. Bhattacharyya,4 P. A. Butler,3 M. P. Carpenter,1 A. J. Chewter,3 J. A. Cizewski,1,5 C. N. Davids,1 K.Y. Ding,5 N. Fotiades,5 J. P. Greene,1 P. T. Greenlees,3 A. Heinz,1 W. F. Henning,1 R.-D. Herzberg,3 R.V. F. Janssens,1G. D. Jones,3 H. Kankaanpää,7 F. G. Kondev,1 W. Korten,6 M. Leino,7 S. Siem,1,8 J. Uusitalo,1 K. Vetter,9 and I. Wiedenhöver1 E * (MeV) 3/21 22/

14 Fission probabilities as a function of nuclear charge of the DI product Contour plot of fission probabilities as a function of excitation energy P fis 14

15 How can we experimentally determine fission barriers of neutron-rich nuclei? 15

16 Earlier fission barrier studies at low energies employing direct nucleon-transfer reactions B.B. Back et al.; Nucl. Phys. A165 (1971) 449 E. Konecny et al.; Phys. Lett. B 45 (1073) 329 RIBs and inverse kinematics C O (d,p) Ϭ f /ϭ p (d,pf) Ϭ f /ϭ p 3/21 22/

17 (p,2p) (p,2p) 4 He Zn (p,2p) 3/21 22/

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19 Production Cross-sections of Neutron-Rich Pb and Bi Isotopes in the fragmentation of 238 U H. Alvarez-Pol et al.; Eur. Phys. J. A 42 (2009) 485 3/21 22/

20 Pb and Bi isotopes observed in 238 U fragmentation Fission barrier (MeV) Pb N= U 23 5 U 238 U 10 N A Th 232 Th 209 Bi Pb Pb Pb Pb 3/21 22/

21 Neutron rich regions with known production cross sections from 238 U fragmentation H. Alvarez-Pol et al.; Eur. Phys. J. A 42 (2009)485 J. Kurcewicz et al.; Phys. Lett. B 717 (2012) 371 Published production cross sections for neutron-rich isotopes in the fragmentation of 238 U 3/21 22/

22 Countrate estimates: Fragmentation yield for 238 U beam and ϭ=100nb 10 pna 238 U 250 mg/cm 2 Be target 100 nb fragment cross section (~ 198 Pt, 214 Pb, 217 Bi) 1 day beam on target N=8.6 x 10 6 fragment events per day Fission yield for (p,2p) 8.6 x 10 6 /day ( 214 Pb or 217 Bi) 1g/cm 2 H 2 target 100μb/MeV (p,2pf) cross section 1 day beam on target N=5 x 10 2 events/day MeV 3/21 22/

23 Approach at high energies with RIBs in inverse kinematics: nucleon knockout i.e., (p, 2p) or (p, pn) etc p p FDC2 SAMURAI 3/21 22/

24 SAMURAI Commissioning May 2012 Commissioning Set up All the detectors and DAQ commissioned with beam and calibrated HI neutron coincidences 17 C 16 C+n 15 B+n 15 C 14 C+n 14 Be 12 Be+2n - RIKEN: K. Yoneda, N. Fukuda, N. Inabe, T. Isobe, T. Kubo, K. Kusaka, T. Motobayashi, J. Ohnishi, H. Otsu, H. Sato, Y. Shimizu, H. Suzuki, H. Takeda, S. Takeuchi - Tohoku U: T. Kobayashi, K. Takahashi, K. Sekiguchi -Tokyo Tech: T. Nakamura, N. Kobayashi, Y. Kondo, R. Minakata, S. Nishi, S. Ogoshi, T. Sako, R. Tanaka - Kyoto U: Y. Matsuda, T. Murakami - Kyushu U: T. Teranishi -France: F. Delaunay, J. Gibelin, M. Miguel - Germany: T. Aumann, Y. Togano - Korea: Y. Sato, J. Hwang, S. Kim

25 RRC RILAC RIBF Layout ZeroDegree (ZDS) (2008) SAMURAI RIPS (2011) frc SRC (2007) IRC BigRIPS (2007) SHARAQ (2009)

26 K. H. Schmidt et al Nucl. Phys. A 665 (2000) U 208 Pb 3/21 22/

27 Fission Fragment Mass Distribution 3/21 22/

28 H. Alvarez Pol et al Phys. Rev C 82 (2010) Beam: 10 8 / sec 238 U 100pb sensitivity in 2 days Factor 5 reduction per each additional neutron 3/21 22/

29 SHE: the limits of heavy nuclei -4 Cold fusion -6-5 Neutron capture -3-2 U -4-2 Th -5 Hot fusion Act.+ 48 Ca Pb Bi U Theory of Nuclear Fission: Understanding the structure and dynamics ofthe prototypical many-body process of the nucleus Fission termination and recycling of the r-process r-process yield for 232 Th and 238 U 3/21 22/