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Using surrogate nuclear reactions to determine (n,f) and (n, g ) cross sections August 8, 2009

Nicholas Scielzo Physics Division, Physical and Life Sciences. Using surrogate nuclear reactions to determine (n,f) and (n, g ) cross sections August 8, 2009. Lawrence Livermore National Laboratory, P. O. Box 808, Livermore, CA 94551.

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Using surrogate nuclear reactions to determine (n,f) and (n, g ) cross sections August 8, 2009

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  1. Nicholas Scielzo Physics Division, Physical and Life Sciences Using surrogate nuclear reactions to determine (n,f) and (n,g) cross sections August 8, 2009 Lawrence Livermore National Laboratory, P. O. Box 808, Livermore, CA 94551 This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 LLNL-PRES-408002

  2. Surrogate Nuclear Reactions Approach The Surrogate Nuclear Reactions approach is an indirect method for determining cross sections of compound-nuclear reactions Used when direct measurements are not possible because of beam and/or target limitations – create compound nucleus through reaction of light-ion beam on a (more) stable isotope Can be used in regular or inverse kinematics

  3. 153Gd 154Gd 154Gd 154Gd n p p g g We measure this ratio Surrogate nuclear reaction method using inelastic scattering “Desired” reaction “Surrogate” reaction t1/2=240 days stable Hauser-Feshbach theory describes the “desired” reaction as a product of entrance channels (saCN – can be calculated reliably) and exit-channel branching ratios (GcCN– can’t be calculated reliably) Alternative (“surrogate”) reaction forms the same compound-nucleus and determines GcCN

  4. 153Gd 154Gd 154Gd 154Gd n p p g g Approximation simplifies technique above ~MeV Weisskopf-Ewing Approximation: branching ratios GcCN are independent of spin and parity when many decay channels are open “Desired” reaction “Surrogate” reaction t1/2=240 days stable Hauser-Feshbach theory describes the “desired” reaction as a product of entrance channels (saCN – can be calculated reliably) and exit-channel branching ratios (GcCN– can’t be calculated reliably) Alternative (“surrogate”) reaction forms the same compound-nucleus and determines GcCN

  5.  Silicon Telescope Array for Reaction Studies (STARS)Livermore Berkeley Array for Collaborative Experiments (LIBERACE) Particle solid angle: 20% g-ray photopeak @ 1 MeV: 1% Fission fragment solid angle: 2 × 20% d-electron & fission fragment shield 140 µm or 500 µm E detector 140 µm fission detector Up to 4×1000 µm E detectors Scattered particle p, d,He, , 18O beam Fission Fragments En determined from scattered particle energy: Gamma Ray Detectors

  6. Surrogate (n,f) measurements Surrogate reactions approach has successfully determined (n,f) cross sections in actinides 233U(n,f)/235U(n,f) from 234U(a,af)/236U(a,af) 237U(n,f)/235U(n,f) from 238U(a,af)/236U(a,af) 237Np(n,f) from 238U(3He,tf) S.R. Lesher et al., Phys. Rev. C 79, 044609 (2009). J.T. Burke et al., Phys. Rev. C 79, 054604 (2006). M.S. Basunia et al., Nucl. Instrum. Meth. B, in press (2009).

  7. Surrogate (n,g) measurements Compound-nuclear Jp distribution is important… Probability of g-ray emission for 156Gd(p,p’) The measured -ray yields compared to calculated yields for different spin distributions (error bars not shown). Sn Extract most-likely Jp distribution from comparison of data and calculations… …and use this information to move beyond Weisskopf-Ewing approximation to extract reliable (n,g) results

  8. Requirements • Experiments benefit from: • up to nano-Amp beams (regular or inverse kinematics) • light-ion reactions • efficient particle detectors with excellent PID and energy resolution • high-efficiency g-ray detector arrays

  9. Collaborators • Lawrence Livermore National Laboratory • L.A. Bernstein, D.L. Bleuel, J.T. Burke, F. Dietrich, J. Escher, S.R. Lesher, • E.B. Norman, N.D. Scielzo, S. Sheets, I. Thompson, M. Wiedeking • U.C. Berkeley and Lawrence Berkeley National Laboratory • M.S. Basunia, R.M. Clark, P. Fallon, J. Gibelin, R. Hatarik, B. Lyles, • M.A. McMahan, L. Moretto, E.B. Norman, L. Phair, S.G. Prussin, E. Rodriguez-Vieitez • University of Richmond • J.M. Allmond, C. Beausang • Rutgers University • J.A. Cizewski, R. Hatarik, P.D. O’Malley and T. Swan

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