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TUNL Seminar

Modernizing the Fission Basis: Measurement of Fission Product Yields from Fast-Neutron-Induced Fission. TUNL Seminar. September 12, 2013. Anton Tonchev for the LLNL-LANL- TUNL collaboration. 622876. Acknowledgements. TUNL Duke C . BHATIA M. BHIKE B. FALLIN C. HOWELL W. TORNOW

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TUNL Seminar

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  1. Modernizing the Fission Basis: Measurement of Fission Product Yields from Fast-Neutron-Induced Fission TUNL Seminar • September 12, 2013 • Anton Tonchev • for the LLNL-LANL-TUNL collaboration 622876

  2. Acknowledgements • TUNL Duke • C. BHATIA • M. BHIKE • B. FALLIN • C. HOWELL • W. TORNOW N.C. State Univ. • M. GOODEN • J. KELLEY • LANL • C. ARNOLD E. BOND • T. BREDEWEG • M. FOWLER • W. MOODY • R. RUNDBERG • G. RUSEV • D. VIEIRA • J. WILHEMY LLNL J. BECKER R. HENDERSON J. KENNEALLY R. MACRI C. RYAN S. SHEETS M. STOYER A. TONCHEV 2

  3. Outline • Motivation • Energy Dependence of Fission-Product Yields • Experimental technique • Results • Future plans

  4. Motivation • Resolve the long-standing difference between LLNL and LANL with respect to selected fission product data • Joint LANL/LLNL fission product review panel endorsed a possible energy dependence of 239Pu(n,f)147Nd fission product yield with fission neutrons: • 4.7%/MeV from 0.2 to 1.9 MeV (M. Chadwick) • 3.2%/MeV from 0.2 to 1.9 MeV (I. Thompson) • Mostly low energy data from critical assembly or fast reactors 239Pu(n,f)147Nd There are no 147Nd data between 1.9 and 14 MeV • Very scarce experimental data at the MeV-range • Large discrepancy (~20%) at 14 MeV M.B. Chadwick et al. Nuclear Data Sheets 111 (2010) 2923; H.D Selby et al. Nuclear Data Sheets 111 (2010) 2891. P. Baisden et al, LLNL-TR-426165, 2010; R. Henderson et al. LLNL-TR-418425-DRAFT; I. Tompson et al. Nucl. Sci. Eng. 171, 85 (2012)

  5. Nuclear Fission Saddle point 0 10-17 Scission point 85% KE 10-15 10-20 Prompt n-emission 10-18 10-12 Prompt g-emission Distance between fragments (cm) 10-15 10-9 Beta decay, delayed n,g 10-6 time (s) Credit: Encyclopædia Britannica, Inc

  6. Mass Distribution Heavy (Es to Lr) Symmetric Medium (U to Cf) Asymmetric Light (Th, Pa ) Triple humped Pre-actinides ((e.g.W,Au,Pb,Bi) Symmetric

  7. Fission Fragment Distribution with Neutron Energy • YiE (A) = fractional yields of mass chain ‘A’ (after b decays) from initial actinide ‘i’ for neutron energy ‘E’. • How does the asymmetry evolve with neutron energy for 235,238U, 239Pu? Depends on actinide Depends on neutron energy Goal: Develop high-precision FPY energy dependence from 1 to 15 MeV

  8. Monoenergetic Neutron Sources available at TUNLDD, DT, PT, and PLi, Sources DENIS source FN TANDEM 10MV Shielded neutron source area Quasi-monoenergetic neutrons 7Li(p,n)7Be; Monoenergetic neutrons: 0.1 – 0.65 MeV 3H(p,n)3He; Monoenergetic neutrons: 0.5 – 7.7 MeV Flux on target (107- 108) cm-2 s-1 Energy spread dE/E = 0.1 to 0.40 2H(d,n)3He; Monoenergeticneutrons: 4.0 – 7.7 MeV 3H(d,n)4He; Monoenergetic neutrons: 14.8 – 20.5 MeV

  9. TUNL TOF Room

  10. 2Hgas Monoenergetic Neutron Irradiation n-detector Dual fission chamber n p or d From VdGaccelerator One thick target ~0.2 g/cm2 Two thin targets ~10 μg/cm2

  11. Dual Fission Chamber Measurements Fission_counts = mf Fσn,fεftf Gamma_counts (147Nd) = mγFσn,fFPY Iγεγtγ mγ( mf) = atoms in the 239Pu thick (thin) target F= neutron flux (n.cm-2.s-1) σn,f= 239Pu(n,f) fission cross section (cm2) FPY = fission product yield of 147Nd per 239Pu fission Iγ = branching ratio of Eg εγ(εf) = counter efficiency of g-ray (fission) detection tγ( tf) = time factor for irradiation and counting periods of g-ray (fission) • (Gamma_count / Fission_count) = (mthick/ mthin) * FPY * C •  FPY = (Gamma_count) / Fission_count) * (mthin / mthick) * C

  12. Error estimation on the FPY Measurements: Relative FPY Ratio (This is what we have promised) 1. Statistical uncertainties of g-ray peak counts (1-2%) 2. Relative HPGe detector efficiency (1-2% including the fit) Absolute FPY energy dependency: Statistical error of g-ray peak counts (1-3%) Absolute detector efficiency (2% including the fit) Branching ratios (0.2 – 8% (147Nd)) Absolute FC efficiency (3% experimentally, 0.5% simulation) Low energy neutrons (<1%) Neutron fluence rate fluctuation (<0.3%) Efficiency conversion ratio between close and standard geometry (<1%) True coincidence summing (<1%) Random coincidence summing (<0.2%) Sample weight (<0.1%) Self-absorption of g-ray (0.1 - 1%)

  13. Need to know? • Room returns neutrons – at ToF area • ToFspectrum from neutron and 3He monitors • Fission chamber design and characteristics

  14. Room Return Neutrons: Why are they Important? Region of interest Not desirable events in our measurements

  15. Room return neutron study with 16 different off-axis foils in ToF area Reactions studied 115In(n, n')115mIn 197Au(n, 2n)196Au 27Al(n, a)24Na 235U (n, f) 133I and 135I Room return neutrons ~ 105 times smallerthan primary flux on target

  16. Need to know? • Room returns neutrons – at ToF area • ToF spectrum from neutron and 3Hemonitors • Fission chamber design and characteristics

  17. ToF spectrum from 0-degree neutron monitor at En=9.0 MeV Neutron and gamma are well separated Break up – Negligible

  18. Need to know? • Room returns neutrons – at ToF area • ToF spectrum from neutron and 3He monitors • Fission chamber design and characteristics

  19. Dual Fission Chamber: The Renaissance of the NIST idea gas cell FC Gas flow in and out • Design and fabricate three fission chambers: one for 239Pu, one for 235U, and one for 238U • Dedicated thin (~10 μg/cm2) 235,238U and 239Pu foils electroplated on 0.5” titanium backing★ • Dedicated thick (200 - 400 mg/cm2) 235U (93.27%) 238U (99.97%) and 239Pu (98.4%) targets • Fission chamber efficiency confirmed: 100%, confirmed with activation measurements • ★Made by LANL

  20. Fission Spectrum at En = 9.0 MeV fission alpha Excellent a / fission separation

  21. Fission Chamber TOF at En = 9.0 MeV in cadmium without cadmium 9 MeV / Background neutrons = 150 / 1

  22. Experimental Results

  23. FPY Ratios to 99Mo for 239Pu at 4.6, 9.0, 14.5, and 14.8 MeV 1 J.E.Gindleret al. Phys. Rev. C 27 (1983) 2058. 2 H.D.Selbyet al. Nucl. Data Sheets 111(2010)2891-2922. 3 J. Laurec et al. Nucl. Data Sheets 111(2010)2965-2980. 4 T.R. England and B.F. Rider, LA-UR-94-3106. 5 M. Mac Innes, M.B. Chadwick, and T. Kawano, Nuclear Data Sheets 112 (2011) 3135–3152 6 D.R.Nethawayand B. Mendoza, Phys. Rev. C 6 (1972) 1827

  24. FPY Ratios to 99Mo for 235U and 238U at 4.6, 9.0, and 14.5 MeV 1 L. E. Glendeninet al. Phys. Rev. C 24 (1981) 2600. 2 H. D. Selby et al. Nucl. Data Sheets 111(2010)2891-2922. 3 J. Laurec et al. Nucl. Data Sheets 111(2010)2965-2980. 4 W.J. Maeck et al., ENICO – 1028 (1980). 5 T.R. England and B.F. Rider, LA-UR-94-3106. 6 M. Mac Innes, M.B. Chadwick, and T. Kawano, Nuclear Data Sheets 112 (2011) 3135–3152. 7 D. R. Nethawayand B. Mendoza, Phys. Rev. C 6 (1972) 1827.

  25. 239Pu FPY Ratios to 99Mo: at 4.6, 9.0, 14.5, and 14.8 MeVPreliminary

  26. 235U FPY Ratios with Respect to 99Mo: Comparison Preliminary

  27. 238U FPY Ratios with Respect to 99Mo: Comparison Preliminary

  28. 239Pu FPY Ratios: 147Nd/99Mo at 4.6, 9.0, 14.5 and 14.8 MeV Preliminary

  29. 239Pu FPY Ratios: 140Ba/99Mo at 4.6, 9.0, 14.5, and 14.8 MeV Preliminary

  30. 239Pu FPY Ratios: 97Zr/99Mo at 4.6, 9.0, 14.5, and 14.8 MeV Preliminary

  31. 147Nd Absolute Fission Product Yield Preliminary

  32. 147Nd Absolute Fission Product Yield Preliminary

  33. 147Nd Absolute Fission Product Yield Preliminary

  34. Comparison with Theory 1. Our absolute magnitude of the 147Nd FPY below 2.5 MeV and at 14.5 MeV neutron energies are slightly higher than the predicted values. 2. We can rule out the two low-yield data at 14.8 MeV. 3. The slope of 147Nd FPY from 4.6 to 14.8 MeV is slightly negative (-1% / MeV). 4. There is no energy dependence (or it is below our experimental sensitivity) for 140Ba and 99Mo fragments. Model calculation ___ Uncertainties ___ J. Lestone. Nuclear Data Sheets 112 (2011) 3120

  35. Summary We start delivering precise(< 2% relative uncertainty) information on FPY ratios obtained at SIX energies in case of 239Pu and at FOUR energies for 235U and 238U We will deliver accurate (4-5% absolute uncertainty) information on the energy dependent fission product yields covering an energy range from 1 < En < 15 MeV Potential experiments: • Reduce 147Ndbranching ratio uncertainty from the current 8% • High-accuracy measurements in the 0-2 MeV range to clarify 144Ce and 147Nd neutron-energy dependence • Strong LLNL-LANL-TUNL Collaborative Effort

  36. Additional Slides

  37. Further Experiment & Theory Needed Future experiments (2013 – 2015): • Reduce147Ndbranching ratio uncertainty from the current 8% • (submitted LLNL LDRD proposal) • Developing a high-intensive 7Li(p,n) neutron source at TUNL • High-accuracy measurements in the 0-2 MeV range to clarify 147Nd neutron-energy dependence using 7Li(p,n) and 3H(p,n) reactions • Two measurements at the both sides of the 2nd chance fission, • i.e. En = 5 and 7 MeV • Thermal measurement at the MIT reactor • Potential theory work: • Guidance on shape from onset of 2nd-chance fission

  38. Summary of identified fragments for 235U, 238U and 239Pu

  39. Extra Slides

  40. Extra Slides

  41. 239Pu FPY Ratios: 147Nd/99Mo at 4.6, 9.0, 14.5 and 14.8 MeV Preliminary

  42. 239Pu FPY Ratios: 147Nd/140Ba at 4.6, 9.0, 14.5 and 14.8 MeV Preliminary

  43. 239Pu Fission chamber spectra at En = 14.5 MeV

  44. 239Pu FPY Ratios: 132Te/99Mo at 4.6, 9.0, 14.5, and 14.8 MeV Preliminary

  45. 239Pu FPY Ratios: 143Ce/99Mo at 4.6, 9.0, 14.5, and 14.8 MeV Preliminary

  46. What We Have Done so Far • Precise FPY measurements on 239Pu, 235U and 238U • En= 1.5, 2.6, 4.6, 9.0, 14.5, and 14.8 MeV • 2. From September 2011 to April 2013: • Total beam on target ~ 1000 hours • Funded by NNSA AA (Multiply by ~$300 / h) • 3. Counting time at TUNL: more than a year of continuous fission products • measurement

  47. Reducing fission-product g-ray branching-ratio uncertainties Produce pure sources using mass-separated CARIBU fission-product beam… (DM/M~10-4… only need DM/M~10-2) (1010 atoms after 1 day) …collaborate with TAMU for high-precision b and g-ray spectroscopy b- 147Nd Qb=0.9 MeV 10.98 d IY: 0.001% b- count b decays with low-threshold 4pbcounter (~100% efficient for bs) 147Pr Qb=2.7 MeV 13.4 m IY: 0.18% b- At TAMU, they have a unique HPGe detector laboriously calibrated to ~0.2% for efficiency 147Ce Qb=3.4 MeV 56.4 s IY: 1.91% N. Scielzo: ER-LDRD proposal

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