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Los Alamos National Laboratory LA-UR-XX-XXXX Independent fission product yields from you 235 U(n th ,f) measured with SPIDER nt wo Fredrik Tovesson Los Alamos National Laboratory 6 th Workshop on Fission and Spectroscopy of Neutron-Rich Nuclei Chamrousse, France, March 20-24, 2017

Los Alamos National Laboratory Introduction • Discrepancies between the LANL and LLNL fission basis led to a closer look at experimental data • For some of the important fission products there were ~5% yield discrepancies • The discrepancies seemed to be connected to the energy dependence of fission product yields (FPY) • By taking into account small variations in the average neutron energy in different experiments the energy dependence of FPY in the fission neutron energy region was fitted based on existing data • This allow for the FPY uncertainties to be reduced • LANL is evolved in two experimental programs to confirm the FPY energy dependence (TUNL and LANSCE) • Models are being developed to support new evaluations 3

Los Alamos National Laboratory The neutron energy dependence of individual yields can be modelled from global trends in the mass yields 2.4 2.4 2.2 2.2 2.0 2.0 147 Nd Yield (%) 1.8 1.8 1.6 1.6 1.4 1.4 12 0 4 8 12 0 4 8 E n (MeV) E n (MeV) Predictions for A=148 (Green) A=147 (Red) A=147 Uncertainty (Black) 4

Los Alamos National Laboratory Theoretical calculations of fission fragment properties • Macroscopic-microscopic description of fission successfully models potential energy of nuclei • New advanced calculations of nuclei advancing through the potential predicts mass, charge and kinetic energy of fission fragments • Theory will provide nuclear data for isotopes that are challenging to measure • Measurements of fission correlation helps constrain theoretical models • SPIDER is a great tool for providing data to refine fission models (several outputs) From A. Sierk, LANL 5

Los Alamos National Laboratory The Los Alamos Neutron Science TPC Chi-Nu fission cross sections neutron output DANCE SPIDER neutron capture, fission ɣ-rays fission yields Weapons Neutron Research (WNR) APOLLO Fission chambers Lujan ɣ- rays for ion beam experiments TKE, fission yields Center 6

Los Alamos National Laboratory LANSCE provide neutrons from thermal energies to hundreds of MeV 7

Los Alamos National Laboratory The SPIDER instrument 2 2 Et M = 2 l 2 2 2 d d d d M æ E ö æ t ö æ l ö = + + ç ÷ ç ÷ ç ÷ 2 2 M è E ø è t ø è l ø • The 2E-2v method can provide 1 amu resolution for light fragments • Demonstrated with Cosi-fan-Tutti at ILL • Measures independent yields • Currently mass • Plans for charge identification 8

Los Alamos National Laboratory Fission fragment Time-of-Flight Measurement 252 Cf (SF) alphas light FF heavy FF Meierbachtol, K. et al ., NIMA, 788 59 (2015); Wiza, J., NIM, 162 587 (1979) 9

Los Alamos National Laboratory Flight Path Measurement 239 Pu FPs • Orthogonal grids, 1 wire/mm • “X” and “Y” coordinates • Parallel signal and reference • Position measured as Δ t (ns) • Built in-house, design by RoentDek • ≤ 2 mm (FWHM) resolution RoentDek MCP Delay Line Detector Manual, v. 11.0.1505.1, www.roentdek.com; Jagutzki, O. et al. , NIMA, 477 244 (2002). 10

Los Alamos National Laboratory Energy Measurement 252 Cf (SF) light FF heavy FF • δ E ≈ 410 keV demonstrated for A = 90, E = 98.2 MeV ions • δ E ≥ 1 MeV typical for Si detector * Si 3 N 3.1 H 0.06 (?) Meierbachtol, K. et al ., NIMA, 788 59 (2015); Oed, A. et al. , NIM, 205 455 (1983). 11

Los Alamos National Laboratory Spontaneous fission of Cf-252 Meierbachtol et al., NIM A788 , 59 (2015) 12

Los Alamos National Laboratory Thermal neutron-induced fission of 235 U • U-235 (n th ,f) was measured using both spectrometer arms • M vs TKE supports models describing deexcitation of fission fragments • Can also be used to study prompt neutron emission • This data, together with 252 Cf(sf) is an important benchmark 13

Los Alamos National Laboratory Thermal neutron-induced fission of 233 U TKE vs M for 233 U(n th ,f) Red Curve = Lit. Data for TKE ν vs M for 233 U(n th ,f) n Red Points = Lit. Data for 14

Los Alamos National Laboratory Thermal neutron-induced fission of 239 Pu 15

Los Alamos National Laboratory The main challenge in 2E-2v measurements is in the energy loss correction Pu239t Fission Product Yield 8 % Yield 7 6 5 4 3 2 1 0 80 90 100 110 120 130 140 150 160 Mass (amu) Energy Loss Correction (based on Ziegler et al.) 6.0 y = -0.0009x 2 + 0.0894x + 3.4146 The average energy loss of R² = 0.99888 5.5 E-loss (MeV) heavy fission fragments appear 5.0 to be underestimated by 4.5 y = 0.1169x - 0.6645 approximately 30% in TRIM R² = 0.91962 4.0 40 50 60 70 80 90 Time-of-Flight (ns) 16

Los Alamos National Laboratory MegaSPIDER • In order to study product yields, especially specific isotope yields over a large range of neutron energies, a higher efficiency detector is needed • Increasing SPIDER from 1 arm pair to 8 arm pairs = 1-2% efficiency • One ‘start’ detector for 4 ‘stop’ detectors and 4 corresponding ionization chambers • Logistical challenges include large volume of high vacuum, 16 ionization chambers flowing isobutane gas, lots of thin films 6’ O.D. 17

Los Alamos National Laboratory Complementary work with the Time Projection Chamber (TPC) and Frisch-gridded ionization chamber • Cross sections • Total kinetic energy (TKE) • Anisotropy • Mass yields with 4-5 amu resolution • Ternary fission • Anisotropy See talk by Brett Manning See talk by Dana Duke 18

Los Alamos National Laboratory Conclusions • The energy dependence of fission products should be address using several experimental techniques • Independent and cumulative yields • Low mass resolution – high efficiency • High mass resolution – low efficiency • Mono energetic neutron sources and white spectrum sources • We need to advance our understanding of fission and develop evaluation tools • New advanced models show promise for predictive capabilities • Semi-empirical models support evaluation process 19

Los Alamos National Laboratory Acknowledgements • Rick Blakeley • Uwe Greife (PI) • Charles Arnold • Walt Loveland • Matt Devlin • Adam Hecht (PI) • Bill Moore • Justin Jorgenson (AET-5) • Dan Shields • Alexander Laptev • John Lestone • Dmitriy Mayorov • Krista Meierbachtol • Willian Santistevan (AET-5) • Arnie Sierk (T-2) • Fredrik Tovesson (PI) • Richard van de Water (P-25) • Morgan White (XCP-5) 20