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ay Operated by Los Alamos National Security, LLC for the U.S. Department of Energy's NNSA 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

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Operated by Los Alamos National Security, LLC for the U.S. Department of Energy's NNSA

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you nt wo

Los Alamos National Laboratory

Independent fission product yields from

235U(nth,f) measured with SPIDER

Fredrik Tovesson Los Alamos National Laboratory

6th Workshop on Fission and Spectroscopy

  • f Neutron-Rich Nuclei

Chamrousse, France, March 20-24, 2017

LA-UR-XX-XXXX

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Los Alamos National Laboratory 3

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
  • f 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
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Los Alamos National Laboratory 4

The neutron energy dependence of individual yields can be modelled from global trends in the mass yields

Predictions for A=148 (Green) A=147 (Red) A=147 Uncertainty (Black)

147Nd Yield (%)

En (MeV)

2.4 2.2 2.0 1.8 1.6 1.4 4 8 12

En (MeV)

2.4 2.2 2.0 1.8 1.6 1.4 4 8 12

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Los Alamos National Laboratory 5

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

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Los Alamos National Laboratory 6

The Los Alamos Neutron Science

Weapons Neutron Research (WNR) Lujan Center TPC

fission cross sections

Chi-Nu

neutron output

DANCE

neutron capture, fission ɣ-rays

SPIDER

fission yields

Fission chambers

TKE, fission yields

APOLLO ɣ-rays for ion beam experiments

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Los Alamos National Laboratory 7

LANSCE provide neutrons from thermal energies to hundreds of MeV

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Los Alamos National Laboratory 8

The SPIDER instrument

  • 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

2 2

2 l Et M =

2 2 2

2 2 ÷ ø ö ç è æ + ÷ ø ö ç è æ + ÷ ø ö ç è æ = l l t t E E M M d d d d

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Los Alamos National Laboratory 9

Fission fragment Time-of-Flight Measurement

alphas light FF heavy FF

252Cf (SF)

Meierbachtol, K. et al., NIMA, 788 59 (2015); Wiza, J., NIM, 162 587 (1979)

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Los Alamos National Laboratory 10

Flight Path Measurement

  • Orthogonal grids, 1 wire/mm
  • “X” and “Y” coordinates
  • Parallel signal and reference
  • Position measured as Δt (ns)
  • Built in-house, design by RoentDek
  • ≤ 2 mm (FWHM) resolution

239Pu FPs

RoentDek MCP Delay Line Detector Manual, v. 11.0.1505.1, www.roentdek.com; Jagutzki, O. et al., NIMA, 477 244 (2002).

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Los Alamos National Laboratory 11

Energy Measurement

252Cf (SF)

light FF heavy FF

Meierbachtol, K. et al., NIMA, 788 59 (2015); Oed, A. et al., NIM, 205 455 (1983).

  • δE ≈ 410 keV demonstrated for A = 90, E = 98.2 MeV ions
  • δE ≥ 1 MeV typical for Si detector*

Si3N3.1H0.06 (?)

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Los Alamos National Laboratory 12

Meierbachtol et al., NIM A788, 59 (2015)

Spontaneous fission of Cf-252

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Los Alamos National Laboratory 13

Thermal neutron-induced fission of 235U

  • U-235 (nth,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 252Cf(sf) is an

important benchmark

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Los Alamos National Laboratory 14

Thermal neutron-induced fission of 233U

ν vs M for 233U(nth,f) Red Points = Lit. Data for n TKE vs M for 233U(nth,f) Red Curve = Lit. Data for TKE

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Los Alamos National Laboratory 15

Thermal neutron-induced fission of 239Pu

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Los Alamos National Laboratory 16

The main challenge in 2E-2v measurements is in the energy loss correction

The average energy loss of heavy fission fragments appear to be underestimated by approximately 30% in TRIM

y = 0.1169x - 0.6645 R² = 0.91962 y = -0.0009x2 + 0.0894x + 3.4146 R² = 0.99888

4.0 4.5 5.0 5.5 6.0 40 50 60 70 80 90 E-loss (MeV) Time-of-Flight (ns)

Energy Loss Correction (based on Ziegler et al.)

Mass (amu) 80 90 100 110 120 130 140 150 160 % Yield 1 2 3 4 5 6 7 8

Pu239t Fission Product Yield

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Los Alamos National Laboratory 17

MegaSPIDER

  • In order to study product yields, especially specific isotope yields over a large range
  • f 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.

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Los Alamos National Laboratory 18

Complementary work with the Time Projection Chamber (TPC) and Frisch-gridded ionization chamber

  • Cross sections
  • Anisotropy
  • Ternary fission
  • Total kinetic energy (TKE)
  • Mass yields with 4-5 amu resolution
  • Anisotropy

See talk by Brett Manning See talk by Dana Duke

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Los Alamos National Laboratory 19

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
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Los Alamos National Laboratory 20

Acknowledgements

  • Charles Arnold
  • Matt Devlin
  • Justin Jorgenson (AET-5)
  • 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)
  • Rick Blakeley
  • Adam Hecht (PI)
  • Uwe Greife (PI)
  • Bill Moore
  • Dan Shields
  • Walt Loveland