Measurement of the 242 Pu neutron induced fission cross section at nelbe Arnd Junghans Helmholtz-Zentrum Dresden-Rossendorf, Germany

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1 Measurement of the Pu neutron induced fission cross section at nelbe Arnd Junghans Helmholtz-Zentrum Dresden-Rossendorf, Germany The new nelbe time-of-flight facility Neutron induced fission cross section of Pu Seite 1

2 Activity of Spent Nuclear Fuel Pu long lived plutonium isotope in spent nuclear fuel Pu(n,f) cross section on High Priority Request List Seite 2 webkorigen simulation 4.5% enriched UOX fuel PWR 55 MWd/kg

3 The first measured Spontaneous Fission Signals Toni Kögler at PTB Braunschweig on The work on Pu(n,f) is the PhD work of Toni Kögler Seite 3

4 HZDR Main Campus and Research Facilities User facilities SC Electron LINAC ELBE 40 MeV, 1.6 ma High-Power Lasers 150 TW (1 PW) High magnetic field lab. 90+ T Ion beam center incl. 6 MV Tandetron PET center (cyclotrons) Institutes Ion beam physics and materials research Radiation physics High-magnetic fields Fluid dynamics Resource ecology (incl. nuclear waste management) Resource technology (natural resources, urban mining) Radiopharmacy TOPFLOW thermo-hydraulics lab. ESRF beam-line / Grenoble Seite 4

5 The Center for High-Power Radiation Sources at HZDR Superconducting electron accelerator ELBE: Electron beam as driver for secondary beams: neutrons, positrons, FEL, THz, x-rays, nelbe Seite 5

6 Nuclear Data Measurements at the photoneutron source nelbe Extending the scope of accurate nuclear data New Isotopes: Minor actinides, New coolants, structural materials New energy range: Fast neutrons New reactions: (in)elastic scattering, (n,tot), (n,fis) New neutron facilities: Helmholtz-Zentrum Dresden-Rossendorf operates the first photoneutron source at a superconducting electron accelerator: CHANDA experiments at new nelbe: 238 U total cross section P. Schillebeeckx et al. TAA 1_3 D(n,n)D elastic scattering (TAA 1_5) Accurate continuous energy differential cross sections for neutron scattering from 56Fe (TAA 1_5) A.J.M. Plompen et al. 56 Fe -ray angular distribution WP8 Task 8.3 Seite 6

7 nelbe neutron spectrum 235 U fission chamber Photoneutron spectrum (measured with the PTB 235 U fission chamber H19) TOF spectrum: Photofission from bremsstrahlung and neutron induced fission Photoneutron spectrum similar to the fission neutron spectrum Neutron time of flight range 100 ns 2,5 µs Neutron energy range from 100 kev 7 MeV Neutron spectral rate on target ca. 2*10 4 n/(cm 2 s MeV ) Measurement time: 81 h, I e- = 30 μa, E e- = 30 MeV Flight path 598 cm, no -ray absorber in the beam Emission peaks: 40,89,179, 254, 314, 605 kev from near threshold photoneutron emission in 208 Pb (strong capture resonances of 207 Pb) R. Beyer et al., NIM A723 (2013) 151 Seite 7

8 Neutron induced Fission of Pu Parallel plate fission chambers high-vacuum metal sealed vessel ( 235 Uran and Pu) P10 Gas flow through ultrapure gas filters 37.3 mg Pu (99,959% + xxx Pu) -activity of 8.7 MBq distributed on 8 targets produced in Jan separate readout necessary use of fast pre-amplifiers (development of HZDR) to reduce pile-up Typical efficiency for neutron detection (1-3)x10-5 Seite 8 Deposit Diameter (mm) Areal density (µg/cm 2 ) Thickness (nm) Pu 74 ± ± Pu deposits made at Institut für Kernchemie, Univ. Mainz K. Eberhardt, J. Runke, A. Vascon (Presentation by Klaus Eberhardt, this workshop)

9 Autoradiograph of a nelbe Pu deposit A. Vascon et al., Quantitative molecular plating of large-area Pu targets with improved layer properties Applied Radiation and Isotopes 95 (2015) Seite 9

10 Fission time of flight experiment Pu FC 235 U (H19) neutron beam Pu Deposit #2 nelbe experiment: (Dec 2014) H19 / PuFC Listmode data acquisition for 16 channels dual range QDC multi-hit multi event TDC α fission fragments ELBE beam optimized for high intensity: Beam energy 30 MeV bunch charge on target 60 pc Repetition rate khz neutron beam diameter 53 mm Flight path cm T. Kögler, PhD thesis in preparation Seite 10

11 Data acquistion scheme T. Kögler, PhD thesis in preparation Seite 11

12 Beam monitoring Plastic scintillator detecting scattered bremsstrahlung and neutrons behind the experimental setup. Seite 12

13 Time of flight spectra from 235 U and Pu Pu measurement time: 81 h gated on fission fragments constant random background subtracted (SF in Pu) Pu: spontaneous fission rate 30 s -1 Neutron-induced fission rate 5.5 s -1 photofission in the -flash Time resolution 2.1 ns (FWHM) 235 U, Pu 235 U (H19) Neutron-induced fission rate 31 s -1 photofission in the -flash 31 s -1 Time resolution 2.3 ns (FWHM) Seite 13 T. Kögler, PhD thesis in preparation

14 Pu Spontaneous fission (SF) half live Weighted average Evaluations Pu T 1/2 = 3.75(2) 10 5 a SF T 1/2 =(6.74 ± 0.09) a P. Salvador-Castineira, Phys. Rev. C (2013) Number of Pu atoms in the FC can be determined from the SF rate. Seite 14

15 Fission cross section relative to the standard 235 U C i tof dependent correction for dead time, loss of energy-tof correlation and transmission through the setup for each Pu deposit ε intrinsic fission fragment detection efficiency n A number density of target atoms σ n,f ( 235 U) Measurement of the SF-rate ε n A Dead time correction of (n,f) measurement cancels out Fission fragment detection efficiency ε cancels out Seite 15

16 Neutron scattering in the experiment Seite 16 neutron track, gamma track, ion,nucleus track, electron track, neutrino track is white

17 Energy-Time-of-flight Correlation Neutron Transport Simulations, Geant 4, 10 8 events 20 GB tree E vs. E(t) linear scale unscattered scattered total Seite 17 2 % of all neutrons have scattered and are detected with a wrong energy deduced from time of flight E. Mendoza, D. Cano-Ott, G4NeutronHPpackage, 2012

18 Transmission Factor through the Setup Geant 4 and MCNP 6 agree very well. About 15 % on average of all neutrons are scattered out of the beam at the last Pu FC cathode. Resonances due to Si-backings in the Pu FC Seite 18

19 Verification of neutron scattering correction in the Pu FC Corrected for transmission Before correction for neutron transmission Neutron beam Pu deposit N(n, f)/ N(SF) decreases exponentially with each segment of the fission chamber Seite 19

20 nelbe data: PhD thesis Toni Kögler in preparation Pu/ 235 U relative cross section measurements 2 ns binning Seite 20 Average deviation of nelbe data between MeV Tovesson+ 2.5(2) % Staples+ 0.8(2) % Weigmann+ 5.3(2)% Tovesson and Staples used the same Pu sample

21 Pu(n,f) normalized with 235 U(n,f) IAEA standard nelbe data 4.5 % higher than ENDF/B VII.I in the range MeV Seite 21

22 Total Correction Factor due to neutron scattering σcorr Pu n,f σcorr 235 U n,f σ Pu n,f σ 235 U n,f Scattering correction around 10 % independent of choice of neutron transport code Seite 22

23 Systematic uncertainties: H19 fission fragment detection efficiency (Nolte et al.2007) ε H19 = (0.945 ± 0.014) (1.48 %) H19 particle areal density (Nolte et al. 2007) n A = (113.8 ± 0.3) cm -2 (0.26 %) Pu SF decay constant (Salvador-Castineira) SF λγ = ln 2/T 1 2 = (3.24 ± 0.03) s 1 (0.93 %) PuFC SF rate (measured in BG run) 8 i=1 Pu N (SF),det Pu deposit size (deposition cell) = ( ± 0.004) (0,01 %) F = (43.0 ± 1.2) cm 2 (2.8 %) Systematic uncertainty of neutron scattering correction C i (0.2 %) Fission fragment anisotropy (Carlson I (1.6 %) Combined systematic uncertainty 3.8 % Alternative analysis of all 8 Pu deposits and weighted average gives very similar results. Seite 23

24 Summary The new nelbe facility is operational: Fast neutron induced reactions of relevance for fundamental research and technology. - (in)elastic scattering - Neutron induced fission - Neutron total cross sections Neutron-induced fission cross section of Pu has been measured using new large area homogeneous deposits from Mainz Normalisation relative to 235 U using the H19 transfer instrument from PTB Number of target atoms from spontaneous fission rate of Pu nelbe is a user facility: External users are very welcome. Seite 24

25 Neutron time of flight group Roland Beyer, Evert Birgersson 1, Anna Ferrari, Roland Hannaske, Mathias Kempe, Toni Kögler, Stefan Müller, Ralph Massarczyk, Andrija Matic 2 Daniel Bemmerer, Eckart Grosse, Klaus-Dieter Schilling, Ronald Schwengner, Andreas Wagner, and Arnd Junghans 1) now AREVA 2) now IBA BIG THANKS TO: The colleagues from Mainz and PTB for providing the Pu deposits (Klaus Eberhardt, Jörg Runke, Alessio Vascon) and the H19 fission chamber (Ralf Nolte) Development of the nelbe photoneutron source together with the Institute for Fluiddynamics and the Central Research Technology Group Maik Partzsch, Jens Steiner, Armin Winter Mechanical construction and electronics by Andreas Hartmann, Klaus Heidel, Matthias Langer, Manfred Sobiella, Daniel Stach Great support from Nuclear Materials and Radiation Safety Bettina Bauer, Andreas Beutmann (VKTA); Heidemarie Heim, Isabel Kösterke and everybody of the ELBE crew for providing stable electron beams. Seite 25