Report

Prediction of Reactor Neutrino Spectra David Lhuillier CEA Saclay - France General Considerations Honolulu - AAP 2012 D. Lhuillier - CEA Saclay 2 Origin of Reactor Antineutrinos • b-decay of the fission products of U and Pu isotopes • Ab initio approach: build up the total spectrum with individual contribution of ~800 nuclei. ee- n n • Reference spectra approach: measure the mean fission b spectrum of U an Pu isotopes and weight them by the predicted fission rates. All predictions require a reactor simulation with core geometry, initial fuel composition and power history. Honolulu - AAP 2012 D. Lhuillier - CEA Saclay 3 Energy Spectrum Exponential decrease of emitted spectrum b-inverse detection reaction n e + p ® e+ + n Detected Spectrum Relevant E range [1.8 – 8] MeV Honolulu - AAP 2012 D. Lhuillier - CEA Saclay 4 © F. Durillon, animea Contributing Nuclei Detection reaction enhances the contribution of high energy b-transitions: - Lot of very unstable nuclei, high above valley of stability - Short lived, reach equilibrium fast w.r.t. experiment time scale Reference fission spectra approach favored w.r.t. ab initio approach. Honolulu - AAP 2012 D. Lhuillier - CEA Saclay 5 Evolution Along a Reactor Cycle Typical evolution of the isotopic composition of a commercial rector At Pth= constant, 239Pu fission leads to 60% less detected neutrinos than 235U fission. ak [%] Burnup [MWd/t] 2000 4000 6000 8000 10000 12000 14000 239Pu ON 238U Refueling with fresh 235U 70 60 50 40 30 20 10 0 0 235U ON 241Pu Total Spectrum: S(E, t) = åak (t) Sk (E) k = 235U, 238U, 239 Pu, 241Pu k • Monitoring of reactor n flux with sensitivity to plutonium content. Honolulu - AAP 2012 D. Lhuillier - CEA Saclay 6 Fission Spectra uncertainties & Non-proliferation • Non proliferation relies on evolution of the neutrino rate along a reactor cycle; Relative variations and/or reference anchor point. • In the case of converted spectra, the normalization and shape uncertainties are mostly correlated for all fissioning isotopes their impact is suppressed. Honolulu - AAP 2012 73 kg of 239Pu removed V. Bulaevskaya and A. Bernstein, nucl-ex/1009.2123 D. Lhuillier - CEA Saclay 7 Re-evaluation of Reference Spectra Honolulu - AAP 2012 D. Lhuillier - CEA Saclay 8 ILL data: reference b- Spectra Emitted b spectra per fission Magnetic BILL spectrometer eTarget foil (235U, 239Pu, 241Pu) in thermal n flux ILL research reactor (Grenoble, France) Honolulu - AAP 2012 A. A. Hahn, K. Schreckenbach et al., Phys. Let. B218,365 (1989)+ refs therein D. Lhuillier - CEA Saclay 9 b- n Conversion 1- Need to break down the total e- spectrum into single b-branches fit the data with 30 virtual branches: 2- Convert each virtual e- branches to n branches 3- Sum all converted n branches to get total n spectrum Honolulu - AAP 2012 D. Lhuillier - CEA Saclay 10 Theory of b-decay Fermi theory: N b (W ) = K p (W -W0 ) F(Z,W ) CShape (W ) F 2 2 Fermi Shape factor function of forbidden Phase space • • • • W = total energy W0 = end-point p = momentum Z = Nuclear charge Corrections: Nb (W ) = NbF (W ) L0 (Z,W) S(Z,W ) C(Z,W) Gb (Z,W ) (1+ dWM W ) Finite size of nuclear electric charge Screening of Atomic e- Finite size distrib. QED of decaying radiative neutron correction Weak magnetism n branch obtained by replacing: WW0-W, GbGn Honolulu - AAP 2012 D. Lhuillier - CEA Saclay 11 Corrections to Fermi theory n spectrum corrections Example of a single branch with Z=46 A=117 E0=10 MeV b spectrum corrections P. Huber • Total fission spectra is a sum over a quasi continuous end-point distribution +/- cancellation at low E, adds up at high E. Honolulu - AAP 2012 D. Lhuillier - CEA Saclay 12 Re-evaluation of Converted Spectra T. A. Mueller et al., Phys. Rev. C83,054615 (2011) • Initiated by the need of accurate prediction for the far detector of Double Chooz • Maximize the use of nuclear data: 90% of the total b spectrum is described by the sum of measured b-decays * Fission yields. Nuclear Data • Use virtual branches only to fill the remaining 10% gap. Honolulu - AAP 2012 D. Lhuillier - CEA Saclay 13 Re-evaluation of Converted Spectra T. A. Mueller et al., Phys. Rev. C83,054615 (2011) • True distribution of Z from all b-decays of databases. • Apply all corrections at the branch level instead of an effective global slope. 0.1 0.05 0 -0.05 -0.1 2 Corrections applied at branch level 3 4 5 Old effective correction 6 “true” Z distribution from nuclear databases 7 8 E (MeV) • Combined effect at low and high energy leading to a global +3% shift Honolulu - AAP 2012 D. Lhuillier - CEA Saclay 14 Reactor Anomaly G. Mention et al., Phys. Rev. D83, 073006, 2011 New Oscilation to sterile n? Atmospheric Oscilation Solar Oscilation Honolulu - AAP 2012 D. Lhuillier - CEA Saclay 15 Confirmed by Complementary Work P. Huber, Phys. Rev. C84, 024617(2011) • Revisit conversion procedure of ILL data with minimal use of nuclear data. New conv. with “extra correction” New conv. P. Huber New conv. T.A. Mueller et al. ILL conversion • • • Honolulu - AAP 2012 Confirms global increase of predicted spectrum Fixes remaining oscillations of first re-evaluation Extra slope correction D. Lhuillier - CEA Saclay 16 Two Predictions in Agreement The two published predictions contain the same physics. Difference in global slope is now understood: • L0 correction not properly implemented in Mueller et al. re-evaluation. • Different expressions of C(Z,W) term. ( f - f ILL ) / f ILL 0.12 Revised Mueller et al. Huber, Phys. Rev. C84, 024617 (2011) 0.14 0.1 0.08 0.06 0.04 0.02 0 -0.02 -0.04 2 Mueller et al., Phys. Rev. C83, 054615 (2011) 3 4 5 6 En [MeV] 7 8 T.A. Mueller, D. Lhuillier Honolulu - AAP 2012 D. Lhuillier - CEA Saclay 17 Updated Reactor Anomaly White paper: K. N. Abazajian et al. , hep-ph/1204.5379 Reactor + Gallium anomaly 7% deficit Honolulu - AAP 2012 ~4% from reactors 1% from tn, 1% from off-eq 1% from previous deficit D. Lhuillier - CEA Saclay 18 Normalization Uncertainty Honolulu - AAP 2012 D. Lhuillier - CEA Saclay 19 Normalization of ILL data • Dominant systematic error : 1.8 % (1 s) • Absolute calibration via internal conversion electron lines of known partial cross section per neutron capture • Correlated across all energy bins of all isotopes directly propagates into the converted antineutrino spectra. 115In(n, g)116mIn & 113Cd(n,g)114Cd Honolulu - AAP 2012 207Pb(n, g)208Pb : absolute normalization : relative normalization D. Lhuillier - CEA Saclay 20 Independent Norm. at 2% level? 2. 10-2 b/fission in 250keV bin centered on 6 MeV: • The required few 106 fissions could be recorded with less intense neutron source (away from reactor background reduction). 10-1 10-2 -3 10 10-4 0 • Same calibration using internal conversion line + Precise counting with evt by evt fission tagging? n rate (a.u.) 2 4 • Magnetic design for e- detection in large solid angle, and well controlled energy resolution. 6 0 to 25h30 1h to 25h30 2h to 25h30 3h to 25h30 4h to 25h30 5h to 25h30 D. Lhuillier - CEA Saclay 10 E (MeV) Honolulu - AAP 2012 6h to 25h30 8 Potential large impact on reactor anomaly… 7h to 25h30 • No off-equilibrium corrections 21 Shape Uncertainty Honolulu - AAP 2012 D. Lhuillier - CEA Saclay 22 Weak Magnetism Approximate expression neglecting nuclear structure: dWM » 4 mp - mn CV ´ E » 0.48% / MeV ´ E 3 M N CA Measurement of dWM through transitions in isobaric analog states: CVC symmetry Magnetic dipole M1 g decay width Honolulu - AAP 2012 dWM D. Lhuillier - CEA Saclay 23 Weak Magnetism dWM » 4 mp - mn CV ´ E » 0.48% / MeV ´ E 3 M N CA , assume 100% error Experimental slope in good agreement for transitions with low ft values Contribution of large ft’s in fission neutrino spectra? P. Huber, Phys. Rev. C84, 024617(2011) Honolulu - AAP 2012 D. Lhuillier - CEA Saclay 24 Weak Magnetism Relative contribution • High log(ft) values have a sizeable contribution to fission n spectra across all E range (reflects the large contribution of forbidden decays) • CVC still valid for very large ft transition which have tiny overlap of wave functions in b-decay? Honolulu - AAP 2012 D. Lhuillier - CEA Saclay 25 Weak Magnetism Total Relat Syst (%) 10 8 6 4 2 0 -2 -4 -6 2 4 Total systematics Nominal dAwm 4*dAwm 3 Honolulu - AAP 2012 1 Upcoming data from DayBay, Reno and Double Chooz near detectors have the potential to confirm the current shape uncertainty! 5 6 7 Evis (MeV) Reanalysis of Bugey3 data may already constrain the weak magn slope at this level. -8 -10 A factor 4 increase of dWM would compensate the +4% deviation from ILL spectra, but also induce a large negative tilt. • Estimated shape uncertainty with ~3.5 105 accumulated neutrinos, dEscale = 0.5% and ~4% 9Li background. D. Lhuillier - CEA Saclay 26 Shape Uncertainty 239Pu / 235U 0.9 0.8 0.7 0.6 0.5 0.4 0.3 WM+Z+Stat 10 8 WM+Z 2 6 4 2 0 -2 -4 -6 -8 -10 Error (%) 2 4 ILL conversion 3 WM 4 New Conversion 3 5 5 6 7 8 En (MeV) 6 7 8 n Kinetic E (Mev) • Correlated across all energy bins and isotopes favorable to non-proliferation and oscillation search Honolulu - AAP 2012 D. Lhuillier - CEA Saclay 27 New Data Honolulu - AAP 2012 D. Lhuillier - CEA Saclay 28 Updated Ab Initio Predictions • Correct for Pandemonium effect by using Total Absorption g-ray Spectrometry (TAS) • Short list of fission products contributing by more than 4% to 2-6MeV bins. A. Algora et al., Phys. Rev. Lett. 105, 202501 (2010) Honolulu - AAP 2012 D. Lhuillier - CEA Saclay 29 Updated Ab Initio Predictions M. Fallot et al. , nucl-ex/1208.3877 • Inclusion of 7 new Tc, Mo and Nb isotopes. • Sizeable correction of predicted spectra within ±10% of new converted spectra. • Analysis and new measurements on-going. • Same uncertainties on slope factors beyond databases systematics. • Toward a competitive prediction of absolute normalization? Honolulu - AAP 2012 D. Lhuillier - CEA Saclay 30 New 238U data New 238U data @ FRMII reactor, Munich • Anchor point of 235U measurement: - Background well understood. - Comparison to ILL spectrum cancels most uncertainties. n flux Natural U foil b MWC Plastic Scintillator N. Haag, K. Schrekenbach et al. Honolulu - AAP 2012 D. Lhuillier - CEA Saclay 31 New 238U Data • N. Haag Ph.D. thesis to be published by end of this year. • Final measurement of 238 U ranges from 2.0 MeV to 6.5 MeV with relative errors of 5% - 15% • Spread of ab Initio flux predictions in the ±10% range Possible update of the reactor anomaly at 1% level with sligthly improved total uncertainty Honolulu - AAP 2012 D. Lhuillier - CEA Saclay 32 Conclusions Demonstrated bias in the conversion procedure of the ILL data. +4% increase of detected rate is confirmed by two independent works. +1% off-equilibrium correction of reactor simulation + 1% updated neutron life-time + 1% previous mean shift with old spectra ~7% deficit of the reactor anomaly Honolulu - AAP 2012 D. Lhuillier - CEA Saclay 33 Conclusions Application to reactor surveillance: - Main uncertainties are common to all isotopes suppressing their impact on relative monitoring - Short baseline oscillations to be tested soon. n rate at one location is affected through U-Pu shape difference only. Challenging independent Xcheck of spectra normalization New data coming soon to consolidate the current error budget: - 238U Spectrum from FRM II - New shape envelope to be measured by near detectors of currently running reactor experiments. Honolulu - AAP 2012 D. Lhuillier - CEA Saclay 34 Back Up Slides Honolulu - AAP 2012 D. Lhuillier - CEA Saclay 35 Complementary Approaches Conversion of total b spectra Ab initio calculations Complete simulation of core evolution Total b spectra of fissile isotopes measured at ILL in the 80’s - Fuel loading, geometry, n-capture and fission physics Fission product inventory Accurate reference electron spectra Conversion to antineutrinos Description of all b-decays - Use of “virtual” b-branches - Fermi theory + corrections - Control of approximations - Nuclear databases - Fermi theory + corrections - Nuclear models b and n total spectra from some 104 b-branches. Honolulu - AAP 2012 Reference n spectra per isotope to be combined with prediction of fissions rates. D. Lhuillier - CEA Saclay 36 Ingredients Sum of all fission products’ activities Sum of all β-branches of each fission product Theory of βdecay Honolulu - AAP 2012 D. Lhuillier - CEA Saclay 37 Status of Spectra Rate Final difference with respect to ILL n spectra : Global rate increase Linear trend with slope ≤1%/MeV enhances this increase in detected rate Emitted Flux Detected Rate Shift (%) Signif. (s) Shift (%) Signif. (s) 235U 2.4 3.7 3.7 2.4 239Pu 2.9 3.9 4.2 2.8 241Pu 3.2 4.0 4.7 3.0 Honolulu - AAP 2012 D. Lhuillier - CEA Saclay 38 Finite Size Correction of Weak Interaction Different expressions of C(Z,W) term: P. Vogel, Phys. Rev. D29, 1918 (1984). D. Wilkinson, Nucl. Phys. Inst. and Meth. A 290, 509 (1990) (Huber-Mueller) / Mueller 0.04 0.02 0 -0.02 -0.04 2 4 Relative Dif erence induced by C(Z,W) 3 5 6 7 8 En (MeV) • Include the envelope of various calculations as extra uncertainty? • Would reach ~2% at 7 MeV. Honolulu - AAP 2012 D. Lhuillier - CEA Saclay 39 Uncertainties 10 8 6 4 2 0 -2 -4 -6 -8 -10 Conversion of b spectra Error (%) 2 WM+Norm+Z+Stat WM+Norm+Z 4 WM+Norm WM 3 Finite size corrections could be further studies by combining nuclear model and lepton scattering data. Not dominant uncertainty. 5 6 7 8 n Kinetic E (Mev) Normalization: - Common to all predictions. - Currently 1.8% at 1 s. - A new measurement should target 1%. Not likely to happen. Quadratically stacked errors Current treatment of weak magnetism neglect the nuclear structure. - Dominant shape uncertainty, 100% error assumed. - Underestimated uncertainty? Honolulu - AAP 2012 D. Lhuillier - CEA Saclay 40 Shape Evolution Along a Reactor Cycle • Expected shape rotation on top of flux reduction • But significant measurement requires very large statistics on month time scale. Honolulu - AAP 2012 D. Lhuillier - CEA Saclay 41 Total Reactor Spectrum S(W, t)tot = åa k (t)Sk (W ) , k = 235U, 238U, 239 Pu, 241Pu k ak = fission fraction, Sk(W)=Reference spectrum Half way through: • Prediction of ak(t) • 238U couldn’t be measured at ILL because it undergoes fission in fast neutron flux. • Extrapolation of the ILL spectra to commercial reactors? Ab initio approach addresses it all Honolulu - AAP 2012 D. Lhuillier - CEA Saclay 42 Ab initio • Build as complete as possible nuclear database coupled to MCNP Utility for Reactor Evolution (*) full core inventory • 235U spectrum matches the ILL data at ~10% level • 238U prediction 10% higher than previous estimate Phys. Rev. C83,054615 (2011) ENSDF only Pandemonium corr. Add gross theory Deviation from Vogel et al., Phys. Rev. C24, 1543 (1981) • Total error in the 10-20% range. Dominated by systematics of nuclear databases. (*) http://www.nea.fr/tools/abstract/detail/nea-1845. Honolulu - AAP 2012 D. Lhuillier - CEA Saclay 43 Ab initio Study of relative spectrum variations to reach equilibrium Off-eq. correction as computed by the MURE ILL reference data are photos of b decays after 12-36h irradiation time. Long-lived isotopes, dominant at low energy, keep accumulating over several weeks. Sizeable correction to ILL data in [53] = Chooz paper below 3 MeV; +1% total detected flux See poster 146, A., Reactor and antineutrino spectrum calculation for the Double Chooz first phase result C. Jones et al. arXiv:nucl-ex/1109.5379v1 Honolulu - AAP 2012 D. Lhuillier - CEA Saclay 44 Error Budget 235U Honolulu - AAP 2012 Phys. Rev. C83,054615 (2011) 239Pu D. Lhuillier - CEA Saclay 241Pu 45 Error Budget Phys. Rev. C84, 024617(2011) Honolulu - AAP 2012 D. Lhuillier - CEA Saclay 46 Bugey Honolulu - AAP 2012 D. Lhuillier - CEA Saclay 47