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IntroductionThe NUCIFER experimentThe STEREO experiment
Reactor antineutrinos at short baselineThe NUCIFER and STEREO experiments
Maxime Péquignot
CEA SaclayCEA/Irfu - Service de Physique Nucléaire
3 December 2013
Maxime Péquignot - JRJC 2013 1 / 27
IntroductionThe NUCIFER experimentThe STEREO experiment
Outlook
1 IntroductionNeutrino historyNuclear reactor and neutrinosDetection principleBackground
2 The NUCIFER experimentNon-proliferationNucifer detectorResults
3 The STEREO experimentReactor antineutrinos anomalyStereo detectorLiquid scintillator choiceNeutrons and gammas backgroundSchedule
Maxime Péquignot - JRJC 2013 1 / 27
IntroductionThe NUCIFER experimentThe STEREO experiment
Neutrino historyNuclear reactor and neutrinosDetection principleBackground
Neutrino history
1930 : hypothesis of "neutrons" by Pauli to explain the β-decay spectrum :
n→ p + e− + ν̄e
Coupling only with weak interaction → hard to detect but ...... 1956 : first detection of electronic antineutrinos by Reines and Cowan with adetector close to a nuclear reactor !1968 : solar neutrino deficit → less detected neutrinos than expected ...Pontecorvo idea : neutrino oscillations.1998 : oscillation observation by Super-Kamiokande.
Pνe→νe = 1− sin2(2θ)sin2(∆m2L4E
)
Three kind of neutrinos observed : electron, muon and tau.
Maxime Péquignot - JRJC 2013 2 / 27
IntroductionThe NUCIFER experimentThe STEREO experiment
Neutrino historyNuclear reactor and neutrinosDetection principleBackground
Reactor antineutrinos
Nuclear reactors are pure and intense sources of ν̄e : 1.9× 1020 νe/s/GWth
⇒ small detector at short baseline is possible despite of the small cross-section.
Antineutrino kinetic energy (MeV)2 3 4 5 6 7 8 9
Arb
itrar
y un
its
Cross-section
Emitted spectrum
Detected spectrum
Maxime Péquignot - JRJC 2013 3 / 27
IntroductionThe NUCIFER experimentThe STEREO experiment
Neutrino historyNuclear reactor and neutrinosDetection principleBackground
Neutrino detection principle
Inverse β-decay utilisation :
ν̄e + p → n + e+
in Gd-loaded liquid scintillator.Very small cross-section ∼ 10−43 cm2
Prompt and delayed events incoincidence.
Prompt
Time
Delayed
>50 µs >100 µs35 µs5 µs
Delayed signal (µs): Edelayed ~ 8 MeV on Gadolinium
Prompt signal (ns): Eprompt a En (1 - 8 MeV)
ne
p n
e+ e-
Gd
g
g
g
g
Maxime Péquignot - JRJC 2013 4 / 27
IntroductionThe NUCIFER experimentThe STEREO experiment
Neutrino historyNuclear reactor and neutrinosDetection principleBackground
Expected backgrounds
Accidental background
Random coincidencebetween a gamma and aneutron capture or anotherenergetic gamma.Shielding to stop them.Measured reactor ON andsubtracted.
Correlated background
Cosmic µ± ⇒ fast n ⇒ correlated signal.Decreased by overburden and the muon veto.PSD rejection.Measured reactor OFF and subtracted.
⇒ Measured neutrino count rate: Nν̄e = NONcorr − NON
acc − (NOFFcorr − NOFF
acc ).Maxime Péquignot - JRJC 2013 5 / 27
IntroductionThe NUCIFER experimentThe STEREO experiment
Neutrino historyNuclear reactor and neutrinosDetection principleBackground
Background rejection with Pulse Shape Discrimination
Time [ns]0
Proton recoil pulse
Total gate Delayed gate
t0 150
e± recoil pulse
tot / Q
tailQ
-10 -8 -6 -4 -2 0 2 4 6 8 100
0.2
0.4
0.6
0.8
1
1.2
Total
Accepted
Rejected
FoM Cut
e+ signal Proton bkg ν̄ prompt, γ, (n,γ) ⇒ low Qtail/Qtotratio.Fast neutron prompt only ⇒ p recoil⇒ high Qtail/Qtot ratio.PSD ⇒ Online rejection of thecorrelated background beforesubstraction of the correlated events.
Maxime Péquignot - JRJC 2013 6 / 27
IntroductionThe NUCIFER experimentThe STEREO experiment
Non-proliferationNucifer detectorResults
The Nucifer experiment
Nucifer
Maxime Péquignot - JRJC 2013 7 / 27
IntroductionThe NUCIFER experimentThe STEREO experiment
Non-proliferationNucifer detectorResults
Antineutrinos for the non-proliferation
Neutrino emission depends on the fuel composition and on the core power :Nν̄e = α ∗ Pth ∗ (1 + k(t)) with k(t) function of the fuel.
Temps (jours)
0 100 200 300 400 500
Tau
x de
rea
ctio
n (f
issi
ons/
s)
0
20
40
60
80
100
120
1810×
Pu (n,fis)239
U (n,fis)235
U initial2353.5% = cte = 3 GWthP
kinetic energy (MeV)ν2 3 4 5 6 7 8
fiss
ions
44 p
er 1
0ν
Det
ecte
d
0
5
10
15
20
25
U235
Pu239Weeks
0 10 20 30 40 50 60 70 80
/week
ν
8000
10000
12000
14000
Weeks
0 10 20 30 40 50 60 70 80
/week
ν
8000
10000
12000
14000
from 235Uν
from 239Puν
rateνTotal
Direct real time informations on reactoroperation.Complementary method to know total burnupreactor.
⇒ IAEA interest for surveillance of reactors.Maxime Péquignot - JRJC 2013 8 / 27
IntroductionThe NUCIFER experimentThe STEREO experiment
Non-proliferationNucifer detectorResults
OSIRIS site and detector caracteristics
70MWth “pool type” research reactor,∼7m from the reactor core,⇒ high gamma flux.
Low overburden⇒ muon flux attenuation = 2.7.
Main caracteristics of NUCIFER :850 L of Gd-loaded (0.2%) liquidscintillator (MPIK scintillator),16 PMTs fixed on an acrylic buffer,central calibration tube.
● Liquid scintillators are fragile:
– Damaged by oxygen
– Only compatible with quartz,acrylic and Teflon
10 cmof lead
14 cm of borondoped polyethylene
2,5
m
Active muon veto: plastic scintillator + PMT
Nitrogen atmosphere16 PMTsAcrylic buffer
Target liquid: 850 L
Stainless steel tank + Teflon
Total: ~ 50 tonnes3 m
3 m
Maxime Péquignot - JRJC 2013 9 / 27
IntroductionThe NUCIFER experimentThe STEREO experiment
Non-proliferationNucifer detectorResults
Reactor spectrum
Single rate ∼200 Hz above 2 MeV, on expectation, but leakage of high energygammas in Edelayed window ⇒ too much accidental background.A lead wall will be added to bring the background on specifications (factor ∼ 30).
Maxime Péquignot - JRJC 2013 10 / 27
IntroductionThe NUCIFER experimentThe STEREO experiment
Non-proliferationNucifer detectorResults
Results (PRELIMINARY)
Prompt
Time
Delayed
>50 µs >100 µs35 µs5 µs
Prompt
Time
Delayed
1 ms
40 µs
Simulatedprompt
>100 µs>50 µs
Results (ON : 22 days, OFF : 5 days):
Accidental rate Correlated rateReactor OFF (33.9± 0.3) /day (124± 6) /dayReactor ON (3131± 2) /day (259± 14) /day
⇒ 135 νe/day ± 15.
Optimized cuts → 293 νe/day, publication in preparation.
Maxime Péquignot - JRJC 2013 11 / 27
IntroductionThe NUCIFER experimentThe STEREO experiment
Non-proliferationNucifer detectorResults
Results (PRELIMINARY)
Correlated events excess = fastneutrons coming from the core ?
High Qtail/Qtot : fast neutrons.Low Qtail/Qtot : γ, neutrino.
No more fast neutrons when thereactor is ON than when it is OFF
⇒ excess at low Qtail/Qtot isdue to neutrinos.
Maxime Péquignot - JRJC 2013 12 / 27
IntroductionThe NUCIFER experimentThe STEREO experiment
Non-proliferationNucifer detectorResults
Results (PRELIMINARY)
Maxime Péquignot - JRJC 2013 13 / 27
IntroductionThe NUCIFER experimentThe STEREO experiment
Reactor antineutrinos anomalyStereo detectorLiquid scintillator choiceNeutrons and gammas backgroundSchedule
The Stereo experiment
Maxime Péquignot - JRJC 2013 14 / 27
IntroductionThe NUCIFER experimentThe STEREO experiment
Reactor antineutrinos anomalyStereo detectorLiquid scintillator choiceNeutrons and gammas backgroundSchedule
Reactor antineutrinos anomalyReevaluation of reactor ν̄e spectra, Th. A. Mueller et al., Phys.Rev.C 83, 054615 (2011)Reanalysis of short baseline experiments ⇒ deficit of 6% (2013 update)
G. Mention et al., Phys. Rev. D 83, 073006 (2011)
atmosphericoscillation
solaroscillation
ReactorAntineutrinosAnomaly
newoscillation ?
KamLAND
Double Chooz,Daya Bay, RENO. . .
Bugey, ROVNO, Goesgen. . .
New oscillations toward a sterile neutrino at very short baselines (∆m2 & 1 eV2).Maxime Péquignot - JRJC 2013 15 / 27
IntroductionThe NUCIFER experimentThe STEREO experiment
Reactor antineutrinos anomalyStereo detectorLiquid scintillator choiceNeutrons and gammas backgroundSchedule
ILL site and detector design
B42
New site
58MWth “pool type” research reactor,∼10m from the reactor core.⇒ High gamma and neutron flux.
Efficient overburden provided by thewater channel (muon attenuation : 4).⇒ Low muon induced.
Main caracteristics of STEREO :6 independent target cells with 4 PMTs,a gamma catcher with 24 PMTs.
Maxime Péquignot - JRJC 2013 16 / 27
IntroductionThe NUCIFER experimentThe STEREO experiment
Reactor antineutrinos anomalyStereo detectorLiquid scintillator choiceNeutrons and gammas backgroundSchedule
STEREO motivationMotivation : to detect a new oscillation pattern in E and L.
Experimental contour covers the 99% C.Lcontour of the reactor anomaly.It includes the best fit at 5σ.
Maxime Péquignot - JRJC 2013 17 / 27
IntroductionThe NUCIFER experimentThe STEREO experiment
Reactor antineutrinos anomalyStereo detectorLiquid scintillator choiceNeutrons and gammas backgroundSchedule
Liquid scintillator choice
Different liquid scintillators are studied based on Petrelad and PXE.
Requested properties :
Attenuation length > 4m in the range of PMTs sensibility (∼ 430nm).
Stable for several years and compatible with detector materials.
Good light yield i.e quantity of photons for one MeV.
Good pulse shape discrimination for background rejection.
Maxime Péquignot - JRJC 2013 18 / 27
IntroductionThe NUCIFER experimentThe STEREO experiment
Reactor antineutrinos anomalyStereo detectorLiquid scintillator choiceNeutrons and gammas backgroundSchedule
Light yield determination
Utilisation of a 60Co source : 2 γ rays (1.15 MeV and 1.35 MeV).Rought calibration using the high E edge of the 60Co spectrum.
All tested liquids have comparable light yields (∼ 7500-8000 photon/MeV).
Maxime Péquignot - JRJC 2013 19 / 27
IntroductionThe NUCIFER experimentThe STEREO experiment
Reactor antineutrinos anomalyStereo detectorLiquid scintillator choiceNeutrons and gammas backgroundSchedule
PSD determination
Same set-up with a 252Cf source (fast neutrons and gammas).
-45000 -40000 -35000 -30000 -25000 -20000 -15000 -10000 -5000 00
0.1
0.2
0.3
0.4
0.5
0.6nTH2D_Qtail_over_Qtail_vs_Qtot_CFD_40ns
Entries 109645Mean x -5937Mean y 0.2252RMS x 4902RMS y 0.09087Integral 1.096e+05 0 22 1 0 109562 0 0 60 0
nTH2D_Qtail_over_Qtail_vs_Qtot_CFD_40ns
Entries 109645Mean x -5937Mean y 0.2252RMS x 4902RMS y 0.09087Integral 1.096e+05 0 22 1 0 109562 0 0 60 0
Qtail/Qtot vs Qtot, time with CFD, delay 40 ns
hQtail_over_Qtot_CFD_40nsEntries 7031Mean 0.2159RMS 0.05688Underflow 0Overflow 0Integral 7020
/ ndf 2χ 2222 / 208Prob 0Constant 0.6± 162 Mean 0.0002± 0.1815 Sigma 0.00015± 0.01703
Qtail/Qtot0.1 0.15 0.2 0.25 0.3 0.35 0.4
# of
ent
ries
0
20
40
60
80
100
120
140
160
180 hQtail_over_Qtot_CFD_40nsEntries 7031Mean 0.2159RMS 0.05688Underflow 0Overflow 0Integral 7020
/ ndf 2χ 2222 / 208Prob 0Constant 0.6± 162 Mean 0.0002± 0.1815 Sigma 0.00015± 0.01703
Qtail/Qtot, time with CFD, delay 40 ns
Very good separation achevied in test cells.Provides margin for an efficient online rejection in the detector..
Maxime Péquignot - JRJC 2013 20 / 27
IntroductionThe NUCIFER experimentThe STEREO experiment
Reactor antineutrinos anomalyStereo detectorLiquid scintillator choiceNeutrons and gammas backgroundSchedule
Site presentation
PN3PN3
Background specifications for STEREO :200 Hz for prompt events (E > 2MeV)1 Hz for delayed events (E > 5MeV)
Maxime Péquignot - JRJC 2013 21 / 27
IntroductionThe NUCIFER experimentThe STEREO experiment
Reactor antineutrinos anomalyStereo detectorLiquid scintillator choiceNeutrons and gammas backgroundSchedule
Thermal neutrons and gammas
Detection of thermal neutrons with a helium tube.High thermal neutron ambiance due to neighbour neutron beam lines.Hotspots close to the wall IN20/PN3.
⇒ Efficient reduction with B4C plate (validated on-site).
Detection of gamma with a HPGe.
hEEntries 5527536
Mean 1417
RMS 1534
Underflow 0
Overflow 0
Integral 1843
Energy (keV)0 1000 2000 3000 4000 5000 6000 7000 8000
)1
Hit
s (
s
310
210
110
1
10
hEEntries 5527536
Mean 1417
RMS 1534
Underflow 0
Overflow 0
Integral 1843
hEEntries 1408647
Mean 1528
RMS 1591
Underflow 0
Overflow 0
Integral 469.5
hEEntries 1408647
Mean 1528
RMS 1591
Underflow 0
Overflow 0
Integral 469.5
IN20 ONOFF, D19 ON
IN20 OFFOFF, D19 ON
Gammas spectrum in PN3
(IN20 ON) spectrum is 4 timeshigher than (IN20 OFF) spectrum80% of gamma comes from IN20.
⇒ Addition of lead.
Maxime Péquignot - JRJC 2013 22 / 27
IntroductionThe NUCIFER experimentThe STEREO experiment
Reactor antineutrinos anomalyStereo detectorLiquid scintillator choiceNeutrons and gammas backgroundSchedule
Neutrons and gammas shieldingAddition of B4C in PN3 and IN20 + lead in PN3.
Maxime Péquignot - JRJC 2013 23 / 27
IntroductionThe NUCIFER experimentThe STEREO experiment
Reactor antineutrinos anomalyStereo detectorLiquid scintillator choiceNeutrons and gammas backgroundSchedule
What about fast neutrons ?
Measurements were done with a PEHD shielding around the helium tube.⇒ Identification of two main sources : IN20 casemate and H7 neutron tube.
MCNPX simulations were done to prove that neutron with an energy higher than6 MeV can not come from the reactor :
6Li produces fast neutrons bythe following reaction :
n(thermal) + 6Li→ 4He + t
t + 6Li→ 8Be + n(fast)
⇒ 6Li will be removed and the plug will stop these fast neutrons coming from H7.
Maxime Péquignot - JRJC 2013 24 / 27
IntroductionThe NUCIFER experimentThe STEREO experiment
Reactor antineutrinos anomalyStereo detectorLiquid scintillator choiceNeutrons and gammas backgroundSchedule
What about fast neutrons from IN20 ?
Addition of CH2 around the IN20collimators to provide enough marginof background reduction.
Tally1_normaliseEntries 207
Mean 0.1946
RMS 0.6032
Underflow 0
Overflow 0
Integral 7.501e+08
Energy (MeV)1 2 3 4 5 6
/s)
2F
lux
(n/c
m
510
610
710
810Tally1_normaliseEntries 207
Mean 0.1946
RMS 0.6032
Underflow 0
Overflow 0
Integral 7.501e+08
Neutrons flux at the end of H13
Tally5_normaliseEntries 120
Mean 0.01661
RMS 0.09361
Underflow 0
Overflow 0
Integral 1.076e+05
Energy (MeV)1 2 3 4 5 6
/s)
2F
lux
(n/c
m
-210
-110
1
10
210
310
410Tally5_normaliseEntries 120
Mean 0.01661
RMS 0.09361
Underflow 0
Overflow 0
Integral 1.076e+05
Neutrons flux before the IN20/PN3 wall
Tally2_normalise
Entries 360
Mean 1.194
RMS 0.9401
Underflow 0
Overflow 0Integral 2064
Energy (MeV)1 2 3 4 5 6
Flu
x (n
/s)
-110
1
10
210
Tally2_normalise
Entries 360
Mean 1.194
RMS 0.9401
Underflow 0
Overflow 0Integral 2064
Neutrons flux in PN3
Maxime Péquignot - JRJC 2013 25 / 27
IntroductionThe NUCIFER experimentThe STEREO experiment
Reactor antineutrinos anomalyStereo detectorLiquid scintillator choiceNeutrons and gammas backgroundSchedule
What are the next steps ?
November 2013 : decommissioning of GAMS5 and H7.
February 2014 : shielding installation in H13 casemate.
Mai 2014 : H7 plug installation.
June 2014 : shielding installation in Stereo casemate.
June-July 2014 : background measurements.
September-October 2014 : detector installation.
November 2014 : Stereo commissioning.
Maxime Péquignot - JRJC 2013 26 / 27
IntroductionThe NUCIFER experimentThe STEREO experiment
Reactor antineutrinos anomalyStereo detectorLiquid scintillator choiceNeutrons and gammas backgroundSchedule
Conclusions
Nucifer sees neutrinos with high stat significance, data from 3 Osiris cycles ondisk.Publication in preparation.Last upgrade of lead shielding planned to reduce accidental background.One full year of data taking with background close to the specifications.
Complete on site background studies, shielding structures being designed.Prototype cell expected early next year to validate the response of the innerdetector.Sequential background cross-checks after reactor restart in July 2014, detectorcommissioning November 2014.
Toward an applied antineutrino physics. . .. . . and a sterile neutrino ?
Maxime Péquignot - JRJC 2013 27 / 27
Back-up
Maxime Péquignot - JRJC 2013 1 / 27
MCNPX Simulations
Maxime Péquignot - JRJC 2013 2 / 27
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