review of neutrino coherent scattering belkis cabrera-palmer march 20, 2009
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Review of Neutrino Coherent Scattering Belkis Cabrera-Palmer March 20, 2009. Sandia National Laboratories Lawrence Livermore National Laboratory. Outline. physics of neutrino coherent scattering cross section and rates NPP monitoring solar neutrino background. - PowerPoint PPT PresentationTRANSCRIPT
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Review of Neutrino Coherent Scattering Belkis Cabrera-Palmer
March 20, 2009
Sandia National LaboratoriesLawrence Livermore National Laboratory
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Outline
physics of neutrino coherent scattering cross section and rates NPP monitoring solar neutrino background
3
Neutrino Coherent Scattering
,k
,k’
N, q
ZR
It has never been observed!
4
Cross section
•Coherence applies when momentum transfer
R1
q <<1/R(Germanium) ~ 38 MeV
1/R(Argon) ~ 47 MeV
kE
,
R, M, Z,N
kE
,
T,q
)cos1(8cos
222
ENG
dd
•Cross section enhanced by N2 (N is # of neutrons) •Same for all neutrino flavors
kg/day 250~~ EN
•Estimation of events for reactor neutrinos: ,seccm
10~ 2
13
MeV3.2~E
5
Challenges: small recoil energy and smaller ionization energy
keV75.1MeV1MeV8
732~)Germanium(
2
max
T
• the nucleus recoil energy is
• quenching: detectable ionization energy is just a fraction of the recoil energy
dTd
0
0 recoil energy T
• for heavy nuclei, the recoil energy is in the few keVs:
keVMeV1
2~2 22
max
E
AME
T cos12
ME
T
TQI
keV2.3~)Argon(maxT
,2.0)Germanium( Q
2.0)Argon( QI ~ hundreds of eV
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Challenges: fewer reactor neutrinos at larger energies
• the cross section increases with neutrino energy: 2~
cos E
dd
but …there are fewer reactor neutrinos at higher energies
QMIE2
min
• the detectable recoil energy threshold constraints the access to lower neutrino energies, since, to produce an event with energy I, the minimum neutrino energy is
8
6
4
2
min
imum
neu
trino
ene
rgy
E, i
n M
eV
35030025020015010050ionization recoil energy I, in eV
Threshold 300eV
Threshold 200eV
Threshold 100eV
Germanium target
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Reactor neutrino spectra
10-5
10-4
10-3
10-2
10-1
100
neu
trino
s/(0
.5 M
eV fi
ssio
n)
8642neutrino energy E , in MeV
Uranium Plutonium
52%Uranium yields 65% more neutrinos with E>8MeV than Plutonium
Neutrinos per MeV fission from Uranium and Plutonium
Estimation ofEvents per eV, day, kg(Ge) vs.the minimum neutrino energy E that produces recoils with
10-3
10-2
10-1
100
101
102
103
104
even
ts/(0
.3 e
V d
ay k
g of
Ge)
86420minimum neutrino energy E, in MeV
Uranium Plutonium
Uranium fission produces 67% more events with I> 300eV than Plutonium fission
57%
QME
I22
From: Klapdor, Metzinger PLB 112,1 (1982)
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Sensitivity to NPP fuel composition
1.0
0.8
0.6
0.4
0.2
0.0
even
ts /k
g da
y a
bove
thre
shol
d Ith
1.00.80.60.40.20.0Uranium fraction
Ith = 300 Ith = 200 Ith = 100
~20 %
About 20% variation in total events during a Nuclear Power Plant fuel cycle
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Scale of a Coherent Scattering Detector
above threshold(eV) for Uranium fraction 80%
for Uranium fraction 50%
Kgs for 3-signal (no bkgnd) in 15 days
300 2.6 2.2 12
200 8.3 7.1 3
100 35.9 31.3 1
Estimated number of counts/day kg above threshold with a Germanium Detector
A 100eV-improvement in detector threshold produces a large reduction in detector size.
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Comparison to solar neutrino background
Detector
above threshold
(eV)
from reactor (U80%,
R=20meters)
from solar neutrinos
Equivalent radius (Km)
300 2.6 3.7e-4 1.7
200 8.3 5.6e-4 2.5
100 35.9 8.4e-4 4.1
Estimated counts/day kg above threshold with Germanium
The solar neutrino background is comparable with the reactor neutrino signal at distances >1.5 km from the reactor core.
The solar background prevents or at least greatly complicates using coherent scatter detectors as standoff reactor monitors beyond a kilometer or so.
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Conclusions
Neutrino Coherent Scattering …
•is hard to detect since the detectable fraction of the released energy is less than few hundreds of eV,
•requires detector with very low noise threshold,
•can be used for NPP monitoring since it is sensitive to fuel composition.
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Muito obrigada.