1. Review of Neutrino Coherent Scattering
Belkis Cabrera-Palmer
March 20, 2009
Sandia National Laboratories
Lawrence Livermore National Laboratory

2. Outline physics of neutrino coherent scattering
cross section and rates
NPP monitoring
solar neutrino background

3. Neutrino Coherent Scattering
,k’ 
,k Z R
N, q
It has never been observed!

4. Cross section Coherence applies when momentum transfer q <<  
1/R(Germanium) ~ 38 MeV
R, M, Z,N   T,
1/R(Argon) ~ 47 MeV 
Cross section enhanced by N2 (N is # of neutrons)
Same for all neutrino flavors
Estimation of events for reactor neutrinos:

5. Challenges: small recoil energy and smaller ionization energy
the nucleus recoil energy is
for heavy nuclei, the recoil energy is in the few keVs:
quenching: detectable ionization energy is just a fraction of the recoil energy
I ~ hundreds of eV

6. Challenges: fewer reactor neutrinos at larger energies
the cross section increases with neutrino energy:
but …there are fewer reactor neutrinos at higher energies
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
Germanium target

7. Reactor neutrino spectra
52%
Uranium yields 65% more neutrinos with E>8MeV
than Plutonium
Neutrinos per MeV fission
from
Uranium and Plutonium
From: Klapdor, Metzinger PLB 112,1 (1982)
Estimation of
Events per eV, day, kg(Ge)
vs.
the minimum neutrino energy E that produces recoils with
Uranium fission produces 67% more events with I> 300eV than Plutonium fission
57%

8. Sensitivity to NPP fuel composition
About 20% variation in total events during a Nuclear Power Plant fuel cycle
~20 %

9. Scale of a Coherent Scattering Detector
Estimated number of counts/day kg above threshold with a Germanium 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
A 100eV-improvement in detector threshold produces a large reduction in detector size.

10. Comparison to solar neutrino background
Estimated counts/day kg above threshold with Germanium
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
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.
Detector

11. 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.

12. Muito obrigada.