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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

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Neutrino Coherent Scattering

,k

,k’

N, q

ZR

It has never been observed!

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Cross section

•Coherence applies when momentum transfer

R

1q <<

1/R(Germanium) ~ 38 MeV

1/R(Argon) ~ 47 MeV

kE

,

R, M, Z,N

kE

,

T,q

)cos1(8cos

222

EN

G

d

d

•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

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Challenges: small recoil energy and smaller ionization energy

keV75.1MeV1

MeV8

73

2~)Germanium(

2

max

T

• the nucleus recoil energy is

• quenching: detectable ionization energy is just a fraction of the recoil energy

dT

d

0

0 recoil energy T

• for heavy nuclei, the recoil energy is in the few keVs:

keVMeV1

2~

222

max

E

AM

ET cos1

2

M

ET

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

Ed

d

but …there are fewer reactor neutrinos at higher energies

Q

MIE

2min

• 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

imu

m n

eu

trin

o e

nerg

y E

, in

Me

V

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)

8642

neutrino 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

eV d

ay k

g of

Ge)

86420

minimum neutrino energy E, in MeV

Uranium Plutonium

Uranium fission produces 67% more events with I> 300eV than Plutonium fission

57%

QM

EI

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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 /

kg d

ay

abov

e th

resh

old

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.