JASON SURBROOKUNC-CH

TUNL-ORNL REU 2014

Understanding neutron backgrounds at Oak Ridge National

Laboratory's Spallation Neutron Source by assessing neutron activation in a p-type point-contact Germanium detector

What is the SNS

Neutron production by Hg spallation

Proton acceleration to 1 GeV, about 1.4 MWatts

Each P “spalls” 20-30 N

Oak Ridge National Lab’s Spallation Neutron Source.

(courtesy of ORNL.gov)

• SNS is a source of intense PULSED neutrino flux!

Motivation

COHERENT collaboration’s CEνNS [sĕns] Coherent Elastic

Neutrino-Nucleus Scattering

Assumed to be important in Supernovae

Well calculable cross-section Strong test of the

Standard Model

A A

n n

Z0

Courtesy Wikimedia Commons

Coherent Elastic Neutrino Scattering

Requires ν’s slower than MeV Faster, and it sees individual nucleons

Deviations from cross section suggest at physics beyond SM

SNS is a great location for neutrino research High intensity, pulsed neutrinos Free! Already being produced at SNS via pion decay SNS MeV; Ideal for scattering!!!

E: n energyT: nuclear recoil energyGF: Fermi constant

M: Nuclear massF: Form factorQw: Weak charge

Free Pulsed Neutrinos

SNS beam operates at 60 Hz flux at 20 meters from targetPulsing allows for 2000x reduction of background

The Detector

0.825 kg High Purity Germanium (HPGe) Excellent energy resolution Established technology

Needs to be LN cooledHas spent time unshielded

in SNS target building Crystal Dislocations? Activation?

Broad Energy Germanium (BEGe)

detector cutaway from Canberra online

catalogue

Detector Motivation

HPGe and/or scintillators Is this particular detector viable? What exposure limits can we impose on HPGe?

2-Phase LXe CsI Crystal PPC HPGe

Courtesy COHERENT collaboration

Crystal Damage

Ge crystal dislocation due to fast neutrons Dislocation sites = charge traps Poor resolution Geometric irregularities

Often skews observed energy peaks down

ν Measurement Noise

Captured neutrons may cause detector radioactivity 68Ge e-captures to 68Ga, Ga emits x-ray at 10.4 keV

Half Life is 271 days Coherent scattering is expected to be in the several

keVee rangeNeutrons also impose prompt broad energy

background Not measurable here, but requires attention!!

Good News, Everyone!

Looking more closely

Shielded Spectra

Shielded Spectra (<20 keV)

Well Defined Peak at 10.22 keV

Cosmogenic Measured

Counts per day

Wrapping Up

ResultsDetector energy resolution is adequate for

CEνNSWhile at SNS, neutrons produced of 68Ge in this

detector About 175x rate due to cosmic rays at sea-level

Future WorkLow energy calibration, to correct the 10.4 keV

peakExplore T β-decay in low energy region of spectraShielding effects on activation rates

Questions?