Probe background, technology, calibration, MCNP
DARIN DESILETSHydroinnova
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The instrument: CRS-1000
80 cm
Bare tube (secondary sensor)
Moderated tube (primary sensor)
Charge controller and30 Ah battery
Data logger
Pulse module
Connection to Iridium or cell phone
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The instrument: CRS-1000/B
Pulse module
Bare or moderated tube inside
130 cm
Charge controller and30 Ah battery
Data logger
Connection to Iridium or cell phoneantenna
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Comparison
Tradeoffs
size/weight
long-term performance
power consumption
sensor cost
expandability
protection from moisture
Sensitivity to soil moisture
CRS1000 CRS1000/B
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Same sensitivity?
0 10 20 30 40 50 60 70350
400
450
500
550
600
650
700
750
CRS1000 CRS1000/B
Days
Neutroncounting
rate(counts per
hour)
majorrainevent
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Neutron scattering theory
ss (barns) x (-)
H 20.0 1.00C 4.8 0.16O 4.2 0.12Si 2.0 0.07
xsPower Moderating
2s
3-
ss
cm
cm nuclei
s
s
N
N
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Neutron scattering theory
a
s
xE < 0.1 eV
E > 10 eV x
sa
1Moderatedtube
Bare tube
as
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Energy sensitivity for moderated and bare detectors
-10 -8 -6 -4 -2 0 20.00.51.01.52.02.53.03.54.04.55.0
bare moderated
Logarithm of neutron energy (MeV)
Logarithmof counting
rate(relative)
a
s
x
sx
1
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Why use bare counter?o Built-in pressure/solar activity correctiono Provides long-term check on stabilityo Separate snow from soil moisture (?)o Basic research
– Canopy snow and water– Biomass
o Added issues:– Presence of local absorbers (no universal cal!)– Some very local responses– Greater depth penetration?
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Bare counter enhancements?
2009
02-Jan 04-Jan 06-Jan 08-Jan 10-Jan 12-Jan
SW
E (c
m)
12
14
16
18
20
Neu
tron
coun
ts p
er 1
5 m
inut
es
1300
1400
1500
1600
1700
1800
Snow Pillow
Cosmic-ray probe
Kerplop!
BareModerated
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Improved uncertainty for soil moisture determinations
o Limiting case 1: bare tube has same sensitivity to soil moisture as moderated tube.Add counting rates, reduce sstat by ~40%
o Limiting case 2: bare tube has low sensitivity to soil moistureUse bare to reduce ssyst
s2total=s2
stat + s2syst
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Modeling neutrons with MCNP
o Monte Carlo Neutral-Particleo The original Monte Carlo applicationo Remains the “gold standard” for neutron
transporto Flexible source specification, geometries,
tallieso Overkill? Maybe so
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Summary
o Current configuration is optimized for COSMOS—but other configurations are possible.
o Bare counter: not critical but has certain advantages when used with mod tube.
o MCNP code: an essential tool for basic research with the cosmic-ray probe.