Development of energydependent scaling for cosmicray neutron intensities and for insitu cosmogenic n

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Development of energy-dependent scaling for
cosmic-ray neutron intensities and for in-situ
cosmogenic nuclide production rates
Marek Zreda - ArizonaDevendra Lal - ScrippsJohn
Clem - BartolDarin Desilets - Arizona
Neutron measurements Neutron modeling Artificial
chemical targets
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Energy spectra for neutrons and nuclides
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Vertical cutoff rigidity (GV) for Epoch 1980
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Spatial variations of neutron intensity
Important discovery Attenuation length in the air
for neutrons depends on energy Dorman function
for neutrons depends on energy
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Neutron Monitor
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polyethylene
counter tube
lead
John Clem - http//www.bartol.udel.edu/clem/nm/di
splay/intro.html
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Arizona mobile neutron monitor
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Sample results from Arizona neutron monitor
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Bare counter (BC) tubes? Lower energy
sensitivity
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Thermal neutron detector (counter)
Specifications Diameter 2.6 cm Length 39.2
cm Total pressure 1.03 MPa Voltage range 1100 -
1600 V Water resistance up to 8 m Background
counting rate 6 cts/hr Counting rate on Mt.
Lemmon, AZ (2788 m) 3830 cts/hr Counting rate in
Tucson, AZ (667 m) 900 cts/hr
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Thermal neutron detector assembly
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Sample results from our neutron detector
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Comparison with previous models (attenuation
lengths for high-energy and thermal neutrons)
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Current data

• NM
• gt 9 latitude surveys
• 2 comprehensive altitude/latitude surveys
• numerous NM stations

• BC
• 1 latitude survey
• 1 comprehensive altitude/latitude survey

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• Possible outcomes
• (1) All nuclides scaled by NM
• (2) All nuclides scaled by BC
• (3) Low-E interactions scaled by BC,
• high-E scaled by NM
• (4) Many scaling functions
• Other results
• Angular sensitivity
• E sensitivity
• Neutron spectrum from NM
• Muon sensitivity

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Attenuation length for production of
36Cl(lava-flow samples, Mauna Kea, Hawaii)
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Comparison of targets with geological samples
Geological samples Targets Cosmic-ray
intensity Estimated (from geological records)
Known Exposure duration Determined (by
geological dating) Known Exposure
geometry Unknown (assessed, guessed)
Known Exposure time Long Short Chemistry Co
mplex Simple Expected accuracy Poor
Good Expected precision Good Good Other
things ?????? ??????
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Proposed target experiments
Primary objectives (1) To determine attenuation
lengths for production of nuclides - at known
magnetic cutoff rigidity - for low- and high
energy reactions (2) To relate these to measured
attenuation lengths for neutrons
Primary objectives (1) To determine attenuation
lengths for production of nuclides - at known
magnetic cutoff rigidity - for low- and high
energy reactions (2) To relate these to measured
attenuation lengths for neutrons Secondary
objective (3) To determine absolute production
rates of selected other nuclides
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Proposed target experiments
Objectives (1) To determine attenuation lengths
for nuclide production (2) To compare with
neutron attenuation lengths (3) To determine
absolute production rates of selected other
nuclides
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Selected targets - primary
High-energy reaction O(n,x)10Be t½ 1.5 My Emed
140 MeV Target H2O (water) Concentration
100 Target size 100-200 kg Exposure time gt3
years Repeated exposure no Measurement AMS
(Purdue)
High-energy reaction O(n,x)10Be t½ 1.5 My Emed
140 MeV Target H2O (water) Concentration
100 Target size 100-200 kg Exposure time gt3
years Repeated exposure no Measurement AMS
(Purdue)
Low-energy reaction 32S(n,p)32P t½ 14.3
days Emed 7 MeV Target CS2 Concentration
100 Target size 10-15 L Exposure time gt2
months Repeated exposure yes Measurement
Quantulus (Arizona)
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Selected targets - secondary
Low-energy reaction K(n,x)36Cl Emed 13
MeV Target KNO3 Concentration 15 Target size
20 kg Exposure time gt3 years Repeated exposure
no Measurement AMS (Purdue)
Low-energy reaction K(n,x)36Cl Emed 13
MeV Target KNO3 Concentration 15 Target size
20 kg Exposure time gt3 years Repeated exposure
no Measurement AMS (Purdue)
Mid-energy reaction Ca(n,x)36Cl Emed 55
MeV Target Ca(NO3)2 Concentration 10 Target
size 40 kg Exposure time gt3 y Repeated
exposure no Measurement AMS (Purdue)
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Field locations
Hawaii - 13 GV Mauna Kea Mauna Loa several
secure locations (government facilities) between
the summit (4 km) and the saddle (1.6 km) Why
Hawaii high magnetic cutoff rigidity large
elevation span much neutron/nuclide data
exist permanent neutron monitor (Maui)
Hawaii - 13 GV Mauna Kea Mauna Loa several
secure locations (government facilities) between
the summit (4 km) and the saddle (1.6 km) Why
Hawaii high magnetic cutoff rigidity large
elevation span much neutron/nuclide data
exist permanent neutron monitor (Maui)
California - 4 GV White Mountains several
secure locations (government facilities) between
the summit (4 km) and the Owens Valley (1.6
km) Why California low magnetic cutoff
rigidity large elevation span close to Arizona
and Scripps permanent neutron monitor (Climax)