Development of energy-dependent scaling for cosmic-ray neutron intensities and for in- situ cosmogenic nuclide production rates Marek Zreda - Arizona Devendra Lal - Scripps John Clem - Bartol Darin Desilets - Arizona Neutron measurements Neutron modeling Artificial chemical targets

Energy spectra for neutrons and nuclides

Vertical cutoff rigidity (GV) for Epoch 1980

Spatial variations of neutron intensity Important discovery Attenuation length in the air for neutrons depends on energy Dorman function for neutrons depends on energy

Neutron Monitor

counter tubelead polyethylene John Clem -

Arizona mobile neutron monitor

Sample results from Arizona neutron monitor

Bare counter (BC) tubes? Lower energy sensitivity

Thermal neutron detector (counter) Specifications: Diameter 2.6 cm Length 39.2 cm Total pressure 1.03 MPa Voltage range 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

Thermal neutron detector assembly

Sample results from our neutron detector

Comparison with previous models (attenuation lengths for high-energy and thermal neutrons)

Current data NM > 9 latitude surveys 2 comprehensive altitude/latitude surveys numerous NM stations BC 1 latitude survey 1 comprehensive altitude/latitude survey

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

Attenuation length for production of 36 Cl (lava-flow samples, Mauna Kea, Hawaii)

Comparison of targets with geological samples Geological samples Targets Cosmic-ray intensityEstimated (from geological records) Known Exposure durationDetermined (by geological dating) Known Exposure geometryUnknown (assessed, guessed) Known Exposure timeLong Short ChemistryComplex Simple Expected accuracyPoor Good Expected precisionGood Good Other things?????? ??????

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 Proposed target experiments

Experimental design matrix Hawaii, 13 GVCalifornia, 4 GV Target type O(n,x) 10 Be yes yes Primary 32 S(n,p) 32 P yes yes Primary K(n,x) 36 Cl yes yes Secondary Ca(n,x) 36 Cl yes yes Secondary Experimental design matrix Hawaii, 13 GVCalifornia, 4 GV Target type O(n,x) 10 Be yes yes Primary 32 S(n,p) 32 P yes yes Primary K(n,x) 36 Cl yes yes Secondary Ca(n,x) 36 Cl yes yes Secondary 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

High-energy reaction: O(n,x) 10 Be t ½ = 1.5 My E med = 140 MeV Target: H 2 O (water) Concentration: 100% Target size: kg Exposure time: >3 years Repeated exposure: no Measurement: AMS (Purdue) High-energy reaction: O(n,x) 10 Be t ½ = 1.5 My E med = 140 MeV Target: H 2 O (water) Concentration: 100% Target size: kg Exposure time: >3 years Repeated exposure: no Measurement: AMS (Purdue) Low-energy reaction: 32 S(n,p) 32 P t ½ = 14.3 days E med = 7 MeV Target: CS 2 Concentration: 100% Target size: L Exposure time: >2 months Repeated exposure: yes Measurement: Quantulus (Arizona) Selected targets - primary

Low-energy reaction: K(n,x) 36 Cl E med = 13 MeV Target: KNO 3 Concentration: 15% Target size: 20 kg Exposure time: >3 years Repeated exposure: no Measurement: AMS (Purdue) Low-energy reaction: K(n,x) 36 Cl E med = 13 MeV Target: KNO 3 Concentration: 15% Target size: 20 kg Exposure time: >3 years Repeated exposure: no Measurement: AMS (Purdue) Selected targets - secondary Mid-energy reaction: Ca(n,x) 36 Cl E med = 55 MeV Target: Ca(NO 3 )2 Concentration: 10% Target size: 40 kg Exposure time: >3 y Repeated exposure: no Measurement: AMS (Purdue)

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) Field locations 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)