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The Cadmium-Lined Outer-Core Irradiation Tube (CLOCIT) is a new irradiation facility for 40Ar/39Ar geochronology at the Oregon State University TRIGA® reactor. We report fluence (i.e., time-integrated flux) parameters from the first four CLOCIT irradiations and compare them with the existing Cadmium-Lined Inner-Core Irradiation Tube (CLICIT). CLOCIT provides an average neutron flux equivalent of 1.45–1.53 × 10−4 J h−1; about 55% of CLICIT. Radial fluence gradients were on the order of 0.2–4.2% cm−1. A planar fit of J-values results in residuals in the range of uncertainty in the J-value, but systematic deviations resolve a non-planar component of the neutron flux field, which has also been observed in CLICIT. Axial neutron fluence gradients were 0.6–1% cm−1, compared with 0.7–1.6% cm−1 for the CLICIT. Production rate ratios of interfering reactions were (40Ar/39Ar)K = (4 ± 6) × 10−4 and (38Ar/39Ar)K = (1.208 ± 0.002) × 10−2, (36Ar/37Ar)Ca = (2.649 ± 0.014) × 10−4, (38Ar/37Ar)Ca = (3.33 ± 0.12) × 10−5 and (39Ar/37Ar)Ca = (9.1 ± 0.28) × 10−4, similar to the CLICIT values.

The Cadmium-Lined Outer-Core Irradiation Tube (CLOCIT) is a new irradiation facility for 40Ar/39Ar geochronology at the Oregon State University TRIGA® reactor. We report fluence (i.e., time-integrated flux) parameters from the first four CLOCIT irradiations and compare them with the existing Cadmium-Lined Inner-Core Irradiation Tube (CLICIT). CLOCIT provides an average neutron flux equivalent of 1.45–1.53 × 10−4 J h−1; about 55% of CLICIT. Radial fluence gradients were on the order of 0.2–4.2% cm−1. A planar fit of J-values results in residuals in the range of uncertainty in the J-value, but systematic deviations resolve a non-planar component of the neutron flux field, which has also been observed in CLICIT. Axial neutron fluence gradients were 0.6–1% cm−1, compared with 0.7–1.6% cm−1 for the CLICIT. Production rate ratios of interfering reactions were (40Ar/39Ar)K = (4 ± 6) × 10−4 and (38Ar/39Ar)K = (1.208 ± 0.002) × 10−2, (36Ar/37Ar)Ca = (2.649 ± 0.014) × 10−4, (38Ar/37Ar)Ca = (3.33 ± 0.12) × 10−5 and (39Ar/37Ar)Ca = (9.1 ± 0.28) × 10−4, similar to the CLICIT values.

A next-generation, high-flux DD neutron generator has been designed, commissioned, and characterized, and is now operational in a new facility at the University of California Berkeley. The generator, originally designed for 40Ar/39Ar dating of geological materials, has since served numerous additional applications, including medical isotope production studies, with others planned for the near future. In this work, we present an overview of the High Flux Neutron Generator (HFNG) which includes a variety of simulations, analytical models, and experimental validation of results. Extensive analysis was performed in order to characterize the neutron yield, flux, and energy distribution at specific locations where samples may be loaded for irradiation. A notable design feature of the HFNG is the possibility for sample irradiation internal to the cathode, just 8 mm away from the neutron production site, thus maximizing the neutron flux (n/cm2/s). The generator's maximum neutron flux at this irradiation position is 2.58 × 107 n/cm2/s ± 5% (approximately 3 × 108 n/s total yield) as measured via activation of small natural indium foils. However, future development is aimed at achieving an order of magnitude increase in flux. Additionally, the deuterium ion beam optics were optimized by simulations for various extraction configurations in order to achieve a uniform neutron flux distribution and an acceptable heat load. Finally, experiments were performed in order to benchmark the modeling and characterization of the HFNG.

A next-generation, high-flux DD neutron generator has been designed, commissioned, and characterized, and is now operational in a new facility at the University of California Berkeley. The generator, originally designed for 40Ar/39Ar dating of geological materials, has since served numerous additional applications, including medical isotope production studies, with others planned for the near future. In this work, we present an overview of the High Flux Neutron Generator (HFNG) which includes a variety of simulations, analytical models, and experimental validation of results. Extensive analysis was performed in order to characterize the neutron yield, flux, and energy distribution at specific locations where samples may be loaded for irradiation. A notable design feature of the HFNG is the possibility for sample irradiation internal to the cathode, just 8 mm away from the neutron production site, thus maximizing the neutron flux (n/cm2/s). The generator's maximum neutron flux at this irradiation position is 2.58 × 107 n/cm2/s ± 5% (approximately 3 × 108 n/s total yield) as measured via activation of small natural indium foils. However, future development is aimed at achieving an order of magnitude increase in flux. Additionally, the deuterium ion beam optics were optimized by simulations for various extraction configurations in order to achieve a uniform neutron flux distribution and an acceptable heat load. Finally, experiments were performed in order to benchmark the modeling and characterization of the HFNG.

Cross sections for the 47Ti(n,p)47Sc and 64Zn(n,p)64Cu reactions have been measured for quasi-monoenergetic DD neutrons produced by the UC Berkeley High Flux Neutron Generator (HFNG). The HFNG is a compact neutron generator designed as a “flux-trap” that maximizes the probability that a neutron will interact with a sample loaded into a specific, central location. The study was motivated by interest in the production of 47Sc and 64Cu as emerging medical isotopes. The cross sections were measured in ratio to the 113In(n,n′)113mIn and 115In(n,n′)115mIn inelastic scattering reactions on co-irradiated indium samples. Post-irradiation counting using an HPGe and LEPS detectors allowed for cross section determination to within 5% uncertainty. The 64Zn(n,p)64Cu cross section for 2.76-0.02+0.01 MeV neutrons is reported as 49.3 ± 2.6 mb (relative to 113In) or 46.4 ± 1.7 mb (relative to 115In), and the 47Ti(n,p)47Sc cross section is reported as 26.26 ± 0.82 mb. The measured cross sections are found to be in good agreement with existing measured values but with lower uncertainty (<5%), and also in agreement with theoretical values. This work highlights the utility of compact, flux-trap DD-based neutron sources for nuclear data measurements and potentially the production of radionuclides for medical applications.

Cross sections for the 47Ti(n,p)47Sc and 64Zn(n,p)64Cu reactions have been measured for quasi-monoenergetic DD neutrons produced by the UC Berkeley High Flux Neutron Generator (HFNG). The HFNG is a compact neutron generator designed as a “flux-trap” that maximizes the probability that a neutron will interact with a sample loaded into a specific, central location. The study was motivated by interest in the production of 47Sc and 64Cu as emerging medical isotopes. The cross sections were measured in ratio to the 113In(n,n′)113mIn and 115In(n,n′)115mIn inelastic scattering reactions on co-irradiated indium samples. Post-irradiation counting using an HPGe and LEPS detectors allowed for cross section determination to within 5% uncertainty. The 64Zn(n,p)64Cu cross section for 2.76-0.02+0.01 MeV neutrons is reported as 49.3 ± 2.6 mb (relative to 113In) or 46.4 ± 1.7 mb (relative to 115In), and the 47Ti(n,p)47Sc cross section is reported as 26.26 ± 0.82 mb. The measured cross sections are found to be in good agreement with existing measured values but with lower uncertainty (<5%), and also in agreement with theoretical values. This work highlights the utility of compact, flux-trap DD-based neutron sources for nuclear data measurements and potentially the production of radionuclides for medical applications.

©2015. American Geophysical Union. All Rights Reserved. The Pamir Plateau, a result of the India-Asia collision, contains extensive exposures of Cenozoic middle to lower crust in domes exhumed by north-south crustal extension. Titanite grains from 60 igneous and metamorphic rocks were investigated with U-Pb + trace element petrochronology (including Zr thermometry) to constrain the timing and temperatures of crustal thickening and exhumation. Titanite from the Pamir domes records thickening from ∼44 to 25 Ma. Retrograde titanite from the Yazgulem, Sarez, and Muskol-Shatput domes records a transition from thickening to exhumation at ∼20-16 Ma, whereas titanite from the Shakhadara dome records prolonged exhumation from ∼20 to 8 Ma. The synchronous onset of exhumation may have been initiated by breakoff of the Indian slab and possible convective removal of the Asian lower crust and/or mantle lithosphere. The prolonged exhumation of the Shakhdara and Muztaghata-Kongur Shan domes may have been driven by continued rollback of the Asian lithosphere concurrent with shortening and northwestward translation of the Pamir Plateau.

©2015. American Geophysical Union. All Rights Reserved. The Pamir Plateau, a result of the India-Asia collision, contains extensive exposures of Cenozoic middle to lower crust in domes exhumed by north-south crustal extension. Titanite grains from 60 igneous and metamorphic rocks were investigated with U-Pb + trace element petrochronology (including Zr thermometry) to constrain the timing and temperatures of crustal thickening and exhumation. Titanite from the Pamir domes records thickening from ∼44 to 25 Ma. Retrograde titanite from the Yazgulem, Sarez, and Muskol-Shatput domes records a transition from thickening to exhumation at ∼20-16 Ma, whereas titanite from the Shakhadara dome records prolonged exhumation from ∼20 to 8 Ma. The synchronous onset of exhumation may have been initiated by breakoff of the Indian slab and possible convective removal of the Asian lower crust and/or mantle lithosphere. The prolonged exhumation of the Shakhdara and Muztaghata-Kongur Shan domes may have been driven by continued rollback of the Asian lithosphere concurrent with shortening and northwestward translation of the Pamir Plateau.

Cenozoic gneiss domes—exposing middle-lower crustal rocks—cover ~30% of the surface exposure of the Pamir, western India-Asia collision zone; they allow an unparalleled view into the deep crust of the Asian plate. We use titanite, monazite, and zircon U/Th-Pb, mica Rb-Sr and 40Ar/39Ar, zircon and apatite fission track, and zircon (U-Th)/He ages to constrain the exhumation history of the ~350 × 90 km Shakhdara-Alichur dome, southwestern Pamir. Doming started at 21–20 Ma along the Gunt top-to-N normal-shear zone of the northern Shakhdara dome. The bulk of the exhumation occurred by ~NNW-ward extrusion of the footwall of the crustal-scale South Pamir normal-shear zone along the southern Shakhdara dome boundary. Footwall extrusion was active from ~18–15 Ma to ~2 Ma at ~10 mm/yr slip and with vertical exhumation rates of 1–3 mm/yr; it resulted in up to 90 km ~N-S extension, coeval with ~N-S convergence between India and Asia. Erosion rates were 0.3–0.5 mm/yr within the domes and 0.1–0.3 mm/yr in the horst separating the Shakhdara and Alichur domes and in the southeastern Pamir plateau; rates were highest along the dome axis in the southern part of the Shakhdara dome. Incision along the major drainages was up to 1.0 mm/yr. Thermal modeling suggests geothermal gradients as high as 60°C/km along the trace of the South Pamir shear zone and their strong N-S variation across the dome; the gradients relaxed to ≤40–45°C/km since the end of doming.

Cenozoic gneiss domes comprise one third of the surface exposure of the Pamir and provide a window into the deep crustal processes of the India-Asia collision. The largest of these are the doubly vergent, composite Shakhdara-Alichur domes of the southwestern Pamir, Tajikistan, and Afghanistan; they are separated by a low-strain horst. Top-to-SSE, noncoaxial pervasive flow over the up to 4 km thick South Pamir shear zone exhumed crust from 30–40 km depth in the ~250 × 80 km Shakhdara dome; the top-to-NNE Alichur shear zone exposed upper crustal rocks in the ~125 × 25 km Alichur dome. The Gunt shear zone bounds the Shakhdara dome in the north and records alternations of normal shear and dextral transpression; it contributed little to bulk exhumation. Footwall exhumation along two low-angle, normal-sense detachments resulted in up to 90 km syn-orogenic ~N-S extension. Extension in the southwestern Pamir opposes shortening in a fold-thrust belt north of the domes and in particular in the Tajik depression, where an evaporitic décollement facilitated upper crustal shortening. Gravitational collapse of the Pamir-plateau margin drove core-complex formation in the southwestern Pamir and shortening of the weak foreland adjacent to the plateau. Overall, this geometry defines a “vertical extrusion” scenario, comprising frontal and basal underthrusting and thickening, and hanging gravitationally driven normal shear. In contrast to the Himalayan vertical extrusion scenario, erosion in the Pamir was minor, preserving most of the extruded deep crust, including the top of the South Pamir shear zone at peak elevations throughout the dome.