Kunihiko Nishiizumi

Bio: Kunihiko Nishiizumi is an academic researcher from University of California, Berkeley. The author has contributed to research in topics: Cosmogenic nuclide & Meteorite. The author has an hindex of 36, co-authored 137 publications receiving 7041 citations. Previous affiliations of Kunihiko Nishiizumi include Space Sciences Laboratory.

Absolute calibration of 10Be AMS standards

Abstract: The increased detection sensitivity offered by AMS has dramatically expanded the utility of 10 Be. As these applications become more sophisticated attention has focused on the accuracy of the 10 Be standards used to calibrate the AMS measurements. In recent years it has become apparent that there is a discrepancy between two of the most widely used 10 Be AMS standards, the ICN 10 Be standard and the NIST 10 Be standard. The ICN (ICN Chemical & Radioisotope Division) 10 Be AMS standard was calibrated by radioactive decay counting. Dilutions, ranging from 5 × 10 −13 to 3 × 10 −11 10 Be/Be, have been prepared and are extensively used in many AMS laboratories. The NIST 10 Be standard, prepared at the National Institute of Standards and Technology (NIST), is calibrated by mass spectrometric isotope ratio measurements. To provide an independent calibration of the 10 Be standards we implanted a known number of 10 Be atoms in both Si detectors and Be foil targets. The 10 Be concentrations in these targets were measured by AMS. The results were compared with both the ICN and NIST AMS standards. Our 10 Be measurements indicate that the 10 Be/ 9 Be isotopic ratio of the ICN AMS standard, which is based on a 10 Be half-life of 1.5 × 10 6 yr, is 1.106 ± 0.012 times lower than the nominal value. Since the decay rate of the ICN standard is well determined, the decrease in 10 Be/ 9 Be ratio requires that the 10 Be half-life be reduced to (1.36 ± 0.07) × 10 6 yr. The quoted uncertainty includes a ±5% uncertainty in the activity measurement carried out by ICN. In a similar fashion, we determined that the value of the NIST 10 Be standard (SRM4325) is (2.79 ± 0.03) × 10 −11 10 Be/ 9 Be, within error of the certified value of (2.68 ± 0.14) × 10 −11 . The Lawrence Livermore National Laboratory (LLNL) internal standards were also included in this study. We conclude that the 9 Be(n, γ) neutron cross section is 7.8 ± 0.23 mb, without taking into account the uncertainty in the neutron irradiation.

The soil production function and landscape equilibrium

Abstract: ). The linear increase of detected photons as a function of laser intensity (100-2,000 W cm -2 ) indicated that saturation and multiphoton processes were negligible in these studies. Typical detected count rates of 5,000-6,000 photons s -1 at 2,000 W cm -2 pumping intensity (,150,000 excitations s -1 ) were achieved, with most of the molecules emitting several

Preparation of 26Al AMS standards

Abstract: Absolute AMS (accelerator mass spectrometry) measurements require reliable standards for calibration. Highly concentrated 26 Al was obtained from NBS (National Bureau of Standards). The 26 Al, SRM 4229, was sequentially diluted with natural Al and 26 Al AMS standards were prepared. These 26 Al AMS standards are widely used as primary standards at major AMS laboratories. A substantial amount of 26 Al AMS standards with 26 Al/Al ratios of 7.444 × 10 −11 , 3.096 × 10 −11 , 1.065 × 10 −11 , 4.694 × 10 −12 , 1.818 × 10 −12 and 4.99 × 10 −13 are now available for the AMS community. Solutions having 26 Al/Al ratios between 10 −12 and 10 −10 were measured by several AMS laboratories; excellent linearity was obtained within the range of 5 × 10 −13 –1 × 10 −10 26 Al/Al.

Persistent Solar Influence on North Atlantic Climate During the Holocene

Abstract: Surface winds and surface ocean hydrography in the subpolar North Atlantic appear to have been influenced by variations in solar output through the entire Holocene. The evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon-14 and beryllium-10 and centennial to millennial time scale changes in proxies of drift ice measured in deep-sea sediment cores. A solar forcing mechanism therefore may underlie at least the Holocene segment of the North Atlantic's "1500-year" cycle. The surface hydrographic changes may have affected production of North Atlantic Deep Water, potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally.

The IntCal20 Northern Hemisphere Radiocarbon Age Calibration Curve (0-55 cal kBP)

Abstract: Radiocarbon (14C) ages cannot provide absolutely dated chronologies for archaeological or paleoenvironmental studies directly but must be converted to calendar age equivalents using a calibration curve compensating for fluctuations in atmospheric 14C concentration. Although calibration curves are constructed from independently dated archives, they invariably require revision as new data become available and our understanding of the Earth system improves. In this volume the international 14C calibration curves for both the Northern and Southern Hemispheres, as well as for the ocean surface layer, have been updated to include a wealth of new data and extended to 55,000 cal BP. Based on tree rings, IntCal20 now extends as a fully atmospheric record to ca. 13,900 cal BP. For the older part of the timescale, IntCal20 comprises statistically integrated evidence from floating tree-ring chronologies, lacustrine and marine sediments, speleothems, and corals. We utilized improved evaluation of the timescales and location variable 14C offsets from the atmosphere (reservoir age, dead carbon fraction) for each dataset. New statistical methods have refined the structure of the calibration curves while maintaining a robust treatment of uncertainties in the 14C ages, the calendar ages and other corrections. The inclusion of modeled marine reservoir ages derived from a three-dimensional ocean circulation model has allowed us to apply more appropriate reservoir corrections to the marine 14C data rather than the previous use of constant regional offsets from the atmosphere. Here we provide an overview of the new and revised datasets and the associated methods used for the construction of the IntCal20 curve and explore potential regional offsets for tree-ring data. We discuss the main differences with respect to the previous calibration curve, IntCal13, and some of the implications for archaeology and geosciences ranging from the recent past to the time of the extinction of the Neanderthals.