@article {broek_improving_2024,
	title = {Improving Ionplus MICADAS performance with recessed graphite},
	journal = {Radiocarbon},
	year = {2024},
	note = {Place: EDINBURGH BLDG, SHAFTESBURY RD, CB2 8RU CAMBRIDGE, ENGLAND Publisher: CAMBRIDGE UNIV PRESS Type: Article; Early Access},
	month = {04/2024},
	abstract = {Cathodes with recessed sample surfaces have several benefits in cesium sputter ion sources, including higher output, more efficient use of sample material, and improved focusing of the extracted ion beam. However, the Ionplus MICADAS uses cathodes with a graphite surface that is essentially flush with the sample holder. To evaluate the performance of recessed graphite with the MICADAS and determine the optimal surface depth, we tested four different depths, including the standard (flush) pressing method, 0.5 mm, 1.0 mm, and 1.5 mm. We found that recessed depths of 1.0 and 1.5 mm resulted in 20\% higher ion beam current compared to the standard method under the same source conditions. The results are consistent with the beam produced from the recessed targets being more narrowly focused with a lower emittance, resulting in better transmission through the accelerator. Small graphite samples (200 mu g C) with recessed surfaces produced higher currents for longer, leading to a 2-3x increase in sample ionization efficiency. Additionally, there was some evidence that isotopic ratio measurements of recessed samples were more stable over time. Overall, samples recessed to 1 mm depth offered numerous advantages over the standard pressing method and we have subsequently started pressing all MICADAS graphite using this approach.},
	keywords = {AMS, MICADAS, radiocarbon},
	issn = {0033-8222},
	doi = {10.1017/RDC.2024.36},
	url = {https://www.cambridge.org/core/journals/radiocarbon/article/abs/improving-ionplus-micadas-performance-with-recessed-graphite/F8B44939DDC06FBFD1ED93D5DB7C8456},
	author = {Broek, Taylor A. B. and Roberts, Mark L.}
}
@article {2944,
	title = {A FRAMEWORK FOR TRANSDISCIPLINARY RADIOCARBON RESEARCH: USE OF NATURAL-LEVEL AND ELEVATED-LEVEL -14- C IN ANTARCTIC FIELD RESEARCHABSTRACT},
	journal = {Radiocarbon},
	volume = {63},
	year = {2021},
	month = {Jan-10-2021},
	pages = {1555 - 1568},
	abstract = {Radiocarbon (C-14) is an isotopic tracer used to address a wide range of scientific research questions. However, contamination by elevated levels of C-14 is deleterious to natural-level laboratory workspaces and accelerator mass spectrometer facilities designed to precisely measure small amounts of C-14. The risk of contaminating materials and facilities intended for natural-level C-14 with elevated-level C-14-labeled materials has dictated near complete separation of research groups practicing profoundly different measurements. Such separation can hinder transdisciplinary research initiatives, especially in remote and isolated field locations where both natural-level and elevated-level radiocarbon applications may be useful. This paper outlines the successful collaboration between researchers making natural-level C-14 measurements and researchers using C-14-labeled materials during a subglacial drilling project in West Antarctica (SALSA 2018-2019). Our strict operating protocol allowed us to successfully carry out C-14 labeling experiments within close quarters at our remote field camp without contaminating samples of sediment and water intended for natural level C-14 measurements. Here we present our collaborative protocol for maintaining natural level C-14 cleanliness as a framework for future transdisciplinary radiocarbon collaborations.},
	keywords = {AMS, contamination, LEUCINE, radiocarbon},
	issn = {0033-8222},
	doi = {10.1017/RDC.2021.55},
	url = {https://www.cambridge.org/core/product/identifier/S0033822221000552/type/journal_articlehttps://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0033822221000552},
	author = {Venturelli, Ryan A and Vick-Majors, Trista J and Collins, Billy and Gagnon, Alan and Kasic, Kathy and Kurz, Mark D and Li, Wei and Priscu, John and Roberts, Mark and Rosenheim, Brad E}
}
@article {2994,
	title = {14C Blank Corrections for 25{\textendash}100 μg Samples at the National Ocean Sciences AMS Laboratory},
	journal = {Radiocarbon},
	volume = {61},
	year = {2019},
	month = {10/2019},
	pages = {1403 - 1411},
	abstract = {Replicate radiocarbon (14C) measurements of organic and inorganic control samples, with known Fraction Modern values in the range Fm = 0{\textendash}1.5 and mass range 6 μg{\textendash}2 mg carbon, are used to determine both the mass and radiocarbon content of the blank carbon introduced during sample processing and measurement in our laboratory. These data are used to model, separately for organic and inorganic samples, the blank contribution and subsequently {\textquotedblleft}blank correct{\textquotedblright} measured unknowns in the mass range 25{\textendash}100 μg. Data, formulas, and an assessment of the precision and accuracy of the blank correction are presented.},
	keywords = {AMS, AMS dating, blank corrections},
	isbn = {0033-8222, 1945-5755},
	doi = {10.1017/RDC.2019.74},
	url = {https://www.cambridge.org/core/journals/radiocarbon/article/14c-blank-corrections-for-25100-g-samples-at-the-national-ocean-sciences-ams-laboratory/494B9CF72445198570213B4A2CC303D0},
	author = {Roberts, M. L. and Elder, K. L. and Jenkins, W. J. and Gagnon, A. R. and Xu, L. and Hlavenka, J. D. and Longworth, B. E.}
}
@article {2450,
	title = {The Growth Stop Phenomenon Of Baobabs (Adansonia Spp.) Identified By Radiocarbon DatingAbstract},
	journal = {Radiocarbon},
	volume = {59504754164661},
	year = {2017},
	month = {Jan-04-2017},
	pages = {435 - 448},
	abstract = {The article reports the growth stop phenomenon, which was documented only for baobabs, i.e. for trees belonging to the Adansonia genus. The identification of growth stop was enabled by radiocarbon dating, which allows a complex investigation of samples collected from the trunk/stems of baobabs. In several cases, the outermost rings of baobabs, which were close to the bark, were found to be old, with ages of several hundreds of years, instead of being very young. Dating results of samples collected from six baobabs are presented. For multistemmed baobabs, the growth stop may occur only for one or several stems. We identified four factors that may induce the growth stop: (i) stress determined by severe climate conditions, (ii) old age, (iii) the need to keep a stable internal architecture, and (iv) the collapse of stems that survive this trauma. Baobabs and their stems affected by growth stop may survive for several centuries, by continuing to produce leaves, flowers, and fruits. This phenomenon was associated with the capacity of baobabs to store large amounts of water in their trunks/stems in the rainy season. This reservoir of water is used during the dry season and allows the trees to survive prolonged drought periods.},
	keywords = {Age determination, AMS, growth stop, Radiocarbon dating, tropical trees},
	issn = {0033-8222},
	doi = {10.1017/RDC.2016.92},
	url = {https://www.cambridge.org/core/product/identifier/S0033822216000928/type/journal_articlehttps://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0033822216000928},
	author = {Patrut, Adrian and Woodborne, Stephan and von Reden, Karl F and Hall, Grant and Patrut, Roxana T and Rakosy, Laszlo and Danthu, Pascal and Pock-Tsy, Jean-Michel Leong and Lowy, Daniel A and Margineanu, Dragos}
}
@article { ISI:000364572000008,
	title = {An effective method of UV-oxidation of dissolved organic carbon in natural waters for radiocarbon analysis by accelerator mass spectrometry},
	journal = {JOURNAL OF OCEAN UNIVERSITY OF CHINA},
	volume = {14},
	number = {{6}},
	year = {2015},
	month = {DEC},
	pages = {989-993},
	type = {Article},
	abstract = {Radiocarbon (C-14) measurement of dissolved organic carbon (DOC) is a very powerful tool to study the sources, transformation and cycling of carbon in the ocean. The technique, however, remains great challenges for complete and successful oxidation of sufficient DOC with low blanks for high precision carbon isotopic ratio analysis, largely due to the overwhelming proportion of salts and low DOC concentrations in the ocean. In this paper, we report an effective UV-Oxidation method for oxidizing DOC in natural waters for radiocarbon analysis by accelerator mass spectrometry (AMS). The UV-oxidation system and method show 95\%+/- 4\% oxidation efficiency and high reproducibility for DOC in both river and seawater samples. The blanks associated with the method was also low (about 3 A mu g C) that is critical for C-14 analysis. As a great advantage of the method, multiple water samples can be oxidized at the same time so it reduces the sample processing time substantially compared with other UV-oxidation method currently being used in other laboratories. We have used the system and method for C-14 studies of DOC in rivers, estuaries, and oceanic environments and have received promise results.},
	keywords = {AMS, dissolved organic carbon, natural waters, radiocarbon, UV-oxidation},
	issn = {1672-5182},
	doi = {10.1007/s11802-015-2935-z},
	author = {Xue Yuejun and Ge Tiantian and Wang Xuchen}
}
@article {1835,
	title = {The Passage of the Bomb Radiocarbon Pulse into the Pacific Ocean},
	journal = {Radiocarbon},
	volume = {52},
	year = {2010},
	note = {Sp. Iss. 2696jo
Times Cited:7
Cited References Count:38
},
	month = {2010},
	pages = {1182-1190},
	abstract = {We report and compare radiocarbon observations made on 2 meridional oceanographic sections along 150 degrees W in the South Pacific in 1991 and 2005. The distributions reflect the progressive penetration of nuclear weapons-produced (14)C into the oceanic thermocline. The changes over the 14 yr between occupations are demonstrably large relative to any possible drift in our analytical standardization. The computed difference field based on the gridded data in the upper 1600 m of the section exhibits a significant decrease over time (approaching 40 to 50 parts per thousand in Delta(14)C) in the upper 200-300 m, consistent with the decadal post-bomb decline in atmospheric (14)C levels. A strong positive anomaly (increase with time), centered on the low salinity core of the Antarctic Intermediate Water (AAIW), approaches 50-60 parts per thousand in Delta(14)C, a clear signature of the downstream evolution of the (14)C transient in this water mass. We use this observation to estimate the transit time of AAIW from its "source region" in the southeast South Pacific and to compute the effective reservoir age of this water mass. The 2 sections show small but significant changes in the abyssal (14)C distributions. Between 1991 and 2005, Delta(14)C has increased by 9 parts per thousand below 2000 m north of 55 degrees S. This change is accompanied overall by a modest increase in salinity and dissolved oxygen, as well as a slight decrease in dissolved silica. Such changes are indicative of greater ventilation. Calculation of "phosphate star" also indicates that this may be due to a shift from the Southern Ocean toward North Atlantic Deep Water as the ventilation source of the abyssal South Pacific.},
	keywords = {AMS, antarctic intermediate water, anthropogenic co2, atlantic, c-14 data, carbon, distributions, graphite, south-pacific, tritium},
	isbn = {0033-8222},
	author = {Jenkins, W. J. and Elder, K. L. and McNichol, A. P. and von Reden, K.}
}
@article {1977,
	title = {Radiocarbon dating of alkenones from marine sediments: I. Isolation protocol},
	journal = {Radiocarbon},
	volume = {47},
	year = {2005},
	note = {993nkTimes Cited:13
Cited References Count:22
},
	month = {2005},
	pages = {401-412},
	abstract = {The chemical and isotopic compositions of long-chain (C-36-C-39) unsaturated ketones (alkenones), a unique class of algal lipids, encode surface ocean properties useful for paleoceanographic reconstruction. Recently, we have sought to extend the utility of alkenones as oceanic tracers through measurement of their radiocarbon contents. Here. we describe a method for isolation of alkenones from sediments as a compound class based on a sequence of wet chemical techniques. The steps involved, which include silica gel column chromatography, urea adduction, and silver nitrate-silica gel column chromatography, exploit various structural attributes of the alkenones. Amounts of purified alkenones estimated by GC/FID measurements were highly correlated with CO2 yields after sample combustion, indicating purities of greater than 90\% for samples containing >= 100 mu g C. The degree of alkenone unsaturation (U-37(K{\textquoteright})) also varied minimally through the procedure. We also describe a high-performance liquid chromatography (HPLC) method to isolate individual alkenones for molecular-level structural and isotopic determination.},
	keywords = {AMS, carbon, indicators, proxy, records, tool},
	isbn = {0033-8222},
	author = {Ohkouchi, N. and Xu, L. and Reddy, C. M. and Montlucon, D. and Eglinton, T. I.}
}
@article {2436,
	title = {Installation of a 134-sample MC-SNICS ion source at NOSAMS and first results},
	journal = {Nuclear Instruments \& Methods in Physics Research Section B-Beam Interactions with Materials and Atoms},
	volume = {172},
	year = {2000},
	note = {8th International Conference on Accelerator Mass SpectrometrySEP 06-10, 1999
VIENNA, AUSTRIA
},
	month = {Oct},
	pages = {247-251},
	abstract = {In April 1999, the National Ocean Sciences AMS (NOSAMS) facility received the shipment of a 134-sample MC-SNICS ion source from the National Electrostatics Corporation (NEC). It replaced one of the two 59-sample spherical ionizer sources (US-AMS Model 3090A, HVEE Model 846). In this paper, we will describe the adaptation of the NEC ion source to the US-AMS/HVEE recombinator injector at NOSAMS. This is the first lime that the two leading sputter ion source designs are directly comparable on the same system. We will present ion beam optics calculations for both in comparison with measured results. Once fully operational, the new ion source will assume all of the sputter sample measurements at NOSAMS, while the remaining 59-sample source will be replaced by the newly developed microwave gas ion source. One of the most desirable features of the MC-SNICS design is the smaller cathode geometry. At comparable extracted currents, the surface diameter of the pressed samples is reduced from 1.5 to 1 mm. A new, automatic sample pressing procedure is being developed for this design. This will improve the capability for preparing and analyzing smaller sputter samples (carbon weight <100 <mu>g). Our US-AMS cathodes showed considerable reduction in the extracted currents when the sample diameter was reduced to 1 mm, even with samples of normal size (>200 mug C). (C) 2000 Elsevier Science B.V. All rights reserved.},
	keywords = {AMS, beam extraction/injection, C-14, ion sources, ocean, pacific},
	isbn = {0168-583X},
	author = {von Reden, K. F. and Bellino, M. and Long, P. and Schneider, R. J. and Loger, R.}
}
@article {2185,
	title = {The radiocarbon content of individual lignin-derived phenols: Technique and initial results},
	journal = {Radiocarbon},
	volume = {42},
	year = {2000},
	note = {365vkTimes Cited:19
Cited References Count:17
},
	month = {2000},
	pages = {219-227},
	abstract = {We present a method for the isolation of phenolic compounds derived from lignin for radiocarbon analysis. These phenols are generated by chemical oxidation of polymeric materials and derivatized for separation and recovery by preparative capillary gas chromatography (PCGC). This technique yields tens of micrograms of pure, stable compounds that can he converted to graphite and analyzed by accelerator mass spectrometry (AMS). Analysis of model flavor compounds and dated woods indicates that, in most cases, the radiocarbon (C-14) contents of the individual compounds, corrected for the contribution of the derivative, agree with that of the bulk material to within 20 parts per thousand.},
	keywords = {AMS, isotope-ratio, NOSAMS, oxidation-products},
	isbn = {0033-8222},
	author = {McNichol, A. P. and Ertel, J. R. and Eglinton, T. I.}
}
