@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 {3004,
	title = {Implications of Single-Step Graphitization For Reconstructing Late Holocene Relative Sea-Level Using Radiocarbon-Dated Organic Coastal Sediment},
	journal = {Radiocarbon},
	year = {2022},
	month = {08/2022},
	pages = {1 - 20},
	abstract = {Late Holocene relative sea-level reconstructions are commonly generated using proxies preserved in salt-marsh and mangrove sediment. These depositional environments provide abundant material for radiocarbon dating in the form of identifiable macrofossils (salt marshes) and bulk organic sediment (mangroves). We explore if single-step graphitization of these samples in preparation for radiocarbon dating can increase the number and temporal resolution of relative sea-level reconstructions without a corresponding increase in cost. Dating of salt-marsh macrofossils from the northeastern United States and bulk mangrove sediment from the Federated States of Micronesia indicates that single-step graphitization generates radiocarbon ages that are indistinguishable from replicates prepared using traditional graphitization, but with a modest increase in error (mean/maximum of 6.25/15 additional 14C yr for salt-marsh macrofossils). Low 12C currents measured on bulk mangrove sediment following single-step graphitization likely render them unreliable despite their apparent accuracy. Simulated chronologies for six salt-marsh cores indicate that having twice as many radiocarbon dates (since single-step graphitization costs \~{}50\% of traditional graphitization) results in narrower confidence intervals for sample age estimated by age-depth models when the additional error from the single-step method is less than \~{}50 14C yr (\~{}30 14C yr if the chronology also utilizes historical age markers). Since these thresholds are greater than our empirical estimates of the additional error, we conclude that adopting single-step graphitization for radiocarbon measurements on plant macrofossils is likely to increase precision of age-depth models by more than 20/10\% (without/with historical age markers). This improvement can be implemented without additional cost.},
	keywords = {age-depth model, mangrove, Massachusetts, Micronesia, Salt marsh},
	isbn = {0033-8222, 1945-5755},
	doi = {10.1017/RDC.2022.55},
	url = {https://www.cambridge.org/core/journals/radiocarbon/article/implications-of-singlestep-graphitization-for-reconstructing-late-holocene-relative-sealevel-using-radiocarbondated-organic-coastal-sediment/41F75E6A0679F0E659C96F438452D64C},
	author = {Sefton, Juliet P. and Kemp, Andrew C. and Elder, Kathryn L. and Hansman, Roberta L. and Roberts, Mark L.}
}
@article {longworth_radiocarbon_2022,
	title = {Radiocarbon measurement of CO2 from carbonate minerals using a hybrid gas ion source with an open split interface},
	journal = {Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms},
	volume = {531},
	year = {2022},
	month = {11/2022},
	pages = {49{\textendash}55},
	abstract = {We have developed a method for measuring radiocarbon in carbonate minerals as CO2 gas via a NEC MCSNICS hybrid sputter gas ion source (HGIS). The method uses helium as a carrier gas to displace CO2 from sample vials to an open split, where a glass capillary samples the mixture for delivery directly to the HGIS. This method skips the gas transfer and quantification steps used in a closed inlet HGIS system, simplifying sample measurement. Samples larger than 8 mg carbonate can be measured. Results from measurements of consensus standards (TIRI I, IAEA C2, and an internal modern shell standard), and samples from a marine core (F14C = 0.4{\textendash}1.15) show that the method agrees well with traditional AMS measurement of the same samples as graphite, and that the 1σ uncertainty is about 1\%. We discuss advantages and disadvantages of continuous flow sample introduction, and the effect of reduced precision on calibrated age-depth models produced using gas-source data.},
	keywords = {Carbonate, Hybrid gas ion source, radiocarbon},
	issn = {0168-583X},
	doi = {10.1016/j.nimb.2022.08.013},
	url = {https://www.sciencedirect.com/science/article/pii/S0168583X2200218X},
	author = {Longworth, Brett E. and Burton, Joshua R. and Pendleton, Simon L. and Moser, Sydney D. and Roberts, Mark L. and Kurz, Mark D.}
}
@article {2632,
	title = {Improved C- efficiency and ion beam currents by modifying SNICS cathode material},
	journal = {Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms},
	volume = {439},
	year = {2019},
	month = {Jan-01-2019},
	pages = {90 - 93},
	abstract = {We investigated the possibility of increasing the C-14 AMS efficiency and maximizing C- beam currents by modifying sample cathode geometry and material. Previously, we reported results which showed an increase in C- beam current and improved ionization efficiency when reducing the cathode sample well diameter from 1 mm to 0.75 mm and using zinc inserts, pressed into the aluminum cathode holder [4]. In this study we expand that effort by using cathodes with inserts made of Fe, Mo, Ni, Ti, Cu, and Zn. We pressed cathodes with 100 mu g of Oxalic Acid I (OX-I) and ran them to exhaustion. C-12 beam currents, C-14 counts, and graphite weight were used to determine ion source efficiency.},
	keywords = {Cathode, Efficiency, Ion source, SNICS},
	issn = {0168583X},
	doi = {10.1016/j.nimb.2018.11.015},
	url = {http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2\&SrcAuth=Alerting\&SrcApp=Alerting\&DestApp=WOS_CPL\&DestLinkType=FullRecord\&UT=WOS:000455693100015},
	author = {Hlavenka, Joshua D. and Abrams, Henry and Roberts, Mark L. and Longworth, Brett E. and Fallon, Stewart}
}
@article {550,
	title = {A high output, large acceptance injector for the NOSAMS Tandetron AMS system},
	journal = {Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms},
	volume = {361},
	year = {2015},
	note = {Cu2hzTimes Cited:0Cited References Count:13},
	month = {Oct 15},
	pages = {211-216},
	abstract = {We have completed a major upgrade of the National Ocean Sciences AMS Facility (NOSAMS) Tandetron AMS system in two stages. First, the simultaneous (recombinator) injector was replaced with a fast-cycling sequential injector and changes to the low-energy acceleration section. Data after the injector commissioning show an improvement in background, with mean machine background (commercial graphite) of Fm 0.0004 (62 ka). Second, we replaced the original ion source with a high-output 40 sample MCSNICS source. This improved beam currents and raw ratio fractionation, and increased sample to detection efficiency fivefold.},
	issn = {0168-583X},
	doi = {10.1016/j.nimb.2015.04.005},
	author = {Longworth, Brett E. and von Reden, Karl F. and Long, Pat and Roberts, Mark L.}
}
@article { ISI:000354878700008,
	title = {Rapid, high-resolution C-14 chronology of ooids},
	journal = {GEOCHIMICA ET COSMOCHIMICA ACTA},
	volume = {159},
	year = {2015},
	month = {JUN 15},
	pages = {126-138},
	type = {Article},
	abstract = {Ooids are small, spherical to ellipsoidal grains composed of concentric layers of CaCO3 that could potentially serve as biogeochemical records of the environments in which they grew. Such records, however, must be placed in the proper temporal context. Therefore, we developed a novel acidification system and employed an accelerator mass spectrometer (AMS) with a gas accepting ion source to obtain radiocarbon (C-14) chronologies extending radially through ooids within one 8-h workday. The method was applied to ooids from Highborne Cay, Bahamas and Shark Bay, Australia, yielding reproducible C-14 chronologies, as well as constraints on the rates and durations of ooid growth and independent estimates of local C-14 reservoir ages. (C) 2015 Elsevier Ltd. All rights reserved.},
	issn = {0016-7037},
	doi = {10.1016/j.gca.2015.03.009},
	author = {Beaupr{\'e}, Steven R. and Roberts, Mark L. and Burton, Joshua R. and Summons, Roger E.}
}
@article {15,
	title = {Ultra-Small Graphitization Reactors for Ultra-Microscale C-14 Analysis at the National Ocean Sciences Accelerator Mass Spectrometry (Nosams) Facility},
	journal = {Radiocarbon},
	volume = {57},
	year = {2015},
	note = {PT: J; TC: 1; UT: WOS:000351052600009},
	pages = {109-122},
	abstract = {In response to the increasing demand for C-14 analysis of samples containing less than 25 mu g C, ultra-small graphitization reactors with an internal volume of similar to 0.8 mL were developed at NOSAMS. For samples containing 6 to 25 mu g C, these reactors convert CO2 to graphitic carbon in approximately 30 min. Although we continue to refine reaction conditions to improve yield, the reactors produce graphite targets that are successfully measured by AMS. Graphite targets produced with the ultra-small reactors are measured by using the Cs sputter source on the CFAMS instrument at NOSAMS where beam current was proportional to sample mass. We investigated the contribution of blank carbon from the ultra-small reactors and estimate it to be 0.3 +/- 0.1 mu g C with an Fm value of 0.43 +/- 0.3. We also describe equations for blank correction and propagation of error associated with this correction. With a few exceptions for samples in the range of 6 to 7 mu g C, we show that corrected Fm values agree with expected Fm values within uncertainty for samples containing 6-100 mu g C.},
	issn = {0033-8222},
	doi = {10.2458/azu_rc.57.18118},
	author = {Walter, Sunita R. Shah and Gagnon, Alan R. and Roberts, Mark L. and McNichol, Ann P. and Gaylord, Mary C. Lardie and Klein, Elizabeth}
}
@article {561,
	title = {Temporal and spatial distributions of cold-water corals in the Drake Passage: Insights from the last 35,000 years},
	journal = {Deep Sea Research Part II: Topical Studies in Oceanography},
	volume = {99},
	year = {2014},
	note = {id: 2278},
	month = {Jan},
	pages = {237-248},
	abstract = {Scleractinian corals have a global distribution ranging from shallow tropical seas to the depths of the Southern Ocean. Although this distribution is indicative of the corals having a tolerance to a wide spectrum of environmental conditions, individual species seem to be restricted to a much narrower range of ecosystem variables. One way to ascertain the tolerances of corals, with particular focus on the potential impacts of changing climate, is to reconstruct their growth history across a range of environmental regimes. This study examines the spatial and temporal distribution of the solitary scleractinian corals Desmophyllum dianthus, Gardineria antarctica, Balanophyllia malouinensis, Caryophyllia spp. and Flabellum spp. from five sites in the Drake Passage which cross the major frontal zones. A rapid reconnaissance radiocarbon method, cooupled with U-Th dating, extends the age range back more than 100 thousand. Within this age range there are distinct changes in the temporal and spatial distributions of these corals, both with depth and latitude, and on millennial timescales. Two major patterns that emerge are: 1) D. dianthus populations show clear variability in their occurrence through time depending on the latitudinal position within the Drake Passage. North of the Subantarctic Front, D. dianthus first appears in the late deglaciation (~17,000 years ago) and persists to today. South of the Polar Front, in contrast, populations existed during the glacial and early deglacial periods, with only few modern occurrences. A seamount site between the two fronts exhibits characteristics similar to both the north and south sites. This shift across the frontal zones within one species cannot yet be fully explained, but it is likely to be linked to changes in surface productivity, subsurface oxygen concentrations, and carbonate saturation state. 2) at locations where multiple genera were dated, clear differences in age and depth distribution of the populations provide clear evidence that each genus has unique environmental requirements to sustain its population.},
	issn = {0967-0645},
	doi = {10.1016/j.dsr2.2013.06.008},
	author = {Margolin, Andrew R. and Robinson, Laura F. and Burke, Andrea and Waller, Rhian G. and Scanlon, Kathryn M. and Roberts, Mark L. and Auro, Maureen E. and van de Flierdt, Tina}
}
@article {93,
	title = {Carbonate as sputter target material for rapid C-14 AMS},
	journal = {Nuclear Instruments \& Methods in Physics Research Section B-Beam Interactions with Materials and Atoms},
	volume = {294},
	year = {2013},
	note = {id: 2244; PT: J; CT: 12th International Conference on Accelerator Mass Spectrometry (AMS); CY: MAR 20-25, 2011; CL: Wellington, NEW ZEALAND; TC: 0; UT: WOS:000313234300064},
	pages = {328-334},
	abstract = {This paper describes a technique for measuring the C-14 content of carbonate samples by producing C- ions directly in the negative ion sputter source of an accelerator mass spectrometer CAMS) system. This direct analysis of carbonate material eliminates the time and expense of graphite preparation. Powdered carbonate is mixed with titanium powder, loaded into a target cartridge, and compressed. Beam currents for optimally-sized carbonate targets (0.09-0.15 mg C) are typically 10-20\% of those produced by optimally-sized graphite targets (0.5-1 mg C). Modern (>0.8 Fm) samples run by this method have standard deviations of 0.009 Fm or less, and near-modern samples run as unknowns agree with values from traditional hydrolysis/graphite to better than 2\%. Targets with as little as 0.06 mg carbonate produce useable ion currents and results, albeit with increased error and larger blank. In its current state, direct sputtering is best applied to problems where a large number of analyses with lower precision are required. These applications could include age surveys of deep-sea corals for determination of historic population dynamics, to identify samples that would benefit from high precision analysis, and for growth rate studies of organisms forming carbonate skeletons. (C) 2012 Elsevier B.V. All rights reserved.},
	issn = {0168-583X},
	doi = {10.1016/j.nimb.2012.05.014},
	author = {Longworth, Brett E. and Robinson, Laura F. and Roberts, Mark L. and Beaupr{\'e}, Steven R. and Burke, Andrea and W. J. Jenkins}
}
@article {84,
	title = {Distribution of Radiocarbon Ages in Soil Organic Matter by Thermal Fractionation},
	journal = {Radiocarbon},
	volume = {55},
	year = {2013},
	note = {id: 2346; PT: J; TC: 0; UT: WOS:000325752100093},
	pages = {1077-1083},
	issn = {0033-8222},
	doi = {10.2458/azu_js_rc.55.16310},
	author = {Plante, Alain F. and Beaupr{\'e}, Steven R. and Roberts, Mark L. and Baisden, Troy}
}
@article {81,
	title = {A High-Throughput, Low-Cost Method for Analysis of Carbonate Samples for C-14},
	journal = {Radiocarbon},
	volume = {55},
	year = {2013},
	note = {id: 2345; PT: J; TC: 0; UT: WOS:000325752100044},
	pages = {585-592},
	issn = {0033-8222},
	doi = {10.2458/azu_js_rc.55.16190},
	author = {Roberts, Mark L. and Beaupr{\'e}, Steven R. and Burton, Joshua R.}
}
@article {171,
	title = {Design and reality: Continuous-flow accelerator mass spectrometry (CFAMS)},
	journal = {Proceedings of the 10th European Conference on Accelerators in Applied Research and Technology (ECAART10)},
	volume = {269},
	year = {2011},
	note = {id: 2157},
	pages = {3176-3179},
	abstract = {In 2007 we published [1] the design of a novel accelerator mass spectrometry (AMS) system capable of analyzing gaseous samples injected continuously into a microwave plasma gas ion source. Obvious advantages of such a system are drastically reduced processing times and avoidance of potentially contaminating chemical preparation steps. Another paper in these proceedings will present the progress with the development of the microwave gas ion source that has since been built and tested at the National Ocean Sciences AMS Facility in Woods Hole [2]. In this paper we will review the original design and present updates, reflecting our recent encouraging experience with the system. A simple summary: large acceptance ion beam optics design is beneficial to accelerator mass spectrometry in general, but essential to AMS with plasma gas ion sources.},
	issn = {0168-583X},
	doi = {10.1016/j.nimb.2011.04.019},
	url = {http://www.sciencedirect.com/science/article/pii/S0168583X11003703},
	author = {von Reden, Karl F. and Roberts, Mark L. and McIntyre, Cameron P. and Burton, Joshua R.}
}
@article {197,
	title = {Rapid radiocarbon ((14)C) analysis of coral and carbonate samples using a continuous-flow accelerator mass spectrometry (CFAMS) system},
	journal = {Paleoceanography},
	volume = {26},
	year = {2011},
	note = {id: 1915; PT: J; UT: WOS:000296649300001},
	pages = {PA4212-PA4212},
	abstract = {Radiocarbon analyses of carbonate materials provide critical information for understanding the last glacial cycle, recent climate history and paleoceanography. Methods that reduce the time and cost of radiocarbon ((14)C) analysis are highly desirable for large sample sets and reconnaissance type studies. We have developed a method for rapid radiocarbon analysis of carbonates using a novel continuous-flow accelerator mass spectrometry (CFAMS) system. We analyzed a suite of deep-sea coral samples and compared the results with those obtained using a conventional AMS system. Measurement uncertainty is},
	issn = {0883-8305},
	doi = {10.1029/2011PA002174},
	author = {McIntyre, Cameron P. and Roberts, Mark L. and Burton, Joshua R. and McNichol, Ann P. and Burke, Andrea and Robinson, Laura F. and von Reden, Karl F. and W. J. Jenkins}
}
@article {459,
	title = {Comparative AMS radiocarbon dating of pretreated versus non-pretreated tropical wood samples},
	journal = {Nuclear Instruments \& Methods in Physics Research Section B-Beam Interactions with Materials and Atoms},
	volume = {268},
	year = {2010},
	note = {id: 2083; PT: J; CT: 11th International Conference on Accelerator Mass Spectrometry; CY: SEP 14-19, 2008; CL: Rome, ITALY; SP: Univ Salento, CEDAD, Second Univ Naples, CIRCE, INNOVA, Ist Nazl Fis Nucl, LABEC, Abdus Salam Int Ctr Theoret Phys; UT: WOS:000277462300058},
	pages = {910-913},
	abstract = {Several wood samples collected from Dorslandboom, a large iconic African baobab (Adansonia digitata L.) from Namibia, were investigated by AMS radiocarbon dating subsequent to pretreatment and, alternatively, without pretreatment. The comparative statistical evaluation of results showed that there were no significant differences between fraction modern values and radiocarbon dates of the samples analyzed after pretreatment and without pretreatment, respectively. The radiocarbon date of the oldest sample was 993 +/- 20 BP. Dating results also revealed that Dorslandboom is a multi-generation tree, with several stems showing different ages. (C) 2009 Elsevier B.V. All rights reserved.},
	issn = {0168-583X},
	doi = {10.1016/j.nimb.2009.10.062},
	author = {Patrut, Adrian and von Reden, Karl F. and Lowy, Daniel A. and Mayne, Diana H. and Elder, Kathryn E. and Roberts, Mark L. and McNichol, Ann P.}
}
