Future of the NOSAMS Tandetron AMS system

Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 268 (2010): 854-857, doi:10.1016/j.nimb.2009.10.048.The NOSAMS 3 MV Tandetron AMS system will soon reach its 20th anniversary of operation. A critical review of all aspects of the system is necessary to assess the analytical, economic, and operational factors that enter into the consideration of either an upgrade or a replacement of the instrument. Recent in‐house experience with the design and construction of a large‐acceptance 14C AMS system gives us a benchmark with which to compare the expected outcome of an upgrade. The present ion analysis efficiency of our Tandetron system is roughly 1%, well below the 4% value of our new system. This affects the lower limit of analyzable sample size, speed of analysis, exposure to systematic errors, and the upper limit of achievable single‐sample counting statistics. At first glance it may seem obvious that a replacement (even at higher cost) would be preferable to an upgrade. However, it will be shown that there are good reasons to consider the latter. One of the most compelling is the fact that the Tandetron is a state‐of‐the‐art and superior high‐current accelerator design with minimal signs of aging and very low maintenance. Ion beam modeling calculations show that the main transmission limitation of the instrument is caused by the design of our injector, a four‐magnet “Recombinator”, making it difficult to perform reliable AMS with negative currents exceeding 80 μA. To be acceptable, an upgrade should bring the Tandetron to at least 3% ion efficiency by replacing the injector with a properly matched high‐transmission device.This work has been supported by the United States National Science Foundation under Cooperative Agreements OCE-0228996 and OCE-0753487

Design and reality : continuous-flow accelerator mass spectrometry (CFAMS)

Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 269 (2011): 3176–3179, doi:10.1016/j.nimb.2011.04.019.In 2007 we published 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. 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

The passage of the bomb radiocarbon pulse into the Pacific Ocean

Author Posting. © Arizona Board of Regents on behalf of the University of Arizona, 2010. This article is posted here by permission of Dept. of Geosciences, University of Arizona for personal use, not for redistribution. The definitive version was published in Radiocarbon 52 (2010): 1182-1190.We report and compare radiocarbon observations made on 2 meridional oceanographic sections along 150°W in the South Pacific in 1991 and 2005. The distributions reflect the progressive penetration of nuclear weapons-produced 14C 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‰ in Δ14C) in the upper 200–300 m, consistent with the decadal post-bomb decline in atmospheric 14C levels. A strong positive anomaly (increase with time), centered on the low salinity core of the Antarctic Intermediate Water (AAIW), approaches 50–60‰ in Δ14C, a clear signature of the downstream evolution of the 14C 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 14C distributions. Between 1991 and 2005, Δ14C has increased by 9‰ below 2000 m north of 55°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.This work was performed under National Science Foundation Grant number OCE-0223434 as well as a cooperative agreement with NSF (most recently OCE-0228996)

Carbon nanotube foils for electron stripping in tandem accelerators

Author Posting. © Elsevier B.V., 2007. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 261 (2007): 44-48, doi:10.1016/j.nimb.2007.03.023.Carbon nanotube technology has rapidly advanced in recent years, making it possible to create meter-long, ~4 cm wide films of multi-walled tubes of less than 3 μg/cm2 areal density in a bench top open-air procedure [1]. The physical properties of individual carbon nanotubes have been well established, equaling or surpassing electrical and thermal conductivity and mechanical strength of most other materials, graphite in particular. The handling and transport of such nanotube films, dry-mounted self-supporting on metal frames with several cm2 of open area, is problem-free: the aerogel films having a volumetric density of about 1.5 mg/cm3 survived the trip by car and air from Dallas to Oak Ridge without blemish. In this paper we will present the results of first tests of these nanotube films as electron stripper media in a tandem accelerator. The tests were performed in the Model 25 URC tandem [2] of the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Laboratory. We will discuss the performance of nanotube films in comparison with chemical vapor deposition and laser-ablated carbon foils.This work was supported by a grant from the “Cecil H. and Ida M. Green Technology Innovation Awards” program of the Woods Hole Oceanographic Institution and in part by the U.S. National Science Foundation through Cooperative Agreement 82899613 and the Robert A. Welch Foundation grant AT-0029

Radiocarbon investigation of the Superlative African Baobabs from Savé Valley Conservancy, Zimbabwe

Author Posting. © Studia Chemia, 2019. Studia Universitatis Babes-Bolyai Seria Chemia is an Open Access Journal (read, download, copy, distribute, print for research use, search, or link to the full texts of articles). The definitive version was published in Studia Universitatis Babes-Bolyai, Seria Chemia , 64(2), Tom II, (2019): 411-419, doi:10.24193/subbchem.2019.2.35.The article reports the radiocarbon investigation results of the superlative African baobabs from Savé Valley, Zimbabwe. Several wood samples collected from these baobab were analysed by AMS (accelerator mass spectrometry) radiocarbon dating. The radiocarbon dates of the oldest samples were 1529 ± 14 BP for Matendere Big baobab, 1179 ± 19 BP for Chishakwe Big tree and 1096 ± 35 BP for Mokore Giant baobab. The corresponding calibrated ages are 1430 ± 15, 1090 ± 40 and 1020 ± 25 calendar yr. The oldest tree from Savé Valley, which we described previously, is the Humani Bedford Old baobab. The radiocarbon date of its oldest sample, 1655 ± 14 BP, corresponds to a calibrated age of 1580 ± 30 calendar yr.Authors would like to acknowledge Léon and Judy Duplessis, the owners of the Matendere Rach, Lisa-Jane Campbell of Chishakwe Ranch, Roger Whittall, the owner of the Humani Ranch and his wife Anne Whittall, Greg and Melanie Duckworth of Mokore Ranch for granting access in the ranches and for authorising the investigation and sampling of the monumental baobabs. The research was funded by the Romanian Ministry of National Education CNCS-UEFISCDI under grant PN-III-P4-ID-PCE-2016-0776, Nr. 90/2017

Radiocarbon investigation of the big baobab of Outapi, Namibia

Author Posting. © Studia Chemia, 2021. This article is posted here by permission of Studia Chemia for personal use, not for redistribution. The definitive version was published in Studia Universitatis Babes: Bolyai Chemia, 66(1), 153-163, http://dx.doi.org/10.24193/subbchem.2021.01.12.The article reports the AMS (accelerator mass spectrometry) radiocarbon dating results of the Big baobab of Outapi, which is the largest African baobab of Outapi, Namibia. The investigation of this monumental baobab revealed that it consists of 8 fused stems, out of which 4 are false stems. The Big baobab exhibits a closed ring-shaped structure. Three stems build the ring, which is now incomplete due to previous damage to the false cavity. Three wood samples were collected from the false cavity and from the longest false stem. Seven segments were extracted from the samples and dated by radiocarbon. The oldest investigated sample segment had a radiocarbon date of 820 ± 17 BP, corresponding to a calibrated age of 780 ± 10 calendar years. According to dating results, the Big baobab of Outapi is 850 ± 50 years old.The investigation and sampling of the baobab was authorized by the Ministry of Environment and Tourism of Namibia under the Research/Collecting Permit No. 1934_2014. The research was funded by the Romanian Ministry of Education and Research CNCS-UEFISCDI under grant PN-III-P4-ID-PCE-2020-2567, No. 145/2021

Radiocarbon dating of the historic Livingstone Tree at Chiramba, Mozambique

Author Posting. © Studia Chemia, 2020. Studia Universitatis Babes-Bolyai Seria Chemia is an Open Access Journal (read, download, copy, distribute, print for research use, search, or link to the full texts of articles). The definitive version was published in Studia Universitatis Babes-Bolyai, Seria Chemia 65, no. 3 (2020): 149-156, doi:10.24193/subbchem.2020.3.11.The article reports the AMS (accelerator mass spectrometry) radiocarbon dating results of the Livingstone Tree, a large African baobab on the right bank of the Zambezi, near Chiramba, Mozambique. In 1858, David Livingstone, who discovered the baobab, carved his monogram on the walls of its inner cavity. In 1996, the historic baobab was uprooted when a cyclone struck the area. Several wood fragments were extracted from the remains of the toppled tree. Five samples which originate from these fragments were subsequently dated by radiocarbon. The oldest sample had a radiocarbon date of 1598 ± 17 BP, that corresponded in 1996 to a calibrated age of 1490 ± 35 calendar years. According to this value, the Livingstone Tree at Chiramba becomes one of the oldest known African baobabs, with an age of over 1500 years. The Livingstone Tree had a closed ring-shaped structure, that consisted of 4 fused stems around a false cavity and also 2 additional stems outside the ring.The research was funded by the Romanian Ministry of National Education CNCS-UEFISCDI under grants PN-II-ID-PCE-2013-76 and PN-III-P4-ID-PCE-2016-0776, Nr. 90/2017

Radiocarbon investigation of a superlative grandidier baobab, the big reniala of Isosa

The article discloses the accelerator mass spectrometry (AMS) radiocarbon dating results of the Big Reniala of Isosa, which is a massive Grandidier baobab (Adansonia grandidieri Baill.) of Madagascar. The investigation of this baobab shows that it consists of 5 perfectly fused stems and exhibits a cluster structure. The calculated wood volume of the tree is 540 m 3 , which makes the Big Reniala of Isosa the largest individual of all Adansonia species and also the biggest known angiosperm in terms of volume. Several samples were collected from the outer part of the stems. The oldest dated sample had a radiocarbon date of 934 ± 24 BP, which corresponds to a calibrated age of 845 ± 25 years. This value indicates an age of 1000 ± 100 years for the big Reniala of Isosa

Final radiocarbon investigation of Platland tree, the biggest African baobab

Author Posting. © Studia Chemia, 2017. This article is posted here by permission of Studia Chemia for personal use, not for redistribution. The definitive version was published in Studia Universitatis Babes-Bolyai, Seria Chemia 62, no. 2, Tom 2 (2017): 347-354, doi:10.24193/subbchem.2017.2.27.The article discloses the main results of our new investigation of Platland tree, a.k.a. Sunland baobab, the largest known African baobab. Our recent research was motivated by the three successive splits of 2016 and 2017, which determined the collapse and demise of the stems that have built the main unit of the tree. According to our new findings concerning the architecture of large and old baobabs, we established that Platland tree has a double closed-ring shaped structure and consists of two units/rings that close two separate false cavities. The larger unit was composed of five fused stems, out of which four toppled and died, while the fifth stem is already broken. The smaller unit, which is still standing, consists of three fused stems. We also determined that the larger unit had an age of 800 yr, while the smaller unit is 1100 yr old.The research was funded by the Romanian Ministry of Scientific Research CNCS-UEFISCDI under grant PN-II-ID-PCE-2013-76

African baobabs with double closed ring-shaped structures and two separate false cavities : radiocarbon investigation of the baobab of Golconda Fort

Author Posting. © Studia Chemia, 2016. This article is posted here by permission of Studia Chemia for personal use, not for redistribution. The definitive version was published in Studia Chemia 2016, no. 4 (2016): 21-30.The article discloses the results of radiocarbon investigation of the baobab of Golconda Fort, Hyderābād, India, which is the largest African baobab outside Africa. Two wood samples were collected from the large inner cavity; of these we extracted several segments for AMS (accelerator mass spectrometry) radiocarbon dating. The oldest sample segment had a radiocarbon date of 342 ± 22 BP, which corresponds to a calibrated age of 430 ± 20 yr. We estimate that the oldest part of the baobab has an age of 475 ± 50 yr. The investigation of the baobab of Golconda Fort revealed that it consists of 6 + 2 fused stems. Six stems build two rings that close two distinct false cavities, while two additional stems are located outside the rings. We called this new type of architecture double closed ring-shaped structure with two separate false cavities.The research was funded by the Romanian Ministry of National Education CNCS-UEFISCDI under grant PN-II-ID-PCE-2013-76