Browsing by Author "Moy, A"

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    Cosmogenic radionuclides as signatures of past Solar storm events
    (Australian National University, 2019-09-09) Smith, AM; Wilcken, KM; Simon, KJ; Dee, MW; Kuitems, M; Scifo, A; Moy, A; Curran, MAJ; Wallner, A; Fink, D; Fujioka, T
    This collaborative project examines the relationship between the ‘Carrington Event’ (CE), the largest solar storm of modern times, and two recently discovered cosmic radiation events of greater magnitude, the ‘Miyake Events’ (ME). The intention is to construct cosmogenic isotope (14C, 10Be and 36Cl) profiles across the CE, so they can be compared with similar data that have already been obtained for the ME. We will use ice cores from Law Dome, East Antarctica, collected under Australian Antarctic Science awards, for the 10Be and 36Cl analyses. The large diameter DSS0506 ice core will permit high-resolution measurements at ANSTO of 10Be and 36Cl across the CE. Furthermore, we also intend to measure 10Be and 36Cl in the main DSS ice core across the ME. These measurements will complement existing data as both isotopes will be measured in the same ice core for each event for the first time and at high temporal resolution. New tree rings spanning the CE and ME, sourced from the Oxford Dendrochronology Laboratory, have been measured for 14C at the University of Groningen at mostly annual resolution. The ultimate goal of this study is to determine whether or not all three events are manifestations of the same phenomena. A secondary goal is to provide a check on the independent DSS-main ice core chronology. The CE of 1859 is known from geomagnetic data and contemporary records of the aurorae, which were observed as far south as the tropics. The event predated ground-based neutron detectors and routine cosmogenic isotope measurement, so the intensity of the incident particle radiation is still a matter of conjecture. Indeed, this question has been thrown into sharp focus recently by new discoveries in palaeoastronomy. Analyses of natural archives (tree-rings and ice-cores) have revealed that production of the cosmogenic isotopes 14C, 10Be and 36Cl spiked dramatically in the years 774-775 AD and 993-994 AD. Such anomalies could only have been generated by sudden bursts of cosmic radiation. Several sources were initially proposed for the radiation, however, the consensus now is that they were driven by solar activity. Here we discuss progress with the measurement of the cosmogenic radioisotopes and consider how the relative production rates of the cosmogenic radioisotopes may be used to substantiate a solar cause for the historical radiation events and to infer the spectral hardness of the initiating solar protons. © The Authors.
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    Cosmogenic radionuclides at Law Dome, East Antarctica, as signatures of past Solar storm events.
    (Australian Nuclear Science and Technology Organisation, 2021-11-17) Smith, AM; Curran, MAJ; Fink, D; Dee, MW; Kuitems, M; Levchenko, VA; Moy, A; Scifo, A; Simon, KJ; Wilcken, KM
    This project investigates evidence for increased atmospheric production of cosmogenic radionuclides in ice core records at Law Dome, East Antarctica, during three extreme events. These events are the Carrington Event (CE) of 1859 AD [1], the largest solar storm of modern times, and two recently discovered cosmic radiation events of even greater magnitude, the Miyake Events (ME) of 774/5 AD [2] and 993/4 AD [3]. Our intention is to determine ¹⁴ C, ¹⁰ Be and ³⁶ Cl profiles, with the highest sub-annual temporal resolution to date, across these events to determine whether or not all three events are manifestations of the same phenomena. Understanding the frequency, origin and magnitude of these events is essential for future-proofing modern communication infrastructure against such high magnitude radiation impacts from space. Identification of the events also provides an independent check on the Law Dome ice chronology. New annual Δ¹⁴ C measurements in tree rings, in combination with earlier published data, show that the ME774 and the ME993 events occurred in close proximity to the point of maximum activity of the 11-year solar cycle [4]. Although it did not leave any radiocarbon signature, the CE1859 event was already known to have occurred around the point of maximum activity of the solar cycle from sunspot records. Ice samples for ¹⁰ Be and ³⁶ Cl analysis are derived from ice cores drilled near the summit of Law Dome, East Antarctica. This is the first time these radionuclides have been measured at the same site for these events, allowing a direct comparison of ME774, ME993 and CE1859 under similar transport conditions. Both ME samples were taken from sections of core where the amount of available ice was limited, and the CE samples were taken from a section where more ice was available. AMS measurements involved some method development at ANSTO, measuring both ¹⁰ Be and ³⁶ Cl in the same samples, with sample sizes challenging for the ME samples. Preliminary ¹⁰ Be results at annual resolution spanning 30 years allowed an exact location of the events. We have clearly identified the expected ME774 and ME993 ¹⁰ Be peaks, which were ~ 4 years and ~ 2 years, respectively, within the error of when the layer-counted DSS ice core chronology had suggested. Accordingly, a further set of ¹⁰ Be samples at sub-annual seasonal resolution have been taken to better define the fine structure and amplitude of the signal but are currently not processed. We will also prepare a set of ³⁶ Cl AMS targets from the sub-annual ice core samples and the initial annual survey samples. No discernible ¹⁰ Be peak or ³⁶ Cl peak was found for CE1859 at annual resolution. © The Authors