Cosmogenic Radionuclides Research Articles

Nitrate ion spikes in ice cores not suitable as proxies for solar proton events

AbstractNitrate ion spikes in polar ice cores are contentiously used to estimate the intensity, frequency, and probability of historical solar proton events, quantities that are needed to prepare for potentially society‐crippling space weather events. We use the Whole Atmosphere Community Climate Model to calculate how large an event would have to be to produce enough odd nitrogen throughout the atmosphere to be discernible as nitrate peaks at the Earth's surface. These hypothetically large events are compared with probability of occurrence estimates derived from measured events, sunspot records, and cosmogenic radionuclides archives. We conclude that the fluence and spectrum of solar proton events necessary to produce odd nitrogen enhancements equivalent to the spikes of nitrate ions in Greenland ice cores are unlikely to have occurred throughout the Holocene, confirming that nitrate ions in ice cores are not suitable proxies for historical individual solar proton events.

Gamma emitters in atmospheric precipitation in Krakow (Southern Poland) during the years 2005–2015

The results of the sum of dry and wet activity deposition for naturally occurring 7Be, 210Pb, 40K, 22Na and anthropogenic 137Cs radionuclides in Krakow (Southern Poland) for the samples collected over 10 years (from August 2005 to July 2015) are presented and discussed. The radionuclides were determined using low background gamma spectrometry with HPGe detectors. Additionally, in this paper there are shown the results of activity concentrations in water from air precipitation for 7Be, 210Pb, 22Na, 40K and 137Cs radioisotopes from the period of 7 years (from August 2008 to July 2015). For all these series the statistical analysis including Spearman correlations, effects of seasonal variation and multiple regression models were conducted. After excluding two months from 2011 affected by the Fukushima accident, high Spearman correlation factors (R > 0.5) for activity deposition were noticed for the pair of the cosmogenic radionuclides 7Be and 22Na (R = 0.508) and between 210Pb and 7Be (R = 0.570). High correlation was noted between activity deposition and amount of precipitation for 7Be (R = 0.677). The seasonal correlations between 7Be–22Na, 40K–137Cs, 210Pb–137Cs and 7Be–210Pb were investigated and the highest correlation coefficient R = 0.731 for the 40K–137Cs pair was in the spring season. High correlations were observed also between 210Pb and 7Be for autumn (R = 0.594), 40K–137Cs in summer (R = 0.582), 7Be–22Na in spring (R = 0.635) and 210Pb–137Cs in autumn (R = 0.672). The multiple regression approach showed the interesting difference in scavenging mechanisms of cosmogenic and terrestrial radionuclides. According to that model, the deposition of cosmogenic nuclides was noticeably related to the amount of precipitation, while the deposition of terrestrial radionuclides did not show such dependence.

Cosmogenic 10 Be denudation rates and geomorphometric analysis in the Ambato range (28°–29°S), Sierras Pampeanas, Argentina

Abstract Quantifying denudation rates along orogenic systems is crucial to understand how tectonics and climate interact with each other to create topography. Long-term mean denudation rates estimated from geologic data in the Ambato range (Sierras Pampeanas) is 0.34 mm/yr. When compared with short-term denudation rates from other studies northward and southward along the Argentine South Central Andes foreland, our results are similar to those found in regions with higher mean annual precipitation. Here we utilize concentrations of 10Be cosmogenic radionuclide (CRN) in river sediments from catchments along the eastern slope of the Ambato range to understand the relationship among short-term (102–104 yrs) catchment-wide denudation rates and long-term denudation rates estimated from geologic data. CRN denudation rates range between ∼0.038 and ∼0.12 mm/yr. The relationship between geomorphometric parameters (local relief, slope, hypsometric integral, and catchment mean channel steepness index, Ksn) and CRN denudation rates shows linear behavior. The best correlation concerned Ksn indicating a strong connection in the Ambato range between tectonics and denudation. When analyzed together with denudation rates from other studies northward and southward along the South Central Andes foreland, our results are similar to those found in more arid regions and suggest that bedrock strength variations should be contemplated in a regional analysis as well as climate.

Temporal and spatial assessment of pollen, radionuclides, minerals and trace elements in deposited dust within Kuwait

Sixty-seven dust collectors were installed in 47 sites all over Kuwait. Nine of these sites contain four collectors for radionuclide collection. The monitoring of dust fallout and associated pollen was conducted for 2 years from August 2009 to August 2011. The highest dust depositional rates were detected within the western areas of Kuwait. The annual amount of dust in Kuwait varies from 10 to 1065 unit with an average of 278 t/km2. The year 2010–2011 was found dustier compared to 2009–2010 by 43 %. The analysis leads to a conclusion that the northwestern, western, and northern winds play a key role in producing dust within Kuwait. Regional areas represent the dominant sources of dust fallout, while local sources contribute appreciable amounts. The very fine and fine sand particles originate from local sources as they move in the form of saltation for a short distance and represent 37 % of the average dust fallout percentages in Kuwait. There is a trend of fining in mean size of dust particles towards the east and the northeast. Mineralogically, carbonates and quartz are the major components of dust in Kuwait, feldspars are found in considerable amounts. Other minerals in the dust are gypsum, anhydrite, bassonite and heavy minerals. Carbonates are more and quartz is less towards the coastal areas compared to desert areas. Natural 40K and 210Pb, man-made (anthropogenic) 137Cs, and cosmogenic 7Be radionuclides were determined. The average monthly depositional rates were 35.4, 11.2, 13.2 and 0.3 Bq m−2 for 7Be, 210Pb, 40K and 137Cs, respectively, which are were comparable to similar climatologically areas around the globe. Pollen originates predominantly from regional sources. However, the presence of a large amount of pollen from Haloxylon sp. Cyperus sp. indicates that close-by regional and local areas are a major contributor of fallen dust.

Granitic Boulder Erosion Caused by Chaparral Wildfire: Implications for Cosmogenic Radionuclide Dating of Bedrock Surfaces

Rock surface erosion by wildfire is significant and widespread but has not been quantified in southern California or for chaparral ecosystems. Quantifying the surface erosion of bedrock outcrops and boulders is critical for determination of age using cosmogenic radionuclide techniques, as even modest surface erosion removes the accumulation of the cosmogenic radionuclides and causes significant underestimate of age. This study documents the effects on three large granitic boulders following the Esperanza Fire of 2006 in southern California. Spalled rock fragments were quantified by measuring the removed rock volume from each measured boulder. Between 7% and 55% of the total surface area of the boulders spalled in this single fire. The volume of spalled material, when normalized across the entire surface area, represents a mean surface lowering of 0.7–12.3 mm. Spalled material was thicker on the flanks of the boulders, and the height of the fire effects significantly exceeded the height of the vegetation prior to the wildfire. Surface erosion of boulders and bedrock outcrops as a result of wildfire spalling results in fresh surfaces that appear unaffected by chemical weathering. Such surfaces may be preferentially selected by researchers for cosmogenic surface dating because of their fresh appearance, leading to an underestimate of age.

An empirical model of heliospheric cosmic ray modulation on long-term time scale

Galactic Cosmic Rays (GCRs) entering the heliosphere are subject to modulation processes due to variable solar magnetic activity. Finding a relationship between cosmic-ray variations and the heliospheric parameters is important for reconstruction of solar activity in the past. Here, we develop a semi-empirical model describing the heliospheric modulation of GCRs in terms of heliospheric parameters such as the open solar magnetic flux, the tilt angle of the heliospheric current sheet and the polarity of the large scale solar magnetic field. Our model is fitted using annual data obtained for the period 1976–2013, which includes the very weak solar minimum during 2008–2010. The model shows a good agreement with the data, and therefore, can be used for reconstructions of the modulation potential at different levels of solar activity. The model’s validity is also tested using the cosmogenic radionuclides 14 C and 10 Be stored in terrestrial archives. The tilt angle used to fit the parameters in our semi-empirical modulation model is reconstructed by a mathematical model described here.

Exploring ice core drilling chips from a cold Alpine glacier for cosmogenic radionuclide (10Be) analysis

Ice cores offer unique multi-proxy paleoclimate records, but provide only very limited sample material, which has to be carefully distributed for various proxy analyses. Beryllium-10, for example, is analysed in polar ice cores to investigate past changes of the geomagnetic field, solar activity, and the aerosol cycle, as well as to more accurately date the material. This paper explores the suitability of a drilling by-product, the so-called drilling chips, for 10Be-analysis. An ice core recently drilled at a cold Alpine glacier is used to directly compare 10Be-data from ice core samples with corresponding drilling chips. Both sample types have been spiked with 9Be-carrier and identically treated to chemically isolate beryllium. The resulting BeO has been investigated by accelerator mass spectrometry (AMS) for 10Be/9Be-ratios to calculate 10Be-concentrations in the ice. As a promising first result, four out of five sample-combinations (ice core and drilling chips) agree within 2-sigma uncertainty range. However, further studies are needed in order to fully demonstrate the potential of drilling chips for 10Be-analysis in alpine and shallow polar ice cores.

Late Devensian deglaciation of the Tyne Gap Palaeo‐Ice Stream, northern England

ABSTRACTThe deglacial history of the central sector of the last British–Irish Ice Sheet is poorly constrained, particularly along major ice‐stream flow paths. The Tyne Gap Palaeo‐Ice Stream (TGIS) was a major fast‐flow conduit of the British–Irish Ice Sheet during the last glaciation. We reconstruct the pattern and constrain the timing of retreat of this ice stream using cosmogenic radionuclide (10Be) dating of exposed bedrock surfaces, radiocarbon dating of lake cores and geomorphological mapping of deglacial features. Four of the five 10Be samples produced minimum ages between 17.8 and 16.5 ka. These were supplemented by a basal radiocarbon date of 15.7 ± 0.1 cal ka BP, in a core recovered from Talkin Tarn in the Brampton Kame Belt. Our new geochronology indicates progressive retreat of the TGIS from 18.7 to 17.1 ka, and becoming ice free before 16.4–15.7 ka. Initial retreat and decoupling of the TGIS from the North Sea Lobe is recorded by a prominent moraine 10–15 km inland of the present‐day coast. This constrains the damming of Glacial Lake Wear to a period before ∼18.7–17.1 ka in the area deglaciated by the contraction of the TGIS. We suggest that retreat of the TGIS was part of a regional collapse of ice‐dispersal centres between 18 and 16 ka.

Application of 10Be Dating Technique for Marine Terrace Studies and Its Limitations

Although Quaternary marine terraces and onshore paleo-shoreline records provide clues to our understanding for the mode and nature of neotectonics in the Korean peninsula, it cannot be accomplished without knowledge on both independent information of the past sea level records and tectonic deformation field together with precise results of numerical dating for higher terraces. This study reported cosmogenic radionuclides () dating results conducted in higher terraces in the eastern and western coasts of the Korean peninsula. As a result, the measured concentration ratio of and the exposure ages were much younger than expected. It implies that either there is possibility of error in experimental processes or the samples experienced a complex exposure history probably included a burial at some stage. Considering the past climatic conditions around the Korean peninsula and a possible complex exposure history after the emergence of marine terrace, the discovery of a suitable study area and a sampling site are an essential part of successful dating technique.

High-sensitivity HPGe gamma-spectrometry analysis of radionuclides in Martian meteorites

Analysis of cosmogenic radionuclides in Martian meteorites is a great radioanalytical challenge because of the high scientific value of these meteorites, and necessity to apply non-destructive methods of analysis, e.g., low-level gamma-ray spectrometry. The measured 54Mn, 22Na, and 26Al levels in two fragments of the Tissint meteorite, a recent fall (18 July 2011), were 0.9, 1.1 and 0.6 Bq/kg in average. The high 22Na/26Al activity ratio (1.89 ± 0.05) measured in the larger sample (908.7 g) indicates an unsaturated production of 26Al in the Tissint meteorite.

Geomorphic development of the Gonghe Basin at the northeastern Tibet constrained by in situ cosmogenic radionuclides

Geomorphic development of the Gonghe Basin at the northeastern Tibet constrained by in situ cosmogenic radionuclides

An Investigation of the Amount of Dose Rate Due to Radioactive Count within Sokoto Metropolis

This paper aims to unveil the level of risk to biological system due to ionizing radiation within Sokoto metropolis. It is known to cause cancer and other related ailments. Thirty (30) randomly sampled points were measured with the aid of Dose Rate Meter, Rados [RDS-120]. The energy deposited to biological systems by gamma-ray flux was measured in micro sivert per hour (  Sv/hr). We found a significant total amount of dose rate at 2.95 Sv/hr with an arithmetic mean of 0.10  Sv/hr with an annual exposure rate of 864.0  Sv/yr. An amount which is quite significant above the world wide effective dose rate of 70  Sv/yr. This result indicates a radiation hazards contributed by either primordial radionuclides or cosmogenic radionuclides which suggest for mitigation actions and calling for further research.

Particle trajectories on hillslopes: Implications for particle age and 10Be structure

AbstractMany geomorphic systems act as conveyor belts onto which material is loaded at a particular rate and is transported in one direction toward another system that serves as a sink. As the material travels, it ages, it changes in grain size, it accumulates cosmogenic radionuclides, it adsorbs or releases nutrients, and it weathers. Here I address the hillslope conveyor. As many geochemical processes are depth‐dependent, the depth history of a particle becomes important to know. I calculate soil particle trajectories in the horizontal‐depth plane and address three cases, one in which horizontal speeds decline exponentially with depth, a second in which they are uniform with depth, and a third in which horizontal speeds are also uniform but all profile values are vertically well‐mixed. Vertical speeds are governed by continuity in an incompressible medium and by the boundary condition of zero vertical particle speed at the soil surface. Particle trajectories must therefore become surface parallel at the surface. Knowledge of soil particle trajectories allows calculation of residence times and concentration profiles of 10Be in the soil. The results inform strategies for interpretation of nuclide concentrations in soils and stream sediments and for inference of transport rate profiles. In all steady cases, the particle age and 10Be structure are uniform with distance from the divide. When significant vertical gradients in horizontal speed occur, the patterns of particle age and of 10Be concentration are dominated by the depth scale of the transport process. In unmixed cases, the particle age and 10Be concentration in near‐surface samples can greatly exceed the vertically averaged values, reflecting the fact that the vertical speeds of particles slow dramatically as they near the surface. In cases in which horizontal speed varies significantly with depth, the vertically averaged concentration of 10Be within the soil can significantly underpredict the mean 10Be concentration of sediment delivered to the channel. Proper averaging requires weighting by particle speed. These results provide the backdrop for addressing chemical evolution of soil on a hillslope.

LONG-TERM VARIATION IN THE SUN’S ACTIVITY CAUSED BY MAGNETIC ROSSBY WAVES IN THE TACHOCLINE

Long-term records of sunspot number and concentrations of cosmogenic radionuclides (10Be and 14C) on the Earth reveal the variation of the Sun's magnetic activity over hundreds and thousands of years. We identify several clear periods in sunspot, 10Be, and 14C data as 1000, 500, 350, 200 and 100 years. We found that the periods of the first five spherical harmonics of the slow magnetic Rossby mode in the presence of a steady toroidal magnetic field of 1200-1300 G in the lower tachocline are in perfect agreement with the time scales of observed variations. The steady toroidal magnetic field can be generated in the lower tachocline either due to the steady dynamo magnetic field for low magnetic diffusivity or due to the action of the latitudinal differential rotation on the weak poloidal primordial magnetic field, which penetrates from the radiative interior. The slow magnetic Rossby waves lead to variations of the steady toroidal magnetic field in the lower tachocline, which modulate the dynamo magnetic field and consequently the solar cycle strength. This result constitutes a key point for long-term prediction of the cycle strength. According to our model, the next deep minimum in solar activity is expected during the first half of this century.

Variations of cosmogenic radionuclide production rates along the meteorite orbits

Cosmogenic radionuclides produced by galactic cosmic rays (GCR) in meteorites during their motion in space are natural detectors of the GCR intensity and variations along the meteorite orbits. On the basis of measured and calculated contents of cosmogenic radionuclides in the freshly fallen Chelyabinsk and Košice chondrites some peculiarities of generation of cosmogenic radionuclides of different half-lives in the chondrites of different orbits and dates of fall onto the Earth are demonstrated. Dependence of production rates of the radionuclides on the GCR variations in the heliosphere is analyzed. Using radionuclides with different half-lives it is possible to compare the average GCR intensity over various time periods. The measurement and theoretical analysis of cosmogenic radionuclides in consecutively fallen chondrites provide a unique information on the space–time continuum of the cosmogenic radionuclide production rates and their variations over a long time scale, which could be useful in correlative analyses of processes in the heliosphere. Some applications of cosmogenic radionuclide depth distribution in chondrites for estimation of their pre-atmospheric sizes are illustrated.

Cosmogenic radionuclides in Chelyabinsk and Kosice chondrites and features of solar cycles 23 and 24

Based on the example of the measured and calculated contents of cosmogenic radionuclides in freshly fallen Chelyabinsk and Kosice chondrites, an indirect approach to studying variations in galactic cosmic rays is presented that uses variations in the rates of production of radionuclides with different half-lives in the meteorites that continuously fall to Earth from orbits of different sizes and inclinations. The advantages of monitoring these data over a long time scale to establish the main regularities of solar modulation processes in the heliosphere are demonstrated. The possible effect of stochastic factors in the operation of the solar dynamo had on the peculiarities of GCR modulation in solar cycles 23 and 24 is discussed.

Cosmogenic nuclides in the Košice meteorite: Experimental investigations and Monte Carlo simulations

AbstractResults of nondestructive gamma‐ray analyses of cosmogenic radionuclides (7Be, 22Na, 26Al, 46Sc, 48V, 54Mn, 56Co, 57Co, 58Co, and 60Co) in 19 fragments of the Košice meteorite are presented and discussed. The activities varied mainly with position of fragments in the meteoroid body, and with fluxes of cosmic‐ray particles in the space affecting radionuclides with different half‐lives. Monte Carlo simulations of the production rates of 60Co and 26Al compared with experimental data indicate that the pre‐atmospheric radius of the meteoroid was 50 ± 5 cm. In two Košice fragments, He, Ne, and Ar concentrations and isotopic compositions were also analyzed. The noble‐gas cosmic‐ray exposure age of the Košice meteorite is 5–7 Myr, consistent with the conspicuous peak (or doublet peak) in the exposure age histogram of H chondrites. One sample likely contains traces of implanted solar wind Ne, suggesting that Košice is a regolith breccia. The agreement between the simulated and observed 26Al activities indicate that the meteoroid was mostly irradiated by a long‐term average flux of galactic cosmic rays of 4.8 particles cm−2 s−1, whereas the short‐lived radionuclide activities are more consistent with a flux of 7.0 protons cm−2 s−1 as a result of the low solar modulation of the galactic cosmic rays during the last few years before the meteorite fall.

Book Review: Cosmogenic Radionuclides: Theory and Applications in the Terrestrial and Space Environments

Book Review: Cosmogenic Radionuclides: Theory and Applications in the Terrestrial and Space Environments

Cosmogenic radionuclides and mineralogical properties of the Chelyabinsk (LL5) meteorite: What do we learn about the meteoroid?

AbstractOn February 15, 2013, after the observation of a brilliant fireball and a spectacular airburst over the southern Ural region (Russia), thousands of stones fell and were rapidly recovered, bringing some extremely fresh material for scientific investigations. We undertook a multidisciplinary study of a dozen stones of the Chelyabinsk meteorite, including petrographic and microprobe investigations to unravel intrinsic characteristics of this meteorite. We also study the short and long‐lived cosmogenic radionuclides to characterize the initial meteoroid size and exposure age. Petrographic observations, as well as the mineral compositions obtained by electron microprobe analyses, allow us to confirm the classification of the Chelyabinsk meteorite as an LL5 chondrite. The fragments studied, a few of which are impact melt rocks, contain abundant shock melt veins and melt pockets. It is likely that the catastrophic explosion and fragmentation of the Chelyabinsk meteoroid into thousands of stones was in part determined by the initial state of the meteoroid. The radionuclide results obtained show a wide range of concentrations of 14C, 22Na, 26Al, 54Mn, 57Co, 58Co, and 60Co, which indicate that the pre‐atmospheric object had a radius >5 m, consistent with other size estimates based on the magnitude of the airburst caused by the atmospheric entry and breakup of the Chelyabinsk meteoroid. Considering the observed 26Al activities of the investigated samples, Monte Carlo simulations, and taking into account the 26Al half‐life (0.717 Myr), the cosmic‐ray exposure age of the Chelyabinsk meteorite is estimated to be 1.2 ± 0.2 Myr. In contrast to the other radionuclides, 14C showed a very large range only consistent with most samples having been exposed to anthropogenic sources of 14C, which we associate with radioactive contamination of the Chelyabinsk region by past nuclear accidents and waste disposal, which has also been confirmed by elevated levels of anthropogenic 137Cs and primordial 40K in some of the Chelyabinsk fragments.

Hillslope lowering rates and mobile-regolith residence times from in situ and meteoric10Be analysis, Boulder Creek Critical Zone Observatory, Colorado

Cosmogenic radionuclides (CRNs) are commonly employed to quantify both the production rates and residence times of mobile regolith. Meteoric and in situ CRNs have different accumulation mechanisms and can independently constrain landscape evolution rates. Here we use both in situ and meteoric 10 Be to investigate where in the regolith 10 Be is stored, and to quantify production rates and residence times of mobile regolith on active hillslopes in Gordon Gulch, within the Boulder Creek Critical Zone Observatory (CZO), Colorado, USA. Our data reveal that two-thirds of in situ 10 Be in regolith is produced within saprolite, and at least one-tenth of the meteoric 10 Be inventories is stored in saprolite, highlighting the importance of consistent terminology and identification of the mobile regolith–saprolite boundary. We find that mobile-regolith production rates are on average 3.1 cm/k.y., and residence times are between 10 and 20 k.y. A notable exception exists at the depositional north-facing footslope, where residence times likely exceed 40 k.y. Close agreement between the meteoric and in situ results indicates that upper- and mid-slope positions are consistent with steady, uniform lowering of the landscape. In addition to comparing the two methods, we develop a one-dimensional analytical model for the 10 Be concentration fields on an active, steady-state catena with uniform erosion. We then compare model predictions with measurements to evaluate how well our sites adhere to the steady-state assumption underlying the calculations for mobile-regolith residence time and production rates. Such comparisons suggest that calculated residence times and lowering rates are likely no closer than ±25% of the geomorphic reality.