Assessing the use of 3H-3He dating to determine the subsurface transit time of cave drip waters
A New Single Vacuum Furnace Design for Cosmogenic 3He Dating
The Christchurch earthquake series had severe consequences and surprised scientists for many reasons. Ground motions were extremely strong despite the relative moderate magnitudes of the quakes M W 5. The events happened on a system of hitherto unknown faults, some of which are located directly below Christchurch. Earthquake environmental effects EEE , especially liquefaction, were intense and widespread.
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The concept of neutron spectroscopy dates back to neutron discovery in Despite several attempts towards an efficient neutron spectroscopy system, such measurements remain cumbersome and detailed neutron spectra are sparse both in scientific laboratories and industrial sites. To-date the most widely used method relies on the 3He n,p 3H reaction, which – however – is more well suited for thermal neutrons and is particularly expensive, given that 3He is scarce.
The neutronSPHERE project will provide a unique alternative to 3He-based detectors for neutron spectroscopy by using the Spherical Proportional Counter SPC , a high-gain large-volume gaseous detector, filled with a nitrogen-based mixture. This breakthrough is enabled by novel developments in SPC instrumentation that the host has played a key role in demonstrating.
The capabilities of the developed neutron spectroscopy system will be demonstrated in two application: Firstly, neutronSPHERE will provide the first high precision measurements of the neutron background spectrum in underground facilities.
ESF Research Conferences
Benjamin H. Mackey, Mark C. Quigley; Strong proximal earthquakes revealed by cosmogenic 3 He dating of prehistoric rockfalls, Christchurch, New Zealand.
Surface exposure dating, using the concentration of cosmogenic nuclides (3He, 21Ne, and 36Cl) in moraine boulders, combined with mapping of glacial.
We present a comprehensive account of tritium and 3He in the Mediterranean Sea since the appearance of the tritium generated by the atmospheric nuclear-weapon testing in the s and early s, based on essentially all available observations. The decline was largely due to radioactive tritium decay, which produced significant amounts of its stable daughter 3He. We present the scheme by which we separate the tritiugenic part of 3He and the part due to release from the sea floor terrigenic part.
This fact makes the Mediterranean unique in offering a potential for the use of tritiugenic 3He as a tracer. The transient distributions of the two tracers are illustrated by a number of sections spanning the entire sea and relevant features of their distributions are noted. By , the 3He concentrations in the top few hundred meters had become low, in response to the decreasing tritium concentrations combined with a flushing out by the general westward drift of these waters.
The transit time dispersion revealed by this new application of tritium-3He dating is considerable. Archives et Traceurs. Documents grand public Logiciels Supports de formations. The transient distributions of nuclear weapon-generated tritium and its decay product 3He in the Mediterranean Sea, – , and their oceanographic potential.
Measured He ages ranged from 8 to 61 Ma, and were reproducible to better than a few percent despite very large variations in [U] and [Th]. In all samples with internal stratigraphy or independent age constraints, the He ages honored the expected relationships. These data demonstrate that internally consistent He ages can be obtained on goethite, but do not prove quantitative 4He retention. To assess possible diffusive He loss, stepped-heating experiments were performed on two goethite samples that were subjected to proton irradiation to produce a homogeneous distribution of spallogenic 3He.
The 3He release pattern indicates the presence of at least two diffusion domains, one with high helium retentivity and the other with very low retentivity at Earth surface conditions. Diffusive loss of 3He from the high retentivity domain is independent of the macroscopic dimensions of the analyzed polycrystalline aggregate, so probably represents diffusion from individual micrometer-size goethite crystals.
Foeken, J. P. T., Day, S., & Stuart, F. M. (). Cosmogenic 3He exposure dating of the Quaternary basalts from Fogo, Cape Verdes: Implications for rift zone.
Tritium 3 H or T is the radioactive isotope of hydrogen that decays with a half life of Tritium is produced naturally in the upper atmosphere by interaction of nitrogen, and, to a lesser extent, oxygen with cosmic rays. After oxidation to HTO, it takes part in the natural water cycle. These tests which were mainly performed in the early s, led to an increase of tritium in precipitation over the continents of the northern hemisphere from roughly 5 TU to levels of the order of TU.
One TU Tritium Unit means a tritium to hydrogen ratio of 10 Whereas the addition of bomb tritium to the environment practically eliminated the use of natural tritium as a tracer, it offered a new tool, i. If the tritium delivery as a function of time can be reconstructed, this penetration process can be used for quantitative studies of water movement through identification of the bomb peak in certain ground water bodies. However, there are natural limits to this method because tritium decay and dispersion make it increasingly difficult to identify the bomb peak in groundwater.
These problems can be overcome by using tritium in combination with its decay product 3 He 3 He trit as first suggested by Tolstykhin and Kamensky and experimentally confirmed by Torgersen et al. If both the tritium and 3 He trit concentrations are measured in TU, it can be calculated as.
Tritium/3He dating of shallow groundwater
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We collected 7 erratic and 2 bedrock surface samples, which are currently being processed for 10Be, 26Al and 3He dating. We will visit the Hudson Mountains.
Cosmogenic isotopes such as 10Be and 26Al are widely used to determine the age and exposure histories of landscape features. Such information is critical to understanding the timing and rate of geologic processes such as active fault ruptures, glacial advances, soil formation and erosion of mountain belts. However, the utility of these isotopes is limited by the high cost and intense labor associated with producing a single measurement. This project proposes development of cosmogenic 3He as a dating tool in common accessory mineral phases such as apatite, sphene and zircon.
If successful, this technique will be unique in several respects. First, it will allow rapid and inexpensive cosmogenic dating of a wide range of rock types, thus increasing the number of samples that can be dated in a single study.
Weathering Geochronology by (U-Th)/He Dating of Geothite
However, this method has rarely been applied to karstified aquifers and in particular to drip water in caves, despite the importance of the information which may be obtained. Besides the determination of transfer times of climate signals from the atmosphere through the epikarst to speleothems as climate archives, 3 H- 3 He together with Ne, Ar, Kr, Xe data may also help to give new insights into the local hydrogeology, e.
In order to check the applicability of 3 H- 3 He dating to cave drips, we collected drip water samples from three adjacent caves in northwestern Germany during several campaigns.
Tritium and helium are important tracers in hydrology, you can find actual examples in the projects section. The history of tritium 3 H and helium as tracers in hydrology began in the s and early s, when large amounts of tritium were released at the tests of thermonuclear bombs in the atmosphere. Soon it was discovered, that the radioactive superheavy hydrogen isotope 3H is an ideal tracer for hydrological processes of all kind, because it is readily incorporated in the water molecule to form HTO, and then takes part in the global water cycle e.
Begemann and Libby, ; Suess, These data form the basis for tracer applications of tritium. As long as a water parcel is in contact with the atmosphere, the tritiogenic 3 He 3 He formed by tritium decay is exchanged with the atmosphere.