Half life of /sup 26/Al

Norris, T. L.; Gancarz, A. J.; Rokop, D.J.; Thomas, Kimberly

doi:10.2172/6143418

Cited by 27 publications

(32 citation statements)

References 3 publications

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“…(Norris et al 1983). This is congruent with a fast formation of planetesimals within 4 Ma (Huss et al 2001).…”

Section: Introductionsupporting

confidence: 53%

Hyper-Velocity Impacts on Rubble Pile Asteroids

Deller¹

2017

Springer Theses

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SummaryMost asteroids in the size range of approximately 100 m to 100 km are rubble piles, aggregates of rocky material held together mainly by gravitational forces, and only weak cohesion. They contain high macroporosities, indicating a large amount of void space in their interiors. How these voids are distributed is not yet known, as in-situ measurements are still outstanding.In this work, a model to create rubble pile asteroid simulants for use in SPH impact simulations is presented. Rubble pile asteroids are modelled as gravitational re-aggregating remnant fragments of a catastrophically disrupted parent body, which are represented by spherical pebbles. It is shown that this approach allows to explicitly follow the internal restructuring of rubble pile asteroids during impact events, while preserving the expected properties of the bulk asteroid as known from observations and experiments. The bulk behaviour of asteroid simulants, as characterized by the stability against disruption and fragment size distribution, follows the expected behaviour and is not sensitive to the exact distribution of voids in the interior structure, but rather to the void fraction as the amount of consolidated void space in between the constituent fragment pebbles. No exact a priory knowledge of the fragment size distribution inside the body is therefore needed to use this model in impact simulations.Modelling the behaviour of the large-scale rubble pile constituents during impact events is used as a tool to infer the internal structure of asteroids by linking surface features like hills or pits to the creation of sub-catastrophic craters.In this work, the small rubble pile asteroid (2867) Šteins is analysed. The flyby of the Rosetta spacecraft at Šteins has revealed several interesting features: the large crater Diamond close to the southern pole, a hill like feature almost opposite to the crater, and a catena of crater pits extending radially from the rim of the crater.A possible link between these two structures and the cratering event is investigated in a series of impact simulations varying the interior of a plausible shape of Šteins prior to the event that formed crater Diamond. A connection between the cratering event and the hill is shown to be highly unlikely. Therefore, the hill is most likely a remnant of the formation of Šteins. Its size therefore helps to infer the initial size distribution of fragments forming the asteroid.The formation of a fracture radially from the crater can be observed for rubble pile simulants with highly collimated voids. This fracture could plausibly form the catena of pits observed on Šteins. This can therefore serve as a link between observable surface features and Šteins internal structure. The interior of Šteins is most likely an aggregate of fragments that themselves are only lightly fractured, and large void spaces might be found inside the asteroid. As Šteins seems to be a good example of a YORPoid, an asteroid that has been evolved to a top-like shape by radiative forces due to the YORP ...

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“…(Norris et al 1983). This is congruent with a fast formation of planetesimals within 4 Ma (Huss et al 2001).…”

Section: Introductionsupporting

confidence: 53%

Hyper-Velocity Impacts on Rubble Pile Asteroids

Deller¹

2017

Springer Theses

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“…At sufficiently large depths, production rates are negligible and as time proceeds, the 10 Be and 26 Al atoms in the sediment will decay at a rate defined by the radioactive half-life (36). The half-life of 10 Be is 1.387 ± 0.012 (37,38) while the half-life of 26 Al is 0.705±0.024 Ma (39). Burial dating with 10 Be and 26 Al, relies on the fact that both, the production rates and the half-lives of 10 Be and 26 Al are known, so that deviations from the steady exposure 26 Al/ 10 Be ratio of ~7:1 can be converted to a burial age.…”

Section: Burial Datingmentioning

confidence: 99%

Tectonic control of Yarlung Tsangpo Gorge revealed by a buried canyon in Southern Tibet

Wang

Scherler

Liu‐Zeng

et al. 2014

Science

185

123

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The Himalayan mountains are dissected by some of the deepest and most impressive gorges on Earth. Constraining the interplay between river incision and rock uplift is important for understanding tectonic deformation in this region. We report here the discovery of a deeply incised canyon of the Yarlung Tsangpo River, at the eastern end of the Himalaya, which is now buried under more than 500 meters of sediments. By reconstructing the former valley bottom and dating sediments at the base of the valley fill, we show that steepening of the Tsangpo Gorge started at about 2 million to 2.5 million years ago as a consequence of an increase in rock uplift rates. The high erosion rates within the gorge are therefore a direct consequence of rapid rock uplift.

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“…For reference, the weighted mean of five determinations of the 26 Al halflife (Samworth et al, 1972;Norris et al, 1983;Middleton et al, 1983;Thomas et al, 1984) summarized by Nishiizumi (2004) is 0.715 ± 0.16 Ma, whereas the unweighted mean of these values is 0.720 ± 0.34 Ma (1r standard deviation). A lower value for t 1/2 ( 26 Al) = 0.705 ± 0.024 Ma (Norris et al, 1983) often is used in cosmogenic nuclide studies (cf. Nishiizumi, 2004).…”

Section: Introductionmentioning

confidence: 99%