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Videos de Conceptos Relacionados

Nuclear Fusion02:45

Nuclear Fusion

The process of converting very light nuclei into heavier nuclei is also accompanied by the conversion of mass into large amounts of energy, a process called fusion. The principal source of energy in the sun is a net fusion reaction in which four hydrogen nuclei fuse and ultimately produce one helium nucleus and two positrons.
A helium nucleus has a mass that is 0.7% less than that of four hydrogen nuclei; this lost mass is converted into energy during the fusion. This reaction produces about...
Atomic Nuclei: Nuclear Spin01:08

Atomic Nuclei: Nuclear Spin

All atomic particles possess an intrinsic angular momentum, or 'spin'. Electrons, protons, and neutrons each have a spin value of ½, although protons and neutrons in nuclei may have higher half-integer spins owing to energetic factors.
Atomic nuclei have a net nuclear spin, , which can have an integer or half-integer value. In atomic nuclei, the spins of protons are paired against each other but not with neutrons, and vice versa. Consequently, an even number of protons does not contribute to...
Atomic Nuclei: Nuclear Spin State Overview01:03

Atomic Nuclei: Nuclear Spin State Overview

NMR-active nuclei have energy levels called 'spin states' that are associated with the orientations of their nuclear magnetic moments. In the absence of a magnetic field, the nuclear magnetic moments are randomly oriented, and the spin states are degenerate. When an external magnetic field is applied, the spin states have only 2 + 1 orientations available to them. A proton with = ½ has two available orientations. Similarly, for a quadrupolar nucleus with a nuclear spin value of one, the...
Atomic Nuclei: Nuclear Spin State Population Distribution01:14

Atomic Nuclei: Nuclear Spin State Population Distribution

Near absolute zero temperatures, in the presence of a magnetic field, the majority of nuclei prefer the lower energy spin-up state to the higher energy spin-down state. As temperatures increase, the energy from thermal collisions distributes the spins more equally between the two states. The Boltzmann distribution equation gives the ratio of the number of spins predicted in the spin −½ (N−) and spin +½ (N+) states.
Atomic Nuclei: Larmor Precession Frequency01:11

Atomic Nuclei: Larmor Precession Frequency

The earth's gravitational field produces a 'twisting force' perpendicular to the angular momentum of a spinning mass (such as a spinning top) that causes the mass to 'wobble' around the gravitational field axis in a phenomenon called precession. Similarly, the magnetic moment (μ) of a spinning nucleus precesses due to an external magnetic field directed along the z-axis. The precession of the magnetic moment vector about the magnetic field is called Larmor precession, and the angular frequency...
Atomic Nuclei: Nuclear Relaxation Processes01:23

Atomic Nuclei: Nuclear Relaxation Processes

In the absence of an external magnetic field, nuclear spin states are degenerate and randomly oriented. When a magnetic field is applied, the spins begin to precess and orient themselves along (lower energy) or against (higher energy) the direction of the field. At equilibrium, a slight excess population of spins exists in the lower energy state. Because the direction of the magnetic field is fixed as the z-axis,  the precessing magnetic moments are randomly oriented around the z-axis. This...

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Simulation of the Planetary Interior Differentiation Processes in the Laboratory
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La formación de núcleos en planetesimales desencadenada por el flujo permeable.

Takashi Yoshino1, Michael J Walter, Tomoo Katsura

  • 1Institute for Study of the Earth's Interior, Okayama University, Yamada 827, Misasa, Tottori-ken 682-0193, Japan. tyoshino@misasa.okayama-u.ac.jp

Nature
|March 14, 2003
PubMed
Resumen

La formación temprana del núcleo planetesimal, impulsada por el calentamiento radiactivo, ocurrió rápidamente. Este proceso, habilitado por la percolación del fundido de hierro y azufre, sugiere que los planetas terrestres se formaron a partir de bloques de construcción pre-diferenciados.

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Área de la Ciencia:

  • Ciencias planetarias Ciencias planetarias.
  • La geofísica es la geofísica.
  • Cosmoquímica es la cosmoquímica.

Sus antecedentes:

  • Los isótopos de tungsteno en los meteoritos sugieren una rápida formación de núcleos en los primeros planetesimales.
  • La segregación metal-silicato requiere superar las limitaciones de humedad en las matrices ricas en olivino.

Objetivo del estudio:

  • Para determinar el umbral de percolación para el hierro-azufre fundido en olivino sólido.
  • Para explicar la rápida escala de tiempo de la formación del núcleo en los primeros cuerpos del Sistema Solar.

Principales métodos:

  • Mediciones de conductividad eléctrica in situ a alta presión y temperatura.
  • Investigando compuestos de hierro-azufre (Fe-S) fundidos en la matriz de olivino.

Principales resultados:

  • Se encontró que el umbral de percolación para el hierro-azufre fundido en la olivina era de aproximadamente el 5% vol.
  • El calentamiento por desintegración radiactiva puede elevar suficientemente las temperaturas para exceder el punto de fusión del Fe-S (~1,000°C).

Conclusiones:

  • Los planetesimales tempranos (>30 km de radio) y los embriones planetarios más grandes probablemente formaron núcleos diferenciados rápidamente.
  • La Tierra y otros planetas terrestres probablemente se acrecentaron a partir de estos planetesimales pre-diferenciados, formando un núcleo compuesto.