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Atomic Nuclei: Nuclear Magnetic Moment00:59

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All atomic nuclei are positively charged. When they have a nonzero spin, they behave like rotating charges. As a consequence of their charge and spin, these nuclei generate a magnetic field (B). This, in turn, gives rise to a magnetic moment (μ), which is randomly oriented in the absence of an external magnetic field. When an external magnetic field (B0) is applied, the magnetic moment vectors can align with the field or against it in 2 + 1 orientations. A hydrogen nucleus, which is just a...
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Many heavier elements with smaller binding energies per nucleon can decompose into more stable elements that have intermediate mass numbers and larger binding energies per nucleon—that is, mass numbers and binding energies per nucleon that are closer to the “peak” of the binding energy graph near 56. Sometimes neutrons are also produced. This decomposition of a large nucleus into smaller pieces is called fission. The breaking is rather random with the formation of a large...
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Atomic Nuclei: Nuclear Relaxation Processes01:23

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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.
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Angular Momentum01:21

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Angular momentum characterizes an object's rotational motion and is defined as the moment of its linear momentum about a specified point O. When a particle moves along a curved path in the x-y plane, the scalar formulation calculates the magnitude of its angular momentum, utilizing the moment arm (d), representing the perpendicular distance from point O to the line of action of the linear momentum. Despite being scalar in formulation, angular momentum is inherently a vector quantity. Its...
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Protons and neutrons, collectively called nucleons, are packed together tightly in a nucleus. With a radius of about 10−15 meters, a nucleus is quite small compared to the radius of the entire atom, which is about 10−10 meters. Nuclei are extremely dense compared to bulk matter, averaging 1.8 × 1014 grams per cubic centimeter. If the earth’s density were equal to the average nuclear density, the earth’s radius would be only about 200 meters.
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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.
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Study of Protein Dynamics via Neutron Spin Echo Spectroscopy
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Angular momentum generation in nuclear fission.

J N Wilson1, D Thisse2, M Lebois2

  • 1Université Paris-Saclay, CNRS/IN2P3, IJC Laboratory, Orsay, France. jonathan.wilson@ijclab.in2p3.fr.

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Summary
This summary is machine-generated.

Nuclear fission fragments gain angular momentum after splitting, not before. This post-scission spin generation, driven by nucleon motion in the neck, challenges prior theories and impacts nuclear reactor physics and super-heavy element research.

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Area of Science:

  • Nuclear Physics
  • Nuclear Fission
  • Quantum Mechanics

Background:

  • Heavy atomic nuclei emerging with significant angular momentum after fission has been a long-standing mystery.
  • Existing theories suggest angular momentum is generated before nuclear splitting (pre-scission) via collective vibrational modes.
  • Lack of experimental data has prevented definitive validation of competing theories for angular momentum generation.

Purpose of the Study:

  • To investigate the mechanism of angular momentum generation in nuclear fission fragments.
  • To determine whether spin is generated pre-scission or post-scission.
  • To propose a new model for angular momentum generation in nuclear fission.

Main Methods:

  • Comprehensive experimental analysis of fragment spins in nuclear fission.
  • Correlation analysis between the spins of fragment partners.
  • Mass and charge dependence studies of fragment spin.

Main Results:

  • No significant correlation was found between the spins of fission fragment partners.
  • Fragment spin is strongly mass-dependent, exhibiting saw-tooth distributions.
  • Fragment spin showed no notable dependence on the partner nucleus's mass or charge.

Conclusions:

  • Angular momentum in nuclear fission is generated after the nucleus splits (post-scission).
  • A proposed model suggests independent torques generated by nucleon motion in the ruptured neck.
  • Findings have implications for nuclear reactor physics, neutron-rich isotope structure, and super-heavy element synthesis.