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Related Concept Videos

Atomic Nuclei: Nuclear Spin State Population Distribution01:14

Atomic Nuclei: Nuclear Spin State Population Distribution

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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.
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Atomic Nuclei: Nuclear Relaxation Processes01:23

Atomic Nuclei: Nuclear Relaxation Processes

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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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Atomic Nuclei: Nuclear Spin State Overview01:03

Atomic Nuclei: Nuclear Spin State Overview

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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...
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Atomic Nuclei: Nuclear Spin01:08

Atomic Nuclei: Nuclear Spin

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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.
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...
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Nuclear Stability03:18

Nuclear Stability

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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.
To hold positively...
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Atomic Nuclei: Nuclear Magnetic Moment00:59

Atomic Nuclei: Nuclear Magnetic Moment

3.0K
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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Angle-resolved Photoemission Spectroscopy At Ultra-low Temperatures
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Nuclear physics. Momentum sharing in imbalanced Fermi systems.

O Hen1, M Sargsian2, L B Weinstein3

  • 1Tel Aviv University, Tel Aviv 69978, Israel. or.chen@mail.huji.ac.il.

Science (New York, N.Y.)
|October 18, 2014
PubMed
Summary
This summary is machine-generated.

Short-range interactions create high-momentum neutron-proton pairs in atomic nuclei. This leads to protons having higher momentum than neutrons in neutron-rich nuclei, contrary to expectations without interactions.

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Area of Science:

  • Nuclear Physics
  • Quantum Chromodynamics
  • Astrophysical Nuclei

Background:

  • Atomic nuclei comprise protons and neutrons (fermions).
  • The Pauli exclusion principle dictates fermion momentum distribution in the absence of interactions.
  • In neutron-rich nuclei, neutrons typically possess higher average momentum than protons.

Purpose of the Study:

  • To investigate the momentum distribution of fermions in atomic nuclei.
  • To determine the impact of short-range interactions on nucleon momentum.
  • To explore implications for nuclear structure and neutron stars.

Main Methods:

  • High-energy electron scattering experiments.
  • Utilized targets of Carbon-12, Aluminum-27, Iron-56, and Lead-208.
  • Analysis of fermion momentum distributions.

Main Results:

  • Observed short-range nucleon-nucleon interactions in heavy nuclei.
  • Identified correlated high-momentum neutron-proton pairs.
  • Found protons more likely than neutrons to exceed Fermi momentum in neutron-rich nuclei.

Conclusions:

  • Short-range interactions significantly alter fermion momentum distributions in nuclei.
  • Proton-neutron correlations challenge simple nuclear models.
  • Findings have relevance for nuclear astrophysics and ultracold atomic gases.