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Related Concept Videos

Atomic Nuclei: Types of Nuclear Relaxation01:28

Atomic Nuclei: Types of Nuclear Relaxation

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Nuclear relaxation restores the equilibrium population imbalance and can occur via spin–lattice or spin–spin mechanisms, which are first-order exponential decay processes.
In spin–lattice or longitudinal relaxation, the excited spins exchange energy with the surrounding lattice as they return to the lower energy level. Among several mechanisms that contribute to spin–lattice relaxation, magnetic dipolar interactions are significant. Here, the excited nucleus transfers...
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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: Magnetic Resonance01:05

Atomic Nuclei: Magnetic Resonance

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The number of nuclear spins aligned in the lower energy state is slightly greater than those in the higher energy state. In the presence of an external magnetic field, as the spins precess at the Larmor frequency, the excess population results in a net magnetization oriented along the z axis. When a pulse or a short burst of radio waves at the Larmor frequency is applied along the x axis, the coupling of frequencies causes resonance and flips the nuclear spins of the excess population from the...
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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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Nuclear Stability03:18

Nuclear Stability

24.0K
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 charged protons together...
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Atomic Nuclei: Larmor Precession Frequency01:11

Atomic Nuclei: Larmor Precession Frequency

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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,...
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Updated: Mar 19, 2026

Preparing an Isotopically Pure 229Th Ion Beam for Studies of 229mTh
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Determination of the Neutron Lifetime Using Magnetically Trapped Neutrons.

S N Dzhosyuk1, A Copete1, J M Doyle1

  • 1Harvard University, Cambridge, MA 02138, USA.

Journal of Research of the National Institute of Standards and Technology
|June 17, 2016
PubMed
Summary

Measuring neutron lifetime with trapped neutrons is crucial. Magnetic field ramping improved trap lifetime measurements, aligning with the free neutron lifetime.

Keywords:
magnetic trappingneutron lifetimesuperthermal neutron productionultracold neutrons

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Area of Science:

  • Nuclear Physics
  • Particle Physics
  • Quantum Mechanics

Background:

  • The neutron lifetime is a fundamental constant in physics.
  • Accurate measurement of neutron lifetime is essential for testing the Standard Model and understanding Big Bang nucleosynthesis.
  • Previous experiments faced challenges with neutron confinement and detection.

Purpose of the Study:

  • To accurately measure the neutron lifetime using magnetically trapped neutrons.
  • To investigate the effect of neutron energy on trap stability.
  • To refine experimental techniques for neutron lifetime measurements.

Main Methods:

  • Utilizing a 1.1 T deep superconducting Ioffe-type trap for neutron confinement.
  • Loading neutrons by scattering 0.89 nm neutrons in isotopically pure superfluid helium-4.
  • Real-time detection of neutron decays via scintillation light produced in helium by beta-decay electrons.
  • Implementing magnetic field ramping to eliminate high-energy neutrons.

Main Results:

  • Initial measurements showed a trap lifetime shorter than the free neutron lifetime due to high-energy neutrons.
  • Magnetic field ramping successfully removed these energetic neutrons.
  • The refined experiment yielded a trap lifetime consistent with the accepted free neutron lifetime value.

Conclusions:

  • Magnetic trapping of neutrons is a viable method for lifetime measurements.
  • Careful control of neutron energy within the trap is critical for accurate results.
  • The experiment provides a precise measurement of the neutron lifetime, supporting current physics models.