Coulomb excitation is a technique in experimental nuclear physics to probe the electromagnetic aspect of
nuclear structure
Understanding the structure of the atomic nucleus is one of the central challenges in nuclear physics.
Models The cluster model
The cluster model describes the nucleus as a molecule-like collection of proton-neutron groups (e.g., alpha particl ...
. In Coulomb excitation, a
nucleus
Nucleus (: nuclei) is a Latin word for the seed inside a fruit. It most often refers to:
*Atomic nucleus, the very dense central region of an atom
*Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA
Nucleu ...
is excited by an
inelastic collision
An inelastic collision, in contrast to an elastic collision, is a collision in which kinetic energy is not conserved due to the action of internal friction.
In collisions of macroscopic bodies, some kinetic energy is turned into vibrational ener ...
with another nucleus through the
electromagnetic interaction
In physics, electromagnetism is an interaction that occurs between particles with electric charge via electromagnetic fields. The electromagnetic force is one of the four fundamental forces of nature. It is the dominant force in the interacti ...
. In order to ensure that the interaction is electromagnetic in nature — and not nuclear — the distance of closest approach of the colliding nuclei has to be sufficiently large. In particular, in low-energy Coulomb excitation (taking place at beam energies of a few
megaelectronvolts per nucleon) the commonly adopted empirical criterion is that if the surfaces of the colliding nuclei are separated by at least 5 femtometers, the contribution of the short-range nuclear interaction to the excitation process can be neglected.
From the measured excitation
cross sections, electromagnetic transition probabilities between the nuclear energy levels can be extracted.
This method is particularly useful for investigating collectivity in nuclei, as collective excitations are often connected by strong
electric quadrupole
A quadrupole or quadrapole is one of a sequence of configurations of things like electric charge or current, or gravitational mass that can exist in ideal form, but it is usually just part of a multipole expansion of a more complex structure re ...
transitions.
Moreover, it is the only experimental method in nuclear physics that is sensitive to electric
quadrupole moments of excited nuclear states with lifetimes shorter than nanoseconds.
References
Nuclear physics
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