Static and dynamic excited states

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Discussion Overview

The discussion revolves around the nature of excited states in atomic nuclei, specifically comparing the shell model and the liquid drop model. Participants explore whether these models describe the same excitation levels or if they represent distinct phenomena, focusing on static versus dynamic excitations.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant notes confusion about whether the static excitations described by the shell model and the dynamic excitations from the liquid drop model refer to the same physical phenomena or different aspects of nuclear excitations.
  • Some participants assert that the excitations are different, with individual nucleons reaching higher energy levels representing static excitations, while the whole nucleus can undergo collective deformations, termed dynamic excitations or giant resonances.
  • A question is raised regarding how to experimentally determine the type of excitation, specifically whether an octupole deformation is due to a nucleon changing its orbital angular momentum or the nucleus undergoing octupole oscillations, suggesting that it may depend on the energy involved.

Areas of Agreement / Disagreement

Participants generally agree that the excitations described by the shell model and the liquid drop model are different, but the discussion remains unresolved regarding the experimental determination of the type of excitation and the relationship between the two models.

Contextual Notes

The discussion highlights the complexity of nuclear excitations and the potential overlap between static and dynamic descriptions, but does not resolve the specific conditions under which one model may be more applicable than the other.

kelly0303
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Hello! I am reading about excited levels in nuclei (I am mainly following Wong's nuclear physics book) and I am a bit confused about the nature of the excited states. In the one particle picture (mainly shell model) the excitation appears as static i.e. one nucleon moves from a certain orbital to another one and that's it. In the liquid drop model the excitation appears dynamic i.e. the energy leads to nucleus to vibrate or rotate. I am a bit confused if these 2 pictures are describing the same excitation levels, or they are two separate things? For example in molecules you have some "static" excitations (i.e. electronic excitations) and some "dynamic" ones (i.e. rotation and vibration). Is it the same here i.e. does the shell model describe static excitations and the liquid drop model describes dynamic ones, or they are the same ones just from 2 different perspectives? Basically when I see a diagram of a nucleus with energy levels (and spin and parity of each level), can any of these transitions (at least in principle) be described by both shell model and liquid drop model (of course one of them might be more adequate for a given nucleus), or each transition can be explain by only one of the two (I am aware that there are many other models out there, but I'd like to stick to these 2 for now). Thank you!
 
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They are different excitations. You can have individual nucleons reaching higher energy levels but you can also have the whole nucleus deform (collective excitations/giant resonances).
Note that - just like for orbitals - these deformations don't need to have a state that changes in time.
 
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mfb said:
They are different excitations. You can have individual nucleons reaching higher energy levels but you can also have the whole nucleus deform (collective excitations/giant resonances).
Note that - just like for orbitals - these deformations don't need to have a state that changes in time.
Thank you for your reply! So experimentally, how can one figure out the type of excitation? For example an excitation with ##\lambda = 3##, which is an octupole deformation, is it because a nucleon changed its orbital angular momentum value by 3, or because the nucleus as a whole was having octupole oscillations? Or it can be both depending on the energy?
 
That will depend on your experiment.
 

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