Phenomenological Nuclear Theory

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    Nuclear Theory
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Discussion Overview

The discussion centers on phenomenological models of nuclear theory, specifically the Liquid Drop model and the Shell model. Participants explore whether these models are formalized within quantum mechanics and their relevance in explaining nuclear properties and behaviors.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant recalls learning nuclear theory through a phenomenological model and questions the existence of more formal models based on quantum mechanics.
  • Another participant mentions the Shell model as a relevant example in the discussion.
  • A participant expresses concern about the Liquid Drop model, questioning if it has been replaced by the Shell model and its applicability in modern nuclear theory.
  • It is noted that the Liquid Drop model cannot explain excited states and is characterized as a classical model.
  • One participant argues that the Liquid Drop model and the Shell model describe different aspects of the nucleus, with the Shell model predicting nuclear spin and excitation levels, while the Liquid Drop model is necessary for understanding the overall shape of the nucleus.
  • Participants acknowledge that both models serve as approximations rather than fundamental theories, with limitations in their applicability.

Areas of Agreement / Disagreement

Participants express differing views on the relevance and applicability of the Liquid Drop model versus the Shell model, indicating that multiple competing perspectives exist regarding their roles in nuclear theory.

Contextual Notes

Participants highlight limitations in the models, such as the inability of the Liquid Drop model to explain certain nuclear phenomena and the Shell model's constraints with high-energy excitations and magic numbers.

Pythagorean
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When I took modern physics (undergrad), we learned nuclear theory through a phenomenological model of the nucleus. I was just curious whether there are more formal models and whether they draw directly on the postulates of quantum mechanics or not. It's been two years since I took the class, so I'm a little rusty.

If not, is it assumed impossible or just undiscovered?
 
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what about the shell model for instance?
 
The Liquid Drop model is the one I'm referring to. I guess I'm wondering if it's been replaced. Does the shell model render the liquid drop model obsolete?
 
the drop model can't explain excited states etc, it is a classical model
 
Pythagorean said:
The Liquid Drop model is the one I'm referring to. I guess I'm wondering if it's been replaced. Does the shell model render the liquid drop model obsolete?

As far as I know, the two models describe different aspects of the nucleus. Shell model predicts nuclear spin and excitation levels, but it can't replace the liquid drop model when you need to consider the overall shape of the nucleus. For example the semi-empirical nuclear mass formula is mainly derived from the liquid drop model (plus quantum-mechanical terms such as asymmetry and parity). Also, the shell model has limitations. It only works well if you are dealing with excitations that are not too high, in nucleons not too far away from the "magic numbers". In the end, both of them are approximations (i.e. phenomenological models) rather than fundamental theories.
 

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