Talk:Semi-empirical mass formula
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[edit] Form of the pairing term
I have the A dependence of the pairing term to be A − 1 / 2 in my undergraduate notes, instead of A − 3 / 4 . Is the 3/4 figure chosen from any particular experiment? Or it one of those things that is open to choice of definition? --Zapateria 15:49, 2 June 2006 (UTC)
- Can anyone give a more detailed explanation how the A1 / 2 comes from, both experimentally and theoretically? —The preceding unsigned comment was added by Shinbu3 (talk • contribs) 10:49, 20 March 2007 (UTC).
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- Roughly speaking, you can imagine the pairing as occurring between pairs of nucleons that are orbiting in the same orbit, but in opposite directions. Classically, they would pass by each other twice per orbit. Since nuclear forces have short ranges, they only have a chance to interact when they're passing by each other. In a heavier nucleus, the orbits are physically bigger, so the passings are less infrequent, so for this kind of naive classical reason, you expect it to be maybe A^-1/3. There may be more careful, explicitly quantum mechanical arguments that produce the exponents -1/2 and -3/4. In reality, you fit this kind of thing to a wide range of data, and the reasons for certain features of the resulting fit may be obscure.--207.233.84.39 02:10, 28 March 2007 (UTC)
[edit] What units does EB have?
Is the output value of EB in eV?
- According to my undergraduate notes, EB should be about 8MeV per nucleon, but as far as I can tell, that's using the "Wapstra" values from the table. 134.226.1.234 21:03, 4 March 2007 (UTC)
[edit] merge
Liquid drop model is a redundant, lower-quality version of Semi-empirical mass formula. I fixed a few of the more egregious errors in Liquid drop model, but I think there's still zero useful content in it that isn't in Semi-empirical mass formula.--207.233.84.39 02:02, 28 March 2007 (UTC)
[edit] pairing energies
I'm a little surprised about the vast difference between the pairing parameters quoted from Wapstra and Rohlf. I think the Rohlf values are right. Is it possible that someone made a mistake in tabulating the Wapstra values, and didn't understand that there was some difference in the definitions or something? I realize that all this stuff depends somewhat on what data set you're fitting, but I can't believe it really varies by a factor of three. Both the external links agree with the Rohlf values.--207.233.84.39 02:02, 28 March 2007 (UTC)
- After looking at the discussion above of the -1/2 and -3/4 exponents, my guess is that Wapstra used one exponent, and Rohlf the other. If that's the case, then it's probably an error to include the Wapstra values here as if they pertained to the same exponent.--207.233.84.39 02:12, 28 March 2007 (UTC)
