M2L9a.txt

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Last class we talked about isotope shifts,
and there was the question, how big are those isotopes for some
of your favorite atoms?
And I just looked up some information on lithium,
which is a light atom.
And this paper here shows calculations
compared with experiments.
The isotope shift between lithium 6 and lithium 7,
due the mass, lithium 6 to lithium 7
is about 10 gigahertz.
The volume effect is only 2 megahertz.
1,000 times smaller.
However, the precision of experiments
is such that if you find an isotope shift,
the mass effect can be exactly calculated
from the atomic masses.
You can still get information about the size
of the atomic nucleus out of it.
So this is the example of a light atom.
10 gigahertz mass effect, 2 megahertz volume effect.

And here is the rubidium atom.
The isotope shift of the D1 line between 85 and 87
is 77 megahertz only.
The mass shift is 56 megahertz.
And the remainder is mainly the volume effect.
There's a specific mass effect due to electronic correlations
if you have multiple electrons, which I think is small here,
but I don't want to discuss it.
So we can now compare the mass effect
in rubidium versus lithium.
First of all, a shift compared to infinite mass.
The reduced mass effect is much bigger in lithium.
It's 20 times bigger in lithium than rubidium.
However, when you go from lithium 6 to lithium 7,
the mass changes by 15%.
So the delta m over m is also much larger for lithium
than rubidium.
And if you add those two factors,
you find that the mass effect is 200 times larger in lithium.
10 gigahertz versus 50 megahertz.
And the nuclear volume effect is 2 megahertz for lithium,
20 megahertz for rubidium.
So that sets the scale.

Any question about that?