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Re: Nuclear topics in physics?

Ludwik Kowalski wrote:

I think that an introductoty physic teachers should make an
effort to include nuclear technology topics.

Yes, that would be nice.

One difficulty is
that a physics course is already overloaded and that adding
more chapters is counterproductive. The old dilemma of
depth versus breadth cannot be ignored

True.

and presenting
nuclear topics in dedicated chapters is not acceptable.

The key issue is not whether it is a dedicated chapter or not.
The key issue is whether it can be done without adding new
burdens to an already overloaded syllabus. Taking new burdens
and spreading them around in old chapters doesn't _necessarily_
make them less burdensome. What Ludwik is really suggesting,
I gather, is specific ways of discussing this topic without
adding to the total burden.

But
these topics could and should be discussed in illustrations
and in numerical problems based on what is already
covered.

Yes. The first-year college course that I took 'way back
when did exactly that.

Here are some suggestions:

1) The E=m*c^2 formula is likely to be introduced, superficially,
when concepts of mass and energy are discussed in mechanics.

The law that you want to remember is E^2 - p^2 c^2 = m^2 c^4

This was introduced in about the 4th week of that course as
an application of the idea of the invariant length of a 4-vector.

this formula is
a clear indication that energy shortages are paradoxical in our
material world.

That is not the right way to think about it.

Everything around has mass and can thus be
used, at least in principle, to obtain useful energy.

There's a difference between energy and useful energy.
Thermodynamics and all that.

But ways
of doing this must be invented; what has been invented so far
is only a beginning. The main motivational message should be:
"Learn what is known and try to build on it. Be creative and
use your brain to promote better technologies. Get ready to
help the mankind by becoming a scientist or an engineer."

OK.

2) Conservation of linear momentum can be illustrated by
examining nuclear collisions, for example, between neutrons
and protons.

The same 4th-week lecture calculated the energy required to
make an antiparticle, exploiting ideas of lab frame, CM frame,
conservation of 4-momentum, conservation of charge,etc. It's
not really more complicated than the usual inelastic-collision
problems with ballistic pendulums, but the result is a lot more
impressive.

Formulas of kinetic theory of gasses can be
used to discuss the process of moderation of neutrons in
contemporary nuclear reactors. Such topics cannot be
developed in depth in the first physics course but bringing
them as illustrations of general principles seems to be
highly appropriate.

Right.

3) Most nuclear topics are likely to be presented in sections
dealing with electricity.

Not necessarily; the antimatter reaction I mentioned was covered
half a year before the first real discussion of electromagnetism.

Nuclear strong force, without
elaboration, can be introduced when Coulomb's Law and
the Law of Universal Gravitation are compared. Here are
typical problems and questions in this area. Calculate kinetic
energy of two fragments after an idealized spontaneous
fission event. How is this energy distributed between the
fragments?

OK.

What happens to the released energy? What
prevents heavy nuclei from fissioning very rapidly?

That seems to be going overboard. Answering those two
questions requires knowing a lot of detail about nuclear
processes. I don't know how to make an idealized/simplified
version of that question without throwing the baby out
with the bathwater.

4) Motion of charged particles in static electric and magnetic
fields offers numerous possibilities for discussing nuclear
topics, for example, Van de Graaff accelerator and mass
spectrometer.

OK.

Knowing how accurate atomic masses were
measured, and using the tabulated results, students may
apply the E=m*c^2 formula and calculate energies released
in fusion and fission. The solaced "solar energy" can then
be discussed in a more profound way.

Be careful here; a really profound discussion will start to
eat up class time, violating the spirit of these suggestions.

5) Radioactivity is always discussed in science courses.
This topic can be linked with the issue of the disposal of
radioactive waste. The nascent technology of transmutation
of radioactive waste, and its challenges, should be widely
disseminated among teachers and students.

Discussion of this or any other _nascent_ technology would
require discussing the pros and cons, which will eat up class
time.

6) Visits to power plants, preferably first traditional
and then nuclear, should be organized at the end of an
introductory science course, if practically possible.

==========================================================

Tangential but important note:

Ludwik makes some important points here about how to handle
the depth versus breadth issue. Students need a certain
amount of breadth. But breadth that is nowhere deep is
not right. The diagram I have in mind is this:

bbbbbbbbbdbdbdbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
bbbbbbbbbdbdbdbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
ddddd
ddddd
ddddd
ddddd
ddddd
ddddd
ddddd
ddddd

where breadth is indicated by "b" and depth (in one or
two topics) is indicated by "d".

This picture is the best possible outcome for a course.
The breadth of background is there ... and the students
see what is involved in thinking deeply about some topic.
In later life, they can do their own deep thinking about
topics that weren't deeply covered in class.

So this is an argument for having a "theme" to the course.
Ludwik is specifically suggesting a nuclear theme, but
that isn't the only choice. You could have a biophysics
theme, or an aerospace transportation theme, or whatever.