Skip to main content

More Quantum Coincidences, the Sudden Approximation and Reading Journals

As I started into work this morning, I had an email announcing a symposium next Monday on symmetry groups and physics.  From the meeting announcement

It is often stated that the set of symmetry operators that leave a Hamiltonian invariant forms a group.

I noticed that the presenter was Dr. Ed Brown, from Rensselaer Polytechnic Institute and immediately remembered... well, it's the tail end of finals week here... remembered.... that I was supposed to remember somebody from that school.  A quick search through my stored articles over on Google Drive pulled up only one article that mentioned Rensselaer.  Strangely that article didn't mention Rensselaer at all, but was titled "Symmetry Groups in Physics"[1].

Sweet!  I now have my background reading material for next weeks symposium!  Rather be lucky than smart!

It turned out that the author of the paper immediately following McVoy's was from Rensselaer.  So, I still didn't know what author from Rensselaer I had meant to write about later this week.  A little more searching though and I was there.  It was Levinger!  Why Levinger you ask?  Well, about a week and a half ago we were presented with the following homework problem:

Sudden excitations of Coulomb system. The nucleus of an ion has the charge Z. The ion has only one electron in the ground state. At the moment t = 0 the nucleus emits beta-electron, whose speed is so high that the orbital electron has not enough time to change its state. Calculate the probability of electron excitation from the ground state. How large must be velocity of beta-electron to justify this approach?
Which at first blush looked a bit horrendous   It turns out though that Levinger actually published the answer to the problem in the +American Physical Society's Physical Review article "Effects of Radioactive Disintegrations on Inner Electrons of the Atom"[2] circa 1953.

My first hiccup with the problem was in asking "What other states can the electron move into?  How will I sum them all up?"  Levinger circumvented the whole issue by just calculating the probability for the electron to stay where it was, in its original ground state, and then subtracting that result from one.  The answer is a good rough estimate of the probability the electron would move into any other state!  Normally I'd work through a few of the missing steps from the article and so on, but Levinger does such a great job, and so succinctly, that I won't even bother.  Here's the few paragraphs he had to offer on the subject

On Reading Journals
Upon arrival at grad school a few folks mentioned to me that I should try to keep up with some of the journals in my field although they admitted that would become an increasingly more daunting task as my workload grew.  Through liberal use of Google Scholar I've found almost exactly the opposite to be true.  By searching journals from the 1920's through the '50s and '60s, I've found several great references for my homework problems.  The articles are generally well written and quite frequently far easier to understand than the textbook sections on the same topics.  This makes sense.  The article's author is focused on the exact subject of interest and doesn't have to produce an entire textbook on a number of additional subjects.

I've had the best luck with the American Journal of Physics which is actually targeted at physics education so it, by nature, has a number of articles tailored towards course subjects.  Its only downfall in my opinion is that a number of the articles are actually overly complicated in what seems to be an attempt by the authors to be taken as impressive physics educators as opposed to impressive physics communicators.

Reviews of Modern Physics is a quarterly journal from the +American Physical Society that has 50 to 150 page review articles on various subjects.  Feynman's dissertation on QED wound up here.  It's a great resource becasue if the topic you're looking for is there, the author had plenty of room to fully explain their topic at their leisure.

Speaking of reading journals, I have one last thought.  I was reluctant to mention this while +Mendeley seemed like the fair haired child of the internet, but now that they've been purchased by Elsevier...  I'm curious if anyone is working on a Mendeley replacement killer app.  I had two huge gripes with Mendeley as it stood.  First, it wanted me to pay for cloud storage when my Google Drive solution was doing quite nicely.  Secondly, and more importantly, the 'social interaction' promised by Mendeley was a complete bust for me.  Basically, it boiled down to this.  If I already knew people interested in the same journal articles as myself, I could interact with them.  As far as finding other interested parties or students researching the same topics though, it was a bust.

It seems like someone could use the open source pdf parser built by Mozilla to parse journal articles and hook a system into Google Drive and Google+ and build a far better app pretty simply.  Is anybody aware of this happening yet?


1.  McVoy on symmetry groups
McVOY K. (1965). Symmetry Groups in Physics, Reviews of Modern Physics, 37 (1) 84-104. DOI:

2.  Levinger on the sudden approximation
Levinger J. (1953). Effects of Radioactive Disintegrations on Inner Electrons of the Atom, Physical Review, 90 (1) 11-25. DOI:


Popular posts from this blog

Cool Math Tricks: Deriving the Divergence, (Del or Nabla) into New (Cylindrical) Coordinate Systems

The following is a pretty lengthy procedure, but converting the divergence, (nabla, del) operator between coordinate systems comes up pretty often. While there are tables for converting between common coordinate systems, there seem to be fewer explanations of the procedure for deriving the conversion, so here goes!

What do we actually want?

To convert the Cartesian nabla

to the nabla for another coordinate system, say… cylindrical coordinates.

What we’ll need:

1. The Cartesian Nabla:

2. A set of equations relating the Cartesian coordinates to cylindrical coordinates:

3. A set of equations relating the Cartesian basis vectors to the basis vectors of the new coordinate system:

How to do it:

Use the chain rule for differentiation to convert the derivatives with respect to the Cartesian variables to derivatives with respect to the cylindrical variables.

The chain rule can be used to convert a differential operator in terms of one variable into a series of differential operators in terms of othe…

Lost Phone

We were incredibly lucky to have both been in university settings when our kids were born.  When No. 1 arrived, we were both still grad students.  Not long after No. 2 arrived, (about 10 days to be exact), mom-person defended her dissertation and gained the appellation prependage Dr. 

While there are lots of perks attendant to grad school, not the least of them phenomenal health insurance, that’s not the one that’s come to mind for me just now.  The one I’m most grateful for at the moment with respect to our kids was the opportunities for sheer independence.  Most days, we’d meet for lunch on the quad of whatever university we were hanging out at at the time, (physics research requires a bit of travel), to eat lunch.  During those lunches, the kids could crawl, toddle, or jog off into the distance.  There were no roads, and therefore no cars.  And, I realize now with a certain wistful bliss I had no knowledge of at the time, there were also very few people at hand that new what a baby…

Lab Book 2014_07_10 More NaI Characterization

Summary: Much more plunking around with the NaI detector and sources today.  A Pb shield was built to eliminate cosmic ray muons as well as potassium 40 radiation from the concreted building.  The spectra are much cleaner, but still don't have the count rates or distinctive peaks that are expected.
New to the experiment?  Scroll to the bottom to see background and get caught up.
Lab Book Threshold for the QVT is currently set at -1.49 volts.  Remember to divide this by 100 to get the actual threshold voltage. A new spectrum recording the lines of all three sources, Cs 137, Co 60, and Sr 90, was started at approximately 10:55. Took data for about an hour.
Started the Cs 137 only spectrum at about 11:55 AM

Here’s the no-source background from yesterday
In comparison, here’s the 3 source spectrum from this morning.

The three source spectrum shows peak structure not exhibited by the background alone. I forgot to take scope pictures of the Cs137 run. I do however, have the printout, and…