Skip to main content

Leak Detector Down but Not Out, Code Crusher Code Objectified! Lab Book 2014_07_29

Alternate Title:  How Could Something So Pretty be So Broken?

It finally became too cumbersome to work with the can crusher simulation code in script form.  the bulk of this morning was spent in meetings and reworking the can crusher code to be object oriented.  The object oriented refactoring was completed and tested and works great!  It’s now very easy to run multiple simulations and compare their results.  The next step is to write code that runs the simulation to the peak current point and then plots the magnet field in on a spherical surface that will correspond to the surface of the superconductor Pb sample being used.  There are other simulations that need to be done as well.  For example, finding out how the current traces change when the temperature of the material is 4.2 K, the temperature of liquid helium.

The leak detector problem has been isolated.  The Pirani gauge that measures the vacuum on the diffusion pump side of the system has burned out.  Since it shows no vacuum in its burned out state, the diffusion pump is never turned on by the leak detectors control logic.  The Pirani gauge is literally a light bulb with the top cut off and its measured resistance varies as a function of the pressure of the air the bulb is immersed in.

Scroll down for background on the experiment.
Can Crusher Code
Moved the can crusher code implementation to object oriented from the Python script based version.  The code is now much easier to test with the ability to instantiate multiple simulations to compare results. 

Vacuum Leak Detector Work
The thermocouple gauge was attached directly to the gauge port on the liquid nitrogen trap.

The gauge that was is installed on the liquid nitrogen trap during normal operation is an Alcatel PI 1, see picture below.  This is a pirani sensor and may be the source of our problems.  For more information on the sensor, see  and

The bulb should have a cold resistance of 70 ohms.  Ours measures as an open circuit.  It seems the bulb is burned out.

Hirsch's theory of hole superconductivity proposes a new BCS-compatible model of Cooper pair formation when superconducting materials phase transition from their normal to their superconducting state[1].  One of the experimentally verifiable predictions of his theory is that when a superconductor rapidly transitions, (quenches), back to its normal state, it will emit x-rays, (colloquially referred to here as H-rays because it's Hirsch's theory).

A superconductor can be rapidly transitioned back to its normal state by placing it in a strong magnetic field.  My experiment will look for H-rays emitted by both a Pb and a YBCO superconductor when it is quenched by a strong magnetic field.
This series of articles chronicles both the experimental lab work and the theory work that’s going into completing the experiment.

The lab book entries in this series detail the preparation and execution of this experiment… mostly.  I also have a few theory projects involving special relativity and quantum field theory.  Occasionally, they appear in these pages.

Call for Input
If you have any ideas, questions, or comments, they're very welcome!


1.  Hirsch, J. E., “Pair production and ionizing radiation from superconductors”, 


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…