Friday, July 10, 2009

Helping Teach Teachers Teach Physics

Over the past few years while working with high school teachers at Fermilab, and also watching my kids go through physics classes at their own high schools, I found that too often kids were being taught "which equations to use when", rather than the principles behind those equations. I remember one teacher was having my stepson's class recite three mnemonics that would help them to remember which equation to use when faced with a problem regarding two-body problems where the bodies traveled in a straight line. One equation was for when the two bodies were both initially in motion. One equation was for when one of the bodies was initially at rest. And the third equation was for when the two bodies "stuck together" after the collision. My son was having trouble remembering "which" to use "when".

I tried to teach my son that there was really only one equation that needed remembering -- the momentum before the collision was equal to the momentum after the collision. Then, you just have to modify this statement to illustrate the problem at hand, and solve it algebraically. He liked that approach, but when he tried it on a quiz he got the problem wrong because he didn't "use the right equation; remember the mnemonics!!!" He never really liked physics, and didn't do too well; but then I found out that the teacher was a well-qualified biology teacher who recently was assigned to teach physics, a subject that she had taken, once, many years ago...

This, of course, is a situation found all over the country. Teachers are "teaching" physics because they had a course in it during college, or ... perhaps not. The fact that they are a science or math teacher, or maybe just had a math course, often means that they are qualified to teach physics to high school seniors contemplating college and their future careers. It's true, I believe, that a smart, motivated kid will find ways to learn what he or she wants to learn, but a really qualified teacher showing the excitement of physics and its usefulness in everyday life, especially the true underlying meaning of all of those "problems" kids are asked to solve should not be substituted by rote memorization of frivolous (to the students if not to the teacher) phrases.

Certainly a great part of the blame in all this lies in the fact that teaching for a while now has no longer been seen as a respectable career, and those who are actually good at it and can do well at it are enticed to move on to "more meaningful" work, like making money for a corporation. If a person knows enough physics to really teach it well to high school students, then they know enough to work for a company or lab, where they can receive salaries 2-3 times or more than a teacher's salary, and receive benefits that cannot be found in the teaching sector (including education reimbursement -- remember, teachers need more education to move up the scale!). They may feel motivated right out of college to go ahead and teach "for the better good," but such science teachers quickly burn out as they see their college friends moving quickly ahead (whatever that means) in life.

This is not something that can be changed overnight. Even though the present presidential administration recognizes the need for stronger educational practices, and stronger scientific education in the country, one cannot just lay off all the unqualified teachers and replace them with new "qualified" teachers. Firstly, the teachers we have today -- though some may not know the subject they teach as well as they would like -- still may have many years of experience in the classroom which is vitally important to any successful program and which the "new" teachers won't immediately have. Secondly, there aren't enough "new" teachers who are trained, readily equipped and who have the desire to change their present careers and go into teaching for such an overhaul to happen over night.

Present teachers, those who are willing to learn and adapt and wish to provide the best education to the students, should be provided special training to better prepare them to teach in the modern physics classroom. There are physicists in this country (one immediately comes to mind) that would truly enjoy spending part of their time for, say, a semester or two, re-teaching high school physics to high school teachers who will potentially need to teach physics. That is, have the scientist show the teachers how THEY would get the points across to students; show them how to use the equipment they find lying around in the back room of the high school science department. Show them how to teach using their own self-made apparatus when the back room doesn't have any equipment lying around! Show the teachers how they, the scientists, approach solving problems (at the high school level). I think the results would be very surprising. Most physicists don't simply recall a mnemonic device that helps them remember which equation to use -- they solve problems like puzzles, starting from basic principles and applying logic. One of the reasons I did so well in physics was that I didn't have to memorize as much as I would have had to in other subjects. (Biology comes to mind...)

Most scientists that I know tell me that there was a teacher or two in their early years that greatly influenced them, their thinking, and their desire to become scientists. If present-day teachers could hear from some of these scientists to learn what sparked them at age 16, then this could be a wealth of information for the teachers to use in their classrooms.

Next time, I'd like to discuss how one can use "everyday" software to use a computer to solve seemingly complicated physics problems using high school physics. I'll ultimately share a problem that I had to work out as a senior in college. How would that possibly be of interest at the high school level? Well, in my college days, computers were main frames that took up entire basements of physics and math buildings, typing out "punch cards" and feeding them into a card reader; I had to use one to solve this problem (actually, part of this problem -- the part I will share next time). Today, kids play video games in THEIR basements on computers that have 100,000 times the power of the one I used in the 1970's. But, while they use the computers as game devices, they don't often realize that they can program the computer themselves to solve problems like calculating trajectories to send a space probe to Mars, or simulating the motion of stars near the center of the galaxy. It's all just Newton's laws, which they learn in high school, and they have all they power they need to "solve the problem -- no mnemonics required!"

Friday, July 3, 2009

Angels and Demons

Even though the movie has been out for a while now, I still receive questions from visitors to Fermilab about our production of antimatter, and whether there is any "validity" in the premise that a "bomb" could be produced using our supply, or the supply that the movie suggests will be generated by the LHC at CERN.

Besides the slight change in the ending (the movie's ending is much better than that in the book!), it was great to see some actual views of CERN and the LHC tunnel in the movie "Angels and Demons". One has to realize that the "control" of the accelerator is not underground nor just outside of the detector, but rather several kilometers away in an above-ground building. And the accelerator operators don't wear lab coats. And... But, the film has enough going for it to make it interesting. What's also interesting, which most people know by now, is that (a) the LHC at CERN will not be used to make antimatter, except as a result of individual particle collisions in the experiments, and (b) even if it were optimized to make antiparticles at an appreciable rate, it would take far too long to get the amount presented in the movie.

Let's make a simple calculation, using the highest antimatter production going on in the world today, the Fermilab Antiproton Source. At Fermilab, beams of protons are accelerated within several stages of accelerators to a final energy of 120 GeV per proton -- that means that each proton is accelerated through a net voltage of 120 Billion volts. The beam of protons is focused and sent into a target made of a Nickel alloy, where the energy of the collisions of the protons with the nuclei of the target is high enough that new particles can be created (E = mc^2). Any particles with a negative charge, and with a momentum of 8.9 GeV/c are collected in a storage ring that is made up of electromagnets and tuned to operate for that particular momentum. Many of those particles, like pions and kaons, etc., will very quickly decay away -- however, stable particles -- like antiprotons -- will remain forever (as far as we know) and can be collected in the ring. In the Fermilab facility, about 20 antiprotons with this particular momentum are collected for every one million (10^6) protons that hit the target.

Now, the facility can produce about 8 trillion (8 x 10^12) protons each with 120 GeV energy every 2.2 seconds to send to the target. That means that 8 x 10^12 x 20/10^6 = 160 x 10^6 antiprotons are produced every 2.2 sec. OR, 0.16 x 10^9 /2.2 s x 3600 s / hr = 26 x 10^10 antiprotons every hour (260 billion/hr).

Thus, if the facility ran non-stop (present conditions generate an effective "up-time" of about 70% throughout a typical year), for 1 billion years, then roughly 26 x 10^10 /hr x 24 hr/day x 365.24 days/ year x 10^9 (1 billion) years x 0.70 = 1.6 x 10^24 antiprotons would be generated.

Coincidentally, the mass of an antiproton is the same as the mass of a proton: 1.6 x 10^-24 gram. Thus, in a BILLION YEARS of running, we could produce *** 1 gram *** of antimatter!

OK, so the 1/4 gram of antimatter that goes "missing" in the movie would only take 250,000,000 years to generate...

"Yes, but couldn't we upgrade the Fermilab accelerator to do better?"

Indeed, if the targeting stations were upgraded, and we could use the full power of the "Main Injector" accelerator (which operates at 120 GeV/proton), then one could imagine 4 x 10^13 every 1.5 seconds at best -- a rate that would be 40/8 x 2.2/1.5 = 7 times better. THUS, it could generate 1/4 gram in "only" about 36 million years!

The other question often asked is, "Isn't the LHC much higher energy? So couldn't it make antimatter that much faster?"

First of all, the LHC can't ramp up and down in 2.2 seconds or anything close to that. It takes many minutes for the accelerator to reach full energy. So, even if it does have over 50 times the energy of the Fermilab Main Injector (it will contain, ultimately, roughly the same number of particles), it takes about 500 times longer to ramp up and down to its final energy. So, the "rate" that it could produce antiprotons is far less than what would be done at Fermlab's machine.

- - -

It's still cool that antimatter exists at all. And, that most of the antimatter produced and accumulated for scientific use in the world so far has been produced right outside of Chicago...

Aerial view of part of the Fermilab accelerator complex. The "oval"-shaped accelerator at the top is the Main Injector, which typically operates at 120 GeV per proton. The small "triangular" arrangement of buildings near the bottom house equipment for the Antiproton Source, located about 20 feet below the surface.