Physicists often seek very strong sources of radiation to improve the statistics of their measurements. In the case of the PAE experiment at Chalk River it had been decided that a “world beater” would result by using a very strong positron source. To accomplish this, the PAE apparatus was installed in the same building that housed our most powerful reactor, NRU.
It often happened that I did supplementary experiments because of my ignorance. In the PAE experiments there was a problem related to reproducibility of the results. This is a serious problem in experimental physics. If I hadn’t been a hayseed physicist I could have guessed the reason right off. Better physicists with an analytic bent cab eliminate useless paths that lead nowhere. On the other hand, such an analytic approach very seldom leads to anything new and I always hoped of find something new.
At that time my office was no longer a broom closet, but a rather comfy room at the end of a long building, next door to Dr. Kim’s. We often talked about physics, God, and life in that order. God arose as a subject because Soo’s father in North Korea had been a Presbyterian minister. Soo had escaped to south Korea under the floor boards of a fishing boat.
Another one of my forays into unknown waters was the two years or so I spent doing positron annihilation experiments (PAE) with Dr. Soo Kim. In these experiments positive electrons (positrons) are directed at targets where they interact with electrons and are annihilated to form two gamma rays of pure energy. This is a classic case where matter is converted into pure energy. In order to conserve momentum these gamma rays fly off in exactly opposite directions if the electron is in a vacuum. However, in solid matter embedded with electrons, there are interactions that depend on the electron movements at the instant of annihilation. From the angular deviation of the gamma rays, it is possible to determine many physical properties of electrons in matter.
Many years later I was doing an experiment at the ILL (Institute Laue-Langevin) laboratory in Grenoble, France when I overheard a couple of guys on the spectrometer next door talking about little old me. One of the guys was saying something like: You know that fellow next door is Martel, the guy who did many of the experiments that we had to read about for background information about the present measurements we’re making on liquid helium. The other guy said: That can’t be so because the guy next door is doing an experiment on crystalline adenine, one of the bases of DNA.
During his visit Dr. Woods asked Dr. Svensson and me to join him in his office to have a chat with Mossbauer. As usual I gave my tens cents worth, saying that I thought the origin of helium’s strange behavior below 2.1 K was due to Bose-Einstein condensation with all the atoms sitting in a zero energy state. There was a very long moment where silence filled the room. Finally Mossbauer said that he thought it was possible. To this day I do not know if he was trying to be kind or supportive of my conjecture. Anyway, the things that impressed me about the visit was Mossbauer’s young secretary, Miss Braun. She was a knockout. Obviously winning the Nobel has its privileges.
An interesting incident occurred during my “helium days”. The discoverer of the Mossbauer Effect (Rudolf Mossbauer) came to visit Dr. Woods. For his discovery of this effect in 1957, Mossbauer received the Nobel Prize soon after, in 1961. The effect occurs at low temperatures where Mossbauer found that solid crystal lattices as a whole could absorb the recoil of a gamma ray from any given atom. This meant that the emitted gamma rays could be very narrow and could be used in studies as wide-ranging as corrosion and verification of Einstein’s general theory relativity.
I was co-author on about a dozen papers dealing with various aspects of superfluid helium, a state of liquid helium that materializes at temperatures below 2.1 degrees Kelvin (-270.9 degrees Celsius). As noted earlier, at these low temperatures a lot of strange phenomena occur. Among other things superfluid helium has zero viscosity. As fate would have it neither of my usual co-authors was available when I had to complete and submit one of the most interesting papers in the series. Not quite realizing how important the paper was, I cavalierly listed P. Martel as the lead author. There were two other famous scientists on the masthead besides the usual trio. They were Roger Cowley and Varley Sears neither of whom I could hold a candle to. The article appeared in the Journal of Low Temperature Physics. I believe that made my co-authors a bit unhappy and my gambol through the fabulous jungle of superfluid helium soon drew to an end.
In another early series of measurements, I worked with Dave Woods and Eric Svensson on studies of superfluid helium. I wondered why Dr. Woods asked me to participate, until I found out that he had done studies on helium for his Ph.D. under Professor Hallett, who had also been my supervisor. Furthermore, the discovery of an important feature of the vibration response of superfluid helium—an energy minimum, had been made in 1960 by Dr. Woods and my first supervisor, Dr. Henshaw. As noted earlier, this feature captured the interest of the foremost theoreticians in the world, including Richard Feynman.
Our measurements on molybdenum-niobium alloys yielded more evidence of the so-called Kohn anomaly with values for the Fermi surface dimensions that were in agreement with other experiments. Furthermore, these measurements permitted us to measure shifts in the position of the Fermi Surface induced by alloying.