The methods for probing the reality of subatomic particles (slippery little devils as they are) began with experiments as simple as those with which the electron, proton and neutron were discovered – firing beams of light or electrons at various substances and then making very precise observations and drawing as many conclusions as possible.
The options were truly rather limited, but physicists such as Ernest Rutherford and Marie Curie showed great ingenuity around the turn of the century and beyond in these experiments and some incredible skills in logic could lead one to some truly profound conclusions about the atomic structure.
They did their best with what they had to work with.
Cosmic Rays
The next great step for particle detection came in 1912, when Austrian-American Physicist Victor Hess first carried detectors with him in a hot air balloon to a height of some 5300 meters, where he made the initial discovery of the “cosmic rays” which shower Earth from all corners of outer space at unbelievably high speeds (he won the Nobel Prize for this discovery in 1936).
While the name itself might be somewhat of a misnomer (cosmic rays are actually streams of particles from outer space), the importance of this cosmic onslaught cannot be stressed enough. These particles, it was eventually realized, had begun their journeys to Earth from heavenly sources such as solar flares from our own sun or even from more distant places within the galaxy such as the remnants of supernovas or the nuclear output of distant stars.
When these cosmic rays were first analyzed, it was realized that they were striking our atmosphere at remarkably high speeds, and in doing so, were likely to be creating all sorts of reactions as they collided with other particles (particularly in the upper atmosphere of Earth); reactions which physicists had not yet been able to create here on Earth in “primitive” experimental devices.
Thus began a mass exodus of excited experimenters into balloons and to the tops of mountains in order to better catch some of these cosmic rays and to analyze them as high into the atmosphere as possible, which seemed to be the best hope at the time for discovering the behavior of particles, as well as discovering new ones.
The First Accelerators
The second key to the boom in the process of particle physics, after the discovery of cosmic rays, was the invention of the very first particle accelerator, the “cyclotron,” in 1929 by Ernest O. Lawrence at the University of California, Berkley, which made performing these subatomic tests a lot simpler. No longer would physicists have to travel to the tops of mountains and up in dangerous balloons in order to perform experiments on the unpredictable cosmic rays.
Particle accelerators simulated cosmic rays by allowing physicists to simply fire a beam of particles at blazingly fast speeds, and then watch what happens when they collided with other particles inside a “detector” region.
These methods of detection originally consisted of “cloud chambers,” which operate, as the name implies, in a very similar way to how clouds and rain are formed in the Earth’s atmosphere. A liquid within the chamber is supercooled, so that the arrival of a particle will ionize the liquid, leaving a condensation trail which can be then studied. So while the particle itself remains absolutely invisible, its path can be traced and photographed.
The detectors used in more recent particle accelerators generally use the much more modern bubble chamber (invented in 1952 by Donald Glaser, who subsequently won a Nobel Prize) which utilizes an opposite principle. In a bubble chamber, a vessel is filled with a pure superheated liquid (that is, a liquid heated beyond its normal boiling point). In this state, the disruption of the liquid by any foreign particle is enough to cause a line of condensation, or “bubbles”.
Successes of Early Technology
These primitive (by modern standards) methods of particle detection paved the way for further leaps forward in science, and certainly became responsible for their share of discoveries along the way.
In simple cosmic ray experiments, for example, several brand new particles were discovered, such as the Muon (discovered by Carl Anderson in 1936) and the Pion (theorized by Hideki Yukawa in 1935 and discovered in 1947.
Cyclotrons, on the other hand, are still being used today – some for their unique abilities at examining further dimensions of nuclear physics, and some, believe it or not, to help treat cancer. Finely tuned ion beams from these machines have been frequently used to target and destroy cancerous tissue in patients. Chalk it up as another great success for particle acceleration.
As wonderful as these early techniques of discovery may have been, however, they pale in comparison to the next stages of particle acceleration.
References:
Asimov, I. (1966). Understanding Physics: 3 Volumes in 1. Barnes and Noble Books.
Carrigan, R. A., & Trower, W. P. (1989). Scientific American: Particle Physics in the Cosmos. New York, NY: Scientific American.
Clay, R., & Dawson, B. (1997). Cosmic Bullets - High Energy Particles in Astrophysics. Australia: Helix Books.
Lederman, L. (1993). The God Particle: If the Universe is the Answer, What is the Question? New York: Dell Publishing.
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