Up and Away and Cosmic Rays

Physicists in the current world of high energy and particle physics cast their collective gaze in the direction of CERN (European Organization for Nuclear Research) and the Large Hadron Collider (LHC). Owing to the Lofty duo’s well-documented interest in all things science—and to the fact that one of us, Doug, used to work at Fermilab, home to what was, formerly, the world’s most powerful particle accelerator, the Tevatron—we’re sure to be writing about the LHC and its discoveries as they unfold.

AMS-02 is lowered into Endeavour's payload bay on March 18, 2011

But first things first. Last week, the Alpha Magnetic Spectrometer (AMS-02) was delivered to the International Space Station by space shuttle Endeavour and her crew and is now offering an unparalleled view of the cosmos by virtue of its purchase 200 miles above the surface of the earth. This new science experiment reminds us that there was a time when, if you wanted to be at the cutting edge of probing the secrets of matter and the universe, you didn’t do it on earth. You used a balloon. Why do science in a balloon-basket? Roll back your memory to the tools and techniques of late 19th-century physics.

The electroscope, sometimes called an electrometer, is often the featured device in high school and freshman physics courses for demonstrating electric charge. 

Electroscopes played an important early role in the discovery and characterization of radioactivity when Ernest Rutherford (1908 Nobel Prize winner who did much early work on alpha and beta radiation) and Pierre and Marie Curie (Nobel Prize winners together in 1903 and for Marie in 1911 who did early work on the theory of radioactivity and isotopes) used the device to make measurements of the intensity of the radioactivity associated with various substances, in particular radium and its decay products, radon and polonium. (Search “radioactivity” here at Lofty Ambitions to see some other interesting takes on this topic.)

As Rutherford, the Curies, and other experimenters continued to use electroscopes in their experiments, they began to run into an odd effect: their electroscopes would continue to “leak” electrical charge, even when they weren’t being exposed to radioactive materials. Efforts to build more robust electroscopes, namely by adding thick lead shielding around the experimental apparatus, failed to completely prevent the leakage effect. Physical intuition convinced a number of scientists that a previously unknown form of radioactivity—and given its ability to pass through lead barriers, a very powerful one—was responsible for the leakage effect.

Stellar Evolution

A natural assumption was that there was some form of radiation present in the earth that was responsible for the effect. Therefore, the next step in understanding radioactivity was to eliminate the effect of earth-based radioactivity by getting off of the ground. In 1910, Jesuit priest Father Thomas Wulf did just that by hauling an electroscope to the upper levels of the Eiffel Tower (he went up approximately 900 feet). In one of those lovely curious moments that litter the scientific record, Wulf discovered that the leakage effect in his electroscope was nearly as great as was predicted by theory. From this result, he inferred that, in addition to earth-based radioactivity, there must also be a source in the heavens as well.

Other physicists took up the challenge posed by Wulf’s results, and the only recourse that presented itself was to go every higher. So, in the years1911-1913, Austrian-born physicist Victor Hess loaded a balloon gondola full of electroscopes and hopped in with what must have been a amazing spirit of adventure. Hess’s experiments soared ever higher, culminating with measurements made at 17,500 feet. His characterization of the intensity of ionizing radiation at various altitudes gave the first proof that, after reaching a minimum at about 5000 feet, ionizing radiation levels continued to climb dramatically, thereby demonstrating the extraterrestrial origin of the rays.

Many other scientists were deeply involved in this research area, too. In fact, it would be American Robert Millikan of the Nobel Prize-winning oil-drop experiment who gave this radiation its name: cosmic rays.

But ballooner Hess would be honored with the discovery of cosmic rays, and in 1936, he was awarded the Nobel Prize in Physics for his high-flying work.

The spirit of Victor Hess and the other researchers who performed early cosmic ray experiments lives on in the AMS-02 that is now orbiting our planet. Those scientists of yore sought to escape as much of the earth’s atmosphere as they could to perform their work. Today, the AMS-02 has done them one better by leaving the earth’s atmosphere to bask in the cosmic rays.


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