Proton: the particle.

The purpose of this article is to review briefly the nature of protons: creation at the Big Bang, abundance, physical characteristics, internal components, and life span. Several particle discoveries by proton as the experimental tool are considered. Protons play important roles in science, medicine, and industry. This article was prompted by my experience in the curative treatment of cancer patients by protons and my interest in the nature of protons as particles. The latter has been stimulated by many discussions with particle physicists and reading related books and journals. Protons in our universe number ≈10(80). Protons were created at 10(-6) -1 second after the Big Bang at ≈1.37 × 10(10) years beforethe present. Proton life span has been experimentally determined to be ≥10(34) years; that is, the age of the universe is 10(-24)th of the minimum life span of a proton. The abundance of the elements is hydrogen, ≈74%; helium, ≈24%; and heavier atoms, ≈2%. Accordingly, protons are the dominant baryonic subatomic particle in the universe because ≈87% are protons. They are in each atom in our universe and thus involved in virtually every activity of matter in the visible universe, including life on our planet. Protons were discovered in 1919. In 1968, they were determined to be composed of even smaller particles, principally quarks and gluons. Protons have been the experimental tool in the discoveries of quarks (charm, bottom, and top), bosons (W(+), W(-), Z(0), and Higgs), antiprotons, and antineutrons. Industrial applications of protons are numerous and important. Additionally, protons are well appreciated in medicine for their role in radiation oncology and in magnetic resonance imaging. Protons are the dominant baryonic subatomic particle in the visible universe, comprising ≈87% of the particle mass. They are present in each atom of our universe and thus a participant in every activity involving matter.

Jean Perrin and the triumph of the atomic doctrine.

One of the central dogmas of modern science is that the world around us can be understood in terms of microscopic chemical entities known as atoms. It may come as a surprise that this notion has only been widely acknowledged since the 1910s. The French physicist Jean Perrin had a hand in many of the key developments that led to the emergence of the atomic doctrine. His life story relates how new technologies were used to 'see' these invisible particles of philosophy and how scientists were able to determine their size and composition. The indivisible atoms of the ancients were replaced by the highly structured elements of chemistry.

The fourfold Democritus on the stage of early modern science.

The renewed success of ancient atomism in the seventeenth century has baffled historians not only because of the lack of empirical evidence in its favor but also because of the exotic heterogeneity of the models that were proposed under its name. This essay argues that one of the more intriguing reasons for the motley appearance of early modern atomism is that Democritus, with whose name this doctrine was most commonly associated, was a figure of similar incoherence. There existed in fact no fewer than four quite different Democriti of Abdera and as many literary traditions: the atomist, the "laughing philosopher," the moralizing anatomist, and the alchemist. Around the year 1600 the doctrines of these literary figures, three of whom had no tangible connection with atomism, began to merge into further hybrid personae, some of whom possessed notable scientific potential. This essay offers the story of how these Democriti contributed to the rise of incompatible "atomisms."

The contribution of the physical sciences to the development of radiation therapy.

Radiation therapy is used in the treatment of about half of all cancer patients in the United States. The development of this specialty has been intimately involved with major advances in the physical sciences, from the discovery of x-rays by Roentgen and radium by the Curies, to the technological breakthroughs of World War II that led to the 60cobalt teletherapy unit and the modern linear accelerator--the principal treatment machines in use today. These historical events are described and the principal characters introduced.