Hydrogen

• The way in which protons were discovered was by understanding the fact that the nucleus of hydrogen was existent in the nuclei of other atoms. Hydrogen atoms contain only one proton in their nuclei and no neutrons (unless referring to deuterium or tritium, which are heavier forms of hydrogen). Obviously, finding the nucleus of hydrogen inside of other atoms suggests that there is a particle they have in common, which has been dubbed "proton," meaning "first" in Greek. The most interesting thing about hydrogen is that the element in its most basic form contains no electrons, simply making it a positively charged particle.
  
  

Protons Have Lifetimes

• Interestingly enough, protons live up to a certain point before they decay. The decay happens gradually through a period of more than 10^33 (10 to the 33rd power) years. Although the decay has never been observed, it is a known fact that protons only live so long before they die. When they die, they can become either pions (subatomic particles made of one quark and one anti-quark) or positrons (an antimatter counterpart of an electron).
  
  

Protons Can Become Neutrons

• It is known that a proton can become a neutron when a highly energetic proton collides with an atom's nucleus, causing an electron to leap out of the atom. Such a reaction is called "electron capture" and involves the loss of an electron (which later becomes a neutrino---a particle with barely any charge that sometimes travels at nearly the speed of light) and the transformation of the impacting proton into a neutron. This process may only happen if the proton is highly charged.
  
  

Antiprotons

• At the European Organization for Nuclear Research, antiprotons were studied and found to be stable, but quickly disappeared when they collided with protons. Antiprotons are protons that basically have a negative charge. In nature, such particles require a temperature of more than 10 trillion degrees Kelvin to form, which is a nearly impossible temperature to reproduce on Earth. Obviously, they had to be discovered by other means. In 1955, antiprotons were discovered at the University of California when Emilio Segrè and Owen Chamberlain shot highly energetic protons at copper. In fact, it was also later discovered that antiprotons had almost everything in common with protons, minus the fact that they were negatively charged.
  
  

Medical Use of Protons

• The use of protons has played an important role in "proton therapy," which is the practice of shooting protons at tissue that has been afflicted by a disease, such as cancer. The point of this therapy is to ruin the strands of DNA contained in the cells of the diseased tissue and ultimately destroy those cells. Since protons have a large mass, they became the perfect candidate for this therapy. The necessity of large particles is due to concerns of risks involved in accidentally bombarding unaffected tissue and effectively creating a new cancer while ridding the body of another. Protons are less likely to scatter inside tissue, making them effective particles for the therapy.