What has this sort of research contributed to society?
	Dr. Yuasa's work on the structure of the atomic nucleus was research of the most basic sort. Basic research is not geared to immediate practical results but to building our understanding of nature's principles one piece at a time, step by step. In this way, scientists have come to understand all manner of phenomena, in our world and in the cosmos. Since Dr. Yuasa's time, radioactivity has come to play a key role in science and medicine. Since every radioactive substance decays into a certain substance at a fixed rate, we can calculate when it began to decay by measuring what portion of it remains in its radioactive state. In this way, we can draw conclusions about the age of the earth by estimating the amount of such radioactive elements as radium in the earth's crust. In the same way, we can tell when a plant died and stopped absorbing carbon from the atmosphere by measuring the quantity of carbon 14--a common radioactive isotope of carbon--that remains. Since the discovery of radioactivity, scientists have created a variety of isotopes, or radioactive versions of ordinary elements, that have important applications in bioresearch and medicine. For example, when sodium mixed with a small amount of a radioactive isotope is injected into an organism, it is possible to track the radiation from outside the organism to see exactly where the sodium goes. This technique is used for certain medical tests as well. Radioactivity is also used to treat cancer, either by exposing the cancerous tissue to radiation from the outside or by injecting isotopes into the body. However, since the energy emitted by the atomic nucleus can be extremely dangerous, great care must be taken whenever that energy is harnessed--be it in medicine or nuclear power generation--to protect people and other living things from its harmful effects. The energy of the sun is itself produced by a nuclear reaction known as fusion, in which four hydrogen nuclei (single protons) join to create helium. As the hydrogen dwindles, a new fusion reaction takes over, with three helium nuclei fusing to create carbon. In much the same way nitrogen and oxygen are created as well. Research in nuclear physics has given scientists insight into the evolution of stars and the nuclear reactions that created the elements that exist here on earth.