Nuclear reactions differ from conventional chemical processes in one crucial respect: the identities of the elements change in a nuclear reaction. Furthermore, nuclear processes frequently result in the release of massive amounts of energy, up to a billion times greater than that generated by chemical reactions. Similarly, changes in temperature, pressure, or the presence of a catalyst have little effect on the yields and rates of nuclear reactions. Isotope chemistry, radiochemistry, radiation chemistry, and nuclear reaction chemistry, and applications, are all included in nuclear chemistry. Radiochemistry is the study of radioactive materials, both natural and man-made, and their use in the research of chemical processes.