The process of nuclear fission

Natural uranium is composed of two different isotopes 99.3% is uranium-238, the nucleus of which contains 238 nucleons, comprising 92 protons and 146 neutrons, while the other 0.7% is made up of uranium-235, which contains 235 nucleons, comprising 92 protons and 143 neutrons. Being positively charged, all the protons in the nucleus exert a repulsive electrostatic 

About 2.4 neutrons on average are produced per fission inside a thermal nuclear reactor. Of these, about 

2 will be lost by absorption into non-fissile nuclei present in the core, namely those of the majority uranium-238 isotope and those of the control rods and of structural materials. A further small number will be absorbed by uranium-235 nuclei without causing fission. The chain reaction will be maintained, however, provided one of the 2.4 neutrons produced goes on to split a uranium-235 nucleus. 

The loss of neutrons to non-fissile absorption represents a significant problem for the reactor designer, particularly near the end of the reactor run, when the fuel is starting to become used up. While very careful attention to neutron economy may allow a reactor to be designed to run on natural uranium (e.g. the UK s Magnox and Canada s CANDU reactors), most commercial reactors use enriched uranium as the fuel. 

---

The process of nuclear fission was discovered more than half a century ago in 1938 by Lise Meitner (1878-1968) and Otto Hahn (1879-1968) in Germany. With the outbreak of World War II a year later, interest focused on the enormous amount of energy released in the process. At Los Alamos, in the mountains of New Mexico, a group of scientists led by J. Robert Oppenheimer (1904-1967) worked feverishly to produce the fission, or atomic, bomb. Many of the members of this group were exiles from Nazi Germany. They were spurred on by the fear that Hitler would obtain the bomb first Their work led to the explosion of the first atomic bomb in the New Mexico desert at 5 30 a.m. on July 16,1945. Less than a month later (August 6,1945), the world learned of this new weapon when another bomb was exploded... 

FIG. 33-8. The process of nuclear fission (linear magnification about IQi-). 

Austrian chemist Lise Meitner. She discovered an isotope of protactinium and helped explain the process of nuclear fission. LIBRARY OF CONGRESS. 

Describe the processes of nuclear fission and fusion, and calculate the amounts of energy released when they occur (Sections 19.5 and 19.6, Problems 37-47). 

Nuclear reactors produce nearly a fifth of the world s electricity, and so must now be accounted a common unit process in the power generation industry. Chapter 21 explains the process of nuclear fission and... 

On any list of scientists who should have won a Nobel Prize but did not, Lise Meitner s name would be near the top. She was the physicist who first realized that the atomic nucleus could be split to form pairs of other atomic nuclei—the process of nuclear fission. Although she received many honors for her work, the greatest of all was to elude her because of the unprofessional conduct of her colleague Otto Hahn. 

The Process of Nuclear Fission 786 The Promise of Nuclear Fusion 789 CHAPTER REVIEW GUIDE 790 PROBLEMS 792... 

LEARNING GOAL Describe the processes of nuclear fission and fusion. 

Nuclear reactors Nuclear power plants use the process of nuclear fission to produce heat in nuclear reactors. The heat is used to generate steam, which is then used to drive turbines that produce electricity. Fissionable uranium(IV) oxide (UO2) is commonly used as fuel in nuclear reactors. Cadmium and boron are used to keep the fission process under control. Continual adjustments are needed to keep the reaction going and under control. 

FRISCH, ROBERT OTTO (1904-1979). Austrian-born physicist. Frisch made several fundamental contributions to nuclear physics, especially to the development of nuclear weapons. In 1939, Frisch and his aunt, Lise Meitner, provided the first mathematical explanation for the results of Otto Hahn and Fritz Strassmann and correctly identified that these results confirmed the process of nuclear fission, a term chosen by Frisch himself. 

MEITNER, LISE (1878-1968). Austrian-bom physicist. With her nephew Robert Otto Frisch, Meitner was the first to provide a mathematical explanation for the results of Otto Hahn and Fritz Strass-mann and correctly identify that these results confirmed the process of nuclear fission. Meitner s private communication of their findings to Niels Bohr in December 1938 spurred U.S. development of a nuclear weapon. 

---