USES OF RADIONUCLIDES●In general, the early part of an exponential plot is straight (linear). The decay of
the radionuclide of intermediate half-life (^13153 I) is small during the 5 days, and its
plot remains in the straight part of the exponential curve.405Half-life 2
(i)iIn nature, uranium atoms consist of approximately 0.7% uranium-235 and the rest uranium-- From Table 21.2, explain why the percentage of uranium-235 was much higher than
this millions of years ago.
(ii)^20187 Fr decays by alpha emission, with a half-life of 0.0048 s.^23190 Th decays by beta
emission, with a half-life of 25 h. (a)Write equations showing the decay of Fr and Th. What
elements are produced in the decay of francium and thorium, respectively? (b)Suppose
that a mixture contains 0.0100 g of^20187 Fr and 0.0100 g of^23190 Th. How much of each
radionuclide will be left after 100 h?
Exercise 21F
Uses of radionuclides
- Nuclear fission of uranium-235
Natural uranium contains about 99.3%^23892 U and 0.7%^23592 U, usually in the form of
uranium oxide (UO 2 ). Purified uranium oxide is used as the ‘fuel’ for most types of
nuclear reactor, with the percentage of the^23592 U artificially raised (enriched) to 2–3%
in order to achieve sufficient fission.
Nuclear fission involves the splitting of the nucleus into two nuclei of roughly
equal mass. Uranium-235 and uranium-238 naturally undergo a type of fission
(known as spontaneous fission) in which the uranium nucleus, without assistance,
breaks up into two nuclei and produces a neutron, but this process is incredibly slow
- even slower than the radioactive decay of these radioisotopes by alpha emission.
Neutrons may be absorbed by uranium-235 nuclei in a process called induced
nuclear fission, commonly simply referred to as nuclear fission. (Initially, the
21.5
Nuclear fission provides about 20% of the electricity
generated within the UK. Economic worries about
the decommissioning of old nuclear stations, and
major accidents in Windscale UK (1957), Three Mile
Island USA (1979) and Chernobyl Ukraine (1986)
have caused many people to question whether or
not more nuclear plants should be built. This is a
photograph of the fourth reactor at the Chernobyl
nuclear power plant where an explosion resulted in
the world’s worst nuclear accident.