Write balanced nuclear equations for the following reactions and identify X

19.48 Why do heavy elements such as uranium undergo fission while light elements such as hydrogen and lithium undergo fusion?

19.49 How does a hydrogen bomb work?

19.50 What are the advantages of a fusion reactor over a fission reactor? What are the practical difficulties in operating a large-scale fusion reactor?

19.51 Describe how you would use a radioactive iodine isotope to demonstrate that the following process is in dynamic equilibrium:

19.52 Consider the following redox reaction:

When KIO₄ is added to a solution containing iodide ions labeled with radioactive iodine-128, all the radioactivity appears in I₂ and none in the ion. What can you deduce about the mechanism for the redox process?

19.71 Tritium contains one proton and two neutrons. There is no proton-proton repulsion present in the nucleus. Why, then, is tritium radioactive?

19.72 The carbon-14 decay rate of a sample obtained from a young tree is 0.260 disintegration per second per gram of the sample. Another wood sample prepared from an object recovered at an archaeological excavation gives a decay rate of 0.186 disintegration per second per gram of the sample. What is the age of the object?

19.73 The usefulness of radiocarbon dating is limited to objects no older than 50,000 yr. What percent of the carbon-14, originally present in the sample, remains after this period of time?

19.77 Calculate the energy released (in joules) from the following fusion reaction:

The atomic masses are , amu, , .

19.83 A person received an anonymous gift of a decorative box, which he placed on his desk. A few months later he became ill and died shortly afterward. After investigation, the cause of his death was linked to the box. The box was air-tight and had no toxic chemicals on it. What might have killed the man?

19.84 Identify two of the most abundant radioactive elements that exist on Earth. Explain why they are still present? (You may need to consult a handbook of chemistry.)

19.85 (a) Calculate the energy released when an U-238 isotope decays to Th-234. The atomic masses are given by: U-238: 238.0508 amu; Th-234: 234.0436 amu; He-4: 4.0026 amu. (b) The energy released in (a) is transformed into the kinetic energy of the recoiling Th-234 nucleus and the α particle. Which of the two will move away faster? Explain.

19.86 Cobalt-60 is an isotope used in diagnostic medicine and cancer treatment. It decays with γ ray emission. Calculate the wavelength of the radiation in nanometers if the energy of the γ ray is 2.4 × 10⁻¹³ J/photon.

19.87 Americium-241 is used in smoke detectors because it has a long half-life (458 yr) and its emitted α particles are energetic enough to ionize air molecules. Given the schematic diagram of a smoke detector, explain how it works.

19.88 The constituents of wine contain, among others, carbon, hydrogen, and oxygen atoms. A bottle of wine was sealed about 6 yr ago. To confirm its age, which of the isotopes would you choose in a radioactive dating study? The half-lives of the isotopes are: ¹³C: 5730 yr; ¹⁵O: 124 s; ³H: 12.5 yr. Assume that the activities of the isotopes were known at the time the bottle was sealed.

19.90 In 1997, a scientist at a nuclear research center in Russia placed a thin shell of copper on a sphere of highly enriched uranium-235. Suddenly, there was a huge burst of radiation, which turned the air blue. Three days later, the scientist died of radiation damage. Explain what caused the accident. (Hint: Copper is an effective metal for reflecting neutrons.)

19.91 A radioactive isotope of copper decays as follows: