E.4 Fission: Practice Questions

In a nuclear fission reaction, a heavy nucleus splits into two lighter nuclei. Which of the following best explains why energy is released during this process?

Immediately after a heavy nucleus splits into two large fragments during fission, they accelerate away from each other. What is the primary source of the initial kinetic energy of these fragments?

Consider the fission of a heavy nucleus into two fragments. According to the Binding Energy per Nucleon curve, which statement best explains why this process releases energy?

Which of the following is a common byproduct of nuclear fission that poses a significant long-term disposal challenge due to its high radioactivity and long half-life?

Consider a fission reaction where a nucleus of \({}^{235}_{92}\text{U}\) absorbs a neutron and splits into \({}^{141}_{56}\text{Ba}\) and \({}^{92}_{36}\text{Kr}\). How many neutrons are typically released in this specific balanced reaction?

(a) A uranium-235 nucleus captures a slow-moving neutron and undergoes fission, producing xenon-140, strontium-94, and a number of neutrons. Write the balanced nuclear equation for this reaction and determine the number of neutrons produced.
(b) Calculate the energy released in this single fission event given the following masses:
\(m(\text{U-235}) = 235.0439\text{ u}\)
\(m(\text{Xe-140}) = 139.9216\text{ u}\)
\(m(\text{Sr-94}) = 93.9154\text{ u}\)
\(m(\text{neutron}) = 1.0087\text{ u}\)
(Assume \(1\text{ u} = 931.5\text{ MeV/c}^2\)).

In a nuclear power plant, uranium-235 undergoes controlled fission.
(a) Distinguish between a moderator and control rods in terms of their function and the materials used.
(b) A specific fission reaction is: \({}^{1}_{0}\text{n} + {}^{235}_{92}\text{U} \rightarrow {}^{141}_{56}\text{Ba} + {}^{92}_{36}\text{Kr} + 3{}^{1}_{0}\text{n}\). Calculate the energy released in this reaction given: \(m(\text{U-235}) = 235.0439\text{ u}\), \(m(\text{Ba-141}) = 140.9144\text{ u}\), \(m(\text{Kr-92}) = 91.9261\text{ u}\), and \(m(\text{n}) = 1.0087\text{ u}\).
(c) Explain what is meant by a critical mass in the context of a fission chain reaction.