Module E.4 IBDP SL/HL Track

Fission

Analyze mass defect metrics, nuclear binding energy shifts, and neutron-induced chains.

01. Observe 02. Think 03. Apply 04. Achieve Excellence

Fission

Introduction

Nuclear fission releases energy when heavy nuclei split into more stable fragments. The guide connects nuclear energy release to chain reactions, reactor control systems, shielding, and waste management.

Guide Focus

  • Explain spontaneous and neutron-induced fission.
  • Describe chain reactions and reactor components.
  • Calculate energy released from mass defect or binding energy changes.

Key Concepts

1. Energy release

Energy is released in fission because the products have a greater total binding energy per nucleon than the original heavy nucleus. The energy appears as kinetic energy of fragments, radiation, and energy of emitted neutrons.

2. Chain reactions

A neutron-induced fission event can release more neutrons, which may trigger further fissions. A sustained chain reaction requires enough neutrons to continue the process.

3. Reactor components

Control rods absorb neutrons, moderators slow neutrons, heat exchangers transfer thermal energy, and shielding absorbs harmful radiation.

4. Fission products and waste

Fission products are often radioactive. Management requires containment, shielding, cooling, and long-term storage decisions.

Common Mistakes

  • Thinking the moderator absorbs most neutrons; that is the role of control rods.
  • Ignoring the energy carried by emitted neutrons and gamma radiation.
  • Discussing fission waste without considering half-life and activity.

Exam Tips

  • Use E = mc^2 when mass defect is given.
  • Use binding energy per nucleon curves to explain why heavy nuclei can release energy by splitting.
  • For reactor descriptions, connect each component to its physical purpose.

Practice Questions

Question 1 (Multiple Choice)

In a nuclear reactor, the main purpose of control rods is to:

A. Absorb neutrons. B. Slow neutrons. C. Transfer thermal energy. D. Contain steam.

Correct Answer: A

Solution Architecture

Control rods absorb neutrons and regulate the chain reaction rate.

Question 2 (Structured Paper 2 Style)

A fission reaction has a mass defect of 3.2 x 10^-28 kg.

(a) Calculate the energy released. [2 marks]

(b) State where this energy appears initially. [1 mark]

Paper 2 Structured Problem

Markscheme Breakdown

Part (a) Solution:

E = mc^2 = 3.2 x 10^-28 x (3.00 x 10^8)^2 = 2.9 x 10^-11 J.

Part (b) Solution:

It appears mainly as kinetic energy of fission fragments and emitted particles, plus radiation.