## Chapter Objectives and Summaries

### CHAPTER 28 Nuclear physics

LEARNING OBJECTIVES
Knowledge of subject matter
• Explain what is meant by 'atomic number, mass number, isotope, proton, neutron, positron neutrino, radio activity, alpha radiation, beta radiation, gamma radiation, nuclear bombardment, half life, artificial radioactivity, bonding energy, nuclear fission, breeder reactor, pair production, nuclear fusion, decay constant (l), background radiation.
• List the common features or properties of radioactivity elements.
• Describe various methods used to detect radioactivity.
• State the properties of alpha, beta and gamma radiation.
• State the safety precautions which must be observed when using radioactive sources.
• Explain what radioactive decay is. Write and interpret equations representing radioactive decay. Plot graphs showing radioactive decay. Formulas: A = DN/Dt = - l N
• Define the term 'halfñlife' and solve problems involving halfñlife: t1/2 = 0.693/l .
• Discuss the use of radioactive isotopes.
• Distinguish between nuclear fission and nuclear fusion. Give examples of each.
• Discuss the productions of energy by nuclear power stations and the use of nuclear weapons.
• Define the dose in terms of Gray (Gy) and Sievert (Sv).

SCIENTIFIC PROCESSES

• Identify application of nuclear energy.
• Model the structure of the nucleus from given data.
• Write decay equations.
• Plot A vs t and lnA vs t graphs; extrapolate, interpolate draw line of best fit and measure slope. Formulas: N = No.e-l t; N = No(1/2)n
• Critically analyse the importance of specific equipment in nuclear reactors.
• Identify measures essential for the safe handling or use of radioactivity.

COMPLEX REASONING PROCESSES

• Interpret graphs and data of nuclear binding energy verses atomic mass to predict the feasibility of fusion or fission reactions.
• Discuss the possibility of fusion reactors.
• Critically analyse the advantages and disadvantages of technology and society of the continued use of nuclear energy.

### CHAPTER 28 SUMMARY

• Any radiation which can remove an electron from an atom and create a heavy positive ion and free electron is termed an ionising radiation. Ionising radiations include electromagnetic radiation (gamma rays, X-rays, and ultraviolet radiation) as well as energetic particles such as alpha and beta.
• Radioactivity is the process whereby atoms emit particles or rays of high energy from their nuclei. It is also known as radioactive decay. The original unstable parent nucleus decays to form a daughter nucleus and at least one other particle.
• In balancing equations, the sum of the atomic mass numbers on the left of the equation must be the same as the sum of the atomic mass numbers on the right; the total charge on the left-hand side of the equation must equal the total charge on the right-hand side. The number of protons determines the name and symbol of the element.
• The force that binds the nucleons together is called the strong nuclear force.
• Radioactivity may be detected by photographic film, fluorescent screens, scintillation counters, electroscopes, spark counters, Geiger counters and cloud chambers.
• Three types of decay are associated with three unstable states of a nuclide: too many neutrons (beta decay); too many protons (positron decay); too many protons and neutrons (alpha decay).
• The half-life of a radioactive isotope is the time taken for half the radioactive atoms in a sample to decay.
• A chain of radioactive decays is called a decay series and it continues until a stable nuclide is formed. The rate at which a radioactive nuclide decays is called its activity (A). The unit for activity is becquerel (Bq) and it will decrease with time.
• In nuclear fusion, the parent nucleus combines with the colliding particle to form a single nucleus of higher mass. In nuclear fission, the parent nucleus is unstable and, on impact with a lighter nucleus or particle, fragments into lighter nuclei and other radiation.
• Mass and energy are not separate quantities; rather, they are different forms of one another. The equation relating the two is E = mc².
• A chain reaction is one in which the products of the reaction initiate further reactions. There are two types: controlled chain reactions in nuclear fission reactors and uncontrolled chain reactions in the nuclear bomb. The minimum mass required to sustain a chain reaction is called the critical mass.
• When high energy radiation passes through tissue, it produces ions and free radicals which disrupt a cell's normal operation. Ionisation is capable of splitting up chains of DNA which are responsible for the replication of cells. Cancer, radiation sickness and death may eventuate.
• Radiation that deposits one joule of energy per kilogram of tissue is called the absorbed dose. It has the units J kg-1 or one gray (Gy). The unit sievert (Sv) is a measure of the dose equivalent. The effective dose is obtained by summing the equivalent doses in all tissues and organs of the body weighted by their sensitivity to radiation.
• Radioisotopes are used for cancer treatment, food irradiation, imaging, wear measurements, power generation etc. Return to Objectives-Summary Menu Page page.