CHAPTER 6: Nuclear Processes

By the end of this chapter, you will be able to:

understand the processes of nuclear fission and fusion and the associated energy changes.

understand the spontaneous and random nature of nuclear decay and interpret decay data in terms of half-life.

know the applications of radioactivity and the dangers associated with exposure to radioactive materials.

understand and appreciate that there are significant social, political and environmental dimensions associated with use of nuclear power

Keywords

1. decay
2. fission
3. fusion half-life
4. nuclear power
5. radioactivity

6.1: Introduction

In Chapter 5, you learnt that everything on Earth is made up of atoms. However, have you ever asked yourself why everything on Earth is not the same? This is because different objects are made up of different combinations of the atoms. You must have realised that the atoms themselves are made up of different amounts the behaviour of all forms of matter. Some of these smaller particles are found in of smaller units called sub-atomic particles.

These are the ones that determine the nucleus of the atom (i.e protons and neutrons). But, do these atoms remain permanently in the same form or they do change with time? If they change, how do they change? What are the products of such changes? In this chapter, you will be able to understand the changes that occur in the nucleus of atoms and the implications of the nuclear changes to mankind.

6.2: Radioactivity

Many significant activities in nature take place around us and are unnoticed. Emission and absorption are some of the phenomena that go unnoticed when it takes place in the atom. Radioactivity is one such property of the matter where the emission of energetic sub-atomic particles takes place spontaneously. In this concept, let us learn more about radioactivity. Some isotopes are unstable – what do you think makes them unstable? As a result, these isotopes will decay in order to reduce their size or become more stable. Therefore, radioactivity is the spontaneous disintegration/splitting of an unstable nucleus of an atom in order to become stable. This is often accompanied with the release of energy.

DID YOU KNOW?

Did you know that the word spontaneous means “uncontrolled” and that disintegration means “separation”?

Activity 6.1 Investigating radioactivity using a 6 sided dice

Key question:

Describe how you can demonstrate radioactivity.

What you need

50 pieces of 6-sided dice.

A small paper bag to put the dice.

Figure 6.1: Small paper bag

Spacious flat working place

What to do

1. Place all the 6-sided dice in the paper bag.

2. Shake them inside the paper bag to ensure they are properly mixed.

3. Pour them on the flat surface making sure none is on top of the other.

4. Count all the dice where the side with number 6 is facing upwards.

5. Remove them and return the remaining dice into the paper bag.

6. Comment on the possibility of attaining a side with number six.

7. How is your comment related to radioactivity?

6.2.1: Products of a Radioactive Decay

When unstable nucleus of an atom disintegrate/decay, the following are possible kinds of decay that take place:

gamma decay (photons having high energy are emitted). ‘

beta decay (emission consists of electrons).

alpha decay (emission consists of helium nucleus).

6.2.1.1 Alpha, α, Decay

During alpha decay, the unstable parent atomic nuclei emits a helium nucleus (alpha particle). The new nucleus resulting from the decay is called the daughter nuclei. The transformation of a nucleus in an alpha decay can be written as follows:

EXERCISE 6.1

If the under-listed nuclides undergo alpha decay, write down the decay equations and identify the daughter nuclides.

HINT: you may need a Periodic table.

1. Sodium-23

2. Cobalt-59

6.2.1.2 Beta, ẞ, Decay

During a beta decay, the unstable parent atomic nuclei emits an electron (beta particle). The transformation of a nucleus in an beta decay can be written as follows:

Activity 6.2 Investigating the characteristics of the radiactivity radiations

Key question:

Describe the characteristics of the radioactivity radiations.

What you need Internet resource Library resource

What to do (in groups)

1. Research on:

a) definitions of alpha particles beta particles and gamma rays.

b)characteristics of alpha particles, beta particles and gamma rays.

c) penetrating powers of alpha particles, beta particles and gamma rays.

2. Make a report about your findings and make a presentation to your class.

6.3: Half-life of a Radioactive Material

A block of radioactive material will contain many trillions of nuclei and not all nuclei are likely to decay at the same time since the decay is spontaneous. It is not possible to say which particular nucleus will decay next, but given that there are so many of them, it is possible to say that a certain number will decay in a certain time. Although scientists cannot tell when a particular nucleus will decay, using statistical methods, it is possible to tell when half the unstable nuclei in a sample will have decayed.

The Half-life of a radioactive material is the time it takes for half of the unstable nuclei in a sample to decay. The decay process is exponential and can be represented by the graph shown in Figure 6.2. Exponential decay means that the higher the number of undecayed nuclides in the sample, the greater the rate of decay of the sample.

Figure 6.2: A graph showing decay of a radioactive substance

6.3.1: Understanding the Decay Curve

Figure 6.3 shows how a radioactive sample is decaying over time.

Figure 6.3: A graph of activity against time for a radioactive substance

Figure 6.5 shows that from the start of timing, it takes two days for the decay activity to drop from 80 to 40. Since the decay activity has taken two days to drop from its initial value of 80 to half its value of 40, the radioactive material is said to have a half-life of two days. Again it takes another two days for the count rate to drop by half, this time from 40 to 20. Note that this second two days do not see the count rate drop to zero, only that it halfs again.

A third, two-day period from four days to six days sees the count rate halving again from 20 down to 10. This process continues and although the count rate might get very small, it does not drop to zero completely. EXAMPLE 6.3 Use the graph shown in Figure 6.4 to answer the questions that follow:

Figure 6.4: A graph of counts per minute against time

(i) What is the initial number of particles present before decay?

Solution

Initial number of particles is 80 counts per minute.

(ii) Estimate the half-life of the radioactive

Solution

Half-life is the time taken for the counts to fall to 40 counts per minute. Therefore, half-life is about 2 days. (ii) From the graph, how long does it take for the sample to decay to 10 counts per minute?

Solution

Time taken is 6 days.

6.4: Uses and Dangers of Radioactivity

The radiations emitted in a process of radioactivity can be used in many different fields. Such fields include medicine, agriculture, industry and security.

ASSIGNMENT 6.1

1. Search on the internet or otherwise for information on how radioactive substances are useful in medicine, Industry, agriculture and security. Write down your findings. 2. In which ways are the radiations harmful to mankind? 3. What precautions can a person take to avoid suffering from the dangers of exposure to the radiations?

6.5: Nuclear Fission and Fusion

Nuclear fission refers to the splitting of a large nucleus to produce two or more smaller nuclei with subsequent release of energy.

Activity 6.3 Investigating about nuclear fusion and fission

Key question: Describe nuclear fusion and fission.

What you need

Internet resource

Library resource

What to do (in groups)

1. Using the relevant resources, make a research on:

a) Nuclear fission

b) Nuclear fusion

c) Conditions for nuclear fusion and fission to occur

d) Uses of the nuclear reactions e) Differences between nuclear fusion and fission.
2. Make a report about your findings and make a presentation to your class.

6.6: Nuclear Energy

Nuclear energy originates from the splitting of the nucleus of atoms in a process called nuclear fission. Nuclear energy provides efficient and reliable electricity around the world. Today many developed countries use this energy. Nuclear energy has one of the lowest environmental impacts on land and natural resources of any electricity source. Thus, nuclear energy is a renewable energy source like hydropower, wind energy, solar power and bio-fuels among others.

ASSIGNMENT 6.2

1. Search on the internet and report on how nuclear energy is related to other

2. Also, compare the advantages and disadvantages of nuclear energy and other sources of energy.

6.7: Nuclear Reactors

DID YOU KNOW?

Did you know that a nuclear reactor is a device in which controlled nuclear chain reactions are generated to release large amounts of steady heat, thereby producing energy?

6.7.1: How a Nuclear Reactor Works

In a nuclear reactor, the nuclear chain reactions produce the heat, which turns water into steam. The pressure of the steam turns the turbines connected to an electro-magnet in a generator, which ends up producing electricity. In thermal power plants, the fossil fuels burn coal, oil or natural gas to generate heat. In a nuclear energy plant, heat is produced by a chain reaction of nuclear fissions. The schematic diagram, showing how nuclear energy is generated is shown in Figure 6.5.

Figure 6.5: A schematic diagram showing how nuclear energy is generated

6.7.2: Social, Political and Environmental Issues Associated With Use of Nuclear Power

DID YOU KNOW?

Did you know that the development of nuclear technology can be a threat to world peace? Cite any two countries that have developed such conflict in the recent past.

Nuclear energy fulfils three of the main fuels represent the cheapest sources of energy however they are process of energy demand all around the world. Whereas fossil objectives that should be pursued for a steady development:

(i) It does not emit Greenhouse gases.

(ii) It is the cheapest produced energy

(iii) It guarantees a security in its supply due to the fact that it is not conditioned by external factors.

6.7.3 Nuclear and Radiation Accidents and Incidents

Did you know that the body that regulates the use of nuclear energy is called the International Atomic Energy Agency (IAEA)? IAEA defines nuclear and radiation accident as “a nuclear event that has led to significant consequences to people, the environment or the facility. Examples include; lethal effects to individuals. large radioactivity release to the environment, reactor core melt.

ASSIGNMENT 6.3

Search on the internet or otherwise and report on:

(i) Cases of nuclear and radiation accidents in the recent past.

(ii) The consequences of the nuclear and radiation accidents to the people and the environment.

Chapter Summary

In this chapter, you have learnt that: • radioactivity is the spontaneous disintegration of unstable nucleus of an atom by loss of energy to become stable.

when unstable nucleus of an atom disintegrate/decay, the following are possible kinds of decay that take place:

(i) gamma decay (photons having high energy are emitted).

(ii) beta decay (emission consists of electrons).

(iii) alpha decay (emission consists of helium nucleus).

the radiations emitted in a process of radioactivity can be used in different fields including, medicine, agriculture, industry and security.

• radioactive decay is a random process. half-life is the time it takes for half of the unstable nuclei in a sample to decay.’

nuclear fission is the splitting of a large nucleus to produce two smaller ones.

nuclear fusion is the joining together of two smaller atomic nuclei to produce a larger nucleus.