Nuclear Processes

Nuclear Processes

Introduction
Nuclear Chemistry is the study of the chemical and physical properties of elements which are influenced by changes in the structure of the atomic nucleus. By now, you already have an idea about nuclear structure; that the nucleus of an atom is composed of protons and neutrons. You may also recall that the number of protons in a nucleus of an atom of an element gives the atomic number of that element, and
the sum of the number of protons and the number of neutrons is the mass number. Protons and neutrons, collectively called nucleons, are packed together tightly in a very small nucleus. To hold the protons together in the very small volume of a nucleus, the strong nuclear force is required. This is because the positively charged protons repel each other so strongly at those short distances that the repulsion can lead to spontaneous decay of the nucleus, which would result into release of energy.
In this chapter, you will learn about the atomic structure and the nuclear processes by which energy is released.

6.1 Atomic Structure and Nuclear Reactions
Structure of an atom
In the following activity, you will draw and describe the structure of an atom:

Activity 6.1 (a) : Reviewing the structure and composition of an atom
Work in groups.
What to do

1. Discuss the three major sub-atomic particles.
2. Draw the structure of an atom, showing the location of the sub-atomic particles
   you have named in (7) above.
3. Copy and complete Table 6.7.
   Table 6.1: Composition of an atom

With a reason, state the region in an atom where the mass is concentrated.
4.Explain the following observations:
5.a) Atoms are electrically neutral, yet they contain charged particles.
b) Atoms of different elements adopt different atomic structures.

6. Natural boron occurs as 5B and 11B
   a) Which term is used to describe the two forms?
   b) What is the difference between them and sub-atomic particles?
   c) State the meaning of the term inuclide’.
7. Share your findings with the rest of the class.

Nuclear reactions
What is going on in the nucleus of an unstable, heavy atom?
Radioactive decay is the process by which unstable atomic nuclei emit sub-atomic particles and energy by (the general term) radiation, and disintegrate into one or more smaller nuclei. Radioactive decay is a nuclear reaction rather than chemical reaction, because it involves only the nuclei of atoms.
A nuclear reaction is a process in which two nuclei, or a nucleus and an external sub- atomic particle, collide to produce one or more new nuclides: the reaction products may contain a different element or a different isotope of the same element.

Radiation
The emission or transmission of energy in the form of waves or particles through space is called radiation. Sunlight is the commonest radiation. Nevertheless, there are those radiations which are invisible, and these include radio waves and television waves.
In Activity 6.7(b), you will research about radiations and find out about the different forms of radiations.

Activity 6.1 (b): Exploring the forms of radiations
Work in groups.
What you need:
Internet relevant Chemistry textbooks
What to do
flip charts

• marker pens

1. Research about the different forms of radiation.
2. State the ro erties of radiation under the following sub-headings.

Discussion and Conclusion
State the changes that occur to an atomic nucleus that emits each of the following radiations:
a) particle
b) ß particle
c) Y ray

Nuclear fission
Nuclear fission is a reaction in which the nucleus of an atom splits into two or more smaller nuclei.

The fission process is initiated by bombarding a heavy unstable nucleus by a slow- moving neutron, which results in a large amount of energy being released.

In Activity 6.7(c), you will find out more about nuclear fission process.

Activity 6.1 (c): Studying nuclear fission processes
Work in groups
What you need
. Internet

• relevant Chemistry textbooks
• support materials
  What to do
  flip charts
  . marker pens
  Manila paper
  Research about nuclear fission process over the Internet, or using any relevant
  science books in the library
  Discussion and Conclusion

1. Explain what a nuclear fission reaction is.
2. Describe how one nuclear fission process can cause another fission process.
3. What is the result of nuclear fission?
4. Which kind of atoms can undergo nuclear fission?
   As a group, prepare a report to present to the whole class, using Manila paper and marker pens.
   The first atomic bomb used in a war was made from a nuclear fission chain reaction. The bomb was detonated on 6th August, 1945 over
   Hiroshima. The second bomb was detonated over Nagasaki on 9th
   August, 1945, and the two bombings (both over Japanese cities) killed between
   129,000 and 226000 people, and remain the only use of nuclear weapons in
   armed conflict on record so far.

Nuclear fusion
Remember that two or more nuclei naturally repel each other because they are composed of the positively charged protons. In order to bring two nuclei together, a lot of energy must be supplied. If two nuclei are brought close enough, the repulsion between them will be overcome by the more powerful strong nuclear force (which only operates over short distances). If this happens, nuclear fusion takes place.
In Activity 6.7(d), you will find out about the meaning of nuclear fusion and how it takes place.

Discussion and Conclusion

1. Explain what nuclear fusion is.
2. Describe how a nuclear fusion process generates energy.
3. What is the result of nuclear fusion?
4. Which kind of atoms can undergo nuclear fusion?
   Advantages and disadvantages of nuclear reactions
   Nuclear radiations cannot be seen or smelt, but we are constantly being exposed to them everyday in different ways. Excess exposure to radioactivity can cause acute health effects.
   In Activity 6.7(e), you will debate on the use of nuclear reactions and its effects on humans.

Activity 6.1 (e): Finding out the advantages and disadvantages
of nuclear fusion and nuclear fission
Work in groups What you need
flip charts

• Internet
  relevant Chemistry textbooks
• marker pens
  What to do
  1.Research about the advantages and disadvantages of nuclear reactions.
  2.Conduct a debate under the motion “Nuclear processes are bad and should not be promoted in Uganda.”
  3.Discuss the precautions that should be taken while carrying out nuclear reactions.
  4.Make conclusions about the debate.

6.2 Radioactivity

Radioactivity is a spontaneous disintegration (breakdown) of unstable atomic nuclei, giving out radiation in form of rays and sub-atomic particles, plus a large amount of energy.
The unstable atomic nucleus gives up some energy in order to attain stability. The process is spontaneous (occurs on its own, without any energy input from
the outside) and so, is not influenced by external conditions like temperature and
pressure.
It is a random process, in that it is impossible to predict when a particular radioactive nucleus will decay.
The heavier atoms which disintegrate are said to be radioactive. Radioactivity is also known as radioactive decay, nuclear decay, nuclear disintegration or radioactive disintegration.
Natural and artificial radioactivity
Nuclear reactions which occur spontaneously are said to be an example of natural radioactivity.
The process of using radiation to make a previously stable material radioactivity, for example, by bombarding the material with high-speed sub-atomic particles, such as neutrons and protons, is called artificial radioactivity.
In Activity 6.2(a), you will research about the random and spontaneous nature of radioactive decay.

Activity 6.2(a): Understanding the spontaneous and random nature of radioactive decay
Work in groups
What you need
flip charts . Internet . marker pens

• relevant Chemistry textbooks
  What to do

1. Research about the spontaneous and random nature of radioactive decay. Write down your findings.
2. Compare random and spontaneous radioactive decay.
3. Prepare a summary of your findings and, then, present to the whole class.

Types of radioactive decay
There are several types of radioactive decay, including alpha (a), beta (ß), and gamma (y) decay. In all three types, nuclei emit radiations, but the nature of the radiations differ, as shown in Figure 6.3.

What to do
1.Carefully study the equation provided as the support tool.
2.Discuss as a pair and complete the equation. Write your response on the fli chart.
3.Identify the element Q which radium decays to.
4.Why do you consider the proton number and not the mass number, determining the new element formed?
5.Share your findings with the rest of the class.

Beta decay
A beta particle is a fast-moving electron. It has negligible mass and a charge of -1. When an atomic nucleus emits a beta particle, the atomic mass remains the same, the atomic number increases by 1.

The nuclear decay that involves emission of beta particles is called beta decay.
Beta particles have the following properties:

1. They are negatively charged. Each beta particle has a charge of -1 and negligible mass.
2. Beta particles are deflected towards the positive electric plate and are repelled by the negative plate.
3. Beta particles are deflected by a magnetic field.
4. The penetrating power of beta particles is moderate. They can be stopped by a block of wood.
5. Because of the low charge, beta particles have an average ionising power.
   In Activity 6.2(c), you will solve nuclear equations involving beta decay.

Activity 6.2(d): Solving equations involving gamma decay
In this activity, you will work in pairs to solve equations involving disintegration of
radioisotopes which emit gamma rays.
What you need:
flip chartS

• marker pens
  support tool (the nuclear equation)
  What to do
• Periodic Table

1. Sodium-25 undergoes gamma decay as shown in the decay equation below.
2. Discuss as a pair and complete the equation. Write your response on the flip chart.
3. Identify the element X, which sodium decays to. Write an explanation for how you arrived at the element.
4. Share your findings with the rest of the class.
5. Half-life
   Different atomic nuclei undergo radioactivity at different rates. Some disintegrate very fast, while others decay slowly. For example, 2 g of 6 C take about 5,730 years to reduce to half of the initial quantity, that is, lg, while the same mass of takes only 1.0 minute to reduce to 1 g.
   In Activity 6.2(e), you will construct the concept of half-life.

Activity 6.2(e): Understanding the concept of half-life
Work in pairs.
What you need:
. notebooks
What to do pens

1. Study and interpreted Figure 6.7, showing results of a radioactive decay process monitored for 16 days.

Discussion questions

1. What was the half-life of the radioactive material?
2. Work out the masses Y and Z obtained at day 4 and day 12, respectively.
3. What percentage of the radioactive substance had been lost at day 8?
4. Predict the mass of the radioactive substance that will remain at day 20.

Analysis
How long did it take for the count rate to reduce from:
(i) 80 to 40?
(ii) 40 to 20?
(iii) 20 to 10?
Application and Conclusion

1. How many days would it take for the count rate to reduce from 10 to 5
2. What conclusions can you make from your solutions to (1) above?
3. Share your findings to the rest of the class.
   Each radioactive form of an element has its own rate of disintegration. Half-life is the time required for a radioactive substance to reduce to half of its initial amount.
4. Discussion question
   O
   Eight grams of substance D were initially present in a sample. The mass of’ D in the sample reduced to half of the original mass in 8 days. Find the mass remaining after 24 days.
   Calculating half-life
   From the definition, after one half-life ofthe original amount of a radioactive substance c remains. After two half-lives, one half of this half (the previous half) remains or one quarter of the original amount of the radioactive substance remains, and so on. Therefore, after n half-lives, Ihn of the original amount of a radioactive substance

Activity 6.2(g): Finding the half-life of a radioactive
substance using a graph
Work in groups.
What you need: graph paper What to do

1. Study the data in Table 6.2.
   pencils, pens
   ruler

Exercise 6.1
The half-life of a certain radioactive isotope is 24 days. If the initial mass is 0.64 g, find:
a) the mass remaining after 120 days.
b) how long it will take to have only 0.04 g remaining undecayed.
6.3 Using Nuclear Power
Nuclear power, which uses radioactive materials, has a variety of important uses in electricity generation, medicine, industry, agriculture, as well as in homes. Nuclear reactions have many applications in agriculture, medicine, industry and research. They greatly improve the day-to-day quality of lives. However, there are major environmental concerns related to nuclear power. These include the creation of
radioactive wastes and how they are disposed of. The wastes can remain radioactive and dangerous to human health for thousands of years.
Dimensions associated with the use of nuclear power
Despite being a large source of clean energy, the use of nuclear power still faces resistance due to social, political and environmental implications. n the next activity, you will research and produce a report on the social, political and environmental dimensions associated with the use of nuclear power.

Activity 6.3: Understanding the dimensions associated
with use of nuclear power
Work in groups.
What to do
Discuss the following questions:
(a) What is the general people’s perception of nuclear power use?
(b) How can their perception be changed for the better?

2. Discuss the environmental risks which are posed by nuclear power,
3. Suggest what can be done to reduce the negative impact of using nuclear power
   Compile your responses in a comprehensive report, present it to the teacher for assessment, and share your findings with other groups.

Assignment 6.1
Consider the fertilizers given in the table below:
Research about the Fukushima Daiichi nuclear disaster of 2011. Write a report on the cause of the disaster and impact of the disaster

Uses of radiation
Despite the many dangers of radiation, it has many uses, some of which are listed below.
a) Medical field
Radioactive chemical’ tracers emitting gamma rays can give information about a person’s internal anatomy and the functioning of specific organs. The radioactive material may be injected into the patient, from where it will target specific areas such as bones or tumors. As a material decays and releases radiation, this can be detected using a special type of camera or other instruments. The radioactive
material that is used for this purpose must have a short half-life so that the radiation can be detected quickly and, also, so that the material is quickly removed from the patient’s body. Using radioactive materials for this purpose can mean that a tumor or cancer may be diagnosed long before these would have been detected using other methods, such as X-rays.
Radiation may also be used to sterilize medical equipment. Baroque Senior F

Assignment 6.2
Carry out research to find out more about the radioactive isotope which are used to diagnose diseases in the following parts of the body:
a) thyroid gland
b) kidneys
c) brain
In each case, try to find out:
(i) which radioactive isotope is used.
(ii) what the sources of that radioactive isotope are.
(iii) how the radioactive isotope enters the patient’s body and how it is monitored.

b) Biochemistry and genetics
Radioisotopes may be used as tracers to label molecules so that chemical processes such as DNA replication or amino acid transport can be traced.
c) Food preservation
Irradiation of food can stop vegetables or plants from sprouting after they have been harvested. It also kills bacteria and parasites, and controls the ripening of fruits.
d) Environment
Radioisotopes can be used to trace and analyze
c e) Archaeology and carbon dating
Natural radioisotopes such as carbon-14 can be used to determine the age of organic remains.
All living organisms (for example, trees and humans) contain carbon. Carbon is taken in by plants and trees through the process of photosynthesis in the form of carbon dioxide and is then converted into organic molecules. When animals feed on plants, they also obtain carbon through these organic compounds. Some of the carbon in carbon dioxide is the radioactive carbon-14, while the rest is a non-radioactive form of carbon. When an organism dies, no more carbon is taken in and there is a limited amount of carbon-14 in the body. From this point onwards, carbon-14 begins to decay. When scientists uncover remains, they are able to estimate the age of the remains by determining how much carbon-14 is left in the body, relative to the amount of non-radioactive carbon. The less carbon-14 there is, the older the remains because radioactive decay must have been taking place for a long time. Because scientists know the exact rate of decay of carbon-14 they can calculate a very accurate estimate of the age of the remains. Carbon dating has been a very important tool in building up accurate historical records.

Chapter Summary
In this chapter, you have learnt that:

• a nucleus reaction is a process, such as the fission of an atomic nucleus, or the fusion of one or more atomic nuclei and / or sub-atomic particles in which the number of protons and / or neutrons in a nucleus change. there are two main types of nuclear reactions, that is, nuclear fission and
  nuclear fusion.
• radioactive decay occurs when unstable atomic nuclei break down to form more energetically stable atomic nuclei. The process releases a lot of energy and occurs with a small amount of mass being converted to energy. the particles and energy released are called radiation and the atom is said
  to be radioactive.
  there are three kinds of particle radiation from radioactive decay: alpha (a), beta (ß), and gamma (y) radiation. during alpha decay, an alpha particle is released. Alpha radiation has low
  penetration power

• during beta decay, a beta particle is released, A beta particle is the electron that is released. Beta radiation has greater penetration power than alpha radiation. during gamma decay, electromagnetic energy is released as gamma rays. Gamma radiation has the highest penetration power as compared with the other two kinds of particle radiation. there are many sources of radiation: some natural and others are man-made.
• natural sources of radiation include cosmic and terrestrial radiation.
• man-made sources of radiation include televisions, smoke detectors and X-ray security systems.
• radiation can be very damaging. Some of the negative impacts of excessive exposure to radiation include damage to cells, genetic abnormalities and cancer
• however, radiation has many positive uses. These include use in the medical field, bio Chemistry and genetics, as well as use in food preservation, the environment and in archaeology.

End-of-Chapter Questions

1. Explain each of the following terms:
   a) radioactive decay
   b) radiocarbon dating
2. For each of the following questions, choose one correct answer:
   a) The part of the atom that undergoes radioactive decay is the…
   (i) neutrons.
   (ii) nucleus.
   (iii) electrons.
   (iv) entire atom.
   b) The radioactive isotope polonium-212 undergoes alpha decay. Which
   of the following statements is true?
   (i) The number of protons in the element remains unchanged.
   (ii) The number of nucleons after decay is 212.
   (iii) The number of protons in the element after decay is 82.
   (iv) The end product after decay is lead-208.
3. 20 g of sodium-24 undergo radioactive decay. Calculate the percentage of the original sample that remains after 60 hours.
4. Nuclear Physics can be controversial. Many people argue that studying the nucleus has led to devastation and huge loss Of life. Others would
   argue that the benefits of Nuclear Physics far outweigh the negative effects that have come from it.
   a) Outline some of the ways in which Nuclear Physics has been used in negative ways.
   b) Outline some of the benefits that have come from Nuclear Physics.

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