NUCLEAR CHEMISTRY

SECOND TERM E-LEARNING NOTES

SUBJECT: CHEMISTRY

CLASS: SS3

WEEK 4

TOPIC:

WEEK 4:

TOPIC: NUCLEAR CHEMISTRY

CONTENTS:

1. RADIOACTIVITY
2. TYPES AND NATURE OF RADIATIONS
3. DIFFERENCES BETWEEN CHEMICAL AND NUCLEAR REACTION
4. HALF-LIFE AND APPLICATIONS OF RADIOCTIVITY

PERIOD 1: RADIOACTIVITY

This is a spontaneous decay of unstable nuclei with the release of energy and radiation such as alpha particle, Beta particle and gamma ray. Radioactivity was discovered by A.B Becquerel in the year 1896 when he found that a sample of uranium could affect the photographic plate even after it had been wrapped in black so as to prevent it fluorescence from reaching the photographic plate.

After uranium had been shown to have this property, there had been other experiments to identify other material of similar behaviour. Other radioactive materials that had been discovered include: radium, thorium, polonium … had been discovered. They exhibit the following properties:

1. They affect photographic plate
2. They ionise gas
3. They produce fluorescence

The ionising effect of radioactive material can be observed using a charge electroscope. The electroscope discharge when a radioactive material is brought its cap. This is because radiation emitted by the material causes ionization (produce electrons which discharge the electroscope).

Radioactive elements

These are elements that undergo disintegration spontaneously emit radiation and particles. Example include; radon, radium, uranium and polonium.

A form of radioactivity which occur spontaneously without doing anything to initiate it nor can anything be done to control it is called NATURAL radioactivity.

A form of radioactivity that is induced in element that would have otherwise being stable is called induced or ARTIFICIAL radioactivity.

Artificial radioactivity is induced by bombarding stable nuclei with fast moving ions such proton or alpha particles. Artificial radioactivity is induced in device called accelerators. Example include: cyclotron, linear accelerator, Van de Graff accelerator.

EVALUATION:

1.What is radioactivity

1. Define artificial transmutation

PERIOD 2: TYPES AND NATURE OF RADIATIONS

There are three main types of radiation emitted from radioactive materials:

1. Alpha particle
2. Beta particle
3. Gamma ray

Radioactivity decay

As a radioactive material emits radiation, it changes into nucleus of other which itself may be radioactive. The new nucleus thereafter emits radiation and change to another nucleus. This could continue until a stable nucleus is attained. This sequence of change is called radioactive series.

The number of disintegration per unit time is called Activity. The activity of a radioactive sample decreases with time.

Types of radioactive decay

1. Alpha decay; when a nuclei undergo alpha decay, the mass number decrease by four and the atomic number decreases by 2

For example,

Thus, the nuclei lose 2 protons and 2 neutrons.

1. Beta decay: when a nucleus undergoes beta decay, the mass number remains unchanged by the atomic number increases by one.

For example,

1. Gamma decay; there is no change in the mass number and the atomic number of the nuclei. The nuclei only undergo transition in its nuclear state.

PERIOD 3: DIFFERENCES BETWEEN NUCLEAR REACTION AND CHEMICAL REACTION

EVALUATION:

State the differences between nuclear and chemical reactions

PERIOD 4: HALF-LIFE AND APPLICATIONS OF RADIOACTIVITY

HALF-LIFE

Decay law

This states that the rate of disintegration of a radioactive material is directly proportional to the amount of the material present (remaining)

Where 𝜆 is constant of proportionality. 𝜆 is called the decay constant.

Integrating both side,

N_o is the initial number of nuclei

N_t is the remaining number of nuclei after t

𝜆 is the decay constant

t is the time.

The graph of N_t against t is shown below

T_½ is called the half life of the radioisotope. It can be define the time taken for the radioisotope to disintegrate to half its original amount.

At t = T_½ ,

Substituting this into (ii), we have

1. Carbon dating
2. Radiotherapy
3. Radio diagnosis
4. Generation of electricity with nuclear reactor
5. Use of radioisotope as tracer element in Agriculture medicine and industry.

Solved problems

EXAPMLE

1. Two radioactive material A and B have half lives of 100 and 50 years respectively. Samples of A and B initially contains equal number of atoms. What is the ratio of the remaining atoms of A to that of B after 200 years?

SOLUTION:

Recall where is the ratio of the remaining number of atoms to the amount present originally. T1/2 is the halflife and t is time

For A,

For B,

Ratio of N_tA : N_tB

This is ratio 4: 1

1. An element whose half life is 3 years has N atoms. How many atoms would have decayed after 9years?

SOLUTION:
recall

The number of atom remaining is ^N/₈ , but the number of atoms that would have decayed is

N – ^N/₈ = ^7N/₈

1. A radioactive substance has a half life of 20 hours. What fraction of the original radioactive nuclide will remain after 80 years?

SOLUTION:

Recall

¹/₁₆ of the nuclide will remain after 80 years

1. A nuclide X is produced by bombarding a nitrogen nucleus with an alpha particle with the release of heavy hydrogen nucleus as shown by the following nuclear equation

Determine the value of p and q in the equation.

SOLUTION

To balance this type of equation, the sum of the sum of nucleons on the right hand side must equal to the sum of the number of the nucleons on the left hand side.

This is also true for the atomic number on both sides.

Re-writing the equation

Number of nucleons:

Atomic number

P = 16 , q = 8

1. A material of mass 1.0 x 10^-3 kg undergoes a fission process which reduces its mass by0.02 %. Calculate the amount f energy released in the process.

SOLUTION:

Mass that decayed = 0.02% of 1.0 x 10^-3

1. Calculate the binding energy of

(atomic mass of Co = 58.9332u , mass of proton = 1.00783u , mass of neutron =1.00867 , unified atomic mass unit u = 931MeV , 1 eV = 1.6 x 10^-19J)

Solution

Mass of proton Mp = zm_p = 27 x 1.00783 =27.21141u

Mass of neutron Mn = (A-z)m_n =(59-27) 1.00867 = 32 x 1.00867 =32.27744u

Total mass of nucleons = Mp + Mn = 27.21141 +32.27744 = 59.48885u

Mass of cobalt = 58.9332u

Mass defect

Converting this to electron volt

BE = (0.55565 x 931) MeV = 517.31MeV = 517.31 x 10⁶ eV

Converting this to J

BE = 517.31 x 10⁶x 1.6 x 10^-19 = 827.7 x 10^-13J

BE = 8.277 x 10^-11J

( please note that the relation BE = was not used to calculate the binding energy. This is because, u has already being expressed in that form u = =931 MeV.

1. The half life of a radioactive element is 5 s. calculate the decay constant.

Solution

Recall

T _½ =5 s

Nuclear reaction

There two types of nuclear reaction

1. Nuclear fission; when a fast moving neutron is used to bombard a uranium nucleus, the nucleus split into two smaller nuclei – krypton and Barium.

Nuclear fission is the splitting of heavy nucleus into two smaller parts of relatively equal mass.

Q

The energy released in this reaction can be obtained from the binding energy.

The fission of uranium produces three other neutrons. These three neutrons can proceed to cause the fission of other three uranium nuclei and thereby produce another nine neutrons. The nine neutrons can cause more fission and this can continue until the reaction becomes self sustaining. This kind of reaction is called chain reaction

For chain reaction to set up, the amount of fissile material present must exceed the critical mass.

The critical mass is the minimum amount of fissile material that must be present for chain reaction to ensure.

If a chain reaction is set up in a sample of fissile fuel that exceed the critical mass, the reaction will continue at a increased rate as long as the material are together until it get out of hand and an explosion will result. This is the basis of the atomic bomb.

A control chain reaction can take place in the nuclear reactor. This can be used to generate electricity or to produce certain useful radioisotope.

1. Nuclear Fusion; this occur when two smaller nuclei fuse together to fuse a larger nuclei. A decrease in mass is expected and this is what account for the energy released during the nuclear fusion.

Nuclear fusion occurs at higher temperature than nuclear fission because of nuclear repulsion of the reactor must be overcome before reaction can take place.

EVALUATION,

1. What is nuclear fusion?

1. State three application of radioactivity
2. What is critical mass?
3. Explain the term half-life of a radioactive element

Nigeria nuclear energy programme.

Global need of nuclear power had become so imperative for the following reason:

• Increases in demand for energy
• Need to discontinue the use of fossil fuel as source of energy because of their negative impact on the environment
• Nuclear energy is a clean source of energy
• Nuclear energy is environmentally friendly and relatively cheap to maintain.

Nonetheless, the use of this energy source demands technical expertise as well as caution. Safety cannot be overemphasizing. The government had put in place statuary regulatory bodies to monitor the use of nuclear energy in the Nigeria. The body charge with this responsibility in Nigeria is the Nigeria nuclear energy commission established in1976 and the Nigeria Nuclear Regulatory Authority established in 2001. They register, license and inspect infrastructure for safety in radiotherapy, uranium mining and milling, research reactors and radioactive waste management.

For capacity building and training of man-power on nuclear energy, the country had established the Centre for Energy Research and Development (CERD), Obafemi Awolowo University (OAU) Ile-Ife and the Centre for Energy Research and Training (CERT) Ahmadu Bello University Zaria and plan for more is on.[mediator_tech]

There are indications that Russia has been contracted to construct Nigeria’s first Nuclear Power Plant that is expected to boost the power generation in the country. The plant is expected to generate up to 1.2 thousand megawatts. This is in line which the projection of the government that nuclear technology should contribute at least 4,000MW to the total National Grid by 2030.

EVALUATION

1. Which of these is not one of the types of radiation emitted during radioactive decay? (a) gamma ray (b) Beta particle (c) alpha particle (d) none of the above
2. Which of these radiations had the highest ionization potential? (a) x-ray (b) gamma ray (c) alpha particle (d) beta particle
3. —- will not be deflected in a magnetic field. (a) alpha particle (b) gamma ray (c) beta particles (d) positron
4. Which of these nuclei is a beta emitter? (a) uranium-236 (b) radium-226 (c) strontium-90 (d) cobalt -60
5. The number of disintegration per second is called —- (a) decay (b) radioactivity (c) activity (d) radio isotope
6. If the half life of a radio isotope is 2days. What fraction of the original sample of the nuclide will remain after 8days? (a) ¼ (b) ½ (c) ¹/₁₆ (d) ¹/₈
7. The Beta particle is a —- (a) proton (b) neutron (c) He-nucleus (d) electron
8. A radioactive sample initially contains 64 atoms, after three half life, the number of atoms that have disintegrate is —- (a) 8 (b) 24 (c) 32 (d) 56
9. 8 -decay and 6-decays are necessary before an atom of achieves stability, the final product has the proton number —- (a) 70 (b) 78 (c) 82 (d) 90

10.The effect on the nucleon number of a radio nuclide when it emits an alpha-particle is that it ….. (a) decreased by 4 (b) decrease by 2 (c) decreases by 3 (d) remains the same

1. Which of these institutions is the statuary body charge with the regulation of the use of nuclear energy in Nigeria? (a) CERT (b) CERN (b) NNRA (d) Shenda
2. Which of these is not a reason for the demand for nuclear energy? (a) it a clean energy source (b) it is a non-renewable energy source (c) it will add to national grid (d) it is more energy friendly than the fossil fuel
3. The mass different between the mass of a nuclei and the sum of the mass of it constituent particle is —- (a) mass defect (b) nuclear defect (c) nuclear mass (d) binding energy
4. Which of these rays originate from the nucleus of an atom? (a) X-ray (b) cathode ray (c) gamma ray (d) ultra-violet rays
5. How many alpha particles are emitted in the radioactive decays of —- (a) 12 (b) 5 (c) 3 (d) 2

ESSAY

1. State the decay law
2. Write a short note on each of the types of radiation emitted during radioactive decay
3. Write an equation to show alpha decay of radon -222
4. Define activity.
5. Complete the following reactions by completing by calculating the proton and nucleon numbers of the missing terms
6. Explain the term decay constant and half life.
7. Sketch the decay curve
8. Itemize four properties of gamma ray
9. if the half life of a sample of radioactive material is 60days, what fraction of the original radioactive nuclear will remain after 120days?
10. State briefly what happens when uranium-235 is bombarded by slow neutrons. Mention one important peaceful practical application of the process.
11. State two

1. (i) differences between nuclear fission and nuclear fussion

(ii) peaceful use of atomic energy

1. (i) explain chain reaction

(ii) state (1) one conditions necessary for chain reaction to occur

(ii) two components in the nuclear reactor used to control cahin reaction

1. (i) A nuclear reaction is given by: what types of nuclear reaction is it

(ii) the isotopes of a nuclide has a half life of 5.4 x10³ s. calculate its decay constant.

WEEKEND ASSIGNMENT

1. Differentiate between

1. Nuclear fission and nuclear fusion
2. Nuclear reaction and chemical reaction
3. If the decrease in mass in a fission process is 0.1 %, how much energy could be obtained from the fission of 1.0 g of the material?

1. (a) what are radioisotope?

(b) explain the terms nuclear fission and nuclear fusion

(c)state two advantage of fusion over fission and explain briefly why in spite of the these advantages fusion not normally ued for the generation of power.

1. the half-life of a radioactive iodine is measure to be 8.0days. a solution contained 1.5mg of this iodine on a certain day. Write down on a table the mass of iodine remaining after 8, 16, 24, 32 days. Plot a graph of mass against time from it deduce the mass fo he iodine that would remain after 30days.