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SS3: PHYSICS - 2ND TERM

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  1. Magnetic Field
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  2. Magnetic Field
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  7. Models of the Atom
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  8. Radioactivity
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SS3: PHYSICS – 2ND TERM Half Life Theory Questions – Nucleus, Radioactivity, Nuclear Reaction
Lesson 9, Topic 8
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Theory Questions – Nucleus, Radioactivity, Nuclear Reaction

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Theory Questions & Answers – Nucleus, Radioactivity, Nuclear Reaction

Theory Questions & Answers – Nucleus, Radioactivity, Nuclear Reaction

1. In a nuclear fission reaction, a nuclide \( \scriptsize ^{235}_{92}U \) is bombarded with a neutron to produce \( \scriptsize ^{93}_{36}Kr \: and \: ^{141}_{56}Ba\)with additional neutrons, the energy involved in the process is Q.

  • \( \scriptsize mass \: of \: ^{235}_{92}U = 235.044\: u\)
  • \( \scriptsize mass \: of \: ^{93}_{36}Kr = 91.898 \:u\) 
  • \( \scriptsize mass \: of \: ^{141}_{56}Ba = 140.914 \:u \)
  • mass of neutron = 1.009 u
  • 1 u = 1.66 × 1027 kg
  • c = 3.0 × 108 ms-1

i. Write down the balanced nuclear reaction equation for the process.
ii. State with reason whether Q is absorbed or released in the process.
iii. Calculate the value of Q in joules.
iv. State three differences between nuclear fusion and nuclear fission.

(WAEC 2023)

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2. (a) (i) What is meant by the term artificial radioactivity?

(ii) Complete the table below.

EmissionNatureChargeIonizing-ability
 High speed
electron		 Moderately
ionizing
  NeutralNegligible
ionizing ability
Alpha particle Positive 

(WAEC 2022)

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3. (a) Define nucleon number

(b) A radioactive isotope of Americium (Am – 241) decays into a nucleus of Neptunium (Np – 237) and an alpha (α) particle as shown in the nuclear equation below.

\( \scriptsize ^{241}_{95}Am\: \to \: ^{237}_{c}Np \: + \: ^b_a \alpha\)

(i) State the number of neutrons in the nucleus of Americium – 241.

(ii) Determine the values of a, b and c.

(c)(i) Why are γ-rays not deflected by electromagnetic field?

(ii) State two properties of gamma rays that make them suitable for sterilizing medical equipment.

(d) A sample of radioactive substance was found to be left with h of its initial count rate after 110 years. Calculate its decay constant.

(WAEC 2015)

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4. (a) Explain the following terms:

(i) mass defect;
(ii) binding energy of a nucleus.

(b)

Screenshot 2025 02 10 at 07.03.13

The diagram above shows part of a radioactive decay series. Use it to answer the following questions;
(i) Name a pair of isotopes.

(ii) Name the isotope with which the series starts.

(iii) Write down a nuclear equation for two examples of each of
(*) alpha decay;
(**) beta decay.

(WAEC 2016)

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5. A piece of ancient bone from an excavation site showed \( \scriptsize ^{14}_6 C\) activity of 9.5 disintegrations per minute per 1.0 × 10-3 kg. If a bone specimen from a living creature shows \( \scriptsize ^{14}_6 C\) activity of 12.0 disintegrations per minute per 1.0 × 10-3 kg, determine the age of the ancient bone.

[Half-life of \( \scriptsize ^{14}_6 C\) = 5572 years]

(WAEC 2017)

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6. (a) List three pieces of evidence to support the claim that X-rays are electromagnetic waves.

(b) List three peaceful uses of nuclear energy.

(WAEC 2018)

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7. Two nuclear equations are given below:

\( \scriptsize ^{222}_{p}RN \to \:\: ^{218}_{84}Po \: + \: ^q_2He\)  ……………….A

\(\scriptsize  ^{214}_{83}Bi \to\:\: ^{214}_{84}Po \:+ \: ^m_nX \) ………………..B

Determine the values of:

(α) p and q in equation A;
(β) m and n in equation B and identify X.

(ii) Give a reason why it is important to dispose of radioactive waste safely.

(WAEC 2014)

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Question 1

In a nuclear fission reaction, a nuclide \( \scriptsize ^{235}_{92}U \) is bombarded with a neutron to produce \( \scriptsize ^{93}_{36}Kr \: and \: ^{141}_{56}Ba\) with additional neutrons, the energy involved in the process is Q.

  • \( \scriptsize mass \: of \: ^{235}_{92}U = 235.044\: u\)
  • \( \scriptsize mass \: of \: ^{93}_{36}Kr = 91.898 \:u\)
  • \( \scriptsize mass \: of \: ^{141}_{56}Ba = 140.914 \:u \)
  • mass of neutron = 1.009 u
  • 1 u = 1.66 × 1027 kg
  • c = 3.0 × 108 ms-1

i. Write down the balanced nuclear reaction equation for the process.

Answer:

⇒ \( \scriptsize \underset{uranium}{_{92} ^{235} \textrm {U}}\: + \: \underset{neutron}{_{0} ^{1} \textrm {n}} \: \rightarrow \: \underset{barium}{_{56} ^{141} \textrm {Ba}} \: + \: \underset{krypton}{_{36} ^{93} \textrm {Kr}} \: + \: \underset{neutrons}{2\: _{0} ^{1} \textrm {n}} \:+ \:Q \)

 

ii. State with reason whether Q is absorbed or released in the process.

Solution/Answer:

Sum of reactant masses:

= (235.044 + 1.099) = 236.053 u

 

Sum of product masses:

= [91.898 + 140.914)  + 2(1.009) = 234.830 u

Q is released because the sum of the masses of reactants is greater than the product masses.

 

iii. Calculate the value of Q in joules.

Solution

Δm = 236.053 u – 234.830 u

Δm = 1.223 u

Q = \( \scriptsize mc^2 \\ \scriptsize = 1.223 \: \times \: 1.66 \: \times \: 10^{-27} \: \times \: \left( 3.0 \: \times \: 10^8 \right)^2\\ \scriptsize  = 1.83 \: \times \: 10^{-10} \: J  \)

 

iv. State three differences between nuclear fusion and nuclear fission.

Answer:

Nuclear Fission: Nuclear Fusion:
This is the breaking up of the nucleus of a heavy
atom or element into nearly two equal parts.		 Two or more light nuclei combine, at
high temperatures, to form a heavier nucleus.
Less energy produced. Greater energy produced.
By-products are radioactive. By-products are non-radioactive.
The raw material for fission is more expensive. The raw material for fusion is cheaper.
Lower initiation temperature. Higher initiation temperature.
Fission process is more dangerous. Fusion process is less dangerous.

Question 2

(a) (i) What is meant by the term artificial radioactivity?

Answer:

Induced radioactivity, also called artificial radioactivity or man-made radioactivity, is the process of using radiation to make a previously stable material radioactive.

It is the process by which a stable nucleus is bombarded with a neutron to make it unstable and so disintegrates/decays with the emission of particles/radiation and energy.

 

(ii) Complete the table below.

Answer:

Emission Nature Charge Ionizing-ability
Beta (β) High speed
electron		 Negative Moderately
ionizing
Gamma (γ) Electromagnetic radiation Neutral Negligible
ionizing ability
Alpha particle (α) Helium nucleus Positive Highly ionizing

Question 3

(a) Define nucleon number

Answer

Nucleon number is the total number of proton of protons and neutrons in an atom of an element.

 

(b) (i) radioactive isotope of Americium (Am – 241) decays into nucleus of Neptunium (Np – 237) and an alpha (α) particle as shown in the nuclear equation below.

⇒ \( \scriptsize ^{241}_{95}Am\: \to \: ^{237}_{c}Np \: + \: ^b_a \alpha\)

State the number of neutrons in the nucleus of Americium 241.

Answer

⇒ \( \scriptsize ^{241}_{95}Am\)

  • nucleon number = 241
  • proton number = 95

Number of neutrons = nucleon number – proton number

Number of neutrons = 241 – 95 = 146

 

(b) Determine the values of a, b and c.

Answer

⇒ \( \scriptsize ^{241}_{95}Am\: \to \: ^{237}_{c}Np \: + \: ^b_a \alpha\)

Recall that \( \scriptsize ^{b}_{a}\alpha =\; ^{4}_{2}He \)

⇒ \( \scriptsize ^{241}_{95}Am\: \to \: ^{237}_{c}Np \: + \: ^{4}_{2}He\)

a = 2

b = 4

95 = c + 2;

c = 93

 

(c) (i) Why are γ-rays not deflected by electromagnetic fields?

Answer

γ-rays have no mass and no charge. Electromagnetic field has no effect on them.

(ii) State two properties of gamma rays that make them suitable for sterilizing medical equipment.

Answer

– High penetrating energy that makes it pass through tissues and kill viruses and bacteria
– Ionization energy: They are ionizing radiations.

 

(d) A sample of radioactive substance was found to be left with 1/32 of its initial count rate after 110 years. Calculate its decay constant.

Solution

Remaining = \( \frac{1}{2} \)

After first half-life = \( \frac{N}{2} \)

Second = \( \frac{N}{2} \: \times \: \frac{1}{2} = \frac{N}{4} \)

Third = \( \frac{N}{4} \: \times \: \frac{1}{2} = \frac{N}{8} \)

Fourth = \( \frac{N}{8} \: \times \: \frac{1}{2} = \frac{N}{16} \)

Fifth = \( \frac{N}{16} \: \times \: \frac{1}{2} = \frac{N}{32} \)

⇒ \( \frac{110}{5} \scriptsize = 22\: years\)

Decay constant, λ = \( \frac{0.693}{t_{\frac{1}{2}}} \\ = \frac{0.693}{22}\\\scriptsize = 0.315 \: s^{-1}\)

Question 4

(a) (i) Explain the following term; mass defect;

Answer

Mass defect is the difference between the mass of a nucleus and the total mass of its nucleons.

– expressed in atomic mass unit ;
– total mass of nucleons – mass of nucleons;
– it is a measure of binding energy

 

(ii) Explain the following term: binding energy of a nucleus.

Answer

Binding energy is the work done/energy needed to separate the nucleus.

– measured in eV or J.  

 

(b)

 

The diagram above shows part of a radioactive decay series. Use it to answer the following questions;

 

(i) Name a pair of isotopes.

Answer

⇒ \( \scriptsize ^{212}_{84} Po \: and \: ^{216}_{84} Po\)

⇒ \( \scriptsize ^{288}_{90}Th \: and \: ^{232}_{90}Th\)

⇒ \( \scriptsize ^{288}_{82}Pb \: and \: ^{212}_{82}Pb\)

Any one  

 

(ii) Name the isotope with which the series starts.

Answer

⇒ \( \scriptsize ^{232}_{90}Th\)

and ⇒ \( \scriptsize ^{228}_{90}Th\)  

 

(iii) Write down a nuclear equation for two examples of each of

(*) alpha decay;

Answer

⇒ \( \scriptsize ^{232}_{90}Th \: \rightarrow \: ^{228}_{88}Ra \: + \: ^{4}_{2}He \: + \: energy\)

⇒ \( \scriptsize ^{212}_{84}Po \: \rightarrow \: ^{208}_{82}Pb \: + \: ^{4}_{2}He \: + \: energy\)  

 

(**) beta decay;

Answer

⇒ \( \scriptsize ^{212}_{83}Bi \: \rightarrow \: ^{212}_{84}Po\: + \: ^{0}_{-1}e \: + \: energy\)

⇒ \( \scriptsize ^{224}_{88}Ra \: \rightarrow \: ^{224}_{89}Ac\: + \: ^{0}_{-1}e \: + \: energy\)

Question 5

A piece of ancient bone from an excavation site showed \( \scriptsize ^{14}_6 C\) activity of 9.5 disintegrations per minute per 1.0 × 10-3 kg. If a bone specimen from a living creature shows \( \scriptsize ^{14}_6 C\) activity of 12.0 disintegrations per minute per 1.0 × 10-3 kg, determine the age of the ancient bone. [Half-life of \( \scriptsize ^{14}_6 C\) = 5572 years]

Solution

λ = \( \frac{0.693}{T^{\frac{1}{2}}} \)

λ = \( \frac{0.693}{5572} \) = 0.0001244 years-1

N = \( \scriptsize Noe^{-\lambda t} \)

⇒ \( \scriptsize e^{-0.0001244t} = 1.2632 \)

0.0001244t = 0.234

t = 1878 years

Question 6

(a) List three pieces of evidence to support the claim that X-rays are electromagnetic waves.

Answer

Required Evidence:

  • Not affected by electric/magnetic fields
  • Can travel through a vacuum
  • Travel with the speed of light
  • Can be polarized
  • Cause Fluorescence

 

(b) List three peaceful uses of nuclear energy

Answer

  • Nuclear energy is used to generate electricity cheaply.

  • Products of nuclear fission are used for radiotherapy. Radiotherapy is a cancer treatment that uses high doses of radiation to kill cancer cells and shrink tumours.

  • Radioisotopes are used in agriculture as tracers and preservatives.

  • Some spacecraft and ships are now powered by nuclear energy.

Question 7

Two nuclear equations are given below:

⇒ \( \scriptsize ^{222}_{p}RN \to \:\: ^{218}_{84}Po  \: + \: ^q_2He\)  ……………….A

⇒ \(\scriptsize  ^{214}_{83}Bi \to\:\: ^{214}_{84}Po  \: + \: ^m_nX \) ………………..B

Determine the values of:

(α) p and q in equation A;

Solution

⇒ \( \scriptsize ^{222}_{p}RN \to \:\: ^{218}_{84}Po  \: + \: ^q_2He\)

p = 84 + 2 = 86

218 + q = 222

q = 222 – 218 = 4

(β) m and n in equation B and identify X.

Solution

⇒ \(\scriptsize  ^{214}_{83}Bi \to\:\: ^{214}_{84}Po  \: + \: ^m_nX \)

m = 214 – 214 = 0; m = 0

n = 83 – 84 = -1;

n = -1;

∴  \(\scriptsize  ^{m}_{n}X = ^{0}_{-1}X \)

 

(ii) Give a reason why it is important to dispose of radioactive waste safely.

Answer

– Toxic
–  Emits harmful radiation

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