CAIE A-Level Physics 23 Nuclear Physics

Practise using mass defect, binding energy, nuclear equations and decay laws to calculate energy release, compare reactions and interpret radioactive data.

Exam points

use mass-energy equivalence, nuclear equations and mass defect to analyse nuclear reactions
interpret binding-energy-per-nucleon data to explain and compare fusion, fission and energy release
calculate nuclear energy release from mass change or binding-energy change
explain the random and spontaneous nature of radioactive decay using count-rate evidence
calculate activity and decay constant from A = ?N and half-life relationships

Covered syllabus points

23.1 Mass defect and nuclear binding energy 23.2 Radioactive decay

[Maximum number: 1]

Use data from (b) to calculate the mass that is converted into energy every second in the Sun.
mass = kg

$\begin{aligned} m=\frac{E}{c^{2}} =\frac{3.83 \times 10^{26}}{3.00 \times 10^{82}} =4.26 \times 10^{9} \mathrm{~kg} \end{aligned}$

A1

[Maximum number: 10]

(a)

A radiation detector is placed close to a radioactive source. The detector does not surround the source.
Radiation is emitted in all directions and, as a result, the activity of the source and the measured count rate are different.

Suggest two other reasons why the activity and the measured count rate may be different.
1.
2.

[ 2 ]

(b)

The variation with time t of the measured count rate in (a) is shown in Fig. 12.1.

Fig. 12.1

[ 5 ]

(i)

State the feature of Fig. 12.1 that indicates the random nature of radioactive decay.

[ 1 ]

(ii)

Use Fig. 12.1 to determine the half-life of the radioactive isotope in the source.
half-life = hours

[ 4 ]

(c)

The readings in (b) were obtained at room temperature.

A second sample of this isotope is heated to a temperature of $500^{\circ} \mathrm{C}$ .
The initial count rate at time t=0 is the same as that in (b).
The variation with time t of the measured count rate from the heated source is determined.

State, with a reason, the difference, if any, in
1. the half-life,
2. the measured count rate for any specific time.

[ 3 ]

[Maximum number: 10]

(a)

State what is meant by nuclear fusion and nuclear fission.
nuclear fusion:
nuclear fission:

[ 3 ]

(b)

A nuclear reaction which may, in the future, be used for the generation of electrical energy is

{ }_{1}^{2} \mathrm{H}+{ }_{1}^{3} \mathrm{H} \rightarrow{ }_{2}^{4} \mathrm{He}+\mathrm{x} .

[ 7 ]

(i)

Name the particle x .

[ 1 ]

(ii)

Data for the binding energy per nucleon $E_{\mathrm{B}}$ of some nuclei are given in Fig. 12.1.

Fig. 12.1

1. State the binding energy per nucleon of x .

binding energy per nucleon =J

2. Calculate the energy change that takes place in this reaction.

energy change =

[ 3 ]

1. zero

A1

2. $\left(4 \times 11.3290 \times 10^{-13}\right)-\left(2 \times 1.7813 \times 10^{-13}\right)-\left(3 \times 4.5285 \times 10^{-13}\right)$

C1

$\begin{aligned} \text { energy change } =45.316 \times 10^{-13}-17.148 \times 10^{-13} =2.82 \times 10^{-12} \mathrm{~J} \end{aligned}$

A1

(iii)

Use your answer in (ii) part 2 to determine the energy release when 2.0 g of deuterium $\left({ }_{1}^{2} \mathrm{H}\right)$ reacts with 3.0 g of tritium $\left({ }_{1}^{3} \mathrm{H}\right)$ .

energy =

[ 3 ]

1.0 mol or $N_{\mathrm{A}}$ nuclei of each
$\begin{aligned} \text { energy } =2.817 \times 10^{-12} \times 6.02 \times 10^{23} =1.7 \times 10^{12} \mathrm{~J} \end{aligned}$

A1

All question bank results loaded

Covered syllabus points

23. Nuclear physics question 1

23. Nuclear physics question 2

Question (a)

Question (b)

Question (i)

Question (ii)

Question (c)

23. Nuclear physics question 3

Question (a)

Question (b)

Question (i)

Question (ii)

Question (iii)