Nuclear Physics Seatwork #5

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Physics Seatwork #5 Topic: Nuclear Physics AY 2024-2025

Grade 11 EFGH Page 1 of 4

SEATWORK

Name :

Class :

Date :

Duration : 20 minutes

Instructions

• Write your name and class in the spaces provided at the top of this page.

• Write in black or dark blue pen.

• Use soft pencil for any diagrams, graphs or rough working only.

• Do not use highlighters, glue or correction fluid/tape. Strikethrough all mistakes.

• Answer all the questions.

• The use of an electronic calculator is expected, where appropriate.

• You are reminded of the need for clear presentation in your answers.

• The number of marks is given in brackets [ ] at the end of each question or part question.

• The total number of marks for this paper is 15.

Directions: Answer all the questions in the spaces provided. You may lose marks if you do not show your working or if you do not use appropriate units.

1 (a) (i) State decay law.

………..………

………..…….. [1]

(ii) Define decay constant.

………..………

………..…….. [1]

(b) A radioactive sample consists of an isotope X of half-life T that decays to form a stable product. Only X and the stable product are present in the sample.

At time t = 0, the sample has activity of A0 and contains N0 nuclei of X.

15

SCORE

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(i) On Fig. 1.1, sketch the variation with t of the number N of nuclei of X present in the sample. Your line should extend from time t = 0 to time t = 3T.

Fig. 1.1

[3]

(ii) From the graph you sketch in Fig.1.1, show that:

λ = 0.693 / T

[1]

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(iii) For sample of nuclide X in Fig. 1.1:

1. Show that the decay constant  is about 0.689 s^-1, if the fraction of ^𝑁

𝑁₀ at t = 1.7 s is 0.31.

 = ……….…….. [2]

2. Determine the half-life T. Show your working.

T = ………..……..…………. [1]

(iv) 1. Determine the percentage number of unstable nuclei of the sample of nuclide X at time = 0.45 min,

percentage = ………. [2]

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2. Determine the percentage number of stable nuclei of the sample of nuclide X at time = 0.45 min,

percentage = ……..………. [1]

(v) On Fig. 1.2 sketch the variation with N of the activity A of the sample for values of N between N = 0 and N = 8.8 x 10^-7. Indicate the value of activity A on the graph.

Space for working to find activity of decay A.

Fig. 1.2

[2]

(c) State the name of the quantity represented by the gradient of your line in Fig. 1.2.

……… [1]

[Total: 15]

* END OF SEATWORK * A / Bq

N / x 10^-7 0 4.4 8.8