Bab 10

CHAPTER 10: RADIOACTIVITY 226 88

Ra

222 86

Rn

+

Figure 8 shows a nuclear reactor where nuclear fission reaction occurs to generate electricity in a nuclear power station. i) What is meant by nuclear fission ?

P

………………………………………………………(2 marks)

1. The equation above shows the reaction which occurs when P particle is emitted during the radioactive decay. a) i) What is meant by radioactive decay?

ii) Referring to figure 8 ,what is the function of a) the graphite core

……………………………………………………(1 mark )

………………………………………………….(1 mark )

ii) Name the P particle ?

b)

………………………………………………………( 1 mark )

………………………………………………….( 1 mark ) d) The equation below represents the fission of a uranium-235 nucleus when bombarded by a neutron.

235 1 U + n 92 0

Figure 7 b) Figure 7 shows the track of beta particles produced in a cloud chamber. i) Why are the tracks thin and not straight ?

93 141 1 Rb + Cs + 2 n + energy 37 55 0

Given that the atomic mass unit (a.m.u) of U-235 = 235.0492, neutron = 1.00867, Rb -93 = 93.92157 , Cs – 141 = 140.91963 c = 3 x 10 8 m s −1 1 a.m.u = 1.66 x 10 −27 kg

…………………………………………………………………

ii)

the Boron/ cadmium rod

…………………………………………………………………. ( 2 marks ) State one usage of beta particles. ……….. …………………………………………( 1 mark)

c)

Determine the energy released by fission.

Figure 8

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( 3 marks)

2.

Diagram 8.1 is part of the decay curve for a sample of an αemitting radioactive isotope.

The results of this experiment are shown in Table 8.

TABLE 8 (i) Name one suitable detector to detect α-particles in air. ............................................................................................. [1 mark] (ii) State the cause of the count rate at a distance of 9 cm from the source.

DIAGRAM 8.1

................................................................................................ [1 mark] (iii) Estimate the count rate that is only due to the source at a distance of 2 cm.

(a) What is meant by isotope? ................................................................................................. [1 mark] (b) Based on Diagram 8.1: (i) Determine the half-life of the isotope.

……………………………………………… ………………

(iv)

........................................................................................... [2 marks] (ii) Complete the curve in Diagram 8.1 as far as time = 20 days. Plot the exact corresponding values of the percentage activity and time. [3 marks] In an experiment to find the range of α-particles in air, the apparatus in Diagram 8.2 is set-up.

[1 mark] Using Table 8, what is the maximum distance αparticles can travel in air?

………………………………………………………… [1 mark] (v) Justify your answer to c(iv). ............................................................................................. ............. [2 marks]

DIAGRAM 8.2

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( i) What is beta particle? ………………………………………… 3. Diagram 3.1 shows the rate of decay of radioactive substance, Iodine131.

(ii)

…………………………

[1mark] Complete the following equation for the decay of Iodine-131.

[1 mark] 4. Radioisotope has many uses in non destructive testing in industry. One of the uses is to detect leakage in underground water pipes. Radioactive salt is dissolved into the water at the treatment plants. Table 7.1 shows a reading collected from a source. Time/hours Radioactivity/ counts per minute

0 2000

20 860

40 480

60 280

80 200

TABLE 7.1 (a)(i) Sketch a graph of radioactivity against time. [2 marks]

DIAGRAM 3.1 a).

What is meant by ‘half – life’?

b)

…………………………………………………………………… [1mark] Based on Diagram 3.1, what is the half – life of Iodine?

c)

…………………………………………………………………… [1mark] What happen to the activity of Iodine-131 after 24 days?

(ii)Using the graph in a(i), determine the half-life of the radioactive salt used.

…………………………………………………………………… [1mark] c) When Iodine-131 decays, it produces a beta particle and Xenon-131(Xe).

(b)(i)Determine the most suitable radiation can be used to detect the leakage. ……………………………………………………………………….. [1 mark]

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(ii)

Name the instrument to detect the radiation in b(i). ……………………………………… …………[1 mark] (ii) Explain how would a worker operating the detector to determine the leakage in the pipe.

(a) Name the material of container X. ..……………………………………………………….... [ 1 mark ] (b) (i) Complete this sentence by underlining one correct phrase in the box.

………. …………………………………………………

an alpha particle

………………………………………………………… … ………………………………………………………… … [2 marks] (c)

a beta particle

Ray P is

a gamma ray [1 mark ] (ii)

The water is safe to drink when the radioactivity is one eighth (⅛) of its initial value. What is the minimum period of time that should be taken before anyone drinks the water .

Give the reason for your answer in (a)(i).

…..………………………………………………………….. [1 mark ] (c) Why the size of deflection of ray P is greater than ray Q? ………………………………………………………… … 6.

[2 marks] 5. A radioactive source emits two rays P and Q is placed in front of an electric field and the radioactive path is shown in Diagram 1.

[1 mark ] Diagram 8.1 shows a method used to detect leakage of pipes laid underground. A little radioisotope substance is dissolved in the water that flows in the pipes. A Geiger Muller which connected to the ratemeter is then moved over the pipes according to the layout plan of the underground pipes. to ratemeter

underground water pipe

DIAGRAM 1

4

A

B

C

D

E

F

DIAGRAM 8.1

[2 marks] (ii) calculate the half life for every radioisotope.

Table 8.1 shows the readings of the ratemeter at the different location. Location of GeigerA B C D E Muller tube Reading of the ratemeter / counts per 300 295 284 372 290 minute TABLE 8.1 (a) What is meant by radioisotope?

(b)

F

[4 marks] (d)

216

Based on your answer in (c) (ii) and Table 8.2, suggest the suitable radioisotope to detect the leakages of pipes. Give two reasons for your answer. …………………………..…………………………….………

……………………….........………………………………… [1 mark] Base on Table 8.1, state the location on the pipe where the leakage takes place. State reason for your answer.

……………………………………..……………….………… [3 marks]

……………………….………………………………………..

(c)

……………………….……………………………………… [2 marks] Table 8.2 shows the time taken for radioisotope of Sodium24, Cobalt-60 and Radium-226 to decay to 12.5% from initial activity and radioactive emission. Time taken to decay to 12.5% 45 hours 15.9 years 4860 years TABLE 8.2

Radioisotope Sodium -24 Cobalt-60 Radium-226

A Polonium nucleus emits alpha particles and gamma ray to become a Plumbum nucleus. (a) Complete the decay equation for Polonium nucleus by writing the appropriate number in the boxes provided. (b) The Polonium nucleus is placed infront of electric field as shown in Diagram 4.1.

Radioactive emission Beta Gamma Alpha

Base on Table 8.2, (i) Write the decay equation for Radium-226 ( decays to Radon (

222 86

226 88

Ra ) if it

Rn ).

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DIAGRAM 4.1

(i) Draw path of ray for alpha particle and gamma ray in diagram 4.1.

[2 marks] (ii) Explain why the rays follow the path as you drawn in Diagram 4.1 Alpha :………..………………………………………………………….. ……..

………………………………………………………………… ……….. ………………………………………………………………… ………….. ………………………………………………………………….. [2 marks]

(b) The radioisotope P has been removed but there is still a small reading on the counter ratemeter. What causes this reading? ………………………………………………………………… …. [1 mark] Diagram 4.2 shows a graph of radioactive activity, N, for radioisotope P against time, t.

Gamma :………………..………………....………………………..… ….. [2 marks] (c) A sample of polonium of mass 120 g has a half-life of 45 s. Determine the mass of polonium that has decayed after 180 second. [2 marks]

Diagram 4.1 shows a Geiger-Muller tube connected to a counter rate meter to detect radioactive rays from a radioisotope P.

Diagram 4.1 (a) (i) Name one radioactive ray which can be detect by a GeigerMuller tube? ………………………………………………………………..[1 mark] (ii) Explain how the radioactive rays is detected by the tube

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Diagram 4.2 (c) Determine the half life of radioisotope P. [2 marks]

(d) State one application of the radioisotope .......................................................................................................... [1 mark]

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