(18)Radioactivity

Chapter 18 Radiation and Radioactivity Date: _______________

Section A: Multiple Choice Questions

1 Which of the following statements about alpha particles (α) is correct?

A. They are massless particles.

B. They are electromagnetic wave.

C. They are traveling at the speed of light.

D. They will be deflected by electric and magnetic field.

2 Which type of radiation sources is suitable to be used to monitor the packaging of washing powder?

A. α source B. β source C. γ source D. Either β or γ source

3 Which of the following is the most possible half-life of uranium-238?

A. 1 year B. 5.3 years

C. 25 years D. 4.5 × 109 years

4 There are two radioactive sources A and B, both of them have the same number of active nuclei at

the beginning. After 10 days, the number of active nuclei in B is more than A. Which of the following

statements is correct?

A. The mass of A is larger than B. B. The mass of B is larger than A.

C. The half-life of B is longer than A. D. The half-life of A is longer than B.

5 Which of the following curves represents a radioactive source of the longest half-life?

A. E

B. F

C. G

D. H

6 Which type of radiation cannot be detected by a photographic film badge used in hospitals?

A. α radiation B. β radiation

C. γ radiation D. X-ray

7 Some kind of lightning conductor use radioactive source to make lightning conductor. Which of the

following statements is/are the correct explanation?

(1) The radiation can ionize the air and give path for the lightning bolt to discharge.

(2) The radioactive source is a better electrical conductor.

(3) The radioactive source is a better heat conductor.

A. (1) only B. (2) only

C. (3) only D. (2) and (3) only

(18)radioactivity.doc

8 Which of the following is/are artificial radioactive sources?

(1) Radon gas (2) Nuclear fallout

(3) Cosmic radiation (4) Carbon-14 in the atmosphere

A. (1) only B. (2) only

C. (3) and (4) only D. (2) and (4) only

9 The figure below shows an experimental set-up to differentiate the type of radiation emitted by

sample radioactive sources X, Y and Z. The radioactive source is placed inside a lead container,

and three counters G1, G2 and G3 are placed at the positions shown. The table shows the

experimental result. Which type(s) of radiation are emitted by samples X, Y and Z?

Sample X Sample Y Sample Z

A. β only α only γ only

B. β and γ only none of them α and γ only

C. α and γ only none of them β and γ only

D. α only γ only β only

10 It is dangerous if we swallow an alpha source into the body. Why?

A. It is relatively large in atomic size.

B. The high penetrating power will hurt the body. C. The alpha particle will further decay into carcinogenic material.

D. The strong ionizing power will affect the body greatly.

11 Which of the following statements about cloud chamber is/are correct?

(1) Alpha, beta and gamma radiation can leave tracks in the cloud chamber without using any dry

ice.

(2) The alpha particle tracks are relatively straight and thick.

(3) We cannot use the cloud chamber to determine the type of charges of the radiation. A. (1) only B. (1) and (2) only

C. (2) and (3) only D. (1), (2) and (3)

12 Which of the following statements about alpha particles is correct? A. They are hydrogen nucleus. B. They are hydrogen atom.

C. They are helium nucleus. D. They are helium atom.


13 Amy tests different type of radiation and found that it moves with the greatest speed and has

properties similar to the X-ray. What is the type of this radiation?

A. Alpha radiation B. Beta radiation

C. Gamma radiation D. Both beta and gamma radiation Section B: Questions

1 Amy bought a balloon filled with helium gas. She knows that the gas is in fact made up of

alpha and beta particles.

(a) What should be the ratio of the number of beta particles to that of the alpha particles

if the gas mixture is to be electrically neutral? Explain the reason.

Ans:

(b) Why are the particles in the balloon no longer harmful?

Ans:

2 Someone is going to perform an experiment to find out the range and half-life of a

radioactive source.

(a) What kind of detector should be used in this experiment?

Ans:

(b) The radioactive source is placed at a distance of 2 cm in front of the detector. The

detector records an average count of 300 counts per minute. He then put the source

8 cm farther. The reading drops significantly. What conclusion can you draw?

Ans:

(c) If the radioactive source is removed, what would you expect the reading now?

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(d) After 10 days, this experiment is repeated again. The source is again placed at a

distance of 2 cm from the detector. What would you expect the reading now

comparing with the average count of 300 counts per minute initially. Assume that the

half-life of this sample is in the order of days.

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3 A sample of radioactive substance is emitting β radiation with a half-life of 5 700 years.

(a) State three properties of β radiation.

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(b) At the beginning, the sample has 1 000 radioactive nuclei. Sketch its corresponding

decay curve for the next coming 17 100 years.

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(c) How many radioactive nuclei are left after 5 half-lives?

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(d) Give an example of radioactive substance, which has a half-life similar to this

sample.

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(e) Does the radioactive substance decay faster at the initial period of time or after

several half-lives? Explain briefly.

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4 The following set-up is used to find out the type of radiation emitted by three radioactive

sources, X, Y and Z. It is known that one of them is pure alpha source, one of them is pure

beta source and the third one emits all three kinds of radiation. The table records the

readings recorded by three GM counters placed at positions A, B and C.

Fig

Table

(a) What is the count rate of the background radiation?

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(b) Which radioactive source emits all three types of radiation?

Ans:

(c) If a voltage supply is not available, suggest another equipment that can be used to

identify the samples.

Ans:

End


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