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CHAPTER 5RADIOACTIVITY

5.1 Understanding the nucleus of an atom [ …………/ 9 x 100 = …………….. % ]

1 A nuclide is an atom of a particular structure

A nucleus for element X is represented by X

What does A , Z and X represent?

A: ____________________ Z:___________________ X: __________________

2 Below are the symbols for five nuclides

Rn Po U Ba Kr

Which of the above nuclides contains. [6 M]

a) The most number of nucleon

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b) The least number of nucleon

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c) The most number of protons

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d) The least number of protons

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e) The most number of neutrons

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f)The least number of neutrons.

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5.2 Analysing radioactive decay [ ………/ 52 x 100 = …………….. % ]

Fill in the blank.

1 Radioactivity is the spontaneous and _________________ emission of radioactive rays

from an__________________ nucleus to become ___________________ nucleus.

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Name of detectors Particles or rays detected, α, β or γ.

Geiger Muller Tube (GM Tube)

Spark Counter

Gold leaf electroscope

Photographic plate

3 Radioactive substances may emit alpha, beta and gamma radiation .Fill in the table to describe the characteristics of the three kinds of radiation. [6 M]

4 The equation below represents a nuclear reaction. What is the value of P,Q,R,S,T and U. [6 M]

i + + + energy

P : ___________________ Q : __________________________

ii +

R : ___________________ S : __________________________

Types of radiation α β γ

Nature Helium nuclei

Ionising effect Moderate

Penetration

High

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iii + + γ

T : ___________________ U : __________________________

5 Show in the diagram below how α, β and γ are affected in

(i) electric field . [ 3M]

(ii) and magnetic field. [3 M]

6 Diagram shows a cloud chamber.

Positive plate (+) Negative plate (-)

Radioactive source

Magnetic field into the paper

Radioactive source

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When a radioactive source is placed inside the chamber . The radiation produced passes through the vapour thus forming tracks in the dense alcohol vapour due to the condensation of the alcohol vapour on the ions formed. These tracks are seen through the transparent plastic lid.

Fill in the balnks and complete the tracks produced and the nature of tracks in the table below to show the detection of different types of radiation by the cloud chamber. [6 M]

Type of radiation Tracks produced Nature of tracks

Α- Particles

1. Tracks are ……………….. because of bigger mass .

2. Tracks are .................because of strong ionising effect.

ß – Particles 1. Tracks are twisted and thinner

2. Easily collides with the vapour molecule

3. Less ionizing effect compare with alpha particles

- rays

1. Track are short,…………. and irregular

2. - rays have the lowest ………… effect

3. ……………. penetrating power.

7 The arrangement of the apparatus is used to study the type of radioactive radiation emitted by a radioactive source.

Table below shows the result of the study.

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What type of radiation is emitted by the radioactive

source ? Why ?

_______________________________________________________________________________

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8 A nucleus of radioactive isotope emits an α- particles when it decays to a nucleus of an element Polonium, Po. [4M]

a. Write down the equation?

b. How many neutrons, protons and electrons are there in a Po atom ?

n :__________________ p :__________________ e:___________________

9 A nitrogen nucleus is bombarded with another particle as shown in the equation below. N + He O + X

(a ) Name the particle used to bombard the nitrogen nucleus?

___________________________________________________________________________

(b) Determine the nucleon number and the proton number of X.

___________________________________________________________________________

10 (a) Describe the difference in structure between H , H and H.___________________________________________________________________________

(b) Name the isotopes

H : _____________ H: ____________ H: ___________

(c) Is there any difference in chemical properties ?. Give reason for your answer

_________________________________________________________________________

_________________________________________________________________________

Absorber Air Paper Aluminium 3 mm Lead 10 cm

Rate meter reading 120 119 50 50

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11 Radium was one of the first substances known to show the property of radioactive decay. Radium has along half-life

(a) What is meant by radioactive decay?

____________________________________________________________________

(b) What is meant by half-life?

_____________________________________________________________________

12 Diagram below is part of the decay curve for a sample of a radioactive isotope. Half life of the isotope is 5 minute. [4M]

(a) What is meant by isotope?

______________________________________________________________________ (b) Based on Diagram

(i) Determine the activity at the 1st half-life of the isotope.

_______________________________________________________________________

(ii) Complete the curve at the diagram above up to 15 minutes.

(c) Predict what happen to the reading if the distance between detector and

the source increases?

___________________________________________________________________________

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13 Using the table below answer the following question.

Radioactive isotope Half-lifeStrontium-90 28 yearsRadium-226 1602 yearsIodine-128 2 minutes

(a) If the samples of strontium-90 and radium-226 both has the same activity nowWhich would have the lower activity in 10 years time. [3M]

___________________________________________________________________________ (b) i) If the activity of iodine is 400 count/min what would be the activity after 6 minutes

___________________________________________________________________________

ii) What is the time taken if the activity of iodine left is only 12.5 count/min ?

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5.3 Understanding the uses of Radioisotopes [ ………/ 19 x 100 = …………….. % ]

Answer the questions below:

1. The nuclei of an element that has the same proton number but

________________________ are called as ______________________.

2. Radioisotopes are ______________________which decay and emits

__________________ emissions such as ______________ particles, ____________

particles or _________________ rays.

3. Give 3 examples of radioisotopes and name the possible radioactive emission.

___________________, ___________________, ___________________

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4 The top part of the diagram shows a section of steel plates which have been welded edge to edge at A, B and C, to make a large steel sheet. A gamma ray source was placed on one side of the sheet, pointing towards gamma ray detector on the other side. As the source and detector were moved together along the steel sheet the output of the detector was measured and is detector shown at monitor screen in the lower part of the output diagram.

(a) Explain what the detector output tells the engineer who did the welding about the joints at A, B and C.

______________________________________________________________________

______________________________________________________________________

(b) Explain how this procedure provides useful information about the steel sheet.

______________________________________________________________________

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5 The thickness of paper can be checked by putting a radioactive source on one side of the paper and a detector on the other side.

(a) Explain why α and γ , sources would not be suitable. α, β and γ

α is not suitable because

____________________________________________________________________

γ is not suitable because

____________________________________________________________________

(b) How would the amount of α radiation passing through the paper be changed if the thickness of the paper increased?

____________________________________________________________________

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(c) In such an experiment it was found that the number of counts per minute varied even when the thickness of the paper was unchanged. Explain this observation.

____________________________________________________________________

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6 In a paper mill, paper pulp is squeezed between rollers to form a paper strip.

The pressure of the rollers is controlled by a signal from a radiation detector as shown radiation in the diagram. A radioactive source is placed on the paper opposite side of the paper to the detector.Suggest how this arrangement produces paper of uniform thickness.

Explain why the radioactive source has to be handled with care.

Fill in the blank

If the radiation detector displays the same reading that is the expected reading when the paper strip passes through the pulp, we conclude that the thickness of paper is

_________________.

If the radiation detector displays higher than the expected reading when the paper strip passes through the pulp, we conclude that the thickness of paper is

__________________.

If the radiation detector displays lower than the expected reading when the paper strip passes through the pulp, we conclude that the thickness of paper is

__________________.

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5.4 Understanding Nuclear Energy [ ………/ 12 x 100 = …………….. % ]

1 1 a.m.u is defined as ______________ of the mass of a carbon-12 atom.

2 1 a.m.u is equals to _____________________________ kg.

3 Nuclear fission is the splitting of a ________________________ nucleus into

________________ nucleus.

4 Nuclear fusion is the combining of _________________ nuclei to form a

____________ nucleus.

5 Table 1 and 2 shows nuclear fission and nuclear fusion

Nuclear fission

Before reaction After reaction

Equation

Pu +

nBa + Sr + 2 n + Energy

Total atomic mass 240.06082 a.m.u 239.85830 a.m.u

TABLE 1Table 2 shows an equation of a reaction and total atomic mass before and after a nuclear fusion.

Nuclear fusion

Before reaction After reaction

Equation H + H He + n + Energy

Total atomic mass 5.03013 a.m.u 5.01043 a.m.u

TABLE 2

a) Compare and contrast fission reaction and fusion reaction.

i). Similarities__________________________________________________________________

__________________________________________________________________

ii) Differences__________________________________________________________________

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b) Find the mass defect of one nucleus of plutonium-239

c) Calculate the energy released in the nuclear reaction. (The velocity of light is 3 108 m s-1 and 1 a.m.u is 1.66 X 10-27kg)

6. Using nuclear fission to generate electricity causes is controversial. State two advantages and disadvantages of using nuclear energy to generate electricity.

a) Advantagei) _____________________________________________________________

ii) _____________________________________________________________

b) Disadvantage

i) _____________________________________________________________

ii) _____________________________________________________________

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5.5 Realising the importance of proper management of radioactive substances

[ ………/ 7 x 100 = …………….. % ]

1 Radioactive emissions are extremely dangerous to living organisms. The________________

effect of radiation can cause genetic damage to the molecules of the cells.

2 Effect of radiation can be categorised into two that is somatic effect and genetic effect. Explain the difference and name the symptoms.

a) i) Somatic effect :_________________________________________________________

ii) Symptoms :____________________________________________________________

b) i) Genetic effect :__________________________________________________________

ii) Symptoms :____________________________________________________________

3. Mutu is carrying out an activity using solid and liquid radioactive sources. The radioactive

sources have long half lives. Among the apparatus used are forceps, rubber gloves, plastic

tray and apron.

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i). What are the precautionary procedure that need to be observed during the

activity.

_______________________________________________________________________

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ii). Describe what steps should Mutu take after the activity to ensure his own safety

and the safety of other users of the laboratory.

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