5.1 Understanding the Nucleus of an Atom / 9 X 100 = %

CHAPTER 5

RADIOACTIVITY

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

A student is able to

5.1.1 describe the composition of the nucleus of an atom in terms of protons and neutrons.

5.1.2 define proton number (Z) and nucleon number (A).

5.1.3 explain the term nuclide

5.1.4 use the nuclide notation X

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

______

b) The least number of nucleon

______

c) The most number of protons

______

d) The least number of protons

______

e) The most number of neutrons

______

f) The least number of neutrons.

______

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

A student is able to:

5.2.1 state what radioactivity is.

5.2.2 name common detectors for radioactive emissions.

5.2.3 compare the 3 kinds of radioactive emissions in terms of their nature.

5.2.4 explain what radioactive decay is.

5.2.5 use equations to represent changes in the composition of the nucleus when particles are emitted.

5.2.6 explain half -life.

5.2.7 determine half-life from a decay curve.

5.2.8 solve problems involving half -life.

Fill in the blank.

1 Radioactivity is the spontaneous and ______emission of radioactive rays

from an______nucleus to become ______nucleus.

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]

Types of radiation / α / β / γ
Nature / Helium nuclei
Ionising effect / Moderate
Penetration / High

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

i + à + + energy

P : ______Q : ______

ii à +

R : ______S : ______

iii à + + 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.

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
g - rays / / 1. Track are short,…………. and irregular
2. g - 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.

Absorber / Air / Paper / Aluminium 3 mm / Lead 10 cm
Rate meter reading / 120 / 119 / 50 / 50

What type of radiation is emitted by the radioactive source ? Why ?

______

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

Write down the equation?

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: ______

______

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.

the source increases?

______

13 Using the table below answer the following question.

Radioactive isotope / Half-life
Strontium-90 / 28 years
Radium-226 / 1602 years
Iodine-128 / 2 minutes

(a) If the samples of strontium-90 and radium-226 both has the same activity now

Which 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 ?

______

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

A student is able to:

5.3.1 define radioisotopes.

5.3.2 name examples of radioisotopes.

5.3.3 describe applications of radioisotopes.

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.

______, ______, ______

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.

______

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?

______

(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.

______

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

______.

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

A student is able to:

5.4.1 define atomic mass unit (a.m.u.).

5.4.2 describe nuclear fission.

5.4.3 give examples of nuclear fission.

5.4.4 describe chain reactions.

5.5.5 describe nuclear fusion.

5.4.6 give examples of nuclear fusion.

5.4.7 relate the release of energy in a nuclear reaction with a change of mass according to the equation E = mc 2 .

5.4.8 describe the generation of electricity from nuclear fission.

5.4.9 justify the use of nuclear fission in the generation of electricity.

5.5.10 solve problems involving nuclear energy.

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 + n / Ba + Sr + 2 n + Energy
Total atomic mass / 240.06082 a.m.u / 239.85830 a.m.u

TABLE 1

Table 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

______

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) Advantage

i) ______

ii) ______

b) Disadvantage

i) ______

ii) ______

5.5 Realising the importance of proper management of radioactive substances

[ ………/ 7 x 100 = …………….. % ]

A student is able to:

5.5.1 describe the negative effects of radioactive substances.

5.5.2 describe safety precautions needed in the handling of radioactive substances.

5.5.3 describe the management of radioactive waste

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.

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

activity.

______

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

and the safety of other users of the laboratory.

______