The Nuclear Atom and Radioactivity

Question 1

What does an atom consist of?

Answer 1

An atom consists of a small nucleus surrounded by electrons

Question 2

What charge do electrons carry?

Answer 2

Negative

Question 3

What does the nucleus contain?

Answer 3

Protons and neutrons

Question 4

What are the charges of protons and neutrons?

Answer 4

Protons are positively charged whereas neutrons do not carry any charge

Question 5

When is an atom neutral?

Answer 5

An atom is neutral if it has an equal number of positive and negative charges in the atom

Question 6

Define an ion

Answer 6

An ion is an atom which has an excess number of protons or an excess number of electrons

Question 7

Define nucleon

Answer 7

Particles in the nucleus are collectively known as nucleon

Question 8

Define nucleon number/mass number

Answer 8

It is the number of protons and neutrons in the nucleus

Question 9

Define nuclei

Answer 9

Plural of nucleus

Question 10

Define nuclide

Answer 10

Term used to refer to an atom

Question 11

Define isotopes

Answer 11

They are atoms of the same element that have the same proton number but different mass numbers

Question 12

Define radioactivity

Answer 12

It is the spontaneous disintegration of the nucleus of a radioactive atom in an attempt to become more stable

Question 13

Dangers of radioactivity (2)

Answer 13

1) It may cause radiation sickness

2) They reduce the lifespan of an individual

Question 14

Precautions required when handling radioactive sources (7)

Answer 14

1) Store radioactive source in special lead boxes
2) Wear a lab coat, gloves, mask and goggles
3) The window of the box myst be opened in a direction away from the experimenter
4) Long tongs should be used to handle a sample of radioactive material
5) The room should be ventilated
6) Mild sources should be used
7) The radiographer must wear a badge that can be checked regularly to see if he has absorbed ionising radiation

Question 15

Charges of alpha, beta and gamma

Answer 15

Alpha +2.
Beta -1.
Gamma 0

Question 16

Mass of alpha, beta and gamma

Answer 16

Alpha - high
Beta - low
Gamma - 0

Question 17

Speed of alpha, beta and gamma

Answer 17

Alpha - 1/10 (speed of light).
Beta - between 1/10 and 9/10 (speed of light)
Gamma - speed of light

Question 18

Range of alpha, beta and gamma

Answer 18

Alpha - short
Beta - moderate
Gamma - very long

Question 19

Ionising strength of alpha, beta and gamma

Answer 19

Alpha - strong
Beta - weak
Gamma - very weak

Question 20

What are alpha, beta and gamma stopped by?

Answer 20

Alpha - thin paper/human skin
Beta - aluminium sheet
Gamma - thick lead or a few meters of concrete

Question 21

Nature of alpha, beta and gamma

Answer 21

Alpha - helium nucleus
Beta - high energy electron
Gamma - high energy E.M wave

(know symbol for each)

Question 22

Define (alpha/beta/gamma) decay

Answer 22

It is the emission of a (alpha/beta/gamma) particle from the nucleus of a radioactive material

Question 23

Equation to represent alpha decay

Answer 23

X —-> Y (atomic number - 4) (mass number -2) + helium nucleus (learn for beta and gamma decay equation)

Question 24

What does the random nature of radiation mean?

Answer 24

We cannot predict which nucleus will decay, how much time it will take to decay and the direction in which it will decay

Question 25

What is background radiation?

Answer 25

A weak radiation present in the atmosphere due to the cosmic effect of cosmic rays in the earths atmosphere or radioactive materials in the earth

Question 26

Define the half life of a radioactive source

Answer 26

It is the time taken for the total number of radioactive atoms to decrease to half its initial value

Question 27

Formula for half life of a radioactive source

Answer 27

Number of atoms after half life = (1/2) to power of n x initial number of atoms. Where n = total time/half time

Question 28

Define nuclear fission

Answer 28

It is the process during which a heavy nucleus splits into smaller nuclei to release energy after bombarding the nucleus with neutrons. E.g. in an atomic bomb, in a power plant to generate electricity

Question 29

Define nuclear fusion

Answer 29

It is the process during which 2 or more light nuclei fuse together to form an intermediate unstable nucleus which in turn releases energ E.g. in a hydrogen bomb and emission of light from the sun

Question 30

Why does nuclear fusion occur around the sun? (not only the sun)

Answer 30

Nuclei do not come together easily since like charges repel but in the sun there is a high temperature and the kinetic energy of the nuclei is large enough to overcome the repulsive forces

Question 31

Uses of radioactivity (2)

Answer 31

1) In the production of electricity | 2) In hospitals for medical diagnosis and therapy of cancer cells

Question 32

Describe ow a star is formed (4)

Answer 32

1) Gravity pulls hydrogen clouds together 2) Temperature of hydrogen cloud increases 3) Process of nuclear fusion of hydrogen takes place and temperature increases further 4) At extremely high temperatures, the cloud lights up to become a star

Question 33

Describe an experiment to check whether a reactive source emits alpha, beta or gamma

Answer 33

Step 1: A G.M tube is used to measure the background radiation (x) Step 2: By placing the G.M tube in front of the radioactive source, its count rate is measured (y) Step 3: Paper is placed between the source and the G.M tube (If the count rate decreases to x, the source contains only alpha but if it remains y it does not contain alpha. If it decreases to a value between x and y the source contains alpha and other radiations) Step 4: Aluminium is placed between the source and the G.M. tube (If the count rate does not decrease, the source does not contain beta but if it decreases to x the source does not contain gamma. If the count rate decreases to a value above x the source will contain gamma and beta.)

Question 34

Describe an experiment that shows that a radioactive source contains only beta

Answer 34

Step 1: A G.M tube is used to measure background radiation (x) Step 2: By placing the G.M tube in front of the radioactive source, its count rate is measured (y) Step 3: Paper is placed between the source and the G.M tube. The count rate remains y. This implies that the source does not contain alpha Step 4: Aluminium is placed between the source and the G.M tube. The count rate will decrease x. This implies that the source contains only beta

Question 35

A nuclear power station generates electrical energy, explain how electricity is produced. Include a block diagram.

Answer 35

1) In the reactor, nuclear fission occurs and there is a continual release of of energy (chain reaction) 2) Heat is absorbed by the coolant which transfers heat to the water. 3) This causes the water to turn into steam to drive the turbine reactor ---> coolant -----> generator and waste

Question 36

What does G.M tube stand for?

Answer 36

Geiger-Muller tube