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Physics > The Nuclear Atom and Radioactivity > Flashcards

The Nuclear Atom and Radioactivity Flashcards

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1
Q

What does an atom consist of?

A

An atom consists of a small nucleus surrounded by electrons

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2
Q

What charge do electrons carry?

A

Negative

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3
Q

What does the nucleus contain?

A

Protons and neutrons

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4
Q

What are the charges of protons and neutrons?

A

Protons are positively charged whereas neutrons do not carry any charge

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5
Q

When is an atom neutral?

A

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

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6
Q

Define an ion

A

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

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7
Q

Define nucleon

A

Particles in the nucleus are collectively known as nucleon

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8
Q

Define nucleon number/mass number

A

It is the number of protons and neutrons in the nucleus

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9
Q

Define nuclei

A

Plural of nucleus

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10
Q

Define nuclide

A

Term used to refer to an atom

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11
Q

Define isotopes

A

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

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12
Q

Define radioactivity

A

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

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13
Q

Dangers of radioactivity (2)

A

1) It may cause radiation sickness

2) They reduce the lifespan of an individual

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14
Q

Precautions required when handling radioactive sources (7)

A

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

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15
Q

Charges of alpha, beta and gamma

A

Alpha +2.
Beta -1.
Gamma 0

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16
Q

Mass of alpha, beta and gamma

A

Alpha - high
Beta - low
Gamma - 0

17
Q

Speed of alpha, beta and gamma

A

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

18
Q

Range of alpha, beta and gamma

A

Alpha - short
Beta - moderate
Gamma - very long

19
Q

Ionising strength of alpha, beta and gamma

A

Alpha - strong
Beta - weak
Gamma - very weak

20
Q

What are alpha, beta and gamma stopped by?

A

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

21
Q

Nature of alpha, beta and gamma

A

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

(know symbol for each)

22
Q

Define (alpha/beta/gamma) decay

A

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

23
Q

Equation to represent alpha decay

A

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

24
Q

What does the random nature of radiation mean?

A

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

25
Q

What is background radiation?

A

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

26
Q

Define the half life of a radioactive source

A

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

27
Q

Formula for half life of a radioactive source

A

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

28
Q

Define nuclear fission

A

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

29
Q

Define nuclear fusion

A

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

30
Q

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

A

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

31
Q

Uses of radioactivity (2)

A

1) In the production of electricity

2) In hospitals for medical diagnosis and therapy of cancer cells

32
Q

Describe ow a star is formed (4)

A

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

33
Q

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

A

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.)

34
Q

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

A

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

35
Q

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

A

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

36
Q

What does G.M tube stand for?

A

Geiger-Muller tube

Physics (23 decks)

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