The Nuclear Atom and Radioactivity Flashcards
What does an atom consist of?
An atom consists of a small nucleus surrounded by electrons
What charge do electrons carry?
Negative
What does the nucleus contain?
Protons and neutrons
What are the charges of protons and neutrons?
Protons are positively charged whereas neutrons do not carry any charge
When is an atom neutral?
An atom is neutral if it has an equal number of positive and negative charges in the atom
Define an ion
An ion is an atom which has an excess number of protons or an excess number of electrons
Define nucleon
Particles in the nucleus are collectively known as nucleon
Define nucleon number/mass number
It is the number of protons and neutrons in the nucleus
Define nuclei
Plural of nucleus
Define nuclide
Term used to refer to an atom
Define isotopes
They are atoms of the same element that have the same proton number but different mass numbers
Define radioactivity
It is the spontaneous disintegration of the nucleus of a radioactive atom in an attempt to become more stable
Dangers of radioactivity (2)
1) It may cause radiation sickness
2) They reduce the lifespan of an individual
Precautions required when handling radioactive sources (7)
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
Charges of alpha, beta and gamma
Alpha +2.
Beta -1.
Gamma 0
Mass of alpha, beta and gamma
Alpha - high
Beta - low
Gamma - 0
Speed of alpha, beta and gamma
Alpha - 1/10 (speed of light).
Beta - between 1/10 and 9/10 (speed of light)
Gamma - speed of light
Range of alpha, beta and gamma
Alpha - short
Beta - moderate
Gamma - very long
Ionising strength of alpha, beta and gamma
Alpha - strong
Beta - weak
Gamma - very weak
What are alpha, beta and gamma stopped by?
Alpha - thin paper/human skin
Beta - aluminium sheet
Gamma - thick lead or a few meters of concrete
Nature of alpha, beta and gamma
Alpha - helium nucleus
Beta - high energy electron
Gamma - high energy E.M wave
(know symbol for each)
Define (alpha/beta/gamma) decay
It is the emission of a (alpha/beta/gamma) particle from the nucleus of a radioactive material
Equation to represent alpha decay
X —-> Y (atomic number - 4) (mass number -2) + helium nucleus (learn for beta and gamma decay equation)
What does the random nature of radiation mean?
We cannot predict which nucleus will decay, how much time it will take to decay and the direction in which it will decay
What is background radiation?
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
Define the half life of a radioactive source
It is the time taken for the total number of radioactive atoms to decrease to half its initial value
Formula for half life of a radioactive source
Number of atoms after half life = (1/2) to power of n x initial number of atoms.
Where n = total time/half time
Define nuclear fission
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
Define nuclear fusion
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
Why does nuclear fusion occur around the sun? (not only the sun)
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
Uses of radioactivity (2)
1) In the production of electricity
2) In hospitals for medical diagnosis and therapy of cancer cells
Describe ow a star is formed (4)
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
Describe an experiment to check whether a reactive source emits alpha, beta or gamma
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.)
Describe an experiment that shows that a radioactive source contains only beta
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
A nuclear power station generates electrical energy, explain how electricity is produced. Include a block diagram.
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
What does G.M tube stand for?
Geiger-Muller tube
