Radiation And Waves Flashcards
What is ionisation?
It is the addition or removal of an electron to create an ion
What happens if you:
(a) Lose an election?
(b) Gain an electron?
(a) Creates a positive ion
(b) Creates a negative ion
How are electrons lost?
Ionising radiation comes close to / collides with the atom and forces the electron away
Name the three types of ionising radiation
Alpha - helium nucleus
Beta - fast moving electron
Gamma - high energy electromagnetic wave
What is the mass and charge of the three radiations?
Alpha - large mass, strong positive charge
Beta - very small mass, negative charge
Gamma - no mass, no charge
What is penetrating power?
Radiation has a different ability to penetrate materials. The material is said to have absorbed the radiation.
Rate the radiations from least penetrating to most
Alpha - thickness of skin
Beta - few millimetres of aluminium
Gamma - several centimètres of lead
What is radioactive decay?
It’s when the nuclei of some atoms are unstable, they naturally release off ionising radiation which allows the nucleus to become stable
What natural resources produce background radiation?
The ground, building materials, food and cosmic rays from space
Which radioactive gas do rocks produce?
Radon
Give examples of artificial radiation
Radioactive waste from nuclear power stations, radioactive fallout from nuclear weapons testing and medical x-rays
What percentage of average background radiation does does artificial sources account for?
15%
How does a Geiger miller tube work?
When radiation enters it produces ions in the gas. The ions produce a current which produces a voltage pulse. These pulses are counted and displayed on a GM tube.
How do you get a proper indication of how radioactive a source is?
Measure the number of ionisations per second or the count rate
What is the count rate usually called and how is it given?
The activity and it’s given by the number of counts or ionisations per second
What is the activity of a radioactive source and how is it measured?
It is the number of decays per second and it’s measured in becquerels
What do the letters stand for and their units in the formula for the activity?
A = N/t
A - activity of source in becquerels (Bq)
N - number of decays
t - time in seconds (s)
What is background radiation?
Radiation from natural sources and man made sources that is around us all the time. Usually less than 1Bq
What is half life?
Half life is the time taken for the activity of a radioactive source to reduce by half
What is absorbed dose?
It is the energy absorbed per unit mass of the absorbing materials
Label the equation and state the units:
D = E/m
D - absorbed does in grays (Gy)
E - energy absorbed in joules (J)
m - mass of absorbing tissue (kg)
What is the radiation weighting factor?
It is the measure of the biological effect of different types of ionising radiation
what are the weighing factors for the radiations below:
Alpha Beta Fast neutrons Gamma Slow neutrons
20 1 10 1 3
What is equivalent does?
It takes into account the type of radiation and the total energy
absorbed
Label and state the units for the formula for equivalent dose below:
H =D x Wr
H - equivalent dose in sieverts (Sv)
D - absorbed dose in grays (Gy)
Wr - radiation weighing factor
What does equivalent dose rate tell us?
The equivalent dose a person receives over a specified period of time
Label and state the units of the formula below:
H = H/t
H - equivalent dose rate in sieverts per hour (Sv/hr)
H - equivalent dose in sieverts (Sv)
t - time (hr)
Name a few examples of how someone can protect themselves from radiation
Keeping distance Using tongs Storing sources in lead lined boxes Labelling all radioactive sources Wearing a film badge to monitor exposure Wearing protective clothing
What are the prefixes and multiplication factors of the symbols below:
M k m G u n
Mega 10x6 Kilo 10x3 Milli 10x-3 Giga 10x9 Micro 10x-6 Nano 10x-9
What is the equation for half life?
Half life in days = number of days / number of half lives
What do waves do and how?
They transfer energy from one point to another by vibrating particles up and down or back and forth
What is the wavelength of a wave?
The length of one complete wave
How do you calculate wavelength?
Wavelength = distance / number of waves
What is the frequency of a wave and how is it measured?
It is how many waves pass a particular point in one second
It’s measured in hertz (Hz)
What is the formula for frequency?
Frequency = number of waves / time
The _____ of a wave is the time for one complete wave to pass a point in seconds
Period (T)
What is the formula to calculate the period?
T = 1/f
What is wave speed?
How far a wave travels in one second
What is diffraction?
When a wave bends around an obstacle or spreads through a gap
What type of wave diffracts more?
Longer waves
How does gap size affect diffraction?
The smaller the gap the bigger the diffraction
What is constructive diffraction?
When two waves that are in-phase meet (crest to crest, trough to trough) the amplitude doubles
What is destructive diffraction?
When two waves out of phase meet (crest to trough, trough to crest) they cancel each other out
What does the law of reflection state?
The angle of incidence is always equal to the angle of reflection
What is refraction?
It is when light passes from one medium to another
What happens to the speed of light when it enters a more dense material like glass?
It slows down then speeds up when it enters a less dense material like air
Which direction does light bend towards the normal?
It bends towards the normal when it passes to dense material and bends away when passing to air
Name the two lenses:
_
\ /
/ \
()
Concave (diverging)
Convex (converging)
What do convex lenses do?
Converges (focuses) the parallel light beams on the focal point. (The light is more intense at the focal point)
What do concave lenses do?
Causes parallel light beams to spread out (diverge)
What is the electromagnetic spectrum?
The em spectrum is a family of waves that don’t require particles to travel
If the em spectrum waves don’t require particles, where can they travel?
A vacuum eg. Space
What speed do em waves travel?
The speed of light 3x10 8
What is the order of the em spectrum?
Radio Microwave Infrared Visible Ultraviolet X-ray Gamma ray
