P1 Atomic Structure Flashcards
In standard form, what is the radius of an atom?
1x10*-10
How does EM absorption effect electrons?
Move electrons to a higher energy level further from the nucleus
How does EM radiation emission effect electrons?
Moved to a lower energy level, nearer to the nucleus
Define an isotope
Same number of protons and electrons, different number of neutrons
Describe the Plum Pudding Model
- JJ Thompson in 1897
- Atoms are balls of positive charge with electrons bedded in it
Describe the Gold Foil Experiment
- 1905, Rutherford and Marsden
- Positive alpha particles fired at a one atom thick sheet of gold foil
Why were some alpha particles reflect back during the gold foil experiment?
- repelled by same charge as alpha particles
- repelling particles are heavier than the alpha particle, or alpha particles would’ve passed through
What are the conclusions of the Gold Foil Experiment?
- mass of atom concentrated in the centre, positive charge
- surrounded by electrons
What did Niels Bohr discover?
Adapted the nuclear model to show electrons orbit at specific distances
What did Chadwick discover?
Neutrons, increases knowledge of isotopes
Why do atomic nuclei emit radiation?
They are unstable
What does type of radiation emitted depend on?
- why the nucleus is unstable
- random and unpredictable
Radioactivity is measured in…
Bequerels
1Bq = 1 count / second
What is radioactive decay measured with?
Geiger Muller tube
Which type of nuclear decay is most ionising?
alpha
Which type of nuclear radiation is most penetrating?
Gamma
Describe alpha radiation
- two neutrons, two protons (helium nucleus)
- absorbed by and damages living cells
Describe beta radiation
- high speed electrons
- ejected from the nucleus when a neutron becomes a proton
- can penetrate through body to inner organs
Describe gamma radiation
- em radiation
- passes through living cells without being absorbed or ionising
What is another type of nuclear decay?
neutron
Define radioactive contamination
unwanted presence of materials containing radioactive atoms on other materials
Why is contamination hazardous?
radioactive decay of contaminating atoms
What is irradiation?
- exposing an object to nuclear radiation
- deliberate or accidental
- object does not become radioactive
How can you prevent unwanted irradiation?
- using sources of lowest activity for shortest time
- wear protective clothing (lead apron)
- don’t handle sources with bare hands
Compare hazards of contamination and irradiation (food, area contaminated with alpha)
- food contaminated with alpha would be more hazardous than gamma as alpha is stronger ionising
- area contaminated with alpha wouldn’t be dangerous unless it was entered, because it isn’t penetrating
gamma would irradiate people nearby as it is highly penetrable
What is half life?
A measure of how long it takes for half of the radioactive atoms to decay
Explain what is meant by radioactivity being a random event
It is impossible to predict what will decay next
Describe isotopes with a short half life
- unstable
- emit radiation quickly
- exposure is hazardous
- aren’t radioactive for long
Describe isotopes with long half lives
- more stable
- radioactive for longer
- emit slowly
- exposure is less harmful
Describe 4 uses of nuclear radiation
MEDICAL TRACERS
- isotope ingested or injected in to body
- can be detected from outside as it travels around body
MONITORING KIDNEY FUNCTION
- isotope used that’ll pass through kidneys
- if it builds upon one kidney but not another, one kidney isn’t working efficiently
INTESTINE BLOCKAGES
- blockage = radioactivity can’t be detected after blockage
- damage = radioactive source can be seen passing out of kidneys to other parts of body where it shouldn’t
TUMOURS
- focussed beam of gamma rays
- radioactive iodine for thyroid rumours, gathers in the gland and destroys cells
When choosing an isotope for medical use, what should be considered?
half life (needs to be long enough to perform task but not too long that it stays radioactive in patient for a long time) , activity, type of radiation
Why are gamma rays best for tracers
- penetrates the body
- can be detected from outside
- least ionising
What are the components of background radiation?
- radon gas
- medical (x-rays)
- nuclear
- cosmic rays
- gamma
- food
13% man made
87% natural
What does someone’s exposure to background radiation depend on?
- location (some places have higher natural background radiation)
- occupation (some jobs are exposed to radiation daily)
Define nuclear fission and how it occurs
- splitting if a large unstable nucleus (uranium or plutonium)
- needs to absorb a neutron (won’t occur on its own)
- absorbs a neutron
- splits into two equal nuclei
- emits: 2/3 neutrons, gamma rays, energy
- all products have kinetic energy
- chain reaction
What are the uses of nuclear fission?
- nuclear reactors ( chain reaction is controlled for constant steady energy release)
- explosions in nuclear weapons are uncontrolled chain reactions
Describe nuclear fusion
- opposite of fission
- two light nuclei join to form a heavier nucleus
- some of the mass is converted in to energy which may be emitted as radiation
Why does nuclear fusion require high temperatures and pressures?
- overcome electrostatic repulsion
- bring positive nuclei close enough for fusion to occur
How is alpha decay represented in nuclear equations?
4
2 He
- mass number -4
- atom number -2
How is beta decay represented in nuclear equations?
0
-1 e
- mass number doesn’t change
- atomic number +1
