Topic 3 - Radioactivity and Atomic Structure Flashcards
(43 cards)
1
Q
What were the first ideas about atoms
A
- John Dalton thought that atoms were tiny balls of matter that couldn’t be broken up
2
Q
Describe the plum pudding model
A
A ball of positive charge with negatively charged electrons embedded in it
3
Q
What was the gold foil experiment
A
- Positively charged alpha particles were fired at a thin gold foil
- Circular detector screen surrounding gold foil detects alpha particles deflected
4
Q
What results were Rutherford expecting?
A
- most of the alpha particles would pass straight through or some would be very slightly deflected ( < 1°)
5
Q
Results of alpha particle experiment
A
- most alpha particles went straight through as expected
- however some were reflected more than expected
- a few alpha particles were reflected straight back at them
6
Q
What did this explain?
A
- most of the atom was empty space because most alpha particles passed through
- nucleus must have large positive charge as some particles reflected/deflected by big angle
- nucleus must be small as very few particles were deflected/ reflected
7
Q
2 differences between nuclear model and plum pudding
A
- nuclear model has positive charge concentrated in small nucleus but P.P has it spread out
- nuclear model is mostly empty space but P.P is a ‘ solid mass ‘
8
Q
3 developments to nuclear model
A
- Niels Bohr discovered that electrons orbit nucleus at certain distances in shells : this stopped atom collapsing
- nucleus could be split into a group of atoms with positive charge(protons)
- James Chadwick proved existence of neutral atoms in nucleus( neutrons)
9
Q
what happens when an atom absorbs/emits EM radiation?
A
- when an atom absorbs EM radiation electrons move to a higher energy level : further
- when an atoms emits EM radiation electrons move to a lower energy level : closer
10
Q
ion
A
atom that has lost or gained electron(s)
11
Q
isotopes
A
different form of same element with same no. of protons but different no. of neutrons
12
Q
Radioactive decay
A
when unstable nuclei emit radiation to try and become stable
13
Q
random nature of radioactive decay
A
- you don’t know which nuclei is going to decay
- and when they are going to decay
14
Q
alpha particle
A
2 protons, 2 neutrons ( helium nucleus )
15
Q
properties of alpha particles
A
- low penetration
- high ionising power
- travels few cm in air
- absorbed by a tissue/ skin cells
16
Q
beta particle
A
electron ejected from unstable nucleus
17
Q
properties of beta particles
A
- medium penetration
- medium ionising power
-travels few metres in air - absorbed by a sheet of aluminium
18
Q
gamma decay
A
high frequency EM radiation released by unstable nucleus
19
Q
properties of gamma decay
A
- high penetration
- low ionising power
-travels few miles in air - absorbed by thick layer of concrete
20
Q
activity
A
how many radioactive decays happen per second ( Bq)
21
Q
what is a Geiger Muller tube
A
records the amount of radiation counts detected per second and measures activity
22
Q
half-life
A
The time it takes for the number of nuclei ( or activity ) of a radioactive isotope to halve
23
Q
dangers of short half-life
A
- initially they can be dangerous due to the high amounts of radiation they emit at the start
- activity falls quickly and and they quickly become safe
24
Q
dangers of long half-life
A
- in the short term they aren’t so dangerous
-in the long term this is dangerous because nearby areas are exposed to radiation for millions of years
25
irradiation
exposure to radiation from a radioactive source
26
how to minimise risk of irradiation
- keep sources in lead- lined boxes ,
- standing behind barriers
- using remote controlled arms to handle sources
27
contamination
unwanted presence of radioactive atoms on or in another material
28
how to minimise risk of contamination
- gloves and tongs when handling sources
- protective suits
29
Why is beta and gamma the main concern with irradiation
- beta and gamma have higher penetration power so can pass through the body and get to delicate organs
- alpha particles can't penetrate skin and easily blocked by small air gap
- high levels of irradiation from bet and gamma are most dangerous
30
Why is alpha the main concern with contamination
- higher ionising power and do all their damage in localised area
- they don't pass through the body so just stay in the body doing damage
- higher chance of causing mutations which can cause cancer
- beta and gamma pass through the body without doing much damage as they have a lower ionising power
31
radiation dose
measure of the risk of harm to the body due to radiation
32
background radiation
low-level radiation that is present at all times
33
sources of background radiation
- naturally occurring unstable isotopes ( air, rocks )
- cosmic rays from space
- man made sources ( nuclear disasters like chernobyl )
34
effect of location
-people who live in higher altitudes are exposed to more cosmic rays
-people living in places with a lot of radioactive rocks like Cornwall
35
effect of occupation
- uranium miners are exposed to a lot of radiation so need to wear face masks and protective clothing
- miners due to lots of rocks
36
ionising radiation effects on living cells
- knock electrons of cells and changes and damages DNA
- this causes mutant cells which divide uncontrollably
- making tumours and causing cancer if it spreads
- high dose can kill cells completely causing radiation sickness
37
using radiation - medical tracers
- radioactive isotopes injected into people
- their progress around the body is followed using detector which shows where the strongest reading come from
- this makes sure that internal organs are working properly
38
what type of isotopes should be used ( gamma )
- they aren't highly ionising and won't do damage in localised area
-they pass directly out of body as well
39
what type of isotopes should be used ( short half life )
- radioactivity inside patient quickly disappears
40
using radiation - medical tracers - radiotherpay
- focusing ionising radiation on cancer cells to kill them
- must be directed carefully and at right dosage to not kill too many helathy cells
41
nuclear fission
when a large unstable nucleus splits into two smaller ones ( usually has to absorb neutron)
42
nuclear chain reaction
- nucleus absorbs a neutron
- it releases energy and splits into two smaller nuclei, also releasing 2 or 3 neutrons
- those neutrons will collide with other nuclei and start the process over again
43
nuclear fusion
- two light nuclei combine to form a heavier, bigger nucleus and also releases energy
