7. Radioactivity & particles Flashcards
(85 cards)
1
Q
definition of atom
A
positively charged nucleus containing protons + neutrons
smaller negative electrons orbiting outside the nuclus in shells
2
Q
definition of mass number
A
protons + neutrons
3
Q
definition of atomic number
A
no. of protons
4
Q
how to work out no. of neutrons
A
mass no. - atomic no.
5
Q
definition of isotope
A
same no. of protons but different no. of neutrons
same atomic no. different mass number
6
Q
in terms of symbol notation which no. is the mass no. and which one is the atomic no.
A
mass no. = top no
atomic no. = bottom no.
7
Q
definition of ion
A
atom which has gained or lost 1 or more electrons
8
Q
loss of electrons = ? charge
A
positive charge
9
Q
gain of electrons = ? charge
A
negative charge
10
Q
what are alpha particles, beta particles and gamma rays
A
ionising radiations emitted from unstable nuclei in a random process
11
Q
what causes ionisation
A
nuclear radiation
12
Q
how does nuclear radiation cause ionisation
A
by bashing into atoms and knocking electrons off them
( the further the radiation can penetrate before hitting an atom the less damage it will do along the way = less ionising)
13
Q
what can be used to detect ionising radiation
A
Geiger-Muller detector
photographic film
14
Q
what is an alpha particle and its properties
A
helium nuclei = 2 protons and 2 neutrons
big, heavy + slow moving
15
Q
what is the penetrating power alpha particles
A
slow moving and heavy = don’t penetrate far into materials but are stopped quickly
16
Q
what can alpha particles be blocked by
A
paper
skin
few cm of air
17
Q
what is an alpha particles ability to ionise like
A
(alpha particles are) big= strongly ionising=
bash into a lot of atoms + knock electrons off them before they slow down = creation of lots of ions
18
Q
what kind of electrical charge do alpha particles have
A
positive
19
Q
what does alpha particles being positively charged result in
A
alpha particles being deflected by electric + magnetic fields
20
Q
what does emitting an alpha particle do to the atomic no. and mass no.
A
atomic no. = -2
mass no. = -4
21
Q
what is a beta particle and its properties
A
electron
electron which has been emitted from the nucleus of an atom when a neutron turns into a proton and an electron
move quite fast + quite small
22
Q
what is the penetrating power beta particles
A
quite fast = penetrate moderately before colliding
23
Q
what can beta particles be blocked by
A
thin metal
24
Q
what is an beta particles ability to ionise like
A
quite small = moderately ionising
25
what kind of electrical charge do beta particles have
negative
26
what does beta particles being negatively charged result in
deflected by electric and magnetic fields
27
what does emitting a beta particle do to the atomic no. and mass no.
atomic no. = +1
| mass no. = stays the same
28
what is a gamma ray and its properties
energy (in the form of an EM wave )
have no mass
( opposite of alpha particles )
29
what is the penetrating power of gamma rays
penetrate a long way into materials without being stopped
30
what can gamma rays be blocked by
thick lead
| thick concreate
31
what is gamma rays ability to ionise like
weakly ionising because pass through rather than collide with atoms ( but eventually hit something and do damage)
32
what kind of charge do gamma rays have
no charge
33
what does gamma rays having no charge result in
not deflected by electric or magnetic fields
34
when does gamma emission occur
always happens after beta or alpha decay
you never get just gamma rays emitted
when a nucleus has excess energy= looses energy by emitting gamma ray
35
what does emitting a gamma ray do to the atomic no. and mass no.
no effect
atomic no. = stays the same
mass no. = stays the same
36
need to be able to balance nuclear equations in terms of mass and charge
???
37
name 2 sources of background radiation
Earth
space
(living things and human activity)
38
explain the sources of background radiation from earth
```
radioactivity comes from:
air
food
building materials
soil
rocks
```
39
explain the sources of background radiation from space
radiation from space ( cosmic rays) - mostly from the sun
40
what happens to the activity of a radioactive source over a period of time
it decreases
41
what is the activity of a radioactive source measured in
definition of activity
becquerels ( Bq) ( 1 Bq = 1 decay per second)
no. of decays in a given time
42
definition of half life
time taken for half of radioactive atoms now present to decay
(time it takes for a radioactive material to lose half of its radioactivity)
( time taken for the activity (or count rate) to fall by half
43
the older something is what happens to the radioactivity
decreases= less radiation is emitted
44
what is the rule about half life
it is varied = different for different radioactive isotopes = some take just a few hours and some millions of years
45
know how to calculate half life in equations and graphs
???
eg 4 half lives of 640=40
640 divided by 2 4 times
easier way = 640 divide by2 to the power of 4
46
uses of radioactivity in medicine
medical tracers
| treat cancers- radiotherapy
47
what kind of radiation do medical tracers use and why
beta and gamma
they penetrate the skin and other body tissues
(alpha = bad= stopped by body tissues= never detect it externally + strong ionising power= harmful if inside you )
48
how do medical tracers work
1. source which emits beta or gamma radiation is injected ( or swallowed) into patients
2. radiation penetrates the body tissues and can be detected externally
3. source moves around body- radiographer uses a detector and computer to monitor its progress
4. doctors use this method to check whether organs of the body are working properly
5. radioactive source = short half life= initial levels are high enough to be easily detected, but radioactivity in patient quickly disappears
49
what kind of radiation does radiotherapy use
gamma rays
50
how does radiotherapy work
1. kills cancer cells + stops them dividing
2. uses a high doses of gamma rays carefully directed to zap the cells in the tumour
3. while minimising the dose to rest of the body
51
uses of radioactivity in industry
sterilisation of food and equipment
tracers
thickness gauges
52
what kind of radiation is used to sterilise food an equipment
gamma rays
53
how does sterilisation work
food and equipment can be irradiated with a high dose of gamma rays to kill all microbes = doesn't go bad as quickly as it would otherwise
54
why is irradiation a good method of sterilisation
unlike boiling, it doesn't involve high temp= fresh fruit or plastic instruments = totally sterilised without being damaged
55
what kind of radiation is used in industry tracers
gamma - can pass through any rocks or earth surrounding pipes
56
how do gamma emitting tracers work
1. detect leaks in underground pipes
2. source flows down pipe and detector used above ground
3. crack in the pipe= more radiation collects outside pipe = detector show extra high radioactivity at that point
4. source = short half life= don't cause long term hazard if it collects somewhere
57
what kind of radiation does thickness gauges (thickness control) use
beta radiation is used in thickness control
paper will partly block the radiation ( if it all goes through or none of it does= reading wont change at all as thickness changes)
58
how does thickness control work
1. direct radiation through stuff being made (eg paper)
2. put detector on other side, connected to control unit
3. detected radiation level changes= paper is coming out to thick or thin
4. control unit adjusts rollers to give right thickness
59
definition of irradiation
exposure to radiation
60
how do you reduce the risk of the irradiation
keeping sources in lead-lined boxes
standing behind barriers
being in different room and using remote-controlled arms
61
definition of contamination
unwanted radioactive atoms get onto or into an object
contaminating atoms might decay =release radiation=harmful
62
why is contamination especially dangerous
radioactive particles could get inside your body
63
how do you reduce the risk of contamination
gloves and tongs - stop particles getting stuck to skin or under nails
protective suits and mask- stop breathing in particles
64
what are dangers of ionising radiation
1. cause mutations in living organisms= cells divide uncontrollably = cancer
2. damage cells and tissues
65
effects of radiation ( bad ones )
low dose= mutated cell = cancer
| high dose = dead cell= radiation sickness
66
what is difficult about the disposals of (high-level) radioactive waste
its is difficult to dispose safely -- stays highly radioactive for tens of thousands of years
67
how is low level radioactive waste disposed ( from nuclear power stations and hospitals eg. clothing +syringes)
burying it in secure landfill sites
68
how is high level radioactive waste disposed
sealed into glass blocks,
then sealed in metal canisters
,then buried deep underground
69
what is the problem with the disposal of high level waste
difficult to find suitable paces to bury it
site needs to be geologically stable ( not suffer from earthquakes) - movement of rock disturb canister = radioactive material to leak out
if material gets into ground water = contaminate soil, plants, rivers + drinking water
70
name 3 types of nuclear reaction
fission
fusion
radioactive decay
71
what are nuclear reactions source of
source of energy
72
definition of nuclear fission
splitting of an atom, which releases energy
73
where is nuclear fission purposely made to happen
nuclear reactor eg. happens to uranium-235
| energy = transferred to thermal energy stores =produce steam =drive turbine
74
what happens to uranium-235 in a nuclear reactor
nucleus can be split ( by fission) by collision with a neutron, = releases energy as kinetic energy of the fission products
75
what does the fission of Uranium-235 produce
2 radioactive daughter nuclei + a small no. of neutrons
76
definition of a chain reaction in terms of fission
slowing moving neutron absorbed by uranium-235= nucleus splits
release small no. of neutrons = go on to hit other uranium-235 nuclei= causing split and so on......
77
describe the neutrons released in a nuclear reactor and their problem
1. neutrons released by fission reactions in nuclear reactor have a lot of energy
2. in order for neutrons to be absorbed by uranium nuclei and sustain a chain reaction they need to be slowed down
78
what 2 methods are used to control the released neutrons
moderator
| control rods
79
definition of moderator ( in a nuclear reactor)
usually graphite or water = slows down neutrons
80
definition of control rods ( in a nuclear reactor)
often made from boron = limits the rate of fission by absorbing excess neutrons
81
what is the role of shielding around a nuclear reactor
used to absorb ionising radiation ( which is released from high energy neutrons and gamma rays which are released during fission )
shielding= thick concreate structure which may contain lead or other metals
82
definition nuclear fusion
creation of larger nuclei resulting in a loss of mass from smaller nuclei, accompanied by a release of energy
opposite of fission = joining small nuclei
2 light nuclei collide at high speed and join (fuse) to create a larger, heavier nucleus.
eg. hydrogen nuclei can fuse to produce a helium nucleus
83
what is fusion the energy source for
stars
| all energy released in stars comes from fusion
84
why does fusion only happen at really high temps and pressures
positively charged nuclei have to get very close to fuse, so need to be moving very fast to overcome the strong force due electrostatic repulsion of protons
85
explain differences between nuclear fission and fusion
```
fission = splitting of nucleus
fusion= joining of nuclei
```
fusion = releases a lot more energy than fission for a given mass of fuel
