topic 6

Question 1

6.2- size of atoms

Answer 1

radios of a nucleus is 1x10^-15

radius of an atom is 1x10^-10

Question 2

6.17- plum pudding model

Answer 2

jj thomson- discovered electrons

said atoms were spheres of positive charge with negative electrons inside

Question 3

6.17 - Rutherford alpha

Answer 3

experimented what happened to positive alpha particles when fired at gold foil
discovered most of alpha particles passed through but some bounced back- the plum pudding model couldn’t explain this
he said that most of the mass was in a central nucleus, electrons were outside the nucleus and that most of the atom is empty space the nucleus must have a positive charge since it repelled the alpha particles

Question 4

bohr model

Answer 4

rutherfords discover was changed slightly by Bohr- he said electrons were in shells as set distances from the nucleus and electrons could only exist in shells and not anywhere in-between

Question 5

6.3- nucleus of isotopes

Answer 5

same atomic number as the nucleus had same number of protons but different mass numbers due to a different number of neutrons

Question 6

6.6- charges of an atom

Answer 6

have equal numbers of protons and electrons and so an atom is neutral
a nucleus has a positive charge

Question 7

6.5charges of subatomic particles

Answer 7

proton- +1, mass of 1
neutron- 0, 1
electron- -1, mass of 1/1835

Question 8

6.7- how do electrons orbit a nucleus

Answer 8

at set distances from the nucleus called shells

Question 9

6.8 how do electrons change orbit

Answer 9

electrons can change orbit when they absorb or emit EM radiation
the part of EM radiation emitted depends on the energy of the atom and the energy levels that the shell moves between, a higher energy means a higher freq of EM radiation

Question 10

6.9- formation of ions

Answer 10

atoms can form a positive charge by losing outer electrons

ionising radiation causes atoms to be formed

Question 11

6.12- what is background radiation

Answer 11

low levels of radiation that is around us from a number of sources

Question 12

6.13- where does background radiation come from

Answer 12

radon gas- radioactive gas produced rocks that contain small amounts of uranium
food
hospital treatments
the sun

Question 13

6.14- how can photographic film be used to measure radioactivity

Answer 13

film becomes darker as more radiation reaches it

dosimeter babes check how much radiation people have been exposed to

Question 14

6.14- how can a geiger muller tube be used to measure radioactivity

Answer 14

radiation passing through the tube ionises gas inside and allows a short pulse of current to flow
the GM tube is connected to s counter that counts the pulses of current or clicks when radiation is detected
the count rate is the number of clicks per second/ minute

Question 15

6.14- how to measure radioactivity of a source

Answer 15

measure levels of background radios first. take several readings and find a mean. subtract this from the measurements of the source

Question 16

6.10 what does an unstable nucleus emit

Answer 16

an unstable nucleus emits alpha, beta minus, positron, gamma rays and neutron radiation at a random process

Question 17

what radiation is ionising

Answer 17

alpha, beta minus, position and gamma

Question 18

what is alpha radiation

Answer 18

a helium nucleus 
mass of 4
charge of 2 
strongly ionising 
short penetration distance, a few cm 
stopped by paper

Question 19

6.15 what are the different particles emitted

Answer 19

an alpha particle is a helium nucleus
a beta particle is an electron emitted from a nucleus
a gamma ray is EM radiation
positrons are particles with same mass as an electron but a charge of +1
mass number deceases by 4
atomic number decreases by 2

Question 20

6.18 what is beta - decay

Answer 20

neutron changes into a proton and an electron

atomic number increases by 1

Question 21

6.19 what is positron (beta +) decay

Answer 21

proton becomes a neurone and a positron

atomic number decreases by 1

Question 22

what is beta radiation

Answer 22

less ionising than alpha
travel a few m
stopped by aluminium

Question 23

what is gamma radiation

Answer 23

gamma rays emitted by a nucleus 
don't change mass or atomic number 
don't have a charge
travel few km 
weakly ionising 
stopped by lead or concrete

Question 24

what is neutron decay

Answer 24

nucleus emits a neutron

mass number decreases by 1

Question 25

6.21 why do atoms emit gamma radiation

Answer 25

nuclei that have undergone radioactive decay often undergo nuclear rearrangement with a loss of energy as gamma radiation

Question 26

6.23- how does the activity of a source decrease over time

Answer 26

each time a radioactive atom decays, one more radioactive nucleus disappears. as the unstable nucleus disappear the activity will decreases

Question 27

6.25- what is half life

Answer 27

is the time taken for half the undecayed nuclei to decay or the activity of a source to decay by half

Question 28

6.26- use of half life

Answer 28

it cannot be predicted when a particular nucleus will decay but half-life enables the activity of a nuclei to be predicted during the decay process. a short hl means the activity falls quickly because the nuclei are unstable and decay rapidly. a long hf means the activity fall slowly because most of the nuclei don't decay for a long time,

Question 29

6.29 fire alarms

Answer 29

contains a source of alpha particles the alpha particles ionise molecules in the air. ions are attracted to plates with opposite charges so a current flows when smoke gets into the air gap it slows down the ions and current slows down if the current drops below a certain level the alarm goes off

Question 30

6.28 irradiating food

Answer 30

gamma rays irradiate food to kill bacteria | makes it last longer

Question 31

6.28 -sterilising equipment

Answer 31

gamma rays kill micro-organism | means plastic instruments can be sterilised as he can't be sterilised with heat

Question 32

6.28 thickness gauges

Answer 32

beta particles directed through stuff being made detector on the other side detects the amount of beta particles when its too thin more beta particles get through and detector detects a higher count rate and so reduces force on rollers

Question 33

6.28 tracers

Answer 33

gamma emitting tracer is added to water to detect leaks In water pipes a GM tube following the path of the pipe will detect higher levels of radiation where there is a leak can be used to detect cancer

Question 34

6.29- dangers of ionising radiation

Answer 34

large amount can cause tissue damage like radiation burns | small amounts over long periods of time can damage DNA causing a mutation. a mutation may lead to cancer

Question 35

6.30- how is the danger of ionising radiation related to half life

Answer 35

materials with long half lives are more dangerous than ones with shorter lives. this is because the effects will last longer because their activity falls more slowly

Question 36

6.31- precautions when using radiation

Answer 36

intensity of radiation decreases with distance so sources are handled with tongs. risk can also be reduced by not pointing sources at people and storing them in lead containers

Question 37

6.31 -precautions in hospitals

Answer 37

measure exposure with dosimeter badges, shielding the source and minimising the time they spend in presence of sources patients are only expose when the benefits are greater than the risk of the radiation sources with short half lives are used to minimise time for which the patient is exposed

Question 38

6.32- contamination and irradiation

Answer 38

irradiated- when someone is exposed to radiation, once a person moves away the irradiation stops contamination- particles of radioactive material get inside their body. they will be exposed until the material has decayed or the material has ben removed contamination is more dangerous as it can get into soil and water and affect wildlife contamination with longer half lives is more dangerous as the effects will last longer §

Question 39

6.33- internal radiation to treat tumours

Answer 39

uses a beta emitter placed inside the body close to a tumour. doesn't require surgery and the patient stays in a room alone while the source is in place. have a long range so can also damage nearby cells short Half lives to limit the time he radioactive substance is inside the body

Question 40

6.33- external radiotherapy

Answer 40

uses beans of gamma rays, X-rays or protons directed at tumour form outside the body several lower strength beams may be directed at tumour from different directions so that only the tumour absorbs the rays and the surrounding tissues are harmed as little as possible. long half lives so they don't need replacing too often

Question 41

6.34- tracers - diagnosing diseases, detecting bleeding, detect tumours

Answer 41

used to diagnose conditions without cutting into patients body a tracer that emits gamma rays is put into the patients body tracers also contains molecules that will be taken up by particular organs many be injected d or swallowed the location of tracer is found using cameras that detect gamma rays can be injected into blood to find sources of internal bleeding- cameras detect area of highest gamma radiation which is where the bleeding is occurring can detect tumours- tracer is made of radioactive glucose because tumour cells are more active so take up ore glucose

Question 42

6.34- PET scans

Answer 42

the tracer emits a positron, when this meets and electron they are both destroyed and 2 gamma rays are emitted in opposite directions the detector in the PET scanner moves around the patient building up a set of images where different amounts of gamma radiation are coming from

Question 43

6.35 why do isotopes used in PET scanners have to be produced nearby

Answer 43

radioactive isotopes used in tracers need to have a short half life so other parts of the body are affected as less as possible this means they lose their reactivity quickly so must be made close to the hospital

Question 44

6.36 advantages of nuclear power

Answer 44

reliable don't realise co2 lots of energy can be generated from a small amount

Question 45

6.36- disadvantages of nuclear fuel

Answer 45

bad public perception - its seen to be dangerous waste disposal- waste products from fission have very long half lives so they will be radioactive for a long time and there is a danger they could leak out and pullet river or land expensive is decommission accidents can be very dangerous

Question 46

6.37sources of energy from nuclear reaction

Answer 46

in radioactive decay the radiation emitted by unstable nuclei transfers energy nuclear fission- large nuclei split to form smaller nuclei and release energy, used in power stations nuclearfusion- two smaller nuclei join to form a big nuclei, happen in the sun, fusion of nuclei release energy.

Question 47

6.38 nuclear fission

Answer 47

hen a nucleus absorbs a neutron it immediately split into 2 daughter nuclei. 2 neutrons are released the 2 nuclei and neutrons have kinetic energy as they are moving fast, energy is transferred from fission by heating the products or fission are radioactive

Question 48

6.39 chain reaction

Answer 48

if the neutrons are released by another nuclei , this nuclei will become unstable and release more neutrons when their nucleus splits. these neutrons can them be absorbed by another nuclei. if this keep happening its a chain reaction

Question 49

6.40 how is a chain reaction controlled in power stations

Answer 49

moderatrors- slows down the neutrons so there is a higher chance they will be absorbed by another uranium nucleus control rods- contain elements that absorb neutrons. can be lowered into reactor core if reaction needs to be slowed down when they are fully lowered the reaction stops

Question 50

6.41 how thermal (heat) energy from the chain reaction is used in the generation of electricity in a nuclear power station

Answer 50

energy released form core is transferred to coolant the coolant is pumped to the heat exchanger where it is used to make steam, thermal to kinetic energy. the steam drives a turbine which turns a generator to produce electricity

Question 51

6.43- what is nuclear fusion

Answer 51

the creation of larger nuclei from smaller the mass of the new nucleus is less than the 2 smaller ones so the lost mass is covered to energy the energy source for stars

Question 52

6.44- difference between fusion and fission

Answer 52

products of fission are radioactive, fusion isn't | fusion only happens at high temps and pressures

Question 53

6.45- why doesn't fusion happen at low temps or pressures

Answer 53

there is electrostatic repulsion between atoms due to protons if the pressures or temps are too low the atoms won't be close enough to Duse so the force of electrostatic repulsion won't be overcome nuclei are more likely to collide at high temps as they will be moving faster. if they aren't close enough or travelling fast enough they can't overcome electrostatic repulsion

Question 54

6.46- why can't fusion be used in power station

Answer 54

its difficult to produce high enough pressure on earth so the temperature inside the reactor will have to be very high, hotter than the sun. its difficult to sustain temp and pressures on earth and it would cost too much