SP6 Radioactivity

Question 1

What’s the particle theory / kinetic theory

Answer 1

Is the model that helps explain properties of liquids and gases and solids

Particles usually represented with spheres

Question 2

When do chemical reactions occur

Answer 2

When atoms in substances become joined in different ways

Question 3

What did J.J Thomson do

Answer 3

Carried out experiments to show atoms contain much smaller subatomic particles called elections - these have a negative charge and hardly any mass

Described as a pudding made of positron charged material with negatively charged electrons (plums) scattered through it

Question 4

What did Ernest Rutherford do

Answer 4

Carried out experiments involving a study of what happened when positively charged subatomic particles (alpha particles) passes through various substances

He discovered most of a particles went through gold foil but a few bounces back - the plum pudding model could not explain this

Question 5

What did Rutherford change about the plum pudding model

Answer 5

Suggested atoms were mostly space with most of mass in the central nucleus with a positive charge and electrons around the nucleus and so would allow some particles to be deflected by a small amount

Question 6

What the radius of a nucleus

Answer 6

1 X 10^-15 m radius

1 X 10^-10 for the atom so atom itself 100,000 times bigger than nucleus inside it

Question 7

What are nucleons

Answer 7

Particles in nucleus

They are protons or neutrons

Protons have a mass of 1 and neutrons a mass of 1

Question 8

What’s the atomic number

Answer 8

The proton number = number of electrons too

Question 9

What’s the mass number or nucleon number

Answer 9

The total number of protons and neutrons in the nucleus

Numbers of neutrons can vary

Question 10

What are isotopes

Answer 10

Two atoms of the same element have different mass numbers as a result of different numbers of neutrons

Question 11

Tell me about electrons shells

Answer 11

Electrons can only exist in certain orbits around the nucleus

Each electron shell is at a different energy level so If ask atom absorbs energy an electron can move to a higher orbit

Question 12

When does an atom emit light

Answer 12

When an atom emits energy it moves to a lower orbit and emits visible light of a particular wavelength

Question 13

What’s the emission spectrum

Answer 13

It’s different for each element

An electron can move down 1 sheep at a time, even 2, maybe 3 or more at a time so different wavelengths are produced which show up on emission spectrum

Question 14

What’s the absorption spectrum

Answer 14

The visible spectrum that passes through an atom

The wavelengths of light that neon gas absorb are the same wavelengths it emits

Question 15

What did Niels Bohr amend about Rutherfords model of the atom

Answer 15

Suggesting electrons can only be in certain shells around the nucleus and can’t be in between so that’s why they are lines on emission and absorption spectra

Question 16

When does ionisation happen

Answer 16

When an atom gains so much energy one or more of the electrons can escape from the atom all together

Radiation that causes electrons to escape is called ionising radiation

This means it has a positive charge as there are more protons so it’s a positive ion

Question 17

What’s backround radiation

Answer 17

We are constantly being exposed to ionising radiation at a low level, from space and naturally radioactive substances in the environment

Question 18

What are the sources of backround radiation

Answer 18

49% radon gas - produced by rocks that contain small amounts of uranium- it diffuses into the air and can build up in houses. Rock type varies so does amount of radon

15% medical 
13% ground and buildings
12% cosmic rays
10% food and drink 
1% nuclear and other

Question 19

What are cosmic rays

Answer 19

High energy charged particles from the sun and other stars

They are stopped by the upper atmosphere but some still reach the surface

Question 20

How can radioactivity be detected using photographic film

Answer 20

It becomes darker and darker as more radiation reaches it

However the film has to be developed in order to measure the amount of radiation (the dose)

Dosimeters are often work to check how much radiation they have been exposed to (badge)

Newer dosimeters use materials that change colour without needing to be developed

Question 21

How can the radioactivity or a source be measured

Answer 21

Using a Geiger müller (GM) tube

Radiation passing through the tube ionises the gas inside it and allows a short pulse of current to flow

The tube can be connected to a counter to count the pulses of current or the GM tube may give a click each time radiation is detected

The count rate is the number of clicks per second or minute

Question 22

What do scientists do before they measure radioactivity of a source

Answer 22

They need to measure the backround radiation first by taking several readings and finding the mean - the mean value is then subtracted from the measurements!!

Question 23

What’s the nucleus of a radioactive substance like

Answer 23

It’s unstable so it fan easily change or decay

Question 24

Tell me about decay

Answer 24

When it occurs radiation is emitted which causes the nucleus to lose energy and become more stable - it’s a random process and you can’t predict it

Question 25

What are alpha particles

Answer 25

Alpha particles contain two protons and two neutrons - just like nucleus of helium atom They have a relative mass of 4 with no electrons Charge of +2 Can be written as fish symbol / weird a Or 4 with 2 under and He by the side

Question 26

Tell me about Beta particles

Answer 26

They are high energy, high speed electrons They have a relative mass of 1/1835 and a charge of -1 they can be written as a welter B with a - minus sign top right corner of it Or 0 with -1 under and e next to it The electrons that are beta particles come from the nuclei of atoms when a neutron transforms into a proton Beta particles do not ionise the atoms as they leave them

Question 27

Tell me about positrons

Answer 27

They are high energy high speed particles with the same mass as electrons but a charge of +1 They can be written as B^+ or 0 with +1 under and e Opposite to beta particles

Question 28

Tell me about gamma rays

Answer 28

written as weird y They are a high frequency electromagnetic waves (they travel at the speed of light) They don't have an electric charge

Question 29

Tell about neutrons is radioactive decay

Answer 29

Neutrons can also be emitter from an unstable nucleus They have a relative mass of 1 and no electric charge

Question 30

What type of radiation are positrons, gamma rays, beta particles and alpha particles

Answer 30

Ionising radiation So they can all penetrate materials

Question 31

Tell me about Alpha particles passing through materials

Answer 31

They are emitted at high speeds Due to this and their high relative mass, they transfer a lot of energy and so are good at ionising atoms they encounter Each time they ionise an atom they lose energy - since they produce many ions in a short distance, they lose energy quickly and have a SHORT PENETRATION DOSTANCE THEY CAN BE STOPPED BU PAPER

Question 32

How far can alpha particles travel

Answer 32

Can be stopped by a few centimetres in air Very ionising Can be stopped by a sheet of paper

Question 33

Tell about beta particles being ionising

Answer 33

Beta particles are much less ionising than alpha particles so it can penetrate further in to matter

Question 34

What can stop beta particles

Answer 34

Will travel a few metres in air Moderately ionising Can be stopped by 3mm thick aluminium

Question 35

Tell me how ionising gamma rays are

Answer 35

They can penetrate much further in to matter they are about 10 times less ionising than beta particles and can penetrate matter easily

Question 36

What can stop gamma rays

Answer 36

They will travel a few km in air Weakly ionising Need thick lead or several metres of concrete to stop them They can use gamma rays to check the inside of lorries to help prevent movement of illegal goods

Question 37

How can an atom become a different element

Answer 37

When an unstable nucleus changes and emits particles, the atomic number can change If this happens to atoms becomes a different element Eg when alpha is emitted th mass number goes down 4 and atomic number by 2

Question 38

When happens to a neutron in beta decay

Answer 38

A neutron changes in to a proton and electron The electron is ejected from the atom. Atomic number increase by 1 mass number don't change Beta particle is the electron

Question 39

What happens in positron decay

Answer 39

A proton becomes a neutron and a positron The atomic number goes down by 1 by mass number don't change

Question 40

What happens with gamma radiation

Answer 40

Nuclei may lose energy as gamma radiation when the subatomic particles in the nucleus are rearranged which helps makes them more stable

Question 41

What's a nuclear equation

Answer 41

Shows what's happened during radioactive decay The equation must be balanced and the total mass number and total charges must be the Same on both sides Look page 101 (just like a half equation in chemistry ish)

Question 42

What did Marie curie do

Answer 42

Made important discoveries with radioactivity Before dangers were known - notebooks are still radioactive

Question 43

What's the ACTIVITY of any radioactive substance

Answer 43

The number of decays per second and is measured in becquerels )Bq£ One becquerel is one nuclear decay each second

Question 44

What's the half life of a radioactive substance

Answer 44

It's the time taken for half the unstable nuclei in a sample of a radioactive isotope to decay We can't predict individual nucleus because it's a random process However the half life does allow us to predict the activity of a large number of nuclei The half life is the same for any mass of a particular isotope Wh Carbon-14 is 5730 years

Question 45

The more stable a nuclei a sample of a substance contains the lower its...

Answer 45

Activity The half life of an isotope is therefor also a measure of how long it takes tor the activity to halve I

Question 46

How can half like be recorded

Answer 46

It can be found by recording the activity of a sample over a period of time

Question 47

Take a break

Answer 47

;)

Question 48

How can gamma rays be used to kill microorganisms

Answer 48

Some bacteria also cause food poisoning, food can be irradiated by gamma rays to kill bacteria - makes it safer to eat do you can store it for longer Also surgical instruments need to be sterilised to kill microorganisms- heat Them but plastic ones are irradiated with gamma rays

Question 49

Tell me about tracers

Answer 49

Radioactive isotopes can be used as tracers - a gamma source added to water is used to detect leaks in water pipes buried underground Where ther is a leak the water flows into the surrounding earth. A Geiger-müller tube following the path of the pipe will detect higher levels of radiation where there is a leak

Question 50

How can radioactivity be used for cancer tracers

Answer 50

It can be used a tracer in the body to find cancer Similar to a leaking pipe

Question 51

How can radioactivity be used to check thickness of paper

Answer 51

A detector is below he paper and a beta source on other side If paper is too thin more beta particles penetrate the paper and the detector records a higher count rate and so rollers to squash paper reduces force to make it thick and oppose happens when paper too thick

Question 52

Tell me about using radioactivity for smoke alarms

Answer 52

It contains a source of alpha particles, there's a gap in an electrical circuit between 2 electrically charged plates and alpha Partjcles ionise air and attract move to opposite charge plate and allow a small electrical current to flow When smoke gets in to gap - air is not ionises as smoke particles slow down jons and so alarm sounds when the current drops below a certain level

Question 53

What can ionising radiation do to your skin m8 this ain't difficult

Answer 53

Damage your tissue - reddened skin from radiation burns Small amount over long time can damage DNA in a cell - may cause cancer - if they occur in gametes they can be passed on to the next generation; not all mutations harmful and cells often capable of repairing damage if the dose is low

Question 54

Why are radioactive sources always handled with tongs

Answer 54

The intensity of radiation decreases with distance from the source, risk can further be redirected by not pointing sources at people and storing them in lead lined containers

Question 55

Tell me about radiation in hospital

Answer 55

Small doses Sources with shortest half life used - minimise time patient is exposed

Question 56

What's irradiation

Answer 56

When someone is exposed to radiation from a nearby radioactive martial - once they move away the irradiation stops

Question 57

Whats contamination

Answer 57

If they inhale, touch or ingest radioactive material - radiation will continue until material has decayed or is removed which isn't always possible Water and soils can be contaminated and spread in the food chain - many people concerned with accidents in nuclear power stations

Question 58

Tell me about radioactive tracers - how they work With gamma

Answer 58

The tracer often contains a radioactive isotope attached to molecules that will be taken up by particular organs in the body - the tracer emits gamma rays It can be ingested, inhaled or injected into blood or organ Gamma cameras detect the tracer

Question 59

What can tracers be used for with gamma

Answer 59

They find sources of internal bleeding - gamma camera detect highest areas of gamma radiation when bleeding is occcuring Gamma cameras also detect tumours - radioactive glucose molecules because cancer cells are very active and uptake glucose more quickly than other cells

Question 60

Give me an example of a radioactive isoptope

Answer 60

Technetium-99m is attached to a drug that collects in the brain

Question 61

Tell me about using tracers with positrons

Answer 61

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

Question 62

Why must radioactive isotopes used in tracers have a short half life

Answer 62

So other parts of the body are affected as little as possible - since they lose there reactivity quickly they must be made close to a hospital and are often used within or even minutes of productions

Question 63

Why are cancer cells more susceptible to being killed by radiation

Answer 63

They divide more rapidly than cells in the body and are so more susceptible

Question 64

What's internal radiotherapy

Answer 64

It uses a beta emitter placed close or in a tumour and the patient stays in the room alone whilst source in place Doesn't always require surgery

Question 65

What's external radiotherapy

Answer 65

Uses Beams of gamma rags or x Rays or protons directed at the tumour from outside the body Serveral lower strength beams may be directed from different directions so that only the tumour absorbs a lot of the energy

Question 66

What are the two types of nuclear reaction that are used as a source of energy on a large scale

Answer 66

Nuclear fission Nuclear fusion

Question 67

Tell me simply what's nuclear fission

Answer 67

Large nuclei such as uranium-235 break up to form smaller nuclei and release energy Fission reactions are used in nuclear power stations

Question 68

Tell me simply what nuclear fusion is

Answer 68

Two small nuclei join together to from larger nucleus, fusion reactions release energy inside the sun

Question 69

Tell me some pros of nuclear fuels

Answer 69

They store a lot more energy per kilogram than any other type of fuel, this makes them useful for naval ships and submarines Nuclear fuels don't burn and don't need air to allow them to release energy and don't produce co2 - most energy is used in power stations to generate electricity Although uranium is non renewable but supplies estimated for over 200 years - much longer than other non renewable fuel

Question 70

Tell me about radioactive waste

Answer 70

They do produce waste that will stay radioactive for millions of years - it's also expensive to treat - sealed in concrete or glass and buried safely Parts of a nuclear power station become radioactive as it is used and this makes it very difficult to decommission (dismantle safely)

Question 71

Tell me about nuclear fission

Answer 71

Uranium 235 nucleus absorbs a nucleus and then splits into 2 smaller daughter nuclei - which are radioactive. 2 or more neutrons are released and both neutrons and nuclei store a lot of kinetic energy, energy also transferred by heating If neutrons released are absorbed by other uranium 235 nuclei become unstable and release more nuetrons and so on It's an uncontrolled nuclear chain reaction

Question 72

What are fuel rods

Answer 72

In a nuclear reactor the the fuel is made into fuel rods - at high speeds neutrons leave the fuel rods and are slowed down to increase chance they will be absorbed by any other uranium nuclear Inside a reactor core, fuel rods are inserted into holes in a material called a moderator which slows down the neutrons

Question 73

What's a moderator

Answer 73

Holes in a material to slow down nuetrons in nuclear fission

Question 74

How is the chain reaction nuclear fission controlled

Answer 74

Using control rods - which contain elements thag absorb nuetrons They are placed in the reactor core, if rate of fission needs to increase, control rods moved out of the core and vice versa When the control rods are fully lowered into the core, the chain reaction stops and the reactor shuts down

Question 75

How is electricity generated from nuclear fission

Answer 75

Energy released from the core is transferred to a coolant - which is lumped through the reactor, coolant can be water, gas or a liquid metal The hot coolant is pumped by a heat exchanger where it's used to make steam which drives a turbine which turns a generator to produce electricity

Question 76

Tell me about nuclear fusion

Answer 76

Occurs when smaller nuclei combine to form larger ones, the mass of the larger one is slightly less than 2 smaller nuclei - lost mass due to converted energy

Question 77

Tell me about fusion in the sun

Answer 77

Hydrogen nuclei combine to form helium Hydrogen-2 deuterium and hydrogen-3 tritium have to be forced together , the protons are positively charged and like charges repel; electrostatic repulsion Sun has strong gravity so very high pressure in centre - so nuclei close together to be more likely to fuse + higher temps and so some can overcome electrostatic repulsion and fuse

Question 78

Why aren't we doing nuclear fusion on earth

Answer 78

A useful fusion reactor needs fusion to happen faster than it does in the sun Very difficult to reproduce very high pressures on earth, so temperature needs to be very high - hotter then the sun so we can't do this on earth or at least to make it efficient Difficult to sustain extreme temps and pressures required - so far no experimental reactors have produced more energy than has been put in

Question 79

Would fusion or fission reactors produce more energy

Answer 79

Fusion theoretically would produce more energy Helium produced is not radioactive, but any materials used to contain fusion reactions do become radioactive - but far less problems with disposing radioactive waste from fusion reactors than fission