Topic 6

Question 1

Who made the plum pudding model

Answer 1

J j Thompson

Question 2

Explain the plum pudding model

Answer 2

Negatively charged electron plums embedded in a uniform positively charged ‘dough’

Shows both positive and negative charges existed in atoms and accounted for the atom being neutral

Question 3

Rutherfords model

Answer 3

Atom must contain a very small positively charged nucleus which electrons orbit - a bit like planets orbiting the sun

Hypothesis was proved to be correct by Geiger and Marsden who fired alpha particles at gold film

Question 4

Rutherford scattering

Answer 4

Source of a particles beam of particles at thing gold foil
Surrounded by a circular fluorescent screen
Some a particles are scattered
Most a particles are undeflected

Question 5

The Bohr model

Answer 5

Niels Bohr showed that electrons had to orbit a positive nucleus in well - defined energy levels or orbits but could move between energy levels if they gained or lost energy

Question 6

How can unstable nuclei undergo radioactive decay

Answer 6

Beta decay

Question 7

What are the two types of beta decay

Answer 7

One where an electron is emitted

One where a positron is emitted

Question 8

What happens in Beta-minus decay

Answer 8

Neutron in nucleus of an unstable atom decays to become a proton and an electron

Proton stays within nucleus but the electron
- which is the B- particle -
Is emitted from the nucleus at High speed as a fast-moving electron

N -> p + e-

Question 9

The decay of carbon-14 to nitrogen-14 by the emission of a B- particles is an example of

Answer 9

B- decay
The mass number does not change
Proton number increased by 1

14C -> 14N + 0 E
6. 7. -1

Question 10

What happens in beta-plus decay

Answer 10

Proton in nucleus decays into
Neutron positron
Neutron stays in nucleus
Positron (B+ particle) is emitted from nucleus at a high speed carrying away a positive charge and very small amount of the nuclear mass

P -> n + e+

Question 11

The decay of sodium-22 into neon-22 by the emission of a positron is an example of

Answer 11

B+ decay
The mass number does not change but the proton number decreases by 1

22Na -> 22Ne + 0B
11. 10. +1

Question 12

Uses of beta decay

Answer 12

Carbon-14 is an unstable isotope of carbon
It emits B- particles it has a half-life of over 5700 years

Means that it can be used for radiocarbon dating, which involves finding the ages of materials that are thousands of years old.
Positrons can be used in hospitals to form images of patients by the use of PET scans

Question 13

When unstable nuclei decay

Answer 13

The changes that occur depend on the radiation that is emitted from the nucleus

Question 14

Alpha radiation changes to the nucleus

Answer 14

Nuclear mass reduced by 4 [-4]

Positive charge reduced by 2 [-2]

Question 15

Beta - changes to the nucleus

Answer 15

No change [0]

Positive charge increases by 1 [+1]

Question 16

Beta + changes to the nucleus

Answer 16

No change [0] on mass of nucleus

Positive charge reduced by 1 [-1]

Question 17

Gamma radiation changes to the nucleus

Answer 17

No effect on either the mass of the charge or a nucleus

Question 18

Neutron radiation

Answer 18

Mass reduced by 1

No change of nuclear charge

Question 19

In any nuclear decay the total mass and charge of the nucleus are conserved

Answer 19

Masses and charged on each side of equation must balance

Question 20

Balancing nuclear decay equations

Answer 20

Searcj YouTube

Question 21

The activity of a radioactive source is

Answer 21

The number of atoms that decay every second

Question 22

The unit for activity is the

Answer 22

Becquerel (Bq)

Question 23

When at atom decays it

Answer 23

Emits radiation but changes into a more stable isotope

Question 24

The activity of a source depends on how many

Answer 24

Unstable atoms there are in a sample and on the particular isotope

As more + more atoms in a sample decay, there are fewer unstable ones left, so the activity decreases

Question 25

What’s the half-life of a radioactive isotope

Answer 25

The time it takes for Half of the unstable atom to decay Time for activity to go down by half

Question 26

Can you predict when a particular nucleus will decay?

Answer 26

No But when there is a very large number of nuclei the half-life gives a good prediction of the proportion of nuclei that will decay in a given time

Question 27

The activity of a radioactive source is 240Bq and it’s half-life is 6 hours. After 1 half-life the activity will halve to 120Bq

Answer 27

After 2 half-lives it will halve again to 60Bq After 3 half-lives it will halve again to 30Bq After 4 half-lives (one day) it will be 15 Bq

Question 28

Used of gamma rays

Answer 28

Kill cancer cells Beams of gamma-rays can be directed at cancer cells to kill them Sterilise surgical instruments Gamma-rays can be used to sterilise plastic instruments which cannot be sterilised by heating Diagnose cancer A tracer solution containing a radioactive isotope that emits gamma-rays is imjected unto the body and taken up by cells which are growing abnormally the places in the body where the tracer collects are detected with a ‘gamma camera’ Preserve food Food irradiated with gamma-rays will last longer as microbes are killed by the high-energy gamma rays. The food does not become radioactive

Question 29

Smoke alarms contain a source of

Answer 29

Alpha particles

Question 30

How to smoke alarms work

Answer 30

Smoke enters the smoke detector Smoke in the machine will absorb alpha particles and make the current fall Alpha particles ionise the air and these charged particles move across the gap forming a current Americium-241 alpha source gives off a constant stream of alpha particles A detector senses the amount of current Siren will sound when the current falls

Question 31

Beta particles being used to control the thickness of paper

Answer 31

If the paper is too thick not as many beta particles get through The rollers press together harder to make the paper thinner or move apart to make it thicker

Question 32

Explain why beta particles are used to control the thickness of paper

Answer 32

Alpha particles would not go through the paper at all Gamma-rays would psd through paper too easily and the amount getting through would hardly change with small changes in the thickness of the paper

Question 33

What can ionising radiation do

Answer 33

Knock electrons out of atoms, turning the atoms into ions This can be very harmful to humans

Question 34

The energy transferred by ionising radiation can remove electrons from atoms to form

Answer 34

Ions Ions are very reactive and can cause mutations to the DNA in cells This can lead to cancer

Question 35

How can ionisation and cellular mutation lead to cancer

Answer 35

Energy transferred by ionising radiation removed electrons from atoms to form ions Ions are reactive and can cause mutations to the DNA in cells Damaged DNA can lead to cancer Ionising radiation can also cause damage to cell tissue in the form of radiation burns. When it’s energy is high enough it can also kill cells

Question 36

How are people protected once they’ve come into contact with ionising radiation

Answer 36

Limiting the time of exposure Keep time that a person needs to be in contact with ionising radiation as low as possible Wearing protective clothing Wearing a lead apron will absorb much of the ionising radiation Increasing the distance from the person to the radioactive source The further a person from, less damaging

Question 37

How could you determine how much radiation a person has been exposed to

Answer 37

By wearing a film badge

Question 38

The greater the half-life of an ionising source, the longer it will

Answer 38

Remain dangerous

Question 39

Precautions of radioactive material

Answer 39

The source is being moved using tongs to keep it as far away from the persons hand as possible. The source is always kept pointing away from people

Question 40

What’s irradiation

Answer 40

Ionising radiation from an external radioactive source travelling to the body It is not breathed in, eaten or drunk Does not refer to non-harmful rays from televisions, light bulbs or other non-ioninisung sources

Question 41

Irrational

Answer 41

Alpha particles are unlikely to be harmful outside the body as they have a very short range in air (5cm) and are unlikely to reach a person Irradiation is the exposure of a person to ionising radiation from outside the body. This could be in the form of harmful gamma-rays, beta particles or X-rays When ionising radiation reached the body, cells may be damaged or killed but you will not become radioactive

Question 42

Contamination

Answer 42

External contamination occurs when radioactive materials come into contact with a persons hair, skin or clothing. Internal contamination occurs when a radioactive source is eaten or drunk. Some nuts, plants, fruits and alcoholic drinks have low levels of radioactivity. This is due to the radioactive minerals that they are exposed to during their growth or manufacture

Question 43

Ionising radiation can be used internally and externally to diagnose

Answer 43

Illnesses and treat cancer

Question 44

Medical tracers are substances that are used in

Answer 44

Biological processes in the body and contain s radioisotope Patient can eat or drink this substance or inject Ionising radiation emitted by tracer can be detected and the biological process monitored Doctors can diagnose the nature and location of any health problems

Question 45

Example of medical travers

Answer 45

Fluorodeoxyglucose (FDG) Radioactive form of glucose that is commonly used as a tracer Once it is in the blood it travels to the tissues that use glucose When part of the brain is affected, less radioactivity is detected because glucose is not being used

Question 46

What are PET scanners used to produce

Answer 46

3D colour images of the internal workings of the patient

Question 47

Explain PET scanners

Answer 47

The tracer is a radioactive material that decays quickly by emitting positrons When these positrons come into contact with electrons in the body, the two particles annihilate each other resulting in formations of gamma- rays These gamma-days are detected by the PER scanner and processed by a computer and an image is then displayed on a computer screen As the travers decay quickly they need to be produced close to where they are used

Question 48

Treating tumours internally

Answer 48

Cancer tumours can be treated internally by using a radioactive source that is inside the patient. Source enters patient by: - injecting the radioisotope into the patient - the patient eating or drinking something which contains the radioisotope in solid or liquid form

Question 49

In the treatment of thyroid cancer the radioactive Elelemt

Answer 49

Iodine - 131 is used It’s swallowed in a capsule Taken up by the thyroid gland but not other parts of the body Ionising radiation is likely to kill the thyroid cancer without affecting other cells surrounding it

Question 50

Treating tumours externally

Answer 50

Several beams of gamma rays are fired, from different positions, towards the cancer Each beam is not energetic enough to kill the tumour but damaged it By moving the beam the amount of ionising radiation received by the surrounding tissues is reduced

Question 51

Explain why internal treatments are used to treat cancer tumours

Answer 51

When internal treatments are used The ionising radiation can be targeted at the tumour Most of ionising radiation goes to the tumour and damage to surrounding areas is reduced With external treatment the ionising radiation has to pass through healthy tissue which can be damaged

Question 52

Electrical energy can be generated in

Answer 52

Power stations that use nuclear fuel ⛽️

Question 53

Energy from the nucleus All nuclear reactions can be a source of energy :

Answer 53

Radioactive decay- can be in the form of alpha or beta particles or gamma rays (electromagnetic waves) Nuclear fusion - the funding of hydrogen nuclei in the sun releases enormous amounts of light and heat, some of which we receive on earth Nuclear fission- uranium nuclei are split by slow-moving neutrons in a nuclear reactor, resulting in the release of enormous amounts of thermal energy

Question 54

Nuclear power and waste

Answer 54

Nuclear power is a highly efficient way of producing electrical energy, much less nuclear fuel is needed compared with coal, oil or gas to produced the same amount of electrical energy However nuclear power stations do produce radioactive nuclear waste which needs to be dealt with. Some of it is radioactive for thousands of years

Question 55

Advantages of nuclear power

Answer 55

Don’t produce carbon dioxide so don’t contribute to climate change Supplied of nuclear fuel will last longer than supplies of fossil fuels (Construction processed produce carbon dioxide so it will be added to atmosphere when the power station is built and when fuel rods are made)

Question 56

Disadvantages of nuclear power

Answer 56

Difficult and expensive to store nuclear waste safely An accident in a nuclear power station can spread radioactive material over a large area Many people think that nuclear power is dangerous and do not want new nuclear power stations to be built (Nuclear power stations do not make the local areas more radioactive when they are working its only in an accident)

Question 57

Explain the disadvantages of nuclear power (3 marks)

Answer 57

Nuclear radiation is very dangerous Nuclear accident could kill many people Much radioactive waste which is difficult and expensive to store and some of it is radioactive for many thousands of years Public perception surrounding nuclear power as a form of energy means that people often distrust it because of previous accidents such as chernobyl and Fukushima

Question 58

The fission of uranium-235 results in the release of a

Answer 58

Large quantity of energy which is used to heat water in power stations

Question 59

What happens in nuclear fission

Answer 59

A large unstable nucleus splits into two smaller ones Eg uranium-235 nucleus splits up when it absorbs a neutron The fission of uranium-235 produces two daughter nuclei, two or more neutrons, and also releases energy The daughter nuclei are also radioactive

Question 60

Describe how a xhain reaction of nuclear fission can be controlled

Answer 60

A chain reaction can be controlled by using a different material to absorb some of the neutrons This slows the reaction down because there are fewer neutrons to cause more nuclei to undergo fission

Question 61

Chain reactions

Answer 61

Neutrons released by fission of U-235 may be absorbed by other nuclei each of these nuclei may undergo fission and produce even more neutrons If this is not controlled there will be a nuclear explosion