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PHYSICS > Topic 6 > Flashcards

Topic 6 Flashcards

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1
Q

Who made the plum pudding model

A

J j Thompson

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2
Q

Explain the plum pudding model

A

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

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3
Q

Rutherfords model

A

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

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4
Q

Rutherford scattering

A

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

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5
Q

The Bohr model

A

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

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6
Q

How can unstable nuclei undergo radioactive decay

A

Beta decay

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7
Q

What are the two types of beta decay

A

One where an electron is emitted

One where a positron is emitted

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8
Q

What happens in Beta-minus decay

A

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-

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9
Q

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

A

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

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

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10
Q

What happens in beta-plus decay

A

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+

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11
Q

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

A

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

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

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12
Q

Uses of beta decay

A

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

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13
Q

When unstable nuclei decay

A

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

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14
Q

Alpha radiation changes to the nucleus

A

Nuclear mass reduced by 4 [-4]

Positive charge reduced by 2 [-2]

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15
Q

Beta - changes to the nucleus

A

No change [0]

Positive charge increases by 1 [+1]

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16
Q

Beta + changes to the nucleus

A

No change [0] on mass of nucleus

Positive charge reduced by 1 [-1]

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17
Q

Gamma radiation changes to the nucleus

A

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

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18
Q

Neutron radiation

A

Mass reduced by 1

No change of nuclear charge

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19
Q

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

A

Masses and charged on each side of equation must balance

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20
Q

Balancing nuclear decay equations

A

Searcj YouTube

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21
Q

The activity of a radioactive source is

A

The number of atoms that decay every second

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22
Q

The unit for activity is the

A

Becquerel (Bq)

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23
Q

When at atom decays it

A

Emits radiation but changes into a more stable isotope

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24
Q

The activity of a source depends on how many

A

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

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25
Q

What’s the half-life of a radioactive isotope

A

The time it takes for Half of the unstable atom to decay

Time for activity to go down by half

26
Q

Can you predict when a particular nucleus will decay?

A

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

27
Q

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

A

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

28
Q

Used of gamma rays

A

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

29
Q

Smoke alarms contain a source of

A

Alpha particles

30
Q

How to smoke alarms work

A

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

31
Q

Beta particles being used to control the thickness of paper

A

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

32
Q

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

A

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

33
Q

What can ionising radiation do

A

Knock electrons out of atoms, turning the atoms into ions

This can be very harmful to humans

34
Q

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

A

Ions

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

This can lead to cancer

35
Q

How can ionisation and cellular mutation lead to cancer

A

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

36
Q

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

A

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

37
Q

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

A

By wearing a film badge

38
Q

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

A

Remain dangerous

39
Q

Precautions of radioactive material

A

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

40
Q

What’s irradiation

A

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

41
Q

Irrational

A

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

42
Q

Contamination

A

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

43
Q

Ionising radiation can be used internally and externally to diagnose

A

Illnesses and treat cancer

44
Q

Medical tracers are substances that are used in

A

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

45
Q

Example of medical travers

A

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

46
Q

What are PET scanners used to produce

A

3D colour images of the internal workings of the patient

47
Q

Explain PET scanners

A

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

48
Q

Treating tumours internally

A

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

49
Q

In the treatment of thyroid cancer the radioactive Elelemt

A

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

50
Q

Treating tumours externally

A

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

51
Q

Explain why internal treatments are used to treat cancer tumours

A

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

52
Q

Electrical energy can be generated in

A

Power stations that use nuclear fuel ⛽️

53
Q

Energy from the nucleus

All nuclear reactions can be a source of energy :

A

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

54
Q

Nuclear power and waste

A

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

55
Q

Advantages of nuclear power

A

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)

56
Q

Disadvantages of nuclear power

A

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)

57
Q

Explain the disadvantages of nuclear power (3 marks)

A

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

58
Q

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

A

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

59
Q

What happens in nuclear fission

A

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

60
Q

Describe how a xhain reaction of nuclear fission can be controlled

A

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

61
Q

Chain reactions

A

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

PHYSICS (10 decks)

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