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Physics > Paper 1 Development of the atom and radioactivity > Flashcards

Paper 1 Development of the atom and radioactivity Flashcards

1
Q

before the discovery of the atom

A

some ancient Greek philosophers believed the atom was the smallest building block of everything
they thought it couldn’t be divided into any smaller parts

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2
Q

the plum pudding model

A

when Thompson discovered the the electron he developed plum pudding model in 1897
atom is sphere of positive charge with negative electrons embedded inside

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3
Q

rutherford’s experiment

A
  1. Rutherford’s shot high-speed alpha particles through thin layer of gold. some went straight through some deflected but some bounced back at very large angles
    shows most of the mass of the atom was concentrated in positive nucleus
    electrons orbit around nucleus at different distances
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4
Q

Niels Bohr’s model

A
  1. adapted rutherford’s saying electrons could only orbit nucleus at specific distances
    this agreed with experimental measurements so was accepted as more accurate than rutherford’s
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5
Q

the proton 1919

A

more experiments conducted in 1919 showing charge of nucleus could be divided into protons. every proton had same positive charge
electrons orbited core nucleus at discrete distances

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6
Q

chadwick’s discovery

A

proved existence of neutron in 1932

mass of nucleus too large to be made of just protons so another neutral particle must be responsible for the mass

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7
Q

what are radioactive substances

A

some isotopes have unstable nuclei and will break down.

when this happens they give out radiation and these substances are said to be radioactive

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8
Q

alpha particle

A

consists of 2 neutrons and 2 protons, same as helium nucleus

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9
Q

beta particle

A

a high speed electron ejected from the nucleus as a neutron changes into a proton

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10
Q

gamma ray

A

high energy electromagnetic radiation from the nucleus

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11
Q

what do nuclear equations represent

A

radioactive decay

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12
Q

alpha decay

A

causes both mass and charge of the nucleus to decrease

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13
Q

beta decay

A

doesn’t cause mass of nucleus to change but does cause the charge of the nucleus to increase

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14
Q

emission of gamma rays

A

doesn’t cause the mass or the charge of the nucleus to change

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15
Q

what happens when alpha, beta of gamma radiation strike atoms in a substance

A

they can knock an electron from one atom onto another

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16
Q

what is an ion

A

an atom that’s gained or lost an electron

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17
Q

what are alpha particles like

A

relatively big, heavy and slow moving
large relative charge (+2)
strongly ionising
bash into a lot of atoms and knock electrons off them before they slow down

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18
Q

what are beta particles like

A

quite small and move quite fast

moderately ionising because their relative charge is smaller (-1)

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19
Q

what is gamma like

A

weakly ionising because gamma isn’t charged

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20
Q

what is alpha’s range in air and what stops it

A

few cm

paper, card + skin

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21
Q

what is beta’s range in air and what stops it

A

few metres

aluminium (5mm thick)

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22
Q

what is gamma’s range in air and what stops it

A

infinite

thick shetts of lead or metres of concrete

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23
Q

what damage can ionising radiation cause

A

damages or kills living cells

damage to the genes in a cell can be passed on and lead to cancer

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24
Q

from the outside which radiation is the safest and which is the most dangerous

A

alpha as it’s the least penetrating

gamma because it’s the most penetrating

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25
Q

from the inside which radiation is the safest and which is the most dangerous

A

gamma because it can easily escape

alpha because it can’t escape

26
Q

what is Alpha used for

A

smoke detectors. ionises air particles, causing current to flow
if smoke in the air, it binds to the ions reducing the number available to carry a current
the current falls and alarm sounds

27
Q

why is alpha used for smoke detectors and why not beta or gamma

A

small range so safest, only one that can be stopped by smoke, most ionising
aren’t used as won’t be stopped by smoke and and won’t ionise the air enough. bigger range so not safe

28
Q

what is beta used for

A

test thickness of thin sheets of metal, as particles aren’t immediately absorbed by the material like alpha would be and don’t penetrate as far as gamma

29
Q

gamma tracers in medicine

A

gamma is used so that it can be detected on the outside of the body
alpha would be too dangerous as highly ionising

30
Q

gamma leak detection in pipes

A

injected into pipe. outside of pipe is checked with Geiger-moller detector to find areas of high radioactivity. this is where the pipe has a leak
useful for underground pipes that’s hard to get to

31
Q

why would alpha and beta not be used for leak detection in pipes

A

they would be blocked by the metal and the earth

32
Q

food irradiation

A

foods like strawberries can be irradiated with gamma radiation, killing any living bacteria or virus meaning less likely to go off

33
Q

What is a half life of a radioactive isotope

A

It’s the average time it takes for the number of nuclei of the isotope in a sample to half, or the time taken for the count rate of the sample to fall to half its initial rate

34
Q

The more nuclei there are in a sample…

A

The more a re likely to decay in one half life so the higher the count rate will be

35
Q

What is net decline of a radioactive substance

A

The fraction of the nuclei that have decayed in a certain time. it’s a fraction, ration or percentage because it doesn’t have a unit

36
Q

What is count rate

A

The time taken for the count rate from a sample containing the radioactive isotope to fall to half its starting level

37
Q

Radioactive tracers

A

Tracers used to trace flow of a substance through an organ.
small amount of radioactive material put into patients body (by injection or ingestion)
Tracer given enough time to travel through body before gamma camera is positioned to detect the radiation from outside the body
multiple images takes to show progress of tracer over time by measuring activity over time

38
Q

Gamma cameras

A

Can be used to image internal organs
as with tracing, a radioactive isotope (gamma emitting) is injected into the patient. The isotope is chosen because it concentrates in the organ

39
Q

How do gamma cameras work

A

Made of a crystal scintillator (sodium iodide) which produces a burst of light
light picked up by photo multiplier tubes which convert energy into an electrical signal. this fed into computer to get an image
Lead grid acts as collimator which only allows rays aligned with the holes to hit the crystal making the image sharper

40
Q

What does ionising mean

A

Means atoms are turned into ions by gaining or losing an electron

41
Q

What is ionising radiation

A

The high frequency end of the electromagnetic spectrum (UV, gamma, x-rays) and gamma and beta radiation

42
Q

What are the dangers of ionising radiation

A

Can damage living cells if small dose, large dose can kill cells this leads to cancer

43
Q

What is gamma radiotherapy

A

Gamma radiation is used in narrow beam to destroy cancer cells in a tumour .
the radiation emitted is from the isotope of cobalt

44
Q

How does gamma radiotherapy work

A

Individual beams that cross over at the target so individual beams less intense and don’t damage healthy cells.
destroys cells by ionising them and gamma because can penetrate further into the body

45
Q

What is that half life of the isotope used in gamma radiotherapy

A

5 years because it needs to last a long time so that it doesn’t need to be replaced and so the dose the patient receives doesn’t decrease

46
Q

Gamma knife

A

used to accurately focus many beams of gamma radiation on one or more brain tumours
each beam low intensity but with 200 beams can be accurately concentrated on small volume

47
Q

Radioactive implants

A

Small seeds or tiny rods used to attack tumour from inside the body. sources place inside tumour or in nearby tissue
with low dose rate the implants can stay in for hours or days

48
Q

What is irradiation

A

When something has been irradiated, the irradiation stops as soon as the source of radiation has been removed

49
Q

What is contamination

A

When contamination has occurred the source of ionising radiation itself is transferred such as when radiation isotopes in sold liquid or gas are introduced into the environment

50
Q

What is nuclear fission

A

Splitting of a large nucleus into 2 smaller nuclei (daughters) releasing energy

51
Q

Which nuclei are usually split in fission reactions

A

Uranium-235 or plutonium-239

the numbers are the mass number so the number of protons and electrons the element has

52
Q

What is induced fission

A

When a neutron is fired at the nucleus, causing it to split

53
Q

What is released in nuclear fission and how is it a chain reaction

A

2 or 3 neutrons released
energy in form of radiation and kinetic energy
Neutrons released may cause further and further fission resulting in a chain reaction

54
Q

What is the energy released in fission used for

A

Used to heat water, turning the it into steam
steam turns turbine which turns generator which transforms kinetic energy into electrical energy
level of energy produced must remain constant for output of power station to be constant

55
Q

What is nuclear fusion

A

Happens when 2 nuclei collide and fuse together, forming a larger nucleus releasing energy in the process
the colliding energy need enough kinetic energy otherwise they’ll repel and not fuse

56
Q

How does fusion work in a fusion reactor

A

Heated by passing and electric current through it
gas becomes so hot it forms a plasma of small nuclei
plasma contained using a magnetic field to prevent it from touching container walls otherwise will cool down and fusion stops
When hydrogen nuclei fuse together helium is formed as one of the products

57
Q

Example of nuclear fusion

A

process powering the sun and stars
in the core of the sun, hydrogen is converted into helium by fusion providing enough energy to keep sun burning an sustain life on earth

58
Q

Ads of fission

A

Concentrated source of energy so more J/kg
no polluting gases
supply of uranium for many years
reliable 24/7

59
Q

Disads of fission

A

Produces radioactive waste
chain reaction to control with severe consequences
expensive

60
Q

Ads of fusion

A

Produces very little radioactive waste-safer
no chain reaction to control
very concentrated source of energy
fuel readily available (hydrogen in water)
renewable and cheap

61
Q

Disads of fusion

A

Not yet viable

fusion on earth needs more energy input than the energy output

Physics (20 decks)

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