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A - Physics GCSE > Topic 3 - Radioactivity and Astronomy > Flashcards

Topic 3 - Radioactivity and Astronomy Flashcards

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1
Q

What is the structure of the atom

A

A positively charged nucleus surrounded by negatively charged electrons,
Pretty much all mass condensed into nucleus

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2
Q

What are the relative sizes of atoms and small molecules

A

1 x 10^-10

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3
Q

How has the model of the atom changed over time

A

-Plum pudding- spheres of positive charge with negatively charged electrons in the “dough”
-Rutherford did Gold foil experiment- fired alpha beam and some went through but others were reflected showing empty space
Bohr model- showed electrons were in fixed orbits from the nucleus called energy levels and only in these orbits
-This model is closest to modern day which says shells are elipse

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4
Q

What is meant by an isotope

A

Different forms of the same element but has a different number of neutrons

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5
Q

What are the relative charges of the 3 subatomic particles

A

proton +1
neutron 0
electron -1

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6
Q

What are the relative masses of the 3 subatomic particles

A

proton 1
neutron 1
electron 0.0005

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7
Q

Why do atoms have no overall charge

A

because they have the same number of electrons as neutrons so they have an equal and opposite charge

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8
Q

Where are electrons found inside atoms

A

In shells or energy levels at different distanced from the nucleus

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9
Q

when can electrons change orbit

A

by moving up an energy level

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10
Q

what is an ion

A

an atom which has lost or gained an electron to form a

  • positively charged ion if it loses an electron
  • negatively charged ion if gained
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11
Q

How does ionisation occur

A

if the outer electron absorbs enough energy it will move so far it leaves the atom and is now a free electron
-the atom is now a positive ion

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12
Q

What is background radiation

A

low level radiation surrounding us all the time coming from building materials, foods and rocks

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13
Q

Why does background radiation occur

A

naturally occuring unstable isotopes radioactively decaying

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14
Q

how does a geiger muller tube work

A

inert gas inside tube becomes conductive of electricity when impacted by a high energy particle

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15
Q

What is exposure to radiation known as?

A

Irradiation - doesnt make it radioactive

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16
Q

What is radioactive contamination

A

unwanted radioactive atoms getting in an object

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17
Q

Why is radioactive contamination bad

A

because radioactive particles could decay inside your body and cause damage to cells

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18
Q

How can we prevent radioactive contamination

A

By wearing gloves and using tongs

protective suits to stop breathing in particles

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19
Q

What are the 5 types of radiation which can be emitted in random processes by an unstable nucleus

A 
Alpha decay
Beta minus
Positron emission
Neutron
Gamma
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20
Q

Describe how Alpha decay effects the charge and mass of the nucleus

A

mass number decreases by 4

atomic number decreases by 2

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21
Q

Describe how Beta-minus decay effects the charge and mass of the nucleus

A

mass number doesnt change
atomic number increases by 1
(one more proton)

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22
Q

Describe how Positron emission effects the charge and mass of the nucleus

A

mass number doesnt change
atomic number decreases by 1
(one less proton)

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23
Q

Describe how Neutron emission effects the charge and mass of the nucleus

A

mass number decreases by 1

atomic number stays the same

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24
Q

Describe how Gamma decay effects the charge and mass of the nucleus

A

Mass and atomic numbers stay the same as nucleus gets rid of excess energy as gamma and returns to a more stable state

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25
Q

Describe What an alpha particle is

A

Helium nuclei (two protons + two neutrons)
dont penetrate far so stopped quickly
absorbed by paper
size makes them strongly ionising as theyre bigger

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26
Q

Describe What an Beta minus particle is

A

`fast moving electron with charge of -1 relatively no mass
moderately ionising
absorbed by sheet of aluminium

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27
Q

Describe What an Beta plus particle is

A

fast moving positron with charge of +1 relatively no mass
moderately ionising
absorbed by sheet of aluminium

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28
Q

What happens when a Positron and electron hit each other

A

They destroy each other and produce gamma radiation in process called annihilation
(used in PET scanning)

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29
Q

Describe Gamma radiation

A

Electromagnetic radiation with a short wavelength
released by nucleus they penetrae far without being stopped
weakly ionising because of this so tend to pass through than collide, eventually hit something causing damage
absorbed by thick lead or concrete

30
Q

How does the activity of a substance change over time

A

the rate something decays is called its activity and you can predict this with a samples half-life

31
Q

What is activity measured in

A

becquerels Bq

1 Bq= 1 decay per second

32
Q

How can amount of radioactivity be measure with photographic film

A

The more radiation the film is exposed to the darker it becomes (just like it does when exposed to light)

33
Q

How is radioactivity used in smoke alarms

A
  • a weak source of alpha radiation is placed in a smoke detector close to two electrodes
  • the source causes ionisation and a current flows
  • when there is a fire the smoke will absorb the radiation
  • this makes the current stop and the alarm sounds
34
Q

How is radioactivity used to irradiate food

A

high dose of gamma rays to kill microbes

this means the food doesnt go off as quickly

35
Q

How is radioactivity used to sterilise medical equipement

A

Using gamma rays to kill microbes by irradiation

36
Q

Why is irradiation a good method of sterilisation

A

its doesnt include boiling at high temperatures so the instruments/ food can be sterilised without damage

it needs a reasonably long half life so it doesnt need replacing

37
Q

how is radioactivity used in tracing and thickness gauging

A

(Gamma is used in industry to detect leaky pipes)

Beta radiation is used in thickness control
you direct the radiation through the material being made with a detector on the other side
-if the amount of detected radiation changes then control the rollers to give right thickness
-it must be beta as the paper needs to partly block the radiation

38
Q

Which two radiations must be the only ones that can pass through the body in medicine

A

beta or gamma NEVER ALPHA as its strongly ionising

beta and gamma can pass through without too much damage

39
Q

How is radioactivity used in cancer diagnosis

A

In PET scanners- inject person with positron in glucose with a low half life to act as a tracer

  • positrons meet the electrons in the organ with cancer cells and annihilate giving off gamma radiation which can be detected accurately on screen
  • distribution of radioactivity matches up with metabolic rate as radioactive glucose is used by cells so an increases metabolism
40
Q

Why must PET scanner be on site of a hospital

A

because if they were off site the isotopes would have to travel a greater distance and wouldnt work as well as activity would decrease

41
Q

What are the hazards of ionising radiation

A

It can cause tissue damage and cell mutations which can cause tumors and cancer

42
Q

How is radioactivity used to treat cancer internally

A

Internally- radioactive material (alpha) place near or in tumour and do damage to the cancerous cells but not as much nearby tissue as its short range
Beta used in implants too but can damage healthy cells due to long range

43
Q

How is radioactivity used to treat cancer externally

A

gamma rays aimed at tumour which penetrate body and is carefully focused on tumour

  • damages healthy cells
  • long half life so doesnt need replacing
  • doctors must stay in shielded room to protect
44
Q

Advantages and disadvantages of treating Cancer internally

A

+damges cancer cells
-can damage other tissues
+/-short half life to reduce time its in their body

45
Q

Advantages and disadvantages of treating Cancer externally

A

+damages cancerous cells
+long half life means doesnt need to keep replacing
-can cause burning
-can kill healthy cells

46
Q

Describe some advantages and disadvantages of nuclear power

A

+reliable
+relatively safe
+0 emissions of fossil fuels
+huge amounts of energy from small source

  • very expensive
  • must be carefully controlled
  • negative public perception
  • waste has long half life
  • risk of catastrophe
47
Q

Describe the process of nuclear fission

A
  • A slow moving neutron is fired at a large unstable nucleus (uranium 235)
  • this makes it unstable so splits into 2 lighter nuclei and lots of energy is released
  • as well as this 2 or 3 slow moving neutrons are released setting off a chain reaction
48
Q

What are are the products of the fission of Uranium- 235

A

Krypton and Barium (radioactive)

49
Q

How is a chain reaction controlled

A
  • uranium fuel rods are placed in moderator such as water to slow down the fast moving neutrons
  • boron control rods absorb excess neutrons to control and keep rate steady
50
Q

How is thermal energy from chain reaction converted to electrical energy

A

-energy is transferred to thermal store of moderator which is transferred to boiler to heat water making steam which powers a turbine which turns to kinetic energy and powers generator creating electrical energy

51
Q

Describe the process of nuclear fusion

A
  • joining together small nuclei to creat a larger heavier nucleus such as two hydrogen to make a helium nuclei
  • as mass of new nucleus doesnt have as much mass as the lighter nuclei did so some is converted into energy and radiation
52
Q

How do stars create energy

A

In nuclear fusion reactions

53
Q

Why are high temperatures and pressures needed for fusion

A

because strong force of electrostatic compulsion needs to be overcome to make 2 positively charged nuclei close enough to fuse at 10,000,000 degrees

54
Q

Why is it difficult to make the conditions of fusion reactions

A

Because any material at those temperatures would be incinerated/ vaporised so reactors are very expensive to build and hard.

55
Q

What are the different bodies that make up the solar system

A 
Sun
Planets
Asteroids 
dwarf planets
moons
artificial satellites 
comets
56
Q

How have ideas about the solar system changed over time

A

geocentric model- sun moon and everything orbited the earth because we didnt have telescopes and you saw the sun and moon travelling across the sky everyday.
Heliocentric- the sun is at the centre of the solar system and all planets orbit the sun in perfect circles (this was explained with galileo’s jupiters moons and proved geocentric model wrong
Gradually evidence increased for this model as we got more technology
We have elliptical orbits not circle

57
Q

What factors effect strength of gravitational field

A

mass of the body creating field, larger=stronger

distance- closer= stronger=more instantaneous velocity needed to balance it

58
Q

Why does gravity have different values on different bodies of the solar system

A

Because it depends on the gravitational field strength

weight force due to gravity

59
Q

What are the orbits of moons, planets, comets and artificial satalites

A

Moons- orbit their planet almost circular, natural satalite
Planets orbit the sun in elliptical orbit
Comets- highly elliptical orbit round sun to edge of solar system
Artificial satallites-orbit earth in fairly circle orbit

60
Q

Why does velocity of an object change even if orbiting at steady speed

A

constant speed means its constantly accelerating
this force is called the centripetal force
-the instantaneous velocity keeps it travelling in a “circle” at right angle to acceleration
-force is from the gravitational force

61
Q

How does a changing speed of a body in orbit affect its radius of its orbit

A

If the speed of the object changes, the size/radius of its orbit changes too
More stable orbits have a smaller radius

62
Q

Describe the life cycle of a star like our sun

A

nebula, protostar, main sequence, red giant, white dwarf

63
Q

Describe the life cycle of a star much larger than our sun

A

nebula, protostar, main sequence, red supergiant, supernova, black hole/ neutron star

64
Q

How does the movement of a wave source affect the observed frequency and wavelength

A

Obserevd increase in wavelength of light from distant galaxies and patterns have been shifted to red end of the spectrum

(when the observed frequency changes so does the wavelength)

65
Q

Explain what red-shift is

A
  • Different elements absorb different wavelength and frequencies of visible light.
  • Each element produces a specific pattern of dark lines at frequencies it absorbs on spectrum
  • as wavelength increases the patterns have been shifted towards the red end of the spectrum
66
Q

Why does red shift provide evidence that the universe is expanding

A

by measuring red shift, we can see that all distant galaxies are moving away from us. these galaxies have greater red shifts and show greater increase in wavelength
this means the universe is expanding

67
Q

What is the steady state theory

A

matter is always being created as the universe expand but density of universe stays the same, there is no beginning or end to the universe
supported by red shift

68
Q

What is the big bang theory

A

All matter started in tiny dense hot space whch exploded and space started expanding and keeps doing
gives us finite age of universe around 13.7 billion years
supported by CMB and Red shift

69
Q

Why do both theories account red shift

A

Because red shift shows objects are moving away from observer so could be observed for either model

70
Q

What is CMB radiation

A

Cosmic microwave background radiation- detected low frequency EM radiation from Microwave part of spectrum
It is the left over energy from the initial explosion

71
Q

Why has CMB led to the Big Bang theory being our current model

A

Because it shows left over energy from an initial explosion which shows the universe had a beginning
-Radio telescopes helped detect this

A - Physics GCSE (9 decks)

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