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nuclear physics Flashcards

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1
Q

what’s the radius of an atom?

A

about 0.05nm

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2
Q

what’s the radius of the smallest nucleus?

A

about 1fm

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3
Q

what happens to the size of the nucleus as more nucleons are added?

A

the size increases

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4
Q

what does a graph look like of ‘radius of nucleus’ against ‘nucleon number’?

A

as nucleon number increases so does the radius of the nucleus
gradient becomes less steep as nucleon number increases

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5
Q

what do you need to plot on a graph to get a linear relationship between radius of nucleus and nucleon number through the orgin?

A

y axis- radius of nucleus
x axis- nucleon number to the power of 1/3

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6
Q

what is R zero equal to in the nucleus radius equation?

A

about 1.4fm

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7
Q

what does the nucleus radius equation show about the volume and density each nucleon takes up?

A

shows that it’s about the same R cubed is proportional to A so volume is proportional to A.
also the mass of each nucleon is about the same so the density of nuclear matter is constant.

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8
Q

is nuclear density greater then atomic density and what does this suggest about the structure of atoms?

A

yes, significantly
-most of an atoms is in its nucleus
-the nucleus is small compared to atom
-atoms contain a lot of empty space

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9
Q

what’s nuclear fission?

A

when large nuclei are unstable and some can randomly split into two smaller nuclei

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10
Q

is energy released in nuclear fission and why?

A

yes energy is released
because the newer smaller nuclei have a higher binding energy per nucleon

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11
Q

what’s nuclear fusion?

A

two light nuclei combine to create one large nuclei

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12
Q

is energy released during nuclear fusion and why?

A

yes a very large amount of energy
because the new large nuclei has higher binding energy per nucleon

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13
Q

what force do nuclei need to overcome for nuclear fusion to occur?

A

the electrostatic force of repulsion as all nuclei are positively charged

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14
Q

what force causes the nuclei to get close enough to stay together in nuclear fusion?

A

the attraction force of the strong interaction

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15
Q

what graph tells you whether a nuclei will undergo nuclear fission or fusion and how?

A

average binging energy per nucleon-nucleon number
only elements to the right of Fe-56 can undergo fission and only elements to the left of Fe-56 can undergo fusion

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16
Q

how can you work out the energy released during nuclear fission or fusion?

A

the change In binding energy per nucleon or use E=mc^2

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17
Q

what’s the activity in a sample?

A

the number of nuclei that decay each second
proportional to the number of unstable nuclei in the sample (N)

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18
Q

what is the decay constant?

A

the constant of proportionality
it’s the probability of a specific nucleus decaying per unit time
a measure of how quick a isotope will decay- bigger value=faster rate of decay

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19
Q

what’s an iterative process?

A

radioactive decay is a iterative process- the number of nuclei that decay in one time period controls the number that is available to decay in the next

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20
Q

how does the number of unstable nuclei change with time?

A

decreases exponentially

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21
Q

what experiment could we do to demonstrate radioactive decay?

A

rolling over 100 fair 6-sided dice
if they land on a chosen number then they have decayed and are removed
keep rolling until all are decayed
each roll counts as 1 unit time

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22
Q

what is molar mass?

A

the mass that one mole of the substance would have
its equal to its relative atomic or relative molar mass

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23
Q

how can you calculate number of atoms in a sample from the number of moles?

A

N=n x the Avogadro constant

where
N=number of atoms
n= number of moles

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24
Q

what is radioactive decay?

A

if an atomic nucleus is unstable it will break down to become more stable
the nucleus decays by releasing energy until reaching a stable form

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25
Q

what is the most penetrating type of radiation?

A

gamma radiation

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26
Q

what is the least penetrating type of radiation?

A

alpha

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27
Q

what is alpha radiation stopped by?

A

absorbed by paper, skin or a few cm of air

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28
Q

what is beta radiation stopped by?

A

absorbed by 3mm of aluminium

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29
Q

what is gamma radiation stopped by?

A

absorbed by many cm of lead or several metres of concrete

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30
Q

what experiment could you do to find out the type of radiation?

A

you need a source, an absorber, Geiger-Müller tube, Geiger counter

  1. record the background radiation with no source present
  2. place the unknown source next to the Geiger-Müller tube and record the count rate
  3. place a sheet of paper between the source and tube and record count rate
  4. replace paper with 3mm thick aluminium and record count rate
  5. take away background radiation and see when count rate significantly decreased
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31
Q

how can you identify type of radiation from magnetic fields?

A

charged particles move perpendicular to a magnetic field are deflected in a circular path
the direction it curves depends on charge and radius of curvature also depends on mass

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32
Q

what are some uses of alpha radiation?

A

smoke alarms

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33
Q

how do smoke alarms work?

A

allow current to flow but not travel very far
when smoke is present, the alpha particles can’t reach the detector which sets the alarm off

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34
Q

what are some uses for beta radiation?

A

controlling thickness of materials being made

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35
Q

how does beta radiation help control thickness of materials?

A

the material is flattened and fed through rollers
the radioactive source is placed on one side of the material and a radioactive detector on the other
the thicker the material, the more radiation will be absorbed so doesn’t reach detector
if too much radiation, rollers will move closer together and other way as well

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36
Q

uses of gamma radiation

A

radioactive tracers
treatment of cancerous tumours

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37
Q

what are radioactive tracers?

A

used to help diagnose patients without the need for surgery
a radioactive source with a short half-life to prevent prolonged radiation exposure
a detector eg. PET scanner then detects emitted gamma rays

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38
Q

how can some risks from using gamma radiation in medial treatments be reduced?

A

shielding- staff leaving room and rotating beams of gamma rays- lessens damage to surrounding tissues

39
Q

which is the one type of radiation not affected by a magnetic field?

A

gamma

40
Q

how can you estimate the radius of an atomic nucleus?

A

using Rutherfords scattering experiment and find the distance of closest approach

41
Q

when does an alpha particle scatter through 180 degrees?

A

at the point where its electric potential energy equals its initial kinetic energy

42
Q

how can you work out initial kinetic energy for an alpha particle being scattered 180 degrees?

A

charge of nucleus x charge on alpha particle / 4 x pi x permittivity of free space x distance of closest approach

43
Q

how is electron diffraction an accurate method for measuring nuclear radius?

A

electrons are leptons so don’t interact with the strong nuclear force

44
Q

when investigating nuclear radius, what does the wavelength and energy levels need to be for the electrons?

A

tiny wavelength and very high energy electrons

45
Q

where will the first minimum appear in electron diffraction?

A

sin(angle) approx = 1.22(landa)/2R

46
Q

with electron diffraction, how does the angle of diffraction effect selective intensity?

A

the intensity of the maxima decreases as the angle of diffraction increases

47
Q

how to record background radiation accurately?

A

-take 3 readings of the count rate using a Geiger counter without a radioactive source present
-average the three readings and subtract the average from each measurement you take of the radioactive sources count rate

48
Q

what are some examples of background radiation?

A

-the air, radon gas is realised from rocks and emits alpha radiation
-the ground and buildings
-cosmic radiation, cosmic rays collide with particles in the upper atmosphere and produce nuclear radiation
-living things, all plants and animals contain carbon some is radioactive
-man made radiation, medical devices small proportion of the background radiation

49
Q

how does the intensity of gamma radiation change with distance from the source?

A

-doubling the distance, quadruples the area its speed out
-intensity decreases by the square of the distance from the source

50
Q

how would you calculate intensity of radiation?

A

constant of proportionality/ distance from source^2

51
Q

investigating the inverse square law RP12

A

-taking measurements of intensity at different distances from a gamma source using a Geiger counter

  1. set up a Geiger counter connected to a geiger-muller tube with one end at the end of a ruler
  2. turn on the Geiger counter and take 3 readings then an average for the background radiation
  3. carefully place the radioactive source at a distance d from the tube
  4. record the count rate at that distance, take three readings
  5. move the source so the distance is doubled between it and the tube again take 3 readings
  6. repeat step 5 for 3d, 4d, 5d …
  7. once finished, put away radioactive source immediately
  8. average the count rate for each distance and eliminate background radiation
  9. plot a graph of corrected count rate-distance of the tube from the source, you should see that as the distance doubles, the corrected count rate will drop to a quarter of its value
52
Q

how to have safe handling of radioactive sources RP12

A

-always hold a source away from your body when transporting it through the lab
-long handled tongs should be used to minimise the radiation absorbed by the body
-sources of gamma radiation should always be stored in a lead box
-only keep gamma radiation out of the box for the shortest time possible

53
Q

what is half-life?

A

the average time it takes for the number of unstable nuclei in a sample to half

54
Q

applications of radioactive isotopes

A

date organic material, diagnose medical problems, sterilise food, smoke alarms

55
Q

what is radioactive dating?

A

-uses the isotope carbon-14
-living plants take in co2 from the atmosphere including carbon-14
-when they die, the activity of carbon-14 will start to fall so from a once-living material we can test the amount of carbon-14 they have and date them

56
Q

why can it be difficult to get a reliable age for carbon dating?

A

-for man made objects crafted from natural materials like wood, you can only find the age of the material used not the object
-the object may have been contaminated by other radioactive sources
-there may be a high background count that obscures the object’s count
-there may be uncertainty in the amount of carbon-14 that existed a thousand years ago
-the sample size or count rate may be small so might be statistically unreliable

57
Q

what radioactive substance is used in medical tracers and why?

A

technetium-99m because it emits gamma radiation with a half life of 6 hours so is long enough to record data but short enough to limit the radiation to an acceptable level and decays to a much more stable isotope

58
Q

what is a medical tracer?

A

its injected into or swallowed by the patient then moves through the body to the region of interest. the radiation emitted is recorded and an image of inside the patient produced
-shows tissue of organ function

59
Q

what radioactive substance do nuclear fission reactors use to generate electricity?

A

uranium-235

60
Q

reasons why a nucleus may become unstable

A

too many neutrons
too few neutrons
too many nucleons altogether
too much energy

61
Q

when does alpha emission occur?

A

in very heavy atoms like uranium and radium
the nuclei of these atoms are too massive to be stable

62
Q

when does beta-minus decay occur?

A

in isotopes that are neutron rich (many more neutrons then protons in the nucleus)

63
Q

what is beta-minus decay?

A

the emission of an electron from the nucleus along with an antineutrino. one of the neutrons in the nucleus is changed to a proton

64
Q

when does beta-plus decay occur?

A

in isotopes that are proton rich (have high proton to neutron ratio). a proton gets changed to a neutron in the nucleus. a neutrino is also emitted

65
Q

what happens during gamma emission?

A

there is no change to the nuclear constituents, the nucleus just loses energy

66
Q

what is electron capture?

A

when a nucleus captures and absorbs one of its own orbiting electrons, which causes a proton to change into a neutron. a neutrino is also released
produces gamma radiation
has the same effect on nucleon and proton number as beta decay

67
Q

what qualities must be conserved in all nuclear reactions?

A

momentum, charge, nucleon number and lepton number

68
Q

what is mass defect?

A

the difference between the mass of a nucleus and the mass of its constituent nucleons

69
Q

what is binding energy?

A

the energy needed to separate all the nucleons in a nucleus
equivalent to the mass defect

70
Q

how would you calculate binding energy from mass defect?

A
  1. convert mass defect into kg
  2. use E=mc^2
71
Q

what is 1u in MeV?

A

931.5

72
Q

how can you work out the average binding energy per nucleon?

A

binding energy / nucleon number

73
Q

what are the key features in a thermal nuclear reactor?

A

control rods
fuel rods
moderator
pump
coolant
concrete casing

74
Q

what are the fuel rods in nuclear reactors made off?

A

uranium-235 or sometimes plutonium-239

75
Q

what is a chained reaction in the nuclear reactor?

A

the fission reactions produce more neutrons which then induce other nuclei to fission

76
Q

what condition do the neutrons need to be for a chained reaction to occur?

A

they need to be slowed down - thermal neutrons

77
Q

what are thermal neutrons?

A

slowed down neutrons

78
Q

what do the fuel rods need to be placed in in a nuclear reactor?

A

a moderator eg water

79
Q

why is a moderator important in nuclear reactors?

A

the slow down the neutrons

80
Q

how does a moderator slow down neutrons?

A

through elastic collisions with nuclei of the moderator material
when neutrons collide with particles that are of a similar mass, they are slowed down more efficiently

81
Q

why is water often used as a moderator?

A

it contains hydrogen which is of similar mass to a neutron

82
Q

what can we assume about a collision between a moderator particle and a neutron?

A

perfectly elastic so KE and momentum are conserved
you can assume the moderator particle is stationary before the collision
if both masses are roughly equal, final velocity of the neutron =0
all KE and momentum would be transferred to the moderator particle

83
Q

what is critical mass?

A

the amount of ‘fuel’ you need for the chain reaction to continue on its own at a steady rate

84
Q

what do control rods do?

A

control the rate of fission
they control the chain reaction by limiting the number of neutrons in the reactor
they absorb neutrons so the rate of fission is controlled

85
Q

what does coolant do in a nuclear reactor?

A

its sent around the reactor to remove heat produced by fission
the material should be liquid or gas at room temperature and be effective at transferring heat
its often the same water being used in the reactor as a moderator

86
Q

safety precautions in place for nuclear reactors

A

-surrounded by a thick concrete case which acts as shielding, prevents radiation from escaping
-in an emergency, the reactor can be shut down automatically by the release of control rods into the reactor
-unused fuel rods emit only alpha radiation so is easily contained

87
Q

what happens to spent fuel rods after?

A

they are initially very hot and are placed in cooling ponds until temperature falls to a safe level
then stored in sealed containers until its activity has fallen sufficiently

88
Q

benefits of using nuclear power for generating electricity

A

there is enough fuel for us to keep generating electricity for centuries to come
fission doesn’t release greenhouse gases
very efficient

89
Q

State what happens to a neutron that is incident on the moderator.

A

the neutron undergoes an elastic collision/bounces off with less speed/kinetic energy

90
Q

State what happens to a neutron that is incident on a control rod

A

the neutron is absorbed

91
Q

A slow-moving neutron is in collision with a nucleus of an atom of the fuel which causes fission.
Describe what happens in the process.

A

the neutron is absorbed/U-236 is formed
(causing) the nucleus (of fuel/uranium) to split into (two smaller) daughter nuclei / nuclei / fragments
releasing (several fast-moving) neutrons

92
Q

the main source of the most dangerous waste

A

The (highly radioactive/ most dangerous) waste are the fission fragments from the fission of uranium-235 or from (spent) fuel rods.

93
Q

how to calculate binding energy

A

(proton number x mass of proton) + (Neutron number x mass of neutron) - nuclear mass

physics paper 2 (5 decks)

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