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Physics > Nuclear Physics Part 1 > Flashcards

Nuclear Physics Part 1 Flashcards

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1
Q

What was matter thought to be during the time of the Ancient Greeks around 5th Century BC?

A

Matter was thought to be made up of little, identical lumps called ‘atomos’.

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2
Q

Who came up with a hypothesis in 1804 that agreed with the Ancient Greeks idea of atoms and what was it?

A

John Dalton came up with a hypothesis which said matter was made up of tiny spheres (‘atoms’) that couldn’t be broken up, and each element was made up of a different type of atom.

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3
Q

Nearly 100 years after 1804, what was discovered about the atom and by whom?

A

J.J Thompson discovered that electrons could be removed from atoms.

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4
Q

What model did J.J Thompson come up with and what did the model show?

A

The Plum Pudding Model - suggested atoms were sphered of positive charge with tiny negative electrons stick in them like fruit in a plum pudding.

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5
Q

What did Rutherford, Geiger and Marsden discover in 1909 and how?

A

They discovered the atomic nucleus using the scattering of alpha particles by thin metal foils.

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6
Q

What was the general procedure of the Rutherford Alpha Particle experiment?

A
  • Stream of alpha particles fired at very thin gold foil
  • When alpha particles strike fluorescent screen, tiny visible flash of light produced
  • Fluorescent screen is circular and surrounds the experiment so alpha particles scattered at an angle can be detected
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7
Q

What were the 3 results of the Rutherford Scattering Experiment?

A

Majority of particles passed straight though, some were deflected at small angles and very few were deflected by angles larger than 90 degrees.

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8
Q

What is the conclusion from the result that most of the particles passed straight through?

A

Atom must be mostly empty space as the majority of particles passed straight through.

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9
Q

What is the conclusion from the result that some particles were deflected at small angles?

A

Atom has a small nucleus which is positively charged.

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10
Q

What is the conclusion from the result that very few particles were deflected at angles larger than 90 degrees?

A

The nucleus constitutes the majority of the atoms mass, the nucleus must have a large positive charge as some particles were deflected, and the nucleus must be very tiny as very few particles were deflected by more than 90 degrees.

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11
Q

When was the proton discovered and how?

A

Was discovered in 1919 when firing high-energy alpha particles at different gases.

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12
Q

What did the discovery of the proton lead to and why?

A

The discovery of the neutron because Rutherford proposed the idea of a “proton-electron doublet”.

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13
Q

What 2 things are equal to each other when an alpha particle is at its shortest distance from the nucleus? (in Rutherfords Scattering Experiment)

A

When it’s electric potential energy is equal to it’s kinetic energy.

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14
Q

How can you get an equation containing the distance of closest approach of the alpha particle to the nucleus?

A

You combine the fact that electric potential energy equals kinetic energy with coulombs law, and therefore
the initial kinetic energy = the electric potential energy = coulombs law

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15
Q

What is an alternative, more accurate way of measuring nuclear radius?

A

Electron diffraction.

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16
Q

What is the equation for the angle which the first minimum from electron diffraction occurs?

A

sin(angle) = 1.22λ / 2R

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17
Q

What does the electron diffraction pattern look like?

A

A central bright maximum (circle) containing the majority of the incident electrons, surrounded by other dimmer rings (maxima).

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18
Q

What is the approximate radius of an atom and what is the approximate radius of the smallest nucleus?

A

Atom - 0.05 nm

Nucleus - 1 fm

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19
Q

What are nucleons?

A

The particles that make up the nucleus (protons and neutrons).

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20
Q

What do you get when you plot a graph of nucleon number against radius of nucleus?

A

A curve starting with a large positive gradient and gradually decreasing.

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21
Q

What is the relationship between nucleon number and radius of the nucleus (straight line graph)?

A

R ∝ A ^ 1/3

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22
Q

What is the approximate value of R0?

A

1.44 x 10 ^ -15 m

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23
Q

How else can you write R ∝ A ^ 1/3 and what does this mean?

A

R ^ 3 ∝ A

This means that the volume is proportional to the area and therefore the density of nuclear matter is constant.

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24
Q

What is the main assumption about nuclei?

A

That they are spherical.

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25
Q

What is radioactive decay?

A

When an atomic nucleus is unstable and it ‘breaks down’ to become more stable. (releases energy and/or particles)

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26
Q

What are the four main types of nuclear radiation?

A

Alpha, Beta-minus, Beta-plus and Gamma.

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27
Q

What are the constituent atoms in alpha radiation?

A

A helium nucleus - 2 protons and 2 neutrons.

28
Q

What is gamma radiation?

A

Short-wavelength, high-frequency EM wave.

29
Q

What is the charge of Alpha, Beta-minus, Beta-plus and Gamma radiation?

A

Alpha - +2
Beta-minus- -1
Beta-plus- +1
Gamma- 0

30
Q

How far can alpha, beta and gamma travel?

A
  • Alpha is absorbed by paper,skin or a few cm of air
  • Beta-minus is absorbed by about 3 mm of aluminium
  • Gamma - absorbed by many cm of lead, or several metres of concrete
31
Q

What equipment can you use to record radiation counts?

A

A radioactive source, a Geiger-Muller tube and a Geiger counter.

32
Q

How can you use magnetic fields to identify types of radiation?

A

Charged particles moving perpendicular to a uniform field will be deflected in a circular path and the direction it goes depends on it’s charge - can use this to determine the radiation.

33
Q

What is one good use of alpha radiation and why?

A

In smoke detectors as alpha particles are very ionising; when smoke is present the alpha particles can’t reach the detector and this sets the alarm off.

34
Q

What is one good use of beta radiation and why?

A

Can be used to control thickness when making things such as paper, aluminium foil or steel. A radioactive source is placed on one side of the material and a detector on the other - thicker the material, less radiation is absorbed and can therefore control thickness.

35
Q

What is one good use of gamma radiation and why?

A

Can be used in medicine as a radioactive tracer - radioactive gamma source taken into body and it’s path can be tracked. Can also be used in treatment of cancerous tumours.

36
Q

State whether alpha, beta +/- and gamma are effected by magnetic fields.

A
  • Alpha - Is effected
  • Beta-minus - Is effected
  • Beta-plus - Annihilated by electron so virtually zero range
  • Gamma - Not effected
37
Q

What do you need to subtract from your final answer when taking readings from a radioactive source?

A

The background radiation count.

38
Q

What are the 5 main sources of background radiation?

A
  • The air - radioactive radon gas released from rocks which emits alpha radiation
  • The ground and buildings
  • Cosmic radiation
  • Living things
  • Man-made radiation
39
Q

How can you investigate the inverse square law of gamma radiation sources?

A
  • Have a gamma source and a geiger counter and measure the count at different distances using a ruler (remember to subtract background radiation readings
  • Plot a graph of corrected count rate against distance from source - should support inverse square law
40
Q

What are 2 things to do to safely handle radioactive sources?

A
  • Hold source away from your body or as far away as possible

- Store sources of gamma radiation in a lead box

41
Q

What is meant by the activity of a sample?

A

The activity of a sample is the number of nuclei that decay each second.

42
Q

What is the decay constant and what is it’s symbol?

A

The decay constant is the constant of proportionality for the activity of a sample - the probability of a specific nucleus decaying per unit time, and its symbol is λ.

43
Q

What does the N stand for in the nuclear equations?

A

Number of unstable nuclei in a sample.

44
Q

What is a good way of simulating radioactive decay?

A
  • Roll lots of dice and count the number of 6’s (these are the decayed nuclei)
  • Plot graph of number of unstable nuclei left in sample against time, and you’ll see the same exponential relationship
45
Q

What is the equation to work out the number of atoms in a sample from a molar mass?

A

N = nNA

N - number of atoms in sample
n - number of moles in a sample
NA - the Avogadro constant

46
Q

What is activity measured in?

A

Becquerels (1 Bq = 1 decay per second)

47
Q

What is the equation for activity in terms of the other decay equation?

A

Same as the other equation (N = N0e ^ -λt) but replacing the N’s with A’s.

48
Q

What is meant by the half-life of an isotope?

A

The average time it take for the number of unstable to halve.

49
Q

What is the easiest way to find the half-life of an isotope?

A

On a decay curve (of number of unstable nuclei remaining against time), you find the time at which the number of unstable nuclei has halved at multiple points and check you get the same answer.

50
Q

How do you derive the half-life equation?

A
  • Use the decay equation (N = N0e ^ λt)
  • When t = T 1/2, N = 1/2 N0 - substitute this in and cancel the N0’s
  • Take the natural logarithm of both sides and rearrange to make T 1/2 the subject
51
Q

What are the three main applications of radioactive isotopes?

A
  • Radioactive dating
  • Medical diagnosis
  • Storage of radioactive waste
52
Q

How does radioactive dating work?

A
  • Living plants take in carbon dioxide, including the radioactive isotope carbon-14
  • When plant dies, activity of the carbon-14 in the plant starts to fall
  • Archaeologists can test the once-living material (like wood) to find the amount of carbon-14 in them and therefore date them
53
Q

Why is it difficult to get a reliable age from radioactive dating?

A
  • Object may be contaminated by other radioactive sources
  • May be high background count which obscures object’s count
  • Sample size may be small and therefore statistically unreliable
54
Q

How can radioactive isotopes be used for medical diagnosis?

A
  • Radioactive tracer injected into or swallowed by patient (such as Technetum-99m), and moves through the body to the region of interest
  • Radiation emitted and recorded and an image of the inside of the patient is produced
55
Q

Where is the nucleon number and the proton number located?

A
  • Nucleon number is to the top left of the element symbol

- Proton number is to the bottom left of the element symbol

56
Q

What are the four ways a nucleus can become unstable?

A
  • Too many neutrons
  • Too few neutrons
  • Too many nucleons altogether
  • Too much energy
57
Q

What do you get if you plot number of neutrons against number of protons on a graph?

A

A stability graph.

58
Q

On a stability graph, what kind of decay do nuclei go through if they are above the line of stability (too many neutrons), below the line of stability (too many protons) or have too many nucleons?

A
  • Too many neutrons - Beta-minus decay
  • Too many protons - Beta-plus decay
  • Too many nucleons - Alpha decay
59
Q

What happens to the nucleon and proton number when an alpha particle is emitted?

A
  • Nucleon number decreases by 4

- Proton number decreases by two

60
Q

When does beta-minus decay happen?

A

When an isotope is ‘neutron rich’.

61
Q

What is released when beta-minus decay occurs and how does the nucleon number/proton number change?

A
  • An electron and an anti-neutrino

- The nucleon number stays the same and the proton number increases by 1

62
Q

When does beta-plus decay happen?

A

When an isotope is ‘proton rich’.

63
Q

What happens in beta plus decay?

A
  • Nucleus ejects a beta plus particle and a neutrino and a proton gets changed into a neutron
  • Proton number decreases by one and the nucleon number stays the same
64
Q

When does gamma emission occur?

A

After alpha or beta decay, the nucleus often has excess energy - this energy is lost by emitting a gamma ray.

65
Q

What is electron capture and what is produced?

A
  • When a nucleus captures and absorbs one of its own orbiting electrons, which causes a proton to turn into a neutron
  • Has the same effect on nucleon and proton number as beta-plus decay - this makes the nucleus unstable and it emits gamma radiation
66
Q

What 5 things are conserved in every nuclear reaction?

A
  • Energy
  • Momentum
  • Charge
  • Nucleon number
  • Lepton number
67
Q

How would you draw an energy level diagram?

A

Horizontal line with a diagonal line coming from right side of it down to new horizontal line which is new element. Horizontal line covers energy change as y-axis is energy.

Physics (8 decks)

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