Nuclear Physics Flashcards

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1
Q

What happened in the Rutherford scattering experiment?

A
  1. Most alpha particles passed through gold leaf undeflected
  2. Some were slightly deflected
  3. A tiny proportion (1 in 8000) reflected
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2
Q

What did Rutherford’s experiment reveal about the atom?

A
  1. Atom is mostly empty space
  2. Centre of atom is small, dense and positively charged (nucleus)
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3
Q

Compare the ionising power of the three main types of radiation

A
  • *Alpha most ionising**
  • *Beta medium ionising**
  • *Gamma least ionising**
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4
Q

Compare the penetrative power of the three main types of radiation

A
  • *Gamma most penetrating**
  • *Beta medium penetrating**
  • *Alpha least penetrating**
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5
Q

Compare the range of the three main types of radiation

A
Alpha = 3-7cm
Beta = 0.2-3m
Gamma = Very long distance
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6
Q

What materials can shield the three main types of radiation?

A
  • *Alpha = Paper**
  • *Beta = Aluminum**
  • *Gamma = Lead or several meters of concrete**
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7
Q

What are the main sources of background radiation?

A
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8
Q

How does a Geiger-Muller tube detect radiation?

A
  1. Radiation ionises gas in tube
  2. Negative ions attracted to metal rod
  3. Positive ions attracted to casing
  4. Small current generated in circuit
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9
Q

How is radiation used to control the thickness of metal?

Why can’t alpha radiation be used?

A

If detector count too low -> metal too thick -> Rollers move closer together

If detector count too high -> metal too thin -> Rollers move apart

Alpha won’t be detected

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10
Q

How is radiation used in a smoke detector?

A

Alpha radiation ionizes air between detector
Ionized air causes current to flow
Smoke blocks ionization of air
Current stops
Alarm sounds

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11
Q

If the detector is moved 3x further away what will happen to the count rate?

A

9x smaller

Gamma radiation follows inverse square law

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12
Q

How should you safely use radiation?

A
  1. Minimise exposure time
  2. Maximize distance from source
  3. Store in shielded containers
  4. Don’t consume food or drink near source
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13
Q

How is radiation used for medical imaging?

A

Medical tracer with short half life injected

Tumors absorb radionuclides and emit gamma

Gamma detected outside body

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14
Q

How is radiation used to destroy tumors?

A

Gamma radiation focused on tumor

High energy breaks apart tumor

Low levels through other tissue

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15
Q

Sketch the graph of nuclear stability

A
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16
Q

On this graph of nuclear stability highlight regions of the decays…

  1. α
  2. β-
  3. β+
  4. Proton emission
  5. Neutron emission
A
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17
Q

What makes a nucleus unstable? (and radioactively decay)

A
  1. An incorrect balance of protons and neutrons (off line of stability)
  2. Too many nucleons
  3. Nucleus in excited state
18
Q

What is electron capture and what is it’s equation?

A

Proton captures inner shell electron and becomes neutron

19
Q

What two forms of radiation are released after electron capture?

A

X-ray → electron de-excites to fill inner shell

γ → Nucleus reorders and de-excites

20
Q

How does distance of closest approach work?

A

KE at distance → PE closest

Use to get rough size of nucleus

21
Q

What two graphs could you plot to prove this relationship?

A
22
Q

What does r0 represent?

A

Average radius of each nucleon

23
Q

How do you calculate the average density of a nucleus?

A
24
Q

Why is the average nucleus density so large? (∼2.3x1017kgm-3)

A

Atom is mostly empty space

25
Q

How was electron scattering used to determine nuclear diameter?

A

Graph plotted

First minima used to calculate diameter

(Don’t need to know equation)

26
Q

How is electron scattering better than alpha recoil to determine nuclear radius?

A

Alpha Recoil

  • Closest approach so only an estimate
  • Recoil of nucleus not considered
  • Effect of strong force not known

Electron Scattering:

  • Not affected by strong force (leptons)
  • Electron λdb tunable
27
Q

Define the decay constant λ

A

The probability that an unstable isotope decays in one second

28
Q

What’s wrong with this calculation?

A

Activity and time must be the same units

29
Q

Define the activity, A, of a radioactive sample

A

The total number of unstable isotopes that decay after one second

30
Q

What does the activity, A, of a radioactive sample depend on?

A
  1. The decay constant λ
  2. The number if unstable isotopes N
31
Q

Define the half life, T½, of a radioactive sample

A

Time taken for either…

  1. Activity of sample to halve
  2. Number of unstable isotopes remaining to halve
32
Q

How do you derive the half life T½ equation?

A

Set N as 0.5N0

33
Q

What do the gradient and y-intercept of this graph represent?

A

where r0average radius of nucleon

34
Q
  1. Derive the equation of this graph
  2. What are the gradient and y-intercept?
A
35
Q

How do you prove this graph is exponential?

A

Find multiple T½ and compare

36
Q

What is the gradient of this graph?

A

r0average radius of nucleon

37
Q

If this unstable isotope of caesium decays by α emission where does it end up on the graph?

A

N → neutron number

Z → Proton Number

38
Q

If this unstable isotope of caesium decays by β- emission where does it end up on the graph?

A

N → neutron number

Z → Proton Number

39
Q

If this unstable isotope of caesium decays by β+ emission where does it end up on the graph?

A

N → neutron number

Z → Proton Number

40
Q

How is electron scattering used to determine the diameter of a nucleus?

A
  1. Tune debroglie wavelength of electron close to size of nucleus
  2. Find angle of first minima
  3. Use equation to solve for D (do not need to learn equation)