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A-level Physics Year 2 > Nuclear Physics > Flashcards

Nuclear Physics Flashcards

(68 cards)

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1
Q

What is the Rutherford Scattering Experiment ?

A

It provides evidence for an atomic structure

  • Scattering of alpha particles by thin metal foils
  • alpha particles from a radioactive source fired at very thin gold foil
  • strikes a fluorescent screen (circular) a tiny visible light if produced
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2
Q

What are the conclusions made from the Rutherford Scattering Experiment ?

A

1) ATOMS MUST BE MOSTLY EMPTY SPACE
- most of the alpha particles just pass straight through
2) NUCLEUS MUST HAVE A LARGE POSITIVE CHARGE
- as some alpha particles are repelled + deflected by large angle
3) NUCLEUS MUST BE TINY
- as very few particles are deflected by angle < 90
4) MOST MASS MUST BE IN THE NUCLEUS
- since fast alpha particles are deflected by the nucleus

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3
Q

How the structure of the nucleus has changed over time ?

A
  • Matter was made of little lumps ‘atomos’
  • Tiny spheres that couldn’t be broken down
  • Plum pudding
  • Rutherford scattering - protons and electrons
  • Evidence for the neutron
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4
Q

What experiments can you measure the Nucleus radius ?

A

1) Close approach of a scattered particle

2) Electron diffraction

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5
Q

How to estimate the Radius of the nucleus using the Close approach of a scattered particle method ?

A

Initial Ek = E(electric potential energy)

E = Qq/4πEor

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6
Q

How to estimate the Radius of the nucleus using the electron diffraction method ?

A
  • more accurate that ‘close approach’
  • can be diffracted due to wave-article duality
  • λ = hc/E
  • FIRST MINIMUM (from diffraction pattern)
    SinѲ = 1.22λ/2R
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7
Q

How does Intensity vary with diffraction angle ?

A
  • central bright maximum containing the majority of the incident electrons
  • intensity decrease as the angle of diffraction increases
  • NEED TO KNOW GPAPH
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8
Q

How to calculate the Nuclear Density ?

A

R = RoA^1/3 -> R^3∝A -> V∝A

  • p = m/v - assume nucleus is spherical
  • p = A x M / 4/3πR^3
  • p = A x M / 4/3π(RoA^1/3)^3
  • p = 3M/4πRo^3 = constant
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9
Q

How to show the nuclear radius (R) is proportional to the cube root of the nucleon number (A)

A

As the nucleon (atomic mass) increase the nuclear radius increases - R/A graph
- linear relation between R and A^1/3
R = RoA^1/3
(Ro = 1.4x10^-15)
- show evidence that nuclear material have a CONSTANT DENSITY

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10
Q

What are the four types of Nuclear Radiation ?

A

1) Alpha
2) Beta-Minus
3) Beta-Plus
4) Gamma

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11
Q

What are the properties of Alpha Radiation (α) ?

A 
CONSTITUENT 
- 2 Protons + 2 Neutrons (He)
IONISING POWER 
- Strong 
SPEED
- Slow 
PENETRATING POWER
- Absorbed by paper/skin or few cm of air
AFFECTED BY MAGNETIC FIELD
- Yes
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12
Q

What are the properties of Beta-Minus Radiation (β-) ?

A 
CONSTITUENT 
- Electron 
IONISING POWER 
- Weak
SPEED
- Fast
PENETRATING POWER
- Absorbed by 3mm of aluminium 
AFFECTED BY MAGNETIC FIELD
- Yes
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13
Q

What are the properties of Gamma Radiation (γ) ?

A 
CONSTITUENT 
IONISING POWER 
SPEED
PENETRATING POWER
AFFECTED BY MAGNETIC FIELD
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14
Q

What are the properties of Gamma Radiation (γ) ?

A 
CONSTITUENT 
- Electromagnetic Wave 
IONISING POWER 
- Very Weak 
SPEED
- Speed of Light 
PENETRATING POWER
- Absorbed by thick lead or concrete 
AFFECTED BY MAGNETIC FIELD
- No
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15
Q

What is Alpha Radiation used for ?

A

Is used for Smoke alarms because they allow current to flow but won’ travel far
- only need to amount of source

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16
Q

How to identify Radiation ?

A

Use a GM-tube ( GEIGER-MULLER )

  • record count-rate/ mins^-1
  • use different materials to receive count-rate
  • repeat 3 times and average
  • Corrected count-rate = CR - BCR
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17
Q

What is Gamma Radiation used for ?

A
  • Radioactive tracers - help diagnose patients without the need of surgery
  • radioactive source injected into body with short half-life to prevent prolonged radiation exposure
  • PET scanner used to detect emitted gamma rays
  • treat cancer by damaging cells (but all cells)
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18
Q

What is Beta Radiation used for ?

A

Is used for measuring the thickness of a material

  • too little radiation being absorbed -> rollers move part so make material thicker
  • too much radiation being absorbed -> rollers move closer so make material thinner
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19
Q

How to safely handle radioactive sources ?

A
  • exposure time is minimum
  • shielding during treatment
  • inside lead box
  • handle with long handling tongs
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20
Q

What is Background Radiation (BR) and type of sources of it ?

A

Is the low level of radiation always present
SOURCES
- Air (radon gas released from rocks)
- Ground and Buildings
- Cosmic radiation
- Living things e.g. plants/animals
- Man-made radiation e.g medical/nuclear power

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21
Q

What is the INVERSE SQUARE LAW ?

A

States the intensity of gamma radiation decreases with distance from a source
ɪ = K/x^2
- Intensity of radiation is the amount of radiation per unit area (Wm^-2)
- K - constant of proportionality (W)
- Graph of CCR/distance - ∝1/d^2

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22
Q

What is RADIOACTIVE DECAY ?

A

Is an unstable nucleus that breakdowns by releasing energy and/or particles to become more stable
- is random and can’t be predicted

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23
Q

What has the same rate of radioactive decay ?

A

ISOTOPES have the same rate of radioactive decay - constant decay probability

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24
Q

What is the ACTIVITY (A) of a sample ?

A

Is the number of nuclei that decay each seconds
- Measured in Bq
A = λN
- λ = decay contsant (s^-1)
- N = number of unstable nuclei in sample

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25
What is the Decay constant (λ) ?
Is the probability of a specific nucleus decaying per unit time - measure of how quickly an isotope will decay - bigger λ - faster the rate of decay
26
How else can Activity be written as ?
``` A = -ΔN/Δt - Is the number of nuclei that decay each seconds - minus sign as always decreasing ΔN/Δt = -λN - model by using spreadsheet modelling ```
27
]What is the Decay Equation ?
N = Noe^-λt A = Aoe^-λt - Both N and A for a radioactive source both decrease exponentially - can get Linear graph In(N) = -λt + In(No)
28
What is the DICE SIMULATION of radioactive decay ?
- Radioactive decay is a random process - there is a constant probability that an unstable nucleus will decay - constant probability of dice is 1/6 - 100 sample - number of 6's represent the nuclei that have decayed - repeat process but remove the decayed dice
29
What are the calculations involving molar mass and Avogadro constant ?
N = nNa ( Number of atoms = Number of moles x Constant) - Molar mass of a substance is the mass that 1 mole of the substance would have (gmol^-1) and is equal to reative atomic mass
30
What is HALF-LIFE of a radioactive isotope ?
is the time taken for number of unstable nuclei in a sample to halve (T1/2)
31
How to calculate half-life from decay curves ?
- read off the value of unstable nuclei when t=0 - go to half original number on the y-axis - draw a horizontal line to curve the vertical line down and read off half-life - repeat for quarter of original then divid time by two to get half-life
32
How to derive Half-life equation ?
- When t = T1/2 so 1/2No = Noe^-λT1/2 - 1/2 = e^-λT1/2 - In(1/2) = -λT1/2 - In(1/2) = -In(2) T1/2 = In(2)/λ
33
What are the types of Applications of radioactive Isotopes ?
1) Radioactive dating 2) Medical diagnosis 3) Storage of radioactive waste
34
What is Radioactive dating ?
- Uses Carbon-14 - Living plants take in CO2 from the atmosphere as part of photosynthesis - When plants die, Activity of C-14 in the plant starts to fall, with half-life of 5730 years - find made from once-living material can be tested to find current amount of C-14 in them, and date them
35
Why is it difficult to get a reliable age from radioactive dating ?
- Man-made objects crafted from natural materials e.g. wood, you can only find age of material not object - object way be contaminated by other radioactive sources - may be high background count - sample/count rate is small so might be unreliable
36
What is Medical Diagnosis ?
- Technetium-99m used in medical tracers - show tissue or organ function - tracer injected into body and move around to point of interest - radiation emitted is recorded and image is produced - Technetium-99m is suitable because has a half-life of 6 hours so can record data but safe
37
Why and how do you need to store radioactive waste ?
- nuclear fission reactors use Uranium-235 to generate electricity which decays into several different radioactive isotopes - emit radiation (alpha to gamma) - has very high half-life so radioactive for long time so stored for years unit activity falls to safe level
38
What makes a Nucleus Unstable ?
- too many neutrons - too few neutrons - too many nucleons altogether e.g. too heavy - too much energy
39
What does the Nuclear Stability Graph look like ?
- N against Z ( Neutrons against Proton number) - Line of stability curves off from N=Z - above line of stability - too many neutrons so undergo β- decay - below line of stability - too may protons so undergo β+ decay - right of line of stability - too my nucleons so undergo α decay
40
How do Protons and Nucleons number change during α, β-, β+ and electron capture (γ) ?
``` APLHA - very heavy atoms - N -> N-4 + α - Z -> Z-2 + α BETA MINUS - neutron rich isotopes - N -> N + β- - Z -> Z+1 + β- BETA PLUS -proton rick isotopes - N -> N + β+ - Z -> Z-1 + β+ GAMMA - excess energy from previous decay - no change in nuclear constituents - nucleus just loses excess energy - radiation produced via ELECTRON CAPTURE ```
41
What is the conservation rule in nuclear reaction ?
Is Momentum, charge, nucleon number, and lepton number must be conserved
42
How to interpret energy level diagrams showing the radioactive decay of a nucleus ?
- energy level as horizontal lines | - energy released from vertical lines
43
What equation applies too all energy changes ?
E = mc^2
44
What is the atomic mass unit (1u) ?
1/12th mass of Carbon-12 nucleus
45
What is 1u equivalent to ?
Is equivalent to a binding energy of 931.5 Mev
46
What is Mass Defect (Δm) ?
is the Mass of the Constituent nucleons - Mass of the nucleus - Measured in u
47
Why is the Mass of the Constituent nucleons > Mass of the nucleus ?
When the nucleons joint together, the total mass decreases - lost mass in converted into energy and released
48
What is the Binding energy (BE) of a nucleus ?
is the amount of energy need to separate all the nucleons in a nucleus - Measured in Mev - equal to the mass defect
49
How to calculate the average binding energy per nucleon ?
= BE/A | binding energy/Nucleon number (A)
50
What does the Average binding energy per nucleon against nucleon number (A) Graph look like ?
- Curve increases till Fe then gradually decreases - Y-axis up to 10 and X-axis to 250 - Fe is turning point as most stable nucleus - highest BE/A
51
What part of the graph represents Nuclear Fission ?
- Right side towards Fe | - Average binding energy per nucleon decreases gently for heavier nuclei
52
What part of the graph represents Nuclear Fusion ?
- Left side towards Fe | - Average binding energy per nucleon increases rapidly for heavier nuclei
53
What is Nuclear Fusion ?
Is combining of two smaller nuclei into one large nucleus - a-lot of energy released due to new nucleus having higher BE/A - energy released as kinetic energy of particles
54
What is Nuclear Fission ?
is Splitting up of large nuclei into two smaller nuclei's - a-lot of energy released due to new smaller nuclei's having higher BE/A - energy released as kinetic energy of particles - can be SPONTANEOUS or INDUCED
55
What must nuclei overcome for Fusion to occur ?
- all nuclei are positively charged - will be electrostatic force of repulsion between them - only fuse if they overcome this electrostatic force and get close enough for the attractive force of the strong interaction to hold them together (1Mev of Ek) - Low-energy nuclei are deflected by electrostatic repulsion
56
What occurs in Induced fission - chain reaction ?
- Neutron fired at Uranium which creates daughter Products and 2 neutrons which are slowed down by Moderator to form thermal neutrons for chain reaction t occur
57
How do Nuclear Fission Reactors consist of ?
- Concrete case - Fuel rods - Control rods - Moderator - Coolant which turn into Steam (turn turbines)
58
What is chain reaction ?
at least one fission neutron subsequently goes onto produce another fission event - induce other nuclei to fission
59
What is the Purpose of the Moderator in Reactor ?
- Fuel rods placed in Moderator e.g Water/Graphite - Slow down fission neutrons to become thermal neutrons (chain reaction) - Slow down by ELASTIC COLLISIONS
60
How is Moderation made from Elastic collisions ?
- Momentum and kinetic energy conserved 1) MnVn = MnV'n+ MmV'm (Momentum) 2) 1/2MnVn^2 = 1/2MnV'n^2+ 1/2MmV'm^2 (Kinetic Energy) - Mn = Mm = M -> V'm = Vn - Similar masses cause all energy transferred to moderator particles
61
What is Critical Mass ?
the amount of fuel needed for chain reactions to continue on its own at a steady rate - < Critical mass - reaction will just petal out
62
What is the Purpose of the Coolant in Reactor ?
- help remove heat produced by fission | - material which is efficient at transferring heat - make steam for turbines
63
What are the Safety aspects of the Nuclear reactor ?
1) Reactor shielding 2) Emergency Shut-down 3) Handling + Store Fission waste products
64
What are the Safety aspects of the Nuclear reactor ?
1) Reactor shielding 2) Emergency Shut-down 3) Handling + Store Fission waste products
65
What is the Emergency Shut-down of a Reactor ?
- shut down automatically by the release of control rods into the reactor - slow down the reaction as quickly as possible - prevent melt-down
66
How to Handle + Store Fission waste products ?
HANDLING - placing in cooling ponds as very hot (serval months) - reprocessing - stored in sealed containers until activity has fallen sufficiently
67
What is Society View on Nuclear Power ?
PRO'S - long lasting than fossil fuels - no greenhouses gases released - very efficient (generate more electrical energy per kg) CON'S - built and designed extremely carefully to minimise the danger of natural disaster
68
What is Society View on Nuclear Power ?
PRO'S - long lasting than fossil fuels - no greenhouses gases released - very efficient (generate more electrical energy per kg) CON'S - built and designed extremely carefully to minimise the danger of natural disaster - radioactive waste products - storage

A-level Physics Year 2 (7 decks)

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