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Physics A-Level > Nuclear A2 > Flashcards

Nuclear A2 Flashcards

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1
Q

Describe Rutherford’s scattering experiment

A

He fired alpha particles at a thin gold foil. Detectors were placed at an equal distance around the gold foil to find how the alpha particles deflect.

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2
Q

What were some observations that Rutherford made

A

Most alpha particles passed straight through the foil. A small percentage of particles deflected by more than 90 degrees

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3
Q

So how was the atom described after Rutherford’s findings

A

The atom is mostly empty space and the centre of the atom contains all the positive charge as a nucleus

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4
Q

How was the deflection from the magnetic field used to describe different types of radiation

A

Alpha and beta particles deflect in opposite directions and gamma doesn’t deflect. This meant that alpha particles are positive, beta particles are negative and gamma doesn’t have a charge as they are photons

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5
Q

Describe the ionisation experiment

A

A radioactive source is directed at a closed chamber full of air particles. The radioactive particles produce ions and these are attracted to the electrode, allowing for electrons to travel through the circuit and create a current

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6
Q

What was learnt from the ionisation experiment

A

Alpha particles are more ionising but has a short range. Beta particles are less ionising but has a longer range. Gamma is least ionising due to the lack of charge

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7
Q

Describe the absorption test

A

A radioactive source is fired at a a abosrber then to a geiger tube. The geiger counts the number of particles of radiation. This is converted into count rate and drawn on a graph against thickness of the absorber

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8
Q

What was learnt from the absorption test

A

Alpha radiation is absorbed completely by paper. Beta particles are absorbed completely by 5mm of metal. Gamma radiation is absorbed completely by several centimeters of lead

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9
Q

What are the ranges of radiation

A

Alpha has a range up to 100mm. Beta has a range up to 1m. Gamma range is unlimited but the count rate decreases over time as the radiation spreads in all directions.

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10
Q

How can the decay of count rate from a gamma source be modelled as

A

Inverse square graph

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11
Q

How can the inverse square law be shown mathematically

A

Intensity of radiation = radiation energy per second/total area = nhf/4πr^2. So, intensity is proportional to 1/r^2

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12
Q

What are the hazards of ionising radiation

A

Damage cells and DNA. Cause cancerous cell mutations

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13
Q

What is background radiation

A

Naturally occurring radiation from rocks, soil and the air. An example is radon gas.

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14
Q

How should radioactive materials be safely stored away

A

Lead-line containers

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15
Q

How should radioactive materials be used

A

No contact with the skin, tongs used, lead aprons

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16
Q

What is the half life

A

Time taken for the number of decaying nuclei to halve

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17
Q

What is the activity

A

The number of nuclei of the isotope that decays per second

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18
Q

What happens to the activity after 1 half life

A

It halves

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19
Q

What is the unit of activity

A

Bacquerel (Bq)

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20
Q

What is the decay constant

A

Probability of a nuclei to decay in one second

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21
Q

What are the axis on the N-Z graph

A

N is neutrons and Z is protons

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22
Q

What occurs for lighter isotopes

A

They mostly follow the line N=Z

23
Q

What occurs as Z increases above 20

A

Nuclei gain more N than Z to help bind the nucleons together and stop the repulsive electrostatic forces between protons

24
Q

Where are the alpha emitters on the N-Z graph

A

Where Z is higher than 60, the nucleus is too large and the strong nuclear force is unable to overcome the electrostatic forces

25
Q

Where are the beta- emitters on the N-Z graph

A

These are on the left of the stability belt where they are neutron rich

26
Q

Where are the beta+ emitters on the N-Z graph

A

These are on the right of the stability belt where they are proton rich

27
Q

What is technetium used for

A

This is used in a generator in hospitals to produce a source which emits gamma radiation only

28
Q

What are the ways we can estimate the radius of the nucleus

A

Closest approach of alpha particles and electron diffraction

29
Q

How can we estimate the radius of the nucleus using alpha particles

A

Alpha particles begin with a certain amount of energy and approach. As it gets closer to the nucleus, it slows down and gains potential energy. The closest distance from the nucleus is an upper limit for the radius

30
Q

How can we estimate the radius of the nucleus using electron diffraction

A

Sin(θ) = λ/d where θ is angle to first minimum and d is the nucleus diameter

31
Q

How to find the equation for density of a nucleus

A

Use the equation for radius in the nucleus. Volume is 4πR₀³/3. Mass as Am, where A is atomic number and m is mass of 1 nucleon

32
Q

How does the graph of intensity against angle of deflection for electron diffraction look

A

Largest peak at θ=0. Goes down unit first minimum, then goes up but lower than max…

33
Q

What is the binding energy

A

Work that must be done to separate a nucleus into its constituent neutrons and protons

34
Q

What is the mass defect

A

Change in mass of separated nucleons and the mass of the nucleus

35
Q

What is binding energy per nucleon

A

Average work done per nucleon to remove all nucleons from a nucleus (measures stability)

36
Q

Describe the graph of mass number against binding energy per nucleon

A

Steep increase at the beginning, then slow decrease. Peak is 8.7MeV per nucleon at A = 56

37
Q

Where do atoms undergo fusion and why

A

Atoms can fuse when A < 56 as fusing these to form a larger atom will increase its binding energy, therefore making it more stable

38
Q

Where do atoms undergo fission and why

A

Fission undergoes when A >56 as a large nucleus splitting up will decrease the mass of each one, so increasing its binding energy, therefore making it more stable

39
Q

What is the proof of fusion producing more energy than fission

A

The change in binding energy in fission is 0.5MeV and fusion can be more than 5MeV

40
Q

What is an atomic mass unit

A

Equal to one twelfth of the mass of an carbon-12 isotope

41
Q

What is induced fission

A

When thermal neutrons are fired at large nuclei, causing them to fission and split up

42
Q

What is meant by a chain reaction

A

After fission, multiple daughter nuclei can be released causing further fission and so on

43
Q

What is the energy released in fission

A

Equal to the change in binding energy

44
Q

What is critical mass

A

Minimum mass of a fissile material to continue a chain reaction

45
Q

What occurs if the mass is less than the critical mass

A

Too many of the neutrons will escape due to the much higher surface area to mass ratio

46
Q

What are the main parts in a nuclear reactor

A

Reactor core, control rods, coolant and moderator

47
Q

What is the function of control rods

A

To absorb neutrons and the height is controlled to keep the number of neutrons in the core constant

48
Q

What is the function of the coolant

A

Used to remove heat and transfer it to electrical generators. Water at high pressure

49
Q

What is the function of the moderator

A

So neutrons can be slowed down to actually cause fission. If neutrons travel too fast, this will not causing fission

50
Q

Examples of materials used for coolant

A

CO2 and H2O

51
Q

Examples of moderator

A

Graphite and water

52
Q

Examples of control rods

A

Boron

53
Q

What are some safety features of a nuclear reactor

A

Fuel stored in steel cans, reactor core is thick steel to absorb temp and radiation, remote handling of fuel, emergency shut down system of fulling submerging control rods to stop fission

54
Q

How is radioactive waste stored

A

Firstly stored underwater, then stored in large steel casks, unused uranium stored for further use

Physics A-Level (19 decks)

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