Nuclear Physics

Question 1

Describe Thomson’s plum pudding model.

Answer 1

atom made up of a sphere that is positively charged with small areas of negative charge scattered evenly.

Question 2

Describe Rutherford experiment.

Answer 2

an alpha source and gold foil placed in an evacuated chamber with a fluorescent coating. hence help to see path of alpha particles with microscope

Question 3

What were the 3 outcomes of the Rutherford experiment and their reason.

Answer 3

• Most of the alpha particle travelled straight through (mostly empty space)
• Small number of particles deflected at small angle (centre is positive charge)
• Few particles deflected more than 90 degrees (centre heavily dense)

Question 4

What is the use of Beta source

Answer 4

Measuring the thickness of certain material (e.g. Aluminium foil)

Question 5

What are the uses of gamma source

Answer 5

• Detector in humans by injecting in patients (short half life)
• Sterilise surgical equipment

Question 6

What is the activity of a radioactive sample

Answer 6

Number of nuclei that decay per second

Question 7

What is dating of object?

Answer 7

Nuclei with long half life (C-14) can be used to date organic objects. This is done by measuring the current amount of C-14 and comparing to initial amount.

Question 8

Why nucleus might become unstable? (neutrons), decays through? proton number?

Answer 8

It has too many neutrons: decays through Beta minus. Proton number increase by 1

Question 9

Why nucleus might become unstable? (protons), decays through? proton number?

Answer 9

It has too many protons: decays through beta plus/ electron capture. Proton number decreases by 1

Question 10

Why nucleus might become unstable? (nucleons), decays through? proton number?

Answer 10

It has too many nucleons: decays through alpha emission. nucleon number decrease by 4 and proton number decrease by 2

Question 11

Why nucleus might become unstable? (energy), decays through?

Answer 11

It has too many energy: decays through gamma emission (occurs after a certain decay as nucleus gets excited and has excess energy)

Question 12

Why is the number of neutrons and protons not constant after 20.

Answer 12

Electromagnetic force of repulsion becomes larger than strong nuclear force keeping nucleus together.

Question 13

What needs to do to make nucleus stable (force)

Answer 13

More neutrons needed to increase distance between proton to lower force, thus stable nucleus

Question 14

What gives an accurate estimate for nuclear radius

Answer 14

electron diffraction

Question 15

What did the diffraction pattern include? and draw what graph after

Answer 15

A set of concentric circles with a central bright spot. This gets dimmer as you move away. Draw intensity/ diffraction angle graph

Question 16

Equation to estimate nucleus radius from graph

Answer 16

sin0 = (0.61* wavelength)/Radius of nucleus

Question 17

What happens when you plot ln(R) against ln(A)

Answer 17

straight line with y intersect is ln(k)
gradient = 1/3

Question 18

What is binding energy?

Answer 18

The energy required to separate the nucleus into its constituents (nucleons)

Question 19

What is nuclear fission?

Answer 19

Splitting of a large nucleus into two daughter nuclei

Question 20

Why is energy released during fission?

Answer 20

The smaller daughter nuclei have a higher binding energy per nucleon

Question 21

Why is energy released during fission?

Answer 21

The smaller daughter nuclei have a higher binding energy per nucleon

Question 22

What is nuclear fusion?

Answer 22

two smaller nuclei join together to form one large nucleus

Question 23

What kind of temperature occurs in fusion

Answer 23

high temperature because lots of energy required to overcome the electrostatic force of repulsion between nuclei

Question 24

What occurs below Fe-56

Answer 24

Fusion

Question 25

What occurs above Fe-56

Answer 25

Fission

Question 26

How is fission induced?

Answer 26

• Firing thermal neutron into uranium nucleus making them instable

Question 27

What happens with the thermal neutrons and neutrons with higher energy

Answer 27

Thermal neutron have low energy so they can induced fission.

Neutron with high energy rebound away from uranium-235 after collision and cause nothing

Question 28

What is a chain reaction?

Answer 28

Each fission goes on to cause at least one more fission

Question 29

What is critical mass?

Answer 29

Minimum mass of fuel required to maintain a steady chain reaction.

Question 30

What does a moderator do in a nuclear reactor?

Answer 30

Slows down the neutrons released in fission reaction to thermal speeds through elastic collision between nuclei of moderator and fission neutrons

Question 31

What happens if the moderator size is close to a neutron’s?

Answer 31

the larger the proportion of momentum transferred thus lower number of collisions required to get to thermal speeds

Question 32

What acts as a moderator and why?

Answer 32

water because contains hydrogen, cheap and not reactive

Question 33

What does a control rod do in a nuclear reactor?

Answer 33

absorb neutron in the reactor in order to control chain reactions

Question 34

What kind of element is the control rod made out of?

Answer 34

Boron

Question 35

What does a coolant do in a nuclear reactor?

Answer 35

absorbs heat released during fission in the core of the reactor. The used to make steam for electricity

Question 36

What acts as a coolant

Answer 36

water because high specific heat capacity