Nuclear Physics

Question 1

Describe the Rutherford Scatteing experiment

Answer 1

● Beam of alpha particles directed at thin gold foil
● Occurred in a vacuum so no collisions between air particles and alpha particles
● Was done to determine structure of an atom

Question 2

In the Rutherford Scattering experiment it was observed that most of the alpha particles passed straight through. What can we infer from that?

Answer 2

Most of the atom consists of empty space

Question 3

What evidence was there that suggested the nucleus had a positive charge?

Answer 3

Because it caused some of the positive alpha particles to be repelled/deflected (like-charges repel)

Question 4

Name 3 types of radiation

Answer 4

Alpha, Beta, Gamma

Question 5

Order Alpha, Gamma and Beta radiation in order of ionising power, starting with the most ionising

Answer 5

Alpha, Beta, Gamma

Question 6

Order Alpha, Gamma and Beta radiation in order of penetration power, starting with the most penetrating

Answer 6

Gamma, Beta, Alpha

Question 7

A sheet of paper can block which type of radiation?

Answer 7

Alpha

Question 8

When a nucleus decays through gamma radiation, how does the atomic number and mass number change?

Answer 8

They remain the same as the number of protons and neutrons doesn’t change

Question 9

Why is ionising radiation seen as dangerous?

Answer 9

Because it can kill or mutate cells, leading to things such as cancer

Question 10

Which radiation is more harmful inside a human body, Alpha or Gamma?

Answer 10

Alpha

Question 11

Give an example of a real life use of Beta decay and explain why Beta is chosen for this

Answer 11

Measuring paper thickness - Alpha is not penetrative enough and Gamma is too penetrative

Question 12

Which type of radiation follows the inverse square law?

Answer 12

Gamma

Question 13

What does the inverse square law state?

Answer 13

The intensity is inversely proportional to the square of the distance from the source

Question 14

What is intensity measured in?

Answer 14

W/m²

Question 15

What is background radiation?

Answer 15

Radiation that is constantly in the surroundings from sources such as rocks and food

Question 16

What is the decay constant (λ)?

Answer 16

The probability of a nucleus decaying per second

Question 17

What are the units for the decay constant (λ)?

Answer 17

S‐¹

Question 18

What is Half-life?

Answer 18

The time it takes for half of the unstable nuclei in a substance to decay

Question 19

What equation can you use to work out the half-life of an object?

Answer 19

T½ = ln(2)/λ

Question 20

Complete the equation, λN = ?

Answer 20

Activity

Question 21

What is activity measured in?

Answer 21

Becquerels (decays per second)

Question 22

True or False: Radioactive isotopes decay exponentially?

Answer 22

True

Question 23

Why is Technetium-99 useful in medicine?

Answer 23

Gamma radiation has a short half life, so it doesn’t stay radioactive for long, and is easy to detect outside patient.

Question 24

What does the graph of N against Z show?

Answer 24

The relationship between Proton number and Neutron number

Question 25

Where on the curve does β- decay occur and why?

Answer 25

Above the stability line - nuclei contain too many neutrons

Question 26

What type of decay occurs below the stability line and why?

Answer 26

β+ as these nuclei contain too many protons

Question 27

How does the heavier nuclei often decay?

Answer 27

Alpha decay

Question 28

An Alpha particle is fired at a nucleus, with the KE at the start known. How can you use energy conservation to find closest approach of a particle?

Answer 28

At this point, the KE and PE are equal, so we can rearrange for distance (r)

Question 29

How is electron diffraction used to determine the diameter of a radius?

Answer 29

● Electron beam fired at thin sheet ● Diffraction pattern produced on screen behind ● Calculate diameter using angle of a minimum

Question 30

What is the relationship between nuclear radius (R) and nucleon number (A)?

Answer 30

Nuclear radius is directly proportional to the cube root of the nucleon number

Question 31

True or False: the density of a nucleus is independent of its radius?

Answer 31

True

Question 32

What equation is used to convert mass to its energy equivalent?

Answer 32

E = mc²

Question 33

What is the mass defect?

Answer 33

The difference between the total mass of all the nucleons separately compared to the mass of the nucleus

Question 34

Why is there a mass defect?

Answer 34

Because energy is needed to bring the parts of a nucleus together, therefore the mass equivalent of the energy is lost and the total mass decreases

Question 35

What is binding energy?

Answer 35

The energy required to separate a nucleus into its constituent parts

Question 36

What is nuclear fission?

Answer 36

Where a large unstable nucleus splits into 2 smaller nuclei, releasing energy

Question 37

What is nuclear fusion?

Answer 37

When 2 small nuclei fuse together to create a large nuclei, releasing large amounts of energy

Question 38

Why is it difficult to make nuclear fusion occur on earth?

Answer 38

There is a large repulsion between the 2 positively-chatged nuclei, therefore a lot of energy is required to overcome the repulsion and fuse them together. It is hard to find a material that can withstand the heat

Question 39

How is nuclear fission used in nuclear reactors?

Answer 39

Rods of Uranium-235 absorb neutrons and become unstable, causing them to spilt into two daughter nuclei

Question 40

What is the purpose of a moderator in a nuclear reactor?

Answer 40

To slow down the neutrons so they travel slow enough to be absorbed by the uranium

Question 41

Why are control rods essential for a nuclear power station?

Answer 41

They stop the chain reaction from getting out of control by absorbing neutrons

Question 42

Is Boron used as a control rod or a moderator?

Answer 42

Control rod

Question 43

Give an example of a material that can be used as a moderator in a nuclear reactor?

Answer 43

Water

Question 44

What is the purpose of using water as a coolant?

Answer 44

It allows heat from the nuclear reactor to escape, stopping the reactor from overheating

Question 45

What is the critical mass?

Answer 45

The minimum mass of fuel needed for a chain reaction to occur

Question 46

Which waste products from a nuclear reactor cause the highest risk?

Answer 46

Spent fuel rods

Question 47

How is high-level waste disposed of?

Answer 47

● First stored in cooling ponds ● Then they are put in sealed steel containers and put deep underwater

Question 48

What is low-level waste contained in?

Answer 48

They are sealed in containers and put underground until they are safe again

Question 49

Why is the constant density of nuclear material derived from the equation R =R⁰A⅓ only approximate?

Answer 49

It assumes a uniform distribution of nucleons within the nucleus

Question 50

How is fission induced?

Answer 50

By firing a thermal neutron into the elements nucleus, causing it to become extremely unstable

Question 51

What is binding energy (mass defect ) equal to?

Answer 51

Mass of nucleons - Mass of nucleus

Question 52

In a fission reactor, what do the control rods do?

Answer 52

Absorb excess neutrons to slow down the chain reaction to stop it from getting out of control

Question 53

In a fission reactor, what does the moderator do?

Answer 53

Slows down the neutrons to allow them to be absorbed easier and to sustain the chain reaction

Question 54

What provides evidence for the existence of energy levels in nuclei?

Answer 54

The existence of gamma radiation