Nuclear

Question 1

What is the plum pudding model of an atom?

Answer 1

Sphere of equally spread positive charge with negatively charged electrons embedded in it

Question 2

What was observed from the Rutherford scattering experiment?
What conclusions can be drawn from these observations?

Answer 2

Most alpha particles passed straight through - most of atom is empty is space

Some alpha particles deflected - nucleus is positively charged

Very few alpha particles deflected at an angle greater than 90 degrees - nucleus is small and dense

Question 3

What can radioactivity be described as?

Answer 3

Spontaneous and random

Question 4

Define activity

What is it’s unit? (2 possibilities)

Answer 4

The number of nuclei decaying per second

Bq or s-1

Question 5

Define decay constant

What is it’s unit?

Answer 5

The probability that an atom will decay

s-1

Question 6

Define half life

How do you find the half life of a LnN against t graph?

Answer 6

The time taken for the number of unstable nuclei in a sample to half

m = -decay constant, plug into half life equation

Question 7

Which values can be described using an exponential decay equation?

What is the value of k in the exponential equation?

Answer 7

N, m and A

Decay constant

Question 8

What is radioactive dating used for?

How does it work?

Answer 8

Used to date once living material

C14 taken in by plants via photosynthesis. C14 activity falls when plants die

Question 9

What are the disadvantages of radioactive dating?

Answer 9

Can be contaminated by other radioactive sources
Sample size is small and unreliable
High background count

Question 10

How is radioactivity used in medical diagnosis?

What state does this atom exist at?

Answer 10

Technetium-99m is used in medical tracers, because it releases gamma radiation but with a small half life and decays to a stable isotope so there is no extended exposure to gamma on the patient

Metastable state

Question 11

Define metastable state

Answer 11

Excited nuclei state with excess energy for a longer period of time than expected

Question 12

When does a nucleus become unstable? What types of decay occur in response?

Answer 12

Too many neutrons - beta decay

Too many protons - positron decay

Too many nucleons - alpha decay

Too much energy (possible due to electron capture) - gamma decay

Question 13

What is electron capture?

What is released due to electron capture?

Answer 13

Nucleus absorbs orbiting electron

Releases a gamma particle

Question 14

What is released as a result of beta emission?

Answer 14

Beta- particle + anti electron neutrino

Question 15

What is conserved in decay equations?

Answer 15

Lepton number
Nucleon number
Momentum
Charge

Question 16

What must the fuel rods in a fusion reactor be rich with?

Answer 16

Uranium-235

Question 17

What is the purpose of the moderator

Give an example of a moderator

Answer 17

Slows down neutrons so fission can occur via elastic collisions with neutrons, by having a similar mass to neutrons

Graphite

Question 18

What is the purpose of the control rods?

Give an example of a control rod material

Answer 18

It controls the rate of fission by limiting the number of neutrons in reactor by absorbing them

Boron

Question 19

Define critical mass

Answer 19

The amount of fuel required for a steady chain reaction

Question 20

What is the purpose of the coolant

Example of coolant

Answer 20

It is an efficient liquid of gas that is sent around the reactor to remove heat that is produced by fission. Generated heat produces steam which is used to power electricity-generating turbines

Water

Question 21

What is the purpose of a concrete steel vessel in a nuclear reactor

Answer 21

Forms a shield to reduce radiation from neutron and gamma radiation

Question 22

Define constant fission rate

Answer 22

There is one further fission event following every fission event

Question 23

How is the reactor shielded? Why?

Answer 23

Reactor surrounded in thick concrete case

Prevents radiation escaping and affecting workers

Question 24

Advantages of nuclear power

3 points

Answer 24

Enough fuel to generate electricity for centuries
Does not release greenhouse gases
Very efficient

Question 25

Disadvantages of nuclear power

Answer 25

Produces waste product which endangers people and environment
Some parts of the process involve greenhouse gases
Danger of nuclear disaster

Question 26

What is the main source of highly radioactive waste from a nuclear reactor?

(1 mark)

Answer 26

Spent fuel rods

Question 27

Describe and explain the nature of the radiation that may be emitted from an excited nucleus of the moderator after collision with a neutron

(2 marks)

Answer 27

Electromagnetic radiation emitted

As the nucleus de excites to a lower energy level

Question 28

Describe what happens to the neutrons as a result of collisions with the moderator

(2 marks)

Answer 28

Momentum/ kinetic energy is transferred to moderator
Neutron loses Ke

Reaching speeds which can cause fission

Question 29

Define an atomic mass unit

Answer 29

1/12 the mass of an atom of carbon-12

Question 30

Define binding energy

Answer 30

The amount of energy per nucleons released when a new nucleus is formed

Question 31

Explain why nuclei in a star must be at a high temperature for fusion to take place

Answer 31

Nuclei must be CLOSE TOGETHER so that strong nuclear force can be involved and allow fusion to take place

Nuclei have positive charge so there is electrostatic repulsion between them

High T = High Ke/ speed to overcome repulsion