Nuclear Flashcards
What is the plum pudding model of an atom?
Sphere of equally spread positive charge with negatively charged electrons embedded in it
What was observed from the Rutherford scattering experiment?
What conclusions can be drawn from these observations?
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
What can radioactivity be described as?
Spontaneous and random
Define activity
What is it’s unit? (2 possibilities)
The number of nuclei decaying per second
Bq or s-1
Define decay constant
What is it’s unit?
The probability that an atom will decay
s-1
Define half life
How do you find the half life of a LnN against t graph?
The time taken for the number of unstable nuclei in a sample to half
m = -decay constant, plug into half life equation
Which values can be described using an exponential decay equation?
What is the value of k in the exponential equation?
N, m and A
Decay constant
What is radioactive dating used for?
How does it work?
Used to date once living material
C14 taken in by plants via photosynthesis. C14 activity falls when plants die
What are the disadvantages of radioactive dating?
Can be contaminated by other radioactive sources
Sample size is small and unreliable
High background count
How is radioactivity used in medical diagnosis?
What state does this atom exist at?
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
Define metastable state
Excited nuclei state with excess energy for a longer period of time than expected
When does a nucleus become unstable? What types of decay occur in response?
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
What is electron capture?
What is released due to electron capture?
Nucleus absorbs orbiting electron
Releases a gamma particle
What is released as a result of beta emission?
Beta- particle + anti electron neutrino
What is conserved in decay equations?
Lepton number
Nucleon number
Momentum
Charge
What must the fuel rods in a fusion reactor be rich with?
Uranium-235
What is the purpose of the moderator
Give an example of a moderator
Slows down neutrons so fission can occur via elastic collisions with neutrons, by having a similar mass to neutrons
Graphite
What is the purpose of the control rods?
Give an example of a control rod material
It controls the rate of fission by limiting the number of neutrons in reactor by absorbing them
Boron
Define critical mass
The amount of fuel required for a steady chain reaction
What is the purpose of the coolant
Example of coolant
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
What is the purpose of a concrete steel vessel in a nuclear reactor
Forms a shield to reduce radiation from neutron and gamma radiation
Define constant fission rate
There is one further fission event following every fission event
How is the reactor shielded? Why?
Reactor surrounded in thick concrete case
Prevents radiation escaping and affecting workers
Advantages of nuclear power
3 points
Enough fuel to generate electricity for centuries
Does not release greenhouse gases
Very efficient
Disadvantages of nuclear power
Produces waste product which endangers people and environment
Some parts of the process involve greenhouse gases
Danger of nuclear disaster
What is the main source of highly radioactive waste from a nuclear reactor?
(1 mark)
Spent fuel rods
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)
Electromagnetic radiation emitted
As the nucleus de excites to a lower energy level
Describe what happens to the neutrons as a result of collisions with the moderator
(2 marks)
Momentum/ kinetic energy is transferred to moderator
Neutron loses Ke
Reaching speeds which can cause fission
Define an atomic mass unit
1/12 the mass of an atom of carbon-12
Define binding energy
The amount of energy per nucleons released when a new nucleus is formed
Explain why nuclei in a star must be at a high temperature for fusion to take place
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
