Nuclear Physics Flashcards
Describe Thomson’s plum pudding model.
atom made up of a sphere that is positively charged with small areas of negative charge scattered evenly.
Describe Rutherford experiment.
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
What were the 3 outcomes of the Rutherford experiment and their reason.
- 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)
What is the use of Beta source
Measuring the thickness of certain material (e.g. Aluminium foil)
What are the uses of gamma source
- Detector in humans by injecting in patients (short half life)
- Sterilise surgical equipment
What is the activity of a radioactive sample
Number of nuclei that decay per second
What is dating of object?
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.
Why nucleus might become unstable? (neutrons), decays through? proton number?
It has too many neutrons: decays through Beta minus. Proton number increase by 1
Why nucleus might become unstable? (protons), decays through? proton number?
It has too many protons: decays through beta plus/ electron capture. Proton number decreases by 1
Why nucleus might become unstable? (nucleons), decays through? proton number?
It has too many nucleons: decays through alpha emission. nucleon number decrease by 4 and proton number decrease by 2
Why nucleus might become unstable? (energy), decays through?
It has too many energy: decays through gamma emission (occurs after a certain decay as nucleus gets excited and has excess energy)
Why is the number of neutrons and protons not constant after 20.
Electromagnetic force of repulsion becomes larger than strong nuclear force keeping nucleus together.
What needs to do to make nucleus stable (force)
More neutrons needed to increase distance between proton to lower force, thus stable nucleus
What gives an accurate estimate for nuclear radius
electron diffraction
What did the diffraction pattern include? and draw what graph after
A set of concentric circles with a central bright spot. This gets dimmer as you move away. Draw intensity/ diffraction angle graph
Equation to estimate nucleus radius from graph
sin0 = (0.61* wavelength)/Radius of nucleus
What happens when you plot ln(R) against ln(A)
straight line with y intersect is ln(k)
gradient = 1/3
What is binding energy?
The energy required to separate the nucleus into its constituents (nucleons)
What is nuclear fission?
Splitting of a large nucleus into two daughter nuclei
Why is energy released during fission?
The smaller daughter nuclei have a higher binding energy per nucleon
Why is energy released during fission?
The smaller daughter nuclei have a higher binding energy per nucleon
What is nuclear fusion?
two smaller nuclei join together to form one large nucleus
What kind of temperature occurs in fusion
high temperature because lots of energy required to overcome the electrostatic force of repulsion between nuclei
What occurs below Fe-56
Fusion
What occurs above Fe-56
Fission
How is fission induced?
- Firing thermal neutron into uranium nucleus making them instable
What happens with the thermal neutrons and neutrons with higher energy
Thermal neutron have low energy so they can induced fission.
Neutron with high energy rebound away from uranium-235 after collision and cause nothing
What is a chain reaction?
Each fission goes on to cause at least one more fission
What is critical mass?
Minimum mass of fuel required to maintain a steady chain reaction.
What does a moderator do in a nuclear reactor?
Slows down the neutrons released in fission reaction to thermal speeds through elastic collision between nuclei of moderator and fission neutrons
What happens if the moderator size is close to a neutron’s?
the larger the proportion of momentum transferred thus lower number of collisions required to get to thermal speeds
What acts as a moderator and why?
water because contains hydrogen, cheap and not reactive
What does a control rod do in a nuclear reactor?
absorb neutron in the reactor in order to control chain reactions
What kind of element is the control rod made out of?
Boron
What does a coolant do in a nuclear reactor?
absorbs heat released during fission in the core of the reactor. The used to make steam for electricity
What acts as a coolant
water because high specific heat capacity
