Nuclear physics (Paper 2) Flashcards
What was Rutherford’s scattering experiment?
● Most alpha particles passed straight through the foil - this
suggested that the atom is mostly empty space
● A small amount of particles were deflected by a large angle - this suggested that the
centre of the atom is positively charged, as positively charged alpha particles were
repelled from the centre and deflected.
● Very few particles were deflected back by more than 90° - this suggested that the that
the centre of the atom was very dense as it could deflect fast moving alpha particles
What was Rutherfords scattering aparatus How was it set up?
Rutherford’s apparatus included an alpha source and gold foil in an evacuated chamber which
was covered in a fluorescent coating, which meant you could see where the alpha particles hit
the inside of the chamber. To observe the path of the alpha particles, there was a microscope
which could be moved around the outside of the chamber.
What is radiation?
Where an unstable nucleus emits energy in the form of EM waves or subatomic
particles in order to become more stable.
What are uses of gamma radiation and why?
● As a detector - a radioactive source with a short half-life (to reduce exposure), which emits gamma radiation, can be injected into a patient and the gamma radiation can be detected using gamma cameras in order to help diagnose patients.
● To sterilise surgical equipment - as gamma radiation will kill any bacteria present on the equipment.
● In radiation therapy - gamma radiation can be used to kill cancerous cells in a targeted region of the body such as a tumour, however it will also kill any healthy cells in that region.
What are sources of background radiation?
● Radon gas - which is released from rocks.
● Artificial sources - caused by nuclear weapons testing and nuclear meltdowns.
● Cosmic rays - enter the Earth’s atmosphere from space.
● Rocks containing naturally occurring radioactive isotopes.
How ionising are the 3 radiation types?
Alpha is the most and can be incredibly dangerous if inhaled or ingested.
Beta is less ionising but can cause tissue damage.
Gamma can damage cells and cause mutation if exposed to for a long time.
What is a specific use of gamma?
Technetium-99m is used for medical imaging because it’s a PURE gamma source (which makes it safe). It’s also easy to prep on sight because it’s safe. The half life is 6 hours so it doesn’t stay in the body too long.
How can you estimate the nuclear radius of an atom?
Closest approach method or electron diffraction
What is the closest approach method?
Used to estimate the nuclear radius of an atom.
As a positive charge is fired towards a nucleus, as it moves towards the positively charged nucleus it will experience an electrostatic force of repulsion and slow down as its kinetic energy is converted to electric potential energy. The point at which the particle stops and has no
kinetic energy is its distance of closest approach.
What is the electron diffraction method for estimating atomic radius?
Equation: (R x Sinθ)=o.61λ(de broglie wavelength)
High energy electrons travelling through an atom will display a diffraction pattern. Much more accurate than closest approach (which is an overestimate).
Electrons are leptons meaning they won’t interact with nucleons in the neutron through the strong nuclear force.
What is the mass defect?
When measuring the nucleus mass and then the mass of the nucleons, the nucleus mass will be lower (mass defect). It’s because mass that’s ‘lost’ is converted into energy and released when the nucleons fuse to form a nucleus.
What is the binding energy of a nucleus? (and equation)
Energy required to separate the nucleus into its constituents (nucleons).
Binding energy=mass defect X C^2
How do I convert atomic mass units to KG?
Multiply by 1.661x10^-27 (one atomic mass unit, 1U)
What is nuclear fission?
The splitting of a large nucleus into two daughter nuclei. It occurs in very
large nuclei, which are unstable (such as uranium), and occurs completely randomly
What is nuclear fusion?
Where two smaller nuclei join together to form one larger nucleus. It only occurs in fairly small nuclei. Energy is released during fusion because the larger nucleus has a much higher binding energy per nucleon.
When can nuclear fusion occur?
Fusion releases far more energy
than fission however fusion can only occur at extremely high temperatures (for example in stars) because a massive amount of energy is required to overcome the electrostatic force of repulsion
between nuclei.
What does the graph of binding energy per nucleon against nucleon number show?
The peak of the curve occurs at a nucleon number of 56; the element iron
has the highest binding energy per nucleon, nuclei smaller than iron can undergo fusion, while
elements larger than iron can undergo fission.
What is a use of fission?
It is used in nuclear power plants to create energy. Large unstable nuclei break into smaller fragments, releasing energy.
235u+neutron–>fission fragments+neutrons+energy
Energy is extracted from fission by placing the nuclei in water so the energy is absorbed by the water and heats up.
What is the process of nuclear fission in a reactor?
Fission is induced by firing neutrons at a nucleus. When the nucleus is struck it splits into 2 or more daughter nuclei. Neutrons are ejected from the nucleus which can collide with other nuclei causing a cascade effect.
A chain reaction is made lasting until all material has undergone fission or halted by moderator.
If it’s not controlled the chain reaction can produce effects of a nuclear bomb.
What are the different parts of a nuclear reactor and what do they do?
Moderator: Helps slow down neutrons by fission to sustain the chain reaction. Normally water or graphite.
Control rods: Controls the power of a nuclear reactor by absorbing neutrons and preventing them from causing further fission. They are held above the reactor so in emergencies they can drop down. Normally boron.
Coolant: A substance circulated through a reactor to remove or transfer heat.
How is nuclear waste disposed of?
It is placed in a cooling pond for numerous years to cool down and complete fission. It is then put into a dry cast. If any uranium is left over it can be extracted and recycled. The waste is then put into deep geological disposal like a cave far away from civilisation.
What are safety aspects of nuclear reactors?
-Around the nuclear reactor is a very thick concrete shielding, which blocks radiation from escaping from the reactor and affecting the workers in the power station. The shielding may become radioactive after long term use.
-The fuel used in nuclear reactors is called enriched uranium, The U-238 absorbs fission neutrons and so helps to control the rate of fission reactions
What does the inverse square law state?
The intensity is inversely proportional to the square of the distance from the source.
What is the intensity of a source?
The radiation energy passing through a unit area per second
What is half-life?
The time taken for a number of radioactive particles present, N, to halve from it’s original value.
What is a use of half-life?
Carbon dating
How many half lives to get from 243 to 17?
243x2^-2x=17
2^-x=17/243
Log2(17/243)=-x
What is a use of alpha radiation?
Smoke detectors because they don’t travel very far
Equation for the density of a nucleus?
3x1.661x10e-27/4xpixR0e3
What particle other than an electron is produced in beta decay?
Anti neutrino
Why is nuclear density a constant?
Protons and neutrons have a very similar mass and volume
How do you measure the thickness of aluminium with beta radiation?
By measuring how much beta can pass through. If the foil is too thick it will absorb the particles so the detector receives less, vice versa.
What are storage issues with long term nuclear waste storage?
Structural degradation of the packages and casting due to slow radiation will happen overtime.
