Nuclear physics

What does Einstein’s mass-energy equation mean?

Mass and energy are equivelent

What are the two interpretations of Einstein’s mass-energy equation?

• mass is a form of energy

• energy has mass

Why is the rest mass of an electron different to an electron in a particle accelerator?

• The electron in the particle accelerator is moving so has more energy than an electron at rest

• Since ∆E = ∆mc², the mass of the electron in the particle accelerator must be greater than the rest mass of an electron

Explain why energy is released in alpha decay

• The total mass of the alpha particle and daughter nucleus are less than the parent nucleus. As such total mass decreases.

• Since the mass has changed, some energy must be released during the decay for mass-energy to be conserved

• Energy is released (not absorbed) as the mass decreases

Explain why energy is released in beta decay

• The total mass of the electron or positron and daughter nucleus are less than the parent nucleus. As such total mass decreases.

• Since the total mass has changed, some energy must be released during the decay for mass-energy to be conserved

• Energy is released (not absorbed) as the mass decreases

What is the value of an atomic mass unit?

1 u = 1.661 × 10^–27 kg

How would you calculate the binding energy from the mass defect?

Binding energy = mass defect × c²

Explain why the binding energy is different for different nuclei.

Different nuclei have different numbers of nucleons so have different bingding energies

Draw a sketch of binding energy per nucleon against nucleon number.

Where on a sketch of binding energy per nucleon against nucleon number do fusion and fission take place?

Which is the most stable nuclei?

iron-56

Which three elements don’t fit the curve?

Helium, oxygen and carbon

What is the composition of mined Uranium?

• 99.3% uranium-238

• 0.7% uranium-235

Why are thermal neutrons needed in a fission reactor?

• The fuel in fission reactors can split spontaneously without neutrons, but this is unlikely.

• Thermal neutrons are needed to indeuce fission: the neutrons are absorbed by the fuel, making it unstable and causing it to decay.

What is the decay equation for the induced fission of uranium-235 by a thermal neutron?

Draw a diagram to show an uncontrolled fission reaction

What is component 1 in this fission reactor?

Control rods – boron/cadmium

What is component 2 in this fission reactor?

Pressuriser

What is component 3 in this fission reactor?

Heat exchanger

What is component 4 in this fission reactor?

Reactor core

What is component 5 in this fission reactor?

Vessel – steel

What is component 6 in this fission reactor?

Steam to turbines

What is component 7 in this fission reactor?

Fuel rods – Enriched uranium, that is, extra U235 added

What is component 8 in this fission reactor?

Moderator (graphite/water) and coolant (water)

What is component 9 in this fission reactor?

Water from turbines

What is component 10 in this fission reactor?

Shielding – reinforced concrete

What is component 11 in this fission reactor?

Pump

What is the purpose of the coolant in a fission reactor?

Takes heat from the reactor (produced from the fission reactions) and tranfers it to the heat exchanger

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

• The fast neutrons produced in fission reactions elasticaly collide with moderator atoms which have small mass.

• Energy is transferred from neutrons to atoms.

• This slows down the fast neutrons to produce thermal neutrons

Why is a moderator needed in a fission reactor?

• Induced fission of uranium-235 produces fast neutrons.

• The chance of these fast neutrons being absorbed by uranium-235 nuclei is quite small, whereas thermal neutrons have a greater chance of producing induced fission.

• As such a moderator is needed to slow down the fast neutrons and produce thermal neutrons

What is the purpose of the control rods in a fission reactor?

Absorbs neutrons to control the rate of the reaction and maintain it at a steady rate where 1 neutron per fission goes on to produce further fission

What is the purpose of the fuel rods in a fission reactor?

To undergo fission and release energy when hit with neutrons

What is its purpose of the shielding in a fission reactor?

• Reduce intensity of gamma rays.

• Absorb some neutrons. (No effect on neutrinos since do not interact with matter.)

What properties do the shielding in a fission reactor have?

• Often thick and high density to absorb gamma rays

• Withstands high temperatures

Why is enriched uranium used in the fuel rods?

What are the benefits of fission reactors?

• They don’t emmit CO₂

• A small quantity of fuel produces large amounts of energy

What are the environmental impacts of fission reactors?

• They produce hazardous and radioactive waste materials such as plutonium 239.

• These materials can have half lives which are tens of thousands of years

• These materials cannot enter our water or food suplies so must be buried underground for centuries

Why is it difficult to get fusion reactors to work?

• Extremely high temperatures are needed for fusion to occur. It is very hard to maintain such temperatures for long enough to sustain fusion.

• It is very hard to confine the extremely hot fuel in a reactor

Show the equations for proton-proton chain.

What is the nuclear symbol for a electron?

What is the nuclear symbol for a positron?

What is the binding energy of a nucleus?

The work that must be done to separate a nucleus into its separate nucleons.

Define the mass defect

The difference between the mass of the separate nucleons and the mass of the nucleus