26 - Nuclear Physics Flashcards

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1
Q

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

A

Energy has mass

Mass is a form of energy

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2
Q

What happens when an electron positron pair annihilate?

A

Their total mass is transformed into energy in the form of two gamma photons.

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3
Q

What happens in pair production?

A

A single photon vanishes and its energy creates a particle anti particle pair.

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4
Q

What is mass defect?

A

The difference between the mass of the separated nucleons and the nucleus of the atom.

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5
Q

What is binding energy?

A

The energy required to completely separate a nucleus into protons and neutrons.

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6
Q

What does binding energy per nucleon tell us?

A

How tightly bound a nucleus is.

How stable the nucleus is.

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7
Q

What does a graph of binding energy per nucleon against nucleon number show us?

A

That for lighter elements, fusion releases energy.

For heavier elements, fission releases energy.

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8
Q

What happens in induced fission?

A

Uranium 235 absorbs a slow moving neutron .
UNSTABLE U-236
Splits into daughter nuclei and three fast neutrons

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9
Q

Compare the total binding energy before and after nuclear fission.

A

The total binding energy after is greater than the total binding energy before.

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10
Q

What is the energy released in nuclear fission a combination of?

A

Kinetic energies of daughter nuclei and neutrons, energy of gamma photons and neutrinos.

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11
Q

What is the rate of growth of a chain fission reaction?

A

3^n

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12
Q

How many slow neutrons are preserved after each fission reaction in a nuclear reactor?

A

1

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13
Q

What are fuel rods made up of.

A

2-3% U-235

Rest U-238

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14
Q

What is the job of the moderator?

A

To slow down the fast neutrons that are produced in a fission reaction so that they have a low enough kinetic energy to be absorbed by another U-235 nucleus and continue the chain reaction.

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15
Q

What is the job of the coolant?

A

To remove the thermal energy from the reactants of each fission reaction.

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16
Q

Give some key features of a moderator?

A

Cheap
Readily available
Relatively low specific heat capacity
Must not absorb neutrons

17
Q

What is a commonly used coolant/moderator in a nuclear reactor?

A

Water

18
Q

What are control rods commonly made from?

A

Boron or Cadmium

19
Q

What is the job of control rods.

A

To absorb neutrons and ensure that exactly one neutron survives after each reaction.

20
Q

What is nuclear fusion?

A

When smaller nuclei combine to make larger nuclei.

21
Q

How close do nuclei need to be to go through nuclear fusion and why?

A

a few fm (mx10^-15)

This is so that the strong nuclear force can attract them into a larger nucleus.

22
Q

What are the stages of fusion in a proton proton cycle?

A

p + p = H + e+ +v

H + p = He₃

He₃ + He₃ = He₄ + 2p