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Nuclear physics Flashcards

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1
Q

What is an electronvolt?

A

The amount of energy required to accelerate one unit charge by one volt. Energy per unit charge.

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2
Q

When would a nucleus emit a gamma photon?

A

When the nucleus needs to lose energy without changing the nucleon number.

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3
Q

What is the value of k?

A

1/ 4 π ε_0 ≈ 9 x 10^9

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4
Q

How many metres are there in one femtometre?

A

1x10^-15

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5
Q

What is rest mass?

A

The mass of an object when it is not moving relative to the observer.

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6
Q

Explain mass defect.

A

The difference between the mass of the nucleons in the nucleus and the sum of their masses separately. This is due to some of the mass being converted into the binding energy leading to the nucleons in the nucleus having less mass than the sum of their seperate masses.

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7
Q

Which equation is used to find the binding energy in the nucleus?

A

e = mc ²

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8
Q

How do you convert Joules to Mev?

A

Divide Joules by e

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9
Q

What is u?

A

Atomic unit for mass, u is constant.

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10
Q

How do you work out the mass of the nucleons when they are seperated?

A

Add the mass of the nucleus and the binding energy.

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11
Q

What is nuclear fission?

A

The splitting of a nucleus into its constituent nucleons.

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12
Q

What did J. J. Thompson come up with?

A

The idea that Atoms were like a plum pudding.

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13
Q

What did Rutherford scattering show?

A

The existence of a nucleus.

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14
Q

What is Rutherford scattering?

A

When alpha particles are projected at a thin sheet of gold foil surrounded by a circular detector screen which flashes when an alpha particle hits it. These particles can be deflected by angles greater than 90 degrees so they can come back to where they came.

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15
Q

How do you find the charge on the nucleus?

A

Multiply the proton number by e.

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16
Q

Do leptons interact with the strong force?

A

No.

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17
Q

What does the strong nuclear force affect?

A

Protons and neutrons.

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18
Q

What is the equation for radius of the nuclei diffracting electrons in the Rutherford scattering experiment?

A

R = 1.22λ/2sinθ Where R is the radius of the nuclei, λ is the de Broglie wavelength and θ is the angle of diffraction.

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19
Q

How are relative intensity and angle of diffraction related?

A

As angle of diffraction increases, relative intensity decreases. On a graph there is one big hump in the middle then very small humps on either side.

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20
Q

What is the typical radius of a nucleus?

A

1fm (1 x 10^-15m)

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21
Q

What does the graph of nuclear radius against nucleon number look like and how are they related?

A

A steep, positive curve which decreases in gradient as nucleon number increases. The radius of the nucleus is directly proportional to the cube root of the nucleon number.

22
Q

What is the most ionising form of radiation?

A

Alpha.

23
Q

What is the range of a beta-plus particle?

A

Virtually zero because it is annihilated by an electron.

24
Q

Which type of radiation is not affected by a magnetic field?

A

Gamma.

25
Q

Why are alpha particles the most ionising?

A

They are strongly positive and can pull electrons off atoms.

26
Q

How do beta-minus particles ionise atoms?

A

By knocking electrons off atoms with their higher speeds.

27
Q

What is usually the largest contributor to background radiation?

A

Radon gas released from rocks.

28
Q

State an experiment to investigate the inverse square law.

A

Use a geiger counter and a radioactive source and a meter ruler to measure how the number of emissions decreases as the distance increases. The background count rate should be measured and subtracted from each value.

29
Q

What is the unit of activity?

A

becquerels (Bq)

30
Q

What is the meaning of one becquerel?

A

One decay per second.

31
Q

What is lambda in terms of radiation?

A

Decay constant.

32
Q

What is the definition of half-life?

A

The half-life (T_1/2) of an isotope is the average time it takes for the number of unstable nuclei to halve.

33
Q

In what way does the number of undecayed particles decrease?

A

Exponentially.

34
Q

How can the equation for radioactive decay be altered to suit activity?

A

Replace N and N_0 with A and A_0 respectively.

35
Q

State four uses of radioactive substances with varying half-lives.

A

To date organic material, diagnose medical problems, sterilise food and in smoke alarms.

36
Q

In what type of nuclei does alpha emission occur?

A

Heavy nuclei.

37
Q

In what type of nuclei does beta minus decay occur?

A

Neutron rich nuclei.

38
Q

In what type of nuclei does gamma radiation occur?

A

Nuclei with too much energy.

39
Q

State the four things that must be conserved in every nuclear reaction.

A

Energy, momentum, charge and nucleon number.

40
Q

What do nuclear fission reactions produce and what does this cause?

A

More neutrons which then induce other nuclei to fission. This is called a chain reaction.

41
Q

What must neutrons be in order to be captured by uranium nuclei in a nuclear reactor?

A

Moving slowly.

42
Q

What is the name of slowed down neutrons in a nuclear reactor?

A

Thermal neutrons.

43
Q

What causes neutrons in a nuclear reactor to be slowed down?

A

Elastic collisions with nuclei of the moderator (usually water).

44
Q

What are control rods for?

A

To limit the number of neutrons in the reactor by absorbing them to control the rate of fission.

45
Q

What is the critical mass in a nuclear reactor?

A

The minimum amount of fuel needed to allow one fission to follow another.

46
Q

What protects the workers from the radiation?

A

A thick concrete case which acts as shielding surrounding the reactor.

47
Q

What is first done with nuclear waste when it is removed from the reactor?

A

It is placed in cooling ponds because it is very hot and left there until it is a safe temperature.

48
Q

How is the handling of nuclear waste done and why?

A

Remotely to protect the workers by limiting the radiation they are exposed to.

49
Q

How is nuclear waste stored?

A

It is formed into glass rods and put in thick concrete or steel containers and left deep underground away from any environments which could be harmed until its activity has fallen sufficiently. Local people are consulted before it is stored near them.

50
Q

What element has the highest average binding energy per nucleon?

A

Iron.

51
Q

What does a graph of average binding energy per nucleon against nucleon number look like?

A

It would increase quickly to start with then the rate of increase would start to decrease but still increasing until iron at nucleon number 56 where the binding energy gradually decreases after that.

52
Q

What does the change in average binding energy give?

A

Energy released.

Physics (14 decks)

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