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Physics > A2 - Nuclear > Flashcards

A2 - Nuclear Flashcards

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1
Q

What were the two main outcomes of Rutherford’s scattering experiment?

A

Most passed through - atom mostly empty space, mass concentrated at centre
1/2000 deflected, 1/10,000 deflected through 90 - small positively charged nucleus

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2
Q

What was the equipment used for rutherford scattering experiment?

A

Evacuated jar to allow alpha particles to travel uninterrupted.

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3
Q

Estimated nuclear size. What is the equation for n layers

A

deflection is 1/1000n
ratio of nucleus/atom is 0.25pid^2/0.25pi*D^2
Rearrange for d^2

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4
Q

Which is the most ionising type of radiation?

A

alpha particles most ionising, followed by beta

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5
Q

How can you measure ionisation

A

ionisation proportional to ions/second impacting electrode in ion chamber

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6
Q

What is a cloud chamber and what does it show?

A

Cloud chamber is air saturated with vapour. Ionising radiation causes water to condense leaving vapour trails

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7
Q

What are the characteristics of alpha ratiation in a cloud chamber?

A

The lines are straight, and of constant length for an given isotope

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8
Q

What are the characteristics of beta radiation in a cloud chamber?

A

Whispy trails due to lower mass and greater effect due to collision with air particles

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9
Q

What are the particles that make up alpha, beta and gamma radiation

A

alpha - helium nucleus
Beta - electron
gamma - high energy photon

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10
Q

How does a geiger tube work

A

There is a tube filled with argon gas with the casing as the negative electrode and the rod in the centre as the positive. The ionising radiation enters the mica window and ionises the argon, causing the ion to be attracted to one of the electrodes. This registers as a current spike as charge has been transferred, which registers as a click.

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11
Q

What is the dead time of a geiger counter? What does this mean for highly radioactive sources

A

The time between ionisations where the tube will not register any further ionisations. It must return to its non-conductive state before more ions can be formed. For highly radioactive sources, some will be missed, so there is a max amount of radiation that a geiger counter can show

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12
Q

What is the law for intensity of gamma radiation at a given distance from source

A

inverse square law

Intensity = energy per second/area=nhf/4pi*r^2

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13
Q

What is the nuclear change for alpha emission?

A

A-4

Z-2

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14
Q

What is the nuclear change for beta emission

A

Z+1

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15
Q

What is the nuclear change for beta + emission

A

z-1

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16
Q

What is the nuclear change for electron capture

A

z-1

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17
Q

What is the nuclear change for gamma emission?

A

No change.

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18
Q

What types of nuclei undergo beta- emission

A

neutron rich (n-p + e-)

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19
Q

What types of nuclei undergo beta+ emission

A

proton rich

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20
Q

Why do nuclei undergo gamma emission

A

To remove excess energy, often having undergone alpha/beta decay, a nucleus will reach a more stable energy level through gamma emission.

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21
Q

What is the type of decay a nucleus undergoes - what is its relationship with time?

A

Exponential decrease with constant half life

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22
Q

Define half life

A

Time taken for half the nuclei in a radioactive sample to decay

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23
Q

What is the rule for probability of decay for a given molecule?

A

It is random. There is no guarantee of which molecules will decay in a given half life, just that half of them will

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24
Q

What is the decay constant

A

lamda - the probability of a single nucleus decaying per second

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25
Q

What is the activity of a sample?

A

the number of disintegrations per second

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26
Q

What is the unit for activity

A

Bq

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27
Q

How does activity of a sample change over time

A

A=A0e^-(lamda)t

28
Q

What is the formula for energy transfer per second?

A

A*energy per decay

29
Q

What can affect the rate of decay of a sample?

A

Nothing. It is an inherent property of the material. You cannot heat it up to make more nuclear stuff come out.

30
Q

What happens the radioactive sample contains more and more nuclei?

A

It becomes closer to an ideal model of decay

31
Q

Why might carbon dating not be accurate for determining the age of a boat?

A

The wood may have been cut some time before the boat was made

There is a large error associated with the initial decay because of the steep gradient.

32
Q

How old can something be before carbon dating is no longer useful?

A

~60,000 years

33
Q

What is used when carbon dating is no longer possible

A

Argon dating

34
Q

What are the requirements for an effective tracer

A

Long enough half life to be observed in the body, not alpha emitters so less ionising, doesn’t stay in the body for 5000 years afterwards

35
Q

What is the definition of mass

A

How hard it is to accelerate a body

36
Q

What is the definition of energy

A

The capacity to do work

37
Q

What does E=mc^2 show us

A

Mass and energy are interchangeable

38
Q

What is the definition of an atomic mass unit

A

equal to 1/12 the mass of carbon 12. Just as an arbitrary reference

39
Q

What is the equivalence between u and energy?

A

1u=931.5MeV

40
Q

How is the energy release during alpha decay shared between the two masses?

A

Inversely proportional to the masses

41
Q

What is binding energy

A

The energy that is required to go from a bound nucleus (lower energy state) to the separated nucleons.

42
Q

Why is binding energy a thing? What does it need to overcome?

A

SNF

43
Q

What is the formula for calculating mass deficit

A

Z(mp)+(A-Z)mn -Mnuc

44
Q

What the reason for the possibility of quantum tunelling by an alpha particle?

A

Higher binding energy in alpha particle compared to nucleus

45
Q

What is the measure of stability of a nucleus

A

Binding energy per nucleon

46
Q

What is the shape of the graph showing binding energy per nucleon against mass nucleon number?

A

It increases sharply up to iron, which is the most stable, then decreases towards the heavy elements like uranium

47
Q

How does the BE/N/A graph show whether fusion or fission would release more energy?

A

The steeper gradient at the start indicates that fusion would release much more energy to go from hydrogen to helium than uranium fission.

48
Q

How is energy released during nuclear fission?

A

One heavy nucleus is split by a neutron into two smaller daughter nucleus, releasing further neutrons and energy.

49
Q

What is critical mass

A

When, on average, one fission goes on to produce one more fission, creating a sustainable chain reaction.

50
Q

How is the nuclear chain reaction controlled?

A

Control rods absorb excess neutrons and slow the rate of fission

51
Q

Why are neutrons slowed down?

A

To reduce their velocity to become thermal neutrons, increasing chances of absorbtion

52
Q

How are neutrons slowed down?

A

Using a moderator such as water

53
Q

What causes the energy release during nuclear fission?

A

Electrostatic repulsion of the fragments leads to gain in kinetic energy as soon as they are outside SNF region.

54
Q

In commercial fission reactors, how is the energy turned into electricity?

A

A heat exchanger transfers energy from the contaminated water of the reactor core to non contaminated water in a separate loop which goes on to evaporate and drive a turbine with steam

55
Q

Why is nuclear waste more dangerous than uranium fuel?

A

Uranium is an alpha emitter which can be shielded to be kept relatively safe. The waste has a long half life and is beta/gamma emitter, so need cooling, containment, and later underground storage

56
Q

What causes nuclear fusion to release energy?

A

The nucleus that is formed is more tightly bound than before, so is more stable. Reaching this stability releases energy.

57
Q

What is the main problem associated with nuclear fusion?

A

The hydrogen plasma must be of high enough temperature to give sufficient Ek to get close enough for SNF to bind nuclei. *10^6 kelvin

58
Q

How should high level nuclear waste be dealt with/

A

Cooling, casing

59
Q

How should intermediate level nuclear waste be dealt with?

A

Casing

60
Q

How should low level nuclear waste be dealt with?

A

Burying.

61
Q

What is the maximum binding energy per nucleon?

A

8.7

62
Q

Where do fission fragments lie on N/Z graph?

A

To the left of the stability line

63
Q

How do fission fragments decay?

A

Neutron rich, so beta decay

64
Q

Define specific latent heat of vapourisation

A

the energy required to change the
state of a unit mass of water to
steam/gas without a change in temperature

65
Q

Define decay constant

A

The probability of decay per unit time. This is a CONSTANT OF PROPORTIONALITY.

Physics (9 decks)

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