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Physics > Chapter 7 - atomic and nuclear physics > Flashcards

Chapter 7 - atomic and nuclear physics Flashcards

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1
Q

What happens referencing subatomic particles when current is passed through a wire ?

A

The wire gets hot, if the wire is hot enough it emits negatively charged particles.

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2
Q

What is a anode ?

A

A positive plate that collects negative particles.

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3
Q

What is a cathode ?

A

A wire that emits negatively charged particles

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4
Q

What is thermonic emission ?

A

The process by which free electrons are emitted from the surface of a metal when external heat is applied

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5
Q

Who created the plum pudding model ?

A

J.J Thomson

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6
Q

What experiment did Rutherford do to discover the positively charged particles ?

A

He fired alpha particles at thin gold foil

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7
Q

What did Rutherford conclude from his experiment ?

A
  • Most of the alpha particles went straight through
  • A few alpha particles were slightly deflected
  • 1 in 8000 were ‘back scattered’
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8
Q

What did Rutherford conclude when an alpha particle passed straight through the foil ?

A

The did not come close enough to any repulsive charge at all. The atom most be mostly empty space.

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9
Q

Where is most of the mass in an atom found ?

A

Dense core (nucleus)

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10
Q

Where did the negative charge come form in the atom?

A

a ‘cloud of electrons’ surrounding the positive nucleus

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11
Q

What did Rutherford conclude when an alpha particle deflected at a large angle ?

A

It approached sufficiently close to a nucleus it was repelled strongly enough.

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12
Q

How did Rutherford conclude that the nucleus was very small ?

A

Only 1 in 8000 alpha particles were back scattered, and this occurs when the A particles hits the nucleus directly. This indicated that the nucleus was very small and contained nearly all the mass of the atom .

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13
Q

What was the Rutherford-Bohr model ?

A

Bohr suggested that the electrons orbited the nucleus in circular paths.

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14
Q

What are protons and neutrons collectively called ?

A

nucleons

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15
Q

What is the atomic number ?

A

the number of protons (symbol Z)

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16
Q

What is the mass number?

A

The number of protons and neutrons

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17
Q

What are isotopes ?

A

Atoms with the same number of protons but a different number of neutrons are called isotopes .

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18
Q

Who and when discovered radiation ?

A

Henry Becquerel (1896)

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19
Q

Why are heavy element such as uranium radioactive?

A

The large number of protons and neutrons can make the nucleus unstable and cause their nuclei to spontaneously emit radiation.

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20
Q

When does an atom become an ion ?

A

When it gains or loses electrons

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21
Q

How an ionising radiation be harmful ?

A

removes electrons from atoms in it’s path

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22
Q

Give two forms of ionising radiation

A

ultraviolet and X-rays.

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23
Q

What is an alpha nucleus made up of ?

A

it is a helium nucleus with two protons and two electrons.

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24
Q

What is the charge of radioactive particles ?

A

alpha - positively charged (deflected by magnetic field)
beta - negatively charged (deflected by magnetic field)
gamma - consists of no charged particles

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25
Q

What is the penetrating powers of all three types of radiation like ?

A

alpha - poor powers of penetration (only few cm of air)
beta - good penetration (stopped by 5mm of Al)
gamma - Best penetration (greatly reduced but not stopped by thick block of lead)

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26
Q

What is the ionising power of each radioactive particle ?

A

alpha - Strongest ionising power
beta - power between alpha and gamma
gamma - weakest ionising power

27
Q

Which of the radioactive particles can penetrate skin ?

A

alpha - cannot pass through the skin
beta - can penetrate skin, will cause damage to cells
gamma - can penetrate skin, will cause damage to cells

28
Q

describe the structure of gamma radiation

A

consists of high-energy waves

29
Q

does gamma radiation have any mass ?

A

No because it is an electromagnetic wave

30
Q

where does the most background activity come from ?

A

natural sources such as cosmic rays, rocks and soil. These contain radon gas.

31
Q

Give some examples of how human activity affects the radiation levels on earth

A
  • medical X-rays
  • radioactive waste from nuclear power plants
  • fallout from nuclear weapons testing.
32
Q

What is background radiation ?

A

Background radiation is a measure of the level of ionizing radiation present in the environment at a particular location which is not due to deliberate introduction of radiation sources.

33
Q

How can we protect ourselves from radiation ?

A
  • wear protective clothing
  • keep source as far away as possible using tongs
  • limiting exposure time
  • keeping radioactive materials in lead-lined containers
34
Q

What’s the formula for alpha radiation ?

A

4
H
2

35
Q

What’s the formula for beta radiation ?

A

0
e
-1

36
Q

In what manner does Radioactive decay occur ?

A

random and spontaneous

37
Q

what is the half-life of a radioactive source ?

A

the time taken for its activity to fall to half of its original value.

38
Q

What is the unit for radioactivity ?

A

Becquerel (Bq)

39
Q

What does 1 Bq equal ?

A

1 disintegration per second

40
Q

What are the uses for radiation in medicine ?

A
  • gamma radiation from the isotope cobalt-60 can be used to treat tumors
  • Iodine-131 is used in investigations of the thyroid gland
  • surgical instruments can be sterilised by gamma radiation
41
Q

How is radiation used in agriculture ?

A
  • Gamma radiation kills bacteria on fresh fruit.
42
Q

How is radiation used in industry ?

A

-Beta radiation can be used to monitor the thickness of a sheet of aluminium.

43
Q

What is a use of radioactive material in the home ?

A

In an ionisation smoke detector a source of alpha radiation is placed in he detector.

44
Q

What is the most common type of radioactive detector ?

A

Geiger-Muller tube (GM tube), connected to a counter.

45
Q

How does a GM tube work ?

A

when radiation enters the gm tube it causes some of the argon gas inside to ionise and give an electrical discharge. This is detected by the counter and recorded.

46
Q

How do you measure the background count rate with a GM tube ?

A
  • Remove known sources of radiation from the lab.
  • set counter to 0
  • Switch on counter and start stopwatch
  • after 30 mins read counter and divide value by 30
  • this will give you counts per minute
  • normal value for counts per minute is around 15
47
Q

How do you measure the approximate range of alpha radiation ?

A
  • get a GM tube and connect to a counter
  • Hold source in front of GM tube and slowly move it backwards
  • at around 3cm the counts should fall dramatically
  • place a thin piece of paper in front of the GM tube.
  • The reading should now be the same as the background count
48
Q

How do you measure the approximate range of beta radiation ?

A
  • Place 1mm of Al in front of the GM tube
  • Bring the beta source up to the AL
  • The reading should be significantly higher than the background rate.
  • Repeat until the thickness of the Al is 5mm. At this stage the reading should be significantly reduced.
49
Q

How do you test the approximate range of gamma radiation ?

A
  • repeat beta test with gamma
  • should be no reduction
  • even when repeated with lead most school gamma sources will still penetrate it.
50
Q

What nuclear process involves the splitting of one heavy nucleus into two lighter nuclei ?

A

Fission

51
Q

When does fission occur ?

A

When the sample is struck by a slow neutron

52
Q

How many more times the energy does fission produce of burning coal ?

A

49,000,000 times more

53
Q

How is fission energy harvested ?

A

The heat energy produced is used to heat water into steam which then drives a turbine to generate electricity.

54
Q

Give some arguments in favour of nuclear energy

A
  • produce vast amounts of energy
  • produces very little carbon dioxide
  • it is available at all times
  • high density source of energy (1kg = 20000kf of coal)
  • provides employment opportunities for people
55
Q

Give some arguments against nuclear energy

A
  • disposal of waste can be dangerous and expensive

- past accident have made people scared (Hiroshima, Chernobyl ….)

56
Q

What is the definition of Fusion ?

A

When energy is emitted when two light nuclei are fused together.

57
Q

Why does Fusion happen in the stars ?

A

The temperature of the sun is about 15,000,000*C so all the atoms are stripped of the orbiting electrons and they move at very high speed. They form plasma. If the nuclei are moving fast enough they can fuse together.

58
Q

What are the two most common isotopes that fusion occurs with ?

A

Deuterium (hydrogen 2) and tritium (hydrogen 3)

59
Q

What is the equation regarding fusion ?

A

2 3 4 1
H + H ——–> He + n + energy
1 1 2 0

60
Q

What is the world record for fusion ?

A

16MW of power form 24MW input

61
Q

What is the main difficulty with fusion ?

A

Keeping the plasma at a high enough temperature for a long enough tme.

62
Q

Where can you find deuterium and tritium ?

A

In sea water

63
Q

What gas does fusion emit?

A

Helium (doesn’t really affect the environment)

64
Q

How many more time the energy does fusion emit over fission ?

A

4 times

Physics (18 decks)

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