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Physics - Unit Two > Atomic Structure and Radioactivity > Flashcards

Atomic Structure and Radioactivity Flashcards

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1
Q

Who first came up with the atom and when?

A

Democritus in the 5th Century BCE. He said that all matter was made up of different lumps.

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2
Q

Who agreed with Democritus and when? What did he conjecture?

A

John Dalton agreed in 1804 that matter is made up of tiny spheres but argued that each element would have its own atom.

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3
Q

Who developed the plum pudding model? What was it?

A

J J Thomson. His plum pudding model showed a positively charged sphere with negative electrons stuck in it like plums in a plum pudding.

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4
Q

What did Rutherford and Marsden do in 1909?

A

They fired a beam of alpha particles at thin gold foil. They kept a circular detector screen around the gold foil and alpha beam source to detect the reflection of alpha particles.

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5
Q

What did Rutherford and Marsden expect to see from their experiment?

A

Very little deflection.

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6
Q

What happened when the alpha beam was fired at the gold foil?

A

Most of the particles went straight through apart from the odd one that shot back at them.

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7
Q

What did Rutherford conclude from their experiment?

A
  • Most of the atom must be empty space as alpha particles passed right through the foil.
  • The nucleus must be positively charge to deflect the positively charged alpha particles so much.
  • The nucleus must be very small as very few alpha particles were deflected at all.
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8
Q

What three particles are found in an atom? What are their charges?

A
  • Electrons (-)
  • Protons (+)
  • Neutrons (none)
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9
Q

What does the nucleus of an atom contain?

A

Neutrons and protons which gives it its positive charge.

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10
Q

Where are the electrons found in an atom?

A

Orbiting the nucleus in energy shells.

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11
Q

Hay are the relative masses of the three particles in an atom?

A

Proton / 1

Neutron - 1

Electron - Negligible

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12
Q

Why do atoms have no overall charge?

A

Because they have the same amount of protons and electrons which cancel each others’ charges out.

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13
Q

What is an ion? The

A

A charged atom.

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14
Q

What is atomic number?

A

The number of protons in the nucleus of an atom

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15
Q

What is the mass number?

A

The number of protons plus the number of neutrons in the nucleus of an atom.

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16
Q

What are isotopes?

A

Forms of the same elements with different numbers of neutrons in their nuclei.

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17
Q

What are radioactive substances?

A

Substances that give out radiation from the nuclei of their atoms at all times.

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18
Q

What is the purpose of radioactive decay?

A

For unstable isotopes to decay into stable isotopes.

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19
Q

What are the three types of radioactive decay?

A

Alpha, beta and gamma.

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20
Q

What is an alpha particle made of?

A

Two neutrons and two protons - the same as a helium nucleus.

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21
Q

What happens when an atom undergoes alpha decay?

A

Two neutrons and two protons are lost from its nucleus.

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22
Q

How penetrative are alpha particles?

A

Not very. They are stopped quickly because they are big, heavy and slow.

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23
Q

How ionising are alpha particles and why?

A

They are strongly ionising beside of their size. They knock into a lot of atoms and knock electrons off them which created a lot of ions.

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24
Q

What is a beta particle?

A

An electron.

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25
Q

What happens when an atom undergoes beta decay?

A

A neutron turns into a proton and an electron is released.

26
Q

What are five qualities of a beta particle?

A
  • Moderately fast
  • Quite small
  • Moderately penetrative
  • Long range in air
  • Moderately ionising
27
Q

What are gamma rays?

A

Very short wave RM waves with no mass or charge.

28
Q

What are three qualities of gamma rays?

A
  • Very penetrative
  • Pass straight through air
  • Weakly ionising as they usually pass atoms but are extremely destructive when they do hit something
29
Q

How are alpha particles shown in equations?

A

Either as He or α with an atomic number of 2 and a mass number of 4.

30
Q

How are beta particles shown in equations?

A

Either as e or β with a mass number of 0 and an atomic number of -1.

31
Q

How are alpha and beta particles affected by magnetic fields?

A
  • They re deflected in opposite directions

* Alpha particles are deflected less than beta particles because of their greater masses despite feeling a larger force

32
Q

What is half-life?

A

The average time it takes for the number of nuclei of a radioactive isotope in a sample to halve.

33
Q

What does a short half life mean?

A

The activity falls quickly because lots of the nuclei decay quickly.

34
Q

What does a long half-life mean?

A

The activity falls slowly because most of the nuclei don’t decay for a long time.

35
Q

What is a Geiger counter?

A

A particle detector that measures activity.

36
Q

How is half life found on a graph?

A

By finding the time interval in the x axis corresponding to the halving of the activity on the y axis.

37
Q

What is a radiation dose?

A

The amount of energy absorbed by your body from radioactive radiation.

38
Q

What two factors affect radiation dose?

A
  • The type of radiation you’re exposed to

* The amount of radiation you are exposed to

39
Q

What are three sources of background radiation?

A
  • Radioactivity of naturally occurring unstable isotopes in air, food, rocks and building materials
  • Cosmic rays
  • Nuclear waste and other man made sources
40
Q

What two locational factors affect the amount of radiation you are exposed to?

A
  • Certain underground rocks give off more radiation at the surface
  • People at high altitudes are exposed to more cosmic rays
41
Q

What four occupational factors can lead to you being exposed to more radiation?

A
  • Nuclear industry workers are exposed to 10% the normal amount of radiation
  • Radiographers are exposed to lots of radiation
  • People who work at high altitudes are exposed to more cosmic waves
  • Underground work increases radiation dose
42
Q

What can the effects of low doses of radiation be on cells?

A

They can cause minor damage without killing cells which can give rise to mutant cells which divide uncontrollably and form a tumour.

43
Q

What can the effects of high doses of radiation be on cells?

A

The cells can die leading to radiation sickness.

44
Q

What forms of radiation are most dangerous outside the body?

A

Beta and Anna because they are very penetrative.

45
Q

What form of radiation are most dangerous inside the body?

A

Alpha because it is the most ionising.

46
Q

What precautions can be taken when working with radioactive materials?

A
  • Only use them for short amounts of time
  • Never allow skin to come into contact with the source - use tongs
  • Hold the source at arms length to decrease the amount of radiation that hits you
  • Keep the source pointing away from you and avoid looking directly at it
47
Q

What element absorbs all three types of radiation?

A

Lead

48
Q

What are three uses of lead to protect you from radiation?

A
  • Radioactive sources are kept in lead boxes
  • Medical professionals wear lead aprons and stand behind lead screens
  • During a medical procedure, the patient is covered with lead anywhere the radiation does not need to act
49
Q

What are four uses of radioactivity?

A
  • Smoke detectors
  • Medical tracers
  • Radiotherapy
  • Sterilisation
50
Q

What type of radiation do smoke detectors use?

A

Alpha

51
Q

How do smoke detectors work?

A

A weak source of alpha radiation is placed in the detector close to two electrodes. The alpha particles cause ionisation of molecules in the air which frees electrons allowing a current to flow between the two electrodes. If there is smoke, the smoke will absorb the radiation and the current will be broken, causing an alarm to sound.

52
Q

Why can’t beta and gamma sources be used in smoke detectors?

A

Their range is too long so try pose a threat to homeowners,

53
Q

Why should the alpha source in a smoke detector have a long half-life?

A

So that the source doesn’t need to be replaced too often.

54
Q

What are medical tracers?

A

Certain radioactive isotopes that can be injected into people and then followed around the body using an external display.

55
Q

What type of radiation is used for medical tracers?

A

Gamma or beta so that the radiation passes out of the body.

56
Q

Why shouldn’t alpha radiation be used for medical tracers?

A

Because they are too ionising

57
Q

What is radiotherapy?

A

The treatment of cancerous cells using ionising radiation.

58
Q

What type of radiation is used for radiotherapy?

A

Gamma

59
Q

Why does the radiation in radiotherapy need to be directed carefully?

A

So that only the target cells are killed.

60
Q

What type of radiation is used for sterilisation?

A

Gamma rays which kill all microbes.

61
Q

What is an advantage of using radiation over boiling for sterilisation?

A

Radiation doesn’t involve high temperatures so objects like apples and plastic instruments can be sterilised without being harmed.

62
Q

What qualities should the isotope used for sterilisation have?

A
  • Should be very strong

* Should have a good half life

Physics - Unit Two (6 decks)

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