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Physics - Lizzie > Radioactivity > Flashcards

Radioactivity Flashcards

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1
Q

What is the atomic number?

A

The number of protons in the nucleus of an atom.

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2
Q

What is the mass number?

A

The total number of protons and neutrons in the nucleus of an atom.

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3
Q

What are isotopes?

A

Atoms with the same number of protons (same atomic number) but a different number of neutrons (different mass number).

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4
Q

What tends to happen to unstable isotopes?

A

They are radioactive with unstable nuclei, and so emit ionising radiations (alpha particles, beta particles, and gamma rays) randomly and spontaneously.

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5
Q

What are the sources of background radiation?

A
  • Artificial: nuclear explosions; nuclear waste; nuclear medicine.
  • Natural: outer space - cosmic rays; Earth - air, food, building materials, rocks; living things.
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6
Q

What is radioactivity measured in?

A

becquerels (Bq)

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7
Q

What is the structure and charge of alpha particles?

A

Made up of 2 protons and 2 neutrons with a charge of 2+.

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8
Q

How penetrating are alpha particles?

A

Not very penetrating - stopped by mm of paper.

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9
Q

How ionising are alpha particles?

A

Heavily ionising - produce lots of ions and can do lots of damage.

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10
Q

What happens during alpha decay?

A

The atomic number will decreas by two and the mass number will decrease by 4.

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11
Q

What is the structure and charge of beta particles?

A

Made up of an electron with a charge of 1-.

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12
Q

How penetrating are beta particles?

A

Moderately - stopped by a minimum of mm of aluminium.

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13
Q

How ionising are beta particles?

A

Less ionising than alpha but still moderately ionising.

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14
Q

What happens during beta decay?

A

The atomic number increases by one and the mass number stays the same.

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15
Q

What is the structure and of gamma rays?

A

Electromagnetic waves which do not have a charge.

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16
Q

How penetrating are gamma rays?

A

Very - cannot be stopped but can be reduced by metres of concrete/lead.

17
Q

How ionising are gamma rays?

A

Not very ionising - tend to pass through things rather than actually collide and interact with atoms.

18
Q

What is the half-life?

A
  • The time it takes for the number of undecayed nuclei to halve.
  • The time it takes for the activity of a radiocatice substance to halve (the number of decays per second)
19
Q

What are the dangers of ionising radiations?

A
  • Mutations in living organisms.
  • Damage to cells and tissue.
20
Q

How can radioactivity be used in medical tracers?

A
  • A beta/gamma emitting source is injected (or swallowed) into a patient.
  • The radiation penetrates the body cells and will show externally - anywhere that radiation cannot get through shows up as somewhere which is not functioning.
  • The radioactive source should have a short half-life so that it does not interact with the body cells and cause harm.
21
Q

How can radioactivity be used in industrial tracers?

A
  • To detect a leak in a pipe, a substance which emits gamma rays is injected into a pipe.
  • In the areas of the pipe where there is a leak, the gamma rays will have a higher reading.
  • Something with a relatively long half-life should be used so that the gamma rays can be detected all the way through the pipe, but they do not cause any damage.
22
Q

How does carbon-dating work?

A

By comparing the ratio of C12 to C14 in an artefact to the ratio in something alive now, you can estimate the age of a substance.

23
Q

What is it called when a neutron collides with the nucleus of uranium-235 and what is produced when this happens?

A
  • (Nuclear) fission.
  • Two daughter nuclei are produced as well as a small number of neutrons.
24
Q

How can a neutron colling with uranium-235 lead to a chain reaction?

A

The nucleus of the uranium splits and releases neutrons, which can be hit/absorbed by different uranium nuclei and produce a chain reaction.

25
Q

What was Rutherford’s nuclear model of the atom?

A
  • The atom contained a small, dense, positively charged nucleus which contained the vast majority of the mass of the atom.
  • There were electrons orbiting the nucleus (like planets orbiting the sun).
  • Almost all of the atom is empty space (the atom’s radius was much larger than the radius of the nucleus).
26
Q

What were the results of Geiger and Marsden’s experiment with gold foil and alpha particles?

A
  • Alpha particles were fired from at a very thing piece of gold leaf.
  • A detector consisting of fluorescent material, which emitted a flash of light whenever it was hit by an alpha particles, was moved around and showed what path the alpha particles after hitting the gold leaf.
  • Almost all alpha particles went straight through, but a few deflected at a whole range of angles (some very big) and some were deflected straight back.
27
Q

What form does the energy released when a neutron collides with uranium-235 take?

A

Kinetic energy of fission products (i.e. daughter nuclei/neutrons).

28
Q

How did Rutherford’s observations lead to the current model of the atom?

A

The ‘Plum Pudding model’ (a positive sphere contained negative electrons dotted inside) would not explain how the atom would exert enough force on an alpha particle to deflect it back at large angles, because the model says that the mass of the atom is evenly distributed and has a l_ow density_. Rutherofrd came up with his new idea of the atom:

  • small nucleus because only a few particles were deflected back (therefore mostly empty space)
  • most of the mass must be concentrated at the centre
  • centre must be positive so that it can expel the alpha particles
29
Q

What factors affect the deflection of alpha particles by a nucleus?

A
  • The faster an alpha particle is travelling, the less it will be deflected by the nucleus.
  • The more positively charged a nucleus is (higher atomic number), the more an alpha particle will be deflected.
30
Q

What role do the control rods play when the fission process is used to create electricity?

A

Control rods (made from boron and cadmium) can be lowered into the reactor vessel to absorb neutrons and control the speed of the reaction - the more neutrons absorbed, the slower the reaction.

31
Q

What role does the pressurised water play when the fission process is used to create electricity?

A
  • Acts as a coolant and conducts heat from the rods.
  • Acts as a moderator to slow down the neutrons and therefore increase the likelihood of collisions and nuclear fission occuring.
32
Q

Useful Energy Transfers in a Nuclear Power Station

  1. heat energy released by the reactor
  2. energy in water/steam
  3. energy in turbine
  4. energy in generator
  5. energy in wires
A
  1. heat energy released by the reactor
  2. kinetic/thermal/heat energy in water/steam
  3. kinetic energy in turbine
  4. kinetic/electrical energy in generator
  5. electrical energy in wires
33
Q

Iodine-131 is a radioactive isotope that emits beta particles. It is used to treat thyroid cancer. The isotope is allowed to enter the tumour. Explain why it is suitable for this treatment.

A
  • Beta particles are (moderately) ionising.
  • Beta has a short range.
  • The Iodine-131 has a short half-life.
  • Iodine is absorbed (easily by the thyroid) and so:
    • damage to healthy cells is reduced
    • the radiation does not penetrate out of the body
    • only tumour cells are killed
34
Q

Describe nuclear fission and how the chain reaction is controlled.

A
  • A nucleus is hit by a neutron (and absorbs it).
  • The nucleus splits into two daughter nuclei.
  • Extra neutrons are released.
  • Kinetic energy is released.
  • Released neutrons hit further nuclei (and split them).
  • Moderator slows down the neutrons (and makes it easier for them to be absorbed).
  • The control rods absorb extra neutrons.
  • The control rods help to prevent a “runaway” chain reaction.
35
Q

Why are some isotopes described as stable?

A

They do not emit any ionising radiations (alpha, beta or gamma rays).

Physics - Lizzie (19 decks)

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