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OCR A-Level Physics > Radioactivity > Flashcards

Radioactivity Flashcards

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1
Q

What are the forces the nucleus undergoes?

A

Strong nuclear force (holding it together), electrostatic force pushing the protons apart. Gravitational force (very weak).

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2
Q

What happens if a nucleus is unstable?

A

It will break down to become more stable.

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3
Q

What can cause instability of a nucleus?

A

Too many neutrons, too many nucleons, too few neutrons, too much energy.

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4
Q

How does a nucleus decay?

A

By releasing energy and/or particles until it reaches a stable form. This is radioactive decay.

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5
Q

How is radioactive decay described?

A

Spontaneous and random. Cannot be predicted.

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6
Q

What are the four types of radiation?

A

Alpha, Beta-mins, Beta-plus and Gamma.

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7
Q

What is the ionising power of alpha?

A

Strong

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8
Q

What is the speed of alpha?

A

Slow

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9
Q

What is the penetrating power of alpha?

A

Absorbed by paper or a few cm of air.

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10
Q

Is alpha affected by a magnetic field?

A

Yes

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11
Q

What is the ionising power of Beta-minus?

A

Weak

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12
Q

What is the speed of Beta-minus?

A

Fast

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13
Q

What is the penetrating power of Beta-mins?

A

Absorbed by 3mm of aluminium.

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14
Q

Is Beta-minus affected by a magnetic field?

A

Yes

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15
Q

What is the ionising power of Gamma?

A

Very weak

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16
Q

What is the speed of Gamma?

A

Speed of light

17
Q

What is the penetrating power of Gamma?

A

Absorbed by many cm of lead, or several m of concrete.

18
Q

Is Gamma affected by a magnetic field?

A

No

19
Q

Why does Beta-plus have virtually zero range?

A

It gets annihilated by electron

20
Q

How do you investigate the penetration of different kinds of radiation?

A
  1. Radioactive source and Geiger-Muller tube placed opposite each other.
  2. Remove source and measure the background count. Measure over long enough time interval and 3 times to find mean to get an accurate and precise reading.
  3. Divide count by time interval to get background count rate. Subtract from all results.
  4. Replace source and insert different materials between source and tube. Record count rate for each material 3 times and find mean.
  5. If the count rate remains about the same then radiation can penetrate material. If count rate drops by large amount then radiation is being absorbed and blocked. If count rate drops to zero then radiation is being completely absorbed.
21
Q

What is conserved in nuclear decay equations?

A

Charge, Energy and Momentum

22
Q

What is the difference in mass called after a nuclear decay?

A

Mass Defect

23
Q

Where does the energy go?

A

Energy released when the nucleons bond together to form the alpha particle. (Accounts for missing mass)

24
Q

When does alpha emission occur?

A

When the nuclei of atoms are very heavy such as uranium and radium.
Nuclei of these atoms are too massive to be stable.

25
Q

When does Beta-minus emission occur?

A

When isotopes are neutron rich. (More neutrons than protons in nucleus).
One of the neutrons in the nucleus decays into a proton and ejects a Beta-minus particle and an anti-neutrino.

26
Q

What happens with Beta-plus emission?

A

A proton gets changed into a neutron, releasing a positron and a neutrino.

27
Q

When does Gamma emission occur?

A

When the nucleus has excess energy, the nucleus is excited. Energy is lost by emitting a gamma ray.

28
Q

What is the decay constant?

A

Activity / number of nucleons left in the sample.

29
Q

What is the activity?

A

The number of nuclei that decay each second.

30
Q

What is half life?

A

The average time it takes for the number of undecayed nuclei to halve.

31
Q

How does carbon dating work?

A

1) Living plants take in carbon dioxide from atmosphere as part of photosynthesis, including radioactive isotope carbon-14. All living things contain the same percentage of carbon-14.
2) When they die, the activity of carob-14 starts to fall, with a half-life of around 5730 years.
3) Archaeological finds made from once-living material can be tested to find the current amount of carob-14 in them. This can be used to calculate how long the material has been dead for.

OCR A-Level Physics (33 decks)

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