Physics - Recall for Chapter 25: Radioactivity
OCR A-Level Physics 2022
Flashcards
Ionising radiation
What is meant by ionising radiation?
Radiation with sufficient energy to ionise atoms.
Alpha radiation
Beta radiation
Gamma radiation
What is gamma radiation?
High frequency electromagnetic waves emitted from a nucleus.
Comparing the radiation types
What is the order of types of ionising radiation from most mass to least mass?
- Alpha
- Beta-minus and beta-plus
- Gamma
What type of nuclear radiation is not deflected by electric and magnetic fields?
Gamma.
What type of nuclear radiation is deflected the most by electric and magnetic fields?
Beta radiation.
Why is beta radiation the most deflected by electric and magnetic fields?
It has a very small mass.
Measuring count rate
When measuring the count rate of a radioactive source, what must be considered?
The background count rate.
How do you find the corrected count rate for a radioactive source from the measured count rate?
Dangers and safety
What procedure is routinely used to minimise the dose when handling radioactive sources in the lab?
Use tongs and hold it far away from your body.
What are the three key steps for reducing radiation dose?
- Maximise distance
- Minimise exposure
- Use shielding
Parent and daughter nuclei
What do we call the nucleus before it undergoes radioactive decay?
Parent nucleus.
What do we call the nucleus after it undergoes radioactive decay?
Daughter nucleus.
Alpha emission
Which type of nuclei are most likely to emit alpha particles?
Large, unstable nuclei.
What is normally true about the proton number of a nucleus likely to emit an alpha particle?
It has a proton number greater than 82.
What happens to the nucleon number and proton number when a nucleus emits an alpha particle?
- Nucleon number: -4
- Proton number: -2
Beta emission
What type of nuclei are most likely to emit a beta minus particle?
Unstable nuclei with too many neutrons.
What type of nuclei are most likely to emit a beta plus particle?
Unstable nuclei with too many protons.
What happens to the nucleon number and proton number when a nucleus emits a beta-minus particle?
- Nucleon number: Same
- Proton number: +1
What happens to the nucleon number and proton number when a nucleus emits a beta-plus particle?
- Nucleon number: Same
- Proton number: -1
What else is emitted during either beta-minus or beta-plus decay?
An (anti)electron neutrino.
Gamma emission
What type of nuclei are most likely to emit gamma radiation?
Nuclei with too much energy.
What happens to the nucleon number and proton number when a nucleus emits a gamma photon?
- Nucleon number: Same
- Proton number: Same
Properties of radioactive decay
Why is radioactive decay said to be random?
It is not possible to predict which nucleus will decay.
Why is radioactive decay said to be spontaneous?
It is not affected by any external factors.
Activity
What is the activity of a radioactive substance?
The rate at which nuclei decay.
Half life and decay pattern
What is half life?
The average time taken for the activity of a sample to halve.
Why does the activity of a radioactive substance decrease with time?
Activity is directly proportional to the number of undecayed nuclei.
What pattern does the activity and the number of undecayed nuclei in a substance follow over time?
Exponential decay.
The decay constant
What is the decay constant of a radioactive substance?
The probability of a nucleus decaying per unit time.
What are some typical units of the decay constant $\lambda$?
What is the relationship between the decay constant $\lambda$ and half life $t _ {1/2}$?
Modelling decay
How can radioactive decay be modelled with iteration?
Repeatedly calculate the number of nuclei that decay in a very short amount of time and subtract this.
Carbon and radioactive dating
What happens to the ratio of carbon-14 to carbon-12 in an organism after it dies?
The carbon-14 decreases.
Why does the carbon-14 in an organism decrease after it dies?
Because the carbon-14 in the atmosphere can’t get into it.
What is the basic principle of carbon dating?
Comparing the ratio of carbon-14 to carbon-12 in an organic sample to the ratio in a similar living organism.
Since rocks are too old to be dated with carbon-14, what element is used instead?
Rubidium-87.