Physics - Recall for Chapter 25; Radioactivity
Flashcards
What is meant by ionising radiation?
Radiation with sufficient energy to ionise atoms.
What does it mean to ionise an atom?
Remove an electron.
What is an alpha particle?
2 protons and 2 neutrons.
What is the charge of an alpha particle?
How ionising is alpha radiation?
Strongly ionising.
What is the range of alpha radiation in air?
Around 5cm.
What is alpha radiation typically absorbed by?
Paper.
What is a beta-minus particle?
A fast moving electron.
What is a beta-plus particle?
A fast moving positron.
What is the charge of a beta-minus particle?
How ionising is beta-minus radiation?
Moderately ionising.
What is the range of beta-minus radiation in air?
Around 1m.
What is beta-minus radiation typically absorbed by?
1-3mm of aluminium.
What is gamma radiation?
High frequency electromagnetic waves emitted from a nucleus.
How heavy is a gamma particle?
It has no mass.
What is the charge of a gamma ray?
It has no charge.
What is the typical speed of gamma radiation?
The speed of light.
How ionising is gamma radiation?
Weakly ionising.
What is gamma radiation typically absorbed by?
A few centimeters of lead.
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.
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?
Why is ionising radiation dangerous?
It can damage living cells and DNA.
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
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.
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
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.
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
What are two properties of natural radioactivity?
- Random
- Spontaneous
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.
What is the activity of a radioactive substance?
The rate at which nuclei decay.
What units are used to measure radioactive activity?
Becquerels.
What is 1 becquerel equivalent to?
One decay per second.
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.
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 $t _ {1/2}$?
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.
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.