Ch25: Radioactivity Flashcards
What does ionising mean?
Something ionising can ionise atoms, removing some of their electrons and leaving a positive ion
What is alpha radiation made up of? What is its charge?
A helium nucleus, 2 protons, 2 neutrons. Charge of +2e
What is beta radiation? What is its charge?
Fast moving electrons or positrons. Beta minus has charge -e. Beta plus has charge +e
What is gamma radiation?
HIgh energy photons with wavelengths less than 10^-13m. No charge.
What is needed to completely absorb alpha particles?
Thin sheet of paper
What is needed to completely stop most beta particles?
1-3mm of aluminium
What is needed to completely absorb gamma ?
few centimeters of lead
What is the typical speed of alpha radiation?
10^6
What is the typical speed of beta radiation?
10^8
What is the typical speed of gamma radiation?
Speed of light.
Briefly describe alpha decay.
A parent nucleus decays into a daughter nucleus, losing 2 protons and 2 neutrons as an alpha particle.
What is released during alpha decay?
Energy, an alpha particle(helium nucleus), and daughter nuclei.
What causes beta decay?
the Weak nuclear force
Briefly describe beta minus decay.
In an unstable radioactive isotope, a neutron decays into a proton, and an electron is emitted as well as an electron anti-neutrino.
Briefly describe beta-plus decay.
In an unstable radioactive isotope, a proton decays into a neutron, emitting a positron and an electron neutrino.
When does gamma decay occur? What does it change?
Occurs when surplus energy is left after beta or alpha emission. Only releases energy, does not change nucleon make up.
Why is radioactive decay considered spontaneous?
- It cannot be predicted when a nucleus will decay.
- Each nucleus in a sample has the same chance of decaying per unit time.
Why is radioactive decay considered spontaneous?
Decay of the nucleus is not affected by:
- Presence of other nuclei in the sample
- External factors e.g pressure
What is the half life of a sample of an isotope?
The average time taken for half the number of active nuclei to decay.
What is the activity of a radioactive source?
The rate at which nuclei decay or disintergrate.
What is activity measured in?
Decays per second, Becquerels Bq
What is decay constant?
probability of decay of an individual nucleus per unit time.
How are half life( t1/2) and decay constant (λ) related?
λ x t1/2 = ln2
What are some limitations of carbon dating?
- Assumes ratio of carbon-14 to carbon-12 stays the same over time; this could have been affected by various events.
- Not accurate for very old or small things where activity is close to that of the background rate.
