25 - Radioactivity Flashcards
What is alpha radiation?
Positively charged particles.
2e
(Helium nucleus)
What is beta radiation?
Fast moving electrons or positrons.
+e or -e
What is gamma radiation?
High energy photons with wavelength < 10⁻¹³m
No charge
How can we distinguish between types of radiation using an electric field?
- Alpha particles are deflected a small amount in one direction due to their larger mass
- Beta particles are deflected the most on both directions as they can be either positive or negative
- Gamma photons are not deflected and pass straight through
Compare the range of the three types of radiation.
- Alpha - short range as large and heavy
- Beta - longer range about a metre
- Gamma -very long range,
How can you stop the three different types of radiation?
Alpha - piece of paper
Beta - thin sheet of aluminium
Gamma - a few centimetres of lead
Compare the ionisation of the three types of radiation.
Alpha - extremely ionising
Beta - less ionising
Gamma - even less ionising
Describe alpha decay.
Nucleus emits an alpha particle.
Nucleon number decreases by 4 (2n, 2p)
Proton number decreases by 2 (2p)
Energy also released.
Why do nuclei go through beta minus decay?
If they have too many neutrons.
What decays in beta minus decay?
A neutron into a proton.
What decays in beta plus decay?
A proton into a neutron.
Why do nuclei go through beta plus decay?>
Because they have too many protons.
What is emitted in gamma decay?
A gamma photon.
When does gamma decay occur?
When a nucleus has extra energy left over after beta or alpha decay.
What must balance in a decay equation?
The nucleon and proton numbers.
Nuclear decay is _ and _.
Random
Spontaneous
Why is nuclear decay random?
We cannot predict when a nucleus will decay.
Why is nuclear decay spontaneous?
It is not affected by external factors.
What is the half life of an isotope?
The average time that it takes for half of a radioactive sample to decay.
What is the activity of a source?
The rate at which nuclei decay.
Decays per unit time
How do we measure activity?
Using a GM tube and a counter.
GM = Geiger Muller
What is the relationship between number of nuclei and activity?
N ∝ A
N ∝ N/t
What is the decay constant?
The proportionality coefficient in the N ∝ A equation.
N = λA
What is the unit for activity?
Bequerels
Bq
What is the unit for the decay constant?
Hz
s-1
Define the decay constant.
The probability of the decay of a nucleus per unit time.
