Radioactivity Flashcards
What is ionising radiation
Beta, gamma and alpha radiation are all ionising because they can remove electrons from atoms leaving positive ions
How to find the absorption of radiation by different materials
Use a counter to measure the background radiation. Then place the radiation source in a sealed container and place the material a fixed distance away from the radiation source. Place the GM tube in front of the material a fixed distance away from the source. Place counter in front of GM Tube. Minus background radiation from result.
What is the absorption of Alpha radiation
Strong Ionisation due to large mass and charge but short range. Stopped by a sheet of paper
What is the absorption of Beta radiation
Less ionising due to smaller mass and charge than alpha particles but can penetrate farther. Stopped by a sheet of aluminium
What is the absorption of Gamma radiation
Least ionising due to having no charge but has high penetrating power, stopped by lead.
What happens during alpha decay
A parent nucleus emits an alpha particle removing 2 protons and 2 neutrons from itself, decaying into the daughter nucleus which is a new element. Energy is released
What happens during Beta decay
Beta minus radiation is emitted due too many neutrons causing instability. Weak nuclear force causes a neutron to decay into a proton, emitting an electron and an electron anti neutrino. Proton number increases thus daughter nucleus is a different element. Beta plus radiation is emitted due to excess protons causing instability. Proton decays into a neutron and a positron and electron neutrino is emitted. Daughter nucleus has one less proton than parent, therefore it is a new element.
What happens during gamma decay
Gamma photons are emitted if a nucleus has excess energy after alpha or beta emission. Nucleus remains the same.
What are the patterns for stability
The stability band shows the stable nuclei. Nuclei to the right of the band have excess protons and will undergo beta plus decay. Nuclei to the left have excess neutrons and undergo beta minus decay. Nuclei with more than 82 protons are likely to undergo alpha decay. Ratio between neutrons and protons increase as protons increase.
Why is radioactive decay a random event
Cannot predict when or which nucleus will decay. Each nucleus has the same chance of decaying per unit time
Why radioactive decay a spontaneous event
It is not affected by any external factors
What is the half life of an isotope
Average time taken for half of active nuclei to decay
What is activity
Number of alpha, beta or gamma particles are emitted from the source per unit time. Measured in Bq (Becquerel). Depends on number of un decayed nuclei present in source and half life of isotope. Given by the equation activity = decay constant * Number of nuclei
What is the exponential decay equation
Number of nuclei = Initial number of nuclei * e^-decay constant * time
Define the decay constant
Probability an individual nucleus will decay per unit time
