25, Radioactivity Flashcards
What is alpha radiation?
A helium nucleus, usually from atoms with 82 protons or higher.
What is beta radiation?
An electron or positron caused by the weak force when there is too many neutrons or protons.
What is gamma radiation?
High energy gamma photons emitted if there is surplus energy following a decay.
How can a magnetic or electric field be used to separate the different forms of radiation?
Gamma is unaffected by both of these fields, however alpha and beta are deflected slightly with beta being deflected much more due to its higher mass (despite alpha moving slower and having twice the charge).
What experiment could you do to investigate absorption of radiation?
Place a source facing towards a Geiger counter, first take several time samples to find the background radiation then place varying amounts of the absorbent material between the tube and source, again measuring count rate over a set time period.
What does it usually take to absorb most alpha radiation?
A few cm of air or a thin sheet of paper.
What does it usually take to absorb most beta radiation?
1-3mm of aluminium.
What does it usually take to absorb most gamma radiation?
A few cm of lead.
What does the term daughter nucleus refer to?
The nucleus left from the decay of the parent nucleus.
Why is alpha radiation most ionising?
Because it moves slower and therefore takes longer to react (despite the fact that all radiation has a similar energy level).
How can a decay chain be represented graphically?
Using an A-Z plot and arrows showing each decay.
What does it mean for decay to be random and spontaneous?
It is random since we cannot predict the next decay and is spontaneous since we cannot affect the chance of a decay.
What are the issues with using die to model decay?
Decay happens continuously not over a set time period so does not follow “true” exponential decay.
Define activity.
The activity of a source is the rate at which nuclei decay (number of alpha/beta particles per unit time).
What is the unit for activity?
becquerel (Bq or s^-1).
What does the equation ΔN/Δt = -λN mean?
The rate of change of the No. (N) of undecayed nuclei (i.e. the amount lost per unit time) = decay constant of a isotope * No. nuclei remaining.
What does the equation A = λN show?
The activity = decay constant * No. undecayed nuclei.
What is the definition of the decay constant?
The probability of decay of an individual nucleus per unit time.
How is half life determined for sources with very large half lives?
Take a source, use its mass to find the number of nuclei and use this and its current activity to work out the decay constant then t_(1/2) = ln(2)/λ.
How can spreadsheets be used to model decay?
Find the % of decayed nuclei in a time period and repeat the use of A = λN with smaller time periods.
How does carbon dating work?
By finding the % of the radioactive carbon-14 relative to the number of carbon-12 and an estimate as to what the original % of carbon-12 should be to find how long it would take for that much carbon-12 to decay.
What are the issues with carbon dating?
It assumes the carbon-12 to 14 ratio in living creatures has stayed roughly constant which it may not have due to different levels of C02 in the air.
