Radioactivity experiments Flashcards
1
Q
What did Rutherford discover?
A
radiation:
- ionised air
- making it conduct electricity
- he made a detector which could measure the radiation from its ionising effect
- was of two types
- one type which he called alpha radiation was easily absorbed
- the other type - which he called beta radiation - was more penetrating
- a third type - gamma radiation - even more penetrating than beta radiation was discovered a year later
2
Q
What did tests show on the magnetic fields with the different types of radiation?
A
- magnetic fields deflects alpha and beta radiation in opposite directions and has not effect on gamma radiation
- from the deflection direction, Rutherford concluded that:
- alpha radiation consists of positively charged particles
- beta radiation consists of negatively charged particles
- gamma radiation was later shown to consist of high energy photons
3
Q
How is the ionisation effect of each type of radiation can be measured using?
A
- using an ionisation chamber and a picoammeter
- chamber contains air at atmospheric pressure
- electrodes
4
Q
How are ions detected?
A
- ions created in the chamber are attracted to the oppositely charged electrode where they are discharged
- electrons pass trhough the picoammeter as a result of the ionisation in the chamber
- the current is propotional to the number of ions per second created in the chamber
5
Q
What was discovered about the ionising effect of each the types of radiation?
A
- alpha radiation caused strong ionisation
- however, if the source is moved away from the top of the chamber, ionisation ceases beyond a certain distance
- this is because alpha radiation has a range in air of no more than a few centremetres
- beta radiation has a much weaker ionising effect than alpha radiation
- its range in air varies up to a metre or more
- a beta particle therefore produceds fewer ions per millimetre along its path than an alpha particle does
- gamma radiation has the weakest ionising effect
- photons carry not charge so they have less of an effect
6
Q
What is a cloud chamber?
A
- contains air saturated with a vapour at a very low temperature
7
Q
What happens as alpha or beta radiation is passed through the cloud chamber?
A
- due to the ionisation of the air
- alpha and beta radiation passing through the cloud chamber leaves a visible track
- track of minute condensed vapour droplets
8
Q
Why is a track left?
A
- this is because the air space is supersaturated
- when an ionising particle passes through the supersaturated vapour, the ions produced trigger the formation of droplets
9
Q
What is the difference between tracks left by alpha and beta particles?
A
- alpha particles produce straight tracks
- radiate from the source
- easily visible
- the tracks from a given isotope are all the same length - indicating that the alpha particles have the same range
- beta particles produce wispy tracks
- easily deflected - as a result of collision with air molecules
- the tracks are not as easy to see as alpha particle tracks because beta particle are less ionising than alpha particles