Radioactivity experiments

Question 1

What did Rutherford discover?

Answer 1

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

Question 2

What did tests show on the magnetic fields with the different types of radiation?

Answer 2

• 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

Question 3

How is the ionisation effect of each type of radiation can be measured using?

Answer 3

• using an ionisation chamber and a picoammeter
• chamber contains air at atmospheric pressure
• electrodes

Question 4

How are ions detected?

Answer 4

• 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

Question 5

What was discovered about the ionising effect of each the types of radiation?

Answer 5

• 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

Question 6

What is a cloud chamber?

Answer 6

• contains air saturated with a vapour at a very low temperature

Question 7

What happens as alpha or beta radiation is passed through the cloud chamber?

Answer 7

• 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

Question 8

Why is a track left?

Answer 8

• 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

Question 9

What is the difference between tracks left by alpha and beta particles?

Answer 9

• 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