Radioactivity experiments Flashcards

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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
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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
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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
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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
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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
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6
Q

What is a cloud chamber?

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