26.2 The properties of alpha, beta, and gamma radiation

Why does radiation make air conduct electricity?

it ionises air

How many types of radiation are there?

3

what are the three types of radiation?

Alpha, beta, gamma

How do magnetic fields affect alpha, beta and gamma particles?

alpha and beta are deflected in opposite directions

gamma is not affected

What can be concluded from how magnetic fields affect alpha, beta and gamma?

alpha is positive

beta is negative

How can the ionisation effect be measured?

ionisation chamber and picoammeter

How does an ionisation chamber and picoammeter produce current?

ions created in the chamber are attracted to the oppositely charged electrode where they are discharged

electrons pass through the picoammeter due to ionisation is the chamber

the current is proportional to the number of ions per second created in the chamber

What type of radiation ha the strongest ionisation?

alpha

What happens when you move the alpha source away from the chamber?

the ionisation effect weakens as alpha has a small range in air

Beta particles have ___________ range than alpha particles

smaller

How long is a beta particle’s range?

over a meter

A beta particles produces _______ ions per mm than an alpha

less

Gamma radiation has a __________ ionisation effect that alpha and beta

smaller

Why does a gamma particle have smaller ionisation effect?

photons do not carry a charge

What does a cloud chamber contain?

air saturated with vapour at a very low temperature

Why do radiation particles leave a visible track in a cloud chamber?

ions produced by ionising particles trigger the formation of droplets in the supersaturated vapour

What kind of tracks do alpha particles leave?

visible straight tracks of the same length

Why do alpha tracks have the same length?

same range

What kind of tracks do beta particles leave?

wispy

Why do beta particles leave wispy tracks?

collision with air particles

Why are beta tracks hard to see?

they are less ionising

count rate

number of counts/ time taken

How do you find the count rate using a Geiger tube?

Place the geiger tube at a fixed distance from the source

measure the count rate with the source

measure the background count

count rate= count rate with source- background count

How can you measure the effect of absorbers on the count rate?

place absorbers of different materials/thickness and find count rate

What does the Geiger tube consist of?

sealed metal tube with argon gas at low pressure

How does the Geiger counter work?

An ionising particle ionising the gas atoms when it enters

negative ions are attracted to the rod

positive ions to the wall

ions accelerate and collide with other gas atoms and create further atoms

until so many ions are created a pulse of charge flows through R causing a voltage pulse which is recorded as a count

How do we know the range of particles?

count rate decreases as source is moved further

Why does the range differ for different sources?

different initial kinetic energies

Faster beta particles travel ___________ in air than slower beta particles

further

The proportion of gamma photons from the source entering the tube decreases according to the

inverse square law

Range of alpha in air

fixed range which depends on energy

up to 100mm

range of beta in air

up to 1m

range of gamma in air

inverse square law

deflection of alpha in a magnetic field

deflected

deflection of beta in a magnetic fiedl

deflected in the opposite direction to alpha

deflection of gamma in a magnetic field

not deflected

absorption of alpha

stopped by paper or thin metal foil

absorption of beta

stopped by ~5mm aluminium

absorption of gamma

stopped/reduced by thick lead

ionisation effect of alpha

produces ~10,000 ions per mm

ionisation effect of beta

produces ~100 ions per mm

ionisation effect of gamma

very weak

energy for a particle of alpha

cons

energy for a particle of beta

varies up to max for a given source

energy for a gamma photon

constant for a given source