2.6 Radioactivity Flashcards
What do radioactive substances emit?
Radiation
What did J.J Thomson come up with?
The plum pudding model for the discovery of the nucleus
Describe the plum pudding model?
A sphere of positive charge with small negative charges throughout
What experiment did Ernest Rutherford conduct with Geiger and Marsden?
They fired alpha particles at thin gold foil (only a fee atoms thick)
What observations did Rutherford find in his experiment?
Most of the Alpha particles went straight through
Some of the Alpha particles were deflected through large angles
Very few of the Alpha particles were deflected straight back
What did Rutherford conclude from his experiment?
The plum pudding model is wrong
The nucleus is very small compared to the rest of the atom containing most of the mass and all of the positive charge
Why did some of the Alpha particles deflect?
They were too close to the nucleus and repelled because the particles and the nucleus are both positively charged
What is the charge of Alpha?
Positive
+2
What is the mass of Alpha?
4
What is the ionisation of Alpha like?
Strong
What is an Alpha particle made of?
2 protons
2 neutrons
Which is a helium nucleus
How is the penetration of Alpha?
Bad
Stopped by paper and a few cm of air
What is the charge of Beta?
-1
What is the mass of Beta?
Negligible
What is the ionisation of Beta like?
Average
What is a Beta particle?
An electron
How is the penetration of Beta?
Average
Stopped by Aluminium and a few metres of air
What is the charge of Gamma?
0
What is the mass of Gamma?
0
What is the ionisation of Gamma like?
Weak
What is a gamma wave?
A Transverse electromagnetic wave
What is the penetration of Gamma like?
Very good
Stopped by lead and concrete
What happens to gamma in a magnetic field?
It is undeflected
What happens to Alpha in a magnetic field?
Slightly deflected
Opposite to Beta
What happens to Beta in a magnetic field?
Larger deflection
Opposite to Alpha
Why do alpha and beta particles go in opposite directions in a magnetic field?
They have opposite charges?
Why is alpha deflected less than beta in a magnetic field?
Alpha has a larger mass
What happens to the new product in Alpha decay?
Mass number goes down by 4
Proton number goes down by 2
What happens to the new product in Beta decay?
Mass number stays the same
Proton number goes up 1
How can a beta particle be emitted if there are no electrons in the nucleus?
A neutron is turned into a proton and an electron
Therefore the electron can be emitted as a beta particle
How is the mass number the same in Beta decay?
The loss of a neutron but the gain of a proton balances out to the original number
What are the origins of background radiation?
Cosmic radiation from space Nuclear weapon testing Nuclear accidents (power stations) Food (banana) Sun
What categories can origins of background radiation be put into?
Natural
Manmade
What is half life?
The time it takes for the number of radioactive nuclei in a sample or count rate to decrease by 50%
How do we measure radioactivity?
By measuring the count rate
How does radioactive decay occur?
It is random
You can’t do anything to make a radioactive substance decay
Does the time taken for half life change?
No
The half life is fixed
Each time it halves it takes the same amount of time
When you are given a graph about half life what must you do?
Draw on the lines to show the decay rates halving
What is an example of radioactivity being used with Alpha particles?
Smoke alarms
How do alpha particles help in smoke alarms?
Alpha particles are sent into a gap in the circuit
They ionise with the air allowing current to conduct
In a fire smoke absorbs the ions preventing current
This sounds the alarm
What is an example of radioactivity being used with Beta particles?
Paper thickness control
How do Beta particles help in paper thickness control?
Beta particles are passed through the paper with a sensor on the other side
If a lot of particles pass through the paper is too thin (rollers expand)
If too few particles pass through the paper is too thick (rollers contract)
What is an example of radioactivity being used with gamma particles?
Leak detection in pipes
Radiotherapy
How do Gamma particles help in leak detection in pipes?
A radioactive isotope is injected into the pipe
On the ground a Geiger counter will detect areas of high radioactivity
This is where the leaks are
How do Gamma particles help in radiotherapy?
A controlled beam of gamma rays is used to kill cancer cells
It needs to be directed perfectly to avoid healthy cells
What is an example of radioactivity being used with gamma particles or beta particles?
Radioactive tracers
How do Beta or Gamma particles help in radioactive tracers?
A source is injected or swallowed by a patient
The progress of the tracer is monitored outside the body
Use a substance with a very short half life so the patient isn’t exposed for long
