P2.5 - Radioactivity Flashcards
What is a radioactive substance?
A substance which contains unstable nuclei that becomes stable by emitting radiation.
What are the types of radiation?
- Alpha
- Beta
- Gamma
When does a radioactive source decay?
Radioactive decay is a random event.
Where does background radiation come from?
It is from radioactive substances in the environment, space or man-made devices such as X-ray machines.
Who discovered radioactivity?
Marie and Pierre Curie
How was the nuclear model of the atom established?
Using measurements from alpha scattering, the idea was proven that an atom had a positively charged central nucleus where most of the mass of the atom is located?
Who initially came up with the nuclear model?
Ernest Rutherford
Why was the plum pudding model rejected?
It could not explain why some alpha particles were scattered through large angles.
Why was the nuclear model accepted?
The nuclear model explained why alpha particles are scattered and some through large angles.
Why must an atom have a positive nucleus based on Rutherford’s results?
The nucleus repelled the positively charged alpha particle.
Why must the nucleus be much smaller than the atom?
Most of the alpha particles passed straight through.
What is an isotope?
An form of an element with the same number of protons but a different number of neutrons.
How does the nucleus of an atom change when it emits alpha particles?
The nucleus loses two protons and two neutrons.
How does the nucleus of an atom change when it emits a beta particle?
A neutron changes into a proton.
How far can alpha radiation travel?
- A few centimetres in air
- Stopped by a piece of paper
What is alpha radiation?
Two protons and two neutrons
What is the range of beta radiation?
- A metre in air
- Stopped by a thin sheet of metal
What is beta radiation?
Fast moving electrons emitted from the nucleus.
What is the range of gamma radiation?
- Unlimited range in air
- Stopped by thick lead
What is gamma radiation?
Electromagnetic radiation
How is a beam of alpha, beta and gamma radiation separated?
A magnetic or electric field
Why are the different types of radiation dangerous?
They ionise substances they pass through which can kill living cells.
Why aren’t gamma rays deflected?
Gamma is electromagnetic radiation so it is uncharged.
Which type of radiation has the greatest ionising effect?
Alpha
What is the half life of a radioactive source?
The average time it takes for the number of nuclei of the isotope in a sample to halve.
What is the activity of a radioactive source?
The number of nuclei that decay per second.
What factors determine the use of a radioactive isotope?
- Half life
- Type of radiation emitted
What type of isotope should be used for monitoring?
An isotope with a long half-life.
What are radioactive tracers made of?
Beta or gamma emitters, usually iodine, that last long enough to monitor but not too long to ensure cells aren’t damaged.
What is radioactive dating?
A process using uranium or carbon used to determine the age of igneous rocks and wood.
What is automatic thickness monitoring?
The use of a beta emitter to regulate the thickness of metal foil.
Explain automatic thickness monitoring.
- There is an emitter on one side of the foil and detector on the other.
- If the thickness increase too much, the detector reading drops.
- The detector sends a signal to increase the pressure on the metal sheet making the foil thinner.
What is the purpose of a radioactive tracer?
Doctors can see whether there is a blockage in a patient’s kidney.
Explain the use of radioactive tracers.
- The patient drinks water containing the radioactive substance.
- A detector is placed against each kidney.
- If the kidney is healthy, the reading goes up then down.
- If not, the reading goes up and stays up.
Why is radioactive iodine best for use as a radioactive tracer?
- It only has a half-life of 8 days giving enough time to do the test.
- It emits gamma radiation which can be detected outside the body.
- It decays into a stable product.
Explain carbon dating.
- Used to find the age of organic material.
- Organic material contains some radioactive carbon with a half-life of 5600 years.
- When dead, the material stops absorbing carbon meaning the amount of radioactive carbon decreases.
- The count rate from the wood is compared to the rate of living wood.
Explain uranium dating.
- Igneous rocks contain radioactive uranium with a half-life of 4500 million years.
- Uranium decays into lead.
- The age is distinguished by comparing the number of atoms of uranium and lead. 1:1 makes the sample 4.5 billion years old.
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