P2.5 Flashcards
Where does radiation come from?
The nucleus of the element it’s coming from
What does a Geiger-muller tube measure?
~ Measures the amount of radioactivity coming through a substance.
~ Measured in counts per minute
What is background radiation?
Radiation that is present naturally and comes from the environment
What makes up about 50% of background radiation?
Radon gas from air
What are some examples of background radiation?
~ Air ~ Food and drink ~ Rocks/ground (building materials) ~ Cosmic rays (outer space) ~ Man made (medical X-rays, nuclear reactors, aeroplanes, nuclear accidents, nuclear weapon tests)
What are alpha particles made up of?
2 protons and 2 neutrons (+2 charge, mass of 4)
What experiment did Rutherford and Marsden do?
They shot alpha particles at thin gold foil in a vacuum chamber (no air) and detected what radiation came out the other side of the gold foil
What did Rutherford and Marsden find?
~ Most alpha particles went straight through the gold foil
~ Some were deflected
~ Some didn’t pass through the foil and bounced back
What did Rutherford and Marsden think the reason for most alpha particles passing through the foil was?
Most of the atom was empty space
What did Rutherford and Marsden think the reason for some alpha particles deflecting was?
There was a positive centre to the atoms
What did Rutherford and Marsden think the reason for some alpha particles coming straight back was?
The positive centre was very dense
Why can’t you predict when a radioactive nucleus will emit radiation?
Because it’s a spontaneous and random action
What is an alpha particle the same as?
A helium nucleus
What is a beta particle?
An electron ejected from the nucleus (-1 charge, mass is too tiny to measure)
What is gamma radiation?
An electromagnetic wave emitted from the nucleus of a radioactive element (no charge, no mass)
What is the range in air of an alpha particle?
Few cms
What is the range in air of a beta particle?
1 metre
What is the range in air of a gamma ray?
Many km/unlimited
What is an alpha particle absorbed/stopped by?
~ Sheet of paper
~ Skin
What is an a beta particle absorbed/stopped by?
Piece of aluminium, few mm thick
What is a gamma ray absorbed/stopped by?
~ Lead a few cm thick
~ Few ft of concrete
What happens to beta particles in a magnetic field?
They’re deflected most towards the positive electric field
Why do beta particles deflect more than alpha particles?
Because they have a lighter mass
What happens to alpha particles in a magnetic field?
Deflected slightly to the negative electric field
What happens to gamma rays in a magnetic field?
No deflection, travels in a straight line
What do radioactive substances do?
Give out radiation from the nuclei
What radiations are detected by both electric and magnetic fields?
Alpha and beta
What is half life?
The time it takes for the number of nuclei of a radioactive isotope in a sample to halve
