P7: Radioactivity Flashcards
What is a radioactive substance?
A substance that contains nuclei that become stable by emitting radiation
What are the three types of radiation that comes from radioactive substances?
- alpha
- bets
- gamma
Why can’t you predict or influence when radioactive decay happens?
Because Radioactive decay is a random event
Radioactive sources emmit?
- alpha radiation
- beta radiation
- gamma radiation
Alpha radiation is stopped by___?
Paper
Beta radiation goes through____
Paper
Rutherford used ____ particles to probe inside atoms
Alpha
What did Rutherford find from his experiment?
Some of the alpha particles were scattered through large angles(1/10000 more than 90 degrees
What did Rutherford deduce from his results?
There is a positively charged nucleus at the centre of every atom
(Because alpha particles are positive and they rebounded)
What was wrong with the plum pudding model?
It could not explain why some alpha particles were scattered through large angles
Most of an atom’s mass is located in the _____
Nucleus
What did the nuclear model correctly exlpain?
Why some alpha particles scattered through large angles
What did Bohr’s model of the atom show?
Electrons in an atom orbit the nucleus as specific distances and have specific energy levels
- his model showed electrons could move to another orbit
- absorbing electromagnetic radiation-away from the neccleus
- emitting elecromagnetic radiation-move closer to the nucleus
Who came up with the nuclear model
Rutherford
What are isotopes!
Atoms of the same elemwnt with different numbers of nuetrons
How can an unstable nucleus become more stable?
-emitting alpha or beta radiation
Or emitting a gamma ray
An alpha particle is made out of what?
2 protons and 2 nuetrons
(Relative charge +2)
(Mass number:4’
(Atomic number:2)
What is a beta particle?
An electron emitted by the nucleus, reltive charge =-1
What is gamma radiation?
Electromagnetic radiation from the nucleus of an atom?
Why does gamma radiation not change the number of protons or nuetrons in an atom?
It is uncharged and has no mass
What is the activty of a radioactive substance?
Number of unstable atoms in the source that decay per second
What does a Geiger do?
Monitors the activty of a radioactive substance
What do you need for a Geiger to monitor the activity of a radioactive substance?
You need to measure the count rate
What is the count rate proportional to?
The activity of the source as long as the distance between the tube and the source stays the same
What is a half life?
The average time taken for the count rate to fall by half is always the same
The half life of a radioactive substance is the average time it takes……………
For the number of nuclei of the isotope in a sample to halve
For the count rate in an isotope from a sample to fall to half its original value
What is the count rate
Number of decays per second
