P2.6 Flashcards
What is a radioactive substances?
Atom with an unstable nucleus.
What types of radiation are given out from a radioactive substance?
- alpha radiation
- beta radiation
- gamma radiation
- background radiation
When does an unstable nucleus decay?
When it emits radiation.
Where does background radiation come from?
- the environment
- from space
- from devices such as X-Ray tubes
When will an unstable nucleus decay?
It’s a random event that happens without anything being done to the nucleus.
Name a radioactive element:
Polonium
How was the nuclear model of the atom established?
Rutherford used his theory to estimate the diameter of the nucleus and then it was quickly accepted.
Why was the plum pudding model of the atom rejected?
Because it couldn’t explain why some alpha particles were scattered through large angles.
What did the nuclear model of the atom explain?
Explained why the alpha particles are scattered and why some are scattered through large angles.
What is an isotope?
Atoms of the same element with different numbers of neutrons.
How does the nucleus of an atom change when it emits an alpha particle or a beta particle?
Alpha- its atomic number goes down by 2and its mass number goes down by 4
Beta- the atomic number goes up by 1 and its mass number stays the same
What happens to gamma radiation when it’s spreads out in air without being absorbed?
It gets weaker.
How can we separate radiations?
By using a magnetic field or an electric field.
How is alpha radiation stopped?
Stopped by paper each composed of two protons and two neutrons.
How is beta radiation stopped?
Stopped by thin metal and consists of fast moving electrons emitted from the nucleus.
How is gamma radiation stopped?
Stopped by thick lead and consists of em radiation.
How can we separate a beam of alpha, beta and gamma radiation?
By a magnetic or an electric field.
Why is alpha, beta and gamma radiation dangerous?
Alpha, beta and gamma radiation ionise substances they pass through which can damage or kill the cell.
What is ionisation?
Radiation from a radioactive substance can knock lecterns out of atoms which become charged because they lose electrons.
What causes ionisation?
X-Ray’s.
Why is alpha radiation more dangerous in the body than beta or gamma radiation?
Because it has a greater ionising effect than beta or gamma radiation.
What does ‘half-life’ of a radioactive source mean?
Average time it takes:
- for the number of nuclei in a sample to halve
- for the count rate the isotope in a sample to fall to half its initial value
What is the activity of a radioactive isotope?
Number of atoms that decay per second.
What is the count rate?
Number of counts per second.
What happens to the activity of a radioactive isotope as it decays?
The activity decreases.
How do we choose a radioactive isotope for a particular job?
Has to have a certain type of radiation and has a suitable half-life.
How can we use radioactivity for monitoring?
The isotope should have a long half-life.
What are radioactive tracers?
Beta or gamma emitters that last long enough to monitor but not too long.
What is radioactive dating?
Radioactive isotope that is present in the sample which has a half-life about the same as the age of the sample.
What are two types of radioactive dating?
- carbon dating
- uranium dating
