Radioactivity Flashcards
What did Rutherford and his pal do to prove the plum pudding method wrong?
- Fired a beam of Alpha particles at thin gold foil
- Expected it too be slightly reflected
- Most particles went straight through, an odd one came back
What did Rutherford show?
- Most of the mass is concentrated at the centre of a tiny nucleus
- Nucleus must be positively charged as it repelled the positively alpha by large angles
What is in the nucleus?
Protons and neutrons
The radius of the atoms nucleus is about ….. times …… than the radius of the atom
10,000
Smaller
What is the Mass of the Proton, electron and neutron
P = 1 N = 1 E = 1/200 (zero)
What is the Charge of the Proton, electron and neutron
P = +1 N = 0 E = -1
Number of protons equals
The number of electron
The charge of an electron is
The same size as the charge on a proton but opposite
Number of protons =
The number of electrons in a neutral form
What is an isotope
An element which has the same amount of protons but different neutrons
When does Radioactivity happen?
Its random, you cant say when one is going to decay
What is background radiation?
It is radiation that is present at all times
Where does the background radiation we receive come from?
- Naturally occurring unstable isotopes (in the air, food, building materials, rocks)
- Radiation from space (Cosmic rays)
- Radiation from man made sources (fallout from nuclear weapons tests, nuclear accidents, dumped nuclear waste)
How can radiation effect you?
- Underground rocks
- High altitudes (jet planes)
- Underground (mines)
- Nuclear industry
- Radiographers in hospitals
Alpha particles are
Helium nuclei (Two neutrons and protons)
Beta particles are
Electrons
With virtually no mass and a charge of -1
Gamma rays are
Very short wavelength EM waves
Alpha particles are..
Big, heavy and slowing moving
They don’t penetrate very far in materials and stop quickly
Beta particles are..
Quite fast moving, quite small
They penetrate moderately into materials before cooling
Gamma rays..
Penetrate far into materials without being stopped and pass straight through air
Because of their size alpha particles…
Strongly ionising - they bash into a lot of atoms and knock electrons off them before slowing down
For every B particle emitted…
A neutron turns to a proton in the nucleus
What is the mass and charge of gamma rays
There is no mass or charge
What are alpha and beta particles deflected by
Electric and magnetic fields
What is the charge of Alpha and beta particles
A = Positive charge B = Negative charge
What do alpha and beta particles deflect in different directions?
Because of their opposite charges
Why do alpha particles deflect less?
Because of their greater mass
Why do gamma rays not deflect?
Because they have no charge
Half-life
The average time it takes for the number of Nuclei in a radioactive isotope sample to halve
What happens each time decay happens
An alpha, Beta or gamma is given out
The older the sample…
The less radiation it will emit
Short half-life
The activity falls quickly, because lots of the nuclei decay quickly
Long half-life
The activity falls more slowly, because most of the nuclei don’t decay for a long time - they sit their unstable
If the initial amount is 640. What is one half-life
320
If the initial amount is 340. What is two half-life
160
If the initial amount is 340. What is three half-life
80
In the example 2 hours represents three half-lives so the half life is
120/30 = 40 minutes
Name 4 uses of radiation
Smoke detectors
Tracers in medicine
Radiotherapy
Sterilisation
What radiation do smoke detectors use
Alpha
- A weak source is placed close to two electrons
- The source causes ionisation and a current flows between the electrodes
- If a fire occurs the smoke will absorb the radiation -> alarm sounds
What radiation do tracers in medicine use
Beta or gamma
