- Are Helium Nuclei. Mass 4, Charge +2, 2 protons and 2 neutrons.
- Big, Heavy and slow moving.
- Don't penetrate - stopped by paper -Not harmful to us.
- Strongly ionising. (because of their size they bash into each other and knock electrons off, before slowing down)
- Are Electrons. no mass, and charge -1 Inbetween Gamma and Alpha
- Quite fast and small.
- penetrate moderateley - stopped by Alluminium - Can get into the body.
- Moderateley ionising
- Very short wavelength - EM waves
- Penetrate a long way - stopped by lead - Get into body, harmful, can damage cells and cause cancer.
- Weakly ionising - they pass through rather than collide.
Definition - How long it takes for half of the Radioactive atoms to Decay.
Simple Half Life Question -
The activity of a Radioisotope is 640 cpm. 2 hours later it has fallen to 40 cpm. Find the half life of the sample.
Initial Count - 1 half life - 2 half lives - 3 half lives - 4 half lives
640 - /2 - 320 - /2 - 160 - /2 - 80 - /2 - 40
It take 4 half lives for it to reach 40 cpm. So 2 hours represents 4 half lives. The half life is 30 mins.
Using a graph -
Subtract the background radiation, count rate on Y-axis and time in hours on X-axis. Plot your curve. Half the first countrate and draw across till it meets your curve, now draw down to your X-axis. This is your half life. Continue to half the countrate to continue halfing.
Definition - Very low levels of radiation that we are constantly exposed to.
Background Radiation changes depending on where you are. -
- Hight Altitude - It increases ( exposure to Cosmic Rays)
- Underground - It increases ( mines because of all the rocks)
- Underground rocks can cause an increase on the surface.
Background Radiation comes from many sources -
- The ground - 7%
- Granite rock - 7%
- food and drink - 12%
- Cosmic Rays from space - 10%
- Medical (X-rays, sterilising...) - 12%
- Radon Gas - 51%
- Nuclear Industry - 1%
Radon Concentration varies across the UK- depending on what rocks your house is built on either Ingneous or Sedimentary
High Doses = Lung Cancer, it breaks down cells. 1 in 2 deaths per year from Lung cancer are because of Radon Gas.
It Rises through the soil - gets into your HOUSE! If Radon Gas gets into your house you need -
- good ventilation.
- Seal cracks
- can buy a Radon Pump
New Houses must be designed with Good Ventilation.