Radioactivity and stars

RUTHERFORD EXPERIMENT

The scattering of alpha partices- alpha particles were shot at sheets of gold. If the structure of an atom is like a "plum pudding" the alpha particles should have gone straight through the sheets of gold however...

Findings...

-Most went straight through

-Some were deflected a small amount

-Very few deflected straight back            

This tells us the "plum pudding" idea didn't work

(The alpha particles are deflected back as they have a positive charge, and positive + positive deflect)

Tells us...

Most alpha particles went through so the atom is mostly empty space. Most of the mass was at the centre of the nucleus i.e. positive charge concentrated in a small dense nucleus.

New idea AFTER the experiment...

Electron orbits ^  

TINY nucleus (protons and neutrons) ^

RECAP

What is an isotope? Isotope- Forms of the same element that contain the same number of protons but different numbers of neutrons.

4               ---------------> Nucleon number

    He

2               ---------------> Proton number

RADIOACTIVITY

alpha +2 charge > 2 protons + 2 neutrons NO ELECTRONS just a     nuclei. Deflected by electric and magnetic fields. Quite big and heavy. Cause ionisation (knock out an electron) when bumping into atoms. They can be stopped by paper and a few cm of air.

beta -1 charge > fast moving electrons from the nucleus. Deflected by electric and magnetic fields in the OTHER DIRECTION to alpha particles. Don't bump into as many atoms. Less ionising that alpha particles and penetrate further. Can be stopped by a few mm of aluminium or a metre or so of air.

gamma NOT AN ATOM BUT an electromagnetic wave. Doesn't ionise much at all. NOT deflected by electric or magnetic fields. Very hard to stop as it keeps its energy. Concrete and lead could be used to stop it Gamma must accompany alpha or beta particles

Radiation exposure: …