Evans SPH 4U1

Physics Grade 12

Unit 10: Radioactivity (Qualitative Only)


Reference: Chapter 13 (Qualitative Only)



Recall - Structure of Atom:


Alpha Decay:




Beta Decay:

Gamma Rays:



Shows alpha decay (loses 2 protons and 2 neutrons)

Daughter (thorium) could become very excited and orbital electrons will drop to a lower energy level and release a photon.


Radioactive Dating:

Talk about carbon 14


Accelerators (discovery of particles):

Accelerate negatively charged hydrogen ions and strip off electrons by passing them through a charged foil.

This leaves proton beams.  Now you can fire the proton beams at a target material and analyze all the bits and pieces (new paticles)

We cannot see the bits and pieces that come flying off so we use:

        1) Cloud chambers - supersaturated gas (verge of condensing) so when particles go through, the gas condenses along the trajectory

        2) Bubble chambers


More Particles!:

At one time scientists thought the atom was the elemental particle.  Then Rutherford determined there were protons and neutrons. NOW physicists believe particles can be grouped into 2 families Quarks and Leptons.

Quarks:     3 Quarks = Proton (2 up spin, one down spin)

                3 Quarks = Neutron (2 down spin, one up spin)


Every particle has an antiparticle.


Lately even quarks are not considered to be elemental and there's a theory called the string theory that says everything is made up of strings.


Leptons are electrons and neutrinos.



1) Electromagnetic Force - atoms join together sharing electrons. Electrons are attracted to atoms' nuclei. Holds matter together.

2) Strong Force - holds nucleus (protons and neutrons together).

3) Weak Force - explains Beta decay.

4) Gravity


Physicists are attempting to come up with one theory to explain all of the above forces "Grand Unified Theory".  They feel they are getting close with "The String Theory".  The string theory says that everything is made up of strings.