Theory
Scattering
Atoms
αβγ decay
Decay Series
Law
Half-life
Geiger
Carbon-14
Fission
Chain Reaction
Nuclear Energy
Nuclear reactors
Fusion

The search for artificially radioactive substances led to the discovery of fission.

The discovery of fission led to the atomic bomb.

Penetrating ability may be thought of as inversely related to ionising ability.

Alpha particles cannot penetrate the dead layer of skin that covers our bodies.

Alpha particles pose no danger when emitted outside the body.

Beta particles can penetrate the skin but usually not as far as internal organs.


Alpha, Beta and Gamma decay

, and -rays differ from each other in many respects including:
  • nature
  • charge
  • mass
  • ionising ability
  • penetrating ability


    A table of comparison is set out below.
 
Alpha
Beta
Gamma
What are these particles made of?

helium nucleus

2 protons 2neutrons

electrons which originate in the nucleus high frequency electromagnetic waves
symbol
electric charge
+2
-1
0
mass
1 a.m.u.
0.0005 a.m.u.
0
deflection by electric and magnetic fields
Yes
Yes
No
penetrating power very weak
several cm of air
stopped by cardboard
moderate
about 30cm of air
stopped by an aluminium foil
very penetrating
stopped by about 15cm of lead
ionising power very ionising less ionising than alpha very low level of ionization

 

Nature of – rays

Rutherford succeeded in measuring the specific change of -rays and thereby established that they were in fact particles. In 1909 Rutherford and Royd preformed an experiment where they allowed
-particles to enter a vacuum. They passed a discharge through a chamber and observed the spectrum of Helium. Together with the result for q/m they were able to conclude that -particles were doubly ionised helium atoms.

Nature of – rays

Becquerel measured the specific change of -rays from a number of radioactive sources and found it to be the same as the value for cathode rays. Therefore -rays were in fact electrons.
However, -particles come from the nucleus not the outer shells of atoms.

Nature of – rays

They were unaffected by electric and magnetic fields and therefore it wasn’t possible to obtain a value for q/m . Perhaps they were unchanged particles or perhaps they were high frequency waves like x-rays. In 1914, Rutherford and Andrade diffracted x-rays using crystals and so confirmed their nature as high frequency electromagnetic radiation.

 
Penetrating ability
 

Some examples of how , and -rays arise are shown below:



Beta



Gamma

-rays are different from or radiation in that they are electromagnetic waves, not electrically charged particles. They are the same as light waves or radio waves except that they have much more energy. rays are just like x-rays except for where they originate. -rays, like and , come from the nucleus of a radioactive atom. X-rays come from outside the nucleus. Because
-rays and x-rays have no charge and no mass. They are able to penetrate deeply through materials.