1) Henri Becquerel discovered that uranium salts would expose photographic plates even when wrapped in black paper, showing they emitted invisible "rays" he called radioactivity. 2) Marie Curie discovered the radioactive elements polonium and radium, and found radium was over a million times more radioactive than uranium. 3) Ernest Rutherford discovered there were at least two types of radiation, which he called alpha and beta based on how far they could penetrate matter and their opposite electric charges.

1. Radioactivity and
radioisotopes

2. A very brief history of the discovery of radioactivity
Dear Marie, do you remember those uranium compounds that glow when I
put them under sunlight? Well, guess what I found out last night as I put them
in my drawer… in the same drawer I had a key on top of a film plate. When I
developed the film the image of the key was impressed on it, although the
film was wrapped! These compounds must emit invisible rays that penetrate
certain materials. I think I’ll call them Radioactivity.
Henri Bequerel
(1852-1908)
Don’t say more dear Professor! I have taken on the work you have passed on
to me and I have already discovered two new elements more radioactive than
uranium, polonium and radium. To isolate 1 g of radium I had to buy a tonne
of pitchblende and separate the radium. The amazing thing is that the radium
is about one million times more radioactive than uranium! Marie Curie
(1867-1934)
Hey guys, thank you for this stuff! Now that we know so much I can find out
the nature of this radioactivity pal! In fact, I have already discovered that
there are at least two kinds of radiation. I’ve called the first alpha. This gets
easily absorbed and it’s positively charged. The second is beta, it is more
penetrative and has negative charge.
Ernest Rutherford (1871-1937)

3. What is radioactivity?
Radioactivity is the spontaneous emission of energy and
particles due to the breaking down (disintegrating) of
the nuclei of unstable atoms.
Energy
Particles

4. What is radioactivity?
It is not known what causes this spontaneous decay of
the nucleus. However we know the nature of the
radioactivity. It can manifest in three forms; alpha and
beta particles and gamma radiation.
Gamma
rays
Beta Alpha
particles particles

5. What is radioactivity?
Suggest reasons why the rate of radioactive
decay seems not to be affected by chemical
reactions, temperature, or pressure.
• Chemical reactions involve only electrons within
atoms and energy of the order of a few eV.
• Even at high temperatures of 6000 K (surface
temperature of the Sun) the vibration energy of
the atoms only about 1 eV.
• But binding energies of nuclei are of the order
of 10 MeV (10000000 eV).

6. The three types of radiation
Use this table to find information about and to compare , and radiation
Alpha ( ) Beta ( ) Gamma ( )
Nature
Charge
Mass
Speed
Ionizing
effect
Most dangerous

7. The three types of radiation
Use this table to find information about and to compare , and radiation
Alpha ( ) Beta ( ) Gamma ( )
It’s a nucleus of It’s an electron It’s an
4
helium 2 He. Two e- electromagnetic
Nature protons and two wave
neutrons
Charge
Mass
Speed
Ionizing
effect
Most dangerous

8. The three types of radiation
Use this table to find information about and to compare , and radiation
Alpha ( ) Beta ( ) Gamma ( )
It’s a nucleus of It’s an electron It’s an
4
helium 2 He. Two e- electromagnetic
Nature protons and two wave
neutrons
Charge +2 -1 0
Mass
Speed
Ionizing
effect
Most dangerous

9. The three types of radiation
Use this table to find information about and to compare , and radiation
Alpha ( ) Beta ( ) Gamma ( )
It’s a nucleus of It’s an electron It’s an
4
helium 2 He. Two e- electromagnetic
Nature protons and two wave
neutrons
Charge +2 -1 0
Mass Relatively large Very small No mass
Speed
Ionizing
effect
Most dangerous

10. The three types of radiation
Use this table to find information about and to compare , and radiation
Alpha ( ) Beta ( ) Gamma ( )
It’s a nucleus of It’s an electron It’s an
4
helium 2 He. Two e- electromagnetic
Nature protons and two wave
neutrons
Charge +2 -1 0
Mass Relatively large Very small No mass
Speed Slow Fast Speed of light
Ionizing
effect
Most dangerous

11. The three types of radiation
Use this table to find information about and to compare , and radiation
Alpha ( ) Beta ( ) Gamma ( )
It’s a nucleus of It’s an electron It’s an
4
helium 2 He. Two e- electromagnetic
Nature protons and two wave
neutrons
Charge +2 -1 0
Mass Relatively large Very small No mass
Speed Slow Fast Speed of light
Ionizing
Strong Weak Very weak
effect
Most dangerous

12. The three types of radiation
Use this table to find information about and to compare , and radiation
Alpha ( ) Beta ( ) Gamma ( )
It’s a nucleus of It’s an electron It’s an
4
helium 2 He. Two e- electromagnetic
Nature protons and two wave
neutrons
Charge +2 -1 0
Mass Relatively large Very small No mass
Speed Slow Fast Speed of light
Ionizing
Strong Weak Very weak
effect
When source is When source is When source is
Most dangerous
inside the body outside the body outside the body