1. Discovery of Radioactivity

2. Roentgen
Becquerel
Curie
Radioactivity
X-rays
Uranium emits
something!
at the end of the 1800’s …

3. Roentgen discovered X-rays: 1895
Roentgen discovered that cathode ray tubes emit x-rays

4. Roentgen quickly discovered uses for X-rays

7. Natural Radioactivity - 1896
1896 Becquerel discovered that uranium substances emit radiation

8. Marie Curie found emission of rays by uranium compounds
atomic property of element uranium (U)
1898 discovered thorium (Th) also gave off radiation
1898: Curies reported 2 new elements:
polonium (Po) & radium (Ra)
also radioactive

9. Radioactivity
nucleus of element emits subatomic particles & electromagnetic waves
nucleus changes into different element
process: nuclear “decay” or “transmutation”
original nucleus is “unstable”

10. Natural Radioactivity
Becquerel & Curie believed more than 1 kind of radiation was emitted by substances:
1899 discovered alpha rays () & beta rays ()
1900 discovered gamma rays ()

11. Radioactivity – Rutherford again!

12. Radioactivity 3 radiation types behave differently in
magnetic & electric fields
3 radiation types: different penetration power
 (alpha rays):
stopped by paper
 (beta rays):
stopped by thin metal foil
 (gamma rays):
only partially blocked by
lead and concrete

13. TABLE O 0 gamma () -1 1/1836 (0.0005) 0 or 0 e beta () +2 40
gamma () -1
1/1836
(0.0005)
0 or 0 e
beta () +2 4
4 He or 4
alpha ()
Charge
Mass
(amu)
Isotope Notation
Type of Radiation
(symbol) 2 2 -1 -1

14. beta particle (negative electron): 1 0 n  1 1 p + 0 -1 e
positron (positive beta particle)
1 1 p  e n