1. Discovery of Radiation
Roentgen (1895)
Studied fluorescent materials that glowed when hit with a beam of electrons.
Discovered a mysterious form of radiation was given off even without electron beam. This radiation could pass through paper and other objects but not dense materials (lead, bone).
Called them X-rays

2. Becquerel (1896) Studied fluorescent minerals containing uranium.
Discovered radioactivity by accident on a cloudy day:
Thought that an external source was needed to produce the mysterious radiation.
Found that uranium emits radiation without external source.

3. Pierre and Marie Curie Thought radioactivity was a
property of heavy elements.
During study, discovered new radioactive elements: Polonium and Radium.
Wondered how small mass can give off large amount of energy:
Explained by Einstein with E=mc2.

4. Rutherford Studied radioactivity and named types of nuclear radiation.
Discovered that elements decay into other elements after emitting nuclear radiation. Called it Nuclear Decay.
Gold foil experiment revealed that the mass of an atom is concentrated in the nucleus (atom is mostly space)

5. Stable vs Unstable Isotopes
Atomic #s 1 − 19
Stable, naturally occurring isotopes
Atomic #s 20 − 83
Mixture of stable and unstable isotopes
Naturally occurring and man made
Atomic #s 84 and higher
All unstable
All man made

6. Unstable Isotopes
Unstable isotopes will automatically change into a more stable form
Transmutation ═ the process of one element changing into another element
Law of Conservation of Mass
Net charge remains unchanged

7. Nuclear Symbol Mass Number X Atomic Number where
Mass Number = Protons + Neutrons
X = Symbol of Element
Atomic Number = # of Protons (Electrons)
**The atomic number tells the symbol to use

8. Types of Radiation Alpha particle () Beta particle (-) Positron (+)
helium nucleus
Beta particle (-)
electron
Positron (+)
positron
Gamma ()
high-energy photon

9. Alpha Emission Numbers must balance!! parent nuclide daughter nuclide
occurs when the nucleus has too many protons which cause excessive repulsion.
parent
nuclide
daughter
nuclide
alpha
particle
Numbers must balance!!

10. Alpha Emission
Ex. Plutonium-239 undergoes alpha decay + = +
239
235 4
Atomic Mass: = 94 92 +
Atomic #: 2
Masses must be equal = Conservation of mass

11. Alpha Emission + = + = - = = + = - = = 210 A 4 210 A 4 206 84 Z 2 84 Z
Ex. Polonium-210 undergoes alpha decay to produce this daughter nuclide. Solve for +
210 = A 4 +
Atomic Mass:
210 = A 4 - =
206 84 = Z 2 +
Atomic #: 84 = Z 2 - = 82 =

12. Beta Emission electron
occurs when the neutron to proton ratio is too great.
electron

13. Beta Emission + = + = - = = + = + = = 210 A 210 A 210 84 Z -1 84 Z 1
Ex. Polonium-210 undergoes beta decay to produce this daughter nuclide +
210 = A +
Atomic Mass:
210 = A - =
210 84 = Z -1 +
Atomic #: 84 = Z 1 + = 85 =

14. Positron Emission positron
Occurs when the neutron to proton ratio is too small.
positron

15. Positron Emission + = + = - = = + = - = = 210 A 210 A 210 84 Z +1 84 Z
Ex. Polonium-210 undergoes positron emission to produce this daughter nuclide +
210 = A +
Atomic Mass:
210 = A - =
210 84 = Z +1 +
Atomic #: 84 = Z 1 - = 83 =

16. Gamma Emission Emission of high energy electromagnetic wave.
occurs when the nucleus is at too high an energy.
Emission of high energy electromagnetic wave.

17. Gamma Emission + = + = = + = = 210 A A 210 84 Z Z 84
Ex. Polonium-210 undergoes gamma decay to produce this daughter nuclide +
210 = A +
Atomic Mass: A =
210 84 = Z +
Atomic #: Z = 84 =

18. Electron Capture electron
occurs when the neutron to proton ratio in the nucleus is too small.
electron

19. Electron Capture + = + = = + = = 210 A A 210 84 Z -1 Z 83
Ex. Polonium-210 captures an electron to produce this daughter nuclide +
210 = A +
Atomic Mass: A =
210 84 = Z -1 +
Atomic #: Z = 83 =