1. Atomic Theory and Radioactive Decay
Natural background radiation exists all around us.
Radioactivity is the release of high energy particles or waves that we call radiation.

3. When atoms lose high energy particles and waves, new atoms can be formed.
Radiation can be beneficial or harmful to us
Benefits
X-rays,
radiation therapy
electricity generation are beneficial.
Harms caused by radiation sources
High energy particles and waves can do damage to DNA in our cells.

4. The Electromagnetic Spectrum

5. Early Discoveries of Radiation
Roentgen named X rays with an “X” more than 100 years ago because they were previously unknown.
Later, more sophisticated devices
such as the Geiger-Müller counter

6. Becquerel realized uranium emitted seemingly invisible energy as well.
Marie and Pierre Curie named this energy radioactivity.

8. Isotopes
are atoms of the same element, with a different number of neutrons.
changing the # of neutrons changes the mass number
Remember: mass # = # protons + # neutrons
isotopes still have the same number of protons and the same element symbol
Atomic mass = average of the mass numbers for all isotopes of an element.

9. Representing Isotopes
Isotopes are written two ways
with the mass number at the end Ex. Potassium – 40
With its chemical symbol Ex.
Mass number
Atomic number

10. Radioactive Decay Can result in new atoms forming.
Radioactivity results from having an unstable nucleus.
Radioactive decay = when nuclei break apart + release energy from the nucleus.
Radioactive decay continues until a stable element forms.
An element may have isotopes that are radioactive called radioisotopes
Ex. carbon-12, carbon-13 and carbon-14
(only C-14 is radioactive)

11. Positive alpha particles were attracted to the negative plate.
Rutherford identified three types of radiation using an electric field.
Positive alpha particles were attracted to the negative plate.
Negative beta particles were attracted to the positive plate.
Neutral gamma particles did not move towards any plate.

12. Alpha Radiation: is a stream of alpha particles, (shown as )
positively charged
weighs the most
are the same as a helium nucleus
Alpha particles are represented by the symbols
2 protons and 2 neutrons make a mass number of 4
it has a charge of 2+ because of the protons

14. Alpha particles are big and slow even a sheet of paper can stop it.

15. Beta Radiation: A Beta particle, , is a high energy electron.
negatively charged, and weigh less than alpha particles.
Beta particles are represented by the symbols
electrons are very tiny, so beta particles are assigned a mass of 0.
one electron gives a beta particle has a charge of 1–.

16. Beta decay occurs when a neutron changes into a proton + an electron.
The proton stays in the nucleus, and the electron is released.
Example: The beta decay of iodine - 131
It takes a thin sheet of aluminum foil to stop a beta particle.

17. Gamma Radiation:
Gamma radiation, , is a ray of high energy, short- wavelength radiation.
has no charge and no mass.
is the highest energy form of electromagnetic radiation.
It takes thick blocks of lead or concrete to stop gamma rays.
Gamma decay results from energy being released from a high- energy nucleus.
Shows unstable nucleus for gamma decay

18. Often, other kinds of radioactive decay will also release gamma radiation.
Uranium-238 decays into an alpha particle and also releases gamma rays.