1. Radioactivity
Changes in the Nucleus

2. Discovery of X-Rays
In 1895 William Conrad Roentgen discovered X-rays, a form of radiation.

3. Radioactivity
In 1896, the French scientist Henri Becquerel was studying a Uranium mineral. He discovered it was spontaneously emitting high-energy radiation.
In 1898, Marie and Pierre Curie attempted to isolate radioactive components of the mineral.

4. Radioactivity
In 1899, Ernest Rutherford, a British scientist, began to classify radiation: alpha (a), beta (b), and gamma (g).

5. Radiation
Look closely at the paths of radiation. Do you notice something about the amount of deflection of each type of particles?

6. Radiation

7. Changes in the Nucleus
Nuclear Reaction- changes that occur in the atom’s nucleus.
Nuclear reactions can change the composition of an atom’s nucleus permanently.

8. Types of Radiation Produced in Nuclear Reactions
Alpha (a)
Beta (b)
Gamma (g)

9. Nuclear Stability Atoms with unstable nuclei are radioactive.
Most atoms have stable nuclei and are, therefore, not radioactive.

10. Neutrons help to stabilize the nucleus.
Nuclear Stability
Neutrons help to stabilize the nucleus.
Elements 1-20 have p+ no
Above element 20, increasingly more no are needed than p+ to maintain nuclear stability.
Element 84 and up, all atoms are radioactive so the nucleus cannot be stabilized regardless of the number of no.

11. Types of Radioactive Decay
Alpha Radiation (a)- stream of high energy alpha particles.
Consists of 2 protons & 2 neutrons making it identical to a He-4 nucleus.
Alpha particles can be represented by:
Most alpha particles are able to travel only a few centimeters through air and are easily stopped by clothing etc.

12. Alpha Decay
parent daughter

13. Types of Radioactive Decay
Beta Radiation (b) – consists of stream of high speed electrons. These electrons are not electrons that are in motion around the atom’s nucleus.
Beta particles can be represented by:
Can penetrate through clothing and damage skin.

14. Beta Decay
parent daughter

15. Types of Radioactive Decay
Gamma Rays (g)- energetic form of light that cannot be seen.
Does not contain particles.
Gamma particles can be represented by:
Can penetrate heavy material including skin. Can only be stopped by lead or concrete.

16. Checking for Understanding
alpha decay
beta decay

17. Half Life
half life- the time required for half of the atoms in any given quantity of a radioactive isotope to decay
Each particular isotope has its own half-life.

18. Half Life
p.689 Sample Problem B
Phosphorus-32 has a half-life of 14.3 days. How many milligrams of phosphorus-32 remain after 57.2 days if you start with 4.0 mg of the isotope?
Ans: 0.25 mg