1. Introduction to Radioactivity and the 3 types of Nuclear Radiation

2. Today’s Objective Define and understand the following terms
Radioactivity
Repulsive Force
Nuclear Force
Isotope
Be able to describe/explain why some atoms are radioactive
Be able to describe and balance
Positive alpha radiation α equations
Negative beta radiation β equations
Neutral gamma radiation γ equations

3. 7.1 – Atomic Theory and Radioactive Decay
Natural background radiation exists all around us.
This radiation consists of high energy particles or waves being emitted from a variety of materials.
Like the sun, radio stations, electronic devices, TV’s, cell phones, lights, etc...
Being exposed to radioactive materials can be beneficial or harmful

4. Beneficial (good) radiation exposure
Light!
X-rays
Radiation therapy (cancer treatment)
Electricity generation (nuclear power plants)

5. Harmful (bad) radiation exposure
Too much of any radiation...
Can cause Cancer
Skin cancer from sun (UV) radiation
Body cancer from high amounts of radiation
Can cause genetic mutations
Radiation affects and mutates the DNA in our body cells and then causes mutations in offspring

6. WHAT IS RADIATION??
Radioactivity (radiation) is the release of high energy particles or waves from unstable nuclei
When atoms lose high energy particles and waves, ions or even new atoms can be formed
High energy waves and particles are called ‘radiation’ when they leave the atom

7. Why are some Nuclei Radioactive?
Note: Radioactive = Unstable
Recall the structure of an atom.
What lives in the nucleus?
Protons
Neutrons
REPULSIVE FORCE P+ N P+ P+
NUCLEAR FORCE N P+ N N P+ N

8. Repulsive and Nuclear Forces
The nucleus is full of positive protons
Like charges want to repel= REPULSIVE FORCE
Fortunately the neutrons are there to help hold the nucleus together= NUCLEAR FORCE
Sometimes there are not enough neutrons in the nucleus.
This means the balance between repulsive forces and nuclear forces is off!

9. UNSTABLE NUCLEI
When the forces do not balance, the nucleus will make adjustments by kicking out particles or energy out of their nucleus.
This is called RADIATION

10. The Electromagnetic Spectrum
The higher the frequency of radiation
(ie. the shorter the wavelength) = The more harmful the radiation is for you!

11. Searching for Invisible Rays
Radiation is everywhere, but can be difficult to detect
Roentgen named X-rays with an “X” 100 years ago because they were previously unknown
Becquerel realized uranium emitted seemingly invisible energy as well
Marie Curie and her husband Pierre named this energy radioactivity
Early discoveries of radiation relied on photographic equipment
Later, more sophisticated devices such as the Geiger counter were developed to more precisely measure radioactivity

12. Isotopes and Mass Number
Isotopes are different atoms of the same element, with the difference between the two atoms being the number of neutrons in the nucleus, the number of protons is the same.
Isotopes have the same number of protons and therefore the same atomic number as each other.
By having different numbers of neutrons, isotopes have different mass numbers.

13. Representing Isotopes
Isotopes are written using standard atomic notation.
Chemical symbol, atomic number & mass number.
Potassium has three isotopes

14. Wait a MINUTE... MASS ATOMIC # Periodic Table Nuclear Symbol CHEMISTS
PHYSICISTS

15. C C Calculating Neutrons 14 12 6 6 6 8
It is now much easier because of the physicists C 6 12 C 14 6
MASS
ATOMIC # 6 8
# Neutrons

16. Practice!
Work with a partner to do the practice problems on page 291 in your notebook. (Don’t write in your textbooks!!!)
Check your answers on page 592

17. Radioactive Decay
Unlike all previously discovered chemical reactions, radioactivity sometimes resulted in the formation of completely new atoms.
Radioactivity results from an atom having an unstable nucleus
When these nuclei lose energy and break apart, decay occurs
Radioactive decay releases energy from the nucleus as radiation
Radioactive atoms release energy until they become stable, often ending up as different atoms
For example: uranium-238 (parent nucleus) decays in several stages until it finally becomes lead-206 (daughter nucleus)
An element may have only certain isotopes that are radioactive. These are called radioisotopes. Carbon-13 is an example.

18. Three Types of Radiation
When atoms are unstable, they break apart to become new, more stable atoms and release radiation... There are 3 types that can be released.
Positive alpha radiation α
Negative beta radiation β
Neutral gamma radiation γ

19. Alpha (α) radiation Alpha radiation is a stream of alpha particles
These particles are the same as a helium nucleus so we represent α radiation as:
Because it has two protons, it has a charge of 2+
The release of alpha particles is called alpha decay
Alpha particles are slow and penetrate materials much less than the other forms of radiation.
A sheet of paper will stop an alpha particle

20. ** Notice – the product side atomic masses add up to the reactant side (as well as the atomic numbers)
You try: Ac  Fr He
Decays to +
____
____
221 89

21. Beta (β) Radiation (Beta decay)
Beta radiation is a stream of beta particles
Beta particles are the same as an electron. So we represent radiation as:
Beta decay occurs when a neutron changes into a proton + an electron. The proton stays in the nucleus and the electron is released.
Beta particles are faster than alpha particles. A sheet of aluminum foil will stop a beta particle.

22. ** Notice – the product side atomic masses add up to the reactant side (as well as the atomic numbers)
You try: Hg  Tl β
Decays to + O -1
___
____
201 81

23. Gamma (γ) Radiation
Gamma radiation is a ray of high energy, short-wavelength radiation
no charge and no mass
the highest energy form of electromagnetic radiation
Occurs when nucleus is in excited state (shown by by *) after emitting an alpha or beta particle, and needs to release more energy. It is shown by:
It takes thick blocks of lead or concrete to stop gamma rays
Sometimes reactions can release more than 1 type of radiation.
For example: Uranium-238 decays into an alpha particle and also releases gamma rays

24. Gamma Radiation
Uranium is releasing an Alpha particle and Gamma Radiation
Nickel is decaying and giving off just Gamma Radiation
Notice – no change in atomic mass or number!

27. Try some radioactive decay questions... (Copy in your notes)
Pa  Ac + ___ C  ___ + β U  Cs + ____ + γ
227
____
____
α / He 89 14
____
____ N 7 Rb 92
____
____ 37

28. Assignment
Try practice problems on page 295 and 296. Check your answers.