1. Warmup: review questions (3 minutes)
1) What determines the identity of a element?
A. # protons B. # neutrons
C. # electrons D. atomic mass
2) Write the isotope symbol for sulfur-33
3) How many neutrons does an atom of sulfur-33 have?
4) Write down everything you know about radiation.

2. Radioactive Decay

3. Types of Radiation alpha particle: + charged helium isotope
Radiation is when an UNSTABLE atom throws out part of itself. This often changes one element to another. ++
alpha particle: + charged helium isotope
other isotopes
neutron
beta particle: an electron
Types of Radiation
proton: hydrogen-1
gamma ray: pure energy
positron: + electron
n and n (no mass or charge)

4. The diagram below shows how different particles can penetrate the same material. Which type of particle is the most harmful?

5. Because they have no charge gamma rays are very “non-interactive”
This allows them to travel through objects….even you…..

6. Why does radiation happen?
Protons and neutrons are held together to form the nucleus by the Strong Nuclear Force.
Like charges repel (Electrostatic Force)….protons push away from each other
Sometimes, the ES force dominates, causing the nucleus to decompose (radiation)
Two other basic forces in nature: gravity, weak nuclear force.

7. 6. Write the isotope symbol for Neptunium-240
*special notation to indicate isotopes
# neutrons = mass - atomic #
Isotopes: 2 atoms of the same element having different masses because the #neutrons differs
5. A carbon atom can have a mass of 12, 13, or 14 AMU. How many neutrons are in a carbon-14 atom?
6. Write the isotope symbol for Neptunium-240
7. How many neutrons are in atom of Neptunium-240? 3

8. The Fate of a Heavy Nucleus
Heavy atoms (atomic number over 84) all have unstable nuclei (so do some light atoms)
Decay into a smaller nucleus (called transmutation – new element formed)
Radioactive decay equations show the changes in mass and atomic #’s; charge and mass must be conserved
Normal Chemical Rxns vs Nuclear Rxns
Involve electrons; compounds form and/or break apart
Protons and neutrons don’t move
Small energy changes
Nucleus opens, protons and neutrons rearrange
Releases a tremendous amount of energy that used to hold the nucleus together (binding energy) 4

9. Electron capture an inner orbital electron is pulled into the nucleus
A proton combines with the electron to make a neutron (and a ‘neutrino’)
1p e  1n v 7

10. 8. Write balanced equations showing the electron capture of: argon-37
iron-55
37Ar + 0e Cl + n 18 17 -1
The atomic number decreases by 1
The mass number stays the same
- Increase # of neutrons by 1
- Decrease # of protons by 1
55Fe + 0e Mn + n 26 25 -1

11. Beta decay
a neutron decays into a proton, a beta particle, (and an antineutrino)
1n p + 0b + n 1 -1 5 5

12. 9. Write balanced equations showing the beta particle decay of:
carbon-14
14C N + 0b + n 6 7 -1
Decrease # of neutrons by 1
Increase # of protons by 1
Mass # stays the same
b. potassium-40
40K Ca + 0b + n 19 20 -1

13. Positron Emission a proton decays into a neutron and a positron
positron (“anti-electron” ) has a charge of +1
1p n + 0b + n 1 +1 7

14. 10. Write balanced equation showing the position emission of:
a. carbon-11 b. potassium-38
11C B + 0b + n 6 5 +1
38K Ar + 0b + n 19 18 +1
The mass number remains the same
Decrease of # protons by 1
Increase # of neutrons by 1

15. Alpha decay
atomic number decreases by 2
mass # decreases by 4 5 5

16. Americium- 241 is the radioactive element used in today's smoke detectors.
a very small quantity is used
( 1/5000th of a gram)
no risk of radiation
half-life is about 432 years - decays extremely slow, emitting very little radiation.
Americium pellet gives off alpha particles
Alpha particles hit atoms (in the air) and knock off their electrons and the atoms become positively charged
An electrical circuit counts the positive atoms
If smoke is present the number of positive atoms changes and the smoke detector sounds the alarm!!

17. 11. Write a balanced equations showing the alpha decay of a
11. Write a balanced equations showing the alpha decay of a. Am-241 and b. Po-212
212Po He + 208Pb 84 2 82

18. *high energy packets of light are sometimes emitted when the nucleus undergoes some other type of decay
*No loss of particles, no change in mass or atomic number
Gamma decay tends to be coupled with another type of decay.
The gamma energy comes from the loss of mass. If you were to do a close measurement of mass, you would notice a small loss in mass with emission of the gamma ray that corresponds to the energy predicted by E=mc2. i

19. 12. What radioactive isotope is produced when one alpha particle is absorbed by boron-10 and 1 neutron is produced?
10B He n +
13N 7 19