1. Nuclear Radiation ??? Radioactivity (Nuclear Decay)
Henri′ Becquerel
Marie Curie
???
1896 Becquerel accidentally develops photo plate with U salts w/o sunlight
Curie exp. and named it radioactivity. Both won Nobel Prize in Physics, she won for Chem later. Died 1934 leukemia.
Radioactivity (Nuclear Decay)
spontaneous emission of high-energy radiation or charged particles from the nucleus of an atom

2. 3 Types of Nuclear Radiation
2 p + 2 n
Alpha (a) +
Beta (b–) e–
Gamma (g)

3. 3 Types of Nuclear Radiation
Penetrating: Least to Most (damaging)  – 
Video clip is “Radioactivity” from Safari playlist (4 min)
or Concrete

4. 3 Types of Nuclear Radiation
Stopped by
Symbol
Charge
Mass
Alpha Particle ()
helium nucleus +2 4
paper
Beta Particle (–)
electron
(smaller, faster)
aluminum –1
Gamma Ray ()
high-energy light (fastest)
3 feet of
Concrete
or Lead

5. Nuclear Decay Rates
Demo – penny ½ life

6. Half-life (t1/2): time at which half of initial amount remains. 6
Ask several questions about calculations. 6

7. Problem #1: The half-life of Zn-71 is 2. 4 minutes. If one had 100
Problem #1: The half-life of Zn-71 is 2.4 minutes. If one had g at the beginning, how many grams would be left after 7.2 minutes has elapsed?
Solution:
7.2 min ÷ 2.4 min per half-life = 3 half-lives
100.0 g ÷ 2 = 50.0 g
50.0 g ÷ 2 = 25.0 g
25.0 g ÷ 2 = 12.5 g remain after 3 half-lives.

8. Problem #2: Os-182 has a half-life of 21. 5 hours
Problem #2: Os-182 has a half-life of 21.5 hours. How many grams of a 10.0 gram sample would have decayed after exactly two half-lives?
Solution:
10.0 g ÷ 2 = 5.00 g
5.00 g ÷ 2 = 2.50 g remain after 2 half-lives.
(21.5 hr length of half-life was irrelevant)

9. Problem #3: After 24 days, 2. 00 mg of an original 32
Problem #3: After 24 days, 2.00 mg of an original mg sample is left. What is the half-life of the substance?
Solution:
32.00 mg ÷ 2 = mg
16.00 mg ÷ 2 = 8.00 mg
8.00 mg ÷ 2 = 4.00 mg
4.00 mg ÷ 2 = 2.00 mg remain after 4 half-lives.

10. Problem #4: A bone contains radioactive carbon-14 with a half-life of 5,000 yrs. The bone is thought to have had 20.0 mg of 14C when the animal died and it now has 2.5 mg of 14C left. How old is the bone?
Solution:
20.0 mg ÷ 2 = 10.0 mg
10.0 mg ÷ 2 = 5.0 mg
5.0 mg ÷ 2 = 2.5 mg after 3 half-lives.
(3 half-lives) x (5,000 yrs/half-life) = 15,000 yrs

11. Certain elements are radioactive because their atoms have
Quick Quiz!
Certain elements are radioactive because their atoms have
more neutrons than electrons.
an unstable nucleus.
a small nucleus.
more neutrons than protons. 11

12. Which property does NOT describe an alpha particle?
Quick Quiz.
Which property does NOT describe an alpha particle?
+2 charge
a relatively large mass
a negative charge
low penetrating power 12

13. Quick Quiz.
When a radioactive nucleus releases a high-speed electron, the process can be described as
oxidation.
alpha emission.
beta emission.
gamma radiation. 13

14.  Quick Quiz. Which of the following is the symbol of a beta particle?14