Outline:
4/16/07
Pick up leftover CAPA outside…
 Special seminar Wednesday pm
 Turn in Seminar reports – to me

Today: Chapter 22 (cont’d)
Nuclear Chemistry
- Modes of decay
- Half-life calculations
Quiz #9
 Please
put away books & papers.
 Turn your paper over when done.
Quiz #9
 Please
pass your quiz to the right…
Nuclear Reactions:
 Types
of radioactive decay:
Alpha (a), Beta (b), and Gamma (g)
fission, fusion,
positron (b+), e- capture (EC)….
 Natural
vs. induced reactions:
Worksheet #13
Balancing equations
Worksheet #13
 Start
filling in the blanks:
nuclear equation writing
Remember: both top and bottom
must balance on both sides of the
equation (conservation of mass
and charge!)
Worksheet #13
(a) 1 + 235 = 131 + ____
105
39
0 + 92 = 53 + ____
105
Y
39
(b) 0 + ____
14 = 14
7 = 6
-1 + ____
14
N
7
(c) 60 = 0 + ____
60
28
27 = -1 + ____
60
Ni
28
Radioactive Decay: 1st order
order decay : N = N0 e - k t
 Half-life:
ln(N/N0) = - k t
 First
ln(1/2) = - k t1/2
0.693 = k t1/2
t1/2 : a convenient way to refer to k
e.g. 14C has k = 1.209 × 10-4 yr-1 ;
what is its half-life?
0.693 = k t1/2
k = 1.209 × 10-4 yr-1
t1/2 = 0.683/k = 5730 yr
e.g. : If 10.0 g of Kennewick Man bone
has 34.6 dpm of 14C, and a present-day
10.0 g bone has 103.7 dpm, how old is
Kennewick Man?
N/N0 = e - k t or ln(N/N0) = - k t
ln(34.6/103.7) = - k t
t = 9080 yrs
Decay calculations:
• Where have you seen these before?
Chapter 15 (pp. 627-630) = Kinetics
PRACTICE!
Worksheet #13 - Question 2
0.02% of 1000g =
0.2 g 14C
0.2 g  1mol/14g = 0.143 mol 14C
0.143 mol 14C  6.022e23 atoms/mol
= 8.60e21 atoms 14C
N/N0 = 7.65e20 / 8.60e21 = 0.0889
ln (0.0889) = - k t
- 2.42 = - 1.209 × 10-4 yr-1 t
t = 20,000 yr