Transcript SPS3c. Explain the process half-life as related to radioactive decay.

SPS3c.
Explain the process half-life as
related to radioactive decay.
EQ: How is the half-life of a
radioactive atom used to determine
the age of ancient object?
How old am I?
• Natural mummy of a
man from about 3300
BC (53 centuries ago).
• HOW DID
SCIENTISTS
FIGURE MY AGE?
http://mrsauve.com/EM.aspx
Story about how scientists determine age
of “ICE” man and other ancient artifacts.
• You probably have seen or read news stories about
fascinating ancient artifacts. At an archaeological dig, a
piece of wooden tool is unearthed and the
archaeologist finds it to be 5,000 years old. A child
mummy is found high in the Andes and the
archaeologist says the child lived more than 2,000 years
ago. How do scientists know how old an object or
human remains are? What methods do they use and
how do these methods work? In today's lesson, we will
examine the methods by which scientists use
radioactivity to determine the age of objects, most
notably carbon-14 dating.
What is Carbon-14 dating?
• Carbon-14 dating is a way of
determining the age of certain
archeological artifacts.
• Biological artifacts can be dated up
to about 50,000 years old.
• It is used in dating things such as
bone, cloth, wood and plant fibers.
• How it works!
Half-life Practice
The SI unit of activity is the becquerel (Bq).
Time
Initial
10 minutes
20 minutes
30 minutes
40 minutes
Mass
72 g
Problem #3
Half-life of 2 hours
Time
Initial
2 hours
4 hours
6 hours
8 hours
10 hours
Mass Left in Nucleus
Problem #4
Time
Mass Left in Nucleus
Initial
400
?
?
3 days
100
Use your notes from 11/1
to complete the circle map:
Halflife
Problem 6
Most Stable to Least Stable
Hint: the longer it takes something to
decay the more STABLE it is.
1.
2.
3.
Problem #8
•
•
•
•
Earth is 4,500,000,000
½ Life of Uranium-238 is 4,500,000,000
Hint = look at the numbers.
How much of the original Uranium-238 is left?
MAKE THE CHART
TIME (half-life given)
add half-life (time given)
Amount or Activity of Nucleus Left
divide by 2
Problem #9
= a WHOLE pie or 100% = INITIAL AMOUNT
= a HALF pie or 50% = ONE HALF LIFE HAS PASSED
= a QUARTER pie or 25% =
SECOND HALF HAS PASSED
More Practice
• Complete Number 4 to 7 on typed side.
• Complete All on hand-written side.
Initial Amount
TIME
Half the Amount
Each Isotope takes a certain length of
time to divide by HALF (half-life).
DIVIDE BY 2!
TOD
• If 100.0 g of Carbon-14 decays
until only 25.0 g of Carbon is left
11,460 years, what is the half-life
of Carbon-14?