※ Half-Life : The time required for half of the nuclei in a sample to decay.

•Half-Life

•Carbon Dating

•Decay Curve

•Parent and Daughter

isotope

By Jenny Lee

• HALF-LIFE is the time required for one-half of a radioactive material to decay into non-radioactive material.

• The different isotopes differ by the length of their half-lives and the number of neutrons.

– Ex. Uranium has several isotopes, and they all have different half-lives.

• The shorter the half-life, the faster the decay rate.

※Isotopes of Uranium and their half-lives. Notice that they all have different lengths of half-life.

http://www.youtube.com/watch?v=opjJ-3Tkfyg

• Half-life can be used for CARBON DATING.

• Carbon dating is the process in which Carbon-12 and Carbon-

14 are used for calculating the age of remains of things.

• Every organism on Earth contains carbon.

• The ratio of the number of Carbon-14 atoms to the number of

Carbon-12 atoms is nearly constant when the organism is

alive. When the organism dies, Carbon-14 starts to decay.

• Then the ratio changes, and the changed ratio can be

measured to estimate the age of the remaining organism.

※Decay of

Carbon-14

※ Carbon

dating of

human femur

1. What’s one characteristic of an isotope that differentiates it

from other isotopes?

a. Number of protons

b. Number of electrons

c. Length of half-life

2. Does every organism on Earth contain carbon?

a. Yes

b. No

3. When does Carbon-14 start to decay?

a. While the organism is alive

b. When the organism dies

c. When the organism is injured

1. C) Length of Half-Life

2. A) Yes

3. B) When the organism dies

http://www.youtube.com/watch?v=phZeE7Att_s

• We use a DECAY CURVE to visually represent half-life.

• A Decay Curve on a graph shows the rate at which radioisotopes

decay.

– It can also be used to estimate the amount of parent isotope

remaining or the amount of daughter isotope produced.

• The original isotope that undergoes radioactive decay is called the

PARENT ISOTOPE.

• Once the parent isotope undergoes radioactive decay, it will

produce a stable isotope, called the DAUGHTER ISOTOPE.

※Notice that as Potassium-40

(parent) is decaying, Argon-40

(daughter) is being produced.

1. What is used to represent half-life visually?

a. Pictures

b. Decay Curve

c. Radioactivity Curve

2. What is the original isotope that undergoes radioactive decay

called?

a. Daughter isotope

b. Son isotope

c. Parent isotope

3. What is the isotope that’s produced during radioactive decay

called?

a. Daughter isotope

b. Son isotope

c. Parent isotope

1. B) Decay Curve

2. C) Parent Isotope

3. A) Daughter Isotope