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Rates of Nuclear Decay
These stone tools
from the
archaeological site
in Cactus Hill,
Virginia, are at least
15,000 years old.
Scientists estimated
the age of the site
based on rates of
nuclear decay.
Half-life
Unlike chemical reaction rates, which vary
with the conditions of a reaction, nuclear
decay rates are constant.
Half-life
A half-life is the time required for one half of
a sample of a radioisotope to decay.
Half-life
The half-life for the beta decay of iodine-131
is 8.07 days.
Half-life
The half-life for the beta decay of iodine-131
is 8.07 days.
Half-life
The half-life for the beta decay of iodine-131
is 8.07 days.
Half-life
The half-life for the beta decay of iodine-131
is 8.07 days.
Half-life
Every
radioisotope
decays at a
specific
rate. Half-lives
can vary from
fractions of a
second to billions
of years.
Decay Series of Uranium-238
Stable
Isotope
Half-life
Iridium-182 undergoes beta decay to form
osmium-182. The half-life of iridium-182 is 15
minutes.
a) After 15 minutes, how much iridium-182
will remain of an original 1 gram sample?
0.5 g
b) After 30 minutes, how much iridium-182
will remain of the original 1 g sample?
0.25 g
Assessment Questions
1. Cesium-137 has a half-life of 30 years. You find a
sample with 3 g of cesium-137. How much
cesium-137 existed in the sample 90 years ago?
a.
b.
c.
d.
9g
27 g
24 g
18 g
Assessment Questions
1. Cesium-137 has a half-life of 30 years. You find a
sample with 3 g of cesium-137. How much
cesium-137 existed in the sample 90 years ago?
a.
b.
c.
d.
9g
27 g
24 g
18 g
ANS: C
Assessment Questions
2. What factors influence nuclear decay rates?
a.
b.
c.
d.
pressure
temperature
concentration
number of neutrons in nucleus
Assessment Questions
2. What factors influence nuclear decay rates?
a.
b.
c.
d.
pressure
temperature
concentration
number of neutrons in nucleus
ANS: D
Transmutation Reactions
• The conversion of an atom of one
element to an atom of another
element is called transmutation.
Transmutation can occur by
radioactive decay.
Transmutation can also occur when
particles bombard the nucleus of an
atom.
Transmutation Reactions
• The first artificial transmutation reaction involved
bombarding nitrogen gas with alpha particles.
Transmutation Reactions
• The elements in the periodic table with
atomic numbers above 92, the atomic
number of uranium, are called the
transuranium elements.
– All transuranium elements undergo
transmutation.
– None of the transuranium elements
occur in nature, and all of them are
radioactive.
Transmutation Reactions
• Transuranium elements are synthesized in
nuclear reactors and nuclear accelerators.