A fossilized treekilled
by a volcano was
studied. It had 6.25% of
the amount of carbon -
14 found in a sample of
the same size from a
tree that is alive today.
When did the volcano
eruption took place?
3.
A rock wasanalyzed using
potassium-40. The half –
life of potassium-40 is 1.25
billion years. If the rock
had only 25% of the
potassium-40 that would be
found in a similar rock
formed today, calculate
how long ago the rock was
formed.
4.
Ash from anearly fire pit was
found to have 12.5% as much
carbon – 14 as would be
found in a similar sample of
ash today. How long ago was
the ash formed?
5.
A rock samplehas
12.5% of the
potassium – 40
that would be
present in a similar
rock formed today.
How old is the
rock sample?
6.
How old isa piece of
wood in which the
carbon – 14 is 3.125% of
that in wood formed
today?
7.
An isotope ofCesium (Cesium –
137) has a half – life of 30 years.
If 1.0 mg of Cesium – 137
disintegrates over a period of 90
years, how many milligram of
Cesium – 137 would remain?
8.
Sodium – 25was used to be in an
experiment, but it took three minutes
to get the sodium from the reactor to
the laboratory. If 5.0 mgs of Na – 25
was removed from the reactor, how
many milligrams of Na – 25 were
placed in the reaction vessel 3 minutes
later if the half – life of Na – 25 is 60
seconds?
9.
If 1 kilogramof Carbon – 11
sample exist at the beginning
of an hour, how many grams
will remain at the end of the
hour if the half – life of
Carbon – 11 is 20 minutes?
10.
A geologist istrying to date a sequence of
igneous rocks with abundant fossils. The
igneous rocks are mostly granite. The
granite contains crystals with 150 ppma
(parts per million by atomic proportions) of
235
U (parent isotope) and 1,050 ppma of
207
Pb (daughter isotope). Determine the
age of the rock. The half life of 235
U is 704
mya.
11.
If 2500 gramsof Vanadium – 49
sample exist at 10:30 in the
morning of day 1, how much
material in kilograms will remain
at the end of 24 months? The
half-life of V-49 is 330 days.
12.
The half lifeof 232
Th is 1.4 x 1010
y
After 9.8 x 1010
y, how
many grams will be left
from a 256 g sample of
232
Th?
13.
How long doesit take a
180g sample of Au-198
to decay to 1/8 its
original mass? The half
life of Au-198 is 2.69
days.
14.
What is thehalf-life of
a radioactive isotope if
a 500.0g sample
decays to 62.5g in
24.3 hours?
15.
The half-life ofI-131 is
8.07 days. If 25 g are left
after 40.35 days, how
many grams were in the
original sample?
16.
What fraction ofa
sample of 32
P will be
left after 42.9 days if
the half-life of 32
P is
14.3 days?
17.
The half-life ofplutonium-239
is 24,300 years. If a nuclear
bomb released 8 kg of this
isotope, how many years would
pass before the amount is
reduced to 1 kg?
