Transcript 25.3 Transmutation

I. Transmutation
• Transmutation - The conversion of one
element to another element.
• All nuclear reactions are transmutation
reactions except for gamma emission, which
does not alter an atom’s atomic number.
II. Induced Transmutation
• Before 1919, the only way to change the
nucleus or cause transmutation was to wait
for nature.
• In 1919 Rutherford was the first to induce
(cause) transmutation.
• He proved that nuclear reactions can be
produced artificially.
• Induced transmutation can occur by
bombarding an atom with alpha particles,
protons or neutrons.
III. Transuranium Elements
• Elements with atomic number above 92.
• All transuranium elements undergo
transmutation
• None of the transuranium elements occur in
nature and have been produced through
induced transmutation.
IV. Half-life
• The time required for one-half of a
radioisotope’s nuclei to decay into its
products
• After each half-life, half of the existing
radioactive atoms have decayed into atoms of
a new element
• Amount remaining at time T = (initial amt)(1/2)n
where n= number of half-lives
• n = total time ÷ time of one half-life
Practice
1. Scientists start with 50.0 g sample of
a radioisotope. How much is left
after four half-lives?
Half-Life Skip count
50.0 g 25.0 g 12.5 g 6.25 g 3.125 g ≈3.13 g
1
2
3
4
2. Iron-59 is used in medicine to diagnose blood
circulation disorders. The half-life of iron 59
is 44.5 days. How much of a 2.000 mg
sample will remain after 133.5 days?
(first find out how many half-lives, then skip
count)
133.5 days
44.5 days
= 3 half-lives
Half-Life Skip count
2.000 mg 1.000 mg
1
0.5000 mg
2
0.2500 mg
3
V. Carbon-14 Dating
• Carbon 14 dating is the process of
determining the age of artifacts that were
once part of a living organism by measuring
the amount of 14C remaining in that artifact
• Carbon-14 is radioactive and undergoes beta
decay. It has a half-life of 5730 years.
Carbon-14
•
14C
evenly spread in the Earth’s biosphere
• Plants incorporate 14C into their structure that
matches the level in the atmosphere.
• When an organism dies, 14C declines at a known
rate. (Half-life of C-14 = 5730 years)
• Comparing the remaining 14C fraction of a sample
to that expected from atmospheric 14C allows the
age of the sample to be estimated.
• Dates carbon-bearing materials up to 62,000
years.
Carbon-14 Decay
• Using the graph, about what % of carbon-14
remains after 11, 400 years?