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Welcome to Mycore Scientific Inc How 210Pb Works for Dating Sediments Other Information Useful in Dating Sediments |
Additional
Information
Accurate interpretation
of 210Pb
concentration versus depth profile requires additional pieces of information about
the cores. This information should be provided by email when the cores
are sent. The 210Pb
measurements on the cores cannot be interpreted until the information is
received. A data sheet from MyCore
is available. When
completed, this sheet provides us with the information we need to complete
analysis of the core. 1. Date the core was
collected. This is used to
ascertain whether the isotopes of 210Pb and 210Po
are in secular equilibrium and to correct for radioactive decay that has
occurred since the core was collected. 2. Area of the core. This is used to calculate the rate of sediment accumulation
in the core per unit area. 3. Dry Weight of each
section. This is needed to
correct for the amount of compaction in the core and to date the core using the
CRS model. Cumulative dry weight
over the entire core is calculated so that the weight is needed for each
section; not just those on which dating are performed.
This information can be obtained by several techniques. The most common
methods are:
a.
Drying the entire section of the core and measuring the weight of the
section
b.
Measuring the total wet weight of each section and determine the dry
weight of a sub-sample of known wet weight.
This enables one to calculate the dry weight of the section from the dry
weight to wet weight ratio of each section and leave most of the material
untouched.
c.
Measuring (or calculating) the volume of each section and determining the
wet weight from the volume of the section.
Then proceed as in b. The
conversion from wet to dry weight and wet weight must be measured very
accurately since only a small fraction of the surface sections of the core are
dry material.
d.
Measuring (or calculating) the volume of each section and using the bulk
density of the sediment to calculate the dry mass in the section.
This method is very inaccurate unless the bulk density is known with good
precision. 4.
Depth of sample(s).
The top and the bottom of the core section that the sample originated
from. 5. Metal
concentrations or Pollen counts. This
information is not essential. However it is very useful to have since it enables
one to examine the top ~5cm of the cores and to determine whether the core has
been mixed (homogenized). If the
core has been mixed then the age of the sections may need to be adjusted.
6. Organic matter
content. This information is not essential. It is very useful to check
and ensure that the material in the core is of similar origin and whether the
background concentration of supported Pb-210 is constant in the core. |
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